GEOLOGY/ GEOMORPHOLOGY

Physiographic Region/Geology/Soil Type

The Niangua Watershed lies in the Salem Plateau subdivision of the Ozark Plateau physiographic region. The watershed is underlain with several hundred feet of Ordovician and Cambrian rock, largely dolomite (Harvey et al., 1983). The edges of the watershed lie in Jefferson City-Cotter dolomite, while streams cut into progressively older Roubidoux, Gasconade, and Eminence formations (MDNR, 1984). There is considerable subsurface movement of water in the watershed through solution dissolved channels in the fractured and jointed dolomite. As a result, karst features such as caves, sinkholes, losing streams, and springs are abundant. Streams which incise into the middle or lower Gasconade have well sustained base flows even during dry periods, due to ample groundwater supplies (MDNR, 1984). Streams which incise into the Roubidoux formation are frequently losing streams and sinkholes are common (Harvey et al., 1983).  Soils in the watershed are classified as residual, alluvial, colluvial, and loess (Harvey et al., 1983). Residual soils consist primarily of material weathered from cherty dolomite, dolomite, and sandstone, and occur on the surface of steep slopes. When they develop in uplands from Roubidoux formations, and Jefferson City - Cotter dolomites, an impervious fragipan usually occurs 18 to 24 inches below the surface. Colluvial soils, which are soils deposited on lower valley slopes by erosion from more elevated sites, are limited in abundance. Alluvial soils are those transported by streams and deposited on level or gently sloping areas in flood plains. They range in size from silt to gravel. Loess soils are silty, windblown material which commonly occur on ridgetops.

Watershed Area

The watershed area of the entire watershed is 1,040 square miles. The LNR watershed is 320 square miles, which is approximately one-third of the drainage of the entire watershed. Watershed areas for all fourth order and larger streams and some third order streams are shown in Table 2. The watersheds of fourth order streams are delineated in Figure 3. Approximately 500 acres of the Niangua Watershed is within Benton County, 164,000 within Camden County, 279,000 within Dallas County, 49,000 within Hickory County, 96,000 within Laclede County, and 69,000 within Webster County.

Stream Order

Stream order was determined from 7.5 minute topographic maps for all streams in the watershed. The NR has two fifth order and 14 fourth order tributaries. The LNR has one fifth order and six fourth order tributaries. Table 2 lists all third order and larger streams in the Niangua Watershed. Table 3 lists the total mileage of third order and larger streams, and the portions inundated by LOZ and Lake Niangua.

Channel Gradient

Stream gradients were determined for all third order and greater streams from the 7.5 minute topographic maps shown in Figure 4 .