ERDC/LAB TR-0X-X xv

Figure 9-14 Bed displacement for Alternative A for the 10-year flood event ................................... 246 Figure 9-15 Bed displacement for Alternative A for the 25-year flood event ................................... 246 Figure 9-16 Bed displacement for Alternative A for the 50-year flood event .................................... 247 Figure 9-17 Bed displacement for Alternative A for the 100-year flood event .................................. 247 Figure 9-18 Bed displacement for Alternative A for the 100-year flood series event ..................... 248 Figure 9-19 Bed displacement for Alternative A for the 100-year flood event with a 1.5 ft sea level rise .............................................................................................................................................. 248 Figure 9-20 Bed displacement for Alternative A for the 100-year flood event with a 5.5 ft sea level rise .............................................................................................................................................. 249 Figure 9-21 Bed displacement for Alternative B for the 10-year flood event ................................... 249 Figure 9-22 Bed displacement for Alternative B for the 25-year flood event .................................. 250 Figure 9-23 Bed displacement for Alternative B for the 50-year flood event .................................. 250 Figure 9-24 Bed displacement for Alternative B for the 100-year flood event ................................ 251 Figure 9-25 Bed displacement for Alternative B for the 100-year flood series ............................... 251 Figure 9-26 Bed displacement for Alternative C for the 10-year flood event ................................... 252 Figure 9-27 Bed displacement for Alternative C for the 25-year flood event ................................... 252 Figure 9-28 Bed displacement for Alternative C for the 50-year flood event ................................... 253 Figure 9-29 Bed displacement for Alternative C for the 100-year flood event ................................ 253 Figure 9-30 Bed displacement for Alternative C for the 100-year flood series ............................... 254 Figure 9-31 Comparison of sediment delivery to Jimmy Durante Bridge for each alternative simulation ............................................................................................................................... 255 Figure 9-32 Comparison of sediment delivery to Jimmy Durante Bridge for the 100-year series simulation with breakdown by sediment class .......................................................................... 256 Figure 9-33 Sedimentation volume zones for Existing Conditions.................................................... 257 Figure 9-34 Sedimentation volume zones for Alternative A ............................................................... 257 Figure 9-35 Details of sedimentation volume zones for Alternative A .............................................. 258 Figure 9-36 Sedimentation volume zones for Alternative B............................................................... 259 Figure 9-37 Sedimentation volume zones for Alternative C ............................................................... 259 Figure 9-38 Summary of sedimentation between El Camino Real and Interstate 5 for each single event and the 100-year series simulations ...................................................................... 260 Figure 9-39 Depth of deposits for Alternative A at the downstream end of the W-19 wetland ....................................................................................................................................................... 261 Figure 9-40 Depth of deposits for Alternative B at the downstream end of the W-19 wetland ....................................................................................................................................................... 262 Figure 9-41 Depth of deposits for Alternative C at the downstream end of the W-19 wetland ....................................................................................................................................................... 263 Figure 9-42 Effects of berm overflow at higher return period floods for Alternative B .................... 264 Figure 9-43 Maintenance volumes for the 100-year series deposition in the entrance to the W-19 wetland as a function of the deposition threshold .............................................................. 265 Figure 9-44 Maximum water surface elevation profile comparison for the 10-year flood event simulation ........................................................................................................................................ 266 Figure 9-45 Maximum water surface elevation profile comparison for the 25-year flood event simulation ........................................................................................................................................ 267

ERDC/LAB TR-0X-X xvi

Figure 9-46 Maximum water surface elevation profile comparison for the 50-year flood event simulation ........................................................................................................................................ 268 Figure 9-47 Maximum water surface elevation profile comparison for the 100-year flood event simulation ........................................................................................................................................ 269 Figure 9-48 Maximum water surface elevation profile comparison for the 100-year flood event simulations for effects of sea level rise ....................................................................................... 270 Figure 9-49 Maximum current velocity magnitudes in the vicinity of the El Camino Real Bridge for the 100-year flood event ......................................................................................................... 271 Figure 9-50 Maximum current velocity magnitudes in the vicinity of the Edison weir for the 100-year flood event .......................................................................................................................... 272 Figure 9-51 Maximum current velocity magnitudes in the vicinity of the Interstate 5 Bridge for the 100-year flood event ........................................................................................................ 273 Figure 9-52 Maximum current velocity magnitudes in the vicinity of the Jimmy Durante Bridge for the 100-year flood event ......................................................................................................... 274 Figure 9-53 Erosion at El Camino Real bridge for the 100-year series simulation ........................ 275 Figure 9-54 Erosion at El Camino Real Bridge for the 10-yr flood event .......................................... 275 Figure 9-55 Erosion at El Camino Real Bridge for the 25-yr flood event ............................................ 276 Figure 9-56 Erosion at El Camino Real Bridge for the 50-yr flood event ........................................... 276 Figure 9-57 Erosion at El Camino Real Bridge for the 100-yr flood event ........................................ 277 Figure 9-58 Erosion at the El Camino Real Bridge for 100-year event with a 1.5-foot sea level rise ...................................................................................................................................................... 278 Figure 9-59 Erosion at the El Camino Real Bridge for 100-year event with a 5.5-foot sea level rise ...................................................................................................................................................... 279 Figure 9-60 Erosion in the vicinity of the utility corridor and Edison weir for the 100-year series simulation ....................................................................................................................................... 280 Figure 9-61 Erosion in the vicinity of the utility corridor and Edison weir for the 10-year flood event simulation .............................................................................................................................. 280 Figure 9-62 Erosion in the vicinity of the utility corridor and Edison weir for the 25-year flood event simulation .............................................................................................................................. 281 Figure 9-63 Erosion in the vicinity of the utility corridor and Edison weir for the 50-year flood event simulation .............................................................................................................................. 281 Figure 9-64 Erosion in the vicinity of the utility corridor and Edison weir for the 100-year flood event simulation .............................................................................................................................. 282 Figure 9-65 Erosion in the vicinity of the utility corridor and Edison weir for the 100-year flood event with 1.5-foot sea level rise simulation ............................................................................... 283 Figure 9-66 Erosion in the vicinity of the utility corridor and Edison weir for the 100-year flood event with 5.5-foot sea level rise simulation ............................................................................... 284 Figure 9-67 Erosion in the vicinity of the Interstate 5 Bridge for the 100-year series simulation ................................................................................................................................................... 285 Figure 9-68 Erosion in the vicinity of the Interstate 5 Bridge for the 10-year flood event simulation ................................................................................................................................................... 285 Figure 9-69 Erosion in the vicinity of the Interstate 5 Bridge for the 25-year flood event simulation ................................................................................................................................................... 286 Figure 9-70 Erosion in the vicinity of the Interstate 5 Bridge for the 50-year flood event simulation ................................................................................................................................................... 286

ERDC/LAB TR-0X-X xvii

Figure 9-71 Erosion in the vicinity of the Interstate 5 Bridge for the 100-year flood event simulation ................................................................................................................................................... 287 Figure 9-72 Erosion in the vicinity of the Interstate 5 Bridge for the 100-year flood event with a 1.5-foot sea level rise simulation ................................................................................................. 288 Figure 9-73 Erosion in the vicinity of the Interstate 5 Bridge for the 100-year flood event with a 5.5-foot sea level rise simulation ................................................................................................. 289 Figure 9-74 Erosion in the vicinity of Jimmy Durante Bridge for the 100-year series simulation ................................................................................................................................................... 290 Figure 9-75 Erosion in the vicinity of Jimmy Durante Bridge for the 10-year flood event simulation ................................................................................................................................................... 290 Figure 9-76 Erosion in the vicinity of Jimmy Durante Bridge for the 25-year flood event simulation ................................................................................................................................................... 291 Figure 9-77 Erosion in the vicinity of Jimmy Durante Bridge for the 50-year flood event simulation ................................................................................................................................................... 291 Figure 9-78 Erosion in the vicinity of Jimmy Durante Bridge for the 100-year flood event simulation ................................................................................................................................................... 292 Figure 9-79 Erosion in the vicinity of Jimmy Durante Bridge for the 100-year flood event with a 1.5-foot sea level rise simulation ................................................................................................. 293 Figure 9-80 Erosion in the vicinity of Jimmy Durante Bridge for the 100-year flood event with a 5.5-foot sea level rise simulation ................................................................................................. 294 Figure 9-81 Erosion in the vicinity of the river mouth for the 100-year series simulation ............. 295 Figure 9-82 Erosion in the vicinity of the river mouth for the 10-year flood event simulation ................................................................................................................................................... 295 Figure 9-83 Erosion in the vicinity of the river mouth for the 25-year flood event simulation ................................................................................................................................................... 296 Figure 9-84 Erosion in the vicinity of the river mouth for the 50-year flood event simulation ................................................................................................................................................... 296 Figure 9-85 Erosion in the vicinity of the river mouth for the 100-year flood event simulation ................................................................................................................................................... 297 Figure 9-86 Erosion in the vicinity of the river mouth for the 100-year flood event with a 1.5-foot SLR simulation ............................................................................................................................ 298 Figure 9-87 Erosion in the vicinity of the river mouth for the 100-year flood event with a 5.5-foot SLR simulation ............................................................................................................................ 299 Figure 9-88 Peak current velocities in the inlet for 100-year flood event for Alternative A ............ 300 Figure 9-89 Deposition volumes in SCE W4 wetland for Alternative A with and without armoring of the utility corridor ................................................................................................................. 301 Figure 10-1 The original (top) and refined (bottom) AdH model mesh resolution .......................... 310 Figure 10-2 Effects of the mesh resolution on sediment delivery to Jimmy Durante Bridge ........ 311 Figure 10-3 Current velocity distribution for existing conditions for 100-year flood event with AdH model run with and without use of the vorticity correction. ................................................ 312 Figure 10-4 Illustration of the effects of stream-wise vorticity correction on surface current patterns and bottom bed-load transport vectors. ................................................................... 313 Figure 10-5 ERDC Riprap test facility application of AdH; No vorticity correction in middle, with vorticity correction on bottom.......................................................................................................... 314 Figure 10-6 Numerical model representation of the pre-Edison condition ..................................... 315

ERDC/LAB TR-0X-X xviii

Figure 10-7 AdH model bed displacement during the 1993 verification simulation ..................... 316 Figure 10-8 AdH model bed displacement during the 1993 verification simulation in the vicinity of the wetland project .................................................................................................................. 316 Figure 10-9 AdH bed displacement in the vicinity of the utility corridor for the 1993 verification event. Note the scale change for the contour interval. .................................................... 317 Figure 10-10 AdH bed displacement for the 100-year flood event simulation for the pre-Edison bathymetric condition. The utility corridor was not armored. ................................................. 317 Figure 10-11 AdH bed displacement for the 100-year flood series simulation for the pre-Edison bathymetric condition. The utility corridor was not armored. ................................................ 318 Figure 10-12 Effects of 100-year event on Existing condition with the Edison Dike removed down to +3m and unarmored with the utility corridor unarmored .................................... 318 Figure 10-13 Effects of 100-year event on Option 2 with the Edison Dike removed down to +3m and unarmored with the utility corridor armored .................................................................... 319 Figure 10-14 Effects of 100-year event on Option 2 with the Edison Dike removed down to +3m and unarmored with the utility corridor unarmored ............................................................... 319 Figure 10-15 Effects of armoring the utility corridor on geomorphology of the 100-year flood event .................................................................................................................................................. 321 Figure 10-16 Differences in bed displacement between Alternative A and existing and with and without utility corridor armoring .............................................................................................. 322 Figure 10-17 Peak erosion in the vicinity of the utility corridor channel crossing ........................... 323 Figure 10-18 Schematic layout of pipelines across the utility corridor ............................................. 324 Figure 10-19 Profile of the existing and Alternative A 10-year flood event erosion along the 10-inch pipeline alignment................................................................................................................ 324 Figure 10-20 Profile of the existing and Alternative A 25-year flood event erosion along the 10-inch pipeline alignment................................................................................................................ 325 Figure 10-21 Profile of the existing and Alternative A 50-year flood event erosion along the 10-inch pipeline alignment................................................................................................................ 325 Figure 10-22 Profile of the existing and Alternative A 100-year flood event erosion along the 10-inch pipeline alignment................................................................................................................ 326 Figure 10-23 Profile of the existing and Alternative A 10-year flood event erosion along the 16-inch pipeline alignment................................................................................................................ 326 Figure 10-24 Profile of the existing and Alternative A 25-year flood event erosion along the 16-inch pipeline alignment................................................................................................................ 327 Figure 10-25 Profile of the existing and Alternative A 50-year flood event erosion along the 16-inch pipeline alignment................................................................................................................ 327 Figure 10-26 Profile of the existing and Alternative A 100-year flood event erosion along the 16-inch pipeline alignment................................................................................................................ 328 Figure 10-27 Profile of the existing and Alternative A 10-year flood event erosion along the 30-inch pipeline alignment ............................................................................................................... 328 Figure 10-28 Profile of the existing and Alternative A 25-year flood event erosion along the 30-inch pipeline alignment ............................................................................................................... 329 Figure 10-29 Profile of the existing and Alternative A 50-year flood event erosion along the 30-inch pipeline alignment ............................................................................................................... 329 Figure 10-30 Profile of the existing and Alternative A 100-year flood event erosion along the 30-inch pipeline alignment ............................................................................................................... 330

ERDC/LAB TR-0X-X xix

Figure 10-31 Erosion potential during 100-year flood event for unarmored utility corridor – east side .................................................................................................................................................. 330 Figure 10-32 Erosion potential during 100-year flood event for unarmored utility corridor – west side ................................................................................................................................................. 331 Figure A--1 Nondimensional vertical profiles of velocity, sediment concentration and sediment flux ............................................................................................................................................. 356 Figure B-1 Bathymetric condition in inlet 19 August 2014 (from Coastal Environments, 2014) ........................................................................................................................................................... 374 Figure B-2 ADH numerical model of the San Dieguito Lagoon .......................................................... 375 Figure B-3 Mesh resolution in the vicinity of the entrance and the NCTB railroad bridge. ............. 376 Figure B-4 Location of cross section for flood impact assessment. ................................................. 377 Figure B-5 Cross section before and after range of flood event return periods for the cross section shown in Figure B-4. ................................................................................................................... 378 Figure B-6 From Chang, 2004. The predicted erosion at the railroad bridge during a 100-yrear river flood using the Fluvial-12 model for the with project (Edison wetland) .......................... 379 Figure B-7 Observed cross sections west of RR bridge (from HDR, 2014) ...................................... 380 Figure B-8 Observed cross sections east of RR bridge (from CE)...................................................... 380 Figure B-9 Variation comparisons east and west of railroad bridge for each survey period ........ 381 Figure B-10 Further illustration of variability in channel conditions ................................................. 382 Figure B-11 Channel bathymetry from 2006. (Coastal Environments, 2006) .............................. 383 Figure B-12 Variability in the apparent channel thalweg inferred from aerial photography .......... 384 Figure B-13. Variation in channel alignment before and after the creation of SCE wetland W4 385 Figure B-14 Aerial photography from 1-11-2003 showing aeration at the water surface just west of the railroad bridge. ............................................................................................................... 386 Figure B-15 Waves for 2013 in the area ............................................................................................... 387 Figure B-16 Wave height estimations from STWAVE coarse grid analysis using a 10-m grid, a significant wave height offshore of 5 m, 10 second period, a TMA spectrum with gamma of 3.3 for MWL............................................................................................................................. 388 Figure B-17 Fine inset grid for inlet area using 5-m resolution. ........................................................ 389 Figure B-18 Fine grid wave model results along railroad bridge, wave height in meters. Ocean wave of 10 seec period , 5m wave height an mean water level at MHHW. .......................... 389 Figure B-19 Variation in wave heights along Railroad bridge for water level at MHHW for a variety of offshore wave conditions .......................................................................................................... 390 Figure B-20 Existing bathymetry model form SANDAG study. ............................................................ 391 Figure B-21 Pre-dredge bathymetry model taken from Figure 1. ...................................................... 392 Figure B-22 Dredging polygons for proposed dredging. ..................................................................... 393 Figure B-23 Post dredge bathymetric model ........................................................................................ 394 Figure B-24 Pacific Ocean tidal boundary condition for model simulation period .......................... 395 Figure B-25 ADH model response for the “existing” conditions for the SANDAG modeling .......... 396 Figure B-26 ADH model response for the pre-dredge current conditions. ...................................... 397 Figure B-27 ADH model response for the post-dredge conditions. ................................................... 398 Figure B-28 Comparison of the tidal response at the railroad bridge for the three bathymetric condition ADH simulations. ................................................................................................ 399

