Figure 5.9: Step 2 in Calculating the Discharge Sensitivity
In 1992, a contractor for TxDOT developed a HEC-1 model of Buttermilk watershed (Area 2) as an undeveloped area. This pre-developed HEC-1 model included areas outside of Buttermilk watershed. These areas were edited, and the new, slightly modified HEC-1 model was imported into HEC-HMS.
The U.S. Corps of Engineers’ Hydrologic Modeling System (HMS) is a “next generation” software for the precipitation-runoff simulation that will supersede HEC-1. HEC-HMS contains most of the watershed runoff and routing capabilities of HEC-1, in addition to continuous hydrograph simulation over long periods of time, and distributed runoff computation using a grid cell depiction of the watershed (HEC-HMS User’s Manual, 2000).
There are two principal parameters that are evaluated in this study with respect to discharge: lag time and drainage area. After modification of the HEC- 1 model, lag times are varied in each sub-basin. For each lag time variation,