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Presentation Program OutlinePresentation Program OutlineLATERAL EROSION CRITERIALATERAL EROSION CRITERIA

MULTI-LEVEL APPROACH

HIOSTRICAL DATA ANALYSIS

GEOMORPHIC ASSESMENT / MAPPING

ENGINEERING METHODS / MODELING

LONG TERM EROSION LIMITS / EROSION HAZARD BOUNDARY

Lateral Erosion Estimates and Hazard Lateral Erosion Estimates and Hazard OVERVIEW / BACKGROUND

BoundariesBoundariesBenefits:Fl d l i t th d t dd i•Floodplain management method to address economic

losses from streambank erosion•Erosion hazards extend beyond floodplain boundariesy pbecause of dynamic alluvial rivers•Adequately define a suitable setback from streambank•Difficulty to acquire environmental permits forDifficulty to acquire environmental permits for conventional streambank revetment

IIssues:•Uncertainties•Data availabilityy

OVERVIEW / BACKGROUND

FEMA Reviewed Lateral ErosionFEMA Reviewed Lateral Erosion

ADOPTED AGENCY PROCEDURES

FEMA Reviewed Lateral Erosion Hazard Criteria

FEMA Reviewed Lateral Erosion Hazard Criteria

• 1999 FEMA St d t• 1999 FEMA Study most comprehensive summary • Reviewed most of the adopted “agency” proceduresagency procedures

•City of Austin•AMAFCA Sediment/Erosion Guide• Arizona lateral migration std.Arizona lateral migration std.•Maricopa County

• Advantages/disadvantages of the various methods•General evaluation methods

•Equilibrium•Fluvial hydraulics•Streambank stability

Lateral Erosion Hazard BoundaryLateral Erosion Hazard BoundaryADOPTED AGENCY PROCEDURES

Prudent Line ConceptPrudent Line Concept

Austin -Sample Erosion Hazard SetbackAustin -Sample Erosion Hazard Setback


Austin Sample Erosion Hazard SetbackAustin Sample Erosion Hazard Setback

Austin - Sample Erosion Hazard SetbackAustin - Sample Erosion Hazard Setback


Austin Sample Erosion Hazard SetbackAustin Sample Erosion Hazard Setback

Data Considered for Defining ErosionData Considered for Defining ErosionData Considered for Defining Erosion Hazard Zones

Data Considered for Defining Erosion Hazard Zones

• Stream Field data • Expected ChannelStream Field data• Historical Channel

Changes• Aerial Photographs

• Expected Channel Pattern

• Meander MigrationE ilib i SlAerial Photographs

• Geologic Surfaces• Longitudinal Profiles• Vertical Streambed Scour

• Equilibrium Slope Analysis

• Armoring PotentialVertical Streambed Scour / Sediment Transport

• Floodplain Hydraulics

• Geotechnical Bank Stability

• Hydraulic Geometry / Regime Equations

• Allowable Velocity• Hydrologic / Historical y g

Flood Data• Geomorphic mapping /

Trends

General Lateral Erosion MethodologiesGeneral Lateral Erosion MethodologiesGeneral Lateral Erosion MethodologiesGeneral Lateral Erosion Methodologies1. Geomorphic Methods – historic data and

geomorphic assessmentsgeomorphic assessments2. Engineering Methods – predictive equations based

on engineering and geomorphic principlesg g g p p p3. Mathematical Modeling Methods – computer

modeling of fluvial processes

Multi-Level Hybrid Approach for Multi-Level Hybrid Approach for OVERVIEW / BACKGROUND

Lateral Erosion AssessmentLateral Erosion AssessmentSTEP TASK TOOLS

1 Field Data – Creek Characterization Classify physical characteristics of floodplain1 Field Data – Creek Characterization Classify physical characteristics of floodplain

2 Geologic Mapping / Geotechnical Data Erosion resistant surfaces and geotechnical bank stability, mechanical grain size distribution

3 Hydrologic Data and Flood History Flood-frequency, gage data, rainfall data, watershed modeling

4 Geomorphic Mapping / Assessment Compute channel characteristics and channel planform

5 Historical Data Analysis Historic aerial photographs, topographic mapping, improvement plans, profiles

HEC RAS d l l it di t ib ti h l6 Floodplain Hydraulics HEC-RAS models, velocity distribution, channel reach identification, bankfull hydraulics

