US CLIVAR/NCAR ASP Researcher Colloquium
Statistical Assessment of Extreme Weather Phenomena under Climate Change
NCAR Foothills Lab, Boulder, Colorado
June 13-17, 2011
Extremes in Floods for Dam Safety and Water Resources at the Bureau of Reclamation
John England, Bureau of Reclamation
Abstract:
The Bureau of Reclamation owns, operates and maintains over 350 high and significant hazard dams in
the 17 western States. These facilities, such as Folsom Dam in California, Grand Coulee Dam in
Washington, and Hoover Dam in Nevada, provide water that is critical to not only the needs of
agriculture, but also municipalities and power providers in both large and small metropolitan areas.
Reclamation utilizes extreme weather and climate information to assess potential impacts to reservoirs
and dams in several areas, such as dam safety, flood control, water supply operations, and for riskbased decision making. Some examples that encompass short-term and long-term planning decisions
include: hydrologic hazards for dam safety; evaluating flood control rule curves; examining options on
additional reservoir storage; flood forecasting; and snowmelt runoff forecasting. Extreme precipitation
and weather-related phenomena with the following characteristics are typically needed: fine spatial
(watershed) scales ranging from a few hundred to thousands of km2; fine temporal scales ranging from
minutes to days (possibly seasons); and annual exceedance probabilities (AEPs) ranging from 1/50 to
1/100,000. Spatial variability of precipitation within these orographic watersheds is high. In some
cases, AEPs < 1/100,000 are needed for dam safety. Some extreme flood estimation tools developed
and used by Reclamation, such as Bayesian flood frequency (with paleoflood data), and stochastic
event-based rainfall-runoff modeling, are briefly described. Case studies for watersheds and dams in
California and Idaho illustrate some of the extreme flood and weather-related applications and needs
for Reclamation.