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Modeling Rainfall Runoff and Snowmelt in the Pine Flat Watershed

Modeling Rainfall Runoff and Snowmelt in the Pine Flat Watershed. By Rachael Hersh-Burdick USACE Water Management Sacramento District UC Davis Civil and Environmental Engineering Department Rachael.Hersh-Burdick@us.army.mil. Goals of Pine Flat Modeling Project.

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Modeling Rainfall Runoff and Snowmelt in the Pine Flat Watershed

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  1. Modeling Rainfall Runoff and Snowmelt in the Pine Flat Watershed By Rachael Hersh-Burdick USACE Water Management Sacramento District UC Davis Civil and Environmental Engineering Department Rachael.Hersh-Burdick@us.army.mil

  2. Goals of Pine Flat Modeling Project • Can HEC-HMS accurately model snowmelt runoff volume? • Inflow model for reservoir operators • Create comfort and familiarity with HEC-HMS in Corps Sac District

  3. Overview • Characteristics of Pine Flat • Model Structure • Snow-Melt Modeling with HEC-HMS

  4. Why model Pine Flat? Pine Flat Reservoir Elev. 970 ft

  5. Central Valley Project Watersheds • Pine Flat Basin • Mean elevation: 7,635 ft • Elevation Range: 700 – 14,000 ft • Area = 1,541 mi2

  6. Why model snowmelt? • Average April 1 volume of water stored in the snow pack = 1.8 MAF • Reservoir Storage = 1.0 MAF 2006 1997

  7. Pine Flat Dam

  8. Pine Flat Precipitation (& Discharge) Gages ’97 Event Kings R Below Trimmer Kings R Above Trimmer Pine Flat Flow in (computed)

  9. Basic Snowmelt Modeling Concepts Temp Rain on snowvsSun on snow Wind Snow cold content f(snow density, temp) Groundmelt

  10. Numerical Snow Models Energy Budget • Components • Wind • Temperature • Water Vapor • Radiation (net) • Precipitation • Advection (rain) • Groundmelt • Detailed (layered) snow pack Temperature Index • Components • Temperature • Precipitation • Single layer snow • Calibration of meltrate coefficient implicitly accounts for other factors (Dr. Steve Daly)

  11. Temperature Index • Degree-day approach • Fixed amount of snowmelt for each degree above freezing • Primary Equation: • Snowmelt= (Air –Freezing Temp)*CC = time variant factor that includes: • total heat transfer at snow surface (LW & SW radiation) • latent heat • sensible heat • wind speed, aspect, slope, vegetation • Meltrate

  12. Kings River Below North Fork ’97 Event Blue = Daily observed Flow; Red = Daily modeled flow

  13. Getting a Better Calibration…. • Different temperature gage • Adjust number of elevation bands • Increase baseflow

  14. Pine Flat SWE & Temperature Gages from ’97 Event

  15. Snow Water Equivalent Blue = Observed; Red= Modeled (in Reynold’s Creek Example)

  16. Getting a Better Calibration…. • Different temperature gage • Adjust number of elevation bands • Increase baseflow • Create more subbasins

  17. The End

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