Judy’s Branch, a small
basin (8.33 mi2) near Glen Carbon, Illinois, has been selected as a
pilot site to analyze sediment delivery and stability of streams draining the
bluff-line hills of the American Bottoms in the Metro East area of Illinois
(figure 1). In the 1800s, much of the
forest and prairie in the watershed, which includes the upland bluffs, was
converted to agricultural land. Since
the 1940’s urbanization has resulted in the uplands. These land-use changes have caused increased stream flows to the
river that result in higher rates of erosion.
Erosion of the upland bluffs has resulted in the loss of private land.
Deposition of sediment in the American Bottoms has resulted in increased
flooding.
Sediment, hydraulic,
geomorphic, and hydrologic data are needed in Judys Branch to assist the
Illinois Department of Natural Resources, Office of Water Resources (IDNROWR),
St. Louis Corps of Engineers, and the U.S Department of Agriculture, Natural
Resources Conservation Service in their analysis of river rehabilitation and
watershed-management alternatives to help control erosion in the upland bluffs.This project
advances the knowledge and understanding of sediment processes and erosion of
wind-blown deposits of loess in Illinois and similar streams in the
Midwest.
Automated streamflow
equipment and sediment samplers are installed at three sites in the
watershed. Information collected at the
gages will be used to calculate sediment yield of the watershed and compare
effects of urbanization on the stream flow and sediment delivery to the
river. All stream flow data will be
used by IDNROWR staff to verify a step-backwater hydraulic model and a
hydrologic model built for the Judys Branch watershed. The streamflow and sediment data also will
help determine the channel-forming discharge.
Lastly, collecting sediment data throughout the life of the project will
be useful in evaluating the effectiveness of the rehabilitation and management
decisions.
The purpose of the geomorphic assessment is to link
processes operating on the bed and banks of the unstable stream, Judy’s Branch,
which is responding to changes in land-use and river management. The geomorphic assessment includes
channel evolution and bank stability analysis.
To help determine the rate of streambank erosion of Judy’s Branch,
twenty-six bank rod locations are installed. Riverbed and bank samples have
been collected at each of the bank rod locations. The undisturbed strength of the riverbanks was determined at the
26 bank rod locations by means of a field measurement instrument, vane shear
apparatus. Soil corings have been
collected at six locations throughout the stream network. IDNROWR personnel have surveyed the majority of the stream channel and
surrounding floodplain at approximately 300 to 500 ft intervals. Future survey information will assist in
documenting the overall geomorphic progression of the river. The above data is being used to
determine the stability of the stream.
The results of this study will
help facilitate river engineering analysis and decisions to help control
erosion in bluff streams.