Final Sediment Watershed TMDL (PDF)

Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 TOTAL MAXIMUM DAILY LOAD (TMDL) DEVELOPMENT For Sediment in the Stekoa Creek Watershed 303(d) Listed Stream Segments Stekoa Creek Scott Creek Pool Creek Chechero Creek Saddle Gap Creek December 28, 2000 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 APPROVAL PAGE for Sediment in Stekoa Creek Watershed, GA The five streams in the Stekoa Creek Watershed were included on the State of Georgia’s 1998 303(d) List because of biological and habitat impairment. Sediment was determined to be the pollutant of concern. Due to the restrictive timeframe imposed by the February 2000 Order on Consent in the Georgia TMDL lawsuit to propose and finalize certain TMDLs, this watershed TMDL was developed that provides estimates of the watershed’s sediment delivery. The Stekoa Creek Watershed TMDL sediment delivery is expressed as an annual load of sediment from the watershed that potentially can reach the stream. The specific 303(d) listed tributaries in the Stekoa Creek Watershed are: Stream • • • • • Stekoa Creek Scott Creek Pool Creek Chechero Creek Saddle Gap Creek Use Support Status Pollutant of Concern Partial Support Excessive Sedimentation Partial Support Excessive Sedimentation Partial Support Excessive Sedimentation Not Supporting Excessive Sedimentation Partial Support Excessive Sedimentation The use support status is based on biological monitoring of the streams conducted during the 1998 and 1999 EPA sampling. The Stekoa Creek and tributary sedimentation problem can be divided into two issues: 1) sediment loading coming from the watershed and 2) instream sedimentation processes such as bank erosion and stream bottom down cutting. This Stekoa Creek Watershed TMDL only develops long – term annual sediment loads for the watershed. If the watershed sediment loads are reduced to an acceptable level, the stream will revert to its natural condition over time and the instream sedimentation processes will no longer be i Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 problematic. If actions are needed to restore these waters more quickly then instream restoration, riparian zone enhancement and stream bank stabilization can be implemented. The TMDL is expressed as an annual long - term loading value. For a biologically unimpacted healthy stream the annual long - term loading watershed sediment load is 90 tons per year per square mile, which includes a 10 percent margin of safety. The Stekoa Creek Watershed TMDL determined the sediment watershed loading percent reductions that are needed to meet the unimpacted area loading rate are as follows: Stream Area (Sq.Mile) Stekoa Creek Scott Creek Pool Creek Chechero Creek Saddle Gap Creek 17 6 5 4.4 3 Existing Watershed Load (Tons/Year/Sq.Mi.) 351 177 106 175 392 Percent Reduction Needed to Meet Target 75 50 15 50 77 It is recommended that the Stekoa Creek watershed be considered a high priority for riparian buffer zone restoration and any sediment reduction BMPs, especially for the road crossings, agriculture activities, and construction activities. Further ongoing monitoring needs to be completed to monitor progress and to assure further degradation does not occur. Point source impacts for the Stekoa Creek watershed were determined to not cause or contribute to the existing impairments as long as the wastewater treatment facility maintains its suspended solid permit limits and any stormwater discharges (i.e., construction permits) meet the requirements of the Georgia general stormwater permit. The February 2000 Order on Consent in the Georgia TMDL lawsuit requires EPA to propose TMDLs to ii Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 address sediment for waters identified as impaired in the Chattooga Basin Report, including those in the Stekoa Creek Watershed, by December 31, 2000 and finalize these TMDLs within 120 days. The Chattooga Basin TMDL will also address the needed scope of an ongoing sediment monitoring plan for the Chattooga Watershed, including the Stekoa Creek Watershed. Waters on the State’s 303(d) list that are located in the Savannah/Ogeechee Basins will be due for TMDL development again in 2004. A ccording to the 1997 Consent Decree in the Georgia TMDL Lawsuit, TMDLs taking into consideration both point and nonpoint sources must be proposed by the State of Georgia on or before June 30, 2004 or by EPA on or before August 30, 2004. The TMDLs developed in this document can then be revisited during that timeframe. APPROVED BY: ________________________ Beverly Banister, Director Water Management Division EPA-Region 4 __________________ Date iii Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Table of Contents Approval Page……………………………………………………………………………………..i Introduction...................................................................................................................................... 1 Location........................................................................................................................................... 1 Problem Definition............................................................................................................................. 2 Target Identification and Model Development .................................................................................... 3 Model Development...................................................................................................................... 3 Sediment Sources ......................................................................................................................... 5 Point Source: ...........................................................................................................................5 Upper Stekoa Creek Watershed – HUC 0306002001.................................................................. 7 Lower Stekoa Creek Watershed – HUC 0306002002.................................................................. 7 Total Maximum Daily Load (TMDL)................................................................................................. 8 Seasonal Variation........................................................................................................................ 8 Margin of Safety........................................................................................................................... 8 TMDL Determination.................................................................................................................... 8 Allocation of Responsibility and Recommendations ............................................................................ 9 Schedule for the Next Phase of the TMDL ........................................................................................ 9 Recommendations............................................................................................................................. 9 iv Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Upper Stekoa Creek Watershed – HUC 0306002001................................................................ 