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ADDRESSING
DOUBLE STANDARDS

Hydrologic & Hydraulic Analysis and Design
Ellis County, TX

Some of the heaviest growth in Texas is occurring in Ellis County, due south of the Dallas-Fort Worth Metroplex. Addressing mobility needs along IH35E falls under jurisdiction of the Texas Department of Transportation (TxDOT) and the Federal Emergency Management Agency (FEMA).

To ensure IH35E's ability to serve the Metroplex and its satellite communitites, TxDOT has identified numerous improvements for this critical north-south corridor. We provided hydrologic and hydraulic analyses on select projects at key points along IH35E. Among them: six bridge-class culverts, four of which are in FEMA-designated flood plains, and two main-lane and frontage road bridges (at North Grove and South Grove Creeks).

Since the two agencies have individual engineering standards, our analyses had to respect both. And they did. Our hydraulic analysis used TxDOT's design criteria, while our hydrologic analysis model combined HEC-HMS (developed by the U.S. Army Corps of Engineers' Hydrologic Engineering Center) with GIS data. Hydraulic analyses for the culverts and bridges were performed using HEC-RAS. This enabled us to satisfy both TxDOT and FEMA. The result: a new floodplain map based upon proposed conditions that included ultimate development of the watershed.