Utilizing paleoflood data for supporting the decisions of USACE hydrology and hydraulics (H&H) practitioners is the subject of a new investigation and report that synthesizes relevant literature and scientific findings related to USACE H&H assessments. Paleohydrology describes the evidence of the movement of water and sediment in stream channels before the time of continuous hydrologic records or direct measurements. Appropriate Application of Paleoflood Information for the Hydrology and Hydraulics Decisions of the U.S. Army Corps of Engineers (pdf, 2.62 MB) investigates utilization of geologically obtained and hydrologically transformed paleoflood data in both the relatively recent past (50-500 years) to the very distant past (500-10,000 years). The main conclusions of the report are:
- The utility of paleoflood information should be considered with respect to the H&H decision at hand, including both the policy and the technical requirements of that decision.
- For situations where paleoflood data is potentially useful to H&H decisions, the resources necessary to conduct the investigation should be weighed against the underlying uncertainties and assumptions.
- Paleofloods can provide direct and useful information about stage histories and can be used, given cautions, to estimate discrete event discharge values. However, there is limited evidence to support using paleoflood information to estimate a series of hydrologic events with multiple peaks, flood volumes or durations.
- Paleoflood information is less useful if it is meant to inform a portfolio of projects or compare locations across a wide geographic region that has varied terrain and geological contexts.
Paleoflood information is not relevant for all H&H decisions. For example, if the decision leads to the design or modification of a high hazard dam, then the utility of paleoflood information is minimal, as the current design standard is based on the "Probable Maximum Floods" standard. Paleoflood information is largely site specific. USACE is responsible for many very large facilities that have been altered through time, either by geologic or anthropogenic processes. These facilities are not suitable for paleoflood analysis.
The report is part of a larger effort to explore processes, methods and guidance for hydrology used in climate change impact assessments and adaptation planning and design.