Problem:Incised river channels throughout the loess belt region of the midsouth and midwestern United States are prone to severe bank erosion and channel widening. Bank erosion often results in the loss of productive riparian land, undermines in-channel and riparian infrastructure, and causes environmental degradation through delivery of large quantities of fine-grained sediments to the channel. The loess belt region is predominantly agricultural and the resources for costly traditional structural countermeasures are frequently not available. Stream corridor restoration projects, involving the use of low-cost vegetative treatments, are often the only economically viable alternative. Due to a lack of knowledge of the interactions between riparian vegetation and stream channel processes, design and evaluation guidelines for these new and innovative restoration projects are at present somewhat crude.
Objective:The objective of this project is to develop a numerical simulation model of channel adjustment for use as a tool for analysis of stream corridors in agricultural watersheds of the SE United States. The model is capable of simulating the physical processes governing adjustment of channel morphology, including the effects of riparian vegetation. These features will allow the model to be used as a tool during project design, and as a tool for evaluating the long-term post-project stability of restoration and stabilization projects which utilize vegetative treatments.
Description of Work:A stream corridor model of river channel evolution which accounts for specific mechanisms of bank erosion and widening, was developed and validated using data from Goodwin Creek, Mississippi. The model predicts changes in channel dimensions through time by solving a set of physically-based governing equations which simulate the governing stream channel processes. Channel width adjustment is accounted for through analysis of failure, deposition and subsequent entrainment of failed bank-material debris. The effects of specific assemblages of riparian vegetation are accounted for through analysis of the effects of vegetation on (1) resistance to the flow, and (2) bank material strength. The effects of riparian vegetation on stable channel dimensions account for cases when (1) riparian vegetation is absent; (2) riparian vegetation consists of herbaceous vegetation only, and; (3) riparian vegetation consists of woody vegetation only.
Benefit:The ALCHEMY model will be used by action agencies such as the Corps of Engineers (COE) and Natural Resources Conservation Service (NRCS) to predict stable channel configurations, and to improve the design of river restoration and engineering projects. In particular, the model will be used by these agencies to evaluate the effectiveness of low-cost vegetative erosion control methods for stabilizing problem reaches.