10 Stekoa Creek Watershed.......................................................................................................10 Scott Creek Watershed..........................................................................................................10 Saddle Gap Creek Watershed................................................................................................10 Lower Stekoa Creek Watershed – HUC 0306002002................................................................ 11 Chechero Creek Watershed...................................................................................................11 Pool Creek Watershed...........................................................................................................11 Figure 1 - Location of Stekoa Creek Watershed.............................................................................. 11 Figure 2 - Watershed Tributaries................................................................................................... 13 Figure 3 – Land Use Distribution..................................................................................................... 14 Figure 4 – Road and Stream Network............................................................................................. 15 Appendix A: Biological and Habitat Data and Information........................................................ 16 Stekoa Creek Watershed............................................................................................................ 16 Appendix B: Model Description and Sediment Modeling and Analysis Methodology ................ 18 Universal Soil Loss Equation....................................................................................................... 18 Sediment Analysis ....................................................................................................................... 21 Sediment Modeling Methodology................................................................................................ 22 Sediment Analysis Inputs............................................................................................................. 25 v Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Sediment TMDL Development Methodology............................................................................... 27 Appendix C: Appendix D: Numeric Sediment Target Determination.................................................................. 28 References and Administrative Record Index........................................................... 33 vi Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Introduction Section 303(d) of the Clean Water Act (CWA) as Amended by the Water Quality Act of 1987, Public Law 100-4, and the EPA’s Water Quality Planning and Management Regulations [Title 40 of the Code of Federal Regulation (40 CFR), Part 130] require each State to identify those waters within its boundaries not meeting water quality standards applicable to the waters’ designated uses. The identified waters are prioritized based on the severity of pollution with respect to designated use classifications. TMDLs for all pollutants violating or causing violation of applicable water quality standards are established for each identified water. Such loads are established at levels necessary to implement the applicable water quality standards with seasonal variations and margins of safety. The TMDL process establishes the allowable loadings of pollutants or other quantifiable parameters for a water body, based on the relationship between pollution sources and in-stream water quality conditions, so that states can establish water-quality based controls to reduce pollution from both point and nonpoint sources and restore and maintain the quality of their water resources. (EPA, 1991) Location The Stekoa Creek Watershed lies within the Tugaloo watershed located in northeastern Georgia (Figure 1). It flows into the Chattooga River and the Tugaloo Rivers at their confluence. Stekoa Creek drains an area of 40.7 square miles (26,066 acres) occupying the central portion of Rabun County, which borders Macon County, North Carolina, to the north. Through the Tugaloo River to the south, Stekoa Creek eventually flows into the Chauga River and Hartwell Reservoir. Biological, habitat and storm-event sampling has been conducted, by EPA during 1998 and 1999 (EPA, 1999a) at the following locations: 1 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Station ID • • • • • • • SC-01 SC-02 SC-03 SC-04 SC-05 SC-06 SC-07 River Mile 2.7 32.7 2.4 3.9 1.1 3.1 2.7 Station Name______________________ Stekoa Creek - 100 yards downstream US 23/441 Bridge Stekoa Creek - Near Boggs Mountain Road Cutting Bone Creek @ Mile 1.0 Scott Creek @ Mile 0.7 Pool Creek @ Mile 0.5; County Road 131 Chechero Creek @ New Hope Church Saddle Gap Creek @ Duggan Hill Road Problem Definition The causes of impairment for waters in the Stekoa Creek Watershed on the State’s 303(d) list were biological and habitat impairment. (EPA 1999a, Appendix A) Field studies confirmed the pollutant of concern to be sediment causing habitat impairment in the stream due to excessive sedimentation. The specific 303(d) listed tributaries in the Stekoa Creek Watershed are: Stream Stekoa Creek Scott Creek Pool Creek Chechero Creek Use Support Status Pollutant of Concern Partial Support Excessive Sedimentation Partial Support Excessive Sedimentation Partial Support Excessive Sedimentation Not Supporting Excessive Sedimentation 2 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Saddle Gap Creek Partial Support Excessive Sedimentation Previous reports, such as the “Sedimentation in the Chattooga River Watershed” report concluded that the Stekoa Creek watershed was the watershed in the Chattooga Basin most impacted by sedimentation, with the major source of the sediment being unpaved multipurpose roads. These roads were associated with about 80% of the sediment sources observed. The remaining sources were identified as timber harvest, agriculture, residential development, and recreation activities. Other contributors to the instream sediment load are heavy trafficking and increased maintenance of the unpaved roads, roads adjacent to the stream, pastures with unfenced riparian zones, ongoing development, “large quantities of fine sediment, both of natural and anthropogenic origin, which are gradually being flushed downstream, primarily during major storm events” and historic and current land use practices. (Vanlear 1995). The Stekoa Creek and tributary sedimentation problem can be divided into two issues: 1) sediment loading coming from the watershed and 2) instream sedimentation processes such as bank erosion and stream bottom down cutting. This Stekoa Creek Watershed TMDL develops long – term annual sediment loads for the watershed. If the watershed sediment loads are reduced to an acceptable level, the stream will revert to its natural condition over time and the instream sedimentation processes will no longer be problematic. If actions are needed to restore these waters more quickly then instream restoration can be implemented. Target Identification and Model Development Model Development For each watershed, the “existing” long – term sediment loading is estimated using the Universal Soil Loss Equation (USLE). The USLE is designed as a method to predict average annual soil loss caused by sheet and rill erosion. While it can estimate long - term annual