Impacts of Rainfall Events on Water Quality in the Houston Metro Area Hanadi Rifai and Anuradha Desai Civil and Environmental Engineering University of Houston, Houston, TX
Acknowledgments TCEQ EPA Houston Endowment My graduate students
Rainfall and Water Quality Tremendous growth in Houston Metro since 80s Metro area is mostly covered with impervious surfaces Complex water sanitary storm network Leaks, bypasses, overflows not uncommon Houston receives > 48 in precipitation annually Rain on average once a week Storm water network includes pipes, ditches and bayous
Effects of Urbanization on Aquatic Resources Hydrology Geomorphology Water Quality Habitat
Development & Imperviousness Imperviousness = Fundamental changes in characteristics of land cover Change in physical structure of streams Change in diversity and abundance of aquatic life More pollutants in streams >10% channel erosion >25% habitat degradation & poor water quality
Brays Land Use/Land Cover
Hydrologic Effects Disruption of natural water balance Increased flood peaks More storm water runoff More frequent flooding Increased bank full flows Lower dry weather flows (not counting effluent)
Increased Runoff
Cumulative Flow Frequency Curves for Buffalo Bayou at West Belt 10000 1000 Flow (cfs) 100 10 1 0% 20% 40% 60% 80% 100% Percentage not exceeding flow 1983 to 1999 1983 to 1990 1991 to 1999
Brays at Houston Flow (cfs) 100000 10000 1000 100 10 1 0.1 0.01 Cumulative Flow Frequency at USGS Station 8075000 Brays Bayou @ Houston Entire record Up to 1990 1991 and after 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage Not Exceeding Flow
More flooding
Effects on Water Quality Increased stream temperature Increased pollutants Increased risk of shellfish/beach closure
Typical Pollutants Suspended solids/sediments Nutrients (nitrogen & phosphorus) Metals (copper, zinc, lead, and cadmium) Oil & greases (PAHs) Bacteria Pesticides and Herbicides Temperature POPs (persistent, bioaccumulative, organic pollutants) Pharmaceuticals etc.
Buffalo Bayou at Westcott
White Oak Bayou at Heights
Bacteria and Bacteria Indicators Disease causing bacteria and viruses Associated with fecal matter E.coli Ref: www.universityofcalifornia.edu/.../ecoli.htm
Coliform Bacteria Total Coliform (many environmental sources) Fecal Coliform (mostly fecal but some other sources) E. coli (good fecal indicator) Pathogenic E. coli
Bacterial Pollution 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
Freshwater Standards in Texas (TCEQ) E. coli Fecal Coliform Geometric mean Single Sample Criteria Geometric mean Single Sample Criteria 126 MPN/dL 394 MPN/dL 200 MPN/dL 400 MPN/dL
Sources of Indicator Bacteria End-of-Pipe Diffuse
WWTP in BB/WO Sampled WWTP (< 1 MGD) WWTP not Sampled (> 1 MGD) n73; 8am and 10am Sampling
Comparison of Daily Flows (MGD) - TVF Predictions to Observed Flows Results presented for TCEQ Permit # WQ0010495-099
Sanitary Sewer Overflows
Pathogens in Urban and Less Urban Watersheds Urban watersheds Higher imperviousness Low flow maintained by WWTP Extensive sewer infrastructure Modified channels Piped surface runoff Less Urban watersheds Natural streams More pervious land Dispersed mammalian and avian populations Not effluent dominated Urban watersheds exhibit frequent and severe exceedances at all flow levels. Less urban watersheds exhibit localized and limited WQ violations.
