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South Dakota Department of Transportation
Project Synopsis
SD2008-01


Title: Application of Paleoflood Survey Techniques in the Black Hills of South Dakota
Project Researcher: Dan Driscoll, USGS SD Water Science Center
Project Manager: Christina Bennett
Research Period: 4/24/2008 - 4/30/2010
Status: Approved
Cost: $300,000.00

Problem Statement: Results of a recently completed South Dakota Department of Transportation research effort - Research Project SD2005-12, "Applicability of Paleoflood Surveys to the Black Hills of Western South Dakota", concluded that a better understanding of flood-frequency for the Black Hills region would result from the application of specific and well-established paleoflood techniques. More precisely, Project SD2005-12 revealed that the abundant limestone bedrock of the Black Hills creates an ideal setting for preservation of slackwater deposits (sediment deposited from floods in quiet-water settings) from past major flood events in caves, alcoves, and rock shelters in canyon sections of most major drainages in the Black Hills. The slackwater deposits contain stratigraphic records of large floods that record minimum stages of flood waters and organic materials that can be radiocarbon-dated to approximate the time since each preserved flood. With subsequent hydraulic analysis, the approximate discharge, as well as timing of previous large floods can be determined. Two specific issues that could be addressed by the application of comprehensive paleoflood techniques in the Black Hills include (1) determination of the frequency, magnitude, and spatial characteristics of large-scale floods for several or all of the major Black Hills drainages; and (2) evaluation of spatial patterns relative to large floods controlled primarily by topography, geology, and climatology. Addressing these issues would substantially improve the understanding of processes for flood generation as well as the frequency of large floods in the in the Black Hills region.

Project SD2005-12 ultimately facilitated the application of paleoflood techniques for site investigations along Spring Creek and French Creek, both sites chosen to demonstrate the quality of high-resolution flood chronologies that are obtainable within suitable environments. Extensive reconnaissance efforts prior to the in-depth site surveys ascertained that the same investigative potential exists within many other applicable stream reaches. Again, the detailed stratigraphic analysis of deposits found at these 2 sites, which represent a common environment in Paleozoic carbonate rocks around the periphery of the Black Hills, would allow for interpretation and dating of flood-deposit sequences that could provide long-term chronologies of large flood events with fairly high levels of confidence. Additionally, various other forms of paleoflood evidence might also be collected at the same time to contribute supporting information for many candidate locations. Application of paleoflood techniques on a broader scale would also warrant inclusion of comprehensive hydraulic and statistical analyses. This would require detailed surveys of channel geometry throughout appropriate stream reaches with good slackwater deposits to support in-depth hydraulic analyses necessary for estimating discharges of previous large flood events. Finally, the use of appropriate statistical analytical procedures incorporating infrequent large flood events would be required for the development of new, robust flood-frequency estimates.

Reconnaissance site investigations would provide the most information on the size and frequency of large-scale flows, particularly if focused on the larger Black Hills drainages similar to the Spring Creek and French Creek sites. Most if not all of these larger drainages have candidate sites with high potential for paleoflood analysis. Results using these approaches would be most meaningful for assessing hazards for the majority of populated areas and infrastructure concentrated along the flanks of the Black Hills. Investigations of higher-elevation and smaller drainages would provide important information regarding flood generation processes and controlling factors such as elevation, topography, and geology. Smaller drainages in the higher elevations generally have few flood deposits preserved, but again, reconnaissance during Project SD2005-12 indicated several possible sites for which detailed investigations probably would provide supporting information on flood-frequency and magnitude. Such information would contribute to site-specific flood-frequency analyses as well as frequency analyses on a regional basis.



Findings:

Research Objectives:
1  Apply paleoflood survey techniques that employ investigations of stratigraphic records preserved in slackwater deposits, as proven and defined in the recently completed SDDOT Research Project, SD2005-12, within a predetermined central corridor of the
2  Perform paleoflood investigations primarily within Paleozoic carbonate rock formations along the periphery of the Black Hills, but also to some extent within the Limestone Plateau at higher elevations of the central Black Hills, to ultimately discern

Research Tasks:
1  Review historical records, accounts, journals, and other literature, and perform interviews with individuals who might be knowledgeable about Black Hills flood history, to gather information that would supplement the paleoflood investigative work on
2  Meet with the project’s technical panel to review the project scope and work plan, and also select the survey sites where paleoflood investigative work will occur from the following list of candidate stream reaches: 1) Elk/Little Elk Creeks, 2) Rapid
3  Along the selected stream reaches, conduct comprehensive paleoflood investigations using stratigraphic records analysis to gather discernible paleoflood evidence. Subsequently, absolute and relative dating techniques can be performed on samples gathe
4  Also along the selected stream reaches, the Research Team will coordinate with the SDDOT in performing topographic surveys of the drainage basins, including detailed channel cross-sections so that peak paleoflood discharge estimates can be formulated
5  Conduct field visits of representative paleoflood survey sites with the Project Technical Panel toward the end of the first summer of field work outlined in Tasks 3 and 4, above.
6  Submit an interim report to the Project Technical Panel that reviews work progress, assesses project accomplishments to date, and provides a general status on work progress after the first summer of field work. This report is assumed to be completed
7  Complete the remaining paleoflood investigations, dating of gathered samples, drainage basin surveys, and hydraulic modeling in the ensuing work phase.
8  Develop and submit for Technical Panel review, as products of the study efforts, updated datasets to derive flood frequency curves through expected moments methods, or other appropriate data analysis techniques.
9  Upon review of the updated datasets and flood frequency curves by the Technical Panel, prepare a final report and executive summary of the research methodology, data derivations, findings, conclusions, and recommendations.
10  Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Documents Available:
SD2008-01_Fact_Sheet_06-11-12.pdf
SD2008-01-F_Final_Report_07-16-12.pdf

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