Study Reach.--The channel reach has a series of bends, as shown in the quadrangle map on the top left. The study reach, approximately 535 ft long, is centered on the bridge on State Highway 149. There are seven surveyed cross sections (surveyed by the Illinois Department of Transportation, in December 1997) available for evaluating the channel geometry in the study reach. The alignment of the study reach, approximate variations in channel width and bank conditions, and locations of surveyed cross sections are shown in the aerial photograph on the top right. Cross-sectional geometries vary gradually and continuously from upstream to downstream. The general shapes of cross sections in the study reach are represented by cross sections at river stations (RS) 2, 3, 4, and 5 (see plots above).
Gage Location.--Lat 37°54'05", long 89°00'50", in NW1/4 sec.20, T.7S., R.2E., on the left bank 0.8 mi upstream from the bridge on State Highway 149, about 1.9 mi downstream from the mouth of the Middle Fork Big Muddy River, and about 0.8 mi north and west of the intersection of Route 149 and Plumfield Road in Franklin County. The auxiliary gage was located at Zeigler, about 4 mi downstream, but was discontinued September 30, 1991. The USGS streamgage station number is 05597000.
Drainage Area.--794 sq mi.
Gage Datum and Elevations of Reference Points.--This is a slope station where the auxiliary gage is located 4 mi downstream from the base gage. The auxilary gage is a wire-weight gage (WWG). Datum of the gage is 353.24 ft. From November 13, 1938, to September 30, 1974, the datum at the auxiliary gage was 5.0 ft higher. The outside gage at the base gage consists of a series of staff gages mounted either on piers, or the landward side of the gage house. The elevation of the brass screw on the staff gage= 360.958 ft. All elevations are referenced to NGVD29.
Stage, Discharge Measurements, and Computed n-Values.--Stage and discharge data for this n-value study were retrieved from measured discharge records for this slope station site. Water-surface elevations were measured from the staff gage at the base gage and from the WWG at Zeigler at the time of each discharge measurement. Discharge measurements were made using the conventional current-meter method. For the present n-value analysis, events of no over-the-bank flows were selected from record prior to September 30, 1991. The computed n-values are listed in the following table. Whenever possible, the computed n-values are associated with a photograph taken at the time of the measurement. The photographs are arranged from low to high discharge in order to illustrate the contributing factors of n-values at a particular discharge.
| Date of Observation | Discharge (ft3/s) | Average Cross Section Area (ft2) | Hydraulic Radius (ft) | Mean Velocity (ft/s) | Slope (ft/ft) | Coefficient of Roughness n |
|---|---|---|---|---|---|---|
| 11/27/1974 | 369.0 | 500.1 | 3.25 | 0.75 | 0.000140 | 0.051 |
| 8/19/1975 | 424.0 | 521.6 | 3.29 | 0.83 | 0.000140 | 0.047 |
| 9/10/1974 | 469.0 | 648.7 | 3.87 | 0.74 | 0.000148 | 0.055 |
| 12/12/1974 | 478.0 | 627.5 | 3.77 | 0.78 | 0.000144 | 0.051 |
| 6/10/1975 | 610.0 | 776.8 | 4.40 | 0.81 | 0.000148 | 0.055 |
| 1/20/1975 | 954.0 | 1178.3 | 5.65 | 0.86 | 0.000145 | 0.062 |
Description of Channel.--This is a natural channel. The study reach can be described as in the straight section of a bend. General cross sectional geometry is trapezoidal in shape. The bed material consists of bedrock overlain with mud and silt. Bottom width of the channel is about 50 ft and the top width varies from approximately 150 to 200 ft. The left bank is wooded and steeper than the right bank. The right bank is only partially wooded. The banks are approximately 12 ft high.
Floods.--May 10, 1961, 42,900 ft3/s; maximum gage height 34.67 ft, present datum; Maximum discharge since construction of Rend Lake, 14,200 ft3/s, May 1, 1996, gage height, 31.83 ft; Maximum gage height since construction of Rend Lake, 31.84 ft, May 4, 1983.
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://il.water.usgs.gov/proj/nvalues/db/sites/05597000.shtml[an error occurred while processing this directive]?
Page Contact Information: David Soong
Page Last Modified: February 4, 2013
