Final Report V2 October 30, 2015 - University of Georgia Hydrodynamic and...Modeling Guidelines...

PREPARED BY:

Tetra Tech, Inc. 2110 Powers Ferry Rd. SE, Suite 202 Atlanta, Georgia 30339 Phone: (770) 850-0949

Final Report V2

October 30, 2015

PREPARED FOR: Department of the Army Savannah District, Corps of Engineers 100 W Oglethorpe Avenue Savannah, Georgia 31401-3640 Contract: 100-ATL-T32468

October 2015 – REV2 Final Report V2, SHEP With-project Model and Modeling Guidelines

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Table of Contents

TABLE OF CONTENTS ........................................................................................................................... I

REVISION HISTORY .............................................................................................................................. II

LIST OF FIGURES ................................................................................................................................. III

LIST OF TABLES ................................................................................................................................ VIII

1.0 INTRODUCTION ........................................................................................................................... 1

2.0 WITHOUT-PROJECT MODEL................................................................................................... 2

3.0 WITH-PROJECT MODEL ........................................................................................................... 7

3.1 NAVIGATIONAL CHANNEL DEEPENING ......................................................................................... 7

3.2 MEETING AREAS AND BEND WIDENERS ........................................................................................ 7

3.3 FLOW REROUTING FEATURES ........................................................................................................ 8

3.4 OXYGEN INJECTION SYSTEMS ..................................................................................................... 10

4.0 MODELING GUIDELINES ........................................................................................................ 11

4.1 DAILY MEDIAN SALINITY MODELING GUIDELINES.................................................................... 15

4.2 DAILY AVERAGE DISSOLVED OXYGEN MODELING GUIDELINES ............................................... 42

4.3 DAILY AVERAGE CROSS SECTION VELOCITY MODEL GUIDELINES ........................................... 69

5.0 REFERENCES .............................................................................................................................. 94


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Revision History

The following table presents the revision history of the Savannah Harbor With-project and Modeling Guidelines Report.

Table i-1 Revision History of Savannah Harbor With-project and Modeling Guidelines Report Revision Number

Release Date Comments

0 February 27, 2015 Draft Report release.

1 June 5, 2015 Final Report V1 release.

2 October 30, 2015 Final Report V2 release. Update DO and salinity guideline figures.


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List of Figures

Figure 2-1 2014 bathymetric survey and 1999 bathymetric survey comparison of the Savannah Harbor

at Station 34+500 ................................................................................................................ 3


at Station 71+000 ................................................................................................................ 3


at Station 83+000 ................................................................................................................ 4


at Station 87+500 ................................................................................................................ 4

Figure 2-5 Longitudinal comparison of SHEP 2015 model navigational channel depth to the current

authorized total project depth .............................................................................................. 6

Figure 2-6 Longitudinal comparison of SHEP 2015 Without-project model navigational channel depth

to the current authorized total project depth ....................................................................... 6

Figure 3-1 Planned flow rerouting features included in the 2015 SHEP With-project model (Source:

Final General Re-evaluation Report, Chapter 9 [USACE 2012b]) ..................................... 9

Figure 3-2 Locations of the dissolved oxygen injection systems included in the 2015 SHEP With-

project model .................................................................................................................... 10

Figure 4-1 Continuous USGS monitoring stations where modeling guidelines were developed ....... 12

Figure 4-2 2015 SHEP Without-project model and With-project model combined daily median

salinity at USGS 02198840 relative to freshwater flows at USGS 02198500 .................. 16

Figure 4-3 2015 SHEP Without-project model and With-project model daily median salinity

confidence intervals at USGS 02198840 relative to freshwater flows at USGS 02198500

.......................................................................................................................................... 17


salinity at USGS 021989784 relative to freshwater flows at USGS 02198500 ................ 18



.......................................................................................................................................... 19





.......................................................................................................................................... 21





.......................................................................................................................................... 23





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.......................................................................................................................................... 27





