PREPARED BY:

Tetra Tech, Inc. 

2110 Powers Ferry Rd. SE, Suite 202 

Atlanta, Georgia 30339 

Phone: (770) 850-0949 

PREPARED FOR:

Georgia Environmental Protection 

Division 

4220 International Parkway 

Suite 101 

Atlanta, Georgia 30354 

Contract: 751-10135 

Amendment: 7 

Watershed Hydrology and

Water Quality Modeling

Report

for

Carters Lake, Georgia

November 30, 2011 

Revision 1
November 2011 REV1 Carters Lake Watershed 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 WATERSHED MODEL ...................................................................................................... 6

2.2 INTEGRATION OF LSPC WITH EFDC ......................................................................................... 6

3.0 WATERSHED MODEL DEVELOPMENT ............................................................................. 7

3.1 OVERVIEW ............................................................................................................................... 7

3.2 WATERSHED SEGMENTATION ................................................................................................... 8

3.3 SIMULATION PERIOD .............................................................................................................. 12

3.4 SOILS ..................................................................................................................................... 12

3.5 METEOROLOGICAL DATA ....................................................................................................... 14

3.6 REACH CHARACTERISTICS ..................................................................................................... 16

3.7 LAND USE REPRESENTATION ................................................................................................. 16

3.8 CHICKEN LAND REPRESENTATION ......................................................................................... 20

3.9 SEPTIC TANK REPRESENTATION ............................................................................................. 24

3.10 POINT SOURCE DISCHARGES .................................................................................................. 24

3.11 MUNICIPAL AND INDUSTRIAL WATER WITHDRAWALS ........................................................... 27

4.0 WATERSHED HYDROLOGY MODEL ............................................................................... 28

4.1 HYDROLOGIC REPRESENTATION ............................................................................................. 28

4.2 OBSERVED FLOW DATA ......................................................................................................... 28

4.3 HYDROLOGY MODEL CALIBRATION ....................................................................................... 28

4.4 HYDROLOGY MODEL VALIDATION ......................................................................................... 28

4.5 HYDROLOGY OBSERVATIONS AND CONCLUSIONS .................................................................. 29

5.0 WATERSHED WATER QUALITY MODEL ........................................................................ 33

5.1 WATER QUALITY MODEL OVERVIEW ..................................................................................... 33

5.2 MODELED PARAMETERS......................................................................................................... 33

5.3 REACH GROUP ....................................................................................................................... 33

5.4 WATER TEMPERATURE........................................................................................................... 34

5.5 DISSOLVED OXYGEN .............................................................................................................. 34

5.6 SEDIMENT .............................................................................................................................. 35

5.7 NUTRIENTS AND PLANKTON ................................................................................................... 35

5.8 WATER QUALITY CALIBRATION ............................................................................................. 36

5.9 SPECIAL CONSIDERATIONS FOR WATER QUALITY .................................................................. 37

Chicken Houses ............................................................................................................................. 37

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

5.10 OBSERVED WATER QUALITY DATA FOR CALIBRATION AND VALIDATION .............................. 39

5.11 WATER QUALITY OBSERVATIONS AND CONCLUSIONS ............................................................ 41
November 2011 REV1 Carters Lake Watershed 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 WITHDRAWALS 

APPENDIX H – HYDROLOGY CALIBRATION PARAMETES 

APPENDIX I – HYDROLOGY CALIBRATION AND VALIDATION 

APPENDIX J – DISSOLVED OXYGEN AND TEMPERATURE CALIBRATION PARAMETES 

APPENDIX K – DISSOLVED OXYGEN AND TEMPERATURE CALIBRATION AND VALIDATION 

APPENDIX L – SEDIMENT CALIBRATION PARAMETES 

APPENDIX M – SEDIMENT CALIBRATION AND VALIDATION 

APPENDIX N – NUTRIENT AND PLANKTON CALIBRATION PARAMETES 

APPENDIX O – NUTRIENT AND PLANKTON CALIBRATION AND VALIDATION 

APPENDIX P – NUTRIENT LOADINGS 

APPENDIXQ – CUMULATIVE UPSTREAM LAND USE FOR HYDROLOGY AND WATER QUALITY 

CALIBRATION AND VALIDATION STATIONS 

APPENDIX R – CARTERS LAKE WEATHER FILE DEVELOPMENT REPORT 

Revision History 

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

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

Revision 

Number Release Date Comments 

0 December 31, 2008 Initial Release of Report. Hydrology Calibration/Validation 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 present) 

Updated Hydrology Calibration (added more USGS gages) 

Calibrated Temp/DO, Water Quality and Sediment 
November 2011 REV1 Carters Lake Watershed 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 Watershed ........................................ 9

Figure 3-2 Sub-delineated 12-Digit HUC Coverage for Carters Lake Watershed ............................ 10

Figure 3-3 Digital Elevation Map (DEM) Coverage for Carters Lake 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 Watershed ......................................... 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 and Percent of Contributing 

Drainage that is Chicken Land using 25% of the Buffer Area ........................................ 22

Figure 3-11 Location of Broiler Chicken Houses in the Carters Lake 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 Stations used in the Hydrology Model . 32

Figure 5-1 Spatial Coverage of Calibration and Validation Stations 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) . 48
November 2011 REV1 Carters Lake Watershed 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 Lake Watershed ............................ 25

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

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

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

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

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

Model ........................................................................................................................... 29

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

Table 4-3 Summary statistics: Model Outlet 1001 vs. USGS 02380500 Coosawattee River near 

Ellijay, Ga. (12-Year Calibration) ................................................................................. 30

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

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

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

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

Table 5-2 Failing Septic Land Use Nutrient Loading Rates ........................................................... 38

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

Model ........................................................................................................................... 39

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

Table 5-5 Score Minimum and Corresponding Qualitative Grade for Nutrients, Temperature and 

Dissolved Oxygen ........................................................................................................ 41

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

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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. Carters Lake is a US Army Corps of Engineers Lake 

(USACE), and has been complete and operational since 1977. Carters Lake was formed by the Carters 

Dam and Reregulation Dam project, from the bed of the Coosawattee River, between Ellijay and Carters. 

