Channel-Bank Conditions and Accumulations of Large-Woody-Debris along White River between Anderson and Indianapolis, Indiana, 2002-Bank Assessment



		Channel-Bank Conditions and Accumulations of Large Woody Debris along White River between Anderson and Indianapolis, Indiana, 2002 Bank Assessment Several channel features can be observed in the field to evaluate bank-erosion conditions. In general, bank stability is promoted by cohesive bank materials--bank materials with a significant silt and/or clay component--and relatively low bank angles. At sites of accelerated bank erosion, one expects to encounter bank materials that lack significant cohesion--bank materials dominated by sands and gravels--and relatively steep bank angles. Also, in most locations, the presence and condition of woody vegetation growing on the channel bank can be used to evaluate relative bank stability. The photographs shown below and the accompanying discussion illustrate how this evaluation is accomplished.

		The rooting system of woody vegetation tends to bind and protect bank materials and promotes bank stability. The above two photographs show channel banks that have been eroding. The rates of bank erosion are undoubtedly quite different, however. The photograph on the left shows a bank devoid of woody vegetation, and field evidence indicates that the bank is retreating rapidly (mapped as severe erosion). The photograph on the right also shows a bank subjected to erosive forces; however, the root masses associated with the woody vegetation have helped to stabilize and protect the bank materials, thereby slowing the erosion process (mapped as slight or moderate erosion based upon a complete evaluation of all field evidence).

		When banks covered by woody vegetation are unstable, the condition of the vegetation can provide the needed evidence to assess the relative rate of bank-material loss. In the photographs immediately above, the channel banks are unstable and the trees growing on these banks are impacted. However, the growth characteristics of the trees in each photograph indicate that these banks are failing at different rates. The photograph on the left shows rapid bank failure; since being tilted, the tree has not had a chance to grow into a more upright position. In contrast, the photograph on the right shows a tree that has been able to adjust gradually its growth form to compensate for the slow removal of bank material. Of the two photographs, the one on the left provides greater evidence of rapid and recent bank failure.
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U.S. Department of the Interior U.S. Geological Survey 5957 Lakeside Boulevard Indianapolis, Indiana 46278-1996 USA Phone: (317)290-3333 Fax: (317)290-3313 URL: http://in.water.usgs.gov/newreports/bankerosion/page5.shtml Last modified:Tuesday, 15-Jan-2013 13:25:35 EST E-mail questions and comments to webmaster USGS Indiana Home Page

Channel-Bank Conditions and Accumulations of Large Woody Debris along White River between Anderson and Indianapolis, Indiana, 2002

Bank Assessment