SWAT and HSPF differ in their spatial discretization and hydrological process representations.
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Peer-reviewed literature demonstrates that SWAT and HSPF differ in their spatial discretization, such as SWAT being a semi-lumped model, and in their hydrological process representations, including differing capabilities for agricultural practices and plant growth modeling.
Watershed-scale nonpoint source (NPS) pollution models have become important tools to understand, evaluate, and predict the negative impacts of NPS pollution on water quality. Today, there are many NPS models available for users. However, different types of models possess different form and structure as well as complexity of computation. It is difficult for users to select an appropriate model for a specific application without a clear understanding of the limitations or strengths for each model or tool. This review evaluates 14 more commonly used watershed-scale NPS pollution models to explain how and when the application of these different models are appropriate for a given effort. The models that are assessed have a wide range of capacities that include simple models used as rapid screening tools (e.g., Long-Term Hydrologic Impact Assessment (L-THIA) and Nonpoint Source Pollution and Erosion Comparison Tool (N-SPECT/OpenNSPECT)), medium-complexity models that require detail data input and limited calibration (e.g., Generalized Watershed Loading Function (GWLF), Loading Simulation Program C (LSPC), Source Loading and Management Model (SLAMM), and Watershed Analysis Risk Management Frame (WARMF)), complex models that provide sophisticated simulation for NPS pollution processes with intensive data and rigorous calibration (e.g., Agricultural Nonpoint Source pollution model (AGNPS/AnnAGNPS), Soil and Water Assessment Tool (SWAT), Stormwater Management Model (SWMM), and Hydrologic Simulation Program Fortran (HSPF)), and modeling systems that integrate various sub-models and tools, and contain the highest complexity to solve all phases of hydrologic, hydraulic, and chemical dynamic processes (e.g., Automated Geospatial Watershed Assessment Tool (AGWA), Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) and Watershed Modeling System (WMS)). This assessment includes model intended use, components or capabilities, suitable land-use type, input parameter type, spatial and temporal scale, simulated pollutants, strengths and limitations, and software availability. Understanding the strengths and weaknesses of each watershed-scale NPS model will lead to better model selection for suitability and help to avoid misinterpretation or misapplication in practice. The article further explains the crucial criteria for model selection, including spatial and temporal considerations, calibration and validation, uncertainty analysis, and future research direction of NPS pollution models. The goal of this work is to provide accurate and concise insight for watershed managers and planners to select the best-suited model to reduce the harm of NPS pollution to watershed ecosystems.
detailed sediment processes implemented in HSPF makes it a suitable tool for addressing the instream portion of the Conestoga River system. HSPF does not contain an integral plant growth model, nor does it provide a library of agricultural cropping, tillage, and fertilization practices, making it a less attractive tool for assessing upland agricultural sources.
In response to these strengths and limitations, we developed a linked SWAT-HSPF watershed modeling system for the Conestoga River watershed building on the strengths of both models. Simulation of flow and sediment loads from upland sources were accomplished using SWAT, while routing of flow and simulation of sediment processes in the stream system were completed using the HSPF model. Simulations using the linked SWAT-HSPF model were completed at a daily time-step. Instream scour and deposition processes vary considerably on a sub-daily level. The daily time-step model adopted here is therefore not optimal for detailed scour and deposition analysis of individual millponds. The approach adopted in this study is however useful in predicting net scour at the watershed scale and the relative magnitudes of scour among millpond reaches. METHODS
Model Development
Spatial datasets required for the development of a SWAT model are a digital elevation model (DEM), landuse/landcover, and soils. We developed the SWAT model for the Conestoga River watershed in the ArcSWAT interface version 12.1 ( Winchell et al. 2013 ). SWAT is a semi-lumped model in which unit-area responses are combined to produce a total subwatershed response. The unit-area components are referred to as hydrologic response units (HRUs), which are unique combinations of landuse, soil characteristics, and slope class in a subbasin. We used the Chesapeake Bay Watershed Land Cover Data Series 2001 (U.S. Geological Survey [USGS], http://www.pasda.psu.edu/uci/DataSummary.aspx?dataset=1332 , Accessed October 2015) to represent landuse in the watershed model (sh
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