.......................................................................................................................................... 29


salinity at USGS 021989715 (Bottom) relative to freshwater flows at USGS 02198500 30


confidence intervals at USGS 021989715 (Bottom) relative to freshwater flows at USGS

02198500 .......................................................................................................................... 31


salinity at USGS 021989715 (Surface) relative to freshwater flows at USGS 02198500 32


confidence intervals at USGS 021989715 (Surface) relative to freshwater flows at USGS

02198500 .......................................................................................................................... 33


salinity at USGS 0219897945 relative to freshwater flows at USGS 02198500 .............. 34



.......................................................................................................................................... 35





.......................................................................................................................................... 37


salinity at USGS 0219897993 relative to freshwater flows at USGS 02198500 .............. 38



.......................................................................................................................................... 39





.......................................................................................................................................... 41

Figure 4-28 2015 SHEP Without-project model and With-project model combined daily average

dissolved oxygen at USGS 02198840 relative to water temperature at USGS 02198840 43

Figure 4-29 2015 SHEP Without-project model and With-project model daily average dissolved

oxygen confidence intervals at USGS 02198840 relative to water temperature at USGS

02198840 .......................................................................................................................... 44


dissolved oxygen at USGS 021989784 relative to water temperature at USGS 02198840

.......................................................................................................................................... 45


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02198840 .......................................................................................................................... 46





02198840 .......................................................................................................................... 48





02198840 .......................................................................................................................... 50



.......................................................................................................................................... 51



02198840 .......................................................................................................................... 52





02198840 .......................................................................................................................... 54



.......................................................................................................................................... 55



02198840 .......................................................................................................................... 56


dissolved oxygen at USGS 021989715 (Bottom) relative to water temperature at USGS

02198840 .......................................................................................................................... 57


oxygen confidence intervals at USGS 021989715 (Bottom) relative to water temperature

at USGS 02198840 ........................................................................................................... 58


dissolved oxygen at USGS 021989715 (Surface) relative to water temperature at USGS

02198840 .......................................................................................................................... 59


oxygen confidence intervals at USGS 021989715 (Surface) relative to water temperature

at USGS 02198840 ........................................................................................................... 60



.......................................................................................................................................... 61


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02198840 .......................................................................................................................... 62



.......................................................................................................................................... 63



02198840 .......................................................................................................................... 64



.......................................................................................................................................... 65



02198840 .......................................................................................................................... 66





02198840 .......................................................................................................................... 68

Figure 4-54 2015 SHEP Without-project model and With-project model combined daily average cross-

sectional velocity at USGS 02198840 relative to freshwater flows at USGS 02198500 .. 70

Figure 4-55 2015 SHEP Without-project model and With-project model daily average cross-sectional

velocity confidence intervals at USGS 02198840 relative to freshwater flows at USGS

02198500 .......................................................................................................................... 71


sectional velocity at USGS 021989784 relative to freshwater flows at USGS 02198500 72



02198500 .......................................................................................................................... 73





02198500 .......................................................................................................................... 75





02198500 .......................................................................................................................... 77





02198500 .......................................................................................................................... 79




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02198500 .......................................................................................................................... 81





02198500 .......................................................................................................................... 83





02198500 .......................................................................................................................... 85


sectional velocity at USGS 0219897945 relative to freshwater flows at USGS 02198500

.......................................................................................................................................... 86



02198500 .......................................................................................................................... 87





02198500 .......................................................................................................................... 89


sectional velocity at USGS 0219897993 relative to freshwater flows at USGS 02198500

.......................................................................................................................................... 90



02198500 .......................................................................................................................... 91





02198500 .......................................................................................................................... 93


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List of Tables

Table i-1 Revision History of Savannah Harbor With-project and Modeling Guidelines Report ..... ii

Table 2-1 Existing project depths (feet below MLLW) ...................................................................... 2

Table 3-1 47-foot planned project depths (feet below MLLW) .......................................................... 7

Table 4-1 List of continuous USGS monitoring stations .................................................................. 11

Table 4-2 Flow exceedance probability bracket ranges for salinity guideline plots at upstream USGS

monitoring stations ........................................................................................................... 13


