### P REPARED BY 

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

### : Georgia Environmental Protection

Division 4220 International Parkway
Suite 101 Atlanta, Georgia 30354
Contract: 751-10135

Amendment: 7 

# W a t e r s h e d H y d r o l o g y a n d

W a t e r Q u a l i t y M o d e l i n g R e p o r t

f o r 

# C a r t e r s L a k e , G e o r g i a

November 30, 2011
Revision 1November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 0 

## Table of Contents

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

................................................... .................................. 0

LIST OF APPENDICES ................................

................................................... .................................... 1

REVISION HISTORY ..................................

................................................... ..................................... 1

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

................................................... ......................................... 2

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

................................................... ......................................... 3

1.0 INTRODUCTION.......................................

................................................... ............................ 4

2.0 MODEL SELECTION ...................................

................................................... ........................ 6

2.1 LSPC W ATERSHED M ODEL

.................................................. ................................................... . 6

2.2 I NTEGRATION OF LSPC WITH EFDC .............................................. ........................................... 6

3.0 WATERSHED MODEL DEVELOPMENT .......................

................................................... ... 7

3.1 O VERVIEW

.................................................. ................................................... .......................... 7

3.2 W ATERSHED S EGMENTATION

.................................................. ................................................. 8

3.3 S IMULATION P ERIOD

.................................................. ................................................... ......... 12

3.4 S OILS

.................................................. ................................................... ................................ 12

3.5 M ETEOROLOGICAL D ATA

.................................................. ................................................... .. 14

3.6 R EACH C HARACTERISTICS

.................................................. ................................................... 16

3.7 L AND U SE R EPRESENTATION

.................................................. ............................................... 16

3.8 C HICKEN L AND R EPRESENTATION

.................................................. ....................................... 20

3.9 S EPTIC T ANK R EPRESENTATION

.................................................. ........................................... 24

3.10 P OINT S OURCE D ISCHARGES

.................................................. ................................................ 24

3.11 M UNICIPAL AND I NDUSTRIAL W ATER W ITHDRAWALS

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

4.0 WATERSHED HYDROLOGY MODEL .........................

................................................... ... 28

4.1 H YDROLOGIC R EPRESENTATION

.................................................. ........................................... 28

4.2 O BSERVED F LOW D ATA

.................................................. ................................................... .... 28

4.3 H YDROLOGY M ODEL C ALIBRATION

.................................................. ..................................... 28

4.4 H YDROLOGY M ODEL V ALIDATION

.................................................. ....................................... 28

4.5 H YDROLOGY O BSERVATIONS AND C ONCLUSIONS

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

5.0 WATERSHED WATER QUALITY MODEL .....................

................................................... 33

5.1 W ATER Q UALITY M ODEL O VERVIEW

.................................................. ................................... 33

5.2 M ODELED P ARAMETERS

................................................... ................................................... ... 33

5.3 R EACH G ROUP

.................................................. ................................................... .................. 33

5.4 W ATER T EMPERATURE

................................................... ................................................... ..... 34

5.5 D ISSOLVED O XYGEN

.................................................. ................................................... ......... 34

5.6 S EDIMENT

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

5.7 N UTRIENTS AND P LANKTON

.................................................. ................................................. 3 5

5.8 W ATER Q UALITY C ALIBRATION

.................................................. ........................................... 36

5.9 S PECIAL C ONSIDERATIONS FOR W ATER Q UALITY

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

Chicken Houses ....................................

................................................... ...................................... 37 Septic Tanks ......................................

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

5.10 O BSERVED W ATER Q UALITY D ATA FOR C ALIBRATION AND V ALIDATION .............................. 39

5.11 W ATER Q UALITY O BSERVATIONS AND C ONCLUSIONS

.................................................. .......... 41November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 1 6.0 INPUT OVERVIEW FIGURES ............................

................................................... ............... 44

7.0 REFERENCES ........................................

................................................... ............................. 49



## List of Appendices

APPENDIX A – SOILS AND WEATHER STATION ASSIGNMENTS

APPENDIX B – PHYSICAL REACH CHARACTERISTICS

APPENDIX C – LAND USE BREAKDOWN BY SUBWATERSHED

APPENDIX D – CHICKEN HOUSES

APPENDIX E – SEPTIC TANKS

APPENDIX F – POINT SOURCES

APPENDIX G – MUNICIPAL AND INDUSTRIAL WATER WITHDRA WALS

APPENDIX H – HYDROLOGY CALIBRATION PARAMETES

APPENDIX I – HYDROLOGY CALIBRATION AND VALIDATION

APPENDIX J – DISSOLVED OXYGEN AND TEMPERATURE CALIB RATION PARAMETES

APPENDIX K – DISSOLVED OXYGEN AND TEMPERATURE CALIB RATION AND VALIDATION

APPENDIX L – SEDIMENT CALIBRATION PARAMETES

APPENDIX M – SEDIMENT CALIBRATION AND VALIDATION

APPENDIX N – NUTRIENT AND PLANKTON CALIBRATION PARA METES

APPENDIX O – NUTRIENT AND PLANKTON CALIBRATION AND VALIDATION

APPENDIX P – NUTRIENT LOADINGS APPENDIXQ – CUMULATIVE UPSTREAM LAND USE FOR HYDROL OGY AND WATER QUALITY

CALIBRATION AND VALIDATION STATIONS

APPENDIX R – CARTERS LAKE WEATHER FILE DEVELOPMENT REPORT



## Revision History

The following table presents the revision history o f Carters Lake Watershed Modeling Report.

Table i-1 Revision History of Carters Lake Watershe d Modeling Report

Revision

Number Release Date Comments

0 December 31, 2008 Initial Release of Report. Hydrology Calibration/Va lidation are through 2007.

1 November 30, 2011 Extended the model to run through the end of 2009 Updated and included more AIR files Updated point sources Updated water withdrawals Updated Land Use to GLUT 2005 Added Representation of Chicken Houses Added Representation of Septic Tanks Checked for Land Application Systems (none present) Checked for Agricultural Irrigation areas (none pre sent) Updated Hydrology Calibration (added more USGS gage s) Calibrated Temp/DO, Water Quality and SedimentNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 2 

## List of Figures

Figure 1-1 Location of Carters Lake ..........................

................................................... ................... 5 Figure 2-1 Linkage between LSPC and other models .............

................................................... ....... 6 Figure 3-1 Georgia 12-Digit HUC Coverage for Carters Lake Wate rshed ........................................ 9 Figure 3-2 Sub-delineated 12-Digit HUC Coverage for Carters La ke Watershed ............................ 10 Figure 3-3 Digital Elevation Map (DEM) Coverage for Carters La ke Watershed ............................ 11 Figure 3-4 Soils Coverage for Carters Lake Watershed .........

................................................... ...... 13 Figure 3-5 Spatial Coverage of Meteorological Stations used in the LSPC Watershed Model ......... 15 Figure 3-6 GLUT 2005 Coverage in Reduced Modeling Units of the Carters Lake Watershed ....... 18 Figure 3-7 GLUT Impervious Coverage of the Carters Lake Waters hed ......................................... 19 Figure 3-8 Regression of 2008 Mean Measured Total Nitrogen and Upstream Chicken House Buffer

area ..............................................

................................................... ............................. 21 Figure 3-9 Regression of 2008 Mean Measured Total Nitrogen and Percent of Contributing Drainage

that is Chicken Land using 25% of the Buffer Area .

................................................... ... 22 Figure 3-10 Regression of 2008 Mean Simulated Total Nitrogen an d Percent of Contributing

Drainage that is Chicken Land using 25% of the Buff er Area ........................................ 22 Figure 3-11 Location of Broiler Chicken Houses in the Carters L ake Watershed with a 0.75-km buffer

surrounding each location .........................

................................................... ................. 23 Figure 3-12 Permitted Discharges in the Carters Lake Watershed

................................................... . 26 Figure 4-1 Spatial Coverage of Calibration and Validation Stat ions used in the Hydrology Model . 32 Figure 5-1 Spatial Coverage of Calibration and Validation Stat ions used in the Water Quality Model

................................................... ................................................... ............................... 40 Figure 6-1 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 1 of 4) . 45 Figure 6-2 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 2 of 4) . 46 Figure 6-3 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 3 of 4) . 47 Figure 6-4 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 4 of 4) . 48November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 3 

## List of Tables

Table i-1 Revision History of Carters Lake Watershed Modeling Report ....................................... 1

Table 3-1 Summary of Meteorological Station for Carters Lake Watershed .................................. 14

Table 3-2 Land Use Representation ...........................

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

Table 3-3 Results of Chicken Land Buffer Area Representation Scenarios .................................... 21

Table 3-4 Summary of Point Source Discharges in the Carters L ake Watershed ............................ 25

Table 3-5 Summary of Data Utilized for the Point Source Disch arges in the Carters Lake Watershed

................................................... ................................................... ............................... 25

Table 3-6 Default Water Quality Concentrations of Constituent s without Data for Rock Quarries . 25

Table 3-7 Summary of Water Withdrawal in Carters Lake Watersh ed .......................................... 27

Table 4-1 USGS Flow Gauges used for Calibration and Validatio n in the Carters Lake Watershed

Model .............................................

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

Table 4-2 Score and Grade for USGS flow gages Carters Lake Wa tershed model ......................... 30

Table 4-3 Summary statistics: Model Outlet 1001 vs. USGS 0238 0500 Coosawattee River near

Ellijay, Ga. (12-Year Calibration) ................

