Reclamation studied options for the improvement of a legacy dam in Washington with a hydraulic fill core and thick deposits of soft liquefiable sediments in the foundation. Deformations driven by seismic strength loss dominate the risk at this facility. To evaluate potential remediation options, Reclamation used finite difference numerical modeling (FLAC2D) to investigate various options to increase the stability of this structure during seismic loading. Numerous modeling challenges were encountered including unusual bedrock geometry, extreme deformations impacting boundary conditions, and the frequent need for model rezoning. Reclamation overcame these challenges and successfully identified two remediation alternatives, deep soil mixing (DSM) and installation of a new toe shear key. A field test section for the deep soil mixing alternative was successfully implemented.

Work supporting Southern California Edison's (SCE) evaluation of the hydrologic hazards of dams under future climate conditions as recommended by the California Public Utilities Commission (CPUC) Climate Vulnerability Assessment will be presented.

Hydrometeorological inputs to a stochastic hydrologic model were adjusted based on global climate model output (CMIP5), provided on cal-adapt.org, to quantify the effects of anthropogenic climate change. Predicted changes in temperature and precipitation (per month) between a historical reference period (1986-2005), and a forecast period (2006-2100) were used to represent two future climate scenarios: hot-dry (hotter temperatures with diminished precipitation magnitudes) and warm-wet (warmer temperatures with enhanced precipitation magnitudes). The most severe scenario, RCP 8.5, was used in the analysis per CPUC recommendations.

The Stochastic Event Flood Model (SEFM) was used to develop hydrologic hazards for the time horizons 2050 and 2070. Climate-adjusted magnitude-frequency relationships for peak reservoir inflow rate, peak reservoir release, maximum 72-hour reservoir inflow volume, and maximum reservoir water surface elevation are presented for each.

The greatest changes in projected precipitation magnitudes occurred in the winter months, which, along with changes in temperature and freezing level, affects snowpack. Temperature is projected to increase throughout the year, with the greatest increases in the summer months.

The Mid-latitude Cyclone (MLC) storm type hydrologic loading curves increased (were more severe, more common) for the warm-wet scenario and decreased (were less severe, less common) for the hot-dry scenario for both future time horizons. The local storm hydrologic loading curves decreased (were less severe, less common) for both scenarios for both future time horizons. The annual exceedance probability of dam overtopping is presented in the tables below for current climate conditions and both climate change scenarios.

A localized thunderstorm produced extreme rainfall and flooding in July 1999 at a high elevation, interior location of Colorado, near the town of Saguache. This storm was utilzied for PMP development during the Colorado-New Mexico Regional Extreme Precipitation Study (CO-NM REPS) and was controlling of PMP depths for the local storm type in mountainous regions in that study. A partnership between Colorado State University, Colorado Department of Water Resources and Applied Weather Associates (AWA) was formed to investigate high-elevation extreme precipitation and runoff events with the goal of updating hydrologic guidelines in Colorado. AWA's Storm Precipitation Analysis System (SPAS) rainfall data were used as input for flood runoff reconstruction to determine if the rainfall as originally analyzed would produce the flooding observed in the location. For the Saguache July 1999 storm, the result of this investigation demonstrated that the original total storm rainfall amounts were likely accurate, however, the exact location and timing needed to be updated. Based on initial modeling, a detailed investigation took place to more accurately quantify the rainfall and flooding associated with this storm. This was completed by performing bucket survey type analyses, talking with witnesses of the event, and investigating radar scan data to derive additional information to update the original storm analysis. These updates were applied to the hydrologic model for sensitivity analysis and ultimately were applied to the CO-NM REPS study and PMP outputs. This presentation will detail the on the ground "bucket survey" that was completed in cooperation with CSU and DWR to derive new data, how those additional data were applied to update the original storm analysis, how the updated storm analysis was applied to the CO-NM REPS tool, and the results of those updates on PMP and flood runoff investigations.