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1.0 Introduction

The 2015 Savannah Harbor Expansion Project (SHEP) model, herein identified as the 2015 SHEP model,

was developed to represent the hydrodynamic and water quality conditions that were present in the

Savannah Harbor and River during the 2013 and 2014 period (Tetra Tech 2015). The 2015 SHEP model

was updated with revised bathymetry, geometry, and loads to represent the selected project channel

deepening and environmental mitigation features outlined in the SHEP Final Environmental Impact

Statement (EIS) and General Re-evaluation Report (GRR) (United States Army Corps of Engineers

[USACE] 2012a and USACE 2012b).

The selected project included the alteration of several navigation features: channel deepening to a

controlling depth of 47 ft below Mean Low Lower Water (MLLW), a 7.3-mile channel extension,

construction of two meeting areas, three bend wideners, and the expansion of the Kings Island Turning

Basin. The selected project also included construction of several mitigation features: construction of a

freshwater diversion structure at McCoys Cut, closure of Rifle Cut, deepening the upper portions of Middle,

Little Back, and Back Rivers, removal of the tidegate piers and abutments, construction of a sill at the mouth

of the sediment basin and fill behind the sill, and construction of a dissolved oxygen (DO) injection system.

The navigation and mitigation features were included in the 2015 SHEP With-project model. This model,

and the 2015 SHEP Without-project model, which did not include the navigation and mitigation features,

were used to develop predictive guidelines at 12 United States Geological Survey (USGS) continuous

monitoring stations located in the Savannah Harbor. The guideline plots were developed for salinity, DO,

and velocity and will be compared to measured USGS data collected during construction of the SHEP

features.



2.0 Without-Project Model

The United States Army Corps of Engineers (USACE) Savannah District used the 2006 SHEP model to

evaluate several different navigational channel deepening scenarios for the SHEP Final EIS and their

impacts on DO and salinity (USACE 2012a). This 2006 SHEP model was also used to evaluate several

potential environmental mitigation projects in the Savannah Harbor, including the McCoy’s Cut diversion

structure, Rifle Cut closure, and oxygen injection facilities.

The existing authorized navigational channel depth was 42 ft. The USACE allowed advanced dredging

maintenance throughout most of the navigational channel, which ranged in depth from 2 ft to 8 ft, bringing

the total authorized depth to 44 ft to 50 ft (Table 2-1). In the SHEP Final EIS, proposed channel navigational

depths of 44 ft, 45 ft, 46 ft, 47 ft, and 48 ft were evaluated, and the 47-foot navigational depth was selected

as the final project navigational depth. For the 47-foot channel deepening scenario evaluation, the

navigational channel depth in the 2006 SHEP model was increased by 5 ft to represent the change in the

navigational channel depth from 42 ft to 47 ft. The channel depth in the 2006 SHEP model included both

the authorized navigational channel depth and the advanced maintenance.

Table 2-1 Existing project depths (feet below MLLW)

Section Limits Existing Project Depths

Lower Upper Authorized

Depth Advance

Maintenance Total Depth

-97+680B -60+000B * * *

-60+000B -14+000B 44 0 44

-14+000B +24+000 42 2 44

+24+000 +35+000 42 4 46

+35+000 +37-000 42 6 48

+37-000 +70+000 42 4 46

+70+000 +102+000 42 2 44

+102+000 +103+000 42 0 42

Kings Island Turning Basin 42 8 50

+103+000 +105+500 36 2 38

+105+500 +112+500 30 2 32 Source: Final General Re-Evaluation Report (USACE 2012b)

The 2006 SHEP model was updated to include 2014 channel bathymetric data, increase the grid resolution

at environmental mitigation project locations, and extend data input boundaries through April 30, 2014.

The updated model was named the 2015 SHEP model and it will be used to evaluate impacts to DO and

salinity throughout the SHEP construction activities.

