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Estimation of Evaporation From Reservoirs

Estimation of Evaporation From Reservoirs. Kevin Stamm, Kellie Bergman, Tim Temeyer Water Management, Omaha District Dr. Steven F. Daly ERDC/CRREL Second Annual Missouri Basin River Forecaster’s Meeting 15-17 November 2010. Overview.

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Estimation of Evaporation From Reservoirs

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  1. Estimation of Evaporation From Reservoirs Kevin Stamm, Kellie Bergman, Tim Temeyer Water Management, Omaha District Dr. Steven F. Daly ERDC/CRREL Second Annual Missouri Basin River Forecaster’s Meeting15-17 November 2010

  2. Overview • Results from a long term, relatively low cost study to estimate evaporation from reservoirs in the Omaha District and NWD-RCC • Requirements: • Physically based • No new instrumentation installed in field • Remove existing evaporation pans • Work within the CWMS framework

  3. Evaporation Estimation Two Processes: • Bulk flux evaporation estimation • 1-D temperature heat budget to estimate vertical temperature profile in reservoir Using: • Met data available through Internet from NWS or estimated • Reservoir geometry data

  4. Bulk-Flux Algorithm • Estimate reservoir surface roughness based on wind speed • Assume neutral stratification in air • Estimate transfer coefficients • Calculate fluxes • Estimate air stratification

  5. Surface Temperature is Key Surface temperature has a strong influence on the evaporation flux because the saturation humidity immediately above the water is a strong function of the water temperature

  6. 1-D temperature heat budget to estimate surface temperature • Heat transfer through surface with atmosphere • Distribution of heat throughout depth of reservoir: 1-D

  7. Flow Through times

  8. Heat transfer through surface with atmosphere • Sensible heat flux • Latent heat flux • Solar radiation • Long wave radiation in and out • Both solar and long wave require information on cloud cover – NWS METAR

  9. Distribution of heat throughout depth of reservoir: 1-D • Solar Radiation penetration • Thermal diffusion • Mixing due to Wind • Mixing due to Potential Energy

  10. Solar Radiation penetration • Majority of solar radiation is absorbed at surface • But the remaining solar energy can penetrate to depth and be absorbed below the surface • The clearer the water the deeper the penetration • Measured using Secchi disk

  11. Wind and Density Mixing • Density mixing cause denser water to mix with less dense water below. (Primarily in the fall) • Wind mixing uses the work of the wind blowing over the surface to mix denser water from below with less dense water above (Anytime the wind blows.) • Algorithms are available for both

  12. TriLakes Chatfield

  13. TriLakes Chatfield

  14. Pipestem

  15. Pipestem

  16. Pipestem

  17. Oahe

  18. Oahe

  19. Application • Operating in Omaha District CWMS • Each reservoir is assigned a NWS station • Decode NWS METAR messages • CWMS runs model once each day for each reservoir • Stores evap. and water temperature profile for next run

  20. Further Work • Resolve CWMS problems • Ice cover model • Convective heat transfer (inflow and outflow)

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