7 Quantitative Geomorphic Assessment Channel pattern relationships, geometry relationships

8 Comparative Aerial Photograph Digital Channel parameter mapping, isopach analysis, 8 Comparative Aerial Photograph Digital Assessment Methods

g yFHWA meander migration tool

9 Engineering Methods Allowable velocity, equilibrium slope, armoring

10 Sediment Transport / Fluvial Modeling HEC-6, SAM. Long and short term vertical adjustments, sediment continuity analysisadjustments, sediment continuity analysis

11 Lateral Erosion Hazard Boundary Mapping Quantify previous historic erosion rates through historic topography comparison procedures

CASE STUDY

San Juan CreekRegional WatershedRegional Watershed(175.4 sq.mi.)

Study Reach = 12,000 ftWatershed Area = 105 sq. mi.

San Juan Creek San Juan Creek -- Study AreaStudy Area

Step 1 -Field Data - CreekStep 1 -Field Data - CreekStep 1 -Field Data - Creek Characterization

Step 1 -Field Data - Creek Characterization

Types of Data Collection:• Bedrock – locations, outcrops• Particle sizes – channel bed, banks, overbanks• Armoring• Vegetation – channel, banks• Evidence of previous large floods–water marks,

avulsionsavulsions• Channel form and location - patterns, floodplain• Mining• Locations of structures – bridges, levees, gradeLocations of structures bridges, levees, grade

control• Location of tributaries• Head cuts / slope breaks – local scour• Field Photographs

OVERVIEW / BACKGROUND

General Work Program OutlineGeneral Work Program Outline

Step 2 – Geologic Mapping /Step 2 – Geologic Mapping /Step 2 – Geologic Mapping / Geotechnical Data

Step 2 – Geologic Mapping / Geotechnical Data

• Geologic setting and history• Geologic Structure

Faulting• Faulting• Soil materials

– Erodibility potential• Bedrock locations• Mechanical grain size

Streambed and banks– Streambed and banks• Slope stability analysis

– Geotechnical setbacks

LegendFloodplain Boundary

Geologic Units

Qafc

Geologic MapGeologic Map

Q

Qal1

Qal2

Qls

Qoal

Qsw

QtQ

Qtr3

Qtr4

Tc

Tm

Tsal

Tt

Ttso

Fault Lines

ABOVE

BELOW

San Juan CreekSan Juan Creek

GEOLOGIC / GEOTECHNICAL DATA

100

1

1 1/

2"

3/4

"

3/8

"

No.

4

No.

8

No.

16

No.

30

No.

50

No.

100

No.

200

3" 1 "

San Juan Creek PA-1 Streambed Grain Size Gradation Curves @ Depth 6'-10'

70

80

901

2

50

60

ent P

assin

g (%

)

3

4

20

30

40

Perc

e

5

6

0

10

20

0 0010 0100 1001 00010 000100 000

Average

0.0010.0100.1001.00010.000100.000

Grain size, D (mm)

Step 3 - Hydrologic Data and FloodStep 3 - Hydrologic Data and FloodStep 3 - Hydrologic Data and Flood History

Step 3 - Hydrologic Data and Flood History

• Watershed characteristics• Identification of wet years

Correlation of historical rainfall• Correlation of historical rainfall events to streambank erosion

• Long term hydrologic trends of rainfall

• Historical wet / dry cycles• Seasonal variation rainfall /flowsSeasonal variation rainfall /flows• Hydrologic modeling – Flood

frequency estimatesN f h d li d fl i l– Necessary for hydraulic and fluvial modeling

Annual Rainfall Comparison to Annual Rainfall Comparison to Historic Aerial Photographs

Historical Aerial PhotographsHistorical Aerial Photographs50

40

45 1930

1938

25

30

35

atio

n (in

)

15

20Prec

ipita

5

10

01947 1957 1967 1977 1987 1997

Years

Step 4 – Geomorphic Mapping /Step 4 – Geomorphic Mapping /Step 4 – Geomorphic Mapping / Assessment

Step 4 – Geomorphic Mapping / Assessment

• Stream Classification– Match stream characteristics with expected river responses