................................................... .............. 30

Table 4-4 Qualitative Grading Scale for USGS 02380500 Coosawa ttee River near Ellijay ............ 31

Table 4-5 Score Minimum and Corresponding Qualitative Grade . ................................................ 31

Table 4-6 Potential Scores Based on Qualitative Grade and Wei ghting Factor .............................. 31

Table 5-1 Non-Failing Septic Tank Water Quality Concentration s ................................................ 38

Table 5-2 Failing Septic Land Use Nutrient Loading Rates ....

................................................... .... 38

Table 5-3 Water Quality Calibration and Validation Stations u sed in the Carters Lake Watershed

Model .............................................

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

Table 5-4 Simulated and Measured Dissolved Oxygen Loads for G AEPD Station 14109901 ........ 41

Table 5-5 Score Minimum and Corresponding Qualitative Grade f or Nutrients, Temperature and Dissolved Oxygen ..................................

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

Table 5-6 Score and Grade for Six Key Water Quality Stations in the Carters Lake Watershed ..... 42November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 4 

## 1.0 INTRODUCTION

Carters Lake lies in the Coosawattee Watershed (HUC # 03150102) in Northwest Georgia, approximately 70 miles north northwest of the city of Atlanta. C arters Lake is a US Army Corps of Engineers Lake (USACE), and has been complete and operational sinc e 1977. Carters Lake was formed by the Carters Dam and Reregulation Dam project, from the bed of t he Coosawattee River, between Ellijay and Carters. It is the deepest manmade reservoir east of the Mis sissippi River and has 62 miles of shoreline with n o development or private docks. The reservoir was de veloped as a multipurpose project for flood control

, hydropower, navigation, water quality, fish and wil dlife enhancement, recreation and spans an area of about 3,220 acres. Five counties are located eithe r completely or partially in the Carters Lake Water shed, therefore making the watershed very important to a wide-range of communities.

USACE generates power at Carters Dam only when dema nd for electricity is greatest. When demand for electricity is low, water is pumped back from a rer egulation pool, via turbines, thus maintaining Cart ers Lake at its optimal power generation level. The Re regulation Dam stores water in the reregulation poo l for the pumped storage operation, and regulates pea k flows from Carters Dam to provide stable

downstream flows to the Coosa River. Carters Lake and the reregulation pool both experience frequent elevation changes as expected with a pump back/stor age system. The minimum Carters Lake pool elevation for power production is 1,022 feet above mean sea level, and a maximum of 1,074 and 1072 feet above mean sea level in summer and winter resp ectively. The reregulation pool year round elevati on operating range is 677 to 696 feet above mean sea l evel, and provides a minimum of 240 cubic feet per

second to the Coosa River. Carters Dam has a drain age area of 372 square miles and the reregulation pool has a drainage area of 148 square miles for a total drainage area at the Reregulation Dam of 520 square miles. This report documents the developmen t and calibration of a watershed model that will be used to approximate watershed flows and nutrient lo adings entering Carters Lake Reservoir.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 5 Carters Lake Watershed - Location Map

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada Allatoona
Lake

Cha t tahoochee River

Fl i nt R iver

FL SC

AL NC TN

A p a l a c h i c o l a

R i v e r O c o n e e R
i v e r

A

l t a m a h a R i v e r

S a t i l l a R i v e r O c m u l g e e R i v e r S a v a n n a h R i v e r Lake
Jackson Lake

Sinclair Lake
Oconee C o o s a R i v e r Legend

Major Waterway

Water

Carters Lake Watershed

Carters Lake Watershed

Elevations (meters)

High : 1232

Low : 206

0 40 80

20 Miles 0 40 80 20 Kilometers Lake Sidney
Lanier

West
Point
Lake J. Strom

Thurmond
Lake

Walter F. George
Reservoir Lake
Blackshear

Lake
Seminole Lake
Hartwell

Brunswick
Harbor

Figure 1-1 Location of Carters LakeNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 6 

## 2.0 MODEL SELECTION

2.1 LSPC Watershed Model

The Loading Simulation Program C++ (LSPC) was used to represent the hydrologic and water quality

conditions in Carters Lake Watershed. LSPC is a co mprehensive data management and modeling system that is capable of representing loading, both flow and water quality, from non-point and point sources and simulating in-stream processes. It is capable of s imulating flow, sediment, metals, nutrients, pestic ides, and other conventional pollutants, as well as tempe rature and pH for pervious and impervious lands and waterbodies. LSPC was configured to simulate the w atershed as a series of hydrologically connected su bwatersheds. LSPC is based on the Mining Data Analy sis System (MDAS), with modifications for nonmining applications such as nutrient and fecal coli form modeling. MDAS was developed by EPA Region 3 through mining TMDL applications.



### 2.2 Integration of LSPC with EFDC

LSPC will be integrated with the Environmental Flui d Dynamics Code (EFDC). EFDC is a hydrodynamic and water quality modeling package use d for simulating one-dimensional, twodimensional, and three-dimensional flow and transpo rt in surface water systems including: rivers, lake s, estuaries, reservoirs, wetlands, and nearshore to s helf scale coastal regions. EFDC has the capabilit y of running the hydrodynamics alone or in conjunction w ith water quality. EFDC will be used to simulate the hydrodynamics and water quality of Lake Lanier, while LSPC will provide flows and water quality concentrations from the adjacent watersheds and tri butaries.



### LSPC

EFDC Flows

Temperatures

Concentrations 

### Models Outputs

Subwatershed Flows

Subwatershed Concentrations (Chl-a, TN, NH3, NOx, OrgN, TP, PO4, OrgP, BOD, DO, Temp, TSS, Fecal)

Water Surface/Tidal Elevations

Temperatures

Salinity (Estuary Only)

Lake/Harbor Concentrations (Chl-a, TN, NH3, NOx, OrgN, TP, PO4, OrgP, BOD, DO, Temp)

Figure 2-1 Linkage between LSPC and other modelsNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 7 

## 3.0 WATERSHED MODEL DEVELOPMENT

3.1 Overview

The watershed model represented the variability of nonpoint source contributions through dynamic representation of hydrology and land practices. Th e watershed model included all point and nonpoint source contributions. Key components of the waters hed modeling included:

• Watershed Segmentation (Section 3.2)

• Simulation period (Section 3.3)

• Soils (Section 3.4)

• Meteorological Data (Section 3.5)

• Reach Characteristics (Section 3.6)

• Land Use Representation (Section 3.7)

• Chicken Land Representation (Section 3.8)

• Septic Tanks Representation (Section 3.9)

• Point Source Discharges (Section 3.10)

• Municipal and Industrial Water Withdrawals (Section 3.11)

• Hydrologic Representation (Section 4.1)

• Observed Flow Data (Section 4.2)

• Hydrology Calibration (Section 4.3)

• Hydrology Validation (Section 4.4)

• Hydrology Observations and Conclusions (Section 4.5 )

• Water Quality Model Overview (Section 5.1)

• Modeled Parameters (Section 5.2)

• Reach Group Representation (Section 5.3)

• Temperature Representation (Section 5.4)

• Dissolved Oxygen Representation (Section 5.5)

• Sediment Representation (Section 5.6)

• Nutrients and Plankton Representation (Section 5.7)

• Water Quality Calibration (Section 5.8)

• Special Considerations for Water Quality (Section 5 .9)

• Observed Water Quality Data Calibration and Validat ion (Section 5.10)

• Water Quality Observations and Conclusions (Section 5.11)November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 8 

### 3.2 Watershed Segmentation

In order to evaluate the sources contributing to an impaired waterbody and to represent the spatial variability of these sources within the watershed m odel, the contributing drainage area was represente d by

a series of sub-watersheds. The sub-watersheds wer e developed using the Georgia 12-digit watershed data layer that was provided by the Georgia Environ mental Protection Division (GAEPD). The Carters Lake Watershed area consists of 28, 12-digit waters heds (Figure 3-1). These sub-watershed representations were used as a guideline for furthe r delineations.

The entire Carters Lake Watershed area was further delineated into 366 sub-watersheds to provide appropriate hydrological connectivity and to ensure that observed and simulated comparison locations were at the pour point of a sub-watershed (Figure 3 -2). The sub-watersheds were delineated using the Digital Elevation Map (DEM) in 1/3 arc-second resol ution (10m) (Figure 3-3), the National Hydrography Dataset (NHD), the US Geological Survey (USGS) flow gage station locations (Figure 4-1), and the coverage for the GAEPD water quality monitoring sta tions sampled during 2008 for the watershed modeling effort (Figure 5-1).

Occasionally, slope associated delineations resulte d in the pour points of two sub-watersheds contribu ting to an observed vs. simulated comparison location. Since the comparison location reflects observed hydrologic and water quality conditions of the comb ination of the two sub-watersheds, a fictitious sub

watershed was created to join the two sub-watershed s together. The outlet of the fictitious sub-water shed was routed downstream and utilized to compare obser ved data and simulated results. In the Carters Lak e Watershed, these fictitious sub watersheds needed t o be created at five locations.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 9 Carters Lake Watershed - 12-Digit HUC Boundaries

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada 

### Legend

Stream/River

Water

12-Digit HUC Boundary

Major City

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-1 Georgia 12-Digit HUC Coverage for Carter s Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 10 Carters Lake Watershed - Model Subwatersheds

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada 

### Legend

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir

Carters

Lake

Figure 3-2 Sub-delineated 12-Digit HUC Coverage for Carters Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 11 Carters Lake Watershed - 30-meter Resolution DEM

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada 

### Legend

Stream/River

Water

County Boundary

Carters Lake Watershed

Elevations (meters)

High : 1232

Low : 206

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-3 Digital Elevation Map (DEM) Coverage for Carters Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 12 

### 3.3 Simulation Period

The US Geological Survey (USGS) recommends looking at a minimum of a 10-year time period for hydrology calibrations. This is due to the fact th at over a 10-year period, a variety of hydrological conditions will exist, and a model that is calibrat ed over this time period will have a greater chance of success in predicting future hydrological condition s. The LSPC model was simulated for the 12-year period from January 1, 1998 through December 31, 20 09. This time period was selected as it captured two drought periods (1999-2001 and 2006-2007) and s everal wet years including 2003 and 2005. To allow the model plenty of “spin-up” time, the model was run for a full year (1997) before the simulati on period began.