It is the deepest manmade reservoir east of the Mississippi River and has 62 miles of shoreline with no 

development or private docks. The reservoir was developed as a multipurpose project for flood control, 

hydropower, navigation, water quality, fish and wildlife enhancement, recreation and spans an area of 

about 3,220 acres. Five counties are located either completely or partially in the Carters Lake Watershed, 

therefore making the watershed very important to a wide-range of communities. 

USACE generates power at Carters Dam only when demand for electricity is greatest. When demand for 

electricity is low, water is pumped back from a reregulation pool, via turbines, thus maintaining Carters 

Lake at its optimal power generation level. The Reregulation Dam stores water in the reregulation pool 

for the pumped storage operation, and regulates peak 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/storage 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 respectively. The reregulation pool year round elevation 

operating range is 677 to 696 feet above mean sea level, and provides a minimum of 240 cubic feet per 

second to the Coosa River. Carters Dam has a drainage 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 development and calibration of a watershed model that will be

used to approximate watershed flows and nutrient loadings entering Carters Lake Reservoir. 
November 2011 REV1 Carters Lake Watershed 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

Chattahoochee River

Flint River

FL

SC

AL

TN NC

Apalachicola

River

Oconee

River

Altamaha River

Satilla

River

Ocmulgee River

Savannah River

Lake

Jackson

Lake

Sinclair

Lake

Oconee

Coosa River

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 Lake 
November 2011 REV1 Carters Lake Watershed 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 comprehensive 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 simulating flow, sediment, metals, nutrients, pesticides, 

and other conventional pollutants, as well as temperature and pH for pervious and impervious lands and

waterbodies. LSPC was configured to simulate the watershed as a series of hydrologically connected subwatersheds. LSPC is based on the Mining Data Analysis System (MDAS), with modifications for nonmining applications such as nutrient and fecal coliform 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 Fluid Dynamics Code (EFDC). EFDC is a 

hydrodynamic and water quality modeling package used for simulating one-dimensional, twodimensional, and three-dimensional flow and transport in surface water systems including: rivers, lakes, 

estuaries, reservoirs, wetlands, and nearshore to shelf scale coastal regions. EFDC has the capability of 

running the hydrodynamics alone or in conjunction with 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 tributaries. 

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 models 
November 2011 REV1 Carters Lake Watershed 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. The watershed model included all point and nonpoint 

source contributions. Key components of the watershed 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 Validation (Section 5.10) 

• Water Quality Observations and Conclusions (Section 5.11) 
November 2011 REV1 Carters Lake Watershed 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 model, the contributing drainage area was represented by 

a series of sub-watersheds. The sub-watersheds were developed using the Georgia 12-digit watershed 

data layer that was provided by the Georgia Environmental Protection Division (GAEPD). The Carters 

Lake Watershed area consists of 28, 12-digit watersheds (Figure 3-1). These sub-watershed 

representations were used as a guideline for further 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 resolution (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 stations sampled during 2008 for the watershed 

modeling effort (Figure 5-1). 

Occasionally, slope associated delineations resulted in the pour points of two sub-watersheds contributing 

to an observed vs. simulated comparison location. Since the comparison location reflects observed 

hydrologic and water quality conditions of the combination of the two sub-watersheds, a fictitious subwatershed was created to join the two sub-watersheds together. The outlet of the fictitious sub-watershed 

was routed downstream and utilized to compare observed data and simulated results. In the Carters Lake 

Watershed, these fictitious sub watersheds needed to be created at five locations. 
November 2011 REV1 Carters Lake Watershed Modeling Report 

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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 Carters Lake Watershed 
November 2011 REV1 Carters Lake Watershed 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 Watershed 
November 2011 REV1 Carters Lake Watershed Modeling Report 

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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 Watershed 
November 2011 REV1 Carters Lake Watershed Modeling Report 

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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 that over a 10-year period, a variety of hydrological

conditions will exist, and a model that is calibrated over this time period will have a greater chance of 

success in predicting future hydrological conditions. The LSPC model was simulated for the 12-year 

period from January 1, 1998 through December 31, 2009. This time period was selected as it captured 

two drought periods (1999-2001 and 2006-2007) and several 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 simulation 

period began. 

