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|Title:||Biological and physical effects of Missouri River spur dike notching|
|Authors:||Pennington, C. H.|
Shields, F. Douglas.
Sjostrom, John W.
Myers, Karla A.
|Keywords:||Dikes (Engineering)--Missouri River--Environmental aspects|
Jetties--Missouri River--Environmental aspects
|Publisher:||Environmental Laboratory (U.S.)|
|Series/Report no.:||Miscellaneous Paper;MP EL-88-11|
|Abstract:||Abstract: Since 1975; the US Army Engineer District, Omaha, has had a program of creating notches or gaps in river training structures along the Missouri River. More than 1,300 notches have been constructed either by excavating stone or by omitting repairs on small portions of damaged structures. An additional 20 spur dike training structures located in two reaches of the Missouri River near Omaha were modified in 1982 and 1983 using a new notch design. Material excavated from notches was used to construct a small reef just downstream of each notch. Results of detailed, semiannual hydrographic surveys of the regions immediately adjacent to 12 of these notch-with-reef structures were analyzed to determine the effects of modification on depths and water surface area. Means and standard deviations of depth adjacent to dikes increased after notching, as did water surface area at a reference stage. Considerable variation in bed response to notch-with-reef construction was observed from dike to dike and between the two reaches studied. Increases in mean depth were greater for the reach with greatest stage variation and for dikes where notch inverts were lowest relative to adjacent downstream bed elevation. In an effort to compare fish use of the notch-with-reef structures with that of other types of training dikes, a study was conducted in one of the two Missouri River reaches mentioned above. Fish, water quality, current velocity, and bed material were sampled during moderate flow in June and August adjacent to nine spur dikes. Three of the dikes were unmodified, three were notched with reefs, and three were simply notched. No significant differences were observed among dike types for any of the variables. However, the areas around the dikes are distinctive from the main channel -- and much more valuable ecologically. It was concluded that Missouri River spur dike notching generally causes small increases in the area of valuable low-velocity aquatic habitat.|
|Appears in Collections:||Miscellaneous Paper|
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