To evaluate the SHEP construction activities, a 2015 SHEP With-project model needed to be created that

used the same methodology to represent the new authorized navigational channel depth of 47 ft and SHEP

environmental mitigation projects as defined in the SHEP Final EIS. However, the navigational channel

depths in the 2015 SHEP model, which used 2014 bathymetric data, were shallower in several locations

than the navigational channel depths in the 2006 SHEP model, which used 1999 and 2002 bathymetric data.

Differences in the bathymetric data were typically less than 1 foot (Figure 2-1 and Figure 2-2), but were as

great as 5 feet in some locations, such as at Station 87+500 and 83+000 (Figure 2-3 and Figure 2-4). In

these shallow locations, navigational channel depth was less than the total authorized depth.



Figure 2-1 2014 bathymetric survey and 1999 bathymetric survey comparison of the Savannah Harbor at Station 34+500




The USACE Savannah District has an annual operations and maintenance (O&M) budget, and funds from

this budget are used to dredge the navigational channel. However, the available O&M budget changes

annually and is usually sufficient to dredge the entire Savannah Harbor to the total authorized project depth,

although areas of the channel may not be dredged for up to three years (Durden 2015). In addition, areas

that are dredged may not be dredged to the total authorized project depth depending on the O&M budget.

For example, if an area has an authorized navigational channel depth of 42 ft and an advanced maintenance

depth of 4 ft, the USACE may have contractors dredge the full 42 ft of the authorized navigational channel

depth but only 2 ft of the advanced maintenance depth. Dredging contractors may also remove an additional

2 feet of allowable overdepth, therefore areas of the channel can be deeper than the total authorized project

depths at times.

When the 2014 bathymetric survey data were collected to develop the 2015 SHEP model, USACE had not

recently performed dredging in the shallow offshore area or from Stations 30+000 through 90+000 (Durden

2015). The USACE Savannah District had a new dredging contract that began January 2015 as part of

ongoing O&M. For this contract, dredging began at Station 93+000 and will go upstream to Station

103+000 before continuing downstream below Station 93+000.

The Savannah Harbor and River are dynamic systems and bed depths are constantly changing, with frequent

shoaling occurring along toe slopes. Bathymetric survey data collected represents the channel depths at that

specific time. Therefore, the 2014 bathymetric survey data represent channel conditions during the winter

and spring of 2014, when the data were collected, which corresponds to the calibration period of the 2015

SHEP model from January 1, 2013 through April 30, 2014.

Due to the timing of the 2014 bathymetric data collection, sections of the 2015 SHEP model navigational

channel were shallower than the existing project total depth (Figure 2-5). To represent the existing project

total depth, an additional model was developed called the SHEP 2015 Without-project model. To create the

model, the 2015 SHEP model navigational channel depth was increased in several locations to the existing

project total depths listed in Table 2-1 (Figure 2-6).

By removing the sediment that had accumulated within the channel in the 2015 Without-Project model, the

model is able to represent expected conditions following the ongoing O&M, and channel conditions most

years.

In addition, by adjusting the navigational channel depth in the model, the 2015 SHEP With-project model

can use the same methodology as the SHEP Final EIS to represent the 47-foot selected authorized depth,

which entailed subtracting 5 ft from the model navigational channel.



Figure 2-5 Longitudinal comparison of SHEP 2015 model navigational channel depth to the current authorized total project depth

Figure 2-6 Longitudinal comparison of SHEP 2015 Without-project model navigational channel depth to the current authorized total project depth



3.0 With-Project Model

The 2015 SHEP With-project model was created by incorporating the total selected project channel depth

and environmental mitigation features design into the 2015 SHEP Without-project model. The 2015 SHEP

With-project model included: (1) a deeper navigational channel to meet the planned project depths, (2) new

meeting locations and bend wideners modifications, (3) flow altering mitigation features, and 4) DO

injection systems. A detailed description of the features included in the 2015 SHEP With-project model is

provided below.

3.1 Navigational channel deepening

The 47-foot selected project channel depth was incorporated into the 2015 SHEP With-project model by

increasing the navigational channel depth in the 2015 SHEP Without-project model by 5 ft. The channel

depth in the 2015 SHEP-project model was either equal to or greater than the total selected project depth

from Table 14.3 of the Final GRR (USACE 2012b) (Table 3-1).