ERDC/LAB TR-0X-X xx

Figure B-29 Comparison of the tidal response at the SCE wetland W4 for the three bathymetric condition ADH simulations. ................................................................................................ 400 Figure B-30 System inundation during spring tide for existing conditions ....................................... 401 Figure B-31 Comparison of the cross section across the channel at the railroad bridge/. The W-19 SANDAG model had a more uniform channel compared to the current conditions. The post-dredge condition is the same as the current at the RR bridge because the dredging was downstream. ............................................................................................... 402 Figure B-32 Tidal variation in current velocity at the railroad cross section for the ADH tidal simulation. ......................................................................................................................................... 403 Figure B-33 Comparison of the peak flood (+) and ebb (-) currents during the tidal simulation for the three simulations. The differences between the pre- and post-dredging conditions are also presented. The differences between current and existing conditions are significantly greater than the pre- and post-dredging conditions ................................................ 404 Figure B-34 Comparison of the peak flood (+) and ebb (-) currents during the tidal simulation for the three simulations. The average velocity distributions for each of the conditions are also presented. The differences between current and existing conditions are again significantly greater than the pre- and post-dredging conditions...................................... 405 Figure B-35 Local shoreline protection on the south side of the river just west of the railroad bridge. ........................................................................................................................................... 406 Figure B-36 Possible explanation of tendency for differential channels for flood and ebb currents at the railroad bridge. The orientation of the railroad combined with the blockage to flow presented by the pile groups can create a funneling effect on the currents that shifts the flood current to the south bank and the ebb currents to the north bank. ........................................................................................................................................................... 407 Figure B-37 Peak current velocity magnitudes for the 100-year river flood event for the existing SANDAG bathymetry. .................................................................................................................. 408 Figure B-38 Design equation used for the sizing of the rock Riprap protection .............................. 408 Figure B-39 Comparison of the velocity used for the design of protective riprap with the peak velocities from the ADH model for specific river flood return periods. ..................................... 409 Figure B-40 Bed displacement for the pre-dredge bathymetry simulation of a 10-year river flood event. Red indicates deposition and blue indicates erosion. ........................................... 410 Figure B-41 Bed displacement for the post-dredge bathymetry simulation of a 10-year river flood event. Red indicates deposition and blue indicates erosion. .......................................... 411 Figure B-42 Bed displacement for the SANDAG existing bathymetry simulation of a 10-year river flood event. Red indicates deposition and blue indicates erosion. .................................. 412 Figure B-43 Comparison of bed displacement for 10-year flood for the bathymetries simulated. ................................................................................................................................................... 413 Figure B-44 Effects of proposed dredging plan on the peak water surface profile for a 10-year river flood. ........................................................................................................................................... 414 Figure B-45 Effects of full dredging of channel (“existing” SANDAG) on the peak water surface profile for a 10-year river flood. ................................................................................................. 415 Figure B-46 Schematized basin model for testing bridge crossing effects on circulation. ............. 416 Figure B-47 Details of model representation of generic bridge crossing, inset showing the material specifications. ............................................................................................................................. 417 Figure B-48 Current velocity magnitude and flow vectors for peak incoming flood tide for the case on skewed pile bents. ................................................................................................................ 417

ERDC/LAB TR-0X-X xxi

Figure B-49 Current velocity magnitude and flow vectors for peak outgoing ebb tide for the case on skewed pile bents. ............................................................................................................... 418 Figure B-50 Residual mean currents (tidally averaged) for the case of skewed pile bents. .......... 418 Figure B-51 Details of residual currents at south shore abutment for the case of skewed pile bents. ................................................................................................................................................... 419 Figure B-52 Aerial photograph during flood tide showing general flow direction inferred from aerated water from drainage canal. .............................................................................................. 420 Figure B-53 Aerial photograph near low water showing the presence of dual deep channels through the railroad bridge, on the south shore and on the north side. .......................... 421 Figure B-54 Details of revised bridge crossing with pile bents aligned with the orientation of the river. .................................................................................................................................................. 422 Figure B-55 Current velocity magnitude and flow vectors for peak incoming flood tide for the case on aligned pile bents. ............................................................................................................... 422 Figure B-56 Current velocity magnitude and flow vectors for peak outgoing ebb tide for the case on aligned pile bents. ............................................................................................................... 423 Figure B-57 Residual mean currents (tidally averaged) for the case of aligned pile bents. .......... 423 Figure B-58 Details of residual circulation near north shore for case of aligned pile bents. ........ 424 Figure B-59 Details of residual circulation near south shore for case of aligned pile bents. .......................................................................................................................................................... 425 Figure B-60 Comparison of velocity magnitudes on flood and ebb currents for aligned pile bents from a simulation without Coriolis effects showing the concentrations of flows into the “funneling” shape of the bridge orientation. .................................................................................. 426 Figure B-61 Comparison of velocity magnitudes on flood and ebb currents for skewed pile bents from a simulation without Coriolis effects showing the concentrations of flows into the “funneling” shape of the bridge orientation. .................................................................................. 427 Figure B-62 Comparison of the peak flood flow velocities for skewed pile bents versus aligned pile bents. ..................................................................................................................................... 428 Figure B-63 Comparison of the peak ebb flow velocities for skewed pile bents versus aligned pile bents. ..................................................................................................................................... 429 Figure B-64 Comparison of the residual velocities for skewed pile bents versus aligned pile bents. ................................................................................................................................................... 430 Figure B-65 Comparison of the residual velocities for skewed pile bents versus aligned pile bents along the south shore. ........................................................................................................... 431 Figure B-66 Comparison of velocity magnitudes at the south shore for peak flood tides ............. 432 Figure B-67 Flume model for running a steady-state flow through the bridge opening ................. 432 Figure B-68 Steady-state flow results for peak flood flows in the flume model .............................. 433 Figure B-69 Model mesh configuration for the bridge crossing perpendicular to the river. .......... 434 Figure B-70 Simulation results for peak flood and ebb for the case of the bridge crossing perpendicular to the river. ........................................................................................................................ 435 Figure B-71 Detail of peak flood velocities at the south shore for the case of the bridge crossing perpendicular to the river.......................................................................................................... 436 Figure B-72 Detail of peak ebb velocities at the south shore for the case of the bridge crossing perpendicular to the river.......................................................................................................... 437 Figure B-73 Residual tidal circulation for the case of the bridge crossing perpendicular to the river. ...................................................................................................................................................... 438

ERDC/LAB TR-0X-X xxii

Tables

Table 4-1 Model sediment grain size specifications and initial distribution ....................................... 30 Table 6-1 Single flood evens for simulations in testing program .......................................................... 58 Table 6-2 Series of flood events in the 100-year series simulation ..................................................... 59 Table 7-1 Summary of sediment supply to Jimmy Durante Bridge for 100-year flood event expressed as a percentage of the sediment delivery for existing condition and marsh sedimentation ............................................................................................................................................... 78 Table 7-2 San Dieguito Lagoon W-19 Hydrodynamic Alternative Evaluation ...................................... 79 Table 8-1 San Dieguito Lagoon W-19 Hydrodynamic Alternative Evaluation after second phase of screening .................................................................................................................................... 119 Table 9-1 Sediment Delivery to Jimmy Durante Bridge (1000s cubic yards) ........................... 225 Table 9-2 Sediment delivery (1000s cubic yards) to Jimmy Durante Bridge for the 100-year series simulation by size class ........................................................................................................ 226 Table 9-3 Volumes of bed displacement for existing conditions with no armoring of the utility corridor in cubic yards .................................................................................................................... 227 Table 9-4 Volumes of bed displacement for Alternative A with no armoring of the utility corridor in cubic yards .............................................................................................................................. 228 Table 9-5 Volumes of bed displacement for existing conditions with armoring of the utility corridor in cubic yards .............................................................................................................................. 230 Table 9-6 Volumes of bed displacement for Alternative A with armoring of the utility corridor in cubic yards .............................................................................................................................. 231 Table 9-7 Volumes of bed displacement for Alternative B with armoring of the utility corridor in cubic yards .............................................................................................................................. 233 Table 9-8 Volumes of bed displacement for Alternative C with armoring of the utility corridor in cubic yards .............................................................................................................................. 235 Table 9-9 Volumes of bed displacement for 100-year series with armoring of the utility corridor in cubic yards .............................................................................................................................. 237 Table 9-10 Peak depth of deposits (m) at the mouth of the W-19 wetland ............................... 239 Table 10-1 Peak scour at the utility corridor (m) ............................................................................. 309 Table B-1 Previous artificial openings by the City of Del Mar ............................................................. 373 Table B-2 Tidal performance in SCE W-4 wetland ............................................................................... 373 Table B-3 Summary of tidal velocities on the south shore ................................................................. 373

ERDC/LAB TR-0X-X xxiii

Preface

This report presents the results of numerical modeling and analyses per-formed by the U.S. Army Engineer Research and Development Center (ERDC), at the request of the U.S. Army Engineer District, Los Angeles (CESPL), to evaluate alternatives for wetland restoration for San Dieguito Lagoon Wetland Study. The work described in this report was performed by Dr. Joseph V. Letter, Jr., retired, formerly with the US Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics La-boratory (CHL), Estuarine Engineering Branch (HFE), under the general supervision of José E. Sánchez, Director, CHL. Direct supervision was provided by Dr. Ty Wamsley, Chief, Flood and Storm Protection Division, CEERD-HF, and Dr. Robert McAdory, Chief of the Estuarine Engineering Branch. Dr. Letter, currently with Joseph V. Letter Consulting LLC, final-ized this report under contract.

COL Bryan S. Green and, formerly, Jeffrey R. Eckstein were Commander and Executive Director of ERDC. Directors during this study were previ-ously Dr. Jeffery P. Holland and currently Dr. David. W. Pittman.

The author acknowledges the support Meris Guerrero, Courtney Stevens, Richard van Sant and Kyle Dahl (all of CESPL-RG-S) who provided USACE project coordination during the course of the study. The author also acknowledges the collaboration and support of the project delivery team that was responsible for the development of the project final design. These include Mr. Gordon Lutes and Mark Tarrall of Dokken Engineering and Mrs. Weixia Jin of Moffatt and Nichol.

ERDC/LAB TR-0X-X xxiv

Unit Conversion Factors

Multiply By To Obtain

acres 4,046.873 square meters

acre-feet 1,233.5 cubic meters

angstroms 0.1 nanometers

atmosphere (standard) 101.325 kilopascals

bars 100 kilopascals

British thermal units (International Table) 1,055.056 joules

centipoises 0.001 pascal seconds

centistokes 1.0 E-06 square meters per second

cubic feet 0.02831685 cubic meters

cubic inches 1.6387064 E-05 cubic meters

cubic yards 0.7645549 cubic meters

degrees (angle) 0.01745329 radians

degrees Fahrenheit (F-32)/1.8 degrees Celsius

fathoms 1.8288 meters

feet 0.3048 meters

foot-pounds force 1.355818 joules

gallons (U.S. liquid) 3.785412 E-03 cubic meters

hectares 1.0 E+04 square meters

horsepower (550 foot-pounds force per second) 745.6999 watts

inches 0.0254 meters

inch-pounds (force) 0.1129848 newton meters

kilotons (nuclear equivalent of TNT) 4.184 terajoules

knots 0.5144444 meters per second

microinches 0.0254 micrometers

microns 1.0 E-06 meters

miles (nautical) 1,852 meters

miles (U.S. statute) 1,609.347 meters

miles per hour 0.44704 meters per second

mils 0.0254 millimeters

ounces (mass) 0.02834952 kilograms

ERDC/LAB TR-0X-X xxv

Multiply By To Obtain

ounces (U.S. fluid) 2.957353 E-05 cubic meters

pints (U.S. liquid) 4.73176 E-04 cubic meters

pints (U.S. liquid) 0.473176 liters

pounds (force) 4.448222 newtons

pounds (force) per foot 14.59390 newtons per meter

pounds (force) per inch 175.1268 newtons per meter

pounds (force) per square foot 47.88026 pascals

pounds (force) per square inch 6.894757 kilopascals

pounds (mass) 0.45359237 kilograms

pounds (mass) per cubic foot 16.01846 kilograms per cubic meter

pounds (mass) per cubic inch 2.757990 E+04 kilograms per cubic meter

pounds (mass) per square foot 4.882428 kilograms per square meter

pounds (mass) per square yard 0.542492 kilograms per square meter

quarts (U.S. liquid) 9.463529 E-04 cubic meters

slugs 14.59390 kilograms

square feet 0.09290304 square meters

square inches 6.4516 E-04 square meters

square miles 2.589998 E+06 square meters

square yards 0.8361274 square meters

tons (force) 8,896.443 newtons

tons (force) per square foot 95.76052 kilopascals

tons (long) per cubic yard 1,328.939 kilograms per cubic meter

tons (nuclear equivalent of TNT) 4.184 E+09 joules

tons (2,000 pounds, mass) 907.1847 kilograms

tons (2,000 pounds, mass) per square foot 9,764.856 kilograms per square meter

yards 0.9144 meters

ERDC/LAB TR-0X-X 1

1 Introduction

Background

The U. S. Army Engineer Research and Development Center (ERDC) was contacted by the US Army Engineer District, Los Angeles, Regulatory Pro-ject Management (CESPL-RG-S) to perform a numerical sedimentation model study for the San Dieguito River Lagoon to facilitate the evaluation of wetland restoration alternatives that created significant lateral variation across the lagoon. That variability required the analysis be conducted in a two-dimensional analysis.

