Thursday, May 22, 2008

Outfall Organization

Because the Houston metropolitan area is flat, has relatively impermeable soils, and is subject to intense rain exceeding 114 centimeters (45 inches) per year, local transportation officials sought a high level of detail on storm water outfalls and the contributing drainage areas.
To capture this information, TxDOT developed an approach to collecting and mapping data on desktop computers that involves the following steps:
* Collecting "as-built" drawings illustrating the final configuration of constructed drainage infrastructure
* Digitizing the drawings and positioning them in the proper coordinate system
* Tracing relevant portions of the drawings so key information on drainage systems can be imported into OTS
* Documenting tabular supporting information about each object, such as a description of the material, shape, size, and location
* Loading the information into OTS
Customized desktop mapping tools and procedures support two mapping processes: inside the right-of-way (ROW) mapping and outside ROW mapping. The former captures information about roadway drainage areas discharging storm water runoff through outfalls. Outside ROW mapping captures information about regional watersheds draining to hydraulic structures, such as culverts, pipes, and channels, at roadway crossings.
"This information is enormously useful in tracing the source of an illicit discharge, one of our most challenging tasks," says Crisp. "ROW mapping also can be called upon in drainage studies and planning efforts."
Peak runoff flow rates at storm water discharge locations can assist agencies with determining pollutant loads as well as aid in planning and designing drainage systems. TxDOT also is developing a way to collect data on hydrologic values that will use traditional calculations to determine the peak runoff flow rates arising from hypothetical storms. These calculations generally follow TxDOT's design manual procedures. Calculated values will be stored in a simple spreadsheet and then uploaded to OTS and the main geodatabase.

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