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ENVI 412 Hydrologic Losses and Radar Measurement

ENVI 412 Hydrologic Losses and Radar Measurement. Dr. Philip B. Bedient Rice University. Lake Energy Budget. Q e = energy used for evaporation Q h = sensible heat Q q = stored energy Q v = advected energy Q N = net radiation absorbed by water body. Lake Evaporation.

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ENVI 412 Hydrologic Losses and Radar Measurement

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  1. ENVI 412Hydrologic Losses and Radar Measurement Dr. Philip B. Bedient Rice University

  2. Lake Energy Budget • Qe = energy used for evaporation • Qh = sensible heat • Qq = stored energy • Qv = advected energy • QN = net radiation absorbed by water body

  3. Lake Evaporation • Function of wind speed, T, and      humidity gradient •  Energy source - solar energy • Mass transfer, energy budget,     and pan evaporation • Penman’s combined (1948)

  4. Mass Transfer E = es - ea (a + bu) Where E = evaporation (cm/day) es = Sat vapor pressure (T) ea = Vapor pres at fixed z u = wind speed in m/sec a,b = constants

  5. Shallow Lake Evap (Kohler, 1955)

  6. Evaporation Pans • Anemometer - wind • Rain Gage - precip. • Pan for water - evap • Level measured daily • Refilled as necessary

  7. Soil Moisture Cycle • Very Complex Soil Physics • Autumn - rainfall recharge • Winter - max soil storage • Spring - some evap loss • Summer - most depleted                     condition

  8. Surface Flow Distribution

  9. Horton’s Infiltration Concept f(t) = Rate of water loss into soil f = fc + (fo - fc) exp (-kt) fc = final rate value fo =initial rate value K = decay rate Can integrate to get F(t) = Vol of infiltration

  10. Horton’s Eqn

  11.  index Method • Assumes constant rate   over time of rainfall • Volume above line is   DRO • Volume below line is F(t) • Trial and error computed

  12. Example of F Index DRO DRO VOL Infiltration F(t)

  13. Example of F Index Assume 4.9 in of DRO from a 560 acre Basin Set up a general Eqn forF index 2(1.4 - F) + 3(2.3- F) +2(1.1- F) +3(0.7- F) + 2(0.3- F) = 4.9 Find Fby trial and error by assuming a value and solving - try F = 1.5 in/hr And it only accounts for 0.8 x 3 = 2.4 in of DRO F = 0.5 in/hr yields 9.0 in of DRO - too much DRO Try F =1.0 in/hr or 2(.4) +3(1.3)+2(.1) = 4.9 inches

  14. Brays Bayou and Harris Gully Harris Gully drains Rice/TMC Area Harris Gully: 4.5 sq. mi. Study Area: 8 sq. mi. Brays Bayou: 129 sq. mi. TMC

  15. 96” 54” 66” 72” 84” 114” Existing Minor Drainage Network 60” 90” 72” 72” 60” 60” 60” 6.5’x10’ 6.5’x10’ Rice 7.5’x11’ Hermann Park 2-11.5’x15’ 66” 2-15’x15’ TMC

  16. High Water Inundation in Rice/TMC Basin Area

  17. Brays Bayou at Main St Bridge

  18. Stream Cross-Section for Q • Measure v at 0.2 and 0.8 of depth • Average v and multiply by DW*D • Sum up across stream to get total Q

  19. Typical Rating Curve for Stream • Plot of z vs. Q • Determined from stream    measurements of V • Unique for each stream • Changes with development • Available for all USGS gages

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