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Title:Hydraulic geometry and carrying capacity of floodplains
Author(s):Bhowmik, Nani G.; Stall, John B.
Contributor(s):Illinois State Water Survey; Park, Chong Mook; Vora, Uday S.; University of Illinois at Urbana-Champaign
Subject(s):Water resources center
Water resources center--Illinois
Hydrology and hydraulics
Hydraulic geometry
Stream order
Cross sections
Carrying capacity
Humid areas
Hypsometric analysis
Flow duration
Geographic Coverage:Illinois (state)
Abstract:Hydraulic geometry relationships for floodplains of nine river basins in Illinois and four river basins outside of the state were developed. Relationships between floodplain width, cross-sectional area, surface area, depth, sinuosity, incision, and stream order have been developed. These hydraulic geometry parameters were also found to be related to the drainage area of the individual stream segments. Hydraulic geometry coefficients of the floodplains of Illinois streams were found to be similar although the developed relationships have different base values. Hypsometric analyses of the Illinois streams indicated that most of the streams in Illinois are in a mature stage of development. All of the hydraulic geometry parameters of the floodplains increased in the downstream direction. However, for some rivers, the cross-sectional areas showed an increase in the downstream direction up to a certain distance and then it decreased to some extent near the mouth of the river. Comparison of the hydraulic geometry parameters of the floodplains and the main streams indicated that the hydraulic geometry parameters of the floodplains increased at a lower rate in the downstream direction than did the corresponding parameters of the main streams. Data, such as number of bends, radius of curvature, deflection angle, and cross-sectional area, from the Embarras River were utilized to perform a statistical analysis. This analysis indicated that the deflection angle of the bends, the radius of curvature, and the length of the bend per unit deflection angle for each order of the stream fitted a log-normal probability distribution with two parameters very well. Actual field data related to the carrying capacity of floodplains were analyzed to determine the distribution of flow in the main channel and in the floodplains. The carrying capacity of floodplains can vary anywhere from a few percent to more than 80 percent of the total flow for the data analyzed for this research. With an increase in the return period of the flood event, the carrying capacity of the floodplain increases. During low flood events, the floodplains act as a combination of conveyance channel and storage reservoir. However, when the return period of the flood event is about 40 years or more, the floodplain and the main channel appear to behave as a single unit carrying a proportionate share of the discharge. Analyses of the average flow velocities in the floodplain and in the main channel for different in-bank and out-of-bank flow conditions also indicated that the character of the floodplains changes from a storage channel to a conveyance channel as the flood event increases in magnitude. Practical applications of the hydraulic geometry relationships are also shown.
Issue Date:1979-09
Publisher:University of Illinois at Urbana-Champaign. Water Resources Center
Genre:Report (Grant or Annual)
Sponsor:U.S. Department of the Interior
U.S. Geological Survey
Rights Information:Copyright 1979 held by Nani G. Bhowmik, John B. Stall
Date Available in IDEALS:2016-05-23

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