SD2013-03-F Connecting South Dakota and the Nation South Dakota Department of Transportation Office of Research Rainfall-Runoff Modeling for Improved Peak Flow Estimates in the Black Hills Area of South Dakota Study SD2013-03 Final Report Prepared by U.S. Geological Survey Dakota Water Science Center Rapid City, SD August 2017 DISCLAIMER The contents of this report, funded in part through grant(s) from the Federal Highway Administration, reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the South Dakota Department of Transportation, the State Transportation Commission, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. The South Dakota Department of Transportation provides services without regard to race, color, gender, religion, national origin, age or disability, according to the provisions contained in SDCL 20- 13, Title VI of the Civil Rights Act of 1964, the Rehabilitation Act of 1973, as amended, the Americans With Disabilities Act of 1990 and Executive Order 12898, Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations, 1994. Any person who has questions concerning this policy or who believes he or she has been discriminated against should contact the Department’s Civil Rights Office at 605.773.3540. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. ACKNOWLEDGEMENTS This work was performed under the direction of the SD2013-03 Technical Panel: Tom Birney .................................................. FEMA Chris Leibrock ................................ Bridge Design Elmer Claycomb ............................ Custer County Bob Longbons ....................................... Research John Foster ............................................ Research Marc Macy ................... Emergency Management Mike Gillespie ............. National Weather Service Daris Ormesher ..................................... Research Sean Kruger ................................................. DENR Steve Van Mullem ............................... Hydraulics ii August 2017 TECHNICAL REPORT STANDARD TITLE PAGE 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. SD2013-03-F 4. Title and Subtitle 5. Report Date Rainfall-Runoff Modeling for Improved Peak-Flow Estimates in the 08/31/2017 Black Hills Area of South Dakota 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Galen Hoogestraat 9. Performing Organization Name and Address 10. Work Unit No. U.S. Geological Survey, Dakota Water Science Center HRY303 1608 Mt. View Rd. 11. Contract or Grant No. Rapid City, SD 57702 311193 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered South Dakota Department of Transportation Final Report Office of Research January 2014 – August 2017 700 East Broadway Avenue 14. Sponsoring Agency Code Pierre, SD 57501-2586 15. Supplementary Notes An executive summary is published separately as SD2013-03-X. 16. Abstract Peak-flow frequency estimates in the Black Hills area of South Dakota are complicated by the occurrence of extreme flood events that do not fit typical statistical distributions. Alternative methods such as a mixed population analysis have been used to help incorporate high-outlier peak-flow events in frequency analyses; however, more information may be needed to help define areas where causal factors for extreme peak-flow events are different than areas where extreme peak-flow events are less common. A rainfall-runoff modeling approach was applied to 18 drainage basins in the Black Hills with a goal of improving future peak-flow frequency estimates. Rainfall-runoff models were developed using the U.S. Army Corps of Engineers’ HEC-HMS software. These event-based hydrologic models were calibrated to several rainfall events that occurred during 2010–2013, and some models also used calibration information from the catastrophic 1972 Black Hills flood event. After the HEC-HMS basin models were calibrated, hypothetical storm scenarios were developed to examine the effects of large runoff events over the Black Hills area. Outputs used from the hydrologic models to assess peak-flow characteristics include normalized peak flows and yield efficiency. Normalized peak flows demonstrate a tendency for lower flood risk in the upper parts of the Spring, Rapid, and Spearfish Creek drainage basins, generally corresponding with the location of the Limestone Plateau on the western flank of the Black Hills. Conversely, the middle sections of Elk, Boxelder, and Rapid Creeks along the eastern downslope flank of the Black Hills show the highest normalized peak flow areas. The same general findings are in previous reports on peak flow potential and flooding in the Black Hills area, but a key benefit of this modeling project is that these characterizations previously supported mainly by recorded streamflow history are confirmed using parametric hydrologic models. Application of a rainfall-runoff modeling approach shows some utility in estimating peak-flow characteristics in the Black Hills, but largely results in confirmation of previously reported characterizations. The spatial distribution of normalized peak flows produced from this research helps delineate regions (eastern flanks) where mixed-population analyses should be required and other regions (western Limestone Plateau area) where standard Bulletin 17B procedures may be appropriate. 17. Keywords 18. Distribution Statement Rainfall-runoff, peak-flow, hydrologic, models, No restrictions. This document is available to the Black Hills, South Dakota public from the sponsoring agency. 19. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 49 Rainfall-Runoff Modeling for Improved Peak-Flow iii August 2017 Estimates in the Black Hills Area of South Dakota TABLE OF CONTENTS DISCLAIMER ............................................................................................................................................................. II ACKNOWLEDGEMENTS ............................................................................................................................................ II TECHNICAL REPORT STANDARD TITLE PAGE .......................................................................................................... III TABLE OF CONTENTS.............................................................................................................................................. IV LIST OF TABLES ........................................................................................................................................................ V LIST OF FIGURES ...................................................................................................................................................... V TABLE OF ACRONYMS ............................................................................................................................................ VI 1 EXECUTIVE SUMMARY .................................................................................................................................... 1 1.1 PROBLEM AND BACKGROUND ........................................................................................................................ 1 1.2 RESEARCH OBJECTIVES ................................................................................................................................. 1 1.3 TASK DESCRIPTIONS ..................................................................................................................................... 1 1.4 FINDINGS AND CONCLUSIONS ........................................................................................................................ 2 1.5 APPLICATION OF RESULTS ............................................................................................................................. 2 1.5.1 Incorporate peak-flow spatial delineation into ongoing frequency update project ........................... 3 1.5.2 HEC-HMS files available for design use .............................................................................................. 3 1.5.3 Benefits could be achieved by additional modeling efforts ................................................................ 3 2 PROBLEM DESCRIPTION .................................................................................................................................. 5 3 RESEARCH OBJECTIVES .................................................................................................................................... 6 3.1 INVESTIGATE RAINFALL-RUNOFF MODELING APPROACHES .................................................................................. 7 3.2 DEMONSTRATE A SELECTED RAINFALL-RUNOFF MODELING APPROACH ................................................................. 7 4 TASK DESCRIPTIONS ........................................................................................................................................ 8 4.1 REVIEW LITERATURE .................................................................................................................................... 8 4.2 MEET WITH TECHNICAL PANEL ......................................................................................................................