RIVER ICE INFLUENCES ON FORT PECK REACH, MISSOURI RIVER
9
riverbank erosion as well as from tributary inflow; the remainder is sand
entrained from the channel bed. The sediment load is close to zero immediately
downstream of Fort Peck Dam.
Riverbanks
The stability of the riverbanks along the Fort Peck reach of the Missouri
River is a longstanding concern (e.g., Haydon 1931, Pokrefke et al. 1998). Only a
few studies have investigated the geotechnical aspects of riverbank stability
concerns along the reach (e.g., Simon et al. 1999). Also, a few studies have
assessed the extent of riverbank erosion along the reach, as well as other reaches
along the Missouri River (e.g., Pokrefke et al. 1998). To date, only one study
considered aspects of winter effects on bank stability along the Missouri River
(Lawson 1983, 1985). That study, however, focused mainly on banks around
reservoirs such as Lake Sakakawea.
At some locations along the Fort Peck reach, especially in channel bends, the
river has cut quite steep riverbanks (Fig. 5). The riverbanks typically are formed
of soils having relatively low shear strength, especially low cohesive strength
(Simon et al. 1999), and typically consisting of silty and sandy layers inter-
spersed with clay or silty clay layers. The occurrence of a layer of sandy or silty
soil at the base of a riverbank makes it prone to erosion. This feature is common
at the sites selected for this survey.
Figure 5. Riverbank along the reach.
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