impacts of rainfall events on water in the houston metro...

Impacts of Rainfall Events on Water Quality in the Houston Metro Area

Hanadi Rifai and Anuradha DesaiCivil and Environmental EngineeringUniversity of Houston, Houston, TX

AcknowledgmentsTCEQEPAHouston EndowmentMy graduate students

Rainfall and Water QualityTremendous growth in Houston Metro since 80sMetro area is mostly covered with impervious surfacesComplex water‐sanitary‐storm networkLeaks, bypasses, overflows not uncommonHouston receives > 48 in precipitation annuallyRain on average once a weekStorm water network includes pipes, ditches and bayous

Effects of Urbanization on Aquatic Resources

HydrologyGeomorphologyWater QualityHabitat

Development & ImperviousnessImperviousness =

Fundamental changes in characteristics of land coverChange in physical structure of streamsChange in diversity and abundance of aquatic lifeMore pollutants in streams

>10% channel erosion>25% habitat degradation& poor water quality

Brays Land Use/Land Cover

Hydrologic EffectsDisruption of natural water balanceIncreased flood peaksMore storm water runoffMore frequent floodingIncreased bank full flowsLower dry weather flows (not counting effluent)

Increased Runoff

1

10

100

1000

10000

0% 20% 40% 60% 80% 100%

Percentage not exceeding flow

Flow

(cfs

)

1983 to 1999 1983 to 1990 1991 to 1999

Cumulative Flow Frequency Curves Cumulative Flow Frequency Curves for Buffalo Bayou at West Beltfor Buffalo Bayou at West Belt

Cumulative Flow Frequency at USGS Station 8075000 Brays Bayou @ Houston

0.01

0.1

1

10

100

1000

10000

100000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%Percentage Not Exceeding Flow

Flow

(cfs

)

Entire recordUp to 19901991 and after

Brays at HoustonBrays at Houston

More flooding

Effects on Water Quality• Increased stream temperature• Increased pollutants• Increased risk of shellfish/beach

closure

Typical PollutantsSuspended solids/sedimentsNutrients (nitrogen & phosphorus)Metals (copper, zinc, lead, and cadmium)Oil & greases (PAHs)BacteriaPesticides and HerbicidesTemperaturePOPs (persistent, bioaccumulative, organic pollutants)Pharmaceuticals etc….

Buffalo Bayou at Westcott

White Oak Bayou at Heights

Bacteria and Bacteria Indicators

Ref: www.universityofcalifornia.edu/.../ecoli.htm

E.coli

Disease causing bacteria and virusesAssociated with fecal matter

ColiformColiform BacteriaBacteria

TotalTotal ColiformColiform(many environmental sources)(many environmental sources)

Fecal Fecal ColiformColiform(mostly fecal but some other sources)(mostly fecal but some other sources)

E. E. colicoli(good fecal indicator)(good fecal indicator)

Pathogenic Pathogenic E. E. colicoli

Leading cause of impairment in coastal shorelines (275 miles impaired) and the second leading cause of violations in rivers and streams (82,100 miles impaired) (US EPA 2007)

46% of 240 impaired water bodies in Texas do not meet contact recreation standards (TCEQ 2002)

Bayous in and around Houston, TX are on the 303(d) list for water quality exceedances of indicator bacteria

Bacterial Pollution

E. coliGeometric mean 126 MPN/dL

Single Sample Criteria 394 MPN/dL

Fecal Coliform

Geometric mean 200 MPN/dL

Single Sample Criteria 400 MPN/dL

Freshwater Standards in Texas (TCEQ)

End-of-Pipe Diffuse

Sources of Indicator Bacteria

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Sampled WWTP (< 1 MGD)Sampled WWTP (< 1 MGD)WWTP not Sampled (> 1 MGD)WWTP not Sampled (> 1 MGD)

n73; 8am and 10am Samplingn73; 8am and 10am Sampling

Comparison of Daily Flows (MGD) Comparison of Daily Flows (MGD) -- TVF Predictions to Observed FlowsTVF Predictions to Observed Flows

Results presented for TCEQ Permit # WQ0010495-099

Sanitary Sewer Overflows

Pathogens in Urban and Less Urban Watersheds

Urban watershedsHigher imperviousnessLow flow maintained by WWTPExtensive sewer infrastructureModified channelsPiped surface runoff

Less Urban watershedsNatural streamsMore pervious landDispersed mammalian and avian populationsNot effluent dominated

Urban watersheds exhibit frequent and severe exceedances at all flow levels. Less urban watersheds exhibit localized and limited WQ violations.

