The average annual precipitation for the Big River basin is 41 inches/year, with 29 inches being rainfall (MDNR 1986). Precipitation usually peaks in May (13") and is lowest in February (6"). Average annual runoff is 12.8 inches.
U.S. Geological Survey Gaging Stations
Three U.S. Geological Survey (USGS) gagging stations (numbers 07017200-Irondale, 07018100-Richwoods, and 07018500-Byrnesville), all on Big River, are active within the basin (Figure Hy01). The Irondale station (RM 115) measures flow from 175 square miles of watershed, and its period of record is July, 1985 to present (Table Hy01). Some water quality data were collected during 1986 (Table Hy02).
The Richwoods (formerly DeSoto) station (RM 53.7) measures flow from 735 square miles of watershed, and its period of record is October 1942 to present (Table Hy01). Sporadic water quality sampling has taken place since 1963, but only 1986 to present is summarized (Table Hy02).
The Byrnesville station (RM 14.1) measures flow from 917 square miles of watershed, and its period of record is October 1921 to present (Table Hy02).
Instantaneous discharge (Table Hy01) and some water quality data (Tably Hy02) have been taken on Coonville Creek at St. Francois State Park since 1992.
Five other low-flow, partial-recording gagging stations were operated on Big River, Dry Branch, Hopewell Spring, Mineral Fork, and Old Mines Creek until the early 1970s. They are currently inactive.
Big River's average annual discharge is 862 cubic feet per second (cfs) at Byrnesville (USGS 1994). Mean streamflow is lowest in August and highest in April (Figure Hy02). The lowest and highest instantaneous flows recorded, 25 cfs (August 30, 1936) and 63,600 cfs (September 25, 1993), occurred at the Byrnesville gagging station (Table Hy03; USGS 1994). However, an estimated discharge (from high-water marks) of 80,000 cfs, at Byrnesville on August 21, 1915, may have been the highest instantaneous flow (USGS 1994). Flows of 116 cfs, 337 cfs, and 1,720 cfs were exceeded 90%, 50%, and 10% of the time, respectively, at the Byrnesville gagging station (Table Hy03).
Data from Big River's Byrnesville gagging station were used to construct a flow duration curve (Figure Hy03) and a 90:10 ratio. The 90:10 ratio of 15 to 1 indicates stable, high flow (Miller et al. 1974).
Frequency of 7-day Q values (low-flow discharges; Table Hy04) and low slope index of 2.3 represent well sustained base flows (Miller et al. 1974), despite only 5 springs of note (6.6 cfs combined, Figure Hy04) being present (Vineyard 1982). Base flows are aided by ample precipitation, numerous small springs and seeps located in fractured limestone and subsurface chert, and artesian flow from old exploratory bore holes in the Old Lead Belt. During leadmining activities, base flow in the upper Big River at Leadington and Flat River was increased by 100-200% by lead mine discharges (Missouri Water Pollution Board 1964).
Flood magnitude for Big River (Table Hy05) is somewhat low for a basin of its size (Hauth 1974). However, increasing urbanization of the watershed and subsequent increased stormwater could increase flood magnitudes. A flood, which on average would happen once/100 years, would generate flows of 40,500 cfs (Table Hy05). The "Great Flood of '93" (63,600 cfs) was well above the 100-year flood level.
Dam and Hydropower Influences
One mainstem dam (RM 132) forms 440-acre Council Bluff Lake along the Washington-Iron County line. The lake was completed in 1981 for flood control and recreation. Five old mill dams , all in Jefferson County, affect Big River (Figure Hy05). The dams at Byrnesmill (RM 7.9), Cedar Hill (RM 18.8), and Morse Mill (RM 29) have been breached and are in varying degrees of disrepair. The dams at House Springs (RM 9.4) and Byrnesville (RM 13.8) remain intact, impounding over 2 miles of river. All these dams can be barriers to fish movement during normal flows.
In 1974, Congress authorized the United States Army Corps of Engineers (USCOE) to proceed with the Meramec Basin flood control project by constructing 5 impoundments on the Big, Bourbuese, and Meramec rivers (USCOE 1982). Two impoundments, 3,700-acre Pine Ford (RM 41) and 4,600-acre Irondale (RM 118) were designed for mainstem Big River. Intense public opposition forced deauthorization of these projects in 1982.
The Big River watershed contains many large (impounding >50 acre-feet of water with a dam height > 25'), privately-owned dams, with Jefferson, Franklin, and Washington counties each containing over 100 (MDNR 1986). The largest, 360-acre Sunnen Lake in Washington County, impounds a portion of Fourche a Renault Creek.
Jefferson, St. Francois, and Washington counties contain 45 dams which retain finely-ground (tailings) and coarsely-ground (chat) lead and barite mine waste (Table Hy06). Most of these dams were improperly constructed or maintained, which has led to erosion of mine waste or dam collapse and large influxes of mine waste.
In a 1992 study, USCOE found that only one of the 45 Big River basin mine dams was safe and 27 received the worst possible rating--high-hazard, unsafe--and could fail during a severe flood or earthquake (Table Hy07). Perhapsthe greatest danger to humans is from the St. Joe State Park dam which could bury Park Hills, Missouri, under 10 to 30 feet of mining waste and inject millions of tons of mine waste into Big River if it should fail. The USCOE study concluded that the Federal government should help stabilize 17 of the high-hazard, unsafe dams based on threat to human life, property loss, extreme long-term environmental damage, and magnitude of the problem (USCOE 1992).
Three lead tailings dams (Leadwood, Eaton, and St. Joe State Park) and tailings piles (including sites at National, Bonne Terre, and Elvins) in St. Francois County are being studied by Missouri Department of Natural Resources (MDNR) and the United States Environmental Protection Agency (USEPA) to determine the proper method of remediation. The Leadwood tailings pond dam was stabilized and spillway enlarged in 1996 (J. Czarnezki, personal communication). A plan for stabilization of the St. Joe State Park dam has been approved. Stabilization of lead tailings began in 1997.