The LSPC watershed hydrology and water quality model 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 Conservation Service (NRCS) into four Hydrologic Soil 

Groups based on the soil’s runoff potential. The four basic Hydrologic Soil Groups are A, B, C, and D, 

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

Watershed was obtained from the U.S General Soil Map (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 the highest percentage of coverage within the 

boundaries of the sub-watershed. Figure 3-4 presents the STATSGO2 mapped coverage of the 

hydrologic soil groups in the Carters Lake Watershed. The qualitative characteristics of two dominant

Hydrologic Soil Groups (Groups B and C) are described 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 moderately 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 Groups to default group numbers: Group A equals 1, 

Group B equals 2, Group C equals 3 and Group D equals 4. Appendix A presents the dominant soil type, 

by default group number and letter, for each sub-watershed in the Carters Lake Watershed model. 
November 2011 REV1 Carters Lake Watershed 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 Watershed 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 14 

3.5 Meteorological Data 

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

from weather stations within the boundaries of, or in close proximity to, the sub-watersheds, were applied 

to the watershed model. An ASCII file (*.air) was generated for each meteorological station used in the 

hydrological evaluations in LSPC. Each meteorological station file contains atmospheric data used in 

modeling the hydrological processes. These data include 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 detailed 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 maintained and operated by the College of 

Agricultural and Environmental Sciences of the University of Georgia. Each station monitors air 

temperature, relative humidity, rainfall, solar radiation, wind speed, wind direction, soil temperature at 2, 

4, and 8 inch depths, atmospheric pressure, and soil moisture every one second and the data are 

summarized at 15-minute intervals (GAEMN, 2009). Three of the stations were National Climate Data 

Center (NCDC) stations, which record daily or hourly 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-watersheds 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 Carters Lake Watershed 
November 2011 REV1 Carters Lake Watershed 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 Stations used in the LSPC Watershed Model 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 16 

3.6 Reach Characteristics 

The LSPC model must have a representative reach defined 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 Dataset (NHD). The channel geometry is 

described by a bank full width and depth (the main channel), a bottom width factor, a flood plain width 

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 and 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, water volume, and outflow in the segment. The 

assumption of a fixed depth, area, volume, outflow relationship rules out cases where the flow reverses 

direction or where one reach influences another upstream of it in a time-dependent way. The routing 

technique falls in the class known as "storage routing" 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 University of Georgia, Georgia Land Use Trends (GLUT) 

coverage, and included the following 19-Class categories: beaches/dunes/mud, open water, utility swaths, 

developed open space, developed low intensity, developed medium intensity, developed high intensity, 

clear-cut/sparse, quarries/strip mines, rock outcrop, deciduous forest, evergreen forest, mixed forest, golf 

courses, pasture, row crop, forested wetland, non-forested wetland (salt/brackish), and non-forested 

wetland (freshwater). In the Carters Lake Watershed model the GLUT coverage represented land use 

conditions in the year 2005. For the LSPC simulation, similar land use classes were grouped together into 

reduced modeling units (RMU), i.e., deciduous forest, evergreen forest and mixed forest were grouped 

together into an RMU called forest. Figure 3-6 shows the spatial coverage of the RMU’s for the Carters 

Lake Watershed. 

The LSPC model requires division of land uses in each sub-watershed into separate pervious and 

impervious land units. For this, the GLUT impervious cover, Figure 3-7, was intersected with the GLUT

land use cover. Any impervious areas associated with 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 associated with medium intensity development and high 

intensity development, were kept separate and placed into two new RMU’s for medium intensity 

development impervious and high intensity development impervious, respectively. Finally, any 

impervious area not already accounted for in the three 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 from, 

how they were processed, and how they were incorporated as unique land uses. Appendix C presents the 

breakdown of each processed land use for each sub-watershed in the model. 

The final list of land uses represented in the Carters Lake Watershed model is presented in Table 3-2. 

Also presented is how the original GLUT classifications were condensed into RMU’s. Table 3-2 also 

shows the final acreage and areal percent of each of the land uses represented in the LSPC watershed 

model. 

Over 80% of the Carters Lake Watershed is covered by Forest with a majority being identified as strictly 

deciduous. About 7% of the watershed is covered by Pasture of which about three fourths was converted
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 17 

to chicken land which is associated with chicken manure. There isn’t a large amount of developed space, 

only about 6%, and the development is highly concentrated 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 Representation 
November 2011 REV1 Carters Lake Watershed 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 Units of the Carters Lake Watershed 
November 2011 REV1 Carters Lake Watershed 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 Watershed 
November 2011 REV1 Carters Lake Watershed 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 to map locations and create a GIS point coverage of 

broiler chicken houses in the Carters Lake Watershed. Tetra Tech found 791 broiler chicken houses 

within and very close to the boundaries of the watershed. 

Broiler chicken houses are buildings that house a large number of birds. A study was conducted that 

showed pasture land within a 0.75-km radius of a chicken house typically received applications of broiler 

manure (Zin, 2008). Initially, the Carters Lake Watershed model was set up to distinguish regular pasture 

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 buffer area to a new land use type called “Chicken Pasture” 

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 quality 

sampling in the watershed. While investigating why this was occurring, it was identified that water 

quality stations simulating low also had higher percentages of Chicken House buffer area, as compared to 

other water quality stations simulating Total Nitrogen well, in their contributing drainage area. This 

prompted a thorough investigation into the representation of chicken land in the water quality model. 