Houston Area Pathogen Impairments #S (X Upper Oyster Creek #S (X (X #S (X (X #S (X #S (X (X #S (X #S (X #S (X #S (X (X #S #S#S #S #S #S (X (X(X (X (X #S #S (X(X (X Scott Bay (X Tabbs Bay Trinity Bay #S (X #S (X Upper Galveston Bay #S (X Cypress Creek Whiteoak Bayou Above Tidal Buffalo Bayou Above Tidal Oyster Creek Spring Creek Greens Bayou Clear Creek Lake Houston San Jacinto River Armand Bayou Clear Lake Dickinson Bayou Cedar Bayou Trinity River East Bay Lower Galveston Bay Gulf of Mexico
Houston Metro Watersheds Greens Buffalo White Oak Halls Brays Sims
Bacteria Indicator Concentrations As a Function of Development EC Geomean MPN/dL 3000 2500 2000 1500 1000 500 0 Greens WQ std Sims 37% 51% 59% 76% 79% % Low to High Intensity Developed Landuse Halls Eastern Houston Brays
E. Coli Concentration Range Single sample standard Geomean standard
E. Coli Exceedances in Brays 1E+06 1E+05 15848 15849 15850 15851 15852 Brays Bayou 11169 11140 15853 16654 15854 16652 15855 11139 15859 11309 11138 E.coli (MPN/dL 1E+04 1E+03 1E+02 Geomean Standard: 126 MPN/dL 1E+01 1E+00 0 km is at boundary of Segment 1007B with Segment 1007 Legend Maximum 35 30 25 20 River km 15 10 5 0 Geometric mean Minimum
E. Coli Geomeans BB/WO
Time Series - BB Shepherd Dr., Buffalo Bayou Fecal Coliform (cfu/100 ml) 1e+6 1e+5 1e+4 1e+3 1e+2 1e+1 1e+0 1/1/76 1/1/84 1/1/92 1/1/00 Water Quality Standard (400 cfu/100 ml) Whiteoak Bayou Buffalo Bayou
E. coli Time series Greens Bayou 100000 Station 16589 394 MPN/dL Std. 1000000 Station 11125 394 MPN/dL Std. 10000 100000 E. coli MPN/dL 1000 100 E. coli MPN/dL 10000 1000 10 100 1 08/12/00 01/29/03 07/17/05 01/03/08 Date 10 08/12/00 01/29/03 07/17/05 01/03/08 Date Regression analysis of log transformed E. coli data vs. time showed significant trends (p < 0.05) at 18 % of total 85 stations analyzed
Indicator Bacteria Concentrations 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
Correlation between E. coli and Flow E. coli MPN/dL 1000000 100000 10000 1000 100 Station 16663 - Eastern Houston E. coli Flow 100 10 1 Flow cfs 1000000 R 2 = 0.78 R 2 = 0.74 E. coli MPN/dL 100000 10000 1000 100 Station 16665 - Halls Bayou E.coli Flow 100 10 1 0 Flow (cfs) 10 5/15/06 5/18/06 6/20/06 7/17/06 7/20/06 0 10 5/15/06 5/19/06 6/20/06 7/17/06 7/20/06 0 Date Date
Correlation between E. coli and Rainfall 1000000 y = 738.68e 5.4664x 100000 R 2 = 0.84 E. coli MPN/dL 10000 1000 100 0.00 0.20 0.40 0.60 0.80 1.00 Previous 24 Hr Rainfall (inch)
Summer Flow @ Heights 1000 Observed Flow Modeled Flow Rain 0 Flow (acre-ft/hour) 100 10 2 4 Precipitation (in) 1 7/1/01 7/11/01 7/21/01 7/31/01 8/10/01 8/20/01 8/30/01 6
Summer EC @ Heights 1E+7 Observed EC 1E+6 1E+5 1E+4 1E+3 1E+2 1E+1 7/1/01 7/16/01 7/31/01 8/15/01 8/30/01
Sampling after June 2004 Rains 3500 3000 Reservoir Storage (/10, acre-ft) 2500 2000 1500 1000 500 0 6/1/04 6/8/04 6/15/04 6/22/04 6/29/04 7/6/04 7/13/04 7/20/04 Reservoirs Closed Addicks Storage Barker Storage
Sampling after June 2004 Rains EC (MPN/dL) 1E+6 1E+5 1E+4 1E+3 1E+2 1E+1 1E+0 Pools Present 7/1/04 7/4/04 7/7/04 7/10/04 7/13/04 7/16/04 7/19/04 7/22/04 Addicks Discharge EC (MPN/dL) 1E+6 1E+5 1E+4 1E+3 1E+2 1E+1 1E+0 Pools Gone 7/1/04 7/4/04 7/7/04 7/10/04 7/13/04 7/16/04 7/19/04 7/22/04 Barker Discharge EC Standard (126 MPN/dL) Pools Present EC Standard Pools Gone (a) (c) 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Precipitation (in) Precipitation (in)
Sampling after June 2004 Rains 600 500 400 300 200 100 EC Geometric Mean (MPN/dL) TSS Average (mg/l) EC Standard (126 MPN/dL) 0 Pools No Pools Excludes wet weather sampling data; average includes TBD1, TBD2, TBD3, 11142, and 11362
The Future Houston is expected to double its population by 2035 Current development practices not sustainable Development + global warming can be devastating Need to attenuate imperviousness Need to manage diffuse sources of pollution (BMPs)