2015 Memorial Day Flood Impacts for Changing Watershed Conditions in Houston

In this study a hindcast analysis was performed of the 2015 Memorial Day flood for Brays Bayou in Harris County, Texas. Point rainfall totals as high as 27.84cm (10.96in.) occurred in this watershed in a 12-h period, causing severe flood damage to 1,185 residential properties. By validating hydrologic and hydraulic models representative of watershed conditions at the time of the storm, this study provides a comprehensive spatial perspective and understanding of the flows and stages, floodplain extents and depths, and residential damages that occurred. In addition, Project Brays, one of the largest urban watershed-scale flood reduction projects in the nation, was nearly halfway complete at the time of the 2015 Memorial Day storm. Subsequently, this study evaluates and compares the flood response to this rainfall event for different watershed conditions representing preproject conditions (2001), May 2015 conditions (current), and postproject conditions (2021 at the earliest). The flood reductions that were provided by Project Brays at the time of the storm and the flood impacts that would have occurred even if the project had been finalized prior to the storm are assessed in detail.