The LSPC watershed hydrology and water quality mode l was calibrated from 1998 through 2009, and

validated to data collected from 1998 to 2009.



### 3.4 Soils

Soils are classified by the Natural Resources Conse rvation Service (NRCS) into four Hydrologic Soil Groups based on the soil’s runoff potential. The f our basic Hydrologic Soil Groups are A, B, C, and D

, where A generally has the lowest runoff potential a nd D the greatest. Soil data for the Carters Lake

Watershed was obtained from the U.S General Soil Ma p (STATSGO2). The NRCS - National Cartography and Geospatial Center (NCGC) previously archived and distributed the State Soil Geographic (STATSGO) Database. The STATSGO spatial and tabular data were revised and updated in

2006. STATSGO has been renamed to the U.S. General Soil Map (STATSGO2). It is available for download from the Soil Data Mart (Soil, 2008). The STATSGO2 data was used to determine the total area that each Hydrologic Soil Group covered within each sub-watershed. Each sub-watershed was represented by the Hydrologic Soil Group that had t he highest percentage of coverage within the boundaries of the sub-watershed. Figure 3-4 presen ts the STATSGO2 mapped coverage of the hydrologic soil groups in the Carters Lake Watershe d. The qualitative characteristics of two dominant Hydrologic Soil Groups (Groups B and C) are describ ed below:

Group B Soils have moderate infiltration rates when wet and consist chiefly of soils that are

moderately deep to deep, moderately to well drained , and moderately to moderately course textures.

Group C Soils have low infiltration rates when wet and consist chiefly of soils having a layer

that impedes downward movement of water with modera tely fine-to-fine texture.

Each dominant Hydrologic Soil Group gets assigned a default group number. Tetra Tech utilizes a standard approach for assigning Hydrologic Soil Gro ups to default group numbers: Group A equals 1, Group B equals 2, Group C equals 3 and Group D equa ls 4. Appendix A presents the dominant soil type, by default group number and letter, for each sub-wa tershed in the Carters Lake Watershed model.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 13 Carters Lake Watershed - Hydrologic Soil Groups

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada Legend

Stream/River

Model Subwatersheds

County Boundary

Hydrologic Soil Group

Water/Rock

B

C

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-4 Soils Coverage for Carters Lake Watershe dNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 14 

### 3.5 Meteorological Data

Nonpoint source loadings and hydrological condition s are dependent on weather conditions. Hourly data

, from weather stations within the boundaries of, or in close proximity to, the sub-watersheds, were app lied to the watershed model. An ASCII file (*.air) was generated for each meteorological station used in t he hydrological evaluations in LSPC. Each meteorologi cal station file contains atmospheric data used in modeling the hydrological processes. These data in clude precipitation, air temperature, dew point temperature, wind speed, cloud cover, evaporation, and solar radiation. These data are used directly, or calculated from the observed data. For a more deta iled discussion of how the ASCII files were developed, refer to Appendix R which is the Weather File Development Report for Carters.

For the Carters Lake Watershed, six meteorological stations were utilized in the hydrologic simulation and are shown spatially in Figure 3-5. One station was a Georgia Automated Environmental Monitoring Network (GAEMN) station. GAEMN stations are mainta ined and operated by the College of Agricultural and Environmental Sciences of the Univ ersity of Georgia. Each station monitors air temperature, relative humidity, rainfall, solar rad iation, wind speed, wind direction, soil temperatur e at 2, 4, and 8 inch depths, atmospheric pressure, and soi l moisture every one second and the data are summarized at 15-minute intervals (GAEMN, 2009). Th ree of the stations were National Climate Data Center (NCDC) stations, which record daily or hourl y observations for precipitation, minimum temperature, and maximum temperature. Lastly, two of the stations were USGS stations which recorded daily observations for precipitation at two of the USGS flow gages.

Meteorological stations were assigned to sub-waters heds using a Thiessen polygon. If a particular watershed was intersected by the polygon boundary, it was assigned to the meteorological station that had the greatest area covered by that stations polygon. Appendix A presents the meteorological station assignment for each sub-watershed.

Table 3-1 Summary of Meteorological Station for Car ters Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 15 Carters Lake Watershed - Meteorological Stations

NAD_1983_UTM_Zone_17N Map produced 10-25-2011 - P. Cada 094648 093115

091863

02382200 02380500

GEMN 355 Legend

Meteorological Station

Agency

NCDC

GEMN

USGS

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-5 Spatial Coverage of Meteorological Stati ons used in the LSPC Watershed ModelNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 16 

### 3.6 Reach Characteristics

The LSPC model must have a representative reach def ined for each sub-watershed. The characteristics for each reach include the length and slope of the reach, the channel geometry and the connectivity between the sub-watersheds. Length and slope data for each reach was obtained using the Digital Elevation Maps (DEM) and the National Hydrography D ataset (NHD). The channel geometry is described by a bank full width and depth (the main channel), a bottom width factor, a flood plain widt h factor and slope of the flood plain. Details about each reach can be found in Appendix B.

LSPC takes the attributes supplied for each reach a nd develops a function table (FTABLE). The FTABLE describes the hydrology, of a river reach or reservoir segment, by defining the functional relationship between water depth, surface area, wat er volume, and outflow in the segment. The assumption of a fixed depth, area, volume, outflow relationship rules out cases where the flow reverse s direction or where one reach influences another ups tream of it in a time-dependent way. The routing technique falls in the class known as "storage rout ing" or "kinematic wave" methods. In these methods, momentum is not considered (USEPA, 2007).



### 3.7 Land Use Representation

The watershed model uses land use data as the basis for representing hydrology and nonpoint source loadings. Land use data was provided by the Univer sity of Georgia, Georgia Land Use Trends (GLUT) coverage, and included the following 19-Class categ ories: beaches/dunes/mud, open water, utility swat hs, developed open space, developed low intensity, deve loped medium intensity, developed high intensity, clear-cut/sparse, quarries/strip mines, rock outcro p, deciduous forest, evergreen forest, mixed forest , golf courses, pasture, row crop, forested wetland, non-f orested wetland (salt/brackish), and non-forested wetland (freshwater). In the Carters Lake Watershe d model the GLUT coverage represented land use conditions in the year 2005. For the LSPC simulati on, similar land use classes were grouped together into reduced modeling units (RMU), i.e., deciduous fores t, evergreen forest and mixed forest were grouped together into an RMU called forest. Figure 3-6 sho ws the spatial coverage of the RMU’s for the Carter s Lake Watershed.

The LSPC model requires division of land uses in ea ch sub-watershed into separate pervious and impervious land units. For this, the GLUT impervio us cover, Figure 3-7, was intersected with the GLUT land use cover. Any impervious areas associated wi th utility swaths, developed open space, and developed low intensity, were grouped together and placed into a new RMU for low intensity development impervious. Impervious areas associate d with medium intensity development and high intensity development, were kept separate and place d into two new RMU’s for medium intensity development impervious and high intensity developme nt impervious, respectively. Finally, any impervious area not already accounted for in the th ree developed impervious RMU’s, were grouped together into a fourth new RMU called catch all for remaining impervious.

Amendments were made to the GLUT land use in order to incorporate chicken land and failing septic

tanks into the model. Sections 3.8 and 3.9 of this report discuss where the data sets were obtained f rom, how they were processed, and how they were incorpor ated as unique land uses. Appendix C presents the breakdown of each processed land use for each sub-w atershed in the model.

The final list of land uses represented in the Cart ers Lake Watershed model is presented in Table 3-2. Also presented is how the original GLUT classificat ions were condensed into RMU’s. Table 3-2 also shows the final acreage and areal percent of each o f the land uses represented in the LSPC watershed

model.

Over 80% of the Carters Lake Watershed is covered b y Forest with a majority being identified as strict ly deciduous. About 7% of the watershed is covered by Pasture of which about three fourths was convertedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 17 to chicken land which is associated with chicken ma nure. There isn’t a large amount of developed spac e, only about 6%, and the development is highly concen trated near the city of Ellijay. A majority of the remaining area is covered by open water (1.5%) and barren land (2.5%) with very small amounts of Row Crops and Wetlands.

Table 3-2 Land Use RepresentationNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 18 Carters Lake Watershed - LU/LC Input for Model

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada 

### Legend

Stream/River

County Boundary

2005 LU/LC (GLUT)

Water

Low Intensity Dev.

Med Intensity Dev.

High Intensity Dev.

Barren

Forest

Golf Courses

Row Crop

Pasture/Fallow Field

Wetland

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-6 GLUT 2005 Coverage in Reduced Modeling U nits of the Carters Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 19 Carters Lake Watershed - Impervious Surface (%)

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada 

### Legend

Stream/River

Water

County Boundary

Impervious Surface (2005)

Value

High : 100

Low : 0

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation

Reservoir Carters

Lake

Figure 3-7 GLUT Impervious Coverage of the Carters Lake WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 20 

### 3.8 Chicken Land Representation

For the Carters Lake Watershed model an additional amendment was made to account for broiler chicken houses. Tetra Tech utilized Google Earth imagery t o map locations and create a GIS point coverage of

broiler chicken houses in the Carters Lake Watershe d. Tetra Tech found 791 broiler chicken houses within and very close to the boundaries of the wate rshed.

