In the lower and upper subbasins, the annual average precipitation is 46 inches and 42 inches, respectively (MDNR 1986). In the upper subbasin, the average annual run off is 16.6 inches and in the lower subbasin, runoff averages 14.5 inches per year (Vandike 1995).
U.S. Geological Survey Gaging Stations
Currently, there are four United States Geological Survey (USGS) streamflow stations operating in the basin. Three stations are located in the upper subbasin (Logan Creek at Ellington, East Fork of the Black River at Highway 72, and Black River at Highway K, just upstream of Clearwater Reservoir). In the lower subbasin, the flow station is located on the Black River at Poplar Bluff. For additional information regarding streamflow (e.g., site map, real time gage height and discharge, or annual streamflow statistics) go to http://waterdata.usgs.gov/mo/nwis/current/?type=flow.
Ozark streams have the highest, most well-sustained base flows in the state because of the high permeability of the carbonate rocks, which store and transmit large quantities of groundwater (Kratzer and Jenkins 1985). The lowland streams, located in Mississippi Alluvial Plain are sustained by ground water contributions from the extensive alluvial deposits.
The average discharge of the Black River at Popular Bluff is 1,330 cubic foot per second (cfs) (Vandike 1995). The 1984 water year (October through September) had the highest average discharge (2,858 cfs). The 1954 water year was the driest with an average discharge of 564 cfs. The maximum and minimum instantaneous discharges ever recorded were 65,000 cfs (12/4/82) and 180 cfs (9/25/66).
In the upper subbasin, the average discharge of the Black River at Highway K is 591 cfs (Vandike 1995). The highest and lowest yearly averages were 1,420 cfs in water year 1985 and 244 cfs in water year 1954. The highest recorded instantaneous discharge was 98,500 cfs on November 11, 1985. On August 12, 1965, the lowest instantaneous discharge (67 cfs) was recorded.
In the upper and lower subbasins there are 17 and 11 springs, respectively (Table Hy01). Pittman (20 million gallons/day) and Keener (14 million gallons/day) are the largest springs in the lower subbasin (Vandike 1995). Warner Bay Spring (11 million gallons/day) is the largest spring in the upper subbasin (Vineyard 1982). For additional information on springs, visit http://www.ozarkcaving.com/
Dam and Hydropower Influences
Two reservoirs exist in the basin and both of these are located in the upper subbasin. Clearwater Reservoir (1650 acres) is located on the Black River and Lower Taum Sauk Lake (200 acres) is located on the East Fork of the Black River.
Clearwater Dam is in Wayne County, but nearly all of the reservoir is in Reynolds County. Clearwater Reservoir was authorized by the Flood Control Act of 1938. Construction was initiated in May 1940 and was completed in 1951. This reservoir is operated by the Corps of Engineers for the primary purpose of flood control, with conservation of fish and wildlife and recreation as other purposes.
Water releases from Clearwater Reservoir are dictated by river stages at the Popular Bluff gage. The authorized regulating plan calls for a maximum river stage of 11? feet from December 1 through March 31 and a maximum river stage of 10? feet from April 1 through November 30.
An environmental assessment is being conducted on proposed changes to the Clearwater Reservoir water control plan. The proposed plan calls for discharge to be regulated both by the Poplar Bluff river stage and Clearwater Reservoir level (Figure Hy01). In the proposal, the conservation pool would be held at 498 NGVD from April 15 through October 14. Starting the October 15th, the conservation pool elevation would be lowered to 494 NGVD.
At an elevation of 494 NGVD, the Reservoir covers 1,650 acres (22,000 acre-feet of water). At the top of the flood pool (567 NGVD), the Reservoir covers 10,250 acres (413,000 acre-feet of water). Approximately 95% of the Reservoir volume (391,000 acre-feet) is for flood control purposes, an extremely high proportion when compared to the other reservoirs. The highest water level ever recorded (566.6') occurred on May 20, 2002.
An AmerenUE dam on the East Fork of the Black River forms Lower Taum Sauk Lake (LTS), the lower lake of a two lake pump-storage hydroelectric plant. The upper reservoir is located on Proffit Mountain, approximately 800 feet higher than the lower reservoir. During peak electrical demand periods, water is released from the upper reservoir through a 6,500-foot tunnel and into the lower reservoir. During low electrical demand periods, water is pumped back into the upper reservoir.
The LTS dam was designed to allow the same amount of water entering the lake from the East Fork of the Black River to exit the lake at the base of the dam. Because the facility is a peak hydroelectric facility, water levels in the lower lake can fluctuate greatly in a short time period. Water levels can rise 15 feet in eight hours during power generation or fall 15 feet in 12 hours during the pumpback process.
To keep river-borne sediment from reducing LTS?s storage capacity or blocking the canal between the power plant and the lake, a dam to trap gravel was constructed across the East Fork of the Black River just upstream of the reservoir. In the past 30 years, this gravel trap has been cleaned out five times. Each time approximately 30,000 cubic yards of material were removed.