Geology and Geomorphology
The entire state of Missouri has three of the major physiographic provinces of the United States: the Central Lowlands, the Interior Highlands, and the Coastal Plains. The Gasconade River watershed lies within the Ozark Plateau of the Interior Highlands. Further subdivision of the Ozark Plateau places the watershed within the Salem Plateau whose elevation is between 1000 - 1400 feet above mean sea level.
Surface geologic formations are composed of dolomite and sandstone of the Ordovician Age. All geologic formations in the watershed are part of the Canadian Series (MDNR 1979). Tributary streams and the main stem Gasconade River cut through a member of the Gunter Sandstone, the Gasconade Formation. This formation has many springs that contribute to the base flow of the main stem Gasconade River. As one moves out of the floodplain toward the uplands, the Gasconade Formation is replaced by the Roubidoux Formation that contains sandstone and cherty dolomite. Farther upland, within the headwaters of the Gasconade River are a composite of Smithville Formation, Powell, Cotter, and Jefferson City dolomites. Rocks in these formations tend to be more weathered with cracks, joints, and solution openings.
A losing stream is defined as a stream that loses 30 percent or more of its flow into an aquifer within two miles of flow discharge (MDNR Clean Water Commission Water Quality Standards 10 CSR 20-7.01, 1994). Permeable rock type is responsible for the movement of water to subsurface levels. Most of the watershed has well sustained base flows. The karst topography causes losing portions in the Osage Fork, Roubidoux, North Cobb, Little Piney, Spring, and Mill creeks, and Gasconade River (MDNR 1986). Approximately 33 miles of the central portion of the Gasconade River comprises the longest losing segment in the watershed (Table Ge01). The Roubidoux, Corn, and Little Piney creeks have 16, 12.5, and 12 miles of losing stream, respectively. These subwatersheds are more densely populated with springs than other subwatersheds.
The collective pattern of soils with their associated relief and drainage makes the Gasconade River watershed a unique natural landscape. The general soils map (Figure Ge01) is useful for planning on a large scale; more detailed maps can be found in NRCS county soil surveys for small scale planning, such as farm or field management or project site selection.
The Gasconade Watershed traverses three land resource areas: Deep Loess Hills, Ozarks, and Ozark Border. The Deep Loess Hills is found mostly in the northwestern part of the state. Some of the soil deposits are found on ridgetops and broad uplands, but the thickest deposits of loess are found along river bluffs with decreasing thickness away from the bluffs. The Gasconade River has one association, Menfro-Winfield-Haymond, in this resource area along the Missouri River. The Ozarks Land Resource Area is found in the southern part of the state. Soils of this resource area cover a broader soil category and greater number of associations. Not only were soils formed in alluvium along narrow bottomland areas, but most soil formations were under forest vegetation with an occasional tall grassy open area or glade area. Ozark Border soils are located in the southeastern part of Missouri. This area was formed under the same conditions as the Ozarks. The bottomland areas tend to have gravelly alluvium soils rather than cherty alluvium soils. Both the Ozarks and the Ozark Border areas have fragipans that tend to restrict plant root growth.
The soil associations in the Gasconade River watershed have several major soil types. These soil types determine soil uses and the distribution of vegetation types.
The Clarksville series consists of those soils found in level to steep terrain, steep-side slopes and narrow ridges, that has good drainage. Formed in a residuum cherty dolomite, the surface soils are a dark grayish-brown cherty dolomite. Deeper layers are a more pale to reddish silt loam and increase in clay content. Because of Clarksville's hazard for draughtiness, thus low moisture holding capacity, most of this series is forested.
The Lebanon series are moderately well drained soils on level or sloping areas. Soil is silty in its upper layers and cherty fragipan in lower layers. The surface layers are dark grayish-brown silt loam and at a depth of about 24 inches is the fragipan. Clay content increases below 31 inches creating a strong-brown silty clay. Most of the soils are in pasture and some hardwood areas remain.