Table 3-1 47-foot planned project depths (feet below MLLW)

Section Limits Selected Project Depths

Lower Upper Authorized

Depth Advance

Maintenance Total Depth

-97+680B -60+000B 49 0 49

-60+000B -14+000B 49 0 49

-14+000B +24+000 47 2 49

+24+000 +35+000 47 4 51

+35+000 +37-000 47 6 53

+37-000 +70+000 47 4 51

+70+000 +102+000 47 2 49

+102+000 +103+000 47 0 47

Kings Island Turning Basin 47 8 55

+103+000 +105+500 36 2 38

+105+500 +112+500 30 2 32

Source: Final General Re-Evaluation Report (USACE 2012b)

3.2 Meeting areas and bend wideners

The 2015 SHEP With-project model included four bend wideners at critical turns and two meeting areas in

the inner harbor (USACE 2012b). The bend wideners were distributed in the 2015 SHEP With-project

model as follows:

Kings Island Turning Basin Bend Widener: Located from 99+000 to 100+500

Ft Jackson Range Bend Widener: Located from 52+500 to 55+000

Lower Flats Range Bend Widener: Located from 27+500 to 31+500

Jones Island Range Bend Widener: Located from -23+000 to -14+000

The meeting areas are distributed as follows:

Oglethorpe Range Meeting Area: Located from 54+800 to 58+800. 100 feet wide plus side slope

of less than 100 feet

Long Island Range Meeting Area: Located from 13+000 to 23+000. 100 feet wide plus side slope

of less than 100 feet



The meeting areas and bend wideners were incorporated into the model by reconfiguring the model cells.

The cells corresponding to the navigation channel were widened while the adjacent cells were narrowed at

the specific locations.

3.3 Flow rerouting features

The flow rerouting features included in the With-project model correspond to the engineering designs

defined in Plan 6a of the Final GRR (USACE 2012b) (Figure 3-1). The modifications included the

following:

McCoys Cut diversion structure

Close lower (western) arm of McCoys Cut

Channel deepening on McCoys Cut to -4m NGVD

Channel deepening Upper Middle and Little Back Rivers to -3m NGVD

Close Rifle Cut

Allow sediment basin to fill to -3.85M NGVD by constructing a submerged sill

Remove tide gate abutments and piers

The diversion structure, closure of lower arm of McCoys Cut and the closure of Rifle Cut were incorporated

into the model by blocking the flow at the south side of model grid cells (11,137) and (12,137) for the

structure, at the south side of cell (5,128) for the lower arm and at the west side of cell (24,107) for Rifle

cut. The cells of the Little Back and Upper Middle Rivers were deepened and the Tidegate abutments and

piers effects were removed from the model by including cells (26,83) and (28,63) in the model.



Figure 3-1 Planned flow rerouting features included in the 2015 SHEP With-project model (Source: Final General Re-evaluation Report, Chapter 9 [USACE 2012b])



3.4 Oxygen injection systems

Oxygen will be injected into the Savannah Harbor and River using ten Speece cones, and injection will

occur during the summer period from June 15 through September 30. The 2015 SHEP With-project model

incorporated three oxygen injection system locations into the 2015 SHEP Water Quality Analysis

Simulation Program Version 7 (WASP7) model (USACE 2012b). The DO was added to the 2015 SHEP

WASP7 model as a point source load (Figure 3-2):

One oxygen injection system containing seven Speece cones in the upper area of Savannah River

near Georgia Power Company’s Plant McIntosh. The amount of oxygen injected at this location

was 28,000 lbs O/day.

One oxygen injection system with two operating Speece cones on the west side and one system

with one operating Speece cone on the east side of Hutchinson Island (Front and Back Rivers

respectively), for a total of two oxygen injection systems at Hutchinson Island. The amount of

oxygen injected was 8,000 lbs O/day in the Front River and 4,000 lb O/day in the Back River.

