ENVI 412 Hydrologic Losses and Radar Measurement
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Transcript of ENVI 412 Hydrologic Losses and Radar Measurement
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ENVI 412ENVI 412Hydrologic Losses and Hydrologic Losses and
Radar MeasurementRadar MeasurementDr. Philip B. BedientDr. Philip B. Bedient
Rice UniversityRice University
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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
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• 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
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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
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Shallow Lake Evap Shallow Lake Evap (Kohler, 1955(Kohler, 1955))
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Evaporation PansEvaporation Pans
• Anemometer - wind
• Rain Gage - precip.
• Pan for water - evap
• Level measured daily
• Refilled as necessary
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Soil Moisture CycleSoil Moisture Cycle• Autumn - rainfall recharge
• Winter - max soil storage
• Spring - some evap loss
• Summer - most depleted
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Surface Flow Surface Flow DistributionDistribution
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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
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Horton’s EqnHorton’s Eqn
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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
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Example of Example of IndexIndex
DRO
VOL Infiltration F(t)
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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 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
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Brays Bayou at Main Brays Bayou at Main St BridgeSt Bridge
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• 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
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• 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
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Standard Flood Alert SystemStandard Flood Alert SystemUse measured rainfall
Predict hydrologic Response in x,y, and t
Alert various agenciesand emergency mgrs
Save lives and damages
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Use of NEXRAD Rainfall for Use of NEXRAD Rainfall for Hydrologic PredictionHydrologic Prediction
Dr. Baxter Vieux, University of OklahomaDr. Baxter Vieux, University of Oklahoma
National Severe Storm LaboratoryNational Severe Storm Laboratory
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• Recent Innovation
• Uses radar - NWS
• DPA every 5 minutes
• Accurate to 230 km
• Provides better spatial
detail than gages
NEXRAD Radar DataNEXRAD Radar Data
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Radar Provides Visual EffectsRadar Provides Visual Effects
Midnight 1 a.m.
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y = 0.8991x - 0.0382
R2 = 0.9033
0
2
4
6
8
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12
0 2 4 6 8 10 12
Gauge (in.)
Radar (in.)
Brays Bayou
Sims Bayou
Radar–Gage CalibrationRadar–Gage Calibration October 17, 1994 October 17, 1994
Tot
al R
ainf
all R
adar
(in
.)
Total Rainfall measured at the Gage (in.)
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Rice Blvd. and Brays Bayou
02468
1012
0 10 20 30 40 50
Time (hr.)
Gauge DataRadar Data
Cum
ulat
ive
Rai
nfal
l (
in.)
October, 1994 CalibrationOctober, 1994 Calibration
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Weather Radar SystemsWeather Radar Systems
Recently deployed weather radar systems such Recently deployed weather radar systems such as NEXRAD offer accurate and reliable as NEXRAD offer accurate and reliable precipitation estimation precipitation estimation
Increased sensitivity coupled with improved Increased sensitivity coupled with improved processing provides high-resolution radar data processing provides high-resolution radar data sets for a variety of applications. sets for a variety of applications.
Provides another source of rainfall information in Provides another source of rainfall information in addition to rain gaugesaddition to rain gauges
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WSR-88D - NEXRADWSR-88D - NEXRAD The first operational WSR-88D was The first operational WSR-88D was
installed in May 1990 at Twin Lakes, OKinstalled in May 1990 at Twin Lakes, OK 160 + deployed nationwide and overseas.160 + deployed nationwide and overseas. Is now being used for much more than Is now being used for much more than
weather forecasts. weather forecasts. Most significant advancement in hydrology Most significant advancement in hydrology
in last 20 years!in last 20 years!
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Users of Radar and Users of Radar and Meteorological DataMeteorological Data
Real-time access to radar and other Real-time access to radar and other meteorological data is now provided to meteorological data is now provided to
users outside of the NWSusers outside of the NWS
Nexrad has spawned a private sector Nexrad has spawned a private sector meteorological services industrymeteorological services industry
Now other users are beginning to Now other users are beginning to experience the benefits within the experience the benefits within the hydrologic communityhydrologic community
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Low Precision 16-level Image
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16-level precision image vs. 256-level data
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FAS2 will add 482 radar rain gauges over Brays
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T.S. Allison Storm TotalJune 8-9, 2001June 8-9, 2001
Bayous
Counties
Highways
Drainage
TMCÊÚStorm Total (in)
0.01 - 0.250.25 - 0.50.5 - 11 - 22 - 44 - 66 - 88 - 1010 - 1212 - 1414 - 1616 - 1818 - 2020 - 2222 - 25> 25
ÊÚ
.-,45
.-,10
.-,59
N
0 5 10 Miles
26.6 in
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Prospects for Flood Modeling Prospects for Flood Modeling in Real-Timein Real-Time
Forecasting urban streams that respond rapidly to heavy rainfall is difficult.
Such forecasts can easily underpredict the river stage with little or no lead time
Why have hydrologic models lagged the development of radar technology and meteorological science?
How can we improve current hydrologic practice in order to forecast flood levels in real-time?