The numerical sediment transport modeling for the San Dieguito Lagoon Wetland (W19) Creation Study was performed in three phases. The initial phase was conducted on various components of the possible wet-land de-sign. These included a brackish marsh and several alternatives for berms and weirs at the brackish marsh. These alternatives were conducted for existing conditions, and various versions of Option 1 and Option 2 from previous analyses (Dokken Engineering, 2011).

The second phase of numerical sediment transport modeling was per-formed on the existing post-Edison condition and five “options” that were screened from the original phase 1 testing.

The final phase of testing was planned to be performed on a final set of very definitive alternatives which were executed for a series of individual storm events (10-, 25- 50- and 100-year storms) and for the 100-year storm series, which included a series of various return period storms de-signed by Chang (2004) to simulate the sediment supply over a long-term period. These alternatives were existing and Alternatives A, B and C. These alternatives were slightly revised versions of phase 2 options.

Project Description

San Dieguito Lagoon is located within the San Dieguito River Valley in the City of San Diego, San Diego County, California (Figure 1-1). The San Die-guito Lagoon W-19 Restoration Project (proposed project) would be lo-cated within San Dieguito Lagoon, east of Interstate 5 (I-5), south of County Highway S6, and west of El Camino Real (Figure 1-2 and Figure

ERDC/LAB TR-0X-X 2

1-3). Features of the existing wetlands are shown in Figure 1-4. The pro-posed project site (W-19) is located within lands owned by the San Die-guito River Park Joint Power Authority (JPA), California Department of Fish and Wildlife (CDFW), 22nd Agricultural District, and the City of San Diego, and is within the Focused Planning Area of the San Dieguito River Park (Figure 1-5).

The San Dieguito River Lagoon is a classical choked coastal lagoon (Kjerfve and Magill, 1989). The San Dieguito River is an ephemeral river. During the dry season tidal effects are seen upstream to El Camino Real Bridge. During flood events tides are completely washed out of the system and flood levels rise 10 to 20 feet over the project area for extreme flood events.

Historically, the San Dieguito Lagoon and its adjoining coastal wetlands occupied much of the western San Dieguito River Valley and included a mix of vegetated salt and brackish marsh, with associated tidal embay-ments, sloughs, and mudflats. The San Dieguito wetlands have experi-enced extensive filling and alteration, beginning as early as the late 1800s.

The U. S. Navy established an emergency landing field during the 1920s in the San Dieguito River Valley in an area east and west of I-5. Around 1938 the air field was used as a municipal airport to serve the Del Mar Fair-grounds. In 1941 the Navy expanded the air field to accommodate modern aircraft, the US Naval Auxiliary Air Facility Del Mar. During World War II the Navy took control of the air field and fair grounds to support the war. After the war the Del Mar Naval Auxiliary Air Facility was decommis-sioned and the fairgrounds returned to the State of California.

The loss of the natural wetlands within the San Dieguito Lagoon between 1928 and 1994 was documented by Kent and Mast (2005). The progres-sive economic development surrounding the lagoon encroached on the wetlands losing 70 percent of the wetlands by 1994 (Figure 1-6).

Between these impacts and simultaneous development of the surrounding area, less than half of the historic wetlands remain intact. Consequently, the ecological function of the tidal marsh ecosystem and the regular influ-ence of the ocean tidal waters have been substantially diminished (SANDAG 2011).

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Development, infrastructure, and the progressive closing of river and la-goon mouths throughout the San Diego region have led to the conversion and loss of coastal wetlands. The creation of coastal wetlands can offset this historic loss, enhance and maintain sensitive wetland habitats and na-tive species, promote coastal biodiversity within the region, and enrich functional wetland habitat within San Diego. The purpose of the proposed project is to create coastal wetlands, which will be used as mitigation for transportation projects within the coastal corridor of north San Diego County and will partially offset wetland losses within the San Dieguito sys-tem.

The proposed project would restore habitat that historically occurred within the lagoon, taking into consideration constraints now imposed by existing adjacent land uses and other recently implemented and planned projects. The proposed project would encompass approximately 141 acres, including an area historically identified as a restoration opportunity by the JPA in their 2000 Park Master Plan for the Coastal Area of the San Die-guito River Valley Regional Open Space Park (SDRPJPA 2000). ln addi-tion, the California Department of Transportation (Caltrans) and San Di-ego Association of Governments (SANDAG) identify the site as part of the overall wetland mitigation strategy for infrastructure projects along the North Coast Corridor within northern San Diego County in the Public Works Plan and Transportation and Resource Enhancement Program (Caltrans 2014). The proposed project is intended to be used for mitigation for infrastructure projects being planned by SANDAG, Caltrans, and/or the City of San Diego (e.g., El Camino Real Bridge Realignment Project). Reserve wetlands and/or uplands for future projects by others could also be created as part of the proposed project.

The proposed project would be incorporated into the overall vision of the restored San Dieguito Lagoon system, including other restoration projects as described below, and of the Park Master Plan, which would be updated as part of the proposed project. The Park Master Plan provides a frame-work for implementing community goals for the restoration of the San Di-eguito Lagoon ecosystem, both tidal and nontidal, and for the provision of public access trails and amenities for public enjoyment and nature study (SDRPJPA 2000). The project would restore areas identified in the Park Master Plan (see areas identified as U19, W36, M32, M33, and M37 in the Park Master Plan), as well as other areas west of El Camino Real owned by

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City of San Diego, CDFW, and 22nd Agricultural District. The existing rec-reational trail system in the San Dieguito Lagoon ecosystem would also be expanded as part of the project. The Park Master Plan would be amended to redesignate the restored areas as W-19 and incorporate the updated boundaries of restoration and proposed habitat types associated with the proposed project.

Other portions of the historic San Dieguito Lagoon system have already undergone restoration efforts, and the proposed project would comple-ment existing restoration efforts. Southern California Edison (SCE) imple-mented the San Dieguito Wetland Restoration Project, which encom-passed approximately 440 acres between El Camino Real and the Pacific Ocean. The SCE project included excavation, restoration of tidal wetlands, reestablishment of historic uplands, and enhancement and expansion of freshwater and seasonal coastal wetland areas, as well as a public access and interpretation component (USFWS and SDRPJPA 2000). The project would be designed to integrate and expand upon SCE's San Dieguito Wet-land Restoration Project. The project would also be designed to accommo-date ongoing efforts at wetland creation and restoration west of I-5 and south of the Del Mar Fairgrounds, as well as integrate with the proposed El Camino Real Bridge Realignment Project planned by the City of San Di-ego. The freshwater brackish marsh portion of the proposed project is an-ticipated to provide mitigation for the City's bridge realignment.

Previous Work

Webb, et al. (1991) analyzed inlet morphology in relation to process and material parameters and compared spatial and temporal patterns of mor-phodynamics at three small southern California tidal inlets, one of which was San Dieguito Lagoon inlet. They found that the inlets became unsta-ble at low river flows and neap tidal conditions when the littoral transport of sediment overwhelmed the capacity to move sediment out of the inlet. This conceptual model of the conflicting balance between coastal forces to close the inlet and riverine processes to keep it open serves well to under-stand the San Dieguito Lagoon inlet.

Chang (1998) performed an analysis of the flow exchange between several proposed wetland restoration areas and the main river channel. The wet-land designs called for berms to separate the wetlands from the main channel. The purpose of the study was to design culverts to minimize the head difference between the river and the wetlands during flood events.

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Elwany, et al. (1998) documented that the condition of the inlet, either be-ing open or closed, is mainly controlled by the river flows. They analyzed 50 years of direct observations of the inlet condition. They found that the inlet was open 34 percent of the time. The conditions were dependent on the littoral supply of sediment and available tidal prism were strong influ-ences. However, dry periods had the inlet open about 12 percent of the time, while wet periods had the inlet open 66 percent of the time. Elwany, et al. (2003) evaluated a detailed history of beach profiles and inlet tran-sects and found that the inlet could be artificially opened without a statisti-cally significant impact on the local beaches.

Chang (2004) applied the Fuvial-12 numerical model to the Southern Cali-fornia Edison W4 Wetland Restoration Project. Because the design fea-tures of the wetland resulted in simple cross sections that could reasonably be represented in a 1D model, the analysis was very appropriate and re-sulted in an effective design that later proved to be very successful.

Jenkins, et al. (2004) studied the potential impact of the Southern Califor-nia Edison wetland restoration (W4) of the San Dieguito Lagoon would have on littoral transport and beach stability in the immediate neighbor-hood of the mouth of the San Dieguito River. They reported that the pe-riod they analyzed showed the inlet at the San Dieguito River was open 75 percent of the time (more often than any other decade in the period of rec-ord), and yet the beaches of Del Mar increased in width over this same pe-riod. They further concluded based on empirical observations and numer-ical modeling that the cyclical erosion at Del Mar beaches is a pre-existing condition. They also concluded that the Edison Restoration Plan would cause no measurable changes to existing beach widths and elevations, that project maintenance plans for the inlet would increase the volume of sedi-ment reaching the beaches and that the erosion in front of the Sandy Lane homes is an ephemeral pre-project condition which should not affected by the restoration.

Young and Ashford (2006) evaluated the sediment characteristics in the littoral zone along the southern California coast against the sand composi-tion in the cliffs along the shore. They found that the dominant source of sediment in the littoral zone was from the cliffs. For one reach they docu-mented that 67 percent of the sediment came from the cliffs, 17 percent from offshore gullies and only 16 percent from the rivers.

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Young, et al. (2010) evaluated the percentage of coarse sand, larger than 0.06 mm in diameter, in the sea cliffs along the southern California Oceanside littoral cell. The Del Mar sea cliff section just south of San Die-guito Lagoon had 53 to 75 percent over several studies. Their study re-ported 61 percent. The Solana Beach sea cliff section just north varied from 53 to 93 percent with their study reporting the 93 percent coarse ma-terial in the cliffs.

Dokken Engineering (2011) documented the results of San Dieguito La-goon W19 Restoration Project feasibility study. The study evaluated three alternatives, similar to the ones reported in this report. The first alterna-tive separated the W19 salt marsh from the main river channel with a dike, with a weir at the eastern end of the salt marsh. This design mimicked the design of the SC Edison W4 wetland design. This was the recommended alternative. The second option replaced the dikes with berms at lower ele-vations that overtopped at high river flows. This alternative failed to meet three of the success criteria and was not recommended for additional con-sideration. The third alternative was similar to the first with an expanded salt marsh area. It did not meet three of the success criteria by small mar-gins; however, it results in a significant increase in tidal wetland area, and therefore was recommended for further study.

The feasibility study sediment transport study was performed using the Fluvial-12 model (Chang, 2006). The model is a one-dimensional model with lateral analytical adjustments for shear stress and sediment bed ex-change. The model treated the salt marsh as part of a complex single cross section in common with the river channel cross section for the second al-ternative. This approach was identified to have some critical flaws and be-yond the capability of a 1D model (CEERD-HF-EL, 2012). The second op-tion essentially included a flow diversion at high river flows. The model predicted erosion downstream of the diversion.

Letter, et al. (2008) showed that for rivers in relative equilibrium that di-verting flow from a river with sediment concentrations less than or equal to the upstream concentration will lead to deposition downstream of the diversion on the main stem of the river. Brown, et al. (2013) confirmed and extended the analysis to response both upstream and downstream of the diversion.

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Objectives

The objectives of the study reported herein was to evaluate newly refined wetland restoration alternatives using a two-dimensional (2D) sediment transport model. In addition, the study has a technology transfer goal to provide local experience in the Southern California numerical modeling community with the AdH numerical model.

Scope

This report documents the numerical modeling performed by ERDC in support of the project and several sensitivity analyses that were performed to provide a better understanding of the historical and general characteris-tics of sedimentation within the San Dieguito River Lagoon.

Figure 1-1 Location of study area

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Figure 1-2 General location of project within the San Dieguito River Lagoon

Figure 1-3 Wetland Restoration Project Location

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Figure 1-4 Features of existing and proposed wetlands

Figure 1-5 Focused Planning Area of the San Dieguito River Park

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Figure 1-6 Aerial photographs of San Dieguito Lagoon used in wetlands change analysis: 1928 and 1945 panchromatic photography; 1975 and 1994 color infrared photography

(from Kent and Mast, 2005).

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2 AdH Model development

Modeling Strategy

The general approach taken for the analysis of this project was designed by the original modeling team of Dokken Engineering and Moffat & Nichol Engineering. ERDC was not involved in the original design but reviewed the approach and found the general approach to be reasonable.

The approach recognizes that the general processes in the project area can be reasonably divided into two classes: riverine flood dominated and coastal processes dominated.

The assumption can be made that the statistics for coastal processes envi-ronment and riverine flood events are independent; therefore, the analysis of the riverine delivery of sediments and the normal coastal lagoon pro-cesses can be performed independently. This is the general approach taken for this study. The ERDC sediment transport modeling evaluated the riverine sediment delivery and flood impacts on wetland sustainability. The ERDC model was an application of the Adaptive Hydraulics (AdH) model developed by ERDC (Appendix A).

The ERDC riverine model included the simulation of the tidal exchange with the ocean. The offshore model boundary was approximately 2 miles west of the inlet. Tidal conditions were simulated during each of the river-ine flood events. Analysis for the railroad bridge (Appendix B) included a short-period wave model that concluded that wave energy does not propa-gate significantly beyond the Camino Del Mar Bridge. During large river-ine flood flows the water surface profile becomes independent of the coastal processes and dependent on the river geometry and flow volume. Sediment volumes delivered to Jimmy Durante Bridge (see Figure 1-2) are assumed to be independent of the coastal processes.

The magnitude of the riverine sediment delivery to the coastal zone will be controlled by the magnitude of the flood flows, not by littoral zone condi-tions. The immediate short-term disposition of the flood-delivered sedi-ment is the formation of an alluvial fan at the mouth of the river. The long-term disposition of those newly delivered sediments will be depend-ent on the long-term littoral conditions rather than the river flows that de-livered them.

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During the periods of non-riverine flood flows, coastal processes deter-mine the tidal flow and sediment circulation in the inlet mouth and tidal lagoons. The tidal range within the lagoon is controlled by the geometry within the mouth of the inlet. Whether the inlet mouth is open (dredged) or closed (shoaled) influences the tidal energy that can propagate from the mouth of the river into the lagoon. The conditions within the river mouth are naturally controlled by a balance between the wave environment in the littoral zone which tends to close the inlet and the scouring during tidal flows and river floods, which tend to open the mouth of the inlet. As a condition of the Southern California Edison (SCE) Coastal permit for their lagoon restoration, SCE must maintain the inlet in an open condition and therefore periodically dredges the inlet.

Observable quantities of riverine sediment are delivered to the ocean with large storm events of 10-year or longer return period probability. To measure the impact of the project and alternatives on riverine sediment delivery, the volume of riverine sediment reaching Jimmy Durante Bridge was compared. Jimmy Durante Bridge was selected for several reasons.