Broiler chicken houses are buildings that house a l arge number of birds. A study was conducted that showed pasture land within a 0.75-km radius of a ch icken house typically received applications of broi ler manure (Zin, 2008). Initially, the Carters Lake Wa tershed model was set up to distinguish regular pas ture land from pasture land that receives chicken manure by creating a 0.75-km radius around each broiler chicken house (Figure 3-11). Then the buffer area was processed with the GLUT land use coverage to convert all pasture land contained within the buffe r area to a new land use type called “Chicken Pastu re”

During the water quality calibration process, a few of the water quality stations were simulating 2008 Total Nitrogen too low. 2008 is being utilized as this is when GAEPD conducted extensive water qualit y sampling in the watershed. While investigating why this was occurring, it was identified that water quality stations simulating low also had higher per centages of Chicken House buffer area, as compared to other water quality stations simulating Total Nitro gen well, in their contributing drainage area. Thi s prompted a thorough investigation into the represen tation of chicken land in the water quality model.

It was found that Chicken Pasture representation/pr ocessing resulted in approximately 16% of the buffe r area receiving applications of broiler manure. Due to the high correlation (r-squared 0.69) when comparing each stations upstream buffer area to mea n measured total nitrogen (Figure 3-8), a series of scenarios were set up utilizing different percentag es (25%, 50% and 75%) of the buffer area for receiv ing applications of broiler manure. Each scenarios sim ulation was compared with observed Total Nitrogen concentrations and a statistical technique called s um of least square errors was utilized to determine

which scenario best fit the observed data. Sum of least square errors suggested that utilizing 25% of the buffer area was the best solution (Table 3-3). Add itionally, comparing regressions of measured Total Nitrogen and the percent of contributing drainage a rea that is chicken land using 25% of the buffer ar ea (Figure 3-9) and simulated Total Nitrogen and the p ercent and the percent of contributing drainage are a that is chicken land using 25% of the buffer area ( Figure 3-10) shows that slopes and intercepts of th e regression equations are very similar which further supports that 25% of the buffer area is a good assumption.

After completing the analysis chicken land was repr ocessed for the watershed model. The total chicken house buffer area in each sub-watershed was multipl ied by 25%. The resultant area was put into a new land use category called Chicken Land. In order to preserve each sub-watersheds area, Chicken Land area was subtracted from 1) Pasture, if this create d a negative number for Pasture then Pasture area w as set to zero and the remaining area was subtracted f rom 2) Barren, if this still resulted in a negative number

for Barren then Barren was set to zero and the rema ining was taken from 3) Deciduous Forest.

Refer to Section 5.9 Special Considerations for Wat er Quality –Chicken Land in this report for a discussion on pollutant loadings utilized for chick en land. Appendix D identifies the number of chick en houses found in each sub-watershed of the Carters L ake Watershed.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 21 Figure 3-8 Regression of 2008 Mean Measured Total N itrogen and Upstream Chicken

House Buffer area

Table 3-3 Results of Chicken Land Buffer Area Repre sentation ScenariosNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 22 Figure 3-9 Regression of 2008 Mean Measured Total N itrogen and Percent of Contributing

Drainage that is Chicken Land using 25% of the Buff er Area

Figure 3-10 Regression of 2008 Mean Simulated Total Nitrogen and Percent of Contributing

Drainage that is Chicken Land using 25% of the Buff er AreaNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 23 Carters Lake Watershed - Chicken Operations

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada Legend

Broiler Chicken House

Chicken House Buffer Land

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-11 Location of Broiler Chicken Houses in t he Carters Lake Watershed with a 0.75-

km buffer surrounding each locationNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 24 

### 3.9 Septic Tank Representation

Tetra Tech received septic system data in two forma ts from GAEPD. The first format was a database of septic tank installations and repairs, for each cou nty, from 2002 through 2007. The second format was a document containing tables with the number of exist ing septic tanks, per county, for each of the major river basins in the state (Ochlocknee, Satilla, St. Mary’s, Suwannee, Altamaha, Ocmulgee, Oconee, Chattahoochee, Flint, Coosa, Tallapoosa, Tennessee, Ogeechee, and Savannah). Each table referenced a year with the number of existing septic tanks.

Tetra Tech utilized the number of existing septic t anks, for each county, for the year that was closes t to 2007. That number was then further modified by the number of installations that occurred from the existing septic tank year until 2007. Therefore, e ach county was represented by a septic tank number that reflected the number of existing septic tanks in th e year 2007.

The number of septic tanks in each sub-watershed wa s determined through an area weighting method. Sub-watersheds were assigned to counties based on t heir outfall or pour point. The percentage of coun ty area, represented by the sub-watersheds assigned to that county, was used to determine the total numbe r of septic tanks represented in those sub-watersheds . The number represented in each sub-watershed was determined by area weighting the individual sub-wat ershed area to the total area of the sub-watersheds assigned to the same county.

Septic tanks contribute to water quality whether th ey are functioning properly or failing. It was ass umed, that at any given time, there are 15% of the overal l number of septic tanks that are failing, and 85% are working properly. The portion of the septic tanks that were considered failing were modeled as a land use (Failing Septic) because it was assumed that no dec ay occurs and raw effluent is directly applied to t he land. It was determined that the average area of a septic field is 6,750 ft2 (Inspectapedia 2009). T he land use that was represented as Failing Septic was subt racted from the Low Intensity Urban Pervious land u se for each sub-watershed. For a few of the sub-water sheds subtracting Failing Septic from Low Intensity Urban Pervious resulted in negative values. For th ese watersheds, all of the failing septic tank area was subtracted from Developed Open Space. The non-fail ing septic tanks were modeled as very small individual point sources for each sub-watershed.

Refer to Section 5.9 Special Considerations for Wat er Quality –Septic Tanks in this report for a discussion on how both failing and non-failing sept ic tanks were handled in the water quality model. Appendix E identifies the number of septic tanks by county, the number modeled by county, and the number of failing and non-failing assigned to each sub-watershed.



### 3.10 Point Source Discharges

Facilities permitted under the National Pollutant D ischarge Elimination System (NPDES) are, by definition, considered point sources. There are fo ur point source discharges located in the Carters L ake Watershed. Of the four point sources, one was a ma jor municipal facility, two were rock quarries, and one was a minor Public Institutional Discharger (PI D). Flows and water quality data for these point source discharges were obtained from GAEPD in the f orm of Discharge Monitoring Reports (DMR). Data obtained from these reports were input directl y into the LSPC model as time-series from 1997 to

2009.

GAEPD provided Tetra Tech data from Compliance Insp ection Monitoring reports (CIM). CIM data was utilized in two ways, either the average value for a particular constituent was directly supplied, or average speciation from the CIM was utilized to calculate v alues for constituents. For example, ammonia was measured and the other nitrogen species were defaul t, so speciation form the CIM was utilized to calculate the other nitrogen constituents from the measured ammonia values.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 25 The two rock quarries did not report loads or conce ntrations for all constituents utilized in the LSPC model input time series (Flow, DO, BOD5, TN, Org-N, NH3, NOx, TP, Org-P, Ortho-P, TSS, Temp). The default concentrations adopted for the missing constituents are found in Table 3-6. Additionally, the municipal and PID facilities did not have effluent temperature so an assumed value of 15°C was utilize d for October-March and 25°C was utilized for April-S eptember.

Table 3-4 presents the point source facilities incl uded in the Carters Lake Watershed model and gives the NPDES number, facility name, facility type, receivi ng water body name, permitted flow, and the LSPC sub-watershed where the facility was input into the model. Table 3-5 is a summary of the data utilize d to create the direct input time-series for each of the facilities, by constituent. Figure 3-12 shows the spatial coverage of the point sources included in the Carte rs Lake Watershed model. All of this information i s reproduced in Appendix F along with time-series plo ts of the data included in the model.

Table 3-4 Summary of Point Source Discharges in the Carters Lake Watershed

Table 3-5 Summary of Data Utilized for the Point So urce Discharges in the Carters Lake

Watershed

Table 3-6 Default Water Quality Concentrations of C onstituents without Data for Rock
QuarriesNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 26

Carters Lake Watershed - Point Sources

NAD_1983_UTM_Zone_17N Map produced 09-18-2009 - P. Cada GA0037834 GA0021369 GA0037818

GA0047210 Legend

Point Source

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 3-12 Permitted Discharges in the Carters Lak e WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 27 

### 3.11 Municipal and Industrial Water Withdrawals

There are two water withdrawals located in the Cart ers Lake Watershed that are represented in the LSPC model (Table 3-7). Monthly average water withdrawa l volume data were obtained from the GAEPD. The withdrawal volume data were developed into a ti me-series from 1/1997 to 12/2009, for inclusion in the model. Less than three month data gaps had the before and after data gap volumes averaged. For longer than three month data gaps, it was ensured t hat the facility was operational and then the long- term monthly average withdrawal volume was supplied.

For security reasons, the locations of the water wi thdrawals cannot be disclosed. Monthly flow data i nput into the model for each water withdrawal is present ed in Appendix G.

