Applicability of SWAT Model for Estimation of Phosphorus Discharge in a Suburban Catchment

Abstract

 To evaluate the applicability of the Soil Water Assessment Tool model (SWAT) for estima-tion of phosphorus load from a suburban catchment, we examined the reproducibility of river discharge, suspended solids (SS), particulate phosphorus (PP) and dissolved inorganic phos-phorus (DIP) concentrations. Results can be summarized as follows. First,the reproducibility of daily river discharge was good throughout the year, although it tended to be overestimated or underestimated in high discharge periods. This result implies that the reproducibility of discharge is a.ected by spatial and temporal resolution of weather data. Secondly, the repro-ducibility of SS concentration shows acceptable results despite empirical equations developed in the United States of America. Reproducibility of PP concentration was also acceptable as well as SS. Therefore, the model was capable of estimating PP caused by soil erosion. Never-theless,results showed that estimation methods used for DIP in urban areas are not fit for use in Japan. The possibility exists of making an error of estimation of DIP in a watershed that is highly in.uenced by domestic wastewater. In this study, the estimation of DIP was improved by considering domestic wastewater as a point source. Consequently, results con.rmed that SWAT is capable of estimating phosphorus discharge. However, results suggest that the model should be used carefully for DIP estimation in urban areas. Furthermore, results underscore the necessity of improving DIP estimation methods.