The Use of 2D Hydrodynamic Models to Predict and Evaluate Restoration Function
Jesse Robinson, PE
University of Louisville Stream Institute
Louisville, KY
Authors: Jesse Robinson, Art Parola, Mike Croasdaile, Bill Vesely
Stream Institute, J.B. Speed School of Engineering, University of Louisville, Louisville, Kentucky
2D hydrodynamic (2DHD) model outputs provide spatially distributed predictions of velocity, boundary shear stress and water depth which can be used to predict the hydraulic function of existing or planned restoration projects. This approach to hydraulic functional evaluation is complementary to the design phase vulnerability assessment that is a typical use of 2DHD models in restoration. Prediction of hydraulic function has multiple applications in restoration, including evaluating the expected benefits from projects constructed to improve water quality, guiding design modifications to increase retention of organic matter and sediment-bound phosphorus, defining potential stress to vegetation, and allowing for hydraulic functions to be considered when prioritizing investments in restoration.
The utility of hydraulic functional evaluation is demonstrated by a multi-year field study evaluating the reliability of 2DHD models to predict areas of vulnerability within restorations. The foundation of this study was the development of 2DHD models in 5 restoration sites located in the Maryland coastal plain of the Chesapeake Bay. High resolution terrain datasets were developed at each site to allow for 2DHD modeling to best approximate variable field conditions. Model development was combined with instrumentation of each site to permit calibration of models to observed flood events.
The results of this study show that each restoration site has distinct functional behavior that can be explained by 2DHD predictions. Areas within sites where 2DHD models predicted high velocities contained stream banks and floodplains with hydraulically stressed vegetation, bare soil due to scour, exposed basal gravels, and minimal retention of organic matter and sediments. Areas with low velocities showed the opposite: vegetation lacking scars or deformation, well vegetated stream banks and floodplains, and observable accumulations of organic matter and sediments.
Additional 2DHD modeling of the 5 restoration sites using extreme event analysis allowed for predicting hydraulic functions across many events, revealing the potential for future loss of function in some areas while other areas remain resilient. The modeling of both frequently occurring and extreme events demonstrates the importance of predicting hydraulic function to aid in quantifying restoration performance and defining the functional behavior of each site.
About Jesse Robinson, PE
Jesse Robinson is a senior research engineer with the University of Louisville Stream Institute (ULSI) and an engineer with Riverine Systems, LLC. His work is in the design of custom stream and wetland restoration solutions, the investigation of functional response to restoration, and the development of techniques for advancing restoration assessment and design.