HYDROLOGICAL MODELING OF THE IROQUOIS RIVER WATERSHED USING HSPF AND SWAT

TLDR

The Iroquois River watershed is a large, tile‑drained agricultural basin that offers distinct conditions for model comparison relative to prior studies. The study evaluates HSPF and SWAT for simulating the Iroquois River watershed hydrology and aims to guide users in model selection through comparative analysis. Both models were calibrated (1987‑1995) and verified (1972‑1986) against observed streamflow, and the study examined tile‑drain effects, noting HSPF lacks a dedicated tile‑drain component while SWAT includes one. Simulated flows from HSPF and SWAT largely match observations, with SWAT slightly outperforming HSPF in low‑flow simulation; discrepancies arise partly from PET estimation differences, where low PET inputs to HSPF may cause overestimation of low flows.

Abstract

ABSTRACT: The performance of two popular watershed scale simulation models — HSPF and SWAT — were evaluated for simulating the hydrology of the 5,568 km2 Iroquois River watershed in Illinois and Indiana. This large, tile drained agricultural watershed provides distinctly different conditions for model comparison in contrast to previous studies. Both models were calibrated for a nine-year period (1987 through 1995) and verified using an independent 15-year period (1972 through 1986) by comparing simulated and observed daily, monthly, and annual streamflow. The characteristics of simulated flows from both models are mostly similar to each other and to observed flows, particularly for the calibration results. SWAT predicts flows slightly better than HSPF for the verification period, with the primary advantage being better simulation of low flows. A noticeable difference in the models' hydrologic simulation relates to the estimation of potential evapotranspiration (PET). Comparatively low PET values provided as input to HSPF from the BASINS 3.0 database may be a factor in HSPF's overestimation of low flows. Another factor affecting baseflow simulation is the presence of tile drains in the watershed. HSPF parameters can be adjusted to indirectly account for the faster subsurface flow associated with tile drains, but there is no specific tile drainage component in HSPF as there is in SWAT. Continued comparative studies such as this, under a variety of hydrologic conditions and watershed scales, provide needed guidance to potential users in model selection and application.