ENVI 412Hydrologic Losses and Radar MeasurementDr. Philip B. BedientRice University

Qe = energy used for evaporation Qh = sensible heat Qq = stored energy Qv = advected energy QN = net radiation absorbed by water body

Lake Energy Budget

Function of wind speed, T, and humidity gradient Energy source - solar energy Mass transfer, energy budget, and pan evaporation Penmans combined (1948)Lake Evaporation

E = es - ea (a + bu)Where E = evaporation (cm/day) es = Sat vapor pressure (T) ea = Vapor pres at fixed zu = wind speed in m/seca,b = constants

Mass Transfer

Shallow Lake Evap (Kohler, 1955)

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

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

Surface Flow Distribution

Hortons Infiltration Conceptf(t) = Rate of water loss into soilf = fc + (fo - fc) exp (-kt)fc = final rate valuefo = initial rate valueK = decay rateCan integrate to get F(t) = Vol of infiltration

Hortons Eqn

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

Example of F IndexDROVOL Infiltration F(t)DRO

Example of F IndexAssume 4.9 in of DRO from a 560 acre BasinSet up a general Eqn for F index

2(1.4 - F) + 3(2.3- F) +2(1.1- F) +3(0.7- F) + 2(0.3- F) = 4.9

Find F by trial and error by assuming a value and solving - try F = 1.5 in/hrAnd it only accounts for 0.8 x 3 = 2.4 in of DROF = 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

Harris Gully drainsRice/TMC AreaBrays Bayou and Harris GullyHarris Gully: 4.5 sq. mi.Study Area: 8 sq. mi.Brays Bayou: 129 sq. mi.TMC

Existing Minor Drainage Network2-15x152-11.5x157.5x119060726.5x1066606072606.5x10Hermann ParkTMCRice

High Water Inundation in Rice/TMC Basin Area

Brays Bayou at Main St Bridge

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

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

Brays Bayou, which drains the Rice area, drains about 126 mi^2 of area, from Highway 6 on the west end, and flows into the Houston Ship Channel on the east side of I-45.

Harris Gully is the local watershed, which used to be an open channel across the Stadium lot, and through what is now the TMC. Harris Gully drains about a 4.5 to 5 sq. mi. area.