The tide and coastal processes have no impact on the riverine sedi-ment analysis upstream of Jimmy Durante Bridge. The comparison of riverine sediment downstream of Jimmy Durante Bridge, in an area influenced by coastal processes would increase the complexity of the modeling. Modeling riverine sediment downstream of Jimmy Durante Bridge would require adding both the short-period coastal littoral wave energy processes and analysis of the timing of the flood peak with various tidal phases.

Comparison at Jimmy Durante Bridge was consistent with the SCE termination of the Fluvial-12 analysis at the Jimmy Durante Bridge.

Therefore, using the Jimmy Durante Bridge as the downstream riverine sediment comparison location provides an accurate analysis of the impacts of the project and project alternatives on the riverine sediment delivery to the coastal zone.

The approach taken for the coastal environment was pragmatic and effi-cient. The approach taken was to first evaluate whether the tidal range within the lagoon was impacted significantly by the construction of the proposed project. If the tidal range impacts are not significant, then the

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coastal littoral processes would be assumed to dominate over minor varia-tions in the tidal range. The general findings of the tidal analysis were that the variation in the lagoon tidal range are much more sensitive to the con-dition of the geometry in the mouth of the inlet, dredged or shoaled (con-trolled by the littoral environment) than to the increase in tidal exchange associated with the proposed project. Therefore, additional numerical modeling of the littoral processes with the tidal lagoon exchange requiring sediment size distribution was not required.

Because of the ephemeral nature of the San Dieguito River and resulting hydrodynamics of the lagoon, the system was subdivided into dry season modeling for tidal performance of the wetlands and wet season modeling for river flood events and the resulting flood control issues and sedimenta-tion that effects the sustainability of the wetlands.

The tidal modeling will be briefly described in Chapter 3 for completeness, but the alternative screening for tidal damping is reported in (Moffatt and Nichol, 2018). ERDC assisted Moffat and Nichol in adapting their model-ing efforts to the application using AdH. Technical consultation was main-tained throughout the current project. That modeling supports the tech-nology transfer goal of ERDC involvement in the project.

The wet season sediment transport modeling is the subject of this report and was performed by CEERDC-HE-EL. The wet season hydrodynamics are riverine dominated, particularly over the reach of the river where the proposed wetlands that are the subject of this report are located. Conse-quently, the influence of the coastal processes has been assumed to have no influence on the performance of the various alternative wetland designs to be evaluated. More directly, it has been assumed that the two processes are independent, such that the conclusions that can be drawn from the comparisons made ignoring the coastal processes would not be invalidated by consideration of coastal processes. One of the criteria for evaluation of alternatives herein is, however, the sediment supply that is delivered to the coastal zone.

Model Meshes developed

Dry Season Tidal Mesh

The dry season tidal mesh domain was limited to the portion of the lagoon subject to tidal conditions. This limited domain also reduced the memory

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requirements of the AdH model which was simulated local computer sys-tem at Moffatt Nichol (2016). The overall domain of the tidal mesh is pre-sented in Figure 2-1. The upstream limit is just west of El Camino Real.

Wet Season Riverine Flood Mesh

The domain of the wet season sediment transport model mesh extends from an ocean boundary (common to the dry season mesh) upstream to just north of the Fairbanks golf course and up to Avenida Feliz adjacent to the Morgen Run golf course, approximately 7 kilometers (4.3 miles) from the ocean. The original wet season model meshes were developed by Moffatt and Nichol Engineers. Initial simulations with the sediment transport model showed that the accurate simulation of the sediment con-centration fields and the resulting bed exchange required higher resolution than the tidal model. Therefore, the meshes were refined throughout, doubling the resolution. Sensitivity testing showed the sediment transport model performed better when significant geomorphic changes began oc-curring within the model domain. The wet season model mesh for the ex-isting conditions is presented in Figure 2-2 showing the overall model do-main.

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Figure 2-1 Model mesh for dry season tidal hydrodynamic model of existing conditions

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Figure 2-2 Model mesh for wet season sediment transport model of existing conditions

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3 Tidal Verification

The secondary goal of the study of technology transfer was advanced by the separating the numerical model study for normal dry conditions dur-ing which the project performance could be evaluated by tidal propagation analysis and for the high river flow conditions under which the wetland sustainability is jeopardized by sedimentation within the wetlands. Loss of wetland performance could be from direct sedimentation within the wetlands or from sedimentation in the access channels that mutes the tides.

The tidal performance modeling was performed by Moffatt and Nichol En-gineering (Weixia Jin) for the dry season analysis and the high river flow modeling was performed by ERDC and is the subject of this report. A brief summary of the tidal modeling will be provided here.

AdH Hydrodynamic Model Calibration

The AdH model mesh constructed for the tidal study is presented in Figure 2-1 and details of the mesh in the project area in Figure 3-1. The model simulations involved wetting and drying of computational nodes associ-ated with tidal fluctuations.

The model verification was performed for both a shoaled condition and for a dredged condition in the entrance channel. Bathymetry was modified for each simulation to reflect the conditions in the channel as appropriate for the period of tidal data collection.

Model Calibration Parameters

The model parameters that were adjusted in order to achieve calibration included primarily the bottom roughness coefficients (Manning’s n), eddy viscosity factors and the wetting and drying shock capture parameter. The shock capturing parameter defines the water depth below which stability parameters are used for stability.

Tidal Verification Results

An example of the tidal boundary forcing signal is presented in Figure 3-2. The tidal signal was taken from the La Jolla, CA NOAA tide gage and was

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applied uniformly over the arch of the model ocean boundary (Figure 2-1). The locations of the tide gages that collected of data for comparison are presented in Figure 3-3.

The model tidal verification at the tide gage just downstream of the Inter-state 5 Bridge (gage T12) for the shoaled condition on November 2004 is presented in Figure 3-4. The ocean tidal boundary signal is included in the figure for reference. The model shows the significant tidal muting ob-served in the observations associated with the shoaled entrance channel.

For the dredged condition during June 2011 the model tides at station T12 are compared to the observed tides in Figure 3-5. The model shows sig-nificantly less tidal damping for the dredged condition, in agreement with the observed tidal signal.

The propagation of the tide upstream of the Interstate 5 Bridge to tide gage T14 is shown in Figure 3-6 for the June 2011 dredged condition. The agreement there is comparable to the agreement at T12, both showing ap-proximately the same tidal response.

The tidal model was then applied to the range of alternatives selected for analysis and the trade-offs of added wetland performance of the W19 wet-lands versus the loss of tidal amplitude in the SCE W4 wetlands evaluated. The full description of the application of the tidal model is documented in Moffatt and Nichol (2016).

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Figure 3-1 Details of model mesh within the lagoon for existing tidal model.

Figure 3-2 Ocean tidal boundary condition for June 2011

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Figure 3-3 Location of tide gages used for model verification.

Figure 3-4 Tidal verification for gage T12, west of I5, for the shoaled condition in the inlet

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Figure 3-5 Tidal verification for gage T12, west of I5, for the dredged condition in the inlet

Figure 3-6 Tidal verification for gage T14, channel between I5 and El Camino Real Bridges, for the dredged condition in the inlet

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4 Sediment Transport Verification

Verification Model Mesh

The sediment transport model was verified to the San Dieguito River flood hydrograph of January through March 1993. That period was used by Chang (1994) in the calibration of the Fluvial-12 model. An aerial photo-graph of the system for the pre-Edison conditions is presented in Figure 4-1. For the verification a pre-Edison wetland numerical model mesh was created. Figure 4-2 presents the model mesh resolution in the study area and Figure 4-3 presents the bathymetry of the mesh. The bathymetry in the mesh was based on a 1992 survey and pre-storm 1993 cross sectional transects (Figure 4-4).

Boundary Input

Bed material gradation

The surficial bed sediment along the San Dieguito River channel was de-fined by Chang (2004). The grain size distributions presented as percent finer by weight are shown in Figure 4-5. There is some tendency for coars-ening of the material in the downstream direction, but there is significant variability. The numerical model was assigned a representation size distri-bution which is also presented in Figure 4-5. That grain size distribution was specified uniformly in space, both horizontally and vertically within the bed. There is insufficient data to specify any variation in model grain size distribution with any confidence.

Flood hydrograph

The hydrograph for the verification period was developed by Chang (2004). The hydrograph is presented in Figure 4-6, with time 0 at mid-night on the 4th of January. The peak of the flood occurred on the 13th (around hour 216). The plotted hydrograph presents the hydrograph used by Chang (2004) and the mean daily flow. Because the time step in the AdH model is much shorter than used in Fluvial-12, a fit was made to the data that conserved the total volume of flow and the approximate timing of the flood peaks. The peak flow occurred on the 13th January was 6650 cfs (188 cms) with secondary flood peaks on 4 February of 2900 cfs (82 cms) and 16 February of 4400 cfs (125 cms). The flood hydrograph is approxi-mately 1400 hours (58 days).

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Tides

The tidal signal from the La Jolla California NOAA station for the verifica-tion period is also presented in Figure 4-6. The peak storm flood event had flood flows rising during neap tides, peaking at a mean tide and then falling during spring tide. The second peak flows rose during spring tide, peaked near mean tide range and flows receded near neap tide. The third peak had flows rise during spring tides, peak near mean tides and receded under mean tide conditions. The river flows varied more slowly than the rise and fall of the tides, such that exact timing of the flood peak with the intertidal phase was less significant.

Model Initial Condition

The model was initiated by performing a model water surface elevation draw-down from an extreme tide level (12 m) and an initial river discharge of 14 cms (494 cfs). The river discharge was held constant and the ocean tide level slowly lowered until the ocean level was at high tide. The draw-down simulation did not simulate sediment transport but allowed the model to initialize the flow inundation over the model domain. The results of the drawdown were then used as starting conditions for river flood sim-ulations with sediment transport activated.

Number of initial bed layers

The number of bed layers within the bed was defined as 10 layers. The first layer, which is initially the bed surface layer, was defined with the ini-tial bed sediment gradation (Figure 4-5). The use of the remaining 9 bed layers is for definition of newly deposited sediment or for the creation of winnowed layers from the initial surficial sediments to armor the bed.

Initial bed layer thickness

The thickness of the initial bed layer was generally set to 4 meters thick. It is assumed that anything below 4 m of the bed is non-erodible. For areas with armoring the initial bed thickness was set to zero. For the bed armor-ing underneath the El Camino Real Bridge the initial bed thickness was set to 2.46 meters to reflect the thickness of sediment overlaying the armor apron there.

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River Sediment Inflow

There was no sediment concentration inflow data for the upstream end of the model that could be used to specify the sediment load of the river. An alternative approach used in similar studies is to define a reach of the up-per end of the model channel that serves as a sediment supply reservoir. The grain size distribution within the bed is fixed and the entrainment of sediment into the water column is governed by the decrement in transport capacity of the flow. For this sediment reservoir reach the bed elevation is held fixed, such that supplying sediment to the water column does not re-sult in erosion. The philosophy of this approach is that the inflow sedi-ment flux at the river inflow boundary is set to zero and this transition re-gion replaces the inflow boundary flux with a bed entrainment flux. At the end of this defined reach the sediment transport is at capacity for the spe-cific flow conditions throughout the flood hydrograph. The portion of the model used for the sediment reservoir is shown in Figure 4-7.

Calibration Parameters

The numerical sediment transport model adjustments available for model calibration were:

Bathymetry

Local model bathymetry was not adjusted with the model except for at the extreme upper end of the model at the river inflow boundary. This was helpful in obtaining model stability by ensuring that no wetting and drying logic was attempted at the boundary. The localized deepening at the boundary is shown in Figure 4-8.

Roughness coefficients

The primary adjustment in obtaining model verification was adjustment of the bottom roughness coefficient. For this study Manning’s roughness co-efficient was used. The model sensitivity to bottom friction adjustments is illustrated in Figure 4-9 , which shows the profile up the river of the water surface elevation and the bed elevation. The successive model simulations reducing the friction lowered the water surface and also deepened the depth of bed scour lowering the bed elevation.

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Initial bed layer thickness

The initial model runs were initiated with a two-meter bed thickness, which proved to be inadequate for the depth of scour experienced. The fi-nal model calibration used a four-meter bed thickness.

Wetting and drying shock capturing parameter

As the river flood passes through the system the water rises onto the flood plain and then recedes after the flood peak passes. The AdH model per-forms wetting and drying calculations during the simulation. When the water depth becomes extremely shallow and the model performs succes-sive nonlinear iterations toward a solution for the time step, wetting and drying can cause a “ringing” were a node in the mesh alternates from wet to dry and then back to wet in successive iterations hindering model con-vergence.

A technique of shock capturing has been developed for these situations that changes the equations being solved in extremely shallow water that overcomes these wetting and drying issues. The shock capturing variable is an input variable to AdH that controls the water depth below which the shock capturing logic is applied. For this model application it was found that a value of 0.25 meters worked well.

Comparison of AdH with cross sectional Surveys

The details of the survey transects used for comparison of before to after cross sections for the 1993 flood event are shown in Figure 4-10. The com-parison of the AdH model simulation results to the survey transects are presented in Figure 4-11 through Figure 4-17 for transects 12 through 18. The model results for the three sensitivity simulations which are shown in Figure 4-9 are also presented in each transect. This provides an additional indication of model sensitivity. The primary model calibration is consid-ered to be the “HD5e” simulation.

Transect 12 shows that the model correctly had erosion on the southern side and deposition on the north side, as seen in the survey data. Both the depth of scour and depth of deposition are in good agreement with the ob-servations.

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Transect 13 is located in the tidal channel that feeds the lagoons to the south and is not a conveyance channel for flood flows. The model cor-rectly showed essentially no change at that cross section.

For transects 14 through 18 the model shows the correct general erosion trend in the appropriate location in the cross section with erosion of the thalweg and slight deposition of the upper elevations. The model erosion was generally more focused in the center of the cross sections while the surveys showed a more evenly distributed erosion over the channel. This suggests that there may be coarser material with depth in the field which was not reflected in the model. No data were available to specify such var-iation in the model.

Comparison between AdH and Fluvial-12

The profile of the water surface elevation, the bed elevation at the peak of the flood and at the end of the flood are compared for the Fluvial-12 model and the AdH model in Figure 4-18. The locations of the Jimmy Durante Bridge (JDB) and the Interstate 5 (I5) are marked on the profile.

The Fluvial-12 model variables are plotted as blue and the AdH as red. The initial bed profiles are not exactly the same. The AdH model has more resolution than the Fluvial-12 model, which has a finite number of cross sections averaging 300 to 400 feet between cross sections. The AdH model has elements that are on the order of 10 to 20 feet in size along the channel.

The water surface profiles between the models is in good agreement up-stream of the I5 bridge, but at the I5 bridge the Fluvial-12 water surface profile drops away from the AdH model downstream. An observation from the field was available that defined the peak flood elevation at the I5 Bridge, shown in the figure to match very well with the AdH simulation.

However, the erosion of the thalweg of the channel is in very good agree-ment overall between the Fluvial-12 and the AdH simulations. Both mod-els show a deep scour hole just downstream of the Jimmy Durante Bridge.

