WATERSHED-SCALE HYDROLOGIC AND NONPOINT-SOURCE POLLUTION MODELS: REVIEW OF APPLICATIONS

TLDR

Three watershed‑scale hydrologic and nonpoint‑source pollution models—SWAT, HSPF, and DWSM—were chosen from a review of eleven models, each comprising hydrology, sediment, and chemical components, with SWAT and HSPF requiring extensive data and calibration while DWSM relies on fewer parameters. The article reviews literature applications of SWAT, HSPF, and DWSM and argues that combining complementary models is warranted to address water quantity and quality issues. The authors compiled 17 SWAT, 12 HSPF, and 18 DWSM applications reported in the literature. SWAT and HSPF accurately predict yearly flow, sediment, and nutrient loads, with monthly predictions generally good except during extreme events, while daily extreme flow simulations are poor; DWSM reasonably predicts distributed flow hydrographs and sediment, nutrient, and pesticide concentrations at short time scales following rainfall.

Abstract

Three watershed-scale hydrologic and nonpoint-source pollution models, all having the three major components(hydrology, sediment, and chemical), were selected based on a review of eleven models (AGNPS, AnnAGNPS, ANSWERS,ANSWERS-Continuous, CASC2D, DWSM, HSPF, KINEROS, MIKE SHE, PRMS, and SWAT) presented in a companion article.Those selected were SWAT, a promising model for long-term continuous simulations in predominantly agricultural watersheds;HSPF, a promising model for long-term continuous simulations in mixed agricultural and urban watersheds; andDWSM, a promising storm event (rainfall) simulation model for agricultural and suburban watersheds. In this article, applicationsof these three models, as reported and found in the literature, are reviewed and discussed. Seventeen SWAT, twelveHSPF, and eighteen DWSM applications are compiled. SWAT and HSPF require a significant amount of data and empiricalparameters for development and calibration. DWSM has efficient physically (process) based simulation routines and thereforehas a small number of calibration parameters. SWAT and HSPF were found suitable for predicting yearly flow volumes,sediment, and nutrient loads. Monthly predictions were generally good, except for months having extreme storm events andhydrologic conditions. Daily simulations of extreme flow events were poor. DWSM reasonably predicted distributed flow hydrographs,and concentration or discharge graphs of sediment, nutrient, and pesticides at small time intervals resulting fromrainfall events. Combined use of these complementary models and perhaps other models having different strengths is warrantedto adequately address water quantity and quality problems and their solutions.