page_title: River bank failure
section_title: Northwestern Minnesota bank failure
hierarchical_section_title: River bank failure / Examples / Northwestern Minnesota bank failure
caption_attribution_description: English: High flows erode the steep banks of the Pembina River, in northeastern North Dakota, contributing to the high sediment load.
context_page_description: River bank failure can be caused when the gravitational forces acting on a bank exceed the forces which hold the sediment together. Failure depends on sediment type, layering, and moisture content.
  All river banks experience erosion, but failure is dependent on the location and the rate at which erosion is occurring.
  River bank failure may be caused by house placement, water saturation, weight on the river bank, vegetation, and/or tectonic activity. When structures are built too close to the bank of the river, their weight may exceed the weight which the bank can hold and cause slumping, or accelerate slumping that may already be active. Adding to these stresses can be increased saturation caused by irrigation and septics, which reduce the soil's strength. While deep rooted vegetation can increase the strength of river banks, replacement with grass and shallower rooted vegetation can actually weaken the soil. Presence of lawns and concrete driveways concentrates runoff onto the riverbank, weakening it further. Foundations and structures further increase stress.
context_section_description: Bank failure was located on the Red River and its tributaries. It was caused by erosion and represents slumping. Failure occurs in this area because river banks are composed of clay, due to glacial and lake deposition, as opposed to more resistant sediments such as sand or gravel. Most commonly, slumping exists in the Sherack Formation, which sits on a less competent formation called the Huot and Brenna Formations. The Sherack Formation is composed of silt and clay laminations, while the Brenna is a clay deposit. These less competent formations become exposed when the overlying Sherack Formation is eroded by the river valley. Cracks can also form in the Sherack Formation, causing weakness in the underlying clay, and slumping. The exposed contact between the formations (commonly in the Red River area), and thus the inherent weakness at this contact, causes mass wasting of the river bank. Human activity near the banks of the river then increases failure risks. Due to this human interference, the river's best mode of defense is to avoid unnecessary loading near the river and to enhance awareness of the issues leading to failure. When failure does occur, an understanding of the geotechnical parameters of the slope are necessary, and are the most heavily relied upon in order to understand the underlying causes. This can be accomplished by obtaining values for the plastic limit and liquid limit of the soils.
  Also of interest are the interactions between streamflows and sediment contribution. The Red River and Minnesota receives contributions from the Pembina River of northeastern North Dakota. Erosion rates are very high for this river, and lead to extensive and steep erosion of the banks of the river. This increased runoff then produces increased streamflow and thus higher erosion events downstream, such as in the Red River.
caption: High flows erode the steep banks of the Pembina River, in northeastern North Dakota, contributing to the high sediment load.
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