Model Calibration/Verification Results

The quality of the AdH model verification is considered to be very good. The comparisons to field surveys and observations found:

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1. The predicted water level matched well with the recorded peak wa-ter level during the 1993 flood event.

2. The predicted post-storm scour depth compared qualitatively well to the cross-section surveys

3. The predicted bed profile changes compared well with Fluvial-12 model

The calibrated AdH model is suitable for options comparison.

The modeling experience for San Dieguito River Lagoon has shown that the hydrodynamics cannot be uncoupled from the sediment transport, due to the magnitude of the bed erosion and deposition that occurs.

The AdH model erosion near the mouth may be strongly influenced by flows during low tide. Tides need to be included within the simulation. However, local sedimentation near the ocean is dramatically influenced by coastal processes. Therefore, the analysis for this study is limited to up-stream of the Jimmy Durante Bridge.

The AdH modeling mesh resolution was increased as mentioned above to increase model stability. In addition to improved stability the higher reso-lution exhibited geomorphological response in the bed displacement as il-lustrated in Figure 4-19. The upper image is of a deltaic feature within the Trinity River delta in Texas. It is classical in the development of delta lobes with incised distributary channels between the lobes. The lower im-age is of the AdH model results for the San Dieguito River model just downstream of the El Camino Real Bridge. It is exhibiting the creation of deltaic lobes with distributary channel features.

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Table 4-1 Model sediment grain size specifications and initial distribution

Size Number Size Class

Grain Size (mm)

Specific Gravity Porosity

Distribution (%)

1 Very Fine Sand 0.088 2.65 0.3 1

2 Fine Sand 0.177 2.65 0.3 15

3 Medium Sand 0.354 2.65 0.3 67

4 Coarse Sand 0.707 2.65 0.3 16

5 Very Coarse Sand 1.414 2.65 0.3 1

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Figure 4-1 Aerial photography of the San Dieguito Lagoon prior (1994) to the construction of the Southern California Edison wetland restoration project

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Figure 4-2 Pre-Edison sediment transport verification model mesh resolution

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Figure 4-3 Pre-Edison sediment transport verification model mesh bathymetry

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Figure 4-4 Location of survey transects documenting the before and after conditions for the

1993 flood event

Figure 4-5 Surficial sediment grain size distributions along the San Dieguito River from which the model sediment distribution was developed (data from Chang, 2004) for a range of River

Miles (RM)

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Figure 4-6 Long hydrograph comparisons for sedimentation verification simulation

Figure 4-7 Zone of model defined as sediment reservoir for development of sediment

transport capacity

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Figure 4-8 Deepening of the model at the river inflow boundary for model stability

Figure 4-9 Sensitivity of sediment transport model profiles to bed friction

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Figure 4-10 Location of survey transects used for sediment transport model verification

Figure 4-11 Comparison of model bed elevation response to observed surveys before and after the 1993 flood event at Transect 12

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Figure 4-12 Comparison of model bed elevation response to observed surveys before and

after the 1993 flood event at Transect 13

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Figure 4-13 Comparison of model bed elevation response to observed surveys before and

after the 1993 flood event at Transect 14

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Figure 4-14 Comparison of model bed elevation response to observed surveys before and

after the 1993 flood event at Transect 15

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Figure 4-15 Comparison of model bed elevation response to observed surveys before and

after the 1993 flood event at Transect 16

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Figure 4-16 Comparison of model bed elevation response to observed surveys before and after the 1993 flood event at Transect 17

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Figure 4-17 Comparison of model bed elevation response to observed surveys before and after the 1993 flood event at Transect 18

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Figure 4-18 Comparison of AdH model results to the Fluvial-12 model for the 1993 verification flood event

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a) Evolving deltaic distributary features within Trinity Bay, Texas

b) AdH model bed displacement features

Figure 4-19 Illustration of AdH ability to simulate the deltaic processes that lead to distributary channels between delta lobes

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5 Alternative Wetland Designs

During the feasibility phase of the San Dieguito Wetland Restoration Pro-ject there were six basic design alternatives to current conditions that were developed. These alternatives are described below.

Existing Conditions

The existing conditions are considered to be the pre-project conditions for the proposed W-19 Wetland Restoration Project. The existing condition is taken as the post-Edison W-4 Wetland Restoration Project construction.

Option 1

Option 1 is presented in Figure 5-1. It includes a salt marsh on the south-ern side of the river between Interstate 5 and El Camino Real. The eastern limit of the salt marsh is the utility corridor. The salt marsh is separated from the river channel by a dike along the northern side and has an over-flow weir along the eastern side adjacent to the utility corridor.

The option also calls for a brackish marsh between the utility corridor and the El Camino Real Bridge on the south side of the river. It includes an overflow weir. The original design of the weir had an elevation of 12 feet NGVD29 (3.66 m). There also are culverts in the dike around the brackish marsh for tidal exchange.

Option 2

Option 2 was designed to be more unconfined and the dikes are replaced by berms that allow for overflow at high flood levels. Option 2 is presented in Figure 5-2. The brackish marsh includes a flow through channel for tidal exchange. The salt wetland footprint is the same as for Option 1.

Option 3

Option 3 is very similar to Option 1 but with an expanded wetland area to the northeast attempting to make the overall floodway width of the river north of the dike more uniform. Option 3 is presented in Figure 5-3. The salt wetland retains the dike and the eastern weir with the brackish marsh the same as Option 1.

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Option 4

Option 4 is an expanded version of Option 2 using berms. Option 4 is pre-sented in Figure 5-4. It is a highly conceptual design without fidelity in the wetland features compared to other options. This alternative was never tested within this study, but general performance expectations were drawn from the other options.

Option 5

Option 5 includes a diked salt marsh with overflow weir, a brackish marsh with options on being diked or unprotected and in addition, an along river wetland north of the dike around the salt marsh. Option 5 is presented in Figure 5-5.

Option 6

Option 6 includes a diked salt marsh with an expanded area to the north-east (Figure 5-6). It includes an overflow weir section on the east at the utility corridor. The brackish marsh is protected from direct inflow from past the El Camino Real Bridge by a dike which is open to flow on the western end to allow for tidal flow into the marsh.

These optional designs are the starting point for alternative screening and were changed as the performance of the options were evaluated in order to achieve project performance criteria.

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Figure 5-1 Original conceptual drawing for W19 Wetland Restoration Option 1

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Figure 5-2 Original conceptual drawing for W19 Wetland Restoration Option 2

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Figure 5-3 Original conceptual drawing for W19 Wetland Restoration Option 3

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Figure 5-4 Original conceptual drawing for W19 Wetland Restoration Option 4

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Figure 5-5 Original conceptual drawing for W19 Wetland Restoration Option 5

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Figure 5-6 Original conceptual drawing for W19 Wetland Restoration Option 6

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6 Model Production Strategy

The modeling production strategy focused on the two primary perfor-mance criteria of concern. The first is that the 100-year flood levels should not be increased. That led to running a single 100-year flood event as a first test for screening. The second criterion was for the sediment delivery to the ocean. For screening purposes, it was decided that the single event 100-year flood could logically serve as a measure of the sediment supply for first screening analysis.

For all model simulations, analysis of the sediment delivery to the ocean was aliased to the sediment delivery to Jimmy Durante Bridge. As dis-cussed previously, because no project features are west of the Interstate 5 bridge and riverine conditions dominate in the vicinity of Jimmy Durante Bridge, it was selected. The choice is consistent with the analysis for SCE wetlands.

Description of Testing Program

The sediment transport model was verified to the 1993 flood event which was used by Chang (2004) for the verification of the Fluvial-12 model. The flood hydrograph for the 1993 verification flood was derived from his flood hydrograph.

Once the model was verified the testing program developed for this project was based on hydrology developed by Chang (2004) in previous modeling for the Edison wetland project located on the north side of the river from the current W-19 wetland project.

Single Flood Events

The resulting testing program includes single flood event hydrographs for flood return periods of 10-, 25-, 50-, and 100-year return periods. The flood hydrographs are presented in Figure 6-1. The 10-year flood event is a broader crested event with the peak discharge occurring earlier (hour 15) compared to the remainder of the single events, which all peak at hour

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23.5 and are simply scaled from the 100-year flood hydrograph. The de-tails of the hydrographs are presented in Table 6-1.

The ocean tide level varied during all model simulations based on a typical tidal variation taken from the La Jolla, CA tide station, located approxi-mately 8 miles south of the mouth of the river. The tidal signal was the same for all model testing. The tides during the 60-hour duration of the single event simulations is shown in Figure 6-2.

100-year Flood Series

In addition, Chang (2004) developed a simulation series that included a sequence of individual flood events designed to provide the equivalent to-tal sediment delivery that would occur over a 100-year period. This test simulation is called the “100-year series” and is presented in Figure 6-3.

The 100-year series simulation duration was 250 hours. The tidal signal for these tests is presented in Figure 6-4. The incorporation of the effects of tidal phase on the testing program was not practical for this study. Be-cause the simulations were run the same for all design alternatives the comparisons between alternatives are appropriate and valid. However, the effects of the tidal phase on the absolute model results (e.g., long-tern average sediment supply) were not explicitly addressed in the testing pro-gram. The relative comparisons between alternatives remains valid. A much more rigorous testing program would be beyond the funding and schedule constraints placed on the engineering analysis for this project.

The theory behind the 100-year series development is that there is some threshold river flow below which no significant sediment transport occurs. If one constructed a full-time series of river flows over a 100-year period and then removed all periods when the flow was below that threshold and collapsed the remaining flow periods together that the duration of that hy-drograph would be very short.

To test the sensitivity of the modeling to such a contraction in the flow hy-drograph the 1993 verification hydrograph (Figure 4-6) was truncated by removing periods when the flow was below 500 cfs (Figure 6-5). For this one hydrograph the duration of the simulation was reduced from 1400

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hours to 1000 hours. That may not seem like much of a gain, but that was for a period of very high flows. When the long durations of essentially no flows is considered then a 100-year period could be shortened quite dra-matically.

The short hydrograph for the 1993 flood was simulated and the sediment transport model results compared for consistency.

The comparison of the profile of the peak water level, the bed elevation at the peak of the flood and the bed elevation at the end of the flood are pre-sented in Figure 6-6. The water surface elevations at the peak are virtually identical. The bed elevations at the peak of the flood are in very close agreement. The final bed elevation does show some quantitative differ-ences, suggesting that the short simulation left a few deeper scour holes. But generally, the two simulations are in very close agreement.

To see a more detailed comparison of the two simulations the differences between the two along the channel are presented in Figure 6-7. The water surface elevations agree generally to within 0.02 m (0.066 ft) throughout the profile with closer agreement farther upstream near the current pro-ject. The bed elevation at the peak of the flood is generally higher for the shortened hydrograph and the bed elevation at the end of the simulation is lower for the shortened hydrograph.

The general agreement between the two simulations is close enough that the truncated hydrograph approach developed by Chang (1998) is consid-ered reasonable for screening alternatives. This approach is very reasona-ble considering that it allows for numerical model simulations that are ca-pable of being performed within the constraints of time placed on the project analysis.

Sea Level Rise

In order to assess the potential impacts of sea level rise on the sedimenta-tion model results the 100-year single event simulations were modified to develop two tests for sea level rise by raising the mean tide level of the ocean tide by 1.5 foot and then by 5.5 feet. These were a simple vertical

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shifting of the tidal signal in Figure 6-2. These two additional tests were simulated only for the existing conditions and for Alternative A.

The effects of sea level rise on the proposed wetlands will be a gradual pro-cess that would be very complicated and difficult to accurately simulate in a numerical model. As the mean water level rises, the resulting impact on the geomorphology of the wetland will be a complicated balance between sediment supply to aggrade the bathymetry and the contribution of bio-mass in the ascension of the bottom. That analysis is beyond the scope of the current modeling effort. However, the approach taken in the current study is to linearly shift the tide upward to provide a bounding analysis. The existing sea level elevation simulations can be viewed as the future condition for any sea level rise, assuming that the tide range in the ocean is unchanged and the overall system sedimentation is able to rise in equilib-rium with the sea level. The sea level rise of 1.5 feet can be viewed as the case were the deposition within the system, although uniform, is unable to keep up with sea level rise by an offset of 1.5 feet.

The impacts of sea level rise on habitat are addressed in the tidal analysis for the dry season (Moffatt and Nichol, 2016).

Table 6-1 Single flood evens for simulations in testing program

Return Period

Peak Discharge Peak Occurs

(cfs) (cms) (hour)

10-year 6,740 191 15

25-year 16,000 453 23.5

50-year 31,400 889 23.5

100-year 41,800 1,184 23.5

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Table 6-2 Series of flood events in the 100-year series simulation

Event Return Period

(years)

Peak Discharge Time to Peak

(cfs) (cms) (hours)

1 10 5700 161 5.4

2 30 20000 566 25.4

3 20 14000 397 49.4

4 40 24000 680 76.4

5 15 11000 312 103.4

6 100 41800 1184 131.4

7 20 14000 397 164.4

8 15 11000 312 188.4

9 70 35000 991 215.4

10 10 5700 161 240.4

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Figure 6-1 Model river discharge inflow hydrographs for single event simulations with a range of return periods

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Figure 6-2 Ocean tidal variation during single event flood simulations

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Figure 6-3 Model inflow river discharge hydrograph for the 100-year series simulation

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Figure 6-4 Ocean tidal variation during 100-year flood series simulation

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Figure 6-5 Shortened hydrograph based on Chang (1998)

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Figure 6-6 Comparison of sedimentation profile results for the short versus the long simulations of the 1993 verification condition.

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Figure 6-7 Profile of differences between the short and long hydrograph sedimentation results

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7 Initial Screening

The initial screening of wetland design options focused on the two primary classes of options: ones that had protection of the salt marsh from flows at extreme flood levels and ones that had no protection.

The protected alternatives included a dike around the majority of the salt marsh at an elevation that ensures there would be no overtopping at the 100-year flood level.

The unprotected options replaced the dikes with berms that allowed for flows to pass across the top of the berm at extreme flood levels. The berms would not be overtopped for a 10-year flood event but would be over-topped at the 25-year flood level.

Because most of the formal design options proposed in the feasibility study (Dokken, 2004) could be classified into one of these categories, the focus of the initial screening was to evaluate the performance of specific design features incorporated into one of the two principle alternatives of each class: Option 1 as the protected design and Option 2 as the unprotected design.

The Option 1 and Option 2 designs were tested as originally designed by simulating the 100-year flood event. The 100-year flood event was chosen as the main screening simulation. If a design option did not perform well for the 100-year event it was reasonable to assign that design with a low score in the decision process.

Therefore, a large number of subtle design features were tested for Op-tions 1 and 2 with the 100-year flood event sedimentation simulation.

Wetland Sustainability

Existing Conditions

The model performance for existing conditions is presented here as a ref-erence for general changes to the system to which the alternatives are to be

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compared. The wetland sustainability is significant to ensure that the cur-rent W-19 wetlands do not impact the existing wetland sustainability (W-4).

