LOCATION.-- Lat 37°13'00", long 89°27'50" (NAD of 1927), in NW 1/4 sec.17, T.15 S., R.3 W., Alexander County, Hydrologic Unit 07140105, near center span on downstream side of railroad bridge at Thebes, 5.0 mi downstream from Headwater Diversion Channel, and at mile 43.7 above Ohio River.

DRAINAGE AREA.-- 713,200 mi², approximately.

PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE

DISCHARGE: October 1932 to current year. Monthly discharge only for some periods, published in WSP 1311. Prior to April 1941, published as "at Cape Girardeau, Mo".

STAGE: March 1933 to February 1938 and October 1939 to current year. Prior to April 1941, published as "at Cape Girardeau, Mo". Since November 1878, under name of "at Grays Point" in files of the U.S. Army Corps of Engineers; January 1879 to May of 1896, published as "at Grays Point"; since May 1896, published as "at Cape Girardeau" in reports of the Mississippi River Commission, February 1891 to February 1894; and since 1904, published as "at Cape Girardeau" in reports of the National Weather Service.

SURFACE-WATER QUALITY

CHEMICAL: January 1973 to current year.

SEDIMENT: October 1980 to current year.

SPECIFIC CONDUCTANCE: October 1974 to September 1981.

WATER TEMPERATURE: October 1974 to September 1981.

REVISED RECORDS.-- WSP 1341: 1844(M). WDR MO-76-1: Drainage area, WDR MO-98-1: Extremes outside period of record.

GAGE.-- Water-stage recorder, U.S. Army Corps of Engineers satellite telemeter and telemark. Datum of gage is 300.00 ft above NGVD of 1929. Mar. 17, 1933, to Dec. 21 1934, nonrecording gage; Dec. 22, 1934, to Apr. 4, 1941, water-stage recorder, at site 8.2 mi upstream at datum 4.65 ft higher; Apr. 5, 1941, to Sept. 30, 1941, nonrecording gage at present site and datum; Oct. 1, 1941, to Oct. 11, 1943, at datum 0.07 ft higher. Prior to Apr. 5, 1941, various auxiliary gages used. Since Oct. 1, 1943, former gage at Cape Girardeau used as auxiliary gage.

REMARKS.-- Natural flow of stream affected by many reservoirs and navigation dams in the upper Mississippi River Basin and by many reservoirs and diversions for irrigation in the Missouri River Basin. NASQAN station January 1973 to September 1986. Illinois Environmental Protection Agency station October 1986 to September 1994 (during the period, samples were analyzed by the Illinois EPA). Re-established as a NASQAN station October 1994 to current year.

EXTREMES FOR PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Maximum discharge, 996,000 ft³/s, August 7, 1993; maximum gage height, 45.91 ft, May 23, 1995; minimum discharge, 23,400 ft³/s, December 13, 1937.

SPECIFIC CONDUCTANCE: Maximum daily, 705 microsiemens per centimeter, Aug. 5-7, 1980; minimum daily, 272 microsiemens per centimeter, Apr. 6, 1979.

WATER TEMPERATURE: Maximum daily, 31.5 °C, July 10 and 11, 1975, and July 17, 1977; minimum daily, 0.0 °C, on several days during winter periods.

SUSPENDED-SEDIMENT CONCENTRATONS: Maximum daily mean, 3,890 mg/L, Dec. 22, 1985; minimum daily mean, 13 mg/L, Jan. 28, 1981.

SUSPENDED-SEDIMENT LOADS: Maximum daily, 6,280,000 tons, Mar. 1, 1985; minimum daily, 2,530 tons, Jan. 28, 1981.

EXTREMES OUTSIDE PERIOD OF RECORD.--

SURFACE-WATER DISCHARGE AND STAGE: Flood of July 4, 1844, reached an elevation of 345.14 ft, present datum, at Grays Point, from floodmarks, discharge, 1,075,000 ft³/s, computed by the U.S. Army Corps of Engineers.

EXTREMES FOR CURRENT YEAR.--

SUSPENDED-SEDIMENT CONCENTRATIONS: Maximum daily mean, 1,300 mg/L, March 10; minimum daily mean, 69 mg/L, Feb. 12.

SUSPENDED-SEDIMENT LOADS: Maximum daily, 1,580,000 tons, March 10; minimum daily, 16,400 tons, Feb. 12.