Two-Dimensional Hydraulic Modeling of Dam Breach Inundation

There are about 194 permitted dams within the Clark Fork Watershed in Montana alone; 51 of these are classified as high hazard. Congruent with state and federal guidelines, all of these high hazard dams are required to have an Emergency Action Plan (EAP) that includes dam breach inundation mapping. The purpose of having an EAP is to protect public safety. Unfortunately, many of these EAP’s are outdated and contain inaccurate data. Historically, one-dimensional hydraulic modeling software, such as HEC-RAS, has been the primary method to model dam breach inundation. One-dimensional models have yielded good results, but can be challenging to construct and have limitations for modeling flow. Two-dimensional modeling software has attracted significant attention because it permits a more detailed and accurate representation of flow. 2-D modeling has been accepted as an accurate and efficient means to calculate and predict conditions under various flow events. In many cases this is the only approach that accurately calculates resulting flow conditions. In addition, this approach has allowed modelers to provide a clearer picture of the potentially devastating effects of a dam breach through Google EarthTM animations, and spatially variable depth and velocity distributions. Despite the acceptance of two-dimensional modeling as an accurate and efficient methodology, only two of the 51 high hazard dams within Montana’s Clark Fork Drainage use this technology. This presentation will give an overview of the dams within the Clark Fork Drainage, explain the differences between two-dimensional and one-dimensional hydraulic models, and then will present examples where 2D modeling was used. These examples include inundation mapping exhibits and Google EarthTM animations generated for dams within and near the Clark Fork Watershed. This presentation will also briefly touch on the benefits of two-dimensional modeling to other hydraulic structures where detailed velocity distribution exhibits can be used to predict scour, fish passage and habitat conditions