Study Reach.--The channel under consideration is constructed in an urban setting. The study reach selected, 1100 ft long, is located from the Emerson Street bridge to the School Street pedestrian footbridge, as shown in the quadrangle map on the top left. Cross-sectional geometries, as described by 22 surveyed cross sections (surveyed by Earth Tech, in July 2001) vary gradually and continuously from upstream to downstream. The general shapes of cross sections in the study reach are plotted above. The alignment of the study reach, approximate variations in channel width and bank conditions, and locations of the surveyed cross sections are shown in the aerial photo on the top right.
Gage Location.--The location of discharge measurement is lat 42°03’10”, long 87°55’54”. This study reach is at SE1/4 SE1/4 SW1/4 sec.12, T.41N., R.11E., Cook County, Hydrologic Unit 07120004, on right bank 10 ft upstream from bridge on State Highway 58 (Golf Road) in Des Plaines, 2 mi west of US Highway 45 and at mile 3.0. USGS streamgage-station number is 05529985.
Drainage Area.--11.6 sq mi.
Gage Datum and Elevations of Reference Points.--Datum of gage is 634.02 ft. Reference points (RP-N) were established for the n-values project. RP-N5 is a bolt in the concrete guardrail on the upstream side of Emerson Street bridge located about midchannel, elevation = 657.989 ft.; RP-N4 is two file marks on the upstream side of the bridge deck frame accessed through an opening in the bridge deck catwalk located just under the "X" formed by the guardrail diagonals on the School Street pedestrian bridge, elevation = 654.999 ft. All elevations are in NGVD 1929 convention.
Stage, Discharge Measurements and Computed n-Values.--Water-surface elevations are made by taping down from RP-N4 on the upstream side of the School Street pedestrian bridge and from RP-N5 on the upstream side of Emerson Street bridge before and after a discharge. Discharge measurements are made on the downstream side of Emerson Street Bridge. Wading measurements are made in the vicinity of the bridge. Discharge measurements are made using the conventional current-meter method where total discharge is the summation of the products of the subsection areas of the stream cross section and their respective average velocities. The computed n-values are listed in the following table. Whenever possible, the computed n-values are associated with a photo taken at the time of the measurement. The photos are arranged from low stage to high stage in order to illustrate contributing factors of n-values at a particular stage.
| Date of Observation | Discharge (ft3/s) | Average Cross Section Area (ft2) | Hydraulic Radius (ft) | Mean Velocity (ft/s) | Slope | Coefficient of Roughness n |
|---|---|---|---|---|---|---|
| 5/2/2006 | 8.4 | 18.9 | 0.96 | 0.50 | 0.001432 | 0.076 |
| 6/26/2006 | 62.0 | 33.3 | 1.48 | 2.05 | 0.000900 | 0.026 |
| 4/25/2007 | 66.6 | 34.2 | 1.50 | 2.14 | 0.000928 | 0.025 |
| 4/25/2007 | 73.4 | 36.0 | 1.56 | 2.23 | 0.000907 | 0.025 |
| 1/12/2005 | 88.0 | 41.8 | 1.73 | 2.29 | 0.000855 | 0.026 |
| 1/12/2005 | 89.9 | 40.6 | 1.73 | 2.42 | 0.000855 | 0.026 |
Description of Channel.--This channel has been modified. Streambed material consists of coarse sand and gravel. The bank consists of interlocking 24-inch A-jacks at the toe with tall grass and weeds anchored in geoweb fabric. The bottom width of the channel ranges from 10 to 20 ft. Top width is from about 50 to 70 ft. The banks are steep with an average height of about 14 ft. The cross sections are fairly uniform and nearly trapezoidal. The channel curves gently to the right the entire reach.
Floods.--Maximum discharge during period of record, 1,590 ft3/s on June 10, 1967, gage height, 15.09 ft.
Estimated n-Values using Cowan’s Approach.--
U.S. Department of the Interior |
U.S. Geological Survey
URL: http://il.water.usgs.gov/proj/nvalues/db/sites/05529985.shtml
Page Contact Information: David Soong
Page Last Modified: Thursday, 06-Mar-2008 10:49:35 CST