soil loss and guide proper cropping, management, and conservation practices, it cannot be applied to a specific year or a specific storm. (Appendix B) 3 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 The sediment TMDL watershed load is calculated using the rainfall erosivity index ( R ), a statistic calculated from the annual summation of rainfall energy in every storm (correlated with raindrop size) times its maximum 30 - minute intensity. The watershed sediment load developed by the TMDL incorporates consistent default parameters and inputs for each watershed. These default parameters include the Multi-Resolution Land Cover (MRLC) land use data, the 30 meter USGS Digital Elevation Model (DEM) data, the STATSGO soil information and Georgia Department of Transportation Road information. The total amount of sediment delivery for each watershed of interest is calculated. The sediment delivery is calculated for the composite or total watershed sediment delivered to the streams and is broken down into the amount of sediment coming from roads and the amount of sediment coming from the various land uses or land covers Narrative Standard The narrative standard is to maintain biological integrity of the waters of the State – Georgia’s Water Quality Standard is established in Georgia’s Rules and Regulations for Water Quality Control, Chapter 391-3-6, Revised July, 2000 Georgia Regulation 391-3-6-.03(2)(a). Numeric Target The working hypothesis for the sediment watershed load is that if the Stekoa Creek Watershed has a long – term annual sediment load similar to a relatively biologically unimpacted healthy stream, then the Stekoa Creek Watershed will remain stable and not be biologically impaired due to sediment. Conversely, if the Stekoa Creek Watershed sediment concentrations exceed the unimpacted stream’s long – term annual sediment load then the stream will be unstable and biologically impaired. Biologically unimpacted streams in the West Fork Watershed of the Chattooga River Basin were used to develop a target sediment watershed load. During the comment period for the proposed August 30, 2000 Stekoa Creek Watershed TMDL, EPA Region 4 and Georgia Environmental Protection Division (GaEPD) representatives have been attending a Sediment TMDL Technical Advisory Group (TAG) established by the Georgia Conservancy. One of the 4 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 comments made by the TAG was the that 8 tons/year/square mile watershed sediment loading rate value included in the proposed TMDL as a target was too low and resulted in an unrealistic sediment runoff value. To better estimate the existing average annual sediment runoff, the following modeling changes were made: 1) The sediment delivery ratio methodology number 2 (the distance and relief sediment delivery method) was used instead of sediment delivery method number 4 (the WEPP based equation). See Appendix B for details. 2) The headwater area that defines a first order stream was decreased from 1 square mile to 0.5 square mile. These changes resulted in a revised biologically unimpacted stream’s watershed sediment loading rate per area average around 100 tons/year/square mile. A sediment loading rate per area of 90 tons/year/square mile was used as the target, this includes a 10 percent margin of safety. A percent reduction TMDL was developed by comparing the impacted watersheds sediment loading rate to the biologically unimpacted watersheds sediment loading rate. Note the percent reductions were approximately the same as those proposed in the August 30, 2000 TMDL. Sediment Sources Point Source: One wastewater treatment facility point source is located in the Stekoa Creek Watershed. The Clayton Wastewater Treatment Facility (Permit # GA0021806) discharges directly to Stekoa Creek below Clayton. With a design discharge flow of 0.5 million gallons per day; the total sediment load is 57 kg/day of Total Suspended Solids (TSS) or 0.04% of the watershed’s allowable low flow year load. This point source sediment load does not represent a significant impact on the stream’s sediment budget. (EPA 2000a) Since the wastewater treatment facility point source load is a minor component and the organic “sediment” being measured by the TSS monitoring does not necessarily cause a habitat problem, this TMDL will only address 5 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 the major sedimentation problems coming from the watershed and not address further the minor point source contributions. Other potential point sources discharges in the Stekoa Creek Watershed are storm water discharges associated with construction activity. The State of Georgia Department of Natural Resources, Environmental Protection Division has developed a general stormwater permit. All existing and new storm water point sources within the State of Georgia, that are required to have a permit, are authorized to discharge storm water associated with construction activity to the waters of the State of Georgia in accordance with the limitations, monitoring requirements and other conditions set forth in Part I through VII of the Georgia Storm Water General Permit. The permit limitations are established to assure that the storm water runoff from these point source sites do not cause or contribute to the existing sediment impairment. A Comprehensive Monitoring Plan with turbidity monitoring requirements is required to assure any storm water discharge from the site does not cause or contribute to the existing sediment problem. Since the point source storm water component is addressed and controlled through the implementation and enforcement Georgia Storm Water Permits, this TMDL only addresses the major sedimentation problems coming from the watershed and will not address further the permitted storm water contributions. Existing Watershed Sediment Loads: The long – term sediment watershed load was broken down by land use sediment sources and road erosion sediment sources. The current estimated long – term area weighted watershed sediment loads for the Stekoa Creek Watershed 303(d) listed tributaries are listed in Table 1. Table 1: Watershed Sediment Loads Stekoa Watershed Tributaries Scott Creek Stekoa Creekabove Clayton Saddle Gap Creek Chechero Creek Pool / She Creek Station ID SC-04 SC-01 SC-07 SC-06 SC-05 Watershed Road (Ton/Year) (Ton/Year) 205 319 205 342 257 873 467 873 395 247 Area (Sq.Mi.) 6.1 1.7 2.7 4.2 4.8 Total Area Weighted (Ton/Year) (Ton/Year/Sq.Mi.) 1078 786 1078 737 504 177 461 392 175 106 6 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Cutting Bone Creek (unimpacted segment) Stekoa @ Boggs Mt Rd. SC-03 SC-02 56 3030 93 4425 2.1 21.3 149 7455 71 351 The individual tributary watersheds are illustrated in Figure 2. A map of the landuse distribution and the road and stream network are illustrated in Figures 3 and 4. The Stekoa Creek Watershed also consists of two 12 digit hydrologic unit code (HUC) watershed delineations, which contain the 303(d) listed streams. For each of these 12 digit HUCs a detailed sediment load by individual land coverage are: Upper Stekoa Creek Watershed – HUC 0306002001 Landuse Open Water Low Intensity Residential High Intensity Residential High Intensity Commercial Bare Rock/Sand/Clay Construction Deciduous Forest