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