Hydrologic Issues for Dams - Association of State Dam Safety Officials

United States will be used to assess the effects of climate change on flood magnitude.[Currently there are no regional paleoflood data for the eastern United States,however, if they become available, they will incorporate them into the analyses.]These data then will be used to test and evaluate various assumptions of hydrologicmodeling scenarios of climate change effects on flood magnitude and frequency.We hope to stimulate discussion of research needs, including optimizing a balance of“ flood chasing” and detailed modeling approaches of paleoflood investigations. Ourresults indicate further research is needed that better accounts for physical processes offlooding, for sediment transport and deposition during flood conditions, and the need toimprove methods for estimating peak discharge of floods and paleoflood. There is muchwork to be done to improve our understanding of the distribution and location ofsediment deposits and erosion thresholds of surfaces from extreme floods. A betterunderstanding of the physics of large flood response and better predictive capabilitiesthan those documented here is needed. Research is needed to identify other types ofPSIs, if they exist, and to better understand geomorphic effectiveness of floods. Morequantification (e.g., using 1-D or 2-D hydraulic modelling to calculate paleoflooddischarges, using absolute-age dating of flood deposits and validation of relative-agdatingmethods, particularly developing guidelines for more robust flood-frequencyparameter estimation procedures, regional flood-frequency analysis with paleoflood data,etc.) are essential for dam safety risk assessments, flood-inundation mapping, flood-plainmanagement, and related environmental investigations. While use of complexprocedures provide slightly more precise quantitative description of the data, dischargeand frequency estimates of extreme floods in a basin may be readily estimated by thecost-effective approach paleoflood techniques described above, the ability to havemultiple approaches that fits the needs and resources specific to a specific water-resources application are needed.Products include several reports and supporting journal articles summarizing unified,state-of-the-art techniques for flood-frequency estimation that have generalapplication for water-resources investigations. Recommendations will be proposedfor changing the flood frequency analysis guidelines for consideration by the IACWDand other water management agencies. Benefits of the proposed study will includeimprove guidelines for flood hazard assessments, flood inundation mapping and asinput to risk assessments for determining appropriate levels of public safety,prioritizing projects, and allocating limited resources. A major benefit of theproposed study supports the National Flood Insurance Reform Act of 1994 mandatesthat the Nation’s flood maps be revised in the near term and subsequently reviewedevery 5 years. The FEMA estimates that updates to existing flood insurance studiesand creating new maps for communities without mapping will cost between $800million and $1,000 million. FEMA’s Map Modernization Plan also emphasizes thatmore cost-effective methods to produce flood maps are essential.Concluding Remarks163Paper 20 – Jarrett et al