The model representation of existing conditions is presented in Figure 7-1. The model bed displacement for the existing conditions during the 100-year flood event is presented in Figure 7-2. The existing conditions show general flood plain deposition and channel incising. There is a shift of the river thalweg away from the Edison dike in the vicinity of the northward bend in the channel midway between the Edison weir and the entrance to the W-4 wetland. Also included in Figure 7-2 is the sediment delivery (SD) to Jimmy Durante Bridge expresses as a percentage of the existing conditions. Hence, the existing has, by definition, SD=100% in Figure 7-2.

The peak current velocity magnitudes during the 100-year flood event for existing conditions is presented in Figure 7-3. The highest velocities are under and just downstream of El Camino Real and just downstream of the Edison weir.

Option 1 (original)

The model schematization of the original Option 1 is presented in Figure 7-4. The upper figure shows the model bathymetry contours and the lower shows the model material specifications. The red color in the mate-rial specification indicates areas that were armored for this simulation. The elevation of the brackish weir was specified at 3.66 m for the original design.

Figure 7-5 presents the bottom bed elevation displacement for the 100-year flood event for Option 1. The results show massive deposition within the brackish marsh due to flow overtopping the brackish marsh weir. The maximum current velocity magnitudes for Option 1 during the 100-year flood are presented in Figure 7-6. The flow across the brackish marsh weir is evident. The basic Option 1 does not meet basic sustainability require-ments due to the loss of the brackish marsh.

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Option 1 with a widened and raised brackish marsh weir

The initial elevation of the Option 1 weir was very low and was overtopped at the 25-year flood level. Figure 7-7 presents the water surface profile in the vicinity of the Brackish Marsh weir and the Edison weir. The location of El Camino Real (ECR) is marked on the profile as well as the weirs. The Edison weir elevation is set at 4.2 m NGVD29. The original 3.2 m eleva-tion for the Option 1 design had greater than a 2-m head over it for the 100-year flood event. Subsequently, several additional Option 1 variations were simulated. First, the elevation of the brackish marsh weir was set at 4.2 m. That provided minor improvement. The brackish marsh weir was the widened and raised to 4.7 m and finally to 4.9 m NGVD29.

The model representation of the Option 1 with a widened and raised brackish marsh weir to 4.9 m NGVD29 is presented in Figure 7-8. The bed elevation displacement for the 100-year flood for this variation is pre-sented in Figure 7-9. The brackish marsh is now free of significant sedi-mentation and only limited sediment deposition is seen in the eastern end of the salt marsh.

Figure 7-10 presents the velocity magnitude contours for the Option 1 with a widened and raised brackish marsh weir to 4.9 m NGVD29 at the peak of the 100-year flood event. The high momentum inertial flow through the brackish marsh has been avoided with the higher weir.

Option 1 with no brackish marsh

The variation of Option 1 without a brackish marsh is presented in Figure 7-11. The bed elevation displacement for the 100-year flood event is pre-sented in Figure 7-12. Without the brackish marsh a flow path is main-tained toward the salt marsh weir with increased sedimentation in the eastern end of the salt marsh and a broad deposition zone between the salt marsh weir and the main river channel along the northern end of the util-ity corridor.

Option 1 with a dike at the brackish marsh

Another option 1 variation to a closed dike around the brackish marsh with a weir is to include a dike along the north side of the brackish marsh

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(Figure 7-13) protecting it from a direct pathway from the channel at El Camino Real. The added dike would be open at the western end to allow for some flow to enter the marsh along the eastern side of the utility corri-dor.

Figure 7-14 presents the bed elevation displacement for the 100-year flood for Option 1 with a brackish marsh training dike. There is deposition around the western end of the Brackish marsh dike and then into the east-ern end of the salt marsh more than with the raised weir but less than without the brackish marsh.

Option 1 with dikes around both marshes

Figure 7-15 presents a modification where the salt marsh is diked all the way around, eliminating the overflow weir, and closing in the brackish marsh to only culvert exchange with the river. The resulting bed displace-ment is presented in Figure 7-16. As expected, there is no sedimentation in either wetland. This option will be judged primarily by the water sur-face profile along the river, which will not have any flow extracted to lower the flood profile.

Option 1 with a brackish marsh training dike and a shifted salt marsh weir

A modification to the Option 1 with the training dike (Figure 7-13) was to shift the salt marsh weir toward the south to make the pathway less hy-draulically efficient. That option is presented in Figure 7-17 and the result-ing 100-year bed displacement is presented in Figure 7-18. The degree of deposition both at the end of the brackish marsh dike and the eastern end of the salt marsh is reduced with the shifted weir.

Option 2 (original)

The numerical model representation of Option 2 as designed is presented in Figure 7-19. The option was conceived to provide a more natural grad-ing to the system without any structures. As seen in Figure 7-20 the tradeoff for an open landscape is massive deposition in both wetlands for the 100-year flood event. Flows have moved through the brackish marsh depositing sediment there and crossed over the utility corridor and depos-ited sediment extensively over the eastern end of the salt marsh.

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Option 2 without Brackish Marsh

Option 2 without the brackish marsh as represented in the numerical model is presented in Figure 7-21. The resulting bed changes for the 100-year flood (Figure 7-22) show that without the brackish marsh the terrain steers the flood flows toward the northern end of the utility corridor before crossing the berm to deposit sediment in salt marsh. This alternative re-sults in a more natural deltaic footprint. However, it is unfortunate that it lands on top of the constructed wetland.

Option 2 with Dike

Option 2 with a dike adjacent brackish marsh is presented in Figure 7-23. As seen in Figure 7-24, during the 100-year flood event the dike serves to focus the flow across the utility corridor with more inertia such that it is transported farther westward into the salt marsh expanding the zone of significant deposition.

Option 2 with Extended Dike

Option 2 with the dike extended to the utility corridor is presented in Fig-ure 7-25. Flows around end of dike still divert into salt wetland and mas-sive deposition occurs during the 100-year flood event (Figure 7-26).

Option 4

Open 4 was modified slightly from what was originally designed. The berm along the north side of the brackish marsh was extended based on the results from the Option 2 simulations. The AdH representation of Op-tion 4 is presented in Figure 7-27. Option 4 has a berm instead of a dike around the brackish marsh and an expanded salt marsh. The 100-year flood event resulted in major sedimentation in the northeastern part of the expanded salt marsh and within the brackish marsh. (Figure 7-28). The velocity magnitude at the peak of the 100-year flood event is presented in Figure 7-29. The flow is spread out over the flood plain at the maximum water levels reducing the transport capacity and leading to deposition.

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Option 5 with Brackish Marsh Dike

As a result of previous design alternatives tested the Option 5 original de-sign (Figure 5-5) was revised to include a training dike on the north side of the brackish marsh (Figure 7-30). In addition, the salt marsh weir on the eastern end of the marsh was shifted to the south. The resulting bed dis-placement for the 100-year flood event was not significant in either the salt marsh or the brackish marsh (Figure 7-31). The velocity magnitude con-tours at the peak of the 100-year flood evet are presented in Figure 7-32. By shifting the salt marsh weir to the south, the velocities over that weir are less than seen in Option 1 (Figure 7-6).

Flood Event Water Surface Elevations

In order to assess the performance of the design options to the criteria re-lated to flood control the longitudinal profiles of water surface elevation along the thalweg of the existing channel were compared. The existing thalweg was chosen as the fixed alignment for comparison. For some of the alternatives the thalweg of the river shifted during the flood event. For consistency in comparison the fixed profile of the existing conditions was used. The criteria for flood control performance is that for the 100-year flood event the peak flood levels should be no higher than 0.1 foot above the existing flood level.

The peak water surface profiles for 100-year flood event for Option 1 and variations are presented in Figure 7-33 compared to the existing condi-tions. The locations of the bridges along the river profile are located within the profile: Highway 101 Bridge (101), the railroad bridge (RR), the Jimmy Durante Bridge (JD), the Interstate 5 Bridge (I5) and the El Camino Real Bridge (ECR). Due to the large number of variations screened it is difficult to differentiate specific options. Therefore, a fo-cused plot of the profile over a shorter range with expanded vertical scale is presented in Figure 7-34. The basic Option 1 has a very favorable flood profile, but that is at the expense of wetland sustainability. The option with the widened and raised brackish marsh weir at 4.7 m (Op-tion_1R_rww47) has a comparable flood profile, but that alternative still had significant deposition in the brackish marsh (not presented herein). The raised weir to 4.9 m (16.1 ft) raised the water profile back closer to the

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existing profile and was considered to be a good option for further evalua-tion.

The peak water surface elevation profiles for Option 2 and its variations are presented in Figure 7-35. For most of the options the flood levels were lowered throughout the profile due to the overall widening of the flood-way. The option without a brackish marsh (Option 2 nbm) had an ele-vated profile in the lower portion of the profile. The benefits of the low-ered flood profile are offset by the loss of wetland sustainability with most of the Option 2 variations.

The flood profiles of the better variations of Option 1 and Option 2 along with the Option 4 and 5 are presented in Figure 7-36 for comparison. Option 4 drops the flood levels dramatically throughout the system. But again, the open graded options result in significant deposition within the wetlands. Option 5 profile is raised dramatically just upstream of Inter-state 5 and will clearly fail the flood control criterion.

Sediment Supply to the Ocean

The sediment supply to the ocean is a critical criterion. Public concern has been voiced over the potential impact of a reduction in sediment supply from the river on critical coastal erosion adjacent to the river inlet. For comparison with other studies the sediment delivery for the AdH 100-year simulations are compared to the delivery for the Fluvial-12 model reported by Moffatt and Nichol (2011) in Figure 7-37. The AdH model results are shown for the base resolution and for the refined resolution model meshes.

The sediment delivery to Jimmy Durant Bridge for Fluvial-12 is lower than the AdH model by a factor of two. In the field of sediment transport that is considered to be the same order of magnitude. The sediment delivery data for Fluvial 12 were taken from Moffatt and Nichol (2011), which used the Engelund and Hanson transport equations. Chang (1994) in his applica-tion of Fluvial-12 to the San Dieguito Lagoon performed sensitivity of the transport equation on the sediment delivery. He tested the transport equations of Yang, Engelund and Hanson and Acker-White total load equations to develop sediment delivery volumes. The Yang equations gave

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approximately 65 percent of the sediment delivery of the Engelund and Hanson. The Acker-White equations gave approximately 300 percent of the Engelund and Hanson. The AdH model solves separately for the bed-load and the suspended load, using the suspended sediment entrainment algorithm of Wright-Parker, the bedload entrainment of Van Rijn and the Eziagaroff hiding factor. The AdH model is computing approximately 200% of the Fluvial-12 sediment delivery to the Jimmy Durante Bridge us-ing Engelund and Hanson. This is within the sensitivity testing performed by Chang (1994).

The AdH model does not include the coastal processes in the lower end of the river, which can dominate under high wave conditions. Consequently. The effective sediment delivery to the ocean will be aliased to the delivery to the Jimmy Durante Bridge. This position was also taken by Moffatt Nichol (2011). Although the profile plots presented within this report may extend downstream to the Highway 101 Bridge, the reference location for sediment delivery to the ocean will be the delivery to Jimmy Durante Bridge.

The sediment delivery during the 100-year flood event is compared for the pre-Edison, Post-Edison (existing) and the existing with the new bridge at El Camino Real in Figure 7-38. This shows that the existing conditions have more delivery than the pre-Edison condition. This is likely due to the confinement of the flood plain by the construction of the dike around the W-4 wetland. The new bridge shows a reduction in the sediment delivery compared to the existing but greater than the pre-Edison condition which had the least sediment delivered. The cross section at the El Camino Real Bridge is compared in Figure 7-39. The new bridge increases the cross section by approximately 4 percent at the 100-year peak flood level. As-suming that the velocities will scale linear with the cross section and that the transport is proportional to the shear stresses, which are scaled by the square of the velocity then the transport capacity at El Camino Real Bridge will be reduced by approximately 8 percent. The reduction in the sedi-ment delivery for the new bridge in Figure 7-38 is on that order of magni-tude.

Sediment delivery during the 100-year flood event for the Option 1 varia-tions are presented in Figure 7-40. These are compared to the existing

ERDC/LAB TR-0X-X 75

sediment delivery. Downstream of the study area all Option 1 variations show reduction in sediment delivery. Most of the alternatives show sedi-ment delivery volumes comparable to the pre-Edison sediment delivery (see Figure 7-38). The original Option 1 design shows an increase in sedi-ment delivery to El Camino Real, which is derived from additional erosion upstream of El Camino Real. The original design had the brackish marsh weir at 12 ft (3.66 m) which created a major flow pathway that significantly reduced the water surface elevation at El Camino Real (see Figure 7-34) resulting in head cutting upstream.

Sediment delivery for Option 2 and variations to the design are presented in Figure 7-41. Every variation to Option 2 has a general widening and deepening of the flood conveyance between El Camino Real and Interstate 5. These result in lowered water surface elevations (see Figure 7-35) and head cutting upstream of El Camino Real. That is reflected in the increase in sediment delivery to El Camino Real for all Option 2 variations. Due to the open conveyance pathways the depositional potential is increased and at Interstate 5 there is an overall reduction in sediment delivery for all Op-tion 2 variations.

Options 4 and 5 sediment delivery for the 100-year flood event are pre-sented in Figure 7-42. Consistent with the other alternatives, the open unprotected Option 4 shows head cutting upstream of El Camino Real and massive sediment loss over the project reach. Option 5 shows a reduction in sediment delivery associated with the sedimentation that occurs within the project wetlands.

Summary of preliminary screening

The modeling of the new bridge at El Camino Real showed that the differ-ences between the old existing and new bridges were not significant enough to redo the numerical model simulations that had already been performed. This assumption will not impact the relative comparison be-tween the proposed design variations being considered.

The various design alternatives can be classified as one of three broad clas-sifications:

ERDC/LAB TR-0X-X 76

1. Unprotected Wetlands (Options 2 and 4)

2. Protected Wetlands (Options 1, 3 and 6)

3. Hybrid Combination of Protected and Unprotected (Option 5)

By adding wetlands to the existing conditions, the average depth of the zone between I-5 and ECR increases, creating a sediment trap. The trap-ping efficiency of the newly created wetlands is dependent on the sediment delivery into the wetlands. The best alternatives are those that keep the flow that carries the sediment in pathways away from the wetlands. The wetland design may not be able to protect wetlands from all deposition without a rise in upstream water surface elevation.

The unprotected wetland designs were considered preferable to some be-cause the overall engineering footprint within the system is less dramatic and the processes remain more natural. However, the modeling per-formed has shown that for sustainability of the constructed wetlands the unprotected wetlands will be subject to significant sedimentation during extreme flood events. Deposition can be sufficient to destroy habitat.

The protected wetlands will have engineered barriers that can essentially eliminate most deposition within the wetlands. This conceptual design has been proven to work effectively, as judged by the performance of the Edison W-4 wetland throughout all of the AdH sediment transport model simulations.

