Geology and Geomorphology
The majority of the Nodaway River basin lies within the Western Glaciated Plains Natural Division with a small area near the mouth in the Big Rivers Upper Missouri Natural Division (Figure Ge01) (Thom and Wilson 1980). The entire basin is in the Dissected Till Plains (MDNR 1986a). The basin topography consists of rolling to hilly glacial plains divided by wide, level stream valleys. In the Iowa portion of the basin, most divides are rounded and parallel to the regional northeast-southwest drainage. Steep irregular loess mounds, formed from wind blown glacial outwash, border the Missouri River flood plain near the mouth of the Nodaway River.
Geology and Soils
The basin soils overlay Cretaceous and Pennsylvanian deposited sedimentary bedrocks (Figure Ge02). The Pennsylvanian-aged formations consist primarily of sandstone, shale, limestone and thin seams of coal (USDA 1981).
Most basin soils are formed from glacial till (a mixture of clay, rock, gravel and sand), alluvium (water deposited soil), and a windblown silt called loess. The soils have their origin in the four periods of continental glaciation with deposits from the final glacial advance (Kansan) overlying earlier deposits. The topography of this region is the youngest in the state of Missouri. When glaciation ceased, the area was covered with a relatively level drift plain. After the last glaciation a thick layer of loess was deposited over the basin. Loess deposits in the basin are some of the deepest in Missouri, ranging from 10 - 30 feet in depth. The depth of the till is highly variable, but it generally ranges between 200 and 400 feet, obscuring most of the bedrock in the region. Occasional pockets or channels of sand are found in the till strata. Glacial sand and gravel may underlie the till (USDA-SCS 1982).
Loess soils cover broad, gently sloping ridges of silty loam and are suitable for farming. Glacial soil occurs on steeper, eroding slopes and it is a less productive brown loam or gritty silt loam. Valleys are covered with alluvial silt and clay loams, and are the most productive soils in the basin (USDA-SCS 1982).
The Nodaway River is a sixth order river with a basin area of 1,820 square miles. The basin covers portions of southwestern Iowa and northwestern Missouri, with 1,230 square miles (68%) in Iowa and 590 square miles (32%) in Missouri. The Nodaway River basin is bound by the Platte River basin to the east and the Grand River and Des Moines River basins to the northeast, with the latter defining the boundary between the Missouri River and Mississippi River basins. The west side is bound by the Tarkio River basin, the northwest by the Nishnabotna River basin, and minor Missouri River tributaries to the southwest. The basin is about 115 miles in length. It averages 12 miles in width in the lower two-thirds and has a maximum width of 35 miles near the upper end. The flood plain width varies between one-half and two and one-half miles. The Nodaway River basin is prone to extensive flooding due to poor land use practices and its tapered top heavy shape (USCOE 1973).
There are 156 third order and larger streams within the basin. Gradient information was calculated using USGS 7.5 minute topographic maps. Gradient information for all streams fourth order and larger are found in Figure Ge03. The Nodaway River was described as a low gradient river with a gradient of two to six feet per mile (USCOE 1973). Current gradient plots including the three main branches (East, Middle, and West Nodaway rivers) in Iowa range from 2.0 to 6.2 feet per mile indicating there has probably been little change in gradient over the past 25 to 30 years. Gradient in the lower 64 miles of the Nodaway River (confluence of the East and West Nodaway rivers to the confluence with the Missouri River) is virtually constant at 2.0 feet per mile. Average gradient values for fifth order streams range from 5.5 to 16.9 feet per mile. Fourth order stream gradients range from 7.6 to 45.0 feet per mile. As a general rule, shorter streams have higher average gradients.