Development and Application of Watershed Models for Simulation and Management of Nonpoint Source PollutantsSlide Number 2Extent of ProblemSlide Number 4Slide Number 5Slide Number 6Hydrologic ModelsHydrologic Models Physically-Based Distributed Parameter Modeling Approach Physically-based distributed parameter Modeling ApproachWhat is GSSHA?Gridded Surface Subsurface Hydrologic Analysis (GSSHA)How does GSSHA Work?GSSHALand Use ChangeSpatial Hydrology: Dealing with Runoff Processes ChangesStorm and Tile DrainsDead Run CreekDrainage NetworksResultsWetland ModelSediment TransportOverland Sediment TransportContinuous SimulationsConstituent Transport GSSHA and WMSWMS OverviewWatershed ModelingSlide Number 29Hawaii Training Ranges EIS/TMDL Program ObjectivesEvaluation MethodsTransport of Sorbed Materials in Isolated HotspotsFurther InformationQuestionsWatershed Management And ModelingDevelopment and Application of Watershed Models for Simulation and Management of Nonpoint Source PollutantsCharles W. DownerCoastal and Hydraulic LaboratoryBilly E. JohnsonEnvironmental LaboratoryEngineer Research and Development CenterWatershed Management And ModelingNon-point Source Pollution According to the US EPA, non-point source pollution (NPSP) Comes from many diffuse sources.  Caused by rainfall or snowmelt moving over and through the ground.  As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water.  These pollutants include: Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas. Oil, grease, and toxic chemicals from urban runoff and energy production; Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks; Salt from irrigation practices and acid drainage from abandoned mines; Bacteria and nutrients from livestock, pet wastes, and faulty septic systemsWatershed Management and ModelingExtent of Problem In it’s 2004 Water Quality Inventory Report to Congress, the USEPA reported. A large portion of the nations water bodies do not meet water quality standards 44% river miles 64% ponds, lakes, and reservoirs 30% of estuauries Water quality impairment attributed to NPSP constitutes a large percentage of the impaired water bodies 65% of river miles 30% of ponds, lakes and reservoirs 40% of estuariesWatershed Management And ModelingSources of Non-Point Source Pollution Urban development Agriculture Land disturbance Construction Military training Timber harvest Fire Natural causesWatershed Management And ModelingPrograms Related to Control of NPSP TMDL Process – Total Maximum Daily Loading Intended to allow states to meet water quality standards The total loading that will allow water quality standards to be met for a given body of water is determined. The total loading is attributed to various sources and land owners. The reduction in total loading needed to meet the water quality standards is also determined. This determines the amount of reduced loading from each source and/or land owner. The EPA, state, land owners develop an implementation plan that will result in the water quality standards being met. Low Impact Development (LID) Development is conducted in a way to minimize the effects of urbanization on hydrology and water quality. Water/sediments/pollutants are captured near their source with various management practices – rain barrels, porous pavement, detention basins, etc.Watershed Management And ModelingConsiderations in Modeling NPSP Sources are unevenly distributed on land surface Hot spots Flow path is important Loss of water and constituents along flow path Infiltration Decay Transformation Exchange with land surface Increased hydraulic efficiency shortens flow paths and reduces loses Streams Canals Subsurface pipe networks  To asses the effects of potential changes to the system, such as future land use change or best management practices a physically-based modeling approach is preferred.Watershed Management And ModelingHydrologic ModelsLumped ModelsProcessingInputOutputKnownUnknownOutflowwPrecipitationWatershed ResponseWatershed Management And ModelingHydrologic ModelsDistributed Models Fine scale physical processes are simulated at element level Plant interception Infiltration Runoff Evapo-transpiration Elemental responses are integrated to determine system responseWatershed Management And ModelingPhysically-Based Distributed Parameter Modeling Approach Physical Bases Allows use of the model with minimal calibration data Allows extension of the model beyond the range of calibration. Distributed Approach Incorporates spatial heterogeneity of watershed features  Provides fine scale information for project analysis Provides Tool for analysis of watersheds at fine time and space scalesA compliment to simpler models which may be used to identify areas that need more rigorous studyWatershed Management And ModelingPhysically-based distributed parameter Modeling Approach Spatially varied heterogeneity Explicitly resolve features in the grid Land use Soil type Depressions BMPs Roads Wetlands Track fate of water, sediment, contaminants along flow path Infiltration along path Settling/erosion along path Reactions along pathWatershed Management And ModelingWhat is GSSHA? GSSHA is a complete watershed simulation and management model used for hydrologic, hydraulic, sediment and quality simulation and management. GSSHA is a fully distributed, physics based model that utilizes a grid to represent the watershed. GSSHA is a product of the US Army ERDC Maintained Supported Distributed GSSHA is a direct descendent of the surface water hydrologic model CASC2D developed at Colorado State University. The original version of GSSHA is the result of my dissertation work at University of Connecticut.Downer, C. W. Identification and Modeling of Important Stream Flow Producing Processes in Watersheds, PhD Dissertation, University of Connecticut, 2002.Watershed Management And ModelingGridded Surface SubsurfaceHydrologic Analysis (GSSHA)Watershed Management And ModelingHow does GSSHA Work? GSSHA works on a uniform spatial