The penalty paid for the protection of the wetlands from deposition is in-creased backwater water levels as the flood waters are required to pass through a more constricted pathway. The solution found for the Edison w-4 wetlands was to include a relief weir that draws off flood waters only at the peak of the flood. The Option 1 alternatives showed that such a de-sign can work for the brackish marsh weir as well. Replacing the weir with a dike with a gap between its west end and the utility corridor provides some relief but may require maintenance to keep the gap open.

Sediment supply to the ocean is considered to be reflected in the sediment supply to Jimmy Durante Bridge. The summary of the performance of the

ERDC/LAB TR-0X-X 77

various design options is delineated in Table 7-1. The sediment supply is defined as a percentage of the existing sediment supply. In addition, the table provides a qualitative indication of the sedimentation in both the salt marsh and the brackish marsh. Although Option 4 showed the greatest sediment delivery of the wetland options, it may be a temporary artifact of the significant head cutting upstream of El Camino Real.

An alternative evaluation matrix is shown in Table 7-2, addressing all of the performance criteria. Based on this evaluation the modeling team recom-mended rejecting Options 3 and 6 and continuing forward with Options 1, 2, 4 and 5 into the second phase of screening.

ERDC/LAB TR-0X-X 78

.

Table 7-1 Summary of sediment supply to Jimmy Durante Bridge for 100-year flood event expressed as a percentage of the sediment delivery for existing condition and marsh

sedimentation

Scenario Sediment Delivery (%)

Sedimentation in Salt Marsh

Sedimentation in Brackish Marsh

Pre-Edison 83%

Post-Edison (Baseline Condi-tion)

100%

Post-Edison w New Bridge 92%

Opt 1 as Proposed 83% Minor Severe

Opt 1 w Raised and Widened Weir to Brackish Marsh

82% Minor Minor

Opt 1 w/o Brackish Marsh 80% Moderate N/A

Opt 1 w Dike Along Brackish Marsh

87% Moderate Moderate

Opt 1 w Dike Around 90% None None

Opt 2 as Proposed 89% Severe Severe

Opt 2 w/o Brackish Marsh 67% Severe N/A

Opt 2 w Dike Along Brackish Marsh

87% Severe Moderate

Opt 2 Extended Dike 74% Severe Minor

Option 4 97% Severe Severe

Option 5 93% Minor Minor

ERDC/LAB TR-0X-X 79

Table 7-2 San Dieguito Lagoon W-19 Hydrodynamic Alternative Evaluation

100-year

Water Level

100-year

Velocity at

Infrastructure

Sediment

Delivery to

Ocean

Tide Muting in

W4 (SCE)

Wetlands

Sustainability

Tide Range in

W19

(SANDAG)

Total

Score

Comments /Sugges-

tions to improve per-

formance

Design

Criteria

Within 0.2 foot

of existing flood

levels @ ECR

Within 0.1 fps of

existing flood ve-

locities

Within 2% of

existing condi-

tions

Both high and low

tide elevations within

0.2 feet existing

Siltation in Wet-

land area to be

less than 3

inches

Mimic SCE W4

Option 1 4 4 4 4 5 5 26 Raise/lengthen weir to reduce

WSEL at ECR

Option 2 5 4 4* 4 0 5 22 Siltation will destroy the wet-

lands w/100-year storm

Option 3 3 4 4 3 5 5 24 Variation of Option 1. Looking

at raising and/or lengthening weir

to reduce WSEL at ECR

Option 4 5 4 3* 3 0 5 20 Unprotected wetlands will be-

come low flow channel after ma-

jor event destroying wetlands.

Option 5 5 4 4* 3** 3 4 23

Creates two salt water wetlands:

smaller unprotected wetland will

be lost with major event, but

could provide temporary wet-

lands

Option 6 3 4 4 3 4*** 5 23 Variation of Option 1. Looking

at raising and/or lengthening weir

Qualitative Ranges: Excellent (5), Good (4), Fair (3), Poor (2), Failing (0) Notes:

1. Evaluation of options 3 and 6 is qualitative based on modeling experience gained from modeling options 1, 2, 4 & 5. 2. We have not compared velocities, but expect no significant difference between options 3. * This option creates more erosion upstream of ECR resulting in larger sediment supply and making it difficult to com-

pare options. 4. Tide Muting in W-4: the larger the created wetlands in W-19 the greater the muting impact on W-4. **Option 5 cre-

ates the largest initial wetlands, scoring 2 or 3, but over the unprotected wetlands will lost leaving the smaller protected wetlands which would rate a 4.

5. Wetlands sustainability: measure of the amount of sedimentation expected in the created wetlands. ***Option 6 is expected to have little or no sediment in the salt water wetlands, but as currently configured moderate to severe sedi-mentation in the brackish marsh.

ERDC/LAB TR-0X-X 81

Figure 7-1 Representation of existing conditions in AdH model

Figure 7-2 Bed displacement for 100-year flood event for existing conditions

ERDC/LAB TR-0X-X 82

Figure 7-3 Maximum velocity magnitudes for existing conditions for 100-year flood event

ERDC/LAB TR-0X-X 83

Figure 7-4 Model schematization of Option 1

Figure 7-5 Bed displacement for 100-year flood event for Option 1 (brackish marsh weir at 3.66 m)

ERDC/LAB TR-0X-X 84

Figure 7-6 Maximum velocity magnitudes for Option 1 for 100-year flood event

Figure 7-7 Localized water surface elevation response near the weirs

ERDC/LAB TR-0X-X 85

Figure 7-8 Model representation of Option 1 with the brackish marsh weir elevation raised to 4.9 m (16.1 ft NGVD) and widened

Figure 7-9 Bed displacement for 100-year flood event for Option 1 with raised (4.9m) and widened brackish marsh weir

ERDC/LAB TR-0X-X 86

Figure 7-10 Maximum velocity magnitudes during 100-year flood event for Option 1 with raised (4.9m) and widened brackish marsh weir

Figure 7-11 Model representation of Option 1 with no brackish marsh

ERDC/LAB TR-0X-X 87

Figure 7-12 Bed displacement for 100-year flood event for Option 1 with no brackish marsh

ERDC/LAB TR-0X-X 88

Figure 7-13 Model representation of Option 1 with a dike without a weir

Figure 7-14 Bed displacement for 100-year flood event for Option 1 with a dike

ERDC/LAB TR-0X-X 89

Figure 7-15 Model representation of Option 1 with closed dike around the salt marsh eastern side and the brackish marsh.

Figure 7-16 Bed displacement for 100-year flood event for Option 1 with closed dike around the salt marsh eastern side and the brackish marsh.

ERDC/LAB TR-0X-X 90

Figure 7-17 Model representation of Option 1 with brackish marsh dike and shifted salt marsh weir

Figure 7-18 Bed displacement for the 100-year flood event for Option 1 with brackish marsh dike and shifted salt marsh weir

ERDC/LAB TR-0X-X 91

Figure 7-19 Model representation of Option 2

Figure 7-20 Bed displacement for 100-year flood event for Option 2

ERDC/LAB TR-0X-X 92

Figure 7-21 Model representation of Option 2 without a brackish marsh

Figure 7-22 Bed displacement for 100-year flood event for Option 2 without a brackish marsh

ERDC/LAB TR-0X-X 93

Figure 7-23 Model representation of Option 2 with dike at brackish marsh

Figure 7-24 Bed displacement for 100-year flood event for Option 2 with brackish marsh dike

ERDC/LAB TR-0X-X 94

Figure 7-25 Model representation of Option 2 with extended dike at brackish marsh

Figure 7-26 Bed displacement for 100-year flood event for Option 2 with extended dike at brackish marsh

ERDC/LAB TR-0X-X 95

Figure 7-27 Model representation of Option 4

Figure 7-28 Bed displacement for 100-year flood event for Option 4

ERDC/LAB TR-0X-X 96

Figure 7-29 Maximum velocity magnitudes during 100-year flood event for Option 4

ERDC/LAB TR-0X-X 97

Figure 7-30 Model representation of Option 5

Figure 7-31 Bed displacement for 100-year flood event for Option 5

ERDC/LAB TR-0X-X 98

Figure 7-32 Maximum velocity magnitudes during 100-year flood event for Option 5

ERDC/LAB TR-0X-X 99

Figure 7-33 Peak water surface profiles for 100-year flood event for Option 1 and variations

ERDC/LAB TR-0X-X 100

Figure 7-34 Local peak water surface profiles for 100-year flood event for Option 1 and variations

ERDC/LAB TR-0X-X 101

Figure 7-35 Peak water surface profiles for 100-year flood event for Option 2 and variations

ERDC/LAB TR-0X-X 102

Figure 7-36 Peak water surface profiles for 100-year flood event for Option 1 and Option 2 variations compared with Options 4 and 5

ERDC/LAB TR-0X-X 103

Figure 7-37 Comparison of the sediment delivery profiles for AdH and Fluvial-12 models for the 100-year flood event

ERDC/LAB TR-0X-X 104

Figure 7-38 Comparison of sediment delivery for prior to and after the Edison wetland restoration project and for the new El Camino Real Bridge for the 100-year flood event

ERDC/LAB TR-0X-X 105

Figure 7-39 Effects of new bridge on the cross section at El Camino Real

ERDC/LAB TR-0X-X 106

Figure 7-40 Comparison of sediment delivery for the 100-year flood event for Option 1 and its variations

ERDC/LAB TR-0X-X 107

Figure 7-41 Comparison of sediment delivery for the 100-year flood event for Option 2 and its variations

ERDC/LAB TR-0X-X 108

Figure 7-42 Comparison of sediment delivery for the 100-year flood event for Options 4 and 5

ERDC/LAB TR-0X-X 109

8 Secondary Screening

The secondary screening was performed for a smaller number of design al-ternatives than processed by the initial screening, but for an expanded number of flood events. The alternatives screened during the second screening were:

a. Existing conditions

b. Option 1 with a widened and raised (to 4.9 m) brackish march weir

c. Option 2 (original design)

d. Option2 with an extended brackish marsh dike

e. Option 4

f. Option 5

The simulations performed for each of the alternatives included the 10-year, 25-year, 50-year and 100-year single event simulations (see Figure 6-1) and the 100-year series simulation (see Figure 6-3).

100-year series simulation

As discussed in Chapter 6, the purpose of the 100-year series simulation was to simulate only the periods of time when significant sediment is mo-bilized from bed. This allows for the simulation of the effective long-term impacts over a relatively short simulation period. It has been assumed that the shortened simulation period will be acceptable for comparisons between alternatives and to serve as the best indicator for the impact on sediment delivery to the coastal zone. As with all numerical model results, however, careful interpretation of simulation results in needed when relat-ing quantitative results back to the real world.

The results of the 100-year series simulation will be analyzed after each of the separate events that comprise the series (see Table 6-2). The times at the end of each event are highlighted in the flood hydrograph shown in

ERDC/LAB TR-0X-X 110

Figure 8-1. The analysis will present the bed bottom elevation displace-ment as cumulative change at each of the times and as incremental bed displacement during each of the ten events within the series. The times at the end of the individual events are hours 14.5, 41.5, 65, 95, 119, 155, 180, 203, 235 and 250.

Existing conditions

The cumulative bed displacement for the analysis hours of the 100-year flood event series for existing conditions are presented in Figure 8-2 through Figure 8-11.

At the end of the first event (hour 14.5) the beginnings of erosion on the outside of the river bends and deposition on the inside are evident, partic-ularly along the Edison dike reach of the river (Figure 8-2). The plot of the hydrograph in the upper left corner of the figure shows the progression through the simulation.

After the second event (hour 41.5 in Figure 8-3) the changes have amplified but remained in the same locations. After the third event (hour 65; Figure 8-4) the zone of erosion just east of the armoring of the Edison weir has moved northward and is beginning to flank the eastern end of the armor there. The erosion is beginning to become evident along the full length of the channel thalweg. The fourth and fifth events (Figure 8-5 and Figure 8-6) continue the bed changes at the locations shown after the first three events.

The sixth event (Figure 8-7), which is a 100-yer flood event, started to erode an additional channel in the area just north of the nesting site. The next two events make little change in the geomorphology, but the ninth event (Figure 8-10) shifts the river channel north of the nesting island fur-ther to the south. The final event showed little difference.

Each of the ten events of the 100-year series simulation for existing condi-tions is evaluated to show the incremental change in the bathymetry for each event. These results are presented in Figure 8-12 through Figure 8-21. The results show that the preceding geomorphological changes in-fluence the subsequent impact of the next event. The largest impacts are

ERDC/LAB TR-0X-X 111

for events 6, 9 and 4 in decreasing order of impact. The lower discharge events are influenced the most by the preceding events.

Option 1 with widened and raised brackish marsh weir

The cumulative bed displacement for the Option 1 with revised brackish marsh weir for the 100-year series simulation at the analysis times shown in Figure 8-1 are presented in Figure 8-22 through Figure 8-31. The incre-mental bed changes for the ten discharge events in the series are presented in Figure 8-32 through Figure 8-41.

When comparing the geomorphological response of Option 1 with the re-vised brackish marsh weir to the existing conditions the impact of a partic-ular flood level for Option 1 is equivalent to the changes for a higher flow rate in the existing. This is evident along the river, where the option 1 con-fines the flood event to pass through a constricted flood plain width, re-sulting in a generally higher transport capacity and therefore, potential for geomorphological change.

Option 2

The cumulative bed displacement for the Option 2 for the 100-year series simulation at the analysis times shown in Figure 8-1 are presented in Fig-ure 8-42 through Figure 8-51. The incremental bed changes for the ten discharge events in the series are presented in Figure 8-52 through Figure 8-61.

The Option 2, which has less constraints on the north-south migration of the flow exhibited greater geomorphological changes over the 100-year se-ries simulation. Sedimentation begins within the brackish marsh at the lowest event within the series (5700 cfs for event 1, Figure 8-52). The peak event with 41,800 cfs (event 6, Figure 8-57) results in the vast majority of the deposition within the salt marsh. By the end of the simulation there has been significant deposition within both the salt marsh and the brack-ish marsh.

The pathway for flow and sediment into the salt marsh is across the utility corridor about half way from the southern edge of the wetland to the river.

ERDC/LAB TR-0X-X 112

Option 2 with extended brackish marsh dike

The cumulative bed displacement for the Option 2 with the extended brackish marsh dike for the 100-year series simulation at the analysis times shown in Figure 8-1 are presented in Figure 8-62 through Figure 8-71. The incremental bed changes for the ten discharge events in the se-ries are presented in Figure 8-72 through Figure 8-81.

The extended dike shifted the flow across the utility corridor northward compared to the case for Option 2. However, the dike directs more of the flow farther down the river to be diverted back across the salt marsh berm at two additional locations on the eastern side of the nesting site. Addi-tional zones of deposition in the middle and western end of the salt marsh are seen.

The shift of the channel north of the nesting site is less dramatic. There is significant diversion of flow and sediment across the berm on the north side of the salt marsh with deposition inside the salt marsh. The majority of the impact is associated with the sixth event (41,800 cfs, Figure 8-67 and Figure 8-77).

