Improved streambank countermeasures: the Des Moines River (USA) case study

Abstract

In the Midwestern USA, bank erosion is a common hazard due to the high erodibility of the bank soils. In this paper, an improved methodology aimed at identifying the optimal countermeasures to control bank erosion was developed and applied in two sites of the Des Moines River (USA). In situ flow measurements, bed bathymetry and soil properties were collected for providing boundary conditions and parameters of the two-dimensional, depth-averaged hydrodynamic finite element surface water modeling system (FESWMS) model. The model was used to compare the hydraulic performances of four streambank countermeasures: riprap lining (referred to as S1); a series of barbs (S2); alternating barbs and spurs (S3); and the combination of barbs with lining (S4). A key feature of FESWMS was its ability to simulate the wetting/drying conditions of mesh elements, which allowed the simulations of unsubmerged or partially submerged structures for different hydraulic conditions. This research showed that the combination of alternating barbs and spurs (S3) was the only design which provided protection during overbank flows at a competitive cost compared to the other designs analysed. The uniqueness of this methodology is found in the coupling of field measurements and theoretical approaches for depth-averaged velocity profiles to calibrate and validate a hydrodynamic model; and in the proposed design to protect streambanks from severe erosion.