Evergreen Forest Mixed Forest Pasture/Hay Row Crops Other Grasses Woody Wetlands Emergent Herbaceous Wetlands Acres 6 89 32 157 1 6 7294 1750 4077 723 204 257 2 0 Tons/Acre 0.00 2.27 0.24 0.19 0.00 74.93 0.04 0.02 0.02 0.21 9.28 0.26 2.40 1.46 Lower Stekoa Creek Watershed – HUC 0306002002 Landuse Open Water Low Intensity Residential High Intensity Residential High Intensity Commercial Construction Deciduous Forest Evergreen Forest Mixed Forest Pasture/Hay Row Crops Other Grasses Acres 4 37 1 6 26 4100 2211 3846 196 40 83 Tons/Acre 0.00 2.84 0.06 0.32 0.17 0.04 0.02 0.03 0.25 11.77 0.28 7 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Woody Wetlands Emergent Herbaceous Wetlands 1 0 1.18 0.09 Total Maximum Daily Load (TMDL) Seasonal Variation Since a long - term annual average sediment load in mass per time units is estimated, seasonality is taken in to account through the rainfall erosivity index (R factor). Margin of Safety The Margin of Safety (MOS) is implicitly assigned by selection of average USLE factors and by an explicit 10 percent reduction in the sediment loading numeric target. TMDL Determination The TMDL is expressed as a percent reduction of an annual long - term watershed sediment loading value. For a relatively biologically unimpacted healthy stream the annual long - term loading watershed load is 100 tons per year per square mile. The TMDL target is 90 tons per year per square mile which includes a 10 percent margin of safety. The Stekoa Creek Watershed TMDL determined the watershed loading percent reductions as follows: Stream Area (Sq.Mile) Stekoa Creek Scott Creek Pool Creek 17 6 5 8 Existing Watershed Load (Tons/Year/Sq.Mi.) 351 177 106 Percent Reduction Needed to Meet Target 75 50 15 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Chechero Creek Saddle Gap Creek 4.4 3 175 392 50 77 Allocation of Responsibility and Recommendations The upper portion of the Stekoa Creek Watershed is the major sediment producing area, while the lower portion of the Stekoa Creek Watershed meets the TMDL target. The sediment coming from the upper watershed and historic instream processes, however, impacts Lower Stekoa Creek. Roads, agriculture and bare ground (construction sites, etc.) sediment sources are the major sediment producing areas in the upper watershed. If appropriate best management practices (BMPs) for these practices and other sediment producing activities are implemented at the sites that are near the stream’s drainage network and the stream’s riparian zone or buffer zones are maintained or restored then the TMDL targets can be met. Schedule for the Next Phase of the TMDL The February 2000 Order on Consent in the Georgia TMDL lawsuit requires EPA to propose TMDLs to address sediment for waters identified as impaired in the Chattooga Basin Report, including those in the Stekoa Creek Watershed, by December 31, 2000 and finalize these TMDLs within 120 days. Waters on the State’s 303(d) list that are located in the Savannah/Ogeechee Basins will be due for TMDL development again in 2004. According to the 1997 Consent Decree in the Georgia TMDL Lawsuit, TMDLs taking into consideration both point and nonpoint sources must be proposed by the State of Georgia on or before June 30, 2004 or by EPA on or before August 30, 2004. The TMDL developed in this document can then be revisited during these timeframes. Recommendations It is recommended that the Stekoa Creek watershed be considered a high priority for riparian buffer zone restoration and any sediment reduction BMPs, especially for the road crossings, agricultural activities, and 9 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 construction activities. Further ongoing monitoring needs to be completed to monitor progress and to assure further degradation does not occur. Upper Stekoa Creek Watershed – HUC 0306002001 Stekoa Creek Watershed A 75 percent sediment load reduction for Upper Stekoa Creek Watershed is needed to meet the estimated watershed sediment loading reduction target. The main contributors to the Stekoa Creek watershed sediment load are 1) surface loadings, mainly construction and crops causing forty percent of the loading and 2) roads causing sixty percent of the loading. To meet the proposed target, specific BMPs should be implemented for crops, construction and roads that reduce each of their respective sediment contributions. Scott Creek Watershed A 50 percent sediment load reduction for Scott Creek Watershed is needed to meet the estimated watershed sediment loading reduction target. The main contributors to the Scott Creek watershed sediment load are 1) surface loadings, mainly construction and crops causing twenty percent of the loading and 2) roads causing eighty percent of the loading. To meet the proposed target, specific BMPs should be implemented for crops, construction and roads that reduce each of their respective sediment contributions. Since roads are a major contributor, this should be a major BMP implementation area. Saddle Gap Creek Watershed A 77 percent sediment load reduction for Saddle Gap Creek Watershed is needed to meet the estimated watershed sediment loading reduction target. The main contributors to the Saddle Gap Creek watershed sediment load are 1) surface loadings, mainly construction and crops causing twenty percent of the loading and 2) roads causing eighty percent of the loading. To meet the proposed target, specific BMPs should be implemented for crops, construction and roads that reduce each of their respective 10 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 sediment contributions. Since roads are a major contributor, this should be a major BMP implementation area. Lower Stekoa Creek Watershed – HUC 0306002002 Chechero Creek Watershed A 50 percent sediment load reduction for Chechero Creek Watershed is needed to meet the estimated watershed sediment loading reduction target. The main contributors to the Chechero Creek watershed sediment load are 1) surface loadings, mainly construction and crops causing forty five percent of the loading and 2) roads causing fifty five percent of the loading. To meet the proposed target, specific BMPs should be implemented for crops, construction and roads that reduce each of their respective sediment contributions. Pool Creek Watershed A 15 percent sediment load reduction for Pool Creek Watershed is needed to meet the estimated watershed sediment loading reduction target. The main contributors to the Pool Creek watershed sediment load are 1) surface loadings, mainly construction and crops causing fifty percent of the loading and 2) roads causing fifty percent of the loading. To meet the proposed target, specific BMPs should be implemented for crops, construction and roads that reduce each of their respective sediment contributions. Figure 1 - Location of Stekoa Creek Watershed 11 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 C HAT O OG A R *A N W S E TA L S TE K OA C R *B AU CH LU Reach File, V 1 Wa ters hed Bo un d ar ies Catalo ging U nit Bou nd aries (0 30 6 01 02 ) PA R TU GA LO CR O R R E *C *F H NT LA H HA RTW ELL RES GA R 3 0 3 6 Mi le s F ig ur e 1- 1. Site Lo ca tio n M ap. ST EK OA CREE K Map Proj ec tion: Data Sourc es Albers Equal A rea GRS 80 U nknow n D ata Source 12 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Figure 