Figure 3-2 Locations of the dissolved oxygen injection systems included in the 2015 SHEP With-project model



4.0 Modeling Guidelines

The 2015 SHEP Without-project and With-project models were used to develop a set of predictive modeling

guidelines to support the assessment of construction progress and performance in the Savannah Harbor and

River. The guideline plots constitute a simplified approach to estimate the magnitude or concentration of

relevant hydrodynamic and water quality variables throughout the estuary for the Without-project and With-

project conditions. During construction and post-construction monitoring, data would be compared to these

ranges to determine if the mitigation is performing as expected. Monitoring data falling outside the expected

ranges will not be triggers for a specific action, but it could indicate that the system may not be performing

as predicted. Should this occur, the USACE may conduct further investigation to determine the cause of

the unexpected measured values.

Guideline plots were developed for salinity and current speed (velocity) at 12 continuous USGS monitoring

stations located throughout the Savannah Harbor (Table 4-1 and Figure 4-1) as a function of the freshwater

flows conditions at the USGS station 02198500 Savannah River near Clyo, GA (upstream model boundary).

Guideline plots were also developed for DO at the 12 continuous USGS monitoring stations as a function

of temperature conditions at the USGS station 02198840 Savannah River (I-95) near Port Wentworth, Ga.

Data collected at the USGS monitoring stations will be compared to the guidelines plots, which include

modeled data predictions, data trend lines, and confidence intervals.

Table 4-1 List of continuous USGS monitoring stations Station ID Name Agency

02198840 Savannah River (I-95) near Port Wentworth, GA USGS

021989784 Little Back River above Lucknow Canal near Limehouse, SC USGS

02198920 Front River at GA 25, at Port Wentworth USGS

02198950 Middle River at GA 25 at Port Wentworth USGS

021989792 Little Back River at GA 25 at Port Wentworth, GA USGS

02198955 Middle River at "Fish Hole" at Port Wentworth, GA USGS

021989793 Little Back River at Hog Island near Savannah, GA USGS

021989715 Front River at Garden City, GA USGS

0219897945 Back River 0.4 miles downstream US17 near Savannah, GA USGS

021989773 Savannah River at USACE Dock, at Savannah, GA USGS

0219897993 Savannah River at Elba Island near Savannah, GA USGS

02198980 Savannah River at Fort Pulaski, GA USGS



Figure 4-1 Continuous USGS monitoring stations where modeling guidelines were developed



The modeling guidelines were developed using predictions of salinity, DO, and velocity from the 2015

Without-project and With-project models for the entire modeling period from January 1, 1997 through April

30, 2014. Since the USGS collects DO and salinity data at or near the water surface, the guideline plots

used model predictions for surface layer concentrations of DO and salinity. The USGS measures cross-

sectional current speed (velocity), and guideline plots for current speed were developed to show average

cross-sectional velocity.

Modeling guideline plots were prepared for the daily average DO concentrations because the 2010 TMDL

for the Savannah Harbor requires that changes to daily average DO concentrations be less than 0.1 mg/L.

The median salinity concentrations were used to develop guidelines plots because the median salinity

concentration was used to evaluate SHEP impacts to wetlands. Both the daily average DO concentration

and median salinity concentration are reported by the USGS at the stations listed in Table 4-1 on the website

http://waterdata.usgs.gov/nwis. Plots were also created for average velocity, which negates the ebb and

flood tidal velocities that occur daily. The USGS does not report daily average velocity, but it can be

calculated from the instantaneous measurements that the USGS collects and reports on their website.

The predictive curves of salinity versus flow, DO versus temperature, and current speed versus flow were

developed by fitting a regression model to the simulated time series of surface salinity and DO. The fitted

models for salinity versus flow used an exponential curve of the form 𝑆𝑎𝑙 = 𝑎 × 𝑒𝑏×𝑄, where Sal is the

salinity concentration in PSU (Practical Salinity Units) at a particular station, 𝑄 is the average daily flow at

Clyo in 𝑓𝑡3/𝑠, and 𝑎 and 𝑏 are regression coefficients estimated using the Levenberg-Marquard algorithm

for Nonlinear Least Squares curve fitting.