It was found that Chicken Pasture representation/processing resulted in approximately 16% of the buffer 

area receiving applications of broiler manure. Due to the high correlation (r-squared 0.69) when 

comparing each stations upstream buffer area to mean measured total nitrogen (Figure 3-8), a series of

scenarios were set up utilizing different percentages (25%, 50% and 75%) of the buffer area for receiving 

applications of broiler manure. Each scenarios simulation was compared with observed Total Nitrogen 

concentrations and a statistical technique called sum 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). Additionally, comparing regressions of measured Total 

Nitrogen and the percent of contributing drainage area that is chicken land using 25% of the buffer area 

(Figure 3-9) and simulated Total Nitrogen and the percent and the percent of contributing drainage area 

that is chicken land using 25% of the buffer area (Figure 3-10) shows that slopes and intercepts of the 

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 reprocessed for the watershed model. The total chicken

house buffer area in each sub-watershed was multiplied 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 created a negative number for Pasture then Pasture area was 

set to zero and the remaining area was subtracted from 2) Barren, if this still resulted in a negative number 

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

Refer to Section 5.9 Special Considerations for Water Quality –Chicken Land in this report for a 

discussion on pollutant loadings utilized for chicken land. Appendix D identifies the number of chicken 

houses found in each sub-watershed of the Carters Lake Watershed. 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 21 

Figure 3-8 Regression of 2008 Mean Measured Total Nitrogen and Upstream Chicken 

House Buffer area 

Table 3-3 Results of Chicken Land Buffer Area Representation Scenarios 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 22 

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 

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

Drainage that is Chicken Land using 25% of the Buffer Area 
November 2011 REV1 Carters Lake Watershed 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 the Carters Lake Watershed with a 0.75-

km buffer surrounding each location 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 24 

3.9 Septic Tank Representation 

Tetra Tech received septic system data in two formats from GAEPD. The first format was a database of 

septic tank installations and repairs, for each county, from 2002 through 2007. The second format was a 

document containing tables with the number of existing 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 tanks, for each county, for the year that was closest to 

2007. That number was then further modified by the number of installations that occurred from the 

existing septic tank year until 2007. Therefore, each county was represented by a septic tank number that 

reflected the number of existing septic tanks in the year 2007. 

The number of septic tanks in each sub-watershed was determined through an area weighting method. 

Sub-watersheds were assigned to counties based on their outfall or pour point. The percentage of county 

area, represented by the sub-watersheds assigned to that county, was used to determine the total number 

of septic tanks represented in those sub-watersheds. The number represented in each sub-watershed was

determined by area weighting the individual sub-watershed area to the total area of the sub-watersheds

assigned to the same county. 

Septic tanks contribute to water quality whether they are functioning properly or failing. It was assumed, 

that at any given time, there are 15% of the overall 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 decay occurs and raw effluent is directly applied to the 

land. It was determined that the average area of a septic field is 6,750 ft2 (Inspectapedia 2009). The land 

use that was represented as Failing Septic was subtracted from the Low Intensity Urban Pervious land use 

for each sub-watershed. For a few of the sub-watersheds subtracting Failing Septic from Low Intensity

Urban Pervious resulted in negative values. For these watersheds, all of the failing septic tank area was 

subtracted from Developed Open Space. The non-failing septic tanks were modeled as very small 

individual point sources for each sub-watershed. 

Refer to Section 5.9 Special Considerations for Water Quality –Septic Tanks in this report for a 

discussion on how both failing and non-failing septic 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 Discharge Elimination System (NPDES) are, by 

definition, considered point sources. There are four point source discharges located in the Carters Lake 

Watershed. Of the four point sources, one was a major municipal facility, two were rock quarries, and

one was a minor Public Institutional Discharger (PID). Flows and water quality data for these point 

source discharges were obtained from GAEPD in the form of Discharge Monitoring Reports (DMR). 

Data obtained from these reports were input directly into the LSPC model as time-series from 1997 to 

2009. 

GAEPD provided Tetra Tech data from Compliance Inspection 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 values for constituents. For example, ammonia was 

measured and the other nitrogen species were default, so speciation form the CIM was utilized to 

calculate the other nitrogen constituents from the measured ammonia values. 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 25 

The two rock quarries did not report loads or concentrations 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 utilized 

for October-March and 25°C was utilized for April-September. 

Table 3-4 presents the point source facilities included in the Carters Lake Watershed model and gives the 

NPDES number, facility name, facility type, receiving 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 utilized 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 Carters Lake Watershed model. All of this information is 

reproduced in Appendix F along with time-series plots 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 Source Discharges in the Carters Lake 

Watershed 

Table 3-6 Default Water Quality Concentrations of Constituents without Data for Rock 

Quarries 
November 2011 REV1 Carters Lake Watershed 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 Lake Watershed 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 27 

3.11 Municipal and Industrial Water Withdrawals 

There are two water withdrawals located in the Carters Lake Watershed that are represented in the LSPC

model (Table 3-7). Monthly average water withdrawal volume data were obtained from the GAEPD. 

The withdrawal volume data were developed into a time-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 that the facility was operational and then the long-term 

monthly average withdrawal volume was supplied. 

For security reasons, the locations of the water withdrawals cannot be disclosed. Monthly flow data input 

into the model for each water withdrawal is presented in Appendix G. 

Table 3-7 Summary of Water Withdrawal in Carters Lake Watershed 
November 2011 REV1 Carters Lake Watershed 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 ultimately 

nonpoint source loadings to a waterbody. The watershed model must appropriately represent the spatial

and temporal variability of hydrological characteristics within a watershed. Key hydrological 

characteristics include interception storage capacities, infiltration properties, evaporation and transpiration 

rates, and watershed slope and roughness. LSPC’s algorithms are identical to those in the Hydrologic 

Simulation Program FORTRAN (HSPF). The LSPC/HSPF modules used to represent watershed 

hydrology include PWATER (water budget simulation for pervious land units) and IWATER (water 

budget simulation for impervious land units). A detailed description of relevant hydrological algorithms 

is presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004). 

