Sediment and Nutrient Modeling for TMDL Development and Implementation

Abstract

At present, there are over 34,000 impaired waters and over 58,000 associated impairments officially listed in the U.S. Nutrients and sediment are two of the most common pollutants included in the list. States are required to identify and list those waters within their boundaries that are not meeting standards, to prioritize them, and to develop Total Maximum Daily Loads (TMDLs) for the pollutants of concern. Models are used to support development of TMDLs, typically to estimate source loading inputs, evaluate receiving water quality, and determine source load allocations so that receiving water quality standards are met. Numerous models are available today, and selection of the most suitable model for a specific TMDL project can be daunting. This article presents a critical review of models simulating sediment and nutrients in watersheds and receiving waters that have potential for use with TMDL development and implementation. The water quality models discussed, especially those with sediment and/or nutrient components, include loading models (GWLF and PLOAD), receiving water models (AQUATOX, BATHTUB, CE-QUAL-W2, QUAL2E, and QUAL2K), and watershed models having both loading and receiving components (AGNPS, AnnAGNPS, CASC2D/GSSHA, DWSM, HSPF, KINEROS2, LSPC, MIKE SHE, and SWAT). Additional models mentioned include another receiving water quality model (WASP), watershed models (ANSWERS storm event, ANSWERS continuous, PRMS storm event, SWMM, and WEPP), and BMP models (APEX, REMM, and VFSMOD). Model sources, structures, and procedures for simulating hydrology, sediment, and nutrients are briefly described for the reviewed models along with an assessment of their strengths, limitations, robustness, and potentials for using in sediment and/or nutrient TMDLs. Applications of AGNPS, APEX, BATHTUB, CE-QUAL-W2, GWLF, and SWAT in TMDL developments are presented. Applications of some of the other models (DWSM, GSSHA, and KINEROS2) relevant to TMDL studies are also presented. The models proved to be useful; however, they require a learning process. Simple models are easy to use but have limitations; comprehensive models are labor and data intensive but offer extensive analysis tools. Finally, recommendations are offered for advancing the sediment and nutrient modeling technologies as applied to TMDL development and implementation. Advances could be made towards: making the best use of existing models, enhancing the existing models, combining strengths of existing models, developing new models or supplemental components with physically based robust routines, numerous field applications, sensitivity analyses, full documentation, and rigorous education and training.

Applications of the SWAT Model Special Section: Overview and Insights

“…These models are designed to operate across a range of scales (e.g., field versus watershed) and environmental conditions, and with varying levels of input data and model structure complexity. Dozens of review studies have been compiled that provide comparisons of either specific components or complete modeling packages for various subsets of existing water quality models (e.g., Borah et al, 2006;Breuer et al, 2008;Refsgaard et al, 2010;Daniel et al, 2011).…”

“…These models are designed to operate across a range of scales (e.g., field versus watershed) and environmental conditions, and with varying levels of input data and model structure complexity. Dozens of review studies have been compiled that provide comparisons of either specific components or complete modeling packages for various subsets of existing water quality models (e.g., Borah et al, 2006;Breuer et al, 2008;Refsgaard et al, 2010;Daniel et al, 2011).The Soil and Water Assessment Tool (SWAT) model (Arnold et al, 1998;Williams et al, 2008) has emerged as one of the most widely used water quality watershed-and river basin-scale models worldwide, representing multiple decades of model development (Gassman et al, 2007;Williams et al, 2008;Arnold et al, 2012b). The model is supported by online documentation (Neitsch et al, 2011;Arnold et al, 2012a), multiple geographic information system (GIS) interface tools (e.g., Di Luzio et al, 2004;Olivera et al, 2006), other supporting software (e.g., White et al, 2014aWhite et al, , 2014c, and online resources (SWAT, 2013).…”

Comparison of three regionalization techniques for predicting streamflow in ungaged watersheds in Nebraska, USA using SWAT model

“…High-speed computer and Geographical Information System (GIS) technological advances during the past three decades have led to the development of a host of ecohydrological watershedsimulation models [1][2][3][4] . These models have the capability to address a range of water resource and water quality issues such as water availability and allocation, the impact of climate and land use change, and the implementation of best management practices.…”

Using AnnAGNPS to Predict the Effects of Tile Drainage Control on Nutrient and Sediment Loads for a River Basin

“…Hydrological models are often used to examine net effects associated with beneficial management practices (BMPs) at watershed scales (e.g., USEPA, 1997;Borah et al, 2006;Santhi et al, 2006;Yuan et al, 2006a). A majority of the modeling studies that examine the implication of tile drainage control at watershed scales focus on nitrogen (N) (Thorp et al, 2008;Jaynes et al, 2010;Luo et al, 2010;Yuan et al, 2011;Ale et al, 2012), and some have addressed phosphorus (P) (Deal et al, 1986).…”