Geology and Geomorphology
Geology and Geomorphology of the Headwater Diversion Watershed
Most of the basin lies entirely within the dissected Salem Plateau Subdivision of the Ozark Plateau (Figure Ge01). The basin, however, has some distinct topographic features associated with the rapidly descending Ozark Escarpment that forms the prominent boundary between the high relief Ozark Plateau and the low relief Mississippi Alluvial Plain Divisions (Missouri Department of Natural Resources 1986). Land elevations range from 1,230 ft NGVD (National Geodetic Vertical Datum of 1929) in the Castor River headwaters to 314 ft NGVD at the Headwater Diversion Channel confluence with the Mississippi River.
The geology of the basin is greatly influenced by the nearby St. Francois Mountains uplift (Ozark Dome) which has exposed outcrops of irregularly distributed Precambrian igneous rock and elevated the upper watersheds (MDNR 1986, Figure Ge02). The tilt of the uplifted strata exposes progressively younger and less resistant limestone and dolomite bedrock in all downstream easterly and southeasterly directions (MDNR 1984). The fractured limestone and dolomite bedrock on all slopes is overlaid by a thick (200 ft at some sites) weathered layer of cherty residuum (Soil Conservation Service 1981).
The ancient uplift has had the time and energy to carve moderately wide floodplain valleys which are overlaid with a deep gravel alluvium that is occasionally interrupted by igneous outcrops (pink granite shut-ins) and remnant limestone bluffs. The soluble cherty residuum, fractured bedrock and unconsolidated alluvium allow rapid groundwater movement that sustains most base flows during dry periods and yields clear water. Springs, however, are not common in the basin. Occasional karst features are restricted to the northeast edge of the basin near the city of Jackson in the upper Byrd Creek and Hubble Creek watersheds.
Soils in the basin are transitional from the dominant Ozark Border region on the west side to the secondary Central Mississippi Valley Wooded Slopes region on the east side (MDNR 1986). Soils formed in the upland loess and cherty limestone residuum are typically infertile, droughty, slightly acidic, extremely gravelly (65% chert by volume) and generally suitable for only woodland and grass production (SCS 1992 and 1986). The more fertile soils formed in the lowland alluvium contain sand, silt, loam and clay components that are marginally to highly suitable for improved pasture and row crop production (SCS 1981).
The primary soil series associated with the basin are: (moving upstream in the basin) Sharkey, Falaya, Wakeland, Wideman and Elk in the bottoms; Holstein, Peridge, Poynor, Goss and Clarksville on the slopes; and Menfro, Goss and Hilderbracht on the ridgetops. Unfortunately, all of these soil classifications share two distinct characteristics -- a large volume of chert which is responsible for excessive gravel bedloads, and severe to hazardous erosion potential when disturbed.
The basin has some of the highest erosion potential in the state. Annual sheet and rill erosion on tilled land (24-30 tons/acre) and undisturbed forest land (0.25-0.50 tons/acre) exceeds most of the other basins in the state (Anderson 1980). Sheet and rill erosion on permanent pasture, however, are considered acceptable with a rate of 2-5 tons/acre. Gully erosion (0.3-0.8 tons/acre) often exceeds the severe rates in north Missouri and is uncharacteristic of the remainder of the Salem Plateau.
Despite the high potential for serious erosion on disturbed soils, relatively little sediment (1.8 tons/acre/year) actually enters basin streams. Active soil conservation programs, good local land management practices, low topographic relief and relatively few acres in row crop production all contribute to the currently low fine-sediment loads in the lower watersheds. Historically, poor timber management practices and conversion of woodland to pasture have contributed to the more serious problem of shifting gravel deposits in the stream channels of the upper watersheds.
The drainage area of the basin is 1,207 square miles. Three primary watersheds, Castor River, Whitewater River and Crooked Creek drain 81 percent of the basin (Table Ge01). The Cape La Croix Creek watershed (50.6 square miles), which is sometimes included as part of the basin in SCS and U.S. Department of Agriculture (USDA) publications, is diverted directly into the Mississippi River. Therefore, the city and suburbs of Cape Girardeau are not part of the Headwater Diversion Basin. Also, Dark Cypress Swamp (Hawker, Cane, Dry, Malone and Gizzard Creeks) drains directly into the Diversion Channel below the Greenbrier Bridge and is included in the Diversion Channel subbasin, not the Castor River watershed.
Stream Mileage, Order and Permanency
A total of 2,366 streams occupying 2,984 miles of channel were identified, ordered, measured (by hand dividers) and classified as either intermittent or permanent as indicated on U.S. Geological Survey (USGS) 7.5 minute topographic maps (Table Ge02). All 104 third order and larger streams were tabulated by name, length, order and basin position (Table Ge03 ). The apparently liberal designation of 715 miles of permanent streams on USGS topographic maps does not agree with the designated 439 miles of permanent streams classified under Missouri Water Quality Standards (CSR 1981). The Missouri Water Quality Standards figure is probably the more accurate estimate. The percentages of second and third order permanent stream mileage measured from USGS topographic maps appear to be much too high, based on field observations by Fisheries District staff.
In this part of Missouri, only 2.7 square miles of watershed are needed to maintain each mile of permanent stream (MDNR 1984). The ratio of watershed area to length of permanent stream is probably the lowest of all Missouri river basins. The high incidence of stream permanency is the result of basin geology and the abundant water supply provided by favorable precipitation, runoff and evaporation patterns in the southeast portion of the state. The influence of geology and weather patterns can even affect stream permanency within the basin. Streams in the southeast portion of the basin tend to have more permanent water and lower watershed to stream length ratios.
Gradient information was calculated from USGS 7.5 minute topographic maps (usally 20-ft contours) and tabulated by stream order, subbasin and position in the basin for 105 third order and larger streams. Gradient plots were preparted for 25 fourth order and larger stream channels (contact authors for Appendix A information). Gradient information for 80 third order stream channels has been tabulated (Table Ge04) and is on file at Fisheries District headquarters for convenient reference and conversion to graphical gradient plots. Diverse channel gradients throughout the basin reflect the complicated influences of variables associated with transcending geological formations, bedrock composition, channel age and watershed size.
Steeper gradients on the west side of the basin (Castor River) are generally a result of the Ozark Escarpment transition from the Salem Plateau to the Mississippi Alluvial Plains. However, steeper gradients also tend to occur in some east sloping drainages (Bear Creek and Little Whitewater Creek) because of the tilt provided by the St. Francois Mountains uplift. The uplift has also exposed scattered outcrops of erosion resistant granites that provide hardpoints, vertical control and rigid channel boundaries which produce some undulating channel profiles in the higher elevations in the northwest part of the basin. The older, larger and lower gradient mainstem channels in the lower reaches of Crooked Creek and the Whitewater River are probably the only stream channels that are nearing the base equilibrium gradient conditions.