4.2 Observed Flow Data 

A query of the National Water Information Center daily surface-water database finds a total of 17 stream 

and lake gage stations, for the Carters Lake Watershed. After filtering out the gages that did not contain 

stream flow measurements during the model simulation period, there were 5 viable stations remaining for 

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, corresponding LSPC sub-watershed, LSPC simulated 

drainage area, how the station was utilized, and the period of record utilized for each gage. Three of these 

gages had a complete period of record for the simulation 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 USGS02381600 – 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 the 

Lake Lanier Watershed. During the calibration process, 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 parameters adjusted included: evapo-transpiration, 

infiltration, upper and lower zone storages, groundwater recession, and losses to the deep groundwater

system. The calibration of the hydrologic parameters was performed from January 1, 1998 through 

December 31, 2007. The final calibrated hydrological parameters are presented in Appendix H. Results, 

comparing observed and simulated flows, are presented in Appendix I. 

4.4 Hydrology Model Validation 

An important step of the modeling process is model validation. Model validation is the process of taking 

the hydrological parameters that have been calibrated, 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 model verification, as essentially you are validating or 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 29 

verifying that hydrological parameters calibrated in one watershed will produce acceptable results in 

another watershed. It is important that when selecting 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 apply to a wide range of conditions. The validation of 

the hydrological parameters was performed from January 1, 2008 through December 31, 2009. Results, 

comparing observed and simulated flows, are presented 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, 02380500, and 02381090) had different flow regimes 

than the USGS gages in the part of the watershed contributing to the Reregulation Reservoir (02381600 

and 02382200). Since a majority of the drainage area is made up of Forest land, adjusting parameters to 

make the gages contributing to Carters Lake look good, resulted in the gages contributing the Regulation 

Reservoir look horrible, and vice versa. To overcome this, two new parameter groups were developed, 12 

and 13, which represented Hydrologic Soil Groups 2 and 3 for the part of the watershed contributing to

the Reregulation Reservoir. The only parameters changed 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 for the two different hydrologic regimes observed in the 

Carters Lake Watershed. 

Tetra Tech has developed a qualitative grading scale ( VG=Very Good, G=Good, F=Fair, and P=Poor) 

based on the quantitative statistical analysis, comparing 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 score 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 observed flows, for the absolute value of each flow 

summary type, for acceptable calibration of a watershed model. The flow summary types are also in 

ascending order of those easiest to hardest to obtain. An example of the grading technique is discussed in 

detail below. 

Period of record error statistics have been placed in the model stat column in Table 4-4. For each flow 

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 is given a value of 4, if less then G but greater than VG it 

is given a value of 3, if less then F but greater than G it is given a value of 2, and if it is greater 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 type. Flow summary types have been assigned a 

weight based on their overall importance for a successful calibration. The error in total volume is most 

important followed by the errors in the high and low flows, then the error in seasonal volumes and finally 

the errors in storm volumes. The score for the flow summary statistics are then summed to produce a 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 30 

total score for each gage. This total score is then compared against the minimum score for each 

qualitative grade (Table 4-5) and the grade assigned. 

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 Carters Lake. 

Table 4-2 Score and Grade for USGS flow gages Carters 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 drainage 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 Recommended 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, GA
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 31 

Table 4-4 Qualitative Grading Scale for USGS 02380500 Coosawattee River near Ellijay 

Table 4-5 Score Minimum and Corresponding Qualitative Grade 

Table 4-6 Potential Scores Based on Qualitative Grade and Weighting Factor 
November 2011 REV1 Carters Lake Watershed 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 Validation Stations used in the Hydrology 

Model 
November 2011 REV1 Carters Lake Watershed 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 calibrated, the model was used to create a water quality 

model of the Carters Lake Watershed. Many components of the water quality model were established 

during hydrology modeling. These components include watershed segmentation, meteorological data, 

land use representation, soils, reach characteristics, and point source discharges. The watershed water 

quality model included all point and nonpoint source contributions. Nutrient loadings from point sources 

were represented by developing direct input time series, for each point source, using discharge monitoring 

report data. Non-point source nutrient loadings were represented by build-up and wash off algorithms 

and assigning nutrient concentrations to the interflow and groundwater flow paths. Nutrients in the 

stream experienced dilutions, accumulations, assimilation, biochemical cycling, and transport 

downstream and out of the watershed 

5.2 Modeled Parameters 

The LSPC water quality model was setup to model Temperature, Dissolved Oxygen, Biochemical 

Oxygen Demand (BOD), Total Nitrogen (TN), Ammonia (NH3), Nitrate+Nitrite (NOx), Organic 

Nitrogen (Org-N), Total Phosphorus (TP), Orthophosphate (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 has the ability to model in-stream biochemical processes, 

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 can 

be assigned differently by reach group include: sediment 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 release, variables for dissolved oxygen reaeration, 

benthic oxygen demand, oxygen scour, all biochemical nutrient transformation parameters, and all 

plankton growth, death and transport parameters. In 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 previous 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 order 

number (Strahler, 1957). Next, reaches that behaved similarly for sediment shear stress were grouped 

together. The results of the above two assignments were then joined together. The resultant reach group 

puts streams in the same reach group only if they are the same in both Strahler stream order and similar in 

sediment shear stress. This approach to assigning reaches into reach groups allows for a more detailed 

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 assignment. 
November 2011 REV1 Carters Lake Watershed 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 identical to those in the Hydrologic Simulation 

Program FORTRAN (HSPF). The LSPC/HSPF modules used 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 using three layers, surface, upper subsurface, and 

groundwater subsurface. The surface layer is the portion of the land segment that determines the overland 

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 regression equation as a function of measured air temperature. 