• Field Observations / AssessmentsArmoring– Armoring

– Avulsions– Bank Erosion– Exposed bedrock control– Headcuts– High water marks– Incisions– Active channel patternsActive channel patterns– Bedforms– Vegetation

• Geomorphic MappingG hi f– Geomoprhic surfaces

Step 5 – Historical Data AnalysisStep 5 – Historical Data Analysis

Data Sources• Historical aerial photograph interpretation

– Digitized and rectifiedDigitized and rectified• Historical topographic mapping• Historic ground photographs

I t l ( t b d l ti / t )• Improvement plans (streambed elevations/geometry)Channel Changes• Lateral bank movements• Vertical channel movement - single events, long terms (profiles)• Channel geometry channels – width, depth• Channel planform changes – pattern, sinuosityChannel planform changes pattern, sinuosity

1986 Aerial Photo Comparison to 2004 Topography1986 Aerial Photo Comparison to 2004 TopographyHistoric Aerial Photographs

1930 Aerial Photo Comparison to 2004 Topography1930 Aerial Photo Comparison to 2004 TopographyHistoric Aerial Photographs

Comparison of 1930 t0 2004 TopographyComparison of 1930 t0 2004 TopographyQUANTIFY HISTORIC EROSION

Historic Mapped Thalweg VariationHistoric Mapped Thalweg Variation

San Juan Creek Profile(Reference: San Juan Creek Study, SLA 1984)

HISTORIC DATA

350

400

Trampas Canyon

Cowcamp Road

300Chiquita

Confluence

Gobernadora Confluence

250

Elev

atio

n

Lower Ortega Highway

Verdugo Canyon

150

200

Bell Canyon

100

Canyon

504 5 6 7 8 9 10 11

River

1970 COE 1964 THALWEG 1978 OCEMA SCOUR STUDY 1960 TOPO 1963 OCEMA SCOUR STUDY

Step 6 – Floodplain HydraulicsStep 6 – Floodplain Hydraulics

Objectives:• Characterize floodplain hydraulic parameters• Data for engineering and geomorphic assessment• Data for engineering and geomorphic assessment• Define channel reaches through similar hydraulic

parametersCorrelation coefficients calculated for each x section– Correlation coefficients calculated for each x-section against hydraulic parameters

– Reaches selected preserves trend in hydraulic parameter and approximately equal reach lengthsp pp y q g

• Bank-full channel hydraulics• Hydraulic parameters for fluvial analysis

Manning’s N Manning’s N –– Roughness CoefficientRoughness Coefficient Mannings N Value0.060.070.0850.1


Legend

100-Yr Velocity Distribution

0 - 2

3 - 4

100100--Year Flood EventYear Flood EventVelocity DistributionVelocity Distribution

5 - 6

7 - 8

9 - 10

11 - 12

13 1413 - 14


Legend

100-Yr Velocity Distribution

0 - 2

3 - 4

100100--Year Flood Event Year Flood Event -- Velocity DistributionVelocity Distribution

5 - 6

7 - 8

9 - 10

11 - 12

13 1413 - 14


Step 7 – Quantitative GeomorphicStep 7 – Quantitative GeomorphicStep 7 – Quantitative Geomorphic Assessment

Step 7 – Quantitative Geomorphic Assessment

Hydraulic Geometry / Regime Equations

• Channel Pattern RelationshipsS– Slope-Discharge Relationships

• Lane equations• Leopold & Wolman equations• Ackers & Charlton equations• Henderson equations

• Channel Geometry Relationships– Bray equations (W, d, V)– Hey equationHey equation– Parker equation– Lacey equation– Chang equation

A k & Ch lt– Ackers & Charlton– AMAFCA equations– Moody & Odem equations

Step 7 – Quantitative GeomorphicStep 7 – Quantitative GeomorphicStep 7 – Quantitative Geomorphic Assessment

Step 7 – Quantitative Geomorphic Assessment

Assessment:• Actual hydraulics performed for 2- through 100-year

flowsflows• Examine trends of channel geometry adjustments at

different flow rates• Compare predicted values of widths, depth, slopes

from channel geometry equation to measured values in HEC-RAS models– Width – predicted width greater than HEC-RAS channel

expected to erode– Depth – Predicted depth greater than HEC-RAS the

t d t dexpected to erode– Slope – Predicted slope is less than the existing slope then

channel slope expected to decrease

Step 8 Comparative Aerial PhotographStep 8 Comparative Aerial PhotographStep 8 – Comparative Aerial Photograph Digital Assessment Methods

