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Little Topashaw Creek - Subsurface Erosion Background
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  Bank failure 1
 

Watersheds in the Yazoo basin are characterized by "flashy" hydrology, banks that are steep and prone to failure, channel beds that are straight, wide, and composed of sand or sand and gravel or cohesive clay, and baseflows that are relatively low in discharge (or none at all) and shallow in depth.               

Yazoo basin

 

Bank failure 2

 

 

Subsurface erosion effects

 Subsurface erosion effects
  
 

Bank failure 3

The soils generally consist of a loess cap over the alternating alluvial layers of sand and clay. Such conditions in which a highly permeable, unconsolidated layer (e.g sandy horizon) occurs above a water-restricting horizon (e.g. clay layer) are highly susceptible to concentrated subsurface flow. Flow through the permeable layer results in erosion of the unconsolidated material at the face of stream bank.