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 temperature and measured air temperature. The average surface 

layer soil temperature was manipulated by a multiplier and an offset to come up with a theoretical upper 

subsurface layer temperature. Monthly regression equations for surface and upper subsurface layers were 

set up using air temperature as the independent variable and layer temperature as the dependent variable. 

This allowed the use of air temperature as the input to the regression equation and the corresponding layer 

temperature was the output. 

Soil temperature is only used to determine the water temperature of the three different flow paths (surface 

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 increase the heat content of the water are absorption of solar 

radiation, absorption of long-wave radiation, and conduction-convection. Mechanisms which decrease 

the heat content are emission of long-wave radiation, conduction-convection and evaporation (Bicknell et 

al. 2004). The calibrated water temperature parameters for each individual model are presented in 

Appendix J. Results for water temperature calibration 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 streams 

or lakes and their associated ecological systems. In relatively unpolluted waters, sources and sinks of 

oxygen are in approximate balance and the concentration remains close to saturation. By contrast, in a 

stream receiving untreated waste waters, the natural 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 algorithms identical to those in the Hydrologic 

Simulation Program FORTRAN (HSPF). The LSPC/HSPF modules used to represent dissolved oxygen 

include PWTGAS (pervious water temperature and dissolved gas concentrations), IWTGAS (impervious 

water temperature and dissolved gas concentrations), and OXRX (primary DO and BOD balances). A 

detailed description of relevant temperature algorithms is presented in the HSPF (v12) User’s Manual 

(Bicknell et al. 2004). 

Setting aside in-stream transformations, which either consume or produce dissolved oxygen, a major 

player in the dissolved oxygen concentration is stream temperature. It is well known that colder water 

can dissolve and hold more gas than warmer water. Another major player is atmospheric reaeration. 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 35 

Atmospheric reaeration takes into consideration the dissolved oxygen concentration to start with, oxygen 

saturation level for a given water temperature, water depth, water velocity, circulation, reaeration rate, 

and a temperature correction coefficient for surface gas invasion. LSPC allows for user defined dissolved 

oxygen concentrations in inter-flow and groundwater by land use and month. The calibrated water 

temperature parameters for each individual model are presented in Appendix J. Results for water 

temperature calibration and validation are presented 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 represent sediment include SEDMNT (pervious 

production and removal of sediment), SOLIDS (accumulation and removal of solids), and SEDTRN 

(transport and behavior of inorganic sediment). A detailed description of relevant sediment algorithms is 

presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004). In short, the algorithms are removing 

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 column 

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 generated 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 Calibration guidance to HSPF (USEPA, 2006) and Sediment 

Calibration Procedures and Guidelines for Watershed Modeling (Donigian et al. 2003). Additionally, the 

in-stream transport component was closely examined and calibrated for each reach group. 

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

either measured or obtained from a literature search, and minimizing the number of calibration parameters 

that would be adjusted. Key processes for sediment include: soil detachment, soil compaction, fraction 

of land use shielded from rain drop impact, sediment wash off rate, and in-stream transport which 

includes settling velocities and flow velocities that contribute to deposition and re-suspension of sediment 

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 algorithms 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 relationships), IQUAL (wash-off of quality constituents using

simple relationships), NUTRX (primary inorganic nitrogen and phosphorus balances), and PLANK 

(plankton populations and associated reactions). A detailed description of relevant sediment algorithms is 

presented in the HSPF (v12) User’s Manual (Bicknell et al. 2004). 

Accumulation and wash-off rates play an important role in the determination of nonpoint source loadings 

to a water body. The watershed model must appropriately represent the spatial and temporal variability of 

hydrological characteristics within a watershed. It must also appropriately represent the rate at which 

nutrient components build-up between rain events and wash off during rain events. Key general water 

quality characteristics include initial storage, wash-off and scour potency, accumulation rates, and 

asymptotic maximum storage amounts. The water supplied to a stream from groundwater and through 

interflow also plays an important role in loading to a water body. LSPC allows the user to supply 

groundwater and interflow concentrations, by hydrologic soil group and land use, by month. The 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 36 

accumulation and wash-off and interflow strongly influence peak flow water quality while groundwater 

reflects base flow water quality. 

Biochemical in-stream processes play an important role on nutrient concentrations spatially and 

temporally. Biochemical processing also has a large influence on dissolved oxygen and ultimately water 

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 plankton populations. In order to accurately represent 

biochemical processing, temperature must be modeled because all transformation rates are temperature 

dependent. Key processes for oxygen include: benthic 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 materials to produce nitrogen and phosphorus. 

