Floodplain Extension Mapping

Coastal Resources, Inc. (CRI) performed hydrologic and hydraulic modeling for three priority areas in Charles County to determine the extents of the 1% probability (100 year) storm upstream from the existing FEMA regulated floodplain. Charles County was interested in learning more about areas that were experiencing flooding and areas that were going to be developed in order to make planning decisions on how to solve or prevent flooding problems.

CRI’s senior water resources engineer investigated each priority area and delineated the extent of each of the watersheds that intersected the area of interest. HEC‑HMS was then used to model the hydrology in each watershed. The excess precipitation from HEC‑HMS was entered in to HEC‑RAS 2D to simulate a storm over the contributing watershed. The existing stormwater pipes and stream culverts were either entered in to the HEC‑RAS model as connections or burned into the digital elevation model (DEM). The resulting maps and animation were provided to the county to aid in decision making concerning flooding and development in the areas of concern. A procedure was developed to document and streamline the floodplain mapping process. Below are some characteristics of the areas and their watersheds.


Charles County, MD


Charles County Office of Planning & Growth Management

Key Services:

  • Hydrologic Modeling
  • Hydraulic Modeling
  • Stormwater BMP Modeling