Average annual precipitation for the basin ranges from 32 inches in the northwest part of the basin to 36 inches in the southeast portion (USDA-SCS 1982). The greatest amount of precipitation normally occurs in May (4.49") and June (5.77") (USDA-SCS 1982). The basin is covered by glacial till, a clayey material that greatly retards movement of water to the subsurface (Detroy & Skelton 1983). Most rainfall runs off the surface of the land rather than soaking into the soil. Streams in the basin show rapid flow increases in conjunction with rains, but quickly return to low flow conditions when runoff stops (MDNR 1984). Runoff increases from 6" in the northwest to 8.5" in the southeast portion of the basin. Most runoff occurs in June (USDA-SCS 1982).
United States Geological Survey (USGS) Gaging Stations
There are four active USGS water stage gages throughout the basin (USGS 1992). Two stations are on the Grand River near Gallatin and Sumner, two are on Thompson River at Trenton and Davis City, IA. Several inactive gaging stations are also located throughout the basin. Figure gs shows the location of the active and inactive gaging stations in the Grand River basin.
There are more than 1,000 third-order and larger streams within the Grand River Basin. Due to the size and complexity of the Grand River Basin, individuals will need to look at specific reaches as the need arises to determine permanency of flow. To facilitate this, a listing of 7.5' topographic maps covering the entire reach of all fifth order and larger streams is provided in Table Hy01. Maps can be ordered from the United States Geological Survey (USGS) in Rolla, MO. The phone number is 1-888-ask-usgs. Most streams in the basin with drainage areas less than 50 square miles will stop flowing for seven consecutive days or more at some time every two years (Detroy and Skelton 1983).
Average Annual Discharge
The average discharge for the Grand River (Table Hy02) near Sumner, Missouri is 3,917 cfs (USGS 1992). The maximum instantaneous peak flow (180,000 cfs) occurred in June, 1947. Peak discharge for Grand River at Sumner during 1993 flooding was 150,000 cfs (Parrett et al. 1993).
Detroy and Skelton (1983) developed an equation for calculating average discharge for streams throughout the basin. Average flow can be estimated using the equation:
Q=0.73 A0.97, where average annual streamflow (Q) is in cubic feet per second, and drainage area (A) is in square miles.
The Grand River basin makes up approximately 1.5% of the Missouri River watershed but contributes 7% of the average annual discharge (USCOE 1989).
7-day Q2 and Q10 Low Flows
According to Detroy and Skelton (1983): Streams in the Grand River Basin are not sustained by ground-water inflow because of the low hydraulic conductivity of the clays and shales of the area. Exceptions are the downstream reaches of the Grand and Thompson rivers.
Most streams in the basin with drainage areas less than 50 square miles will cease to flow for 7 days every other year. Approximately half of the streams with drainage areas of 50 to 200 square miles will also cease to flow every two years. The other half of those streams will have flow of less than 0.7 cfs.
Streams with drainage areas less than 150 square miles will almost always cease flowing every ten years. Approximately half of the streams draining 150 to 500 square miles will have seven day low flows of less than 2 cfs. Drainage area is not a good predictor of low flow in streams that drain larger watersheds.
Dam and Hydropower Influences
There are no major dams within the basin. Seven large flood control reservoirs were designed by the Corps of Engineers (USCOE 1963). A follow-up report concluded that the reservoirs and associated channel modification was not economically feasible. The projects were deauthorized in 1989 (USCOE 1989). Due to extensive flooding throughout the basin during 1993, support for reauthorization of these projects has surfaced in some areas. A federal buyout and relocation of Pattonsburg, Missouri appears to have satisfied most people in the area.
In the 1970's, there was an unsuccessful proposal to impound a large reach of Locust Creek in association with a proposed coal gasification plant near Milan (approximately river mile 46). In 1990, there was a renewed interest in constructing the same 5,800 acre lake for water supply and recreation. This second attempt was also unsuccessful because the Locust Creek Lake Committee could not acquire sufficient funding to construct the reservoir. This lake would have inundated several miles of unchannelized stream and altered downstream flows. There is still local interest in creating a water supply and recreation lake near Milan.
The number of lakes larger than two acres has changed dramatically since 1984. There are approximately 30 lakes larger than 50 acres within the basin. Numerous 5-10 acre watershed structures have been built both on public and private land in association with PL-566 and erosion control projects. There are concerns regarding the impact of numerous small flood control structures and their impact on low flow conditions. These structures intercept runoff and make no provisions for maintenance of stream flows.