Year Established: 2011 Start Date: 2011-03-01 End Date: 2013-02-28
Total Federal Funds: $28,985 Total Non-Federal Funds: $57,313
Principal Investigators: Marcelo Garcia, David Waterman
Abstract: Ven Te Chow Hydrosystems Laboratory (VTCHL) at the University of Illinois at Urbana‐Champaign (UIUC) has been actively conducting research in river meandering for several decades (Garcia et al, 1994). The most recent development by VTCHL staff is a software platform named RVR Meander (Abad and Garcia, 2006; and Motta et al, 2010), which is a tool to predict long‐term, large‐scale river migration and to assist engineers, geomorphologists, and biologists in river restoration projects. The most recent efforts to refine the RVR Meander platform have involved incorporating bank erosion physics as an alternative to the traditional migration coefficient approach, which effectively lumps all physical erosion processes together into a single parameter. Incorporating bank erosion physics is a significant advance in modeling large‐scale meandering, but like all numerical models, the quality of the results are largely dependent upon inputting realistic parameters into the model. Field work was recently conducted along the Mackinaw River in Tazewell County, Illinois, with the objective of characterizing critical bank shear stresses and consequent erosion rates to provide accurate parameters for input into an RVR Meander simulation of this river reach. Accepted in situ experimental methods to characterize bank erosion under fluid shear stresses are intended primarily for cohesive sediments; they are less effective in non‐cohesive sand; and they are entirely ineffective in banks containing gravel. The reach of the Mackinaw River investigated contains lower banks comprised almost entirely of sands and gravels, and the lower bank is where the most significant erosion occurs, precipitating mass failures of the upper banks. The field methods available do not allow meaningful testing of the lower banks. In order to characterize erosion of non‐cohesive bank materials, analytical and laboratory experimental research have been relied upon in the past, under the assumption that the erosion of noncohesive materials are much easier to characterize physically through single grain analysis. Although these past results are useful, significant complications arising from heterogeneous field conditions can greatly complicate the response of the banks to fluid shear stress. As such, to truly capture the physics of bank erosion for streams with gravelly banks, a field experimental method would be a significant advance. The objective of this proposal is to develop and implement an in situ experimental measurement technique to measure critical shear stresses required to initiate bank erosion and to quantify the subsequent erosion rates with increasing shear stress. The proposed experimental method will allow observation of critical stages of the erosion process, such as initial removal of sands from the matrix followed by exposure of gravel subject to single‐grain forces. The experimental apparatus will be a modified version of an inverted flume developed recently by VTCHL to measure fine‐grained river bed sediment entrainment in Bubbly Creek, Chicago, Illinois (Waterman et al., 2009). The new apparatus will be designed to be seated on the bank and to convey longitudinal flows as the shear‐generating mechanism, rather than the perpendicular‐directed flows generated by accepted bank erosion techniques such as the jet test. The new apparatus will be designed to achieve high shear stresses necessary to move coarse gravel bank material. The apparatus will incorporate a means of capturing mobilized soil material in order to quantify the erosion process. The knowledge gained will be incorporated into the RVR meander migration model to predict streambank erosion and long‐term lateral migration of streams in Illinois.