Table 3-7 Summary of Water Withdrawal in Carters La ke WatershedNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 28 

## 4.0 Watershed Hydrology Model

4.1 Hydrologic Representation

Watershed hydrology plays an important role in the determination of nonpoint source flow and ultimatel y nonpoint source loadings to a waterbody. The water shed model must appropriately represent the spatial and temporal variability of hydrological characteri stics within a watershed. Key hydrological characteristics include interception storage capaci ties, infiltration properties, evaporation and tran spiration rates, and watershed slope and roughness. LSPC’s a lgorithms are identical to those in the Hydrologic Simulation Program FORTRAN (HSPF). The LSPC/HSPF m odules used to represent watershed hydrology include PWATER (water budget simulation f or pervious land units) and IWATER (water budget simulation for impervious land units). A de tailed description of relevant hydrological algorit hms is presented in the HSPF (v12) User’s Manual (Bickn ell et al. 2004).



### 4.2 Observed Flow Data

A query of the National Water Information Center da ily surface-water database finds a total of 17 stre am and lake gage stations, for the Carters Lake Waters hed. After filtering out the gages that did not co ntain stream flow measurements during the model simulatio n period, there were 5 viable stations remaining fo r calibration and validation (Figure 4-1).

Table 4-1 presents the USGS gages utilized for the Carters Lake Watershed and contains the following information: published USGS drainage area, corresp onding LSPC sub-watershed, LSPC simulated drainage area, how the station was utilized, and th e period of record utilized for each gage. Three o f these gages had a complete period of record for the simul ation period from January 1, 1998 through December 31, 2009. These gages, USGS02382200 – Talking Rock Creek near Hinton, GA, USGS02380500 – Coosawattee River near Ellijay, GA, and USGS0238160 0 – Fausett Creek near Talking Rock, GA were used as calibration gages. The two remaining gages , USGS02381090 – Mountaintown Creek at GA Hwy 282, near Ellijay, GA, and USGS02379500 – Cartecay River near Ellijay, GA, had very short periods of record and were utilized as validation gages.



### 4.3 Hydrology Model Calibration

Initial values for the hydrological parameters were taken from a default data set from work done on th e Lake Lanier Watershed. During the calibration proc ess, model parameters were adjusted based on local knowledge of soil types and groundwater conditions, within reasonable constraints as outlined in Technical Note 6 (USEPA 2000), until an acceptable agreement was achieved between simulated and observed stream flow. Key hydrologic model paramet ers adjusted included: evapo-transpiration, infiltration, upper and lower zone storages, ground water recession, and losses to the deep groundwater system. The calibration of the hydrologic paramete rs was performed from January 1, 1998 through December 31, 2007. The final calibrated hydrologic al parameters are presented in Appendix H. Results

, comparing observed and simulated flows, are present ed in Appendix I.



### 4.4 Hydrology Model Validation

An important step of the modeling process is model validation. Model validation is the process of tak ing the hydrological parameters that have been calibrat ed, applying those parameters to other watersheds, and comparing the simulated flow to measured flow from a USGS stream gauging station for the same period

of time. Model validation is sometimes called mode l verification, as essentially you are validating o rNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 29 verifying that hydrological parameters calibrated i n one watershed will produce acceptable results in another watershed. It is important that when selec ting watersheds to perform validations, those watersheds represent a wide variety of land uses as well as drainage areas. This will help to ensure that the hydrological parameters that were calibrated ap ply to a wide range of conditions. The validation of the hydrological parameters was performed from Janu ary 1, 2008 through December 31, 2009. Results, comparing observed and simulated flows, are present ed in Appendix I.

Table 4-1 USGS Flow Gauges used for Calibration and Validation in the Carters Lake

Watershed Model



### 4.5 Hydrology Observations and Conclusions

During the hydrology calibration/validation process it noticed that USGS gages in the part of the watershed contributing to Carters Lake (02379500, 0 2380500, and 02381090) had different flow regimes than the USGS gages in the part of the watershed co ntributing to the Reregulation Reservoir (02381600 and 02382200). Since a majority of the drainage ar ea is made up of Forest land, adjusting parameters to make the gages contributing to Carters Lake look go od, resulted in the gages contributing the Regulati on Reservoir look horrible, and vice versa. To overco me this, two new parameter groups were developed, 1 2 and 13, which represented Hydrologic Soil Groups 2 and 3 for the part of the watershed contributing to the Reregulation Reservoir. The only parameters ch anged between 2 and 12 and 3 and 13 were Groundwater Recession constants and losses to deep groundwater. Adding in the two new parameter groups resulted in acceptable calibration results f or the two different hydrologic regimes observed in the

Carters Lake Watershed.

Tetra Tech has developed a qualitative grading scal e ( VG=Very Good, G=Good, F=Fair, and P=Poor) based on the quantitative statistical analysis, com paring simulated and observed flows, from our spreadsheet utilized for calibrating and validating watershed hydrology models. Table 4-3 shows the period of record quantitative statistical analysis for gage USGS 02380500. The numbers in the column

“error statistics” were utilized to calculate a sco re based on their deviation from the zero with zero meaning that simulated and observed are equal. The column “recommended criteria” is the USGS

recommended maximum deviation of simulated and obse rved flows, for the absolute value of each flow summary type, for acceptable calibration of a water shed model. The flow summary types are also in ascending order of those easiest to hardest to obta in. An example of the grading technique is discuss ed in

detail below.

Period of record error statistics have been placed in the model stat column in Table 4-4. For each fl ow summary statistic, the absolute value of the model statistic is compared against the values in columns VG, G, F and P. If the value is less than VG then it i s given a value of 4, if less then G but greater th an VG it is given a value of 3, if less then F but greater t han G it is given a value of 2, and if it is greate r than P it is given a value of 1 (Table 4-6). The assigned value of the flow summary statistic is multiplied by the weight to produce a score for each flow summary typ e. Flow summary types have been assigned a weight based on their overall importance for a succ essful calibration. The error in total volume is m ost important followed by the errors in the high and lo w flows, then the error in seasonal volumes and fin ally

the errors in storm volumes. The score for the flo w summary statistics are then summed to produce aNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 30 total score for each gage. This total score is the n compared against the minimum score for each qualitative grade (Table 4-5) and the grade assigne d.

Table 4-2 shows the score and grade for each of the USGS flow gages utilized in the Carters Lake Watershed model. The summary provided in Table 4-2 , along with the other visual and statistical summaries in Appendix I indicate that the hydrology model will perform very well for the intended purpose of approximating watershed flows into Carte rs Lake.

Table 4-2 Score and Grade for USGS flow gages Carte rs Lake Watershed model

Table 4-3 Summary statistics: Model Outlet 1001 vs. USGS 02380500 Coosawattee River near Ellijay, Ga. (12-Year Calibration)

LSPC Simulated Flow Observed Flow Gage

REACH OUTFLOW FROM SUBBASIN 1001

12-Year Analysis Period: 1/1/1998 - 12/31/2009 Hydrologic Unit Code: 3150102
Flow volumes are (inches/year) for upstream drainag e area Latitude: 34.67508566
Longitude: -84.5085398 Drainage Area (sq-mi): 236

Total Simulated In-stream Flow: 23.01 Total Observed In-stream Flow: 23.55

Total of simulated highest 10% flows: 6.86 Total of Observed highest 10% flows: 6.93

Total of Simulated lowest 50% flows: 6.13 Total of Observed Lowest 50% flows: 5.62

Simulated Summer Flow Volume (months 7-9): 4.80 Observed Summer Flow Volume (7-9): 4.50 Simulated Fall Flow Volume (months 10-12): 4.96 Observed Fall Flow Volume (10-12): 4.72 Simulated Winter Flow Volume (months 1-3): 7.25 Observed Winter Flow Volume (1-3): 7.44 Simulated Spring Flow Volume (months 4-6): 6.02 Observed Spring Flow Volume (4-6): 6.89

Total Simulated Storm Volume: 4.45 Total Observed Storm Volume: 4.68 Simulated Summer Storm Volume (7-9): 0.87 Observed Summer Storm Volume (7-9): 1.01

Errors (Simulated-Observed) Error Statistics Recommen ded Criteria

Error in total volume: -2.27 10

Error in 50% lowest flows: 9.04 10 Error in 10% highest flows: -1.11 15

Seasonal volume error - Summer: 6.61 30

Seasonal volume error - Fall: 5.09 30

Seasonal volume error - Winter: -2.61 30 Seasonal volume error - Spring: -12.74 30

Error in storm volumes: -4.82 20

Error in summer storm volumes: -13.64 50
Nash-Sutcliffe Coefficient of Efficiency, E: 0.726 Model accuracy increases Baseline adjusted coefficient (Garrick), E': 0.598 as E or E' approaches 1.0 USGS 02380500 COOSAWATTEE RIVER NEAR ELLIJAY, GANovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 31 Table 4-4 Qualitative Grading Scale for USGS 023805 00 Coosawattee River near Ellijay

Table 4-5 Score Minimum and Corresponding Qualitati ve Grade

Table 4-6 Potential Scores Based on Qualitative Gra de and Weighting FactorNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 32 Carters Lake Watershed - Flow Calibration Stations

NAD_1983_UTM_Zone_17N Map produced 10-26-2011 - P. Cada 02379500 02381090

02382200 02381600 02380500 Legend

Flow Calibration Station

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 4-1 Spatial Coverage of Calibration and Vali dation Stations used in the Hydrology

ModelNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 33 

## 5.0 Watershed Water Quality Model

5.1 Water Quality Model Overview

Once the LSPC watershed hydrology model was calibra ted, the model was used to create a water quality model of the Carters Lake Watershed. Many componen ts of the water quality model were established during hydrology modeling. These components includ e watershed segmentation, meteorological data, land use representation, soils, reach characteristi cs, and point source discharges. The watershed wat er quality model included all point and nonpoint sourc e contributions. Nutrient loadings from point sour ces were represented by developing direct input time se ries, for each point source, using discharge monito ring report data. Non-point source nutrient loadings we re represented by build-up and wash off algorithms and assigning nutrient concentrations to the interf low and groundwater flow paths. Nutrients in the stream experienced dilutions, accumulations, assimi lation, biochemical cycling, and transport

downstream and out of the watershed



### 5.2 Modeled Parameters

The LSPC water quality model was setup to model Tem perature, Dissolved Oxygen, Biochemical Oxygen Demand (BOD), Total Nitrogen (TN), Ammonia ( NH3), Nitrate+Nitrite (NOx), Organic Nitrogen (Org-N), Total Phosphorus (TP), Orthophosp hate (PO4), Organic Phosphorus (Org-P), Total Suspended Solids (TSS), Phytoplankton, Chlorophyll a , and Benthic Algae.



