Modeling Stream Hydraulics Before and After a Meander Restoration Project
thesisposted on 08.02.2018 by Jose Javier Marquez Reina
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Humans have engineered rivers and watersheds to suit their needs, and in the process, have caused numerous impacts to the environment. Recently, stream restoration projects have become increasingly popular means of mitigating and reversing the detrimental effects of urbanization (Walsh et al., 2005). The operating assumption of many stream restoration projects is that altering channel geomorphology to resemble pre-existing conditions will lead to the recovery of aquatic habitat and thus recovery of native species, however, some research disagrees with this premise (Palmer et al., 2010; Violin et al. 2011). This study focuses on a meander restoration carried out at Spring Brook, a small stream near Chicago, Illinois. In 2015 meanders were constructed on the previously straightened, channelized stream. The goals of this project were to (1) provide a habitat with varied water depths and flow velocities suitable for aquatic species and (2) promote hydraulic connection between stream channel and floodplain. In this study, we use the HEC-RAS model to estimate changes in stream hydraulics resulting from the meander restoration project. Field data (e.g. periodic flow measurements and continuous depth recordings from in situ instrumentation) were collected in order calibrate/validate the HEC-RAS model. Based on pre- and post-restoration modeling results, we find that the restored meanders at Spring Brook allow for improved variations of hydraulic conditions, including flow velocity and water depth in the new, restored reach in comparison to the previous straight, channelized stream reach, while shear stress and stream power values have decreased slightly. Additionally, model simulations of various flow events demonstrate that the meandered stream achieves a more continuous hydraulic connection between the stream and the floodplain compared to pre-restoration conditions. Overall, the modeling results suggest that the meandering restoration has obtained the hydraulic objectives of the project.