TMDL Watershed Analysis with the Physics-Based Hydrologic, Sediment Transport, and Contaminant Transport Model GSSHA

The Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) model has been developed with research funding from the US Army, the US Environmental Protection Agency (EPA), US Army Corps of Engineer (USACE) civil research programs (LMS and SWWRP), and with funding for civil and military applications to fill an existing need; GSSHA has the ability to explicitly simulate spatially-varied hydrologic processes to solve a variety of common engineering problems. The GSSHA model features two-dimensional overland flow, sediment and water quality transport, coupled to one-dimensional stream flow, sediment and water quality transport, integrated with two-dimensional groundwater flow. GSSHA simulation times can be minimized by running GSSHA on parallel architectures, such as 64-bit multi-processor PCs, or any shared memory resource. Model setup and post-processing are greatly aided by the DoD Watershed Modeling System (WMS). Recent additions/improvements to the GSSHA model include: subsurface pipe networks for urban and agricultural drainage, improved sediment erosion and transport, simulation of wetlands, lakes, and reservoirs, and coupling of GSSHA to the Nutrient Sub-Module (NSM) to allow complex interaction among nitrogen and phosphorous species, with the intent to add more contaminants as modules are developed. GSSHA has been used for analysis and prediction of a wide range of issues and measures including: surface water runoff, soil moisture, groundwater recharge, transport of sediments and associated contaminants, transport of volatile contaminants, management of military training lands, and effects of urbanization on runoff and sediment loading. This paper focuses on improvements of the GSSHA erosion source and sediment transport routines.