ENVI 412ENVI 412Hydrologic Losses and Hydrologic Losses and
Radar MeasurementRadar MeasurementDr. Philip B. BedientDr. Philip B. Bedient
Rice UniversityRice University
Qe = energy used for evaporation
Qh = sensible heat
Q = stored energy
Qv = advected energy
QN = net radiation absorbed by water body
Lake Energy BudgetLake 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 EvaporationLake Evaporation
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
Mass TransferMass Transfer
Shallow Lake Evap Shallow Lake Evap (Kohler, 1955(Kohler, 1955))
Evaporation PansEvaporation Pans
• Anemometer - wind
• Rain Gage - precip.
• Pan for water - evap
• Level measured daily
• Refilled as necessary
Soil Moisture CycleSoil Moisture Cycle Very Complex Soil Physics
• Autumn - rainfall recharge
• Winter - max soil storage
• Spring - some evap loss
• Summer - most depleted condition
Surface Flow Surface Flow DistributionDistribution
Horton’s Infiltration ConceptHorton’s Infiltration Conceptf(t) = Rate of water loss into soilf(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
Horton’s EqnHorton’s Eqn
index Methodindex 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 Example of IndexIndex
DRO
VOL Infiltration F(t)
DRO
Example of Example of IndexIndexAssume 4.9 in of DRO from a 560 acre BasinSet up a general Eqn for indexindex
2(1.4 - +3(0.7-
Find by trial and error by assuming a value and solving - try = 1.5 in/hrAnd it only accounts for 0.8 x 3 = 2.4 in of DRO0.5 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 drainsRice/TMC Area
Brays Bayou and Harris Brays Bayou and Harris GullyGully
Harris Gully: Harris Gully: 4.5 sq. mi.4.5 sq. mi.Study Area: Study Area: 8 sq. mi.8 sq. mi.Brays Bayou: Brays Bayou: 129 sq. mi.129 sq. mi.
TMC
Existing Minor Drainage NetworkExisting Minor Drainage Network
2-15’x15’
2-11.5’x15’
7.5’x11’
90”
60”
72”
6.5’
x10’
66”
60”
60”
72”
60”6.
5’x1
0’
66”
72”
96”
114”
54”
84”
Hermann Park
TMC
Rice
High Water Inundation in Rice/TMC Basin Area
Brays Bayou at Main Brays Bayou at Main St BridgeSt 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 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 gages
Typical Rating Curve for StreamTypical Rating Curve for Stream