Effects of Main Stem Impoundments and Channelization upon the Limnology of the Missouri River, Nebraska

Abstract

Rigid control has been imposed upon the Missouri River by impounding over one-half of the upper 1500 miles and by channeling most of the remaining river within permanent, narrow banks. These controls have caused environmental changes in the lower Missouri River, as shown by this study, of adjacent unchannelized and channelized sections of river below the main stem impoundments. Impoundments have regulated flow by evening maximum and minimum discharges and improved downstream water quality by decreasing turbidity and indirectly raising the dissolved oxygen. In addition the impoundments have contributed a limnetic cladoceran, Leptodora kindti, to the drift and have affected the distribution of benthos through the modification of turbidity. Channelization of the river has reduced both the size and variety of aquatic habitat by destroying key productive areas. Average standing crops of benthos were similar in un-channelized and channelized river (0.63 and 0.67 pounds per acre, respectively) but the benthic area had been reduced 67% by channelization. In the channelized river the average standing crop of drift was 8 g per acre-foot while in the unaltered river the average standing crop was 68 g per acre-foot. There was little similarity between the organisms of the drift and benthos; however there was similarity between the organisms in the drift and the aufwuchs.

Patterns of fish diversity in a mainstem Missouri River reservoir and associated delta in South Dakota and Nebraska, USA

“…Further, studies have shown that Missouri River reaches with braided river channels and a diversity of aquatic habitats within the floodplain have diverse fish communities (Schmulbach et al, 1975;Kallemeyn and Novotny, 1977;Jacobson et al, 2001) and are superior for sport fish production as compared to channelized and/or modified reaches (Groen and Schmulbach, 1978). Such reaches also support more diverse invertebrate communities (Morris et al, 1968).…”

Classification of reaches in the Missouri and lower Yellowstone Rivers based on flow characteristics

“…After channelization, however, the Missouri River below Sioux City, Iowa, was changed into a fairly narrow and swift flowing river, resulting in a shortening of the channel by 125 km and reduction of the wetted area by nearly 64% (Whitley and Campbell, 1974). Likewise, the construction of six major reservoirs in the middle reaches of the river has changed water quality above and below the dams (Morris et al, 1968) and altered the hydrology of the river (Hesse and Mestl, 1993). These major alterations have essentially divided the Missouri River into three zones, an upper zone upstream from the major alterations, a middle zone with short free-flowing reaches between reservoirs, and a zone downstream of the impoundments which is entirely channelized except for the reach between Yankton, South Dakota and Sioux City, Iowa (Figure 1).…”

Hydrological alteration along the Missouri River Basin: A time series approach

“…Six mainstem dams were also constructed between 1937 and 1963, primarily to control flooding and to provide adequate depth for navigation on the lower river (Galat et al, 1996). The associated reservoirs cover nearly half of the upper 2,500 km of the Missouri River (Morris et al, 1968). The result of these alterations has been a metamorphosis from a once natural, complex floodplain river to a relatively artificial, simple system (Whitley and Campbell, 1974), with division of the river into three management zones: an upper, relatively unaltered (or least altered) zone upstream from the reservoirs, a zone between the reservoirs where short stretches of unchannelized river remain, and a lower channelized zone (Fig.…”