Geology and Geomorphology
Physiographic Region, Geology, Soils
The Salt River basin lies in the eastern section of the Glaciated Plains Division of Missouri (Thom and Wilson 1980), also known as the Dissected Till Plains (Figure Ge01). The Till Plains were formed by glaciers that deposited drift composed mostly of clay with some rock, gravel, and sand lenses (MDNR unpublished). In the upper portion of the basin, where local relief is generally low (North Fork, Middle Fork, South Fork), the glacial till is overlain by loess deposits, except in a few areas where streams have incised Pennsylvanian or Mississippian aged rock. Although highly variable, till is generally less than 200 feet thick and composed predominantly of clay with some rock fragments and sand lenses. Beneath the till in upland areas may be a thin layer of sand and gravel and then a layer up to 200 feet thick of alternating deposits of Pennsylvanian age sandstone, siltstone, shale, limestone, and coal (Figure Ge02). An exception is the central portion of the North Fork sub-basin where glacial till is underlain by thickly bedded limestones interbedded with thin Mississippian age shales. In the valleys of the Middle and South Fork sub-basins, streams have eroded the Pennsylvanian rocks to expose limestone bedrock and shales. In the central portion of the basin around Mark Twain Lake, relief increases and glacial till shallows to less than 100 feet thick. Exposed limestone and shales in the valley walls and streambeds are more prevalent. Till quickly shallows in the lower Salt River sub-basin (below the re-regulation dam) to less than 50 feet as valleys become more abrupt with high relief. A relief of 440 feet is attained at the lower end of the basin near Louisiana. Exposed Mississippian and Ordovician age shales and limestone are common in both the valley walls and streambeds. Detailed geological history of the basin can be found in Klein and Daley (1974).
Nearly all of the basin is located in the Central Claypan region (Allgood and Persinger 1980). Central Claypan soils are primarily Putnam-Mexico and Mexico-Leonard-Armstrong-Lindley associations formed in loess or glacial till. Putnam-Mexico soils are generally deep, nearly level to gently sloping soils with a silt loam surface overlying a silty clay subsoil of very low permeability. Mexico-Leonard-Armstrong-Lindley soils are deep, level to steep, well drained to poorly drained, loamy and clayey uplands soils. Mexico and Leonard soils in this association have a silt loam surface overlying a silty clay subsoil while Armstrong and Lindley soils have loam surface overlying a clay loam subsoil. Subsoil permeability is slow.
The extreme lower portion of the basin is located the Central Mississippi Valley Wooded Slopes region. The Menfro-Winfield-Lindley soils in this area are moderately well drained with a loam or silt loam surface overlying silty clay loam subsoil of slow permeability. Poorly drained, loamy soils of the Arbela-Piopolis-Blackoar association are found on the lower floodplains of major streams in the basin. These alluvial soils generally have a silt loam or silty clay loam surface overlying a silt loam subsoil of moderate to slow permeability. As the Salt River enters the Mississippi River floodplain soils turn to loamy, silty, or clayey alluvium of the Westerville-Fatima-Wabash association.
Due to the clay content of the till and underlying shale and limestone, vertical movement of water from the surface to groundwater is limited throughout the basin (MDNR unpublished). Few significant springs exist in the basin so base flow is not well sustained during dry periods.
Streams were identified on USGS 7.5 minute topographic maps and ordered according to Strahler (1957). A stream code was assigned to each third-order or higher stream based on the method of Pflieger et al. (1981). There are 165 third-order and larger streams in the basin (Table Ge01). The mainstem Salt River and the South Fork Salt River are the only seventh-order streams, and North Fork and Middle Fork are the only sixth-order streams. Fifth-order streams include Bear Creek (North Fork sub-basin), Long Branch (South Fork sub-basin), Elk Fork (Middle Fork sub-basin), and Spencer Creek (lower Salt River sub-basin). All other streams in the basin are fourth-order or smaller.
The Salt River watershed drains 2,914 square miles (1,867,900 acres) of land. The North Fork, South/Middle Fork, and lower Salt River sub-basins compose 32%, 41%, and 27% of the Salt River basin, respectively (SCS 1992). Drainage area of other fifth-order and larger streams in the basin, estimated by digitizing 1:100,000 topographic maps, are approximately as follows: Bear Creek-124 square miles, Middle Fork-352 square miles (excluding Elk Fork), Elk Fork-292 square miles, Long Branch-188 square miles, and Spencer Creek-215 square miles.
Channel gradients for all third-order and higher streams were determined using USGS 7.5 minute topographic maps and digitizing software (Table Ge01). The average gradient for each stream is based on the change in elevation from the stream's uppermost point to its mouth. Gradients were also calculated separately for each order within an individual stream.
Channel gradients for the major streams in the upper Salt basin are relatively low. Of the fifth-order and larger streams in the basin, Bear Creek (North Fork sub-basin) has the highest gradient (5.4 feet/mile). Although the lower Salt River has an average gradient of only 1.4 feet/mile, many of the smaller streams in its watershed have high gradients due to high local relief. For example, an unnamed third-order stream in Pike County has a gradient of 87 feet/mile. Ten other streams in this sub-basin have gradients exceeding 50 feet/mile.
Soil Conservation Projects
Under the authority of the Watershed Protection and Flood Prevention Act, P.L. 83-566, three soil conservation projects have been proposed for the basin (Table Ge02). The Middle Fork Salt River application is inactive because a referendum to re-authorize the watershed subdistrict failed. The other two applications are also inactive because they were determined to be economically unfeasible. There are nine SALT projects and one EARTH project in the basin covering 235,688 acres (Table Ge02).
The North Fork Project, which evolved from the Mark Twain Water Quality Initiative, is an education and outreach program that provides information, training, and networking opportunities on water quality issues, including soil conservation, in the basin. This project is coordinated by the Clarence Cannon Wholesale Water Commission and University of Missouri Outreach and Extension and is partially funded under Section 319 of the Clean Water Act.
There are seventeen conservation and stream access areas totaling 7,648 acres within the Salt River basin (Table Ge03; Figures Ge03, Ge04, and Ge05). Many of the areas provide access to basin streams. Boat ramps are provided at Paris, Santa Fe, Hunnewell, and Indian Camp accesses and at Ted Shanks CA. Several accesses are located within a few miles of each other and provide excellent drop-off and pick-up points for one or two day fishing/float trips (e.g. Pin Oak to Arrow-wood-10 miles, Arrow-wood to Mound View-12.5 miles, Mound View to Hunnewell-7.3 miles). In addition to Mark Twain Lake, the Missouri Department of Conservation manages the fisheries of eight small impoundments in the basin with a combined total of 566 surface acres.
Other publicly owned areas in the basin includes land managed by the U.S. Army Corps of Engineers surrounding Mark Twain Lake. Much of the 33,845 acres around the lake are available for public use. Mark Twain State Park (Missouri Department of Natural Resources) encompasses another 2,285 acres near the lake.
Corps of Engineers 404 Jurisdiction
The Salt River basin is under the jurisdiction of the St. Louis District of the Army Corps of Engineers. Application for 404 permits should be sent to: 1222 Spruce St. St. Louis, Missouri 63103-2833, (314) 331-8575.