PREDICTING SEDIMENT AND PHOSPHORUS LOADS IN THE ROCK RIVER BASIN USING SWAT

Abstract

The Rock River is considered degraded from excessive amounts of phosphorus. Individual programs are ongoing to reduce phosphorus from point and nonpoint sources. However, a comprehensive phosphorus management approach may prove more cost effective and beneficial. To be successful, such an approach must take into consideration phosphorus from all sources and seek geographically targeted, cost–effective, and holistic solutions. This study utilized the SWAT (Soil and Water Assessment Tool) model to quantify phosphorus sources throughout the basin and quantify impacts from the application of basin–wide BMPs. Results of this study indicate that, under existing land use and management conditions, an average annual phosphorus load of approximately 764,000 kg enters the Rock River and it tributaries. Point sources account for 41% of this value, and nonpoint sources account for 59%. Model results show that, under existing conditions, approximately 160,000 tons of sediment is delivered to the streams and surface water bodies on an average annual basis. Modeling results indicate that implementation of improved tillage practices (predominantly conservation tillage) can reduce sediment yields by almost 20%.