### 5.3 Reach Group

For in-stream water quality simulation, the user ha s the ability to model in-stream biochemical proces ses, for the modeled reaches, by assigning them to reach groups. Assigning reaches into groups allows for the assignment of unique values, for each reach group, for certain LSPC parameters. The parameters that c an be assigned differently by reach group include: se diment bed storage parameters, cohesive and noncohesive suspended sediment variables for in-stream transport, temperature for stream groups, bed heat conduction parameters, land to stream mapping (non- point nutrient loading speciation), variables associated with BOD sinking, decay, and benthic rel ease, variables for dissolved oxygen reaeration, benthic oxygen demand, oxygen scour, all biochemica l nutrient transformation parameters, and all plankton growth, death and transport parameters. I n LSPC, reach group is analogous to the RCHRES block in HSPF. A detailed description of relevant in-stream and transport algorithms is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004).

Reaches were assigned into reach groups based on pr evious modeling work completed on the

Chattahoochee River Watershed for the Assimilative Capacity and Water Quality Standards review contract as part of the Georgia State Water Plan. First, reaches were assigned a Strahler stream orde r number (Strahler, 1957). Next, reaches that behave d similarly for sediment shear stress were grouped together. The results of the above two assignments were then joined together. The resultant reach gr oup puts streams in the same reach group only if they a re the same in both Strahler stream order and simil ar in sediment shear stress. This approach to assigning reaches into reach groups allows for a more detaile d sediment transport parameterization so that streams are not continually aggrading or degrading bed sediments but also preserves the ability to assign nutrient biochemical transformation parameters longitudinally due to the Strahler stream order ass ignment.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 34 

### 5.4 Water Temperature

In-stream temperature is an important parameter for simulating biochemical transformations. LSPC models in-stream temperatures by using algorithms i dentical to those in the Hydrologic Simulation Program FORTRAN (HSPF). The LSPC/HSPF modules use d to represent water temperature include PSTEMP (soil temperature) and HTRCH (heat exchange and water temperature). A detailed description of relevant temperature algorithms is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004)

. Simulation of soil temperature is accomplished by u sing three layers, surface, upper subsurface, and groundwater subsurface. The surface layer is the p ortion of the land segment that determines the over land flow water temperature. The upper subsurface layer determines interflow temperature while the groundwater subsurface layer determines groundwater temperature. Surface and upper subsurface layer temperatures were estimated by applying a regressio n equation as a function of measured air temperatur e. The groundwater subsurface temperature was given a temperature which reflected the mean average earth temperature for west central Georgia.

Data for determining surface and upper sub-surface regression equations were obtained from the Georgia Automated Environmental Monitoring Network stations at Ellijay, Georgia. Data obtained included the measured daily average surface layer soil temperatu re and measured air temperature. The average surfa ce layer soil temperature was manipulated by a multipl ier and an offset to come up with a theoretical upp er subsurface layer temperature. Monthly regression e quations for surface and upper subsurface layers we re set up using air temperature as the independent var iable and layer temperature as the dependent variab le. This allowed the use of air temperature as the inpu t to the regression equation and the corresponding layer temperature was the output.

Soil temperature is only used to determine the wate r temperature of the three different flow paths (su rface outflow, upper subsurface/interflow outflow, lower subsurface/groundwater outflow) contributing to stream flow. Once the water is in the stream, the temperature is impacted by mechanisms that can

increase or decrease the heat content of the water and these mechanisms are dependent on the weather forcing file (*.air). Mechanisms which can increas e the heat content of the water are absorption of s olar radiation, absorption of long-wave radiation, and c onduction-convection. Mechanisms which decrease the heat content are emission of long-wave radiatio n, conduction-convection and evaporation (Bicknell et al. 2004). The calibrated water temperature parame ters for each individual model are presented in Appendix J. Results for water temperature calibrat ion and validation are presented in Appendix K.



### 5.5 Dissolved Oxygen

Dissolved oxygen concentration is generally viewed as an indicator of the overall well-being of stream s or lakes and their associated ecological systems. In relatively unpolluted waters, sources and sinks of oxygen are in approximate balance and the concentra tion remains close to saturation. By contrast, in a stream receiving untreated waste waters, the natura l balance is upset, bacteria predominate, and a significant depression of dissolved oxygen results (Bicknell et al. 2004).

LSPC models in-stream dissolved oxygen by using alg orithms identical to those in the Hydrologic Simulation Program FORTRAN (HSPF). The LSPC/HSPF m odules used to represent dissolved oxygen include PWTGAS (pervious water temperature and diss olved gas concentrations), IWTGAS (impervious water temperature and dissolved gas concentrations) , and OXRX (primary DO and BOD balances). A detailed description of relevant temperature algori thms is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004).

Setting aside in-stream transformations, which eith er consume or produce dissolved oxygen, a major player in the dissolved oxygen concentration is str eam temperature. It is well known that colder wate r can dissolve and hold more gas than warmer water. Another major player is atmospheric reaeration.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 35 Atmospheric reaeration takes into consideration the dissolved oxygen concentration to start with, oxyg en saturation level for a given water temperature, wat er depth, water velocity, circulation, reaeration r ate, and a temperature correction coefficient for surfac e gas invasion. LSPC allows for user defined disso lved oxygen concentrations in inter-flow and groundwater by land use and month. The calibrated water temperature parameters for each individual model ar e presented in Appendix J. Results for water temperature calibration and validation are presente d in Appendix K.



### 5.6 Sediment

LSPC models sediment by using algorithms identical to those in the Hydrologic Simulation Program FORTRAN (HSPF). The LSPC/HSPF modules used to repr esent sediment include SEDMNT (pervious production and removal of sediment), SOLIDS (accumu lation and removal of solids), and SEDTRN (transport and behavior of inorganic sediment). A detailed description of relevant sediment algorithm s is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004). In short, the algorithms are removi ng sediment from the land due to rain drop impact and erosion and carrying it to the stream. Once the sediments are in the stream they either deposit or scour dependent on the conditions in the water colu mn for each reach.

Sediment is one of the most difficult water quality parameters to accurately simulate with watershed models. Therefore the approach to modeling sediment in the Carters Lake Watershed model consisted of borrowing final calibrated parameter values generat ed during the Lake Allatoona TMDL development. The borrowed parameters were adjusted in accordance with guidelines established in EPA BASINS

Technical Note 8 Sediment Parameters and Calibratio n guidance to HSPF (USEPA, 2006) and Sediment

Calibration Procedures and Guidelines for Watershed Modeling (Donigian et al. 2003). Additionally, th e in-stream transport component was closely examined and calibrated for each reach group.

The approach for Lake Allatoona consisted of inputt ing data for the calibration parameters that were

either measured or obtained from a literature searc h, and minimizing the number of calibration paramet ers that would be adjusted. Key processes for sediment include: soil detachment, soil compaction, fracti on of land use shielded from rain drop impact, sedimen t wash off rate, and in-stream transport which includes settling velocities and flow velocities th at contribute to deposition and re-suspension of se diment particles. The calibrated sediment parameters for each individual model are presented in Appendix L.

Results for sediment calibration and validation are presented in Appendix M.



### 5.7 Nutrients and Plankton

LSPC models nutrients and plankton by using algorit hms identical to those in the Hydrologic Simulation Program FORTRAN (HSPF). The LSPC/HSPF modules used to represent nutrients and plankton include PQUAL (quality constituents using simple relationsh ips), IQUAL (wash-off of quality constituents using simple relationships), NUTRX (primary inorganic nit rogen and phosphorus balances), and PLANK (plankton populations and associated reactions). A detailed description of relevant sediment algorith ms is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004).

Accumulation and wash-off rates play an important r ole in the determination of nonpoint source loading s to a water body. The watershed model must appropri ately represent the spatial and temporal variabilit y of hydrological characteristics within a watershed. I t must also appropriately represent the rate at whi ch nutrient components build-up between rain events an d wash off during rain events. Key general water quality characteristics include initial storage, wa sh-off and scour potency, accumulation rates, and asymptotic maximum storage amounts. The water supp lied to a stream from groundwater and through interflow also plays an important role in loading t o a water body. LSPC allows the user to supply groundwater and interflow concentrations, by hydrol ogic soil group and land use, by month. TheNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 36 accumulation and wash-off and interflow strongly in fluence peak flow water quality while groundwater reflects base flow water quality.

Biochemical in-stream processes play an important r ole on nutrient concentrations spatially and temporally. Biochemical processing also has a larg e influence on dissolved oxygen and ultimately wate r quality. The watershed model should appropriately represent some of the major biochemical processes occurring within in the stream, including dissolved oxygen and biochemical oxygen demand balances, organic and inorganic nutrient balances, and plankt on populations. In order to accurately represent biochemical processing, temperature must be modeled because all transformation rates are temperature dependent. Key processes for oxygen include: bent hic oxygen demand, sinking and benthic release of BOD material, reaeration, and oxygen depletion due to decay of BOD. Key processes for nutrients include: nitrification, denitrification, adsorption /desorption of ammonia and ortho-phosphorus, assimilation, and decomposition of organic material s to produce nitrogen and phosphorus.