2 - Watershed Tributaries 13 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Figure 3 – Land Use Distribution Landuse - Stekoa Creek Watersheds Roads Reach File, V3 Landuse Bare Soil & Construction Deciduous Forest Emergent Herb aceous Wetl ands Evergreen Forest High I ntensity Commercial/Industrial/Transportation High I ntensity Residential Low Intensity Residential Mixed Forest Open Water Other Grasses (Urban/recreatio nal; e.g. parks, lawns, g W Pasture/Hay Quarries/Strip Mines/Gravel Pits Row Crops & Const ruction Woody Wetlands No Data 3 0 3 6 Miles N E S 14 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Figure 4 – Road and Stream Network R oad s and Strea m s S tekoa _C reek R F3 R o ad_typ e S tate H yw C o u n ty Ro ad C ity R o ad s U n p aved R o ad s N o D ata W atersh e d .sh p W N E S 3 0 3 6 M ile s 15 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Appendix A: Biological and Habitat Data and Information Stekoa Creek Watershed Excerpts from “Assessment of Water Quality Conditions Chattooga River Watershed”, USEPA Region 4. 1999. Stekoa Creek The results of the analyses on Stekoa Creek at both SC01 and SC02 indicate that the designated uses of this stream are partially supported. The biological ranking was fair at both SC01 and SC02 indicating some impairment of the community. The biological community at both locations are impacted and community structure reflect the poor conditions of the stream. The results of the analyses indicate that the cause of the impairment is likely due to the increase in sediment which is primarily sands. The habitat rankings of both the RBP and Pfankuch indicated impacted habitat conditions at SC01. Some improvement in habitat was noted at SC02; however, the ranking was still in the fair range for the Pfankuch rating. The bottom substrate characteristics indicated that sand size and smaller particles were very prominent in this stream. Stekoa Creek is currently listed on Georgia EPD’s 303(d) list with fecal coliform being the pollutant of concern. Due to the impacted condition of the aquatic macroinvertebrate community, this stream should also be listed as partially meeting designated uses due to impairment of the biological community with the likely pollutant of concern listed as sediment. Five streams that are tributaries to Stekoa Creek were also sampled. Three of these streams showed adverse impacts to the biological community. Pool Creek and Saddle Gap Creek had fair ratings for the macroinvertebrate community and Chechero Creek rated poor at the sample station location. Scott Creek, Saddle Gap, and Chechero Creeks had fair RBP habitat ratings while Pool Creek had poor habitat conditions. Analysis of the sediments of the stream indicated that these streams also had substrates dominated by fine sediments and sand sized particles. The biological condition of Scott Creek was good; 16 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 however, due to habitat degradation, primarily related to the large amount of sand in the substrate, the designated use support is threatened. Based on the results of the analyses Stekoa Creek and the tributaries of Chechero Creek, Saddle Gap Creek, and Pool Creek are not fully supporting designated uses. Therefore, these streams should also be included on Georgia EPD’s 303(d) list with sediment listed as the pollutant of concern. Cutting Bone Creek was also sampled and the biological community was rated as good and the habitat was rated as good. However, observations of field personnel and sediment measures indicated that the stream substrate showed areas of increasing sediment deposits. The stream is recommended to be listed as fully supporting designated uses but placed on a “watch” list to provide increased attention to controlling sources of sediment inflow to the stream. 17 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Appendix B: Model Description and Sediment Modeling and Analysis Methodology Universal Soil Loss Equation The USLE, developed by Agriculture Research Station (ARS) scientists W. Wischmeier and D. Smith, has been the most widely accepted and utilized soil loss equation for over 30 years. Designed as a method to predict average annual soil loss caused by sheet and rill erosion, the USLE is often criticized for its lack of applications. While it can estimate long - term annual soil loss and guide conservationists on proper cropping, management, and conservation practices, it can not be applied to a specific year or a specific storm. The USLE is mature technology and enhancements to it are limited by the simple equation structure. However based on its long history of use and wide acceptance by the forestry and agriculture communities, it was selected as an adequate tool for estimating long-term annual soil erosion, for evaluating the impacts of landuse changes and evaluating the benefits of various Best management Practices (BMPs). The Sediment Tool, which incorporates the USLE equation, is an extension of the Watershed Characterization System (WCS). For more detailed information on WCS, refer to the WCS user’s manual. The Sediment Tool can be used to perform the following tasks: • • • Estimate extent and distribution of potential soil erosion in the watershed. Estimate potential sediment delivery to receiving waterbodies. Evaluate effects of land use, BMPs, and road network on erosion and sediment delivery. Soil loss from sheet and rill erosion is mainly due to detachment of soil particles during rainfall. It is the major soil loss from crop production and grazing areas, construction sites, mine sites, logging areas, and unpaved roads. The magnitude of soil erosion is normally estimated through the use of the Universal Soil Loss Equation (USLE). The USLE equation is a multiplicative function of crop and site specific 18 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 factors that represent rainfall erosivity (R), soil erodibility (K), soil slope (S), slope length (L), cropping or conservation management practices (C), and erosion control practices (P). The R factor describes the kinetic energy generated by the frequency and intensity of rainfall. The K factor represents the susceptibility of soil to erosion (i.e. soil detachment). The L and S factors represent the effect of slope length and slope steepness on erosion, respectively. The C factor represents the effect of plants, soil cover, soil biomass and soil disturbing activities on erosion including crop rotations, tillage and residue practices. Finally, the P factor represents the effects of conservation practices such as contour farming, strip cropping and terraces. The USLE equation for estimating average annual soil erosion is: A = RKLSCP • • • • • • A = average annual soil loss in t/a (tons per acre) R = rainfall erosivity index K = soil erodibility factor LS = topographic factor - L is for slope length & S is for slope C = cropping factor P = conservation practice factor Evaluating the factors in USLE: R - the rainfall erosivity index Most appropriately called the erosivity index, it is a statistic calculated from the annual summation of rainfall energy in every storm (correlates with raindrop size) times its maximum 30 - minute intensity. As expected, it varies geographically. 