How Hydrologic Evaluations in HEC-RAS Can Influence Stream Restoration Design
Victoria Nelson, PE, CFM
AECOM
Germantown, MD
HEC-RAS is one of the most common modeling software used to evaluate the impact of stream restoration designs. Over the years the capabilities of HEC-RAS have broadened, now offering a wide selection of methods for evaluating stream restoration designs. This includes several options for hydrologic input. Although the focus of input parameters for models typically consists of land use and terrain, some hydrologic methods may be better suited for specific project areas.
The choice of which hydrologic methodology to select depends on the project site characteristics, goals of the restoration and expected level of result accuracy. It can be difficult to strike a balance between what the model can do versus allotted time, effort and budget. How hydrology is applied to the model may impact the magnitude and extent of high velocity and shear stress, which are used to guide the design. Approximate or generalized results can lead to under or over designing.
There are three unsteady hydrologic input methods that can be used to evaluate stream restoration design. These include direct point input, rain on grid and spatial varying precipitation. Direct point input consists of applying a flow hydrograph directly to the mesh and rain on grid and spatial varying precipitation are both combined hydrologic/hydraulic methodology, applying precipitation to the 2D cells. Rain on grid applies precipitation uniformly and spatial varying precipitation is a non-uniform application.
This presentation will focus on if and how much influence the hydrologic input methodology has on the evaluation of a restoration design.
About Victoria Nelson, PE, CFM
Tori is a P.E. in Virginia who has 11 years of experience and specializes in hydrologic and hydraulic analysis. She holds a bachelor's degree in Biological Systems Engineering from Virginia Tech and is a Certified Floodplain Manager. She has experience in consulting, working on Federal, State, and Municipal projects in HnH analysis, stormwater management, stream restoration, and MS4 compliance.