The U.S. Army Corps of Engineers (USACE) owns and/or operates over 700 dams and over 15,000 miles of levees throughout the United States with authorized purposes including flood control, water supply, hydropower generation, and navigation. The performance of these structures are evaluated via risk assessments which incorporate hydrologic hazard curves, system response, and consequence information. A well-developed hydrologic hazard curve provides estimates of flow, duration, and stage across the entire range of possible loadings. Multiple inputs are required to fully develop a hydrologic hazard curve including flow- and stage-frequency.
Paleoflood data often consists of geologic, geomorphic, and botanical evidence indicating evidence of large floods (paleostage indicators, PSI) and/or the lack thereof (non-exceedance bounds, NEB), as shown below. Paleoflood data help improve flow-frequency curves especially when extrapolating to remote annual exceedance probabilities. This can reduce uncertainties and improve confidence in results for decision makers during risk analyses.
First, detailed field investigations are used to identify locations with paleoflood data. Then, elevations of the relevant data are surveyed while ages are estimated using age-dating techniques. Finally, discharges needed to form, equal, exceed, or not exceed the various hydrographic features are estimated using hydraulic simulations, like HEC-RAS, as shown below.
After discharges have been estimated for the paleoflood data, they can be integrated within a flood frequency analysis to improve the characterization of flow- and stage-frequency estimates. The following tutorials and guides demonstrate this process within HEC-SSP.
HEC-SSP version 2.3 was used to create these tutorials. You will need to use HEC-SSP version 2.3, or newer, to open the project files.
Download a copy of the HEC-SSP project here: Paleoflood_Tests.zip