The models for DO versus temperature and current speed versus flow used a linear curve of the form 𝐷𝑂 =𝑐 + 𝑑 × 𝑇, and 𝐶𝑆 = 𝑒 + 𝑓 × 𝑄 where DO and CS represent the DO concentration in 𝑚𝑔/𝐿 and the current

speed in 𝑓𝑡/𝑠 at a particular station, 𝑄 is the average daily flow at Clyo in 𝑓𝑡3/𝑠, 𝑇 is the water temperature

at the Port Wentworth station and 𝑐, 𝑑, 𝑒 and 𝑓 are regression coefficients estimated by traditional Least

Squares. The guideline plots included two sets of confidence intervals around the plot trendlines. The

confidence intervals were expressed as ± 1, ± 2, 𝑎𝑛𝑑 ± 3 standard deviations around the fitted curve,

which represent the 68%, 95%, and 99.7% confidence intervals.

The modeling guideline trendlines and confidence intervals for salinity and velocity were developed for

modeled data associated with measured flows at Clyo that had an exceedance probability of 95% or less.

The remaining 5% of flows represented high and extreme flows conditions with low occurrences. At the

upstream USGS monitoring stations where the salinity intrusion was moderate or limited, the confidence

intervals were bracketed for two to four flow exceedance probability ranges to better represent the change

in dispersion, specifically in the high flow conditions where salinity concentrations were at or near to 0

PSU. The bracket ranges for the six upstream USGS stations can found in Table 4-2.

Table 4-2 Flow exceedance probability bracket ranges for salinity guideline plots at upstream USGS monitoring stations

Station ID Name

Flow Exceedance Probability

Bracket Ranges (BR) (%)

BR1 BR2 BR3 BR4

021989784 Little Back River above Lucknow Canal near

Limehouse, SC 0-65 65-95 – –

02198920 Front River at GA 25, at Port Wentworth 0-65 65-80 80-90 90-95

02198950 Middle River at GA 25 at Port Wentworth 0-70 70-90 90-95 –

021989792 Little Back River at GA 25 at Port Wentworth, GA 0-65 65-80 80-90 90-95



Station ID Name

Flow Exceedance Probability

Bracket Ranges (BR) (%)

BR1 BR2 BR3 BR4

02198955 Middle River at "Fish Hole" at Port Wentworth, GA 0-65 65-80 80-90 90-95

021989793 Little Back River at Hog Island near Savannah, GA 0-70 70-85 85-95 90-95

Two modeling guideline plots are provided for each station and each parameter in Section 4.1 through

Section 4.3. The first plot displays the combined modeling results of the 2015 SHEP With-project and

Without-project model scenario runs and the associated confidences intervals. By combining the model

outputs from two model scenarios, the guideline plots display an expected range of median salinity

concentrations, average DO concentrations, and average velocities over the course of project construction.

However, depending on construction schedule, expected values may be above or below the guideline plot

expected ranges for short periods of times. The second plot displays the confidence intervals lines for both

the 2015 SHEP Without-project and With-project model scenario runs. These plots display the expected

changes in median salinity concentrations, average DO concentrations, and average velocities due to

channel deepening and mitigation features project construction.

The With- and Without-project guideline plot confidence interval ranges confirm modeling work completed

for the SHEP Final EIS. Based on the guideline plot figures, some areas of the Savannah Harbor are

expected to experience an increase or reduction in salinity levels once all project features are constructed.

In the upstream region of the Front River, the salinity values are expected to decrease between 1 and 2 PSU

(USGS station 021989784, Figure 4-5), while in the middle and downstream regions of the Front and

Middle Rivers the salinity levels may increase between 1 and 2 PSU under normal or low flow conditions

(USGS station 02198920 and USGS station 02198950, Figure 4-7 and Figure 4-9 respectively). In the Back

River, the salinity values are expected to decrease between 2 and 4 PSU due to construction of the McCoys

Cut diversion structure.