The growth and death of plankton and algae, both floating and attached, is a natural process occurring

within all streams. Plankton can have an impact on water quality by contributing organic matter to the 

benthos, changing dissolved oxygen through photosynthesis and respiration, and tie up nitrogen and 

phosphorus to have it later released through mineralization. The calibrated nutrient and plankton 

parameters for each individual model are presented in Appendix O1 through O4. Results for nutrient and 

plankton calibration and validation are presented in Appendix P1 through P4 for each individual model. 

5.8 Water Quality Calibration 

Temperature was the constituent calibrated after hydrology because the remaining parameters use water 

temperature in their algorithms. Temperature was calibrated by first slightly adjusting surface and 

interflow slopes and intercepts and groundwater temperature and then secondly focusing on the in-stream 

mechanisms, i.e. impact of solar radiation as well as the impact of bed thermal conduction. After 

temperature was calibrated, dissolved oxygen was brought into close agreement with the observed data by 

adjusting reaeration, and interflow and groundwater dissolved oxygen concentrations. At this point 

dissolved oxygen was only partially calibrated because the water quality simulation was only partially

active. Next, the sediment module was turned on and the parameters borrowed from the Lake Allatoona 

LSPC model development were adjusted until the simulated data closely matched the observed data. 

After the above three modules were either calibrated or brought into reasonable agreement, the calibration 

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-off and assigning land use associated concentrations in 

groundwater and interflow. Build-up/wash-off removes constituents from the land and carries them into

the stream. Therefore, adjustments were made to monthly accumulation rate, monthly storage limit, 

interflow concentration, and groundwater concentration 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 the total constituents were in range, a flow path 

associated fractionation was assigned. This fractionation assigned percentages of each constituent 

making up the total to the modeled total value. Total nitrogen was broken down into nitrate+nitrite, 

ammonia, organic nitrogen and sediment adsorbed ammonia, 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 interflow, 

and pervious groundwater flow. The fractionation by flow path was adjusted until the modeled data 

closely resembled the observed field data. In-stream biochemical transformations occur and a new 

biochemically transformed value for total phosphorus and total nitrogen was generated. The new total 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 37 

values consisted of adding up the constituents making up the transformed total and the values were 

checked against the previous un-transformed total value to assure the new total values made sense. 

Once the build-up/wash-off and fractionation were close, 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. Decay and transformation rates were calibrated by 

balancing dissolved oxygen and in-stream nutrient concentrations. For example, if both BOD and 

dissolved oxygen were simulating too high then a change was made to increase the BOD decay rate. This

change will decrease simulated BOD and also decrease 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 in 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 in 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 “Chicken-Land” in which the chicken manure was 

applied. 

For phosphorus, it was assumed that the chicken land received 6.73 Mg ha-1 per year of broiler litter (Lin, 

2008). This translates to a rate of 16.45 pounds per acre per day of broiler litter applied to the chicken 

land, land use. Of the 16.45 lbs per day of broiler 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; therefore indicating an instant build-up. Since an 

“instant build-up” was assumed, this meant that the wash-off rate was the main parameter of calibration 

for this land use. 

To calculate the amount of nitrogen applied to the pasture land used by poultry, it was assumed that of the 

16.45 pounds per acre per day of broiler litter, total 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 equal 

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

Septic Tanks 

To represent the contribution of water quality from non-failing septic tanks, septic flow concentration 

data were obtained from literature (Gerner, 2004, Lihua, 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 to the septic tank. It was also assumed that it takes an 

average of 60 days for the septic flow to reach a body of water, so a first order decay rate was applied to 

each constituent to determine the concentration after 60 days. Table 5-1 presents the concentration of 

septic tank effluent, decay rates for each constituent, 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-watershed, and in the computational domain is handled like a 

point source 

For failing septic tank land use loading representation, effluent loadings were obtained from literature 

(USEPA, 2002) and are shown in Table 5-2. Pound per acre septic tank loadings were multiplied by 4 to

determine the Failing Septic land use asymptotic maximum storage limit. 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 38 

Table 5-1 Non-Failing Septic Tank Water Quality Concentrations 

Table 5-2 Failing Septic Land Use Nutrient Loading Rates 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 39 

5.10 Observed Water Quality Data for Calibration and Validation

During 2008, GAEPD intensively sampled rivers and streams 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 Quality Modeling and Water Quality Standards Review 

contract as part of the Georgia State Water Plan, GAEPD 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 shapefile, were thoroughly compared with those of the 

2008 intensive sampling and a final list of 24 stations were utilized for water quality calibration and 

validation. The list of stations and how they were utilized are in Table 5-3 and the station locations are 

shown spatially in figure 5-1. 

Five of the 24 stations had more than one year of data so they were chosen to be calibration stations. The 

remaining 19 stations were utilized as validation stations. 

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

Watershed Model 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 40 

Carters Lake Watershed - Water Quality Calib. Stations

NAD_1983_UTM_Zone_17N

Map produced 10-26-2011 - P. Cada

14119901

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14119261

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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 Validation Stations used in the Water Quality 

Model 
November 2011 REV1 Carters Lake Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 41 

5.11 Water Quality Observations and Conclusions 

Similar to hydrology, Tetra Tech has developed a qualitative grading ranking (VG=Very Good, G=Good, 

F=Fair, and P=Poor) based on the quantitative analysis, comparing simulated and observed loads, from 

our spreadsheet utilized for calibrating and validating watershed water quality models. However, unlike 

hydrology, there are not 9 error statistics for comparison and calculation. The water quality qualitative 

grading rannking simply utilizes the period of record average, observed and simulated load difference,

and compares it to criteria defined for the water quality calibration. An example of the grading technique 

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

The calculated simulated and calculated measured, period of record yearly average load percent 

differences absolute value (Table5-4) is compared with the values found in Table 5-5 and assigned the 

corresponding qualitative grade. For this example, the dissolved oxygen period of record yearly average 

load percent differences absolute value of 5.68, is less than 10, which is the maximum difference allowed 

to be considered very good, so this gage has a qualitative 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 better capture acceptable error for temperature, 

dissolved oxygen and nutrients. To be very good for Temperature and Dissolved oxygen thee error needs

to be within 10% which roughly equates to 1-2 degrees Celsius and about 1 mg/l for dissolved oxygen. 

