Geomorphic Considerations In Stream Restoration Efforts

Paul Hartfield
U.S. Fish and Wildlife Service, 6578 Dogwood View Parkway, Jackson, MS, 39213. (601/321-1125)

One of the greatest and most widespread problems in river and stream alluvial channels is accelerated geomorphic change. Geomorphic change implies significant and adverse erosional modification, and includes several inter-related processes such as channel degradation, streambank erosion, and excessive sedimentation. Accelerated implies that these changes are occurring rapidly, over a few years or decades. For the most part, they are triggered by human activities. These events are biologically significant in that they may result in the local extirpation of riparian and aquatic species. They are economically significant in that they result in substantial loss of public and private property, as well as diminished recreational values associated with lotic and riparian habitats. Among the most extreme examples of accelerated geomorphic change are headcuts. Headcuts are most often associated with activities that cause changes in channel slope, depth, width, sediment/water balances, etc.. Common practices that may precipitate headcuts or more localized manifestations of accelerated geomorphic channel changes, include channelization, dredging or other navigation maintenance practices, and sand and gravel mining within or adjacent to channels. At different stages of the process, headcuts are evidenced by falling tributaries (indicating lower base level), extensive bank erosion, shallowing and widening of the channel, and point bar development. Biotic responses to headcuts include loss of characteristic riparian flora, loss of aquatic fauna, and shifts in aquatic community dominance. Understanding the causes, processes, and progression of accelerated geomorphic changes is an essential step in stream and river restoration projects. Plans to address erosion or sedimentation problems may include identifying and stopping adverse activities, reducing or controlling adverse activities to decrease effects on the system, or, in extreme cases, the construction of protective structures.