SH 130 Watershed Mapping,

H&H Modelingand Design

S&B Infrastructure, Ltd. (S&BI) served as lead drainage design engineer for the largest design-build transportation project in the state of Texas. S&BI is responsible for drainage design, including hydrologic modeling and hydraulic data, for the project, which spans 4 counties and includes 25 watersheds totaling over 40,000 square miles. The project limits encompass 37 waterway crossings, of which, 25 are Zone A and 12 are Zone AE.

 

Data Collection and Delivery System

Existing data for the project was obtained from federal state and local entities including USGS, FEMA, TxDOT, Travis, Williamson, Caldwell and Guadalupe Counties, Cities of Austin, Cedar Park, Hutto, Georgetown and Round Rock. Data collected was imported into HEC-GeoRAS and included aerial imagery, USGS DEM data, topographic survey and aerial planimetric data. Also imported into the GIS Maps were digital terrain models created using Geopak 3D spatial data. Maps, channel cross sections and digital terrain models were used to develop watershed limits and characteristics.

 

Each waterway was modeled to determine the impacts of proposed improvements on flow characteristics and water surface elevations utilizing HEC-HMS, HEC-2, WSPRO, TR-55, TRAP and HEC-RAS. The SCS Type III, 24-hour distribution was used to develop peak flow rates for the 10 yr, 25 yr, 50 yr, and 100 yr storm events.  Hydrology was also developed based on the City of Austin 3-hour distribution for comparison purposes. Software applications used include HEC-HMS and TR-55.

 

S&BI provided stream modeling analysis and floodplain reports that are in compliance with FEMA and NFIP requirements regarding bridge freeboard and allowable rise in water surface elevation (WSE) from existing to proposed conditions in zone “AE” streams using WSP2 and HEC-2 computer modeling programs. Additional services include a floodplain impact analysis report using the HEC-RAS computer modeling program. As applicable, CLOMRs, LOMRs and LOMAs were developed for the entire project.

 

Program Management

S&BI quickly mobilized for this project going to 75 FTEs in less than 4 months, including setting up IT systems, developing design standards and implementing QA/QC procedures.

 

S&BI developed the floodplain report format for Zone “AE” studies in an effort to standardize the contents of all such reports. S&BI also developed a Design Task Protocol (DTP) for Zone “A” (Designated) streams that outline the procedures and methodologies to be followed when developing a floodplain study.

 

S&BI developed and tracked schedules for each Zone “A” and “AE” floodplain study and developed checklists for submittals to the Design Quality Assurance Firm (DQAF). The S&BI Team has also continually acted in a proactive manner to minimize excessive revisions & comment periods, which prevented several delays to the project.

 

The S&BI Team coordinated with city and county entities to help identify community improvement projects within the areas of study that might impact the floodplain analysis

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