Formed in cherty colluvium, the Viraton series consists of well drained soils with cherty fragipan. They are sloping to moderately steep. Surface layers are brown cherty silt loam. A cherty silty clay loam exists to 18 inches and a thick fragipan follows. Below the 18-inch fragipan is a yellowish-red silt loam. Like the Lebanon series low moisture holding capacity creates drought conditions. Idle areas and pasture make up most of this series.
Found in floodplains, the Haymond series is very deep and well drained silt loam. Surface layers are dark grayish brown silt loam. Deeper layers vary only slightly in color. Flooded during brief periods, these soils are cultivated for corn, soybeans, and wheat, and some small areas are wooded.
The Soil Conservation Service (now know as the Natural Resources Conservation Service (NRCS)) in a 1977 National Erosion Inventory estimated that the soil loss from sheet erosion amounts to 2.7 tons/acres/year in the Gasconade River watershed (Anderson 1980). In the same survey, sheet and rill erosion, involving the removal of thin layers of soil from an area by water, and creating channels about 30 centimeters in depth, in the Gasconade River watershed did not exceed allowable limits of 2.5 - 5 tons/acre/year on pasture land; however, sheet and rill erosion did reach 18 - 24 tons/acre/year on tilled land (Anderson 1980). Twenty tons per year is equivalent to one-eighth of an inch of soil. For comparison, in forest soils, with many roots to maintain soil integrity, losses in the Gasconade River watershed are 0.25 - 0.5 tons/acre/year. Gully erosion problems, extreme soil losses causing trenches that exceed 30 centimeters in depth, are moderate in the Gasconade River watershed. Actual sediment reaching streams is low (0.8 tons/acre/year) in comparison to other watersheds in the state.
The drainage of the Gasconade Watershed excluding the Big Piney River covers 1,797,130 acres or 2806.9 square miles (Table Ge02). The watershed is approximately 130 miles long. Considerably wider at the upper reaches, 50 miles wide, the watershed narrows north of the 38E latitude to approximately 10 miles in width (Vandike 1995). The major tributaries such as Third Creek, Roubidoux River, Little Piney Creek, Upper Osage Fork, and Lower Osage Fork have drainage areas of 64,910, 181,220, 190,720, 214,960, and 109,440 square miles, respectively.
Stream order was determined using a system of classification that was first defined by Horton (1945) and later modified by A. N. Strahler (1952). Strahler called all unbranched tributaries first-order streams; two first-order streams join to make a second-order stream, and so on downstream to the stream mouth. MDC East Central Region Fisheries personnel determined stream gradient and stream order from United States Geological Survey (USGS) 1:24,000-scale topographic maps (Table Ge03) for all third-order and greater streams within the Lower Gasconade River watershed (HUC # 10290203) and all fourth-order and greater streams within the Upper Gasconade River watershed (HUC #10290201).
East Central Region Missouri Department of Conservation biologists collected elevation and distance data from USGS 7.5 minute topographic maps (usually 20-feet contours). Gradient by stream order and watershed were tabulated, measuring the vertical drop over a given distance for the number of streams that were fourth-order or greater. When comparing stream gradient between stream systems, the average value provides a useful means of summarizing this type of continuous data. Average gradient for the Upper Gasconade River watershed is 27.6 feet/mile, and the average gradient for the Lower Gasconade River watershed is 3.9 feet/mile. The last mile of the upper Gasconade River more than doubles in gradient from 101.1 feet/mile to 218.9 feet/mile. Little Piney Creek has an average gradient of 46.8 feet/mile. Roubidoux Creek has an average gradient of 6.9 feet/mile from its mouth to the confluence with the East Fork and West Fork Roubidoux Creek, which have average gradients of 60.1 and 58.1 feet/mile, respectively. The Osage Fork and Beaver Creek have gradients that average 25.7 and 20.1 feet/mile.
Gradient plots are useful for understanding channel steepness in relation to geology. The relief of the land influences drainage, runoff, and other factors such as erosion. The gradient of the river decreases downstream, so the overall profile is a hyperbolic curve that decreases in gradient downstream (Figure Ge02). Within a watershed, gradient plots for all fourth-order or greater streams were created. A plot of the entire Gasconade River and its major tributaries shows relatively moderate gradient (Figure Ge02).