Option 4

The cumulative bed displacement for the Option 4 for the 100-year series simulation at the analysis times shown in Figure 8-1 are presented in Fig-ure 8-82 through Figure 8-91. The incremental bed changes for the ten discharge events in the series are presented in Figure 8-92 through Figure 8-101.

There is significant deposition with Option 4 in the brackish marsh. The deposition in the salt marsh is more distributed east to west related to the overtopping of the berm on the north side of the salt marsh. During the 100-year series simulation the river flows bifurcated just northeast of the nesting site. That gave sufficient relief in the water level profile that there was then no diversion across the utility corridor to create a channel through the eastern end of the salt marsh as was seen in both Option 2 and Option 2 with the extended brackish marsh dike.

ERDC/LAB TR-0X-X 113

The brackish marsh was completely closed off with sedimentation in the access channel. The deposition in the entrance to the Edison marsh (W4) shows a distinctly different pattern with Option 4 from any of the other al-ternatives. The deposition is no longer distributed across the entrance but is confined to the east side and has two pathways of deposition northward into the wetland. This is the result of the bifurcation of flows around the nesting site and the dual direction of the flow momentum approaching the entrance from upstream.

Option 5

The cumulative bed displacement for the Option 5 for the 100-year series simulation at the analysis times shown in Figure 8-1 are presented in Fig-ure 8-102 through Figure 8-111. The incremental bed changes for the ten discharge events in the series are presented in Figure 8-112 through Figure 8-121.

The on-river wetland provides an alternative efficient hydraulic pathway for high river flows. This pathway helped support the southward shift of the river thalweg north of the nesting site. The dike around the salt marsh was effective at keeping sedimentation out of the salt marsh.

The high 100-year flood event of 41,800 cfs (event 6; 1184 cms) has the dominant impact on the geomorphology of the system (Figure 8-117). The second highest flow of event 9 (991 cms) further incised the river channel and continued deposition in the flood plain (Figure 8-120).

Summary of 100-year Series Geomorphology

The overall impact of the 100-year series simulations on the geomorphol-ogy of the study area between El Camino Real and Interstate 5 are summa-rized by comparing the initial bathymetry with the final bathymetry at the end of the simulation.

Figure 8-122 presents the beginning and ending bathymetry for the exist-ing conditions. The model simulation shows significant overbank deposi-tion on the flood plain between El Camino Real and approximately the Ed-ison Weir. Significant channel incising is evident along the river channel throughout the system. Downstream from the Edison Weir there was less

ERDC/LAB TR-0X-X 114

flood plain deposition, but a realignment of the primary channel to the south. The model exhibited channel braiding adjacent to the Edison Weir and also just north of the nesting Island.

The starting and ending bathymetry for Option 1 with the widened and raised brackish marsh weir during the 100-year series simulation are pre-sented in Figure 8-123. The protective dike around both the salt marsh and the brackish marsh resulted in limiting the deposition to the access channel for the brackish marsh and the entrance channel for the salt marsh. The primary wetlands themselves had no deposition. The main river channel north of the salt marsh dike was realigned to the south. The channel was braided just east of the Edison Weir into three separate smaller channels with deltaic lobes in between.

Option 2 initial and final bathymetry for the 100-year series simulation are presented in Figure 8-124. There was loss of wetland function in both the salt marsh and the brackish marsh. There was some channel shifting and braiding along the main river channel.

Option 2 with the extended dike initial and final bathymetry are presented in Figure 8-125. The primary feature of the performance of this alternative is the multiple pathways of flow and sediment making its way into the salt marsh.

Option 4 initial and final bathymetry are presented in Figure 8-126. This option showed extensive impacts both in the deposition in the wetlands and changes in the channel alignments.

Option 5 initial and final bathymetry are presented in Figure 8-127. The performance of Option 5 is very similar to Option 1. The design keeps the discharge moving down the main channel and results in a shifted straighter channel.

The model has exhibited the tendency to have more meandering and braided channels for lower flows and a straightened channel for higher flows. This is facilitated by flow diversions from the main river channel that effectively reduce the discharge. The existing channel carries some of

ERDC/LAB TR-0X-X 115

the flow in the overbank flood plain, Options 1 and 5 force the flow to re-main close to the channel (higher channel flow), both Option 2 alterna-tives lose flow across the salt marsh berm and Option 4 loses a dramatic fraction of the river flow to the salt marsh pathway. These alternatives ex-hibit a slightly meandering channel for existing, a straightened channel for Options 1 and 5, meandering and braiding for both Options 2 and mean-dering and braiding to a finer scale for Option 4.

Sediment Delivery

The sediment delivery to the primary bridges along the river are presented in Figure 8-128 for the 100-year series simulations for each wetland design option. The options that have an unprotected feature have several things in common. Because the unprotected wetlands retain the full flood plain width of the existing conditions the flow cross section becomes large at peak flood levels, reducing the average velocity and lowering the backwa-ter water surface elevation profile. The lower profile results in higher ve-locities upstream of the study area and head-cutting upstream of El Camino Real. That results in a higher sediment delivery to El Camino Real. These unprotected options, however, are also more efficient sedi-ment traps and therefore they have lower sediment delivery to Interstate 5. That lower delivery is extended to the ocean.

The cumulative sediment delivery to Jimmy Durante Bridge is presented in Figure 8-129 which shows the time series of the sediment delivery throughout the 100-year series simulation. This illustrates the nonlinear-ity of the sediment transport response to varying river discharges.

Geomorphology of Single Flood Events

For the second phase of screening each of the selected alternatives were simulated for the single flood events associated with the 10-, 25-, 50- and 100-year return periods (see Figure 6-1). For ease of comparison each of the four return-period model simulation results for bed displacement are presented in single figures.

The bed displacement for individual flood events for existing conditions are presented in Figure 8-130.

ERDC/LAB TR-0X-X 116

The bed displacement for individual flood events for Option 1 withe the widened and raised brackish marsh dike are presented in Figure 8-131.

The bed displacement for individual flood events for Option 2 are pre-sented in Figure 8-132.

The bed displacement for individual flood events for Option 2 with the ex-tended brackish marsh dike are presented in Figure 8-133.

The bed displacement for individual flood events for Option 4 are pre-sented in Figure 8-134.

The bed displacement for individual flood events for Option 5 are pre-sented in Figure 8-135.

Summary of Sediment Delivery for all Simulations

The sediment delivery for all of the secondary screening options and flow conditions are compared in Figure 8-136 through Figure 8-138 for the de-livery to El Camino Real Bridge, Interstate 5 Bridge and Jimmy Durante Bridge, respectively. These are compared as bar plots. These show clearly that Option 1 provides the best performance with regard to sediment deliv-ery.

The difference in sediment supply between Interstate 5 and El Camino Real, between Jimmy Durante Bridge and Interstate 5 and between Jimmy Durante Bridge and El Camino Real are presented in Figure 8-139 and Fig-ure 8-141, respectively. These show that Option 1 performs best, but also that when comparing differences, it is even clearer that Option1 is the pre-ferred option.

Water Surface Elevation Profiles

Option 1 with revised brackish marsh weir

The comparison of Option 1 with the modified brackish marsh weir to the existing conditions water surface elevation profiles for the 10-, 25-, 50- and 100-year flood events are presented in Figure 8-142. The Option 1 profile is lower than the existing throughout the system for the 10- and 25-

ERDC/LAB TR-0X-X 117

year flood events. The 50-year flood event water surface profile is virtually identical for Option 1 and existing conditions. For the 100-year flood event profile the Option 1 profile is slightly higher than the existing down-stream of the utility corridor and slightly lower upstream.

Option 2

The comparison of Option 2 to the existing conditions water surface eleva-tion profiles for the 10-, 25-, 50- and 100-year flood events are presented in Figure 8-143. The water surface elevation profiles for Option 2 are uni-formly lower than the existing conditions for all flood events, with the dif-ferences being greater for higher flows.

Option 2 with extended brackish marsh dike

The comparison of Option 2 with the extended brackish marsh dike to the existing conditions water surface elevation profiles for the 10-, 25-, 50- and 100-year flood events are presented in Figure 8-144. The water sur-face elevation profiles for Option 2 with the extended brackish marsh dike are also uniformly lower than the existing conditions for all flood events, with the differences being greater for higher flows. However, the differ-ences are less than seen for the original Option 2.

Option 4

The comparison of Option 4 to the existing conditions water surface eleva-tion profiles for the 10-, 25-, 50- and 100-year flood events are presented in Figure 8-145. Generally, the flood profiles for Option 4 are lower than seen for the existing conditions for all flood return periods. However, over a reach of the river just upstream of Interstate 5 the water surface eleva-tion is locally higher for Option 4 than for existing conditions. This may be associated with the diverted flows into the salt marsh recombining with the main river channel flows from a different direction. Combining flows convert lateral momentum into downstream momentum by storing energy temporarily as potential energy (higher water surface elevation) before converting back to kinetic energy (velocity downstream).

ERDC/LAB TR-0X-X 118

Option 5

The comparison of Option 5 to the existing conditions water surface eleva-tion profiles for the 10-, 25-, 50- and 100-year flood events are presented in Figure 8-146. The water surface profiles for Option 5 are very similar to those seen for Option 4. However, the local increase in the water sur-face for Option 5 is less than seen for Option 4 and is over a longer reach of the river. For the 25-year event the zone of higher profile extends down-stream almost to Jimmy Durante Bridge. For the 50-and 100-year flood events the increase is very small.

Summary of Second Phase Screening

The results of the secondary screening of the design alternatives are sum-marized in Table 8-1. The revised evaluation of alternatives takes into consideration the results of the 100-year series simulations for wetland sustainability associated with geomorphological responses and the flood control issues documented in the single event simulations.

The optimum wetland design needs to balance the wetland sustainability gained by providing protection of the wetlands from flow conveyance through the wetland which carries damaging sedimentation with the flood control issues associated with keeping the flow in the main stem of the river.

Modeling team recommends rejecting Options 3, 4 and 6 and continuing forward with Options 1, 2 and 5 into preliminary engineering and the envi-ronmental document phase. The final phase of modeling supported that effort.

ERDC/LAB TR-0X-X 119

Table 8-1 San Dieguito Lagoon W-19 Hydrodynamic Alternative Evaluation after second phase of screening

100-year

Water Level

100-year

Velocity at

Infrastructure

Sediment

Delivery to

Ocean

Tide Muting in

W4 (SCE)

Wetlands

Sustainability

Tide Range in

W19

(SANDAG)

Total

Score

Comments /Sugges-

tions to improve per-

formance

Design

Criteria

Within 0.1 foot

of existing flood

levels

Within 0.1 fps of

existing flood ve-

locities

Within 2% of

existing condi-

tions

Both high and low

tide elevations within

0.2 feet existing

Siltation in Wet-

land area to be

less than 3

inches

Mimic SCE W4 Total

Option 1 5 4 4 4 5 5 27 Raise/lengthen weir to reduce

WSEL at ECR

Option 2 5 4 4 4 0 5 22 Siltation will destroy the wet-

lands w/100-year storm

Option 3 3 4 4 3 5 5 24 Variation of Option 1. Looking

at raising and/or lengthening weir

to reduce WSEL at ECR

Option 4 5 4 3 3 0 5 20 Unprotected wetlands will be-

come low flow channel after ma-

jor event destroying wetlands.

Option 5 4 4 4 3 3 5 23

Creates two salt water wetlands:

smaller unprotected wetland will

be lost with major event, but

could provide temporary wet-

lands

Option 6 3 4 4 3 4 5 23 Variation of Option 1. Looking

at raising and/or lengthening weir

Qualitative Ranges: Excellent (5), Good (4), Fair (3), Poor (2), Failing (0) Notes:

1. Evaluation of options 3 and 6 is qualitative based on modeling experience gained from modeling options 1, 2, 4 & 5. 2. We have not compared velocities, but expect no significant difference between options 3. Options 2 & 4 create more erosion upstream of ECR resulting in larger sediment supply and making it difficult to com-

pare options. 4. Tide Muting in W-4: the larger the created wetlands in W-19 the greater the muting impact on W-4. 5. Wetlands sustainability: measure of the amount of sedimentation expected in the created wetlands. 6. Option 6 is expected to have little or no sediment in the salt water wetlands, but as currently configured moderate to

severe sedimentation in the brackish marsh.

ERDC/LAB TR-0X-X 121

Figure 8-1 Times for analysis of bed displacement for the 100-year series simulations

ERDC/LAB TR-0X-X 122

Figure 8-2 Cumulative bed displacement for Existing 100-year series – hour 14.5

Figure 8-3 Cumulative bed displacement for Existing 100-year series – hour 41.5

ERDC/LAB TR-0X-X 123

Figure 8-4 Cumulative bed displacement for Existing 100-year series – hour 65

Figure 8-5 Cumulative bed displacement for Existing 100-year series – hour 95

ERDC/LAB TR-0X-X 124

Figure 8-6 Cumulative bed displacement for Existing 100-year series – hour 119

Figure 8-7 Cumulative bed displacement for Existing 100-year series – hour 155

ERDC/LAB TR-0X-X 125

Figure 8-8 Cumulative bed displacement for Existing 100-year series – hour 180

Figure 8-9 Cumulative bed displacement for Existing 100-year series – hour 203

ERDC/LAB TR-0X-X 126

Figure 8-10 Cumulative bed displacement for Existing 100-year series – hour 235

Figure 8-11 Cumulative bed displacement for Existing 100-year series – hour 250

ERDC/LAB TR-0X-X 127

Figure 8-12 Incremental bed displacement for Existing 100-year series Event 1

Figure 8-13 Incremental bed displacement for Existing 100-year series Event 2

ERDC/LAB TR-0X-X 128

Figure 8-14 Incremental bed displacement for Existing 100-year series Event 3

Figure 8-15 Incremental bed displacement for Existing 100-year series Event 4

ERDC/LAB TR-0X-X 129

Figure 8-16 Incremental bed displacement for Existing 100-year series Event 5

Figure 8-17 Incremental bed displacement for Existing 100-year series Event 6

ERDC/LAB TR-0X-X 130

Figure 8-18 Incremental bed displacement for Existing 100-year series Event 7

Figure 8-19 Incremental bed displacement for Existing 100-year series Event 8

ERDC/LAB TR-0X-X 131

Figure 8-20 Incremental bed displacement for Existing 100-year series Event 9

Figure 8-21 Incremental bed displacement for Existing 100-year series Event 10

ERDC/LAB TR-0X-X 132

Figure 8-22 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 14.5

Figure 8-23 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 41.5

ERDC/LAB TR-0X-X 133

Figure 8-24 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 65

Figure 8-25 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 95

ERDC/LAB TR-0X-X 134

Figure 8-26 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 119

Figure 8-27 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 155

ERDC/LAB TR-0X-X 135

Figure 8-28 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 180

Figure 8-29 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 203

ERDC/LAB TR-0X-X 136

Figure 8-30 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 235

Figure 8-31 Cumulative bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series – hour 250

ERDC/LAB TR-0X-X 137

Figure 8-32 Incremental bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series Event 1

Figure 8-33 Incremental bed displacement for Option 1 with widened and raised weir (4.9 m) 100-year series Event 2