Laserfiche WebLink
<br />watershed over recent years. The watershed is very complex and has large amounts of flood plain storage, . <br /> <br /> <br />low basin relief, a wide variety of hydraulic structures, and varying soil conditions. <br /> <br />The FEQ program (Linsley, Kraeger Associates, 1995) is a fully dynamic flood-wave-routing model. FEQ <br /> <br /> <br />is designed to take outputs of a continuous hydrologic model to simulate the flood wave moving through <br /> <br /> <br />river reaches and hydraulic structures. The continuous-simulation hydrologic model utilized in this <br /> <br /> <br />analysis was the Hydrological Simulation Program - FORTRAN (HSPF) (EPA, 1993). The HSPF model <br /> <br /> <br />was used to develop runoff time series of unit runoff for different combinations of land cover, soil type, <br /> <br /> <br />and ground slope. The time series file is then used in the FEQ model to compute the lateral inflows to <br /> <br /> <br />each branch and reservoir in the model. This approach differs from the standard engineering practice <br /> <br /> <br />where a single-event rainfall-runoff model is developed and a steady-state hydraulic model is used. The <br /> <br /> <br />continuous-simulation unsteady flow modeling approach has many advantages which include: <br /> <br />. backwater and flood plain storage effects are represented <br /> <br />. historical precipitation records can be utilized to produce long, continuous flow records <br /> <br />. actual storm events are simulated rather than hypothetical events which never occurred <br /> <br />. spatial and temporal patterns of rainfall are considered <br /> <br />. soil moisture conditions are tracked from storm to storm <br /> <br />. potential impacts of development on flooding can be simulated <br /> <br /> <br />. effects of proposed flood hazard mitigation projects can be simulated <br /> <br />. <br /> <br />. frequency analysis can be carried out on water levels from continuous simulation rather than <br />on storm rainfall or peak discharges <br /> <br />Model Development <br /> <br />The hydraulic model for the West Branch DuPage River was d(,veloped in three segments to facilitate <br /> <br /> <br />model development and computational debugging. Figure I shows a schematic representation of the <br /> <br /> <br />project area. The model was developed through a joint effort by Woodward-Clyde Consultants (WCC), <br /> <br /> <br />Rust E&I, Linsley, Kraeger Associate, and DEe. The continuous hydrologic model. HSPF, was developed <br /> <br /> <br />by the Northern Illinois Planning Commission (NIPC), Land use was based on DuPage County's Planning <br /> <br /> <br />Department 1990 Surveys and the subbasin areas were delineated using DEC's 2-foot contour mapping <br /> <br /> <br />(DuPage DEC. 1995) and USGS topography. <br /> <br />Surveying for the main stem of the West Branch DuPage River was performed by several <br /> <br /> <br />surveying/engineering firms. Additional cross sections were extrapolated from the County's digital <br /> <br /> <br />topographic mapping when no other survey data was available. <br /> <br />. <br />