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Cypress Creek

Trinity Bay

Trinity River

Upper Oyster Creek

East Bay

Lake Houston

Greens Bayou

Clear Creek

Dickinson Bayou

Gulf of Mexico

Lower

Galvest

on Bay

Clear Lake

Whiteoak Bayou Above TidalBuffalo Bayou Above Tidal

Spring Creek

San Jacinto River

Cedar Bayou

Upper Galveston Bay

Oyster Creek

Scott Bay

Tabbs Bay

Armand Bayou

Houston Area Pathogen ImpairmentsHouston Area Pathogen Impairments

BuffaloWhiteOak

Brays

Sims

Greens

Halls

Houston Metro Watersheds

0

500

1000

1500

2000

2500

3000

37% 51% 59% 76% 79%% Low to High Intensity Developed Landuse

Hal

ls

Gre

ens

Bra

ys

Sim

s

Eas

tern

Hou

ston

EC

Geo

mea

n M

PN/d

LBacteria Indicator ConcentrationsAs a Function of Development

WQ std

E. Coli Concentration Range

Single sample standardGeomean standard

Brays Bayou

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

05101520253035

River km

E.c

oli (

MPN

/dL

1113

8

1585

4

1585

316

654

1116

911

140

1585

1

1585

0

1584

915

848

1585

5

1113

9

1665

2

1130

9

1585

2

1585

9

Geomean Standard: 126 MPN/dL

0 km is at boundary of Segment 1007B with Segment 1007

Legend

Maximum

Geometric mean

Minimum

E. E. Coli ExceedancesColi Exceedances in Braysin Brays

E. Coli Geomeans BB/WO

Time Series Time Series -- BBBB

Shepherd Dr., Buffalo Bayou

1/1/76 1/1/84 1/1/92 1/1/00

Feca

l Col

iform

(cfu

/100

mL

)

1e+0

1e+1

1e+2

1e+3

1e+4

1e+5

1e+6

Water Quality Standard(400 cfu/100 mL)

Whiteoak Bayou

Buffalo Bayou

Whiteoak Bayou

Buffalo Bayou

Station 16589

1

10

100

1000

10000

100000

08/12/00 01/29/03 07/17/05 01/03/08Date

E. c

oli M

PN/d

L

394 MPN/dL Std.

Station 11125

10

100

1000

10000

100000

1000000

08/12/00 01/29/03 07/17/05 01/03/08Date

E. c

oli M

PN/d

L

394 MPN/dL Std.

E.

coli

Time series –

Greens Bayou

Regression analysis of log transformed E. coli data vs. time showed significant trends (p < 0.05) at 18 % of total 85 stations analyzed

Influenced by seasons and rainfall:•

About 22% of Metro stations (n = 60) exhibited

statistical differences (p<0.05) between warmer and cooler months

•

About 60% of stations had a higher geomean during warmer seasons

•

About 50% of stations (n = 25) exhibited a significant negative correlation (p value < 0.05)

between number of days after rain and E. coli•

Rainfall raises E.

coli

concentrations beyond their

background levels

Indicator Bacteria Concentrations

Station 16663 - Eastern Houston

10

100

1000

10000

100000

1000000

5/15/06 5/18/06 6/20/06 7/17/06 7/20/06

Date

E. c

oli M

PN/d

L

0

1

10

100

Flow

cfs

E. coliFlow

Station 16665 - Halls Bayou

10

100

1000

10000

100000

1000000

5/15/06 5/19/06 6/20/06 7/17/06 7/20/06

Date

E. c

oli M

PN/d

L

0

0

1

10

100

Flow

(cfs

)

E.coliFlow

Correlation between E. coli

and Flow

R2 = 0.78 R2 = 0.74

y = 738.68e5.4664x

R2 = 0.84

100

1000

10000

100000

1000000

0.00 0.20 0.40 0.60 0.80 1.00

Previous 24 Hr Rainfall (inch)

E. c

oli M

PN/d

L

Correlation between E. coli

and Rainfall

Summer Flow @ HeightsSummer Flow @ Heights

1

10

100

1000

7/1/01 7/11/01 7/21/01 7/31/01 8/10/01 8/20/01 8/30/01

Flow

(acr

e-ft/

hour

)

0

2

4

6

Prec

ipita

tion

(in)

Observed Flow Modeled Flow Rain

Summer EC @ HeightsSummer EC @ Heights

1E+1

1E+2

1E+3

1E+4

1E+5

1E+6

1E+7

7/1/01 7/16/01 7/31/01 8/15/01 8/30/01

Observed EC

Sampling after June 2004 RainsSampling after June 2004 Rains

0

500

1000

1500

2000

2500

3000

3500

6/1/04 6/8/04 6/15/04 6/22/04 6/29/04 7/6/04 7/13/04 7/20/04

Rese

rvoi

r Sto

rage

(/10

, acr

e-ft)

Addicks StorageBarker Storage

Reservoirs Closed


1E+0

1E+1

1E+2

1E+3

1E+4

1E+5

1E+6

7/1/04 7/4/04 7/7/04 7/10/04 7/13/04 7/16/04 7/19/04 7/22/04

EC (M

PN/d

L)

0

1

2

3

4

5

6

7

Prec

ipita

tion

(in)

(a)

Addicks Discharge

Pools Present Pools Gone

1E+0

1E+1

1E+2

1E+3

1E+4

1E+5

1E+6

7/1/04 7/4/04 7/7/04 7/10/04 7/13/04 7/16/04 7/19/04 7/22/04

EC (M

PN/d

L)

0

1

2

3

4

5

6

7

Prec

ipita

tion

(in)

(c)

Barker Discharge

Pools Present Pools Gone

EC Standard (126 MPN/dL)

EC Standard


0

100

200

300

400

500

600

Pools No Pools

EC Geometric Mean(MPN/dL)TSS Average (mg/L)

Excludes wet weather sampling data; average includes TBD1, TBD2, TBD3, 11142, and 11362

EC Standard (126 MPN/dL)

The Future…Houston is expected to double its population by 2035Current development practices not sustainableDevelopment + global warming can be devastatingNeed to attenuate imperviousnessNeed to manage diffuse sources of pollution (BMPs)

impacts of rainfall events on water in the houston metro...

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