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Hydrologic Losses and Hydrologic Losses and Radar MeasurementsRadar Measurements
CIVE 6361 – Chapter 1CIVE 6361 – Chapter 1
Spring 2010Spring 2010
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
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
Traditional Flood Alert SystemTraditional Flood Alert SystemUse measured rainfall
Predict hydrologic Response in x,y, and t
Alert various agenciesand emergency mgrs
Save lives and damages
Use of NEXRAD Rainfall for Use of NEXRAD Rainfall for Hydrologic PredictionHydrologic Prediction
• Recent Innovation
• Uses radar - NWS
• DPA every 5 minutes
• Accurate to 230 km
• Provides better spatial
detail than gages
NEXRAD Radar DataNEXRAD Radar Data
Radar Provides Visual EffectsRadar Provides Visual Effects
Midnight 1 a.m.
Radar–Rainfall RelationshipsRadar–Rainfall Relationships
Z = 300 R 1.4 Standard
Z = 250 R 1.2 Tropical
Z = radar reflectivity in dBZR = rainfall rate in in/hr
Ratio of gage value to radar value = BIAS
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
Rain Gage and Radar Rainfall Estimates
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
5 P
M t
o 6
PM
6 P
M t
o 7
PM
7 P
M t
o 8
PM
8 P
M t
o 9
PM
9 P
M t
o 10
PM
10 P
M t
o 11
PM
11 P
M t
o 12
AM
12 A
M t
o 1
AM
1 A
M t
o 2
AM
2 A
M t
o 3
AM
3 A
M t
o 4
AM
4 A
M t
o 5
AM
June 8 - 9, 2001
Hou
rly R
ainf
all (
in)
.
Main St. Radar Pixel, 12.21 inches Total
Main St. Gage - HCOEM, 12.13 inches Total
Rice University Gage, 14.74 inches Total
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
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!
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 experience the Now other users are beginning to experience the benefits within the hydrologic communitybenefits within the hydrologic community
Low Precision 16-level Image
16-level precision image vs. 256-level data
T.S. ALLISON RADAR RAINFALL OVER BRAYS BAYOU WATERSHED12 HOUR TOTALS BY SUBAREA
FAS2 will add 482 radar rain gauges over Brays
#
#
#
#
#
#
#
#
#
#
#
#
ð
ð
ð
ð
ð
ð
ð
ð
ð
ð
ð
ð
T.S. Allison Storm TotalT.S. Allison Storm TotalJune 8-9, 2001June 8-9, 2001
Bayous
Counties
Highways
Drainage
TMCÊÚStorm Total (in)
0.01 - 0.25
0.25 - 0.5
0.5 - 1
1 - 2
2 - 4
4 - 6
6 - 8
8 - 10
10 - 12
12 - 14
14 - 16
16 - 18
18 - 20
20 - 22
22 - 25
> 25
ÊÚ
.-,45
.-, 10
.-,59
N
0 5 10 Miles
26.6 in
Prospects for Flood Modeling Prospects for Flood Modeling in the Futurein the Future
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
CASA radars may help revolutionize our ability to see and predict rainfall
CASA funded as an NSF ERC to several universities including UMass, OU, CSU, Rice
NETRAD Sites and coverage over Houston, Texas.
NSF Proposed ERC for Houston Testbed New Radar Technology for 2005-2010 time periodProvide data at 200 meter scale accuracy
NETRAD Sites and coverage over Houston, Texas.
New CASA Radars for Deployment to Oklahoma
Harris Gully Harris Gully Watershed AnalysisWatershed Analysis
Philip B. BedientCivil and Environmental Engineering
Rice University
Engineering ResearchEngineering Research This research was funded by:This research was funded by:
City of Houston City of Houston Rice UniversityRice University Texas Medical CenterTexas Medical Center Harris County Flood Control DistrictHarris County Flood Control District
Special thanks to Walter P. Moore Associates, Inc. Special thanks to Walter P. Moore Associates, Inc. and JF Thompson, Inc. for their assistance on the and JF Thompson, Inc. for their assistance on the projectproject
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
Stormwater ModelingStormwater Modeling
Four Key ElementsFour Key Elements
RainfallRainfall Minor Drainage System Minor Drainage System
Pipes, culverts, inlets, leadsPipes, culverts, inlets, leads Major Drainage System Major Drainage System
Streets, sheet flow, open channels, storageStreets, sheet flow, open channels, storage Tailwater Conditions — Brays BayouTailwater Conditions — Brays Bayou
Harris Gully WatershedHarris Gully Watershed
BraysBayou
Alumni Drive facing South - 8 amAlumni Drive facing South - 8 am
RMC Jones School
TMC
© Rik Hovinga
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
Major SystemMajor System
All water that cannot flow through the All water that cannot flow through the minor system must:minor system must: Be stored in small or large depressions, or Be stored in small or large depressions, or
man-made pondsman-made ponds Flow down streetsFlow down streets Flow overland as sheet flowFlow overland as sheet flow
Major system modeled as storage areas Major system modeled as storage areas interconnected by weirs.interconnected by weirs.