19 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 K - the soil erodibility factor This factor quantifies the cohesive or bonding character of a soil type and its resistance to dislodging and transport due to raindrop impact and overland flow. LS - the topographic factor Steeper slopes produce higher overland flow velocities. Longer slopes accumulate runoff from larger areas and also result in higher flow velocities. Thus, both result in increased erosion potential, but in a non - linear manner. For convenience L and S are frequently lumped into a single term. C - the crop management factor This factor is the ratio of soil loss from land cropped under specified conditions to corresponding loss under tilled, continuous fallow conditions. The most computationally complicated of USLE factors, it incorporates effects of: tillage management (dates and types), crops, seasonal erosivity index distribution, cropping history (rotation), and crop yield level (organic matter production potential). P - the conservation practice factor Practices included in this term are contouring, strip cropping (alternate crops on a given slope established on the contour), and terracing. Appropriate values for the USLE parameters should be provided for each of the management activities. 20 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Literature values are available, but site-specific values should be used when available. Estimates of the USLE parameters and thus the soil erosion as computed from the USLE equation are provided by the Natural Resources Conservation Service’s National Resources Inventory (NRI) 1994. The NRI database contains information of the status, condition and trend of soil, water and related resources collected from approximately 800,000 sampling points across the country. Soil loss from gully erosion occurs in sloping areas mainly as a result of natural processes. It is exacerbated by farming practices such as livestock grazing. Gullies are caused by the deepening of rill erosion. The amount of sediment yield from gully erosion is generally less than that caused by sheet and rill erosion. There are no exact methods or equations to quantify gully erosion, but Dunne and Leopold (1978) provide percent sediment yield estimates for various regions of the country. In a small grazed catchment near Santa Fe, New Mexico, gully erosion was found to contribute only 1.4 percent of the total sediment load as compared to sheet erosion and rainsplash, which contributed 97.8 percent of the sediment load. Dunne and Leopold report that in most cases (nationally and internationally) gully erosion contributes less than 30 percent of the total sediment load, although the percentages have ranged from 0 percent to 89 percent contribution (Dunne and Leopold, 1978). The soil losses from the erosion processes described above are localized losses and not the total amount of sediment that reaches the stream. The fraction of the soil losses in the field that is eventually delivered to the stream depends on several factors, which include the distance of the source area from the stream, the size of the drainage area, and the intensity and frequency of rainfall. Soil losses along the riparian areas are expected to be delivered into the stream with runoff-producing rainfall. Sediment Analysis The watershed sediment loads for selected watersheds are determined using the USLE and available GIS coverage. The sediment analysis produces the following outputs: • • Source Erosion and Sediment Stream Grid 21 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 • Sediment Delivery on Stream The sediment analysis also is able to evaluate default scenario by, for example, changing land uses and BMPs. The following are some of the parameters that may be altered: • • • • • C and P Lookup values Land Use Change Layer BMP Layers Add/Delete Roads Create Road Control Structure Layer The sediment analysis can be run for a single watershed or multiple watersheds. For TMDL development purposes the basic sediment analysis was used for developing relative impacts. Other applications are the evaluation of the effectiveness of BMPs and development of implementation plans. Sediment Modeling Methodology The watersheds of interest are delineated. The stream grid for each delineated watershed, based on the DEM data, is created so that the stream matches the elevation (i.e., the stream corresponds to the lower elevations in the watershed). The system uses this threshold to determine whether a particular grid cell corresponds to a stream. Grid cells having flow accumulation values higher than the threshold will be considered as part of the stream network. The RF3 stream network is used as a reference or basis of comparison to obtain the desired stream density. A stream grid corresponding to the stream network that has fifty 30 by 30 meter headwater cells is the default. For each 30 by 30 meter grid cell the potential erosion based on USLE and potential sediment delivery to the stream network is estimated. The potential erosion from each cell is calculated using the USLE and the sediment delivery to the stream network can be calculated using one of four available sediment 22 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 delivery equations. (1) Distance-based equation 1 (Sun and McNulty 1988) Md = M * (1 - 0.97 * D / L), L = 5.1 + 1.79 * M, where Md is the mass moved from each cell to the closest stream network(US tons/acre/yr); D (feet) is the least cost distance from a cell to the nearest stream network; and L (feet) is the maximum distance that sediment with mass M (US ton) may travel. (2) Distance-based equation 2 (Yagow et al. 1998) DR = exp (-0.4233 * L * Sf), Sf = exp (-16.1 * (r / L + 0.057)) - 0.6, where DR is the sediment delivery ration; L is the distance to stream in meters and r is the relief to stream in meters. (3) Area-based equation (converted from a curve from National Engineering Handbook by Soil Conservation Service 1983 DR = 0.417762 * A ^ (-0.134958) - 0.127097, DR <=1.0, where DR is the sediment delivery ratio and 23 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 A is area in square miles; (4) WEPP-based regression equation (L.W.Swift, Jr.,2000) Z=0.9004-0.1341*X-0.0465*X^2+0.00749*X^3-0.0399*Y+0.0144*Y^2+0.00308*Y^3, X>0,Y>0, where Z is percent of source sediment passing to next grid cell, X is cumulative distance downslope, Y is percent slope in grid cell. During the comment period for the proposed August 30, 2000 Stekoa Creek Watershed TMDL, EPA Region 4 and Georgia Environmental Protection Division (GaEPD) representatives have been attending a Sediment TMDL Technical Advisory Group (TAG) established by the Georgia Conservancy. One of the comments made by the TAG was the that 8 tons/year/square mile watershed sediment loading rate value included in the proposed TMDL as a target was too low and resulted in an unrealistic sediment runoff value. To better estimate the existing average annual sediment runoff, the following modeling changes were made: 3) The sediment delivery ratio methodology number 2 (the distance and relief sediment delivery method) was used instead of sediment delivery method number 4 (the WEPP based equation). See Appendix B for details. 