United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory Research Abstract Government Performance Results Act (GPRA) Goal 2 Annual Performance Measure 284 Significant Research Findings: MODELING PROTOCOLS FOR DEVELOPING SEDIMENT TMDLs Scientific Computing a TMDL can be challenging because of the differences between point and Problem and nonpoint source loadings of contaminants (i.e., stressors) to receiving waters. Policy Issues Temporally, point source loadings are usually continuous in time, while most nonpoint source loadings occur intermittently (e.g., during and immediately after runoff-generating events). Spatially, point source loadings are mass fluxes of contaminants that enter receiving waters at discrete, easily identifiable locations, typically conveyed to the receiving waters through conduits, e.g., pipes, storm water drains. By contrast, nonpoint source loadings are mass fluxes of contaminants that enter receiving waters as line sources (e.g., eroding banks along streams/rivers; runoff, transporting contaminants, flowing directly into surface waters along the shorelines of the water bodies) or area sources (e.g., upward flux of contaminated groundwater through the hyporheic zone; downward flux of airborne contaminants via both dry and wet atmospheric deposition). Sediments are listed as a nonpoint source contaminant or stressor in some water bodies in that they can cause impairment to the designated uses of these waters. Designated uses of surface waters include, but are not limited to, potable water supply to nearby municipalities, fisheries, and recreational use (e.g., swimming, boating, fishing). In the latest National 303(d) list, ""sediment/siltation" is the third most listed type of impairment, pathogens and metals being the first and second impairment, respectively. There are three other sediment-related impairments listed - suspended solids, turbidity, and stream bottom deposits. If all four of these sediment-related impairments are combined, then sediment moves to the top of the impairment list. This observation emphasizes the magnitude of the sediment-related problems in our nation's surface waters. Most types of sediment-related impairments result from excessive quantities of sediments entering a given water body or reach (i.e., section) of the water body. However, both too much and too little sediment can negatively impact the biological health of a water body. Excessive sedimentation can result in degradation of the aquatic habitat by covering stream/riverbeds with fine sediment. Too little sediment (i.e., sediment starved) can result in erosion of banks and river beds; the latter processes can eventually lead to a change in the morphology of the water body that in turn will affect the hydraulics of the flow and subsequently the sediment transport. ------- This modeling protocol supplements the document entitled "Protocol for Developing Sediment TMDLs" prepared by the USEPA's Office of Water (USEPA 1999). The stated objective of that report was to "provide EPA regions, states, territories, and tribes with an organizational framework for establishing TMDLs for sediment". The more detailed discussion of two components of a sediment TMDL that is included in this report (i.e., sediment source assessment and linkage of water quality indicators/targets and sources) provides needed guidance to EPA regions, states, territories, and tribes in performing these two critical components of a sediment TMDL. The developed modeling protocols consist of specific procedures recommended for performing sediment source assessment and linkage of water quality indicators/targets and sources. Two new sediment transport models, EFDC1D and GSTARS-1D, are included in these recommended protocols. Results and The recommended modeling protocols for developing sediment TMDLs and the Impact accompanying new sediment transport models, will be made available to the States, Tribes and EPA Regions. Sediment TMDLs developed using the guidance provided in USEPA (1999) and in this report should be more scientifically accurate. The modeling protocols provide specific guidance for performing source assessment and linkage of water quality indicators/targets to sources, both of which are defined below. Source assessment: determines the sources of the sediment that are causing the impairment to the listed water body. The assessment needs to include, at a minimum, the type of sediment (e.g., cohesive or noncohesive sediment) and quantity of sediment being supplied to the water body, and the source(s) of the sediment (e.g., banks, sediment beds, roads that parallel or cross the water body, including sources from outside the riparian zone, such as land development in the source watershed). Specific guidance is provided in the protocols for performing this assessment. Linkage of water quality indicators/targets and sources: determines the linkage that defines the cause-and-effect relationship between the identified sediment sources and the impairment caused by the sediment. The step also includes estimation of the loading capacity. The protocols include guidance on deciding the appropriate level of analysis, and if modeling is