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

Table 5-5 Score Minimum and Corresponding Qualitative Grade for Nutrients, Temperature 

and Dissolved Oxygen 
November 2011 REV1 Carters Lake Watershed 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 stations that are included in Appendix P Water Quality 

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) represent key locations in the watershed (i.e. two drainages 

above the major point source, three drainages to Carters Lake, and one drainage to the Reregulation 

Reservoir) and it is assumed that if the water quality model is performing well at these locations then one 

can conclude that the water quality model as a whole 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 acceptably with rankings of Good and Very Good 

respectively. Additionally, nutrients have an acceptable calibration as all qualitative rankings are in the 

Good to Very Good range. Lastly, sediment is ranked 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 acceptably with rankings of Very Good and Good 

respectively. Additionally, nutrients have an acceptable calibration as all qualitative rankings are in the 

Good to Very Good range. Lastly, sediment is ranked 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. Both temperature and dissolved oxygen are Very Good and 

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 are expected at this station since it is immediately

downstream of a major point source and the water quality conditions are largely controlled by the point 

source. This station being Very Good suggests that the direct timeseries input for the point source is 

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-series 

and 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 14116001 is located on Tails Creek and is the third largest tributary to Carters Lake. Similar 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 this is still being investigated as the time-series and 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 immediately 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 Watershed Modeling Report 

Prepared by Tetra Tech, Inc. 43 

The summary provided in Table 5-6, along with the other visual and statistical summaries in Appendices

O and P indicate that the Water Quality model should perform reasonable well for the intended purpose of 

approximating Nutrient Loads into Carters Lake. 
November 2011 REV1 Carters Lake Watershed 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, sub-watershed delineations, flow and water quality 

stations and point source dischargers are shown. The 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 Carters 

Lake Watershed 

. 
November 2011 REV1 Carters L

Prepared by Tetra Tech, Inc. 

Carters Lake Watershed

NAD_1983_UTM_Zone_17N

Map produced 11-08-2011 - P. Cada

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Legend

Point SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty Boundary

CartersReregulationReservoir

CartersLake

Figure 6-1 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 1 of 4) 
November 2011 REV1 Carters L

Prepared by Tetra Tech, Inc. 

Carters Lake Watershed

NAD_1983_UTM_Zone_17N

Map produced 11-08-2011 - P. Cada

GA0037834

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Point SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty Boundary

CartersReregulationReservoir

CartersLake

Figure 6-2 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 2 of 4) 
November 2011 REV1 Carters L

Prepared by Tetra Tech, Inc. 

Carters Lake Watershed

NAD_1983_UTM_Zone_17N

Map produced 11-08-2011 - P. Cada

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Point SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty Boundary

Figure 6-3 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 3 of 4) 
November 2011 REV1 Carters L

Prepared by Tetra Tech, Inc. 

Carters Lake Watershed

NAD_1983_UTM_Zone_17N

Map produced 11-08-2011 - P. Cada

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Point SourceFlow Calibration StationWater Quality Calib. StationStream/RiverWaterModel Subwatershed12-digit HUC BoundaryCounty Boundary

Figure 6-4 Visual Summary of Model Input for the Carters Lake Watershed Model (Panel 4 of 4) 
November 2011 REV1 Carters Lake Watershed Modeling 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 View, California. 

Donigian, A.S., and J.T. Love, 2003. Sediment Calibration Procedures and Guidelines for Watershed 

Modeling. Aqua Terra Consultants, Mountain View, California. 

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

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

Natural Resources. 

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

Jones, Lyle, 2005. Septic Systems as a Source of Bacteria, Nitrogen, and Phosphorus. Deleware 

Department of Natural Resources. 

Lihua, Cui, 2002. Treatment and Utilization of Septic 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 Service, 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 Hydraulic Function Tables for Reservoirs in 

BASINS. Office of Water, U.S. Environmental Protection Agency. Washington, DC. 

USEPA, 2006. BASINS Technical Note 8: Sediment Parameter and Calibration Guidance for HSPF. 

Office of Water, U.S. Environmental Protection Agency. Washington, DC. 

USEPA, 2002. Onsite Wastewater Treatment Manual. EPA 625/R-00/008. National Risk Management 

Research Laboratory, Office of Water. Washington DC. 

USEPA, 2000. BASINS Technical Note 6. Estimating Hydrology and Hydraulic Parameters for HSPF. 

Office of Water, U.S. Environmental Protection Agency. Washington, DC. 

USEPA, 1985. Rates, Constants, and Kinetics Formulations in Surface Water Quality Modeling (Second 

Edition). Environmental Research Laboratory, U.S. Environmental 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 Effect of Landuse Change. 43 pages.