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Hydrologic Evaluation of El Vado Dam: Risk Reduction Study

Conduct a corrective action study addressing failure modes under Reclamation's Safety of Dams Program. Combining historical peak discharge data and developing rainfall-runoff models for watershed above El Vado Dam to estimate flood risk.

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Hydrologic Evaluation of El Vado Dam: Risk Reduction Study

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  1. El Vado Dam Hydrologic Evaluation Joseph Wright, P.E. Bureau of Reclamation Technical Services Center Flood Hydrology and Meteorology Group

  2. Reclamation Dam Safety 2011-SOD-A: “Conduct a corrective action study to address the hydrologic failure modes under Reclamation’s Safety of Dams Program” The 2010 risk analysis identified three potential failure modes that justify taking risk-reduction actions. The potential failure modes included failure of the emergency spillway in addition to the service spillway.

  3. Flood Risk For a Corrective Action Study, Reclamation best practices guidelines require that multiple methods are used to estimate the flood risk. • Method 1 – We combined observed historical peak discharge data with estimated pre-historical data and fit a statistical distribution to determine annual peak discharge exceedance probabilities. • Method 2 – We developed a stochastic event rainfall-runoff model for the watershed above El Vado Dam.

  4. Method 1 - Observed Peak Discharge • 97 Observations • 101 Years 08283500 – Rio Chama at Park View 1913, 1925 – 1955, 31 Years of Data 08284100 – Rio Chama near La Puente 1956 – 2014, 59 Years of Data 08285500 – Rio Chama below El Vado 1914 – 1924, 7 Years of Data

  5. Pre-Historical Peak Discharge • A flood terrace was observed and studied at 10 different locations downstream of El Vado Dam on the Rio Chama. • Soil stratigraphic relationships suggest a large flood occurred at least once during the past 4,300 to 4,500 years. • 2-dimensional hydraulic modeling of the Rio Chama below El Vado Dam suggests the peak discharge of this flood was between 11,000 and 14,000 ft3/s. • A non-exceedance bound with a discharge between 65,000 and 75,000 ft3/s has not occurred during the past 8,000 to 10,000 years.

  6. Peak Discharge Timeline

  7. Peak Discharge Estimate - EMA

  8. Method 2 - Stochastic Rainfall-Runoff Model • Develop physical based 1-dimensional rainfall-runoff using hydrologic runoff units (HRU’s) • Estimate a precipitation frequency curve using the L-Moments method of regional statistics • Randomly sample the frequency precipitation curve as well as a storm pattern to determine an annual maximum storm event • Randomly determine the initial model conditions • Repeat steps 3 and 4 to develop a simulate time-series of maximum flood events • Fit a statistical distribution to the time series of annual maximum events

  9. Physical Based Model 18 Subbasins

  10. Soils 10 Soil Zones (including Water)

  11. Mean Annual Precipitation (MAP) 9 MAP Zones

  12. Elevation 10 Elevation Zones

  13. HRU’s 900 HRU’s (excluding subs) 16,200 unique HRU’s

  14. Regional Precipitation Analysis

  15. Regional Precipitation Analysis • 154 Precipitation Gages • 2,911 station years of data • L-Moments was used to determine the L-skewness, and L-kurtosis • A Generalized Extreme Value (GEV) distribution was fit to the L-Moments

  16. Regional Precipitation Analysis

  17. Spatial and Temporal Storm Pattern

  18. Spatial Storm Pattern – Sep 10,2003

  19. Temporal Precipitation Pattern Sep 10, 2003 Storm 18 Sub-basins

  20. Sep 10, 2003 Storm Max 24hr Sea Level Temperature = 82.4 deg F Max 24hr Freeze Level = 14,398 ft

  21. Runoff Calculation Evapotranspiration Rain + Snowmelt Surface Runoff Soil Moisture Storage (Root Zone) Gravitational or Intermediate Vadose Zone Interflow Deep Percolation

  22. Runoff Transformation (HEC-1)

  23. Calibrate

  24. Monte Carlo Select Month of Occurrence Select Storm Characteristics Select All Hydrometeorological, Hydrologic, And Hydraulic Parameters that are Dependent Upon Month of Occurrence Repeat n Times Select Remaining Parameters that are Independent of Other Parameters Select Remaining Parameters that are Dependent Upon Other Parameters Do Flood Modeling and Reservoir Routing Rank All Events in Descending Order of Magnitude Develop Flood Magnitude-Frequency Curves

  25. Rank and Plot Peak Discharge

  26. El Vado Peak Discharge

  27. El Vado Hydrologic Loading • This study defines hydrologic loading as Maximum Routed Reservoir Elevation • Each SEFM simulated hydrograph is routed through El Vado Dam (As well as Heron Dam) • The initial reservoir water surface elevation is determined by sampling historic data. The historic data is correlated with antecedent precipitation. • The maximum routed reservoir elevations are ranked and plotted on a probability plot to determine the frequency-elevation curve.

  28. El Vado Hydrologic Loading

  29. Questions?

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