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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

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
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
overview
Overview
  • Characteristics of Pine Flat
  • Model Structure
  • Snow-Melt Modeling with HEC-HMS
why model pine flat
Why model Pine Flat?

Pine Flat Reservoir

Elev. 970 ft

central valley project watersheds
Central Valley Project Watersheds
  • Pine Flat Basin
    • Mean elevation: 7,635 ft
    • Elevation Range: 700 – 14,000 ft
    • Area = 1,541 mi2
why model snowmelt
Why model snowmelt?
  • Average April 1 volume of water stored in the snow pack = 1.8 MAF
  • Reservoir Storage = 1.0 MAF

2006

1997

slide8

Pine Flat Precipitation (& Discharge) Gages ’97 Event

Kings R Below Trimmer

Kings R Above Trimmer

Pine Flat Flow in (computed)

basic snowmelt modeling concepts
Basic Snowmelt Modeling Concepts

Temp

Rain on snowvsSun on snow

Wind

Snow cold content

f(snow density, temp)

Groundmelt

slide10

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)

slide11

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
kings river below north fork 97 event
Kings River Below North Fork ’97 Event

Blue = Daily observed Flow; Red = Daily modeled flow

getting a better calibration
Getting a Better Calibration….
  • Different temperature gage
  • Adjust number of elevation bands
  • Increase baseflow
snow water equivalent
Snow Water Equivalent

Blue = Observed; Red= Modeled (in Reynold’s Creek Example)

getting a better calibration1
Getting a Better Calibration….
  • Different temperature gage
  • Adjust number of elevation bands
  • Increase baseflow
  • Create more subbasins