Stormwater Plan Studies How Surface Water Moves

The southeastern US has seen record rainfall over the last 12 months. For Grand Prairie, Texas, and the rest of the Dallas-Fort Worth metroplex, 2015 was a record-setting year for flooding, ending a years-long severe drought. In May of last year, heavy rains flooded Grand Prairie streets, damaged homes and cars, and caused neighborhood evacuations and millions of dollars of damage. Thankfully, no lives were lost, but the folks who live and work in Grand Prairie experienced firsthand the catastrophic results of unchecked stormwater.

More than one third of Grand Prairie lies in a FEMA-designated floodplain and is prone to severe flooding. The other two thirds of the city risks severe flash flooding from overland runoff trying to reach the floodplain.

The city has always taken a proactive approach to floodplain management and capital improvement project (CIP) planning. But even though the city’s engineering staff had targeted specific flooding mitigation projects, limited funds just wouldn’t allow implementation. At least, not using traditional stormwater engineering solutions.

That’s when the city decided to adopt an innovative approach to stormwater master planning that employs state-of-the-art technology to maximize the budget while executing high-value projects.

“Rather than taking a traditional engineering approach that focuses on 100-year solutions and employs large, expensive pipes, we are taking into account how surface water moves to better divert it to the existing drainage system,” said Brenda Gasperich, PE, CFM, regional engineering manager for stormwater with McKim & Creed.  “We’re developing shorter-duration solutions that deliver maximum impact with minimal cost.”

Specifically, the project team—which includes McKim & Creed, Burton Johnson Engineering, Inc., RLG Consulting Engineers, Halff Associates and Lockwood, Andrews & Newman, Inc.—is using 2D surface flow hydraulic modeling, LiDAR data, GIS and updated survey benchmarks to generate citywide inundation maps. These will serve as the foundation for future capital improvement project planning, to assess problem drainage areas, and to alleviate localized neighborhood flooding.

“Ultimately, this will lead to the prioritization of CIP projects and better communication with stakeholders. Lower cost, more constructable CIP projects will help Grand Prairie address future flood protection issues without overextending the current budget,” Brenda said.

“The City of Grand Prairie is excited to work with McKim & Creed and their team of professional consultants to consolidate and fine-tune our drainage needs,” said Romin A. Khavari, PE, CFM, city engineer. “The results will help us prioritize projects and provide an overall updated approach and general strategy for our stormwater master plan.”

 

2D surface flow modeling shows location of rainfall runoff routes and effectiveness of storm drain infrastructure.

 

 

Two thirds of the City of Grand Prairie is prone to flash flooding, due to runoff flowing toward streams.