The growth and death of plankton and algae, both fl oating and attached, is a natural process occurring within all streams. Plankton can have an impact on water quality by contributing organic matter to th e benthos, changing dissolved oxygen through photosyn thesis and respiration, and tie up nitrogen and phosphorus to have it later released through minera lization. The calibrated nutrient and plankton parameters for each individual model are presented in Appendix O1 through O4. Results for nutrient an d plankton calibration and validation are presented i n Appendix P1 through P4 for each individual model.



### 5.8 Water Quality Calibration

Temperature was the constituent calibrated after hy drology because the remaining parameters use water temperature in their algorithms. Temperature was c alibrated by first slightly adjusting surface and interflow slopes and intercepts and groundwater tem perature and then secondly focusing on the in-strea m mechanisms, i.e. impact of solar radiation as well as the impact of bed thermal conduction. After temperature was calibrated, dissolved oxygen was br ought into close agreement with the observed data b y adjusting reaeration, and interflow and groundwater dissolved oxygen concentrations. At this point dissolved oxygen was only partially calibrated beca use the water quality simulation was only partially active. Next, the sediment module was turned on an d the parameters borrowed from the Lake Allatoona LSPC model development were adjusted until the simu lated data closely matched the observed data.

After the above three modules were either calibrate d or brought into reasonable agreement, the calibra tion process turned to nutrients and plankton.

The first step in nutrient and plankton calibration involved looking at BOD, TN, and TP only. These three constituents were modeled by build-up/wash-of f and assigning land use associated concentrations in groundwater and interflow. Build-up/wash-off remov es constituents from the land and carries them into the stream. Therefore, adjustments were made to mo nthly accumulation rate, monthly storage limit, interflow concentration, and groundwater concentrat ion for BOD, TN, and TP until the simulated data was in range with the observed field data.

After the build-up/wash-off simulated values for th e total constituents were in range, a flow path associated fractionation was assigned. This fracti onation assigned percentages of each constituent making up the total to the modeled total value. To tal nitrogen was broken down into nitrate+nitrite, ammonia, organic nitrogen and sediment adsorbed amm onia, and total phosphorus was fractionated into ortho-phosphorus, organic phosphorus, and sediment adsorbed ortho-phosphorus. The flow paths assigned to the total constituents were impervious surface flow, pervious surface flow, pervious inter flow, and pervious groundwater flow. The fractionation b y flow path was adjusted until the modeled data closely resembled the observed field data. In-stre am biochemical transformations occur and a new biochemically transformed value for total phosphoru s and total nitrogen was generated. The new totalNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 37 values consisted of adding up the constituents maki ng up the transformed total and the values were checked against the previous un-transformed total v alue to assure the new total values made sense.

Once the build-up/wash-off and fractionation were c lose, plankton and decay rates became the last step in calibrating the watershed model for nutrients. The growth and death of plankton and the biochemical cycling of nutrients impacts dissolved oxygen. Dec ay and transformation rates were calibrated by balancing dissolved oxygen and in-stream nutrient c oncentrations. For example, if both BOD and dissolved oxygen were simulating too high then a ch ange was made to increase the BOD decay rate. This change will decrease simulated BOD and also decreas e dissolved oxygen because more BOD material is being decayed and consuming oxygen in the process. Decay and transformation rates were, initially set by, and adjusted in accordance with, values found i n EPA rates and constants (EPA, 1985).



### 5.9 Special Considerations for Water Quality

Chicken Houses

It is well known that chicken manure is very high i n phosphorus and nitrogen concentrations, and it is common for chicken manure to be applied to pasture land. As mentioned in Section 3.8, a separate land

use was created for the watershed models called “Ch icken-Land” in which the chicken manure was applied.

For phosphorus, it was assumed that the chicken lan d received 6.73 Mg ha-1 per year of broiler litter (Lin, 2008). This translates to a rate of 16.45 pounds p er acre per day of broiler litter applied to the ch icken land, land use. Of the 16.45 lbs per day of broile r litter, 1.3% was assumed to be total phosphorus ( 0.214 lbs per day) (Radcliffe 2008). It was assumed that the 0.214 pounds per day was the accumulation rate and that the maximum storage was 0.214 pounds; ther efore indicating an instant build-up. Since an “instant build-up” was assumed, this meant that the wash-off rate was the main parameter of calibratio n for this land use.

To calculate the amount of nitrogen applied to the pasture land used by poultry, it was assumed that o f the 16.45 pounds per acre per day of broiler litter, to tal nitrogen makes up 3.13% (0.515 lbs per day) (Radcliffe 2008). Similar to total phosphorous, it was assumed that the load of total nitrogen, was e qual

between the accumulation rate and the maximum stora ge value indicating an “instant build-up”.



### Septic Tanks

To represent the contribution of water quality from non-failing septic tanks, septic flow concentratio n data were obtained from literature (Gerner, 2004, L ihua, 2002, Jones, 2005). It was assumed that each septic tank serves a household of 2.8 people, each person accounts for 70 gallons/day of water use and

15% of the water used in the house never makes it t o the septic tank. It was also assumed that it tak es an average of 60 days for the septic flow to reach a b ody of water, so a first order decay rate was appli ed to

each constituent to determine the concentration aft er 60 days. Table 5-1 presents the concentration o f septic tank effluent, decay rates for each constitu ent, and the concentration after 60 days of decay. For phosphorus, it was also assumed that 90% was sorbed to sediment; therefore only 10% of the effluent concentration was used to calculated decay after 60 -days. Non-Failing septic tank data was developed into a direct input time-series, for each sub-water shed, and in the computational domain is handled li ke a point source

For failing septic tank land use loading representa tion, effluent loadings were obtained from literatu re (USEPA, 2002) and are shown in Table 5-2. Pound pe r acre septic tank loadings were multiplied by 4 to determine the Failing Septic land use asymptotic ma ximum storage limit.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 38 Table 5-1 Non-Failing Septic Tank Water Quality Con centrations

Table 5-2 Failing Septic Land Use Nutrient Loading RatesNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 39 

### 5.10 Observed Water Quality Data for Calibration an d Validation

During 2008, GAEPD intensively sampled rivers and s treams in the Carters Lake Watershed, specifically for use in developing the TMDL. This sampling was conducted at 23 key locations throughout the watershed. For the Assimilative Capacity Water Qua lity Modeling and Water Quality Standards Review contract as part of the Georgia State Water Plan, G AEPD provided Tetra Tech with a GIS coverage of water quality monitoring locations in the State of Georgia. The water quality monitoring stations in the Carters Lake Watershed, from the whole state shapef ile, were thoroughly compared with those of the 2008 intensive sampling and a final list of 24 stat ions were utilized for water quality calibration an d validation. The list of stations and how they were utilized are in Table 5-3 and the station location s are shown spatially in figure 5-1.

Five of the 24 stations had more than one year of d ata so they were chosen to be calibration stations. The remaining 19 stations were utilized as validation s tations.

Table 5-3 Water Quality Calibration and Validation Stations used in the Carters Lake

Watershed ModelNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 40 Carters Lake Watershed - Water Quality Calib. Stati ons

NAD_1983_UTM_Zone_17N Map produced 10-26-2011 - P. Cada 14119901 14119981

14119261 14119251 14116001 14115001

14114301 14114201 14114101

14114031 14114001

14109931 14109901

14079011

14075511 14070001 14064901

14063901 14056821 14056701

14056501

14056401

14056301

14056901 Legend

Water Quality Calib. Station

Stream/River

Water

Model Subwatersheds

County Boundary

0 4 8 2 Miles 0 4 8 2 Kilometers Carters Reregulation
Reservoir Carters

Lake

Figure 5-1 Spatial Coverage of Calibration and Vali dation Stations used in the Water Quality

ModelNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 41 

### 5.11 Water Quality Observations and Conclusions

Similar to hydrology, Tetra Tech has developed a qu alitative grading ranking (VG=Very Good, G=Good, F=Fair, and P=Poor) based on the quantitative analy sis, comparing simulated and observed loads, from our spreadsheet utilized for calibrating and valida ting watershed water quality models. However, unli ke hydrology, there are not 9 error statistics for com parison and calculation. The water quality qualita tive grading rannking simply utilizes the period of reco rd average, observed and simulated load difference, and compares it to criteria defined for the water q uality calibration. An example of the grading tech nique

is discussed in detail below for one constituent at one location.

The calculated simulated and calculated measured, p eriod of record yearly average load percent differences absolute value (Table5-4) is compared w ith the values found in Table 5-5 and assigned the corresponding qualitative grade. For this example, the dissolved oxygen period of record yearly avera ge load percent differences absolute value of 5.68, is less than 10, which is the maximum difference allo wed to be considered very good, so this gage has a qual itative grade of VG=Very good for Dissolved Oxygen. As can be seen in Table 5-5 three different ranges have been set up for Nutrients, Temperature and Dissolved Oxygen. This has been done in order to b etter capture acceptable error for temperature, dissolved oxygen and nutrients. To be very good fo r Temperature and Dissolved oxygen thee error needs to be within 10% which roughly equates to 1-2 degre es Celsius and about 1 mg/l for dissolved oxygen.

