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

Q e = energy used for evaporation Q h = sensible heat Q  = stored energy Q v = advected energy Q N = 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 Penman’s combined (1948) Lake Evaporation

E = e s - e a (a + bu) Where E = evaporation (cm/day) e s = Sat vapor pressure (T) e a = Vapor pres at fixed z u = wind speed in m/sec a,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 conditi on

Surface Flow Distribution

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

Horton’s 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  Index DRO VOL Infiltration F(t) DRO

Example of  Index Assume 4.9 in of DRO from a 560 acre Basin  index Set up a general Eqn for  index  2(1.4 -   +3(0.7-  Find  by trial and error by assuming a value and solving - try  = 1.5 in/hr And it only accounts for 0.8 x 3 = 2.4 in of DRO  0.5 in/hr yields 9.0 in of DRO - too much DRO Try  1.0 in/hr or 2(.4) +3(1.3)+2(.1) = 4.9 inches

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

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

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  W*D Sum up across stream to get total Q Stream 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 gages Typical Rating Curve for Stream