Methodology and Application of the Combined SWAT-HSPF Model

Abstract

This paper shows the output of a research study that involves developing a new model for diffuse source pollution requiring the integration of a complex distributed catchment model with a model of contaminant transport. It explains in details the various model components, modifications and assumptions that have been made in the construction of the new combined model (NCM) based on Hydrological modules of Hydrological Simulation Program FORTRAN (HSPF) and Phosphorus transformations modules of Soil and Water Assessment Tool (SWAT) model, as well as the approach adopted. Three Irish catchments have been tested, namely Oona, Bawn and Dripsey. Model performance for both calibration and validation periods, and model parameter sensitivity and uncertainty analysis results were examined extensively with the outputs of SWAT model and HSPF. The NCM showed promising potential for better estimation of phosphorus losses from catchments for Irish conditions with some drawback for baseflow dominant catchments. It gives good results in terms of flow and phosphorus modelling, and is generally better than SWAT or HSPF alone for most of the cases tested. An uncertainty analysis based on model parameters was conducted using the PARASOL method implemented in SWAT 2005, and uncertainty bounds for the flow and the total P load predictions were compared with the observed values for each catchment.