Table 5-4 Simulated and Measured Dissolved Oxygen L oads for GAEPD Station 14109901

Table 5-5 Score Minimum and Corresponding Qualitati ve Grade for Nutrients, Temperature and Dissolved OxygenNovember 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 42 Table 5-6 shows the score and grade for each of the GAEPD water quality stations for which Tetra Tech has developed loads. These stations are the same s tations that are included in Appendix P Water Quali ty Loads. Tetra Tech chose to develop loads at these locations because 1) they are calibration stations and therefore have the most data available, and 2) repr esent key locations in the watershed (i.e. two drai nages above the major point source, three drainages to Ca rters Lake, and one drainage to the Reregulation Reservoir) and it is assumed that if the water qual ity model is performing well at these locations the n one can conclude that the water quality model as a whol e is performing well. .

Table 5-6 Score and Grade for Six Key Water Quality Stations in the Carters Lake

Watershed

Station 14056901 is located above the Ellijay Water Pollution Control Plant on the Ellijay River. Temperature and Dissolved Oxygen are calibrated acc eptably with rankings of Good and Very Good respectively. Additionally, nutrients have an acce ptable calibration as all qualitative rankings are in the Good to Very Good range. Lastly, sediment is ranke d as being Very Good.

Station 14079011 is located above the Ellijay Water Pollution Control Plant on the Cartecay River. Temperature and Dissolved Oxygen are calibrated acc eptably with rankings of Very Good and Good respectively. Additionally, nutrients have an acce ptable calibration as all qualitative rankings are in the Good to Very Good range. Lastly, sediment is ranke d as being Good.

Station 14109901 is located below the Ellijay Water Pollution Control Plant on the Coosawattee River which is the largest tributary to Carters Lake. Bo th temperature and dissolved oxygen are Very Good a nd all nutrients are also Very Good with the exception on Organic Phosphorus which is Good. Sediment is ranked as being Very Good. All of the Very Goods a re expected at this station since it is immediately downstream of a major point source and the water qu ality conditions are largely controlled by the poin t source. This station being Very Good suggests that the direct timeseries input for the point source i s acceptable.

Station 14115001 is located on Mountain Town Creek and is the second largest tributary to Carters Lake

. Both temperature and dissolved oxygen are Very Good and all of the nutrients are in the Good to Very good range. Sediment however is poor. The reason for this is still being investigated as the time-se ries and other load plots suggest that the calibration i s low but the yearly load is calculated as being hi gh. This could simply be due to a calculation error.

Station 14116001 is located on Tails Creek and is t he third largest tributary to Carters Lake. Simila r to station 14115001 Temperature, Dissolved Oxygen, and all of the Nutrients are in the good to very good range with sediment being poor. The reason for thi s is still being investigated as the time-series an d other load plots suggest that the calibration is low but the yearly load is calculated as being high. This could simply be due to a calculation error.

Station 14119981 is located on Talking Rock Creek i mmediately above the Reregulation Reservoir. All of the constituents are in the Fair to Poor range. This directly attributable to only having data in 2008 and the Hydrology model for 2008 in this area is poor.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 43 The summary provided in Table 5-6, along with the o ther visual and statistical summaries in Appendices O and P indicate that the Water Quality model shoul d perform reasonable well for the intended purpose of approximating Nutrient Loads into Carters Lake.November 2011 REV1 Carters Lake Water shed Modeling Report

Prepared by Tetra Tech, Inc. 44 

## 6.0 Input Overview Figures

A series of figures were developed to help visually summarize information presented in the previous sections (Figure 6-1 through 6-4). Specifically, s ub-watershed delineations, flow and water quality stations and point source dischargers are shown. T he study area was zoomed into in order to label the features in support of the tables presented in the preceding sections.

Appendix Q presents contributing land use breakdown , by hydrologic soil group for each of the

calibration and validation stations utilized in the Hydrology and Water Quality modeling for the Carte rs Lake Watershed

.November 2011 REV1Carters Lake Watershed Modeling ReportPrepared by Tetra Tech, Inc.45Carters Lake WatershedNAD_1983_UTM_Zone_17NMap produced 11-08-2011 - P. Cada2617433336532834033353583053093383153663493223043453173463103363503063203123613303073423323313432803143292812823212903373033113273473392793443413253523263082853242773562953623573233593003483641942833553513163631903533133603542923012992842932942983182912783343190238220002381600GA0037834141199811411990114119261140755110 2 41 Miles0 2 41 KilometersLegendPoint SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty Boundary192CartersReregulationReservoirCartersLakeFigure 6-1 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 1 of 4)November 2011 REV1Carters Lake Watershed Modeling ReportPrepared by Tetra Tech, Inc.46Carters Lake WatershedNAD_1983_UTM_Zone_17NMap produced 11-08-2011 - P. CadaGA00378341411998114119261141192511411600114115001141099311410990114079011140755111405690123810902381600238050026101579784333328340333530518111338315302241829830431733619110035110131113079331291091914102383933730344123293327108339962791827177188112325114163269510332427732330017931342017337331902629836105187101223012829915231719229130211061071893341781041809499GA00213690 1 20.5 Miles0 1 20.5 KilometersLegendPoint SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty BoundaryCartersReregulationReservoirCartersLakeFigure 6-2 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 2 of 4)November 2011 REV1Carters Lake Watershed Modeling ReportPrepared by Tetra Tech, Inc.47Carters Lake WatershedNAD_1983_UTM_Zone_17NMap produced 11-08-2011 - P. Cada14115001141143011411420114114101141140311411400114109931141099011407901114064901140639011405690114056821140567011405650114056401140563012381090238050010886172561811124215117815722516011978981481241184715515371891757355351406611013111874816229109191474102383913817176135824412642061423293164154128431081571462126813152182720113621777177186801126290671271631142271616822883951035391591697911615217614518575166492261971651411392075817960130636131342021417320337336551229202161184855412970218159469217014316726224361051561474245101222101377221328174144208251991491252315012615812284308821106223107151134219502091151781201331042166918318021112341205113944099221121132GA00213690 2.5 51.25Miles0 2.5 51.25 KilometersLegendPoint SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty BoundaryFigure 6-3 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 3 of 4)November 2011 REV1Carters Lake Watershed Modeling ReportPrepared by Tetra Tech, Inc.48Carters Lake WatershedNAD_1983_UTM_Zone_17NMap produced 11-08-2011 - P. Cada14079011140755111407000114064901140639012381600340335181338215225275182256346336286246191240242280297281282271274290222231237267230206245248108339279212243341201220177188186255259228285233266277239195264295185236204226238300197194283262273207179249232214234289203229202184257190241218265258287296292224288198298260187210213301268299284269263261208293199294247253272192235276291244278193250223252270219209196189178254216183180211200205251221GA0021369GA00472100 1 20.5 Miles0 1 20.5 KilometersLegendPoint SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty BoundaryFigure 6-4 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 4 of 4)November 2011 REV1 Carters Lake Watershed M odeling Report

Prepared by Tetra Tech, Inc. 49 

## 7.0 References

Bicknell, Brian R., J.C. Imhoff, J.L. Kittle, Jr., T.H. Jobes, A.S. Donigian, Jr., 2004. HSPF Version 12 User’s Manual. Aqua Terra Consultants, Mountain Vi ew, California.

Donigian, A.S., and J.T. Love, 2003. Sediment Cali bration Procedures and Guidelines for Watershed Modeling. Aqua Terra Consultants, Mountain View, C alifornia.

GAEMN, 2009. GAEMN Homepage. 1 June 2009 http://w ww.georgiaweather.net/

Gerner, Jay, 2004. Nitrogen and Phosphorus Loading from Septic Systems. Delaware Department of

Natural Resources.

Inspectipedia, 2009. Septic Drainfield Design: Se ptic Size Requirements Guide. (http://www.inspectnyu.com/septic/fieldsize.htm).

Jones, Lyle, 2005. Septic Systems as a Source of B acteria, Nitrogen, and Phosphorus. Deleware Department of Natural Resources.

Lihua, Cui, 2002. Treatment and Utilization of Sep tic Tank Effluent using Vertical Flow Constructed Wetlands and Hydroponic Cultivation of Vegetables. South China Agricultural University.

Radcliffe, D.E. Personnel Communication on October 24, 2008.

Soil Survey Staff, Natural Resources Conservation S ervice, United States Department of Agriculture. U.S. General Soil Map (STATSGO2). Available online at http://soildatamart.nrcs.usda.gov. Accessed [08/26/2008].

Strahler, Arthur N. 1957. Quantitative Analysis of Watershed Geomorphology. Transactions, American Geophysical Union. Vol38, No.6

Tetra Tech, 2011. Weather File Development Report for Carters Lake. Tetra Tech 2011.

USEPA, 2007. BASINS Technical Note 1: Creating Hyd raulic Function Tables for Reservoirs in BASINS. Office of Water, U.S. Environmental Protect ion Agency. Washington, DC.

USEPA, 2006. BASINS Technical Note 8: Sediment Par ameter and Calibration Guidance for HSPF. Office of Water, U.S. Environmental Protection Agen cy. Washington, DC.

USEPA, 2002. Onsite Wastewater Treatment Manual. EPA 625/R-00/008. National Risk Management Research Laboratory, Office of Water. Washington D C.

USEPA, 2000. BASINS Technical Note 6. Estimating H ydrology and Hydraulic Parameters for HSPF. Office of Water, U.S. Environmental Protection Agen cy. Washington, DC.

USEPA, 1985. Rates, Constants, and Kinetics Formul ations in Surface Water Quality Modeling (Second Edition). Environmental Research Laboratory, U.S. E nvironmental Protection Agency. Athens, GA.

EPA/600/3-85/040

Z. Lin, D.E. Radcliffe, L.M. Risse, J. Romeis, C.R. Jackson, 2008. Modeling Phosphorus Transport in Lake Allatoona Watershed (Georgia) using SWAT: II E ffect of Landuse Change. 43 pages.