A Conceptual Geomorphic Model for Mid-Atlantic Streams

Although river restoration takes many different forms, one common goal of river restoration is the wholesale redesign of a reach. When this is attempted, the entire river geometry must be "redesigned", a process that includes specifying the channel's cross-section, slope, and channel planform morphology. The goal of this type of restoration is often to create a channel that is perceived as being "stable". In this context, the term "stable" usually implies that the river will not materially modify the design morphology during the design life of the restoration (whether this life is actually specified as part of the design or, more typically, left implicit). In practice, this means that erosion and deposition in the design reach will either be negligible, or else minimized so that erosion will be balanced by deposition, and the channel morphology will thereby be maintained. Additionally, (though it is rarely explicitly considered), stability also requires the channel to transport the sediment supplied to the reach without significant erosion or storage. If the restoration design involves placing substantial structures or planting riparian vegetation, then the design will not be able to tolerate significant erosion or deposition, and "stability" actually requires the channel to change as little as possible through time. The goal of this paper is to review some historical origins of the geomorphic concept of fluvial equilibrium, and to evaluate the validity of this idea as a current paradigm in fluvial geomorphology.