INSIDE THE DOT
South Dakota Department of Transportation
Rainfall-Runoff Modeling for Improved peak-Flow Estimates in the Black Hills of SD
Dan Driscoll, USGS SD Water Science Center
Peak-flow characteristics for “gaged” streams typically are estimated by the U.S. Geological Survey (USGS) in statewide projects using probability analyses of datasets of the largest annual peak flow for streamgages (see http://pubs.usgs.gov/sir/2008/5104/). Error bars about the estimates (uncertainties) for any stream may be relatively small for the smaller recurrence intervals, such as the 2-year through 10- or 25-year floods, but uncertainties generally increase substantially for increasing recurrence intervals. These “at-site” estimates typically are then used in statewide “regionalization” projects for estimating peak-flow characteristics for ungaged streams, where further increases in uncertainties are inherent. Peak-flow characterization is especially complex in the Black Hills region, where geology, climate, and topography can vary substantially across small spatial scales. In this region, classifying many streamgages based on proximity for regionalization estimates may not be the most accurate approach. An alternative approach using design rainfall events with known frequency estimates to drive calibrated hydrologic models may result in more accurate estimation of peak-flow frequencies, regardless of the observed flow records. Various types of rainfall-runoff modeling (such as HEC-HMS) can be used to estimate peak-flow characteristics for many applications, but typically are considered to be less reliable than estimates for gaged datasets, when available. However, rainfall-runoff modeling can perform very well in accounting for watershed characteristics and, especially when calibrated using available precipitation and streamflow data, could provide an excellent tool for improving peak-flow estimates for the Black Hills area. In particular, modeling could be used to identify specific watersheds with distinctively different potential for peak-flow generation and to which different approaches for peak-flow characterization could be applied.
1 Investigate the feasibility of applying selected rainfall-runoff modeling approaches in estimating peak-flow characteristics associated with the complex hydrology in the Black Hills area.
2 Apply, test, and validate accuracy of selected modeling approach for improving peak-flow characterization for the Black Hills area.
1 Review and summarize literature and consult with agencies such as Federal Emergency Management Agency and U.S. Army Corps of Engineers that commonly use rainfall-runoff modeling for estimating peak-flow characteristics for engineering applications.
2 Meet with the project’s technical panel to review the project scope and work plan.
3 Identify and evaluate existing rainfall-runoff modeling approaches with potential application to the Black Hills area.
4 Identify and evaluate potential watersheds and available datasets for the Black Hills area suitable for application of selected modeling approaches.
5 Meet with the project’s Technical Panel to review results of tasks 1-4 and to confirm plans for calibrating, applying, and validating selected rainfall-runoff modeling approaches.
6 Calibrate and apply the selected rainfall-runoff modeling approaches to accomplish improved peak-flow characterization for the Black Hills area.
7 Evaluate the accuracy of selected modeling approaches against known precipitation and streamflow inputs.
8 Prepare a final report summarizing research methodology, findings, preliminary conclusions, and recommendations.
9 Meet with the project’s Technical Panel to review results, findings, and recommendations.
10 Make an executive presentation to the South Dakota Department of Transportation Research Review Board at the conclusion of the project.
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