4) The headwater area that defines a first order stream was decreased from 1 square mile to 0.5 square mile. These changes resulted in a revised biologically unimpacted stream’s watershed sediment loading rate per area average around 100 tons/year/square mile. A sediment loading rate per area of 90 tons/year/square mile was used as the target, this includes a 10 percent margin of safety. A percent reduction TMDL was developed by comparing the impacted watersheds sediment loading rate to the biologically unimpacted watersheds sediment loading rate. Note the percent reductions were approximately the same as those 24 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 proposed in the August 30, 2000 TMDL. The sediment analysis provides the calculations for six new parameters. • • • • Source Erosion – estimated erosion from each grid cell due to the land cover Road Erosion – estimated erosion from each grid cell representing a road Composite Erosion – composite of the source and road erosion layers Source Sediment – estimated fraction of the soil erosion from each grid cell that reaches the stream (sediment delivery) • Road Sediment – estimated fraction of the road erosion from each grid cell that reaches the stream • Composite Sediment – composite of the source and erosion sediment layers The sediment delivery can be calculated based on the composite sediment, road sediment, or source sediment layer. The sources of sediment by each land use type is determined showing the types of land use, the acres of each type of land use, and the tons of sediment estimated to be generated from each land use Sediment Analysis Inputs Before conducting a sediment analysis, a number of data layers must be available. These include the following: • DEM (grid) – The DEM layers that come with the WCS distribution system are shapefiles and are of coarse resolution (300x300 m). The user needs to import a DEM grid layer. A higher resolution DEM grid layer (30x30 m) was downloaded from USGS web site or from a state’s GIS data clearinghouse • Road – The road layer is needed as a shape file and requires additional attributes such as C 25 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 (road type), P (road practice) and ditch (value of either 3 or 4, indicating presence or absence of side ditch, respectively). If these attributes are not provided, the Sediment Tool automatically assigns default values of road type 2 (secondary paved roads) ditch 3 (with ditch) and road practice 1 (no practices). • SSURGO Soil – The SSURGO (1:24k) soil data may be imported into the WCS project if higher-resolution soil data is required for the estimation of potential erosion. If the SSURGO soil database not available, the system uses the STATSGO Soil data (1:250k) by default. • • The Multi-Resolution Land use Classification (MRLC) data are also used. Rainfall erosivity index is either provide based on a rainfall index of the USA or can be calculated based on precipitation data. The Universal Soil Loss Equation (USLE) R, K, LS, C, and P factors are calculated from the above data as follows: A = RKLSCP • • • • A = average annual soil loss in t/a (tons per acre) is calculated. R = rainfall erosivity index is provide based on a rainfall index of the USA. K = soil erodibility factor calculated based on soil types. LS = topographic factor - L is for slope length set at 30 meters and S is for slope calculated based on the 30 meter DEM data. Presently a watershed average LS term is used. • • C = cropping factor or land use factor. P = conservation practice factor or BMP implementation. 26 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Sediment TMDL Development Methodology For each watershed of interest, the “existing” long – term sediment loading is estimated via the USLE sediment analysis, using default parameters and estimated C and P values. The USLE is designed as a method to predict average annual soil loss caused by sheet and rill erosion. While it can estimate long term annual soil loss and guide on proper cropping, management, and conservation practices, it cannot be applied to a specific year or a specific storm. The resultant sediment TMDL calculation for each watershed is therefore expressed as a long - term annual soil loss expressed in tons per year calculated for the R - the rainfall erosivity index, a statistic calculated from the annual summation of rainfall energy in every storm (correlates with raindrop size) times its maximum 30 - minute intensity. The watershed sediment TMDL target is based on the long - term annual soil loss expressed in tons per year calculated for relatively unimpacted watershed with demonstrated healthy biology and habitat. For the initial TMDL development consistent default parameters and inputs are used for each watershed. These include the MRLC land use data, the USGS DEM data, STASTGO soil information and watershed average C and P values for each land use type. The long - term annual soil loss calculated by the Sediment Tool analysis will be compared, in the future, to this equation and the estimated annual average sediment load, along with the steady flow and storm event sediment data collected by EPA in 1998, 1999 and 2000. The Load Allocation (LA) for each watershed will be estimated for each land use source or other sediment sources. 27 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Appendix C: Numeric Sediment Target Determination The following provides the projected watershed sediment loads for the monitored streams in the Stekoa Watershed. Stekoa Watershed Scott Creek Stekoa above Clayton Saddle Gap Creek Chechero Creek Pool / She Creek Cutting Bone Creek Stekoa @ Boggs Mt Rd. Station ID SC-04 SC-01 SC-07 SC-06 SC-05 SC-03 SC-02 Watershed (Ton/Year) 205 319 205 342 257 56 3030 Road (Ton/Year) 873 467 873 395 247 93 4425 Area (Sq.Mi.) 6.1 1.7 2.7 4.2 4.8 2.1 21.3 Total Area Weighted (Ton/Year) (Ton/Year/Sq.Mi.) 1078 177 786 461 1078 392 737 175 504 106 149 71 7455 351 Comparing the Stekoa Watershed and the Warwoman Watershed (adjoining similar watershed) projected existing sediment loads to the Use Support Evaluation, an average projected sediment watershed load of 100 tons/year/sq.mi. relates to a relatively unimpacted watershed. The Use Support Evaluation is based on the EPA Rapid Biological Procedures for determining wadeable stream biological and habitat conditions. Stekoa Watershed Station ID Ton/Year/Sq.Mi. Use Support Rating 2 2 4 3 2 1 2 Biological Rating 2 2 2 3 2 1 2 RPB Habitat Rating 2 3 2 2 1 2 2 Stekoa above Clayton Stekoa @ Boggs Mt Rd. Cutting Bone Creek Scott Creek Pool / She Creek Chechero Creek Saddle Gap Creek Warwoman Watershed WarWoman Creek @ Black Diamond Rd Warwoman Creek @ Warwoman Ford Martin / Finney Creek Roach Mill Creek Tuckaluge Creek Hoods Creek SC-01 SC-02 SC-03 SC-04 SC-05 SC-06 SC-07 461 351 71 177 106 175 392 WW-01 WW-02 WW-03 WW-04 WW-05 WW-06 125 104 92 162 103 108 2 4 4 2 4 4 2 3 3 2 3 4 1 3 3 2 3 3 28 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Walnut Fork Sarah's Creek Morsingills Creek Goldmine Branch WW-07 WW-08 WW-09 WW-10 65 51 110 100 4 4 3 3 4 3 3 3 4 3 1 1 Use Support Ratings and Projected Sediment Yield Sediment Yield (tons/year/sq.mi.) Saddle 500 400 300 200 100 0 Chechero 5 4 3 2 1 0 Morsingills Pool / She Roach Mill Warwoman Martin / Walnut Stream Name 