Step 8 – Comparative Aerial Photograph Digital Assessment Methods

• Digital stream mapping characteristics• Isopach analysis

– Recompilation of 1930 aerial photographs– Recalibrate with Focal length data– Topographic differential mapping

• FHWA Meander Migration GIS Mapping Tool– Procedures outlined in FHWA – Handbook for Predicting

Stream Meander Migrationg– GIS based measurement tool – Channel Migration Predictor

• Locate bankline of meander• Best-fit circle radiusBest fit circle radius• Apply consecutive historic aerial photographs to estimate rate• Use predictor to extrapolate future bankline

Oblique Topographic VariationOblique Topographic VariationISOPACH ANALYSIS

1930 to 20041930 to 2004

• Information

Oblique Topographic VariationOblique Topographic Variation

ISOPACH ANALYSIS

Oblique Topographic Variation 1930 to 2004

Oblique Topographic Variation 1930 to 2004

• Information

Oblique Topographic VariationOblique Topographic Variation

ISOPACH ANALYSIS

Oblique Topographic Variation1930 to 2004

Oblique Topographic Variation1930 to 2004

Step 9 – Engineering Methods Step 9 – Engineering Methods

Allowable Velocity• Fortier & Scobey• Mavis & Laushey equation• Neil equation• USACOE permissible velocityEquilibrium Slope

AMAFCA equations• AMAFCA equations• BRUEC equation• Bray equation• Henderson equation• Henderson equation• Schoklitsch• Meyer-Peter Mueller• Shields• Lane’s Tractive Force

Step 9 – Engineering Methods Step 9 – Engineering Methods

Armoring• Meyer-Peter Mueller bedload transport function• Competent bottom velocity• Shields diagram

Y i i i t ti• Yang incipient motion• Depth to armor equation

Step 10 – Sediment Transport / FluvialStep 10 – Sediment Transport / FluvialStep 10 – Sediment Transport / Fluvial Modeling

Step 10 – Sediment Transport / Fluvial Modeling

Analysis:• Channel width adjustments

– FLUVIAL model• Long term vertical erosionLong term vertical erosion

– HEC-6 modeling (60-year horizon selected per Section 577 NFIRA)– Long term hydrograph developed from gage data and linearized

• Short term / general scourHEC 6 modeling (single storm hydrograph)– HEC-6 modeling (single storm hydrograph)

• Sediment continuity Analysis– SAM ACOE– Apply on reach-by-reach basis

D t i dj t t f idth d t b d t i t i di t– Determine adjustments of width and streambed to maintain sediment balance

– 50-year erosion predicted from 6 time the 10-year width adjustment plus the single 100-year adjustment

– Used to compare results from fluvial modelingUsed to compare results from fluvial modeling

Step 11 – Lateral Erosion HazardStep 11 – Lateral Erosion HazardStep 11 – Lateral Erosion Hazard Boundary Mapping

Step 11 – Lateral Erosion Hazard Boundary Mapping

• Future lateral erosion predictionp– Combined results of different levels of analysis and

procedures to estimate magnitude of future erosion– Extrapolated future erosion magnitudes of different methodsExtrapolated future erosion magnitudes of different methods

compared for short term and long term values (60-year)– Calculated at each (1) reach, and (2) cross section

L t i b d• Long term erosion boundary– Added geotechnical setback for slope stability– Application of safety factor for level of uncertainty

Erosion Hazard BoundariesErosion Hazard Boundaries

Erosion Hazard Mapping

SummarySummary1 Combine results of multiple levels of analysis from hydraulics1. Combine results of multiple levels of analysis from hydraulics,

geomorphology, and fluvial analysis2. Additional digital tools available to perform assessments with

historical datahistorical data3. Additional erosion buffer applied to total setback based on

uncertainties and higher velocity / geomorphic trends4 A li ti f b k t t li i t i h d4. Application of bank revetment eliminates erosion hazard zone,

but Erosion Hazard Zone defines required minimum setback from top of bank

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