Experimental and Theoretical Studies of Bank Erosion in Rivers and its Prevention by Low-Cost Means

The present report is devoted to the topic of river bank erosion and its prevention. Emphasis is placed on a physically-based model of bank erosion, into which various kinds of bank protection can be imbedded. For simplicity, the study is restricted to straight channels. The methods developed here can, however, be applied to the broader context of meandering channels. The report consists of two parts. The first part is devoted to an experimental study of the problem. The process of bank erosion of coarse material is first studied. The channel is allowed to erode until such point as a stable equilibrium is attained. Such experiments provide a baseline against which to test the effectiveness of various means of bank protection. The type of bank protection studied falls under the category of distributed drag. Such methods use timber-pile permeable dikes, jacks, jetties, or trees in conjunction with the Palmiter method to slow the flow down in the vicinity of the bank. In the present study, screens similar to permeable dikes were used to accomplish this. It was shown that a sufficient density of distributed drag elements can substantially slow or stop bank erosion. When fine, suspendable material was added to the water, this material tended to settle out preferentially in the near-bank field of retarded velocity due to distributed drag. As a result, not only could bank erosion be prevented, but eroded banks could be reconstructed by means of deposition from suspension. The second part of the study was devoted to a theoretical and numerical model of bank erosion and its prevention, in parallel with the experiments. The theory is based on a description of bedload transport on side slopes up to the angle of repose. The Finite Element Method was used to model the flow and sediment transport field, as well as describe the time evolution of the channel. At present, the model has proved successful in describing the process of bank erosion documented in the experiments. Numerical work continues on the subject of bank protection by means of distributed drag.Legislative Commission on Minnesota Resource