29 Use Support Rating (Dashed Line) Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Appendix D: EPA’s “Protocol for Developing Sediment TMDLs” Excerpts from EPA’s “Protocol for Developing Sediment TMDLs”, October 1999 • The traditional approach to TMDL formulation is to identify the total capacity of a waterbody for loading of a specific pollutant while meeting water quality standards. This loading capacity is not to be exceeded by the sum of pollutant loads allocated to individual point sources, nonpoint sources, and natural background. Therefore, TMDLs have often been expressed in terms of maximum allowable mass load per unit of time. However, alternative approaches to sediment TMDL analysis might also be appropriate. In many cases, it is difficult or impossible to relate sediment mass loading levels to designated or existing use impacts or to source contributions. These analytical connections can be difficult to draw for several reasons, including the following: Sediment yields vary radically at different spatial and temporal scales, not only within a watershed, but across the country, making it difficult to derive meaningful “average” sediment conditions. Sediments are a natural part of all waterbody environments, and it can be difficult to determine whether too much or too little mass loading is expected to occur in the future and how sediment loads compare to natural or background conditions. A significant level of uncertainty is associated with sediment delivery, storage, and transport estimates. Fortunately, it is acceptable for TMDLs to be expressed through appropriate measures other than mass loads per time (40 CFR 130.2). It is important to note, however, that some of the limitations associated with mass load approaches, such as high temporal variability, are also present in the alternative approaches and the consequences of these limitations should be assessed and acknowledged. The alternative measures for sediment TMDLs can take several forms, including the following: o Expression of numeric targets in terms of substrate or channel condition, aquatic biological indicators, or hillslope indicators such as road stream crossings with diversion potential or road culvert sizing. The hillslope indicators and targets should complement in-stream indicators and targets. o Expression of numeric targets and source allocations in terms of time steps different from 30 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 daily loadings and as functions of other watershed processes such as precipitation or runoff. o Expression of allocations in terms other than loads or load reductions (e.g., specific actions shown to be adequate to result in attainment of TMDL numeric targets and water quality standards). Some erosion occurs in all watersheds, even those which are completely undisturbed. Some watershed types are extremely prone to periodic major sedimentation events. Designated uses located in such settings have often adapted to naturally high sediment conditions. TMDLs need to distinguish sedimentation rates associated with human activities in the study watershed from those associated with naturally occurring (and presumably uncontrollable) sediment sources. Human land management activities can change the magnitude, locations, and timing of land erosion or runoff events as well as the key physical characteristics of receiving waters. Methods sensitive to changes in the driving forces that influence sedimentation (e.g., models like RUSLE, HSPF, and WRENSS) will be useful in comparing natural and anthropogenic sources if data about key processes are available for the TMDL study area and reference watersheds. Methods that estimate sediment loading or yields as a function of sediment concentration and streamflow (e.g., rating curves) are less useful in evaluating how existing sedimentation rates differ from natural sedimentation rates. Where rating curve methods are used, careful comparison to reference watersheds (and the underlying differences in land use or land characteristics) can assist in comparing natural and human-caused sedimentation. A sediment budget is an “accounting of the sources and disposition of sediment as it travels from its point of origin to its eventual exit from a drainage basin” (Reid and Dunne, 1996). Sediment budget analyses are useful both for the conceptualization of sediment problems and as a tool for estimating sediment loadings. Full-scale sediment budgeting provides an inventory of the sources of sediment in a watershed and estimates sediment production and delivery rates from each source. Component processes are identified, and process rates are usually evaluated independently of one another. All of the relevant processes are quantified, including hillslope delivery processes (creep, mass movement), channel sources (e.g., bank collapse), in-channel storage, bedload and suspended sediment transport capacity, and net sediment yield from the basin. If the effects of particular land use activities on each process are known, 31 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 the overall influence of a suite of existing or planned land use activities can be estimated. One method for establishing target values is comparison to reference sites—waterbodies that are representative of the characteristics of the region and subject to minimal human disturbance. Where narrative standards are involved, assessing environmental conditions in receiving waters often depends on comparing observed conditions to expected conditions. This comparison is typically done by comparing data collected from impaired sites to similar data from the same sites collected before impairment and/or from one or more appropriate reference sites where designated uses are in good condition. Conditions at the reference site (e.g., suspended sediment concentrations) can then be interpreted as approximate targets for the indicators at the impaired site. A disadvantage to this approach is that it might not aid in determining an impairment threshold. Reference sites may represent the completely unaffected state, a relatively unaffected state, or increasing degrees of existing impact. 32 Final Sediment TMDL: Stekoa Creek Watershed December 28, 2000 Appendix D: References and Administrative Record Index Rules and Regulations for Water Quality Control, Chapter 391-3-6-.03, Water Use Classifications and Water Quality Standards, July 2000 Sierra Club v. EPA & Hankinson USDC-ND-GA Atlanta Div. #1: 94-CV-2501-MHS, 1998 USEPA. 1991. Guidance for Water Quality-based Decisions: The TMDL Process. U.S. Environmental Protection Agency, Office of Water, Washington, D.C. EPA/440/4-91-001, April 1991. USEPA Region 4. 1999a. “Assessment of Water Quality Conditions Chattooga River Watershed” USEPA. 1999b. “Protocol for Developing Sediment TMDLs, First Edition” USEPA Region 4. 2000a. Total Maximum Daily Load (TMDL) Development for Sediment in the Stekoa Creek Watershed. May 2000 USEPA Region 4. 1999. Chattooga River Watershed Hydrologic / Sedimentation Study. Bruce A. Pruitt, U.S. Environmental Protection Agency, Region 4 Science and Ecosystem Support Division. April 1999 Vanlear 1995. “Sedimentation in the Chattooga River Watershed” Technical Paper No. 19. Clemson University. Vanlear, Taylor and Hansen. 33