Digital Elevation ModelDigital Elevation ModelBased on 1999 Aerial Survey
DEM Used to Determine Overland Flow Connectivity and Storage
High Water Inundation in Rice/TMC Basin Area
Tailwater EffectsTailwater Effects High tailwater in Brays reduces the flow capacity High tailwater in Brays reduces the flow capacity
of the minor system up to 80%of the minor system up to 80%
When the minor system is full, the major system When the minor system is full, the major system (streets) starts to fill(streets) starts to fill
High tailwater will flood some areas near the High tailwater will flood some areas near the bayou directly, and cause others to flood due to bayou directly, and cause others to flood due to reduction of flow in the minor systemreduction of flow in the minor system
ElevationElevation and and DurationDuration of Elevationof Elevation are are extremely importantextremely important
Why a Computer Model?Why a Computer Model?
Analysis tool Analysis tool Why did it flood in the first place?Why did it flood in the first place?
Predictive tool Predictive tool How much rain will cause flooding in the How much rain will cause flooding in the
future?future?
Design tool Design tool What can we do to reduce flooding danger? What can we do to reduce flooding danger?
Rainfall and Stormwater ModelsRainfall and Stormwater Models
US Army Corps of Engineers’ HEC-HMSUS Army Corps of Engineers’ HEC-HMS Convert rainfall to flowsConvert rainfall to flows Approximates effects of inlets and leadsApproximates effects of inlets and leads
Storm Water Management Model (SWMM)Storm Water Management Model (SWMM) Dynamic hydraulic model of pipes and Dynamic hydraulic model of pipes and
overland flow and storageoverland flow and storage Includes tailwater conditions in bayouIncludes tailwater conditions in bayou
Modeling the Existing SystemModeling the Existing System Enter Major and Minor system structure Enter Major and Minor system structure
and connectivityand connectivity Input rainfall data from AllisonInput rainfall data from Allison Input tailwater data from AllisonInput tailwater data from Allison Run SWMM using Allison input dataRun SWMM using Allison input data Compare Allison results to observed high Compare Allison results to observed high
water marks near Rice and TMCwater marks near Rice and TMC Use calibrated model to analyze various Use calibrated model to analyze various
alternatives for the systemalternatives for the system
37.0’
20.8’
Note: All elevations are based on 1987 Datum
39.3’
TS Allison Peak 41.8’
Box Culvert
TS Allison CalibrationTS Allison CalibrationBackwater Computation HEC-RASBackwater Computation HEC-RAS
SWMM Model Results and Observed High Water MarksSWMM Model Results and Observed High Water Marks
Mitigation Options – Harris GullyMitigation Options – Harris Gully
Use model to evaluate other major culvertsUse model to evaluate other major culverts Kirby Dr, MacGregor Dr, Hermann DriveKirby Dr, MacGregor Dr, Hermann Drive
Evaluate natural overland drainage swale and Evaluate natural overland drainage swale and storage area in the Hermann Park area along storage area in the Hermann Park area along the Bayouthe Bayou
Evaluate all options for Harris Gully including Evaluate all options for Harris Gully including impact of the depressed SW freeway and impact of the depressed SW freeway and model their impacts on water levels in TMC model their impacts on water levels in TMC area.area.
Evaluate effect of Brays Federal Project, Evaluate effect of Brays Federal Project, which lowers Brays Bayou levels near TMCwhich lowers Brays Bayou levels near TMC
Possible Mitigation Possible Mitigation AlternativesAlternatives
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”
KirbyMacGregor
Hermann
CulvertTMC
Project BraysProject BraysFederal Flood Control Federal Flood Control
$ 455 Million$ 455 Million
Beltway 8
Bellaire
SH
6
UpstreamElement
UpstreamElement
ChannelEnlargements
ChannelEnlargements
I-45L
oo
p
610
288
BridgeReplacements
BridgeReplacements
US 59
DetentionAreas
DetentionAreas
ChannelEnlargements
ChannelEnlargements
Willow WaterholeBayou Detention
Willow WaterholeBayou Detention
Downstream Element
Downstream Element
Project BraysProject BraysChannel Enlargements: (Mid Reach)Channel Enlargements: (Mid Reach)
Final Thoughts…Final Thoughts…
The model indicates that under heavy rainfall, The model indicates that under heavy rainfall,
serious street flooding resultsserious street flooding results
Improve local drainage systemImprove local drainage system
Better manage overland flow thru TMCBetter manage overland flow thru TMC
Better use of advanced flood warning Better use of advanced flood warning
Brays Bayou ProjectBrays Bayou Project – reduces tailwater in the – reduces tailwater in the
range of 3 - 5 ft in 5 years.range of 3 - 5 ft in 5 years.
Flood Protection SystemsFlood Protection Systemsin the Futurein the Future
EmergencyEmergencyResponse - TMCResponse - TMC
Flood DoorsFlood Doors Flood GatesFlood Gates Facility EntrancesFacility Entrances CommunicationsCommunications OperationsOperations TrainingTraining