How Effective is HEC-RAS 2D at Predicting Stream Instability? A Study Based on Natural Channel Design Stream Restoration Sites
Blair M. Borries
RES (Resource Environmental Solutions)
Louisville, Kentucky
HEC-RAS is a popular hydraulic modeling tool developed by the US Army Corps of Engineers (USACE) that is the standard for establishing base flood elevations in communities across the US. The recent addition of user-friendly and free two-dimensional modeling capabilities has led to the adoption of 2D models in far more projects. Under the assumption that the model is more exact than previous one-dimensional models, practitioners may add, remove, or modify design components based on visually observed results of the model that identify “hot spots” or computations of threshold velocities and shear stresses at spatially explicit locations. In this presentation, we use readily available as-built surveys of completed stream restoration projects to test the effectiveness of HEC-RAS 2D in identifying potential locations of channel instability. A number of stream mitigation sites that were designed utilizing Natural Stream Design principles surveyed post-construction, and monitored by our team were modeled through HEC-RAS 2D to develop result maps of velocity and shear stress. These results are then compared to quantitative cross-section measurements and qualitative observations collected during routine monitoring visits to determine if the model results identified the areas where instability was observed as “hotspots” of relatively higher velocity or shear stress based upon observed monitoring results. The relatively homogenous dataset used in the study will provide an objective view of HEC-RAS 2D modeling to calibrate our expectations of the model’s usefulness in predicting stream stability on future stream restoration designs.
About Blair M. Borries
Blair Borries is a Designer with Resources Environmental Solutions (RES). He has shaped his nearly 20-year career with the skills and technologies of today while building on lessons from ecological restoration efforts of the past. He employs state-of-the-art design techniques and technology to streamline and implement large, complex stream and wetland designs that are supported by detailed modeling efforts. As a graduate researcher on the long-term performance of two of the first large-scale stream and wetland restoration projects – built in 1979 and 1991 – Blair gained unique insight into restoration techniques across an era and helped establish the importance of riparian corridors in the 2016 Federal Stream Protection Rule. As an avid naturalist, Blair finds one of the biggest rewards to working in ecological restoration is exploring restoration sites on public lands and sharing with friends and family.
