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The Use of Geomorphological Classification for Risk Management of Streams

Changes in the amount and types of land use in a watershed can destabilize stream channel structure, increase sediment loading and degrade in-stream habitat. Stream classification systems (e.g., Rosgen) may be useful for determining the susceptibility of stream channel segments to erosion and bank failure, and may help to identify stable endpoints for stream channel restoration and BMP (best management practice) placement. We are using this approach to determine if streams can be classified to assess the risk of increased erosion resulting from changes in land use. One of the hypotheses associated with the survey work is that a stream can resist change up to a certain level threshold, but beyond that threshold the stream will change classifications and alter both its channel formation and erosional properties. Understanding these thresholds will assist in the evaluation of risks from development and aid in the design and implementation of both structural and non-structural BMPs.

Stream classifications are developed based on geomorphological data, which can be collected by a variety of methods, most notably intense surveying or interpretation of existing data sets (aerial photographs and topographic maps). The initial phase of this research consisted of collecting geomorphic data at several levels of intensity in terms of both effort and cost for the purpose of determining minimum requirements for assessing a stream’s condition. It has been found that when aerial photographs and topographic maps are used to calculate slope and sinuosity, the uncertainty in the values is greater than when these metrics are obtained by extensive surveying, however, the resulting stream classifications obtained in Ohio are the same. The accuracy of these values when confirmed by short site visits is adequate for rapid reconnaissance, followed by more intense evaluation of areas identified as having greater risk factors. This work has been confined to assessment of data collection methodology (surveying) and data interpretation (stream classification) at the scale of a stream reach.

Continuing research will focus on three aspects of this work:

  1. the relationship between the geomorphic metrics and the biological criteria used to determine impairment,
  2. the ability of the data collection methods to be expanded to the watershed scale with identification of specific areas for more intense review and
  3. the applicability of the classification methods to the prediction of impairment within physiographic ecoregions and between different ecoregions.

Contact: Christopher Schultz, 513/569-7047; Joseph Schubauer-Berigan, 513/569-7734; Matthew Morrison, 513/569-7441 (EIMS#116424)

Office of Research & Development | National Risk Management Research Laboratory

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