Hydrologic Model of the Vermilion River Watershed for Streamflow Simulations

              This project was funded through the Illinois Department of Natural Resources and the Illinois State
Geological Survey. Illinois State Water Survey Contract Report 2004-10.
Hydrologic Model of the Vermilion River Watershed
for Streamflow Simulations
Jaswinder Singh
Watershed Science Section
Illinois State Water Survey
Abstract
In continuation of the efforts made by the Illinois State Water Survey to develop a
detailed hydrologic and water quality simulation model of the entire Illinois River Basin, a
hydrologic simulation model was developed for the Vermilion River Watershed (one of the
major tributaries of the Illinois River) to simulate streamflows using available climatic data. The
model was developed using Hydrologic Simulation Program – FORTRAN (HSPF, version 12)
under the BASINS (Better Assessment Science Integrating Point and Nonpoint Sources, version
3.0), a multipurpose environmental analysis system developed by the U.S. Environmental
Protection Agency (USEPA). The watershed was sub-divided into 25 smaller, hydrologically
connected sub-watersheds and their stream reaches. Hydrologic Response Units (HRUs) were
created within each sub-watershed based on landuse and hydrologic soil groups. Streamflow data
from two USGS streamflow gaging staions in the watershed and climate data from six
representative staions for 1970-1995 was used. Model was calibrated using data for 1987-95 at
the USGS gage at Pontiac, IL and then verified using 1972-1986 data from the same station, and
using 1972-1995 data from the USGS gage at Leonore, IL. Model simulated the monthly
streamflows with correlation coefficients and Nash-Sutcliffe Efficiency (NSE) of close to or
greater than 0.8 during calibration as well as verification periods. Flow-duration curves of the
daily observed and simulated streamflow data indicated good simulation for all flow conditions,
except for some very low flow periods. The flood year of 1993 was under-simulated by the
model whereas some very low flow years were generally over-simulated.
Introduction
Most of the significant rivers in the State of Illinois, including the Vermilion River, drain
into the Illinois River. Illinois River carries the runoff, sediment, nutrient, and pollutants from
these tributaries down to the Mississippi River. The Illinois State Water Survey (ISWS) has