One Mile Creek Floodplain Evaluation – Mobile Gas

Mobile, Alabama

McFadden Engineering, Inc. was retained by Mobile Gas Service Corporation (MGSC) to provide a “No-Rise” Certification for the proposed option of site modifications at the corporation’s property, situated at the intersection of Broad Street and Dr. Martin Luther King Jr. Avenue in downtown Mobile, Alabama. The subject property is a former manufactured gas plant site.

As part of the remedial activities for the Mobile Gas property conditions, a preliminary option of covering the site with two feet of clean fill had been proposed. The site was modeled to provide data that proposed site improvements will not raise the water surface elevation of the 100-year floodplain. It should be noted the final disposition of the property will be determined by MGSC in accordance with future data collected from site investigation activities and input from regulators, the City of Mobile and stakeholders.

For the purpose of this study, the U.S. Army Corps of Engineers’ River Analysis System (HEC-RAS) software was used to perform one-dimensional steady flow computations in One Mile Creek during a 100-year storm event. McFadden Engineering used the HEC-RAS model to successfully simulate a 100-year storm event at the existing conditions of the site as well as the 100-year storm event once the proposed site improvements are in place. The project included:

• Field reconnaissance and feature identification;
• Determination of data requirements;
• Data collection survey for developing stream cross sections;
• Model setup;
• Performing data input and calibration;
• Performing model simulation for existing conditions;
• Performing model simulation for proposed conditions;
• Evaluation of model simulations;
• Development of conclusions.