required, further detailed guidance is provided on which type of model(s) should be used. Two new ID sediment transport models that can be used to develop the linkage in streams and low order rivers were developed as part of this research. A brief description of these models is given below. EFDC1D: Thisisanew 1-D hydrodynamic and sediment transport model that can be applied to stream networks (Hamrick 2001). The model code, two sample data sets, and the User Manual are included on the distribution CD in Hayter el al. (2001). Some of the model's capabilities are: Research Approach 1. Simulation of bi-directional unsteady flows and the ability to accommodate ------- unsteady inflows and outflows associated with upstream inflows, lateral inflows and withdrawals, groundwater/surface water interaction, evaporation, and direct rainfall. 2. Representation of hydraulic structures such as dams and culverts. 3. Simulation of cohesive and noncohesive sediment transport, including settling, deposition, and resuspension of multiple size classes of cohesive and non-cohesive sediments. 4. The sediment bed is represented by multiple layers of mixed sediment classes. 5. A bed consolidation model is used to predict time variations of bed depth, void ratio, bulk density, and shear strength. 6. The sediment bed representation is dynamically coupled to the cross- sectional area representation to account for area changes due to deposition and resuspension. GSTARS-1D: This is a hydraulic and sediment transport numerical model developed to simulate flows in rivers and channels with or without movable boundaries. Some of the model's capabilities are: 1. Computation of water surface profiles in a single channel or channel networks. 2. Steady and unsteady flows, with subcritical flows in steady hydraulic simulations, and subcritical, supercritical, and transcritical flows in unsteady simulations. 3. Steady and unsteady sediment transport models. 4. Transport of cohesive and noncohesive sediments simultaneously. 5. Cohesive sediment aggregation, deposition, erosion, and consolidation. 6. Many different non-cohesive sediment transport equations that are applicable to a wide range of hydraulic and sediment conditions. 7. Floodplain simulation, with simulated exchange of water and sediment between main channel and floodplains. 8. Fractional sediment transport, bed sorting, and armoring. 9. Computation of width changes using the theory of stream power minimization and other minimizations. 10. Point and non-point sources of flow and sediments. 11. Internal boundary conditions, such as time-stage tables, rating curves, weirs, bridges, and radial gates. A three-year IAG with the U.S. Bureau of Reclamation funded the development and testing of GSTARS-1D. A Work Assignment with Tetra Tech, Inc. funded the development of EFDC ID. Publications from these extramurally funded projects are: Hayter, E. J., J. M. Hamrick, B. R. Bicknell, and M. H. Gray. 2001. "One- Dimensional Hydrodynamic/Sediment Transport Model for Stream Networks," Technical Report EPA/600/R-01/072. EPA Ecosystems Research Division, Athens, Georgia. Research Collaboration and Research Products Hamrick, J. 2001. "EFDC ID, A One Dimensional Hydrodynamic and Sediment ------- Transport Model for River and Stream Networks - Model Theory and Users Guide," Tetra Tech, Inc., Fairfax, Virginia. Yang, C. T., J. Huang, B. P. Greimann. 2004. "User's Manual for GSTARS-1D 1.0 (Generalized Sediment Transport model for Alluvial River Simulation - One Dimensional Version 1.0)," U.S. Bureau of Reclamation, Denver, CO. Future Research The ID sediment transport models developed as part of this research are currently being applied to 12-Mile Creek, SC, which is atributary to Lake Hartwell, GA. One purpose of these modeling applications is to investigate the abilities of the models to simulate the impact of dam removal on the sediment deposit behind the dams. The ERD database for the South Fork Broad River, GA, is currently being evaluated for the requisite data needed to test these models. CSED-2D, Version 2 (formerly named HSCTM-2D), is scheduled for release in FY 2005 through the Center for Exposure Assessment Modeling (CEAM). This is atwo- dimensional (depth-integrated) model that predicts the transport of both cohesive and noncohesive sediment in nonstratified water bodies. EFDC (described in Section 5 ofthe report) is a three-dimensional hydrodynamic and sediment transport model. It is scheduled to be released through the CEAM in FY2005 as well. In FY2008, a first principles-based, two-dimensional riverine geomorphological model is scheduled to be released. Pending available funding, the development of this model will start in FY 2005. Questions and inquiries can be directed to: Earl J. Hayter, Ph.D. U.S. EPA, Office of Research and Development National Exposure Research Laboratory 960 College Station Road, Athens, GA 30605-2700 Phone: 706.355.8303 E-mail: hayter.earl@epa.gov Funding for this project was through the U.S. EPA's Office of Research and Development, National Exposure Research Laboratory, and the work was conducted by the Ecosystems Research Division. Contacts for Additional Information ------- |