DO concentrations are expected to decrease approximately 0.5 mg/L throughout the Savannah harbor

during the winter period once all project features are constructed. During this time period the DO oxygen

injection systems will not be in operation because DO concentrations will be above critical values. In the

critical summer months when the DO oxygen injection systems are operational, DO concentrations in the

Savannah Harbor are expected to be similar to or greater than the Without-project DO concentrations.

Cross section velocity changes are expected to be minor, typically less than 0.25 ft/s, throughout the

Savannah Harbor. However, in the Back River at USGS station 021989784 the velocity may increase above

0.25 ft/s following completion of projects. This increase is caused by higher flows in the Back River caused

by the McCoys Cut diversion structure.



4.1 Daily Median Salinity Modeling Guidelines



Figure 4-2 2015 SHEP Without-project model and With-project model combined daily median salinity at USGS 02198840 relative to freshwater flows at USGS 02198500



Figure 4-3 2015 SHEP Without-project model and With-project model daily median salinity confidence intervals at USGS 02198840 relative to freshwater flows at USGS 02198500



Figure 4-16 2015 SHEP Without-project model and With-project model combined daily median salinity at USGS 021989715 (Bottom) relative to freshwater flows at USGS 02198500



Figure 4-17 2015 SHEP Without-project model and With-project model daily median salinity confidence intervals at USGS 021989715 (Bottom) relative to freshwater flows at USGS 02198500



Figure 4-18 2015 SHEP Without-project model and With-project model combined daily median salinity at USGS 021989715 (Surface) relative to freshwater flows at USGS 02198500



Figure 4-19 2015 SHEP Without-project model and With-project model daily median salinity confidence intervals at USGS 021989715 (Surface) relative to freshwater flows at USGS 02198500



4.2 Daily Average Dissolved Oxygen Modeling Guidelines



Figure 4-28 2015 SHEP Without-project model and With-project model combined daily average dissolved oxygen at USGS 02198840 relative to water temperature at USGS 02198840



Figure 4-29 2015 SHEP Without-project model and With-project model daily average dissolved oxygen confidence intervals at USGS 02198840 relative to water temperature at USGS 02198840



Figure 4-42 2015 SHEP Without-project model and With-project model combined daily average dissolved oxygen at USGS 021989715 (Bottom) relative to water temperature at USGS 02198840



Figure 4-43 2015 SHEP Without-project model and With-project model daily average dissolved oxygen confidence intervals at USGS 021989715 (Bottom) relative to water temperature at USGS 02198840



Figure 4-44 2015 SHEP Without-project model and With-project model combined daily average dissolved oxygen at USGS 021989715 (Surface) relative to water temperature at USGS 02198840



Figure 4-45 2015 SHEP Without-project model and With-project model daily average dissolved oxygen confidence intervals at USGS 021989715 (Surface) relative to water temperature at USGS 02198840



4.3 Daily Average Cross Section Velocity Model Guidelines



Figure 4-54 2015 SHEP Without-project model and With-project model combined daily average cross-sectional velocity at USGS 02198840 relative to freshwater flows at USGS 02198500



Figure 4-55 2015 SHEP Without-project model and With-project model daily average cross-sectional velocity confidence intervals at USGS 02198840 relative to freshwater flows at USGS 02198500



5.0 References

Durden, Ned. 2015. Personal Communication. United States Corps of Engineers (USACE) Savannah

District. January 2015. <[email protected]>

Tetra Tech. 2015. Hydrodynamic and Water Quality Modeling Report for the Savannah Harbor, Georgia.

USACE Savannah District. June 2015.

United States Corps of Engineers (USACE). 2012a. Final Environmental Impact Statement. Savannah

Harbor Expansion Project. Chatham County, Georgia and Jasper County, South Carolina. USACE

Savannah District. January 2012. Revised July 2012.

United States Corps of Engineers (USACE). 2012b. Final General Re-evaluation Report for Savannah

Harbor Expansion project. Chatham County, Georgia and Jasper County, South Carolina. USACE

Savannah District. January 2012.

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