RESTORATION APPROACHES FOR INCISED STREAMS

The majority of streams located in alluvial valleys of the eastern United States have been severely impacted from past and current land use practices. Starting in the mid 1700s, settlers cleared uplands and hill slopes for agricultural purposes. This caused extreme soil erosion from the uplands and subsequent valley aggradation. In most cases, the valleys aggraded 6 to 10 feet. In the early 1900s, soil conservation practices were implemented and upland erosion decreased. However, as soil conservation practices increases, so did channelization. Streams were straightened and moved over to the edge of the valley to maximize agricultural production. Channelization still continues in both agricultural and urban areas to maximize land availability and control flooding.

Channelization typically increases stream power by increasing channel slope. This often causes the channel to incise, which leads to a series of vertical and lateral adjustments. These adjustments result in large quantities of bed and bank erosion, which destroys aquatic habitats and adjacent property. The purpose of this paper is to provide several case studies that use natural channel design approaches to restore morphological and biologic function to incised stream corridors. Examples will include cases where the original streambed elevation is reclaimed, thus re-connecting the stream to the original floodplain. This approach restores channel, floodplain, and wetland functions. Other cases will include the construction of a new floodplain at an elevation that is lower than the original floodplain. This approach restores channel and limited floodplain and wetland functions. Finally, cases will be provided where site constraints prevent raising the bed or building a new floodplain. In this case, in-stream structures and “benches” are used to create a stable step-pool channel. This approach restores channel function but does not restore floodplain or weltand functions. The case projects will include a variety of settings and site constraints including rural projects with no constraints to urban projects where restoration is limited by roads and utilities.