Urban Hydrology

Construction ImpactsConstruction Impacts

• Disturbed areas allow erosion to occur• High concentrations of sediment can

impact creeks and ponds• Construction General Permit• Storm Water Pollution Prevention Plan

(SWPPP) must be prepared for project• Plan specifies measures to reduce

discharge of sediment

• Disturbed areas allow erosion to occur• High concentrations of sediment can

impact creeks and ponds• Construction General Permit• Storm Water Pollution Prevention Plan

(SWPPP) must be prepared for project• Plan specifies measures to reduce

discharge of sediment

Silt FenceSilt Fence

HydromulchHydromulch

Control FailureControl Failure

Degradation of Hill Country StreamsDegradation of Hill Country Streams

Green Hole on Lick Creek, west Travis County, Summer 2003

Green Hole on July 27, 2004, after rainfall caused overflow from the West Cypress Hills subdivision detention pond for development construction

Degradation of Hill Country Streams (cont.)Degradation of Hill Country Streams (cont.)

Dead Mans Hole on Dead Mans Creek, east Hays County, before construction of a small dam in the watershed

Dead Mans Hole after construction of the dam

Degradation of Hill Country Streams (cont.)Degradation of Hill Country Streams (cont.)

Hamilton Pool prior to June 2007

Road cut for land development in Hamilton Creek basin began June, 2007

Degradation of Hill Country Streams (cont.)Degradation of Hill Country Streams (cont.)Road cut along Hamilton Creek

Hamilton Pool--first rain after road cut construction began

Bee CreekBee Creek

Bee Creek near Hwy 71, West Travis County, prior to development in basin

Bee Creek, August 2007, immediately after development began in basin

Austin Rainfall/Runoff Austin Rainfall/Runoff

Bear Creek

ShoalCreek

Fort Branch

Boggy Creek

Channel DegradationChannel Degradation

E. Bouldin Creek

Walnut Creek

Tannehill Branch

Shoal Creek

Little Walnut Creek

More of the SameMore of the Same

Shoal CreekShoal Creek

0 10 20 30 40 500

5

10

15

20

25

30

35

Connected imperviousness (%)

Num

ber

of s

peci

es

Y = 10 log10(x)*(-0.585)+1.775 - 1

Types of PollutionTypes of Pollution

• Point Sources– Conventionally industrial or wastewater

treatment

– Any discharge from a pipe or ditch

• Non-Point Source– Agriculture

• Point Sources– Conventionally industrial or wastewater

treatment

– Any discharge from a pipe or ditch

• Non-Point Source– Agriculture

Constituents in Urban RunoffConstituents in Urban Runoff

• Bacteria

• Nutrients

• Insecticides

• Herbicides

• Metals – zinc, copper, lead

• Hydrocarbons – PAHs

• Sediment

• Bacteria

• Nutrients

• Insecticides

• Herbicides

• Metals – zinc, copper, lead

• Hydrocarbons – PAHs

• Sediment

Sources of PollutantsSources of Pollutants

• Vehicles – Tires, Brake pads, Fluids, Tracking• Atmospheric Deposition• Fertilizers• Pesticides• Pets• Pavement abrasion• Channel Erosion

• Vehicles – Tires, Brake pads, Fluids, Tracking• Atmospheric Deposition• Fertilizers• Pesticides• Pets• Pavement abrasion• Channel Erosion

Buildup of PollutantsBuildup of Pollutants

First Flush of PollutantsFirst Flush of Pollutants

Stenstrom & Kayhanian, 2005

Zinc vs. Impervious CoverZinc vs. Impervious Cover

Copper vs. Impervious CoverCopper vs. Impervious Cover

TSS vs. Impervious CoverTSS vs. Impervious Cover

Runoff ConcentrationsRunoff Concentrations

Constituent Avg. C Standard Exceedance

Gross Solids ??? 0 100%

Lead 49 g/L 0.66 97%

Copper 39 g/L 3.2 97%

Zinc 207 g/L 41 52%

Fecal C. 1415 400 42%

Runoff ConcentrationsRunoff Concentrations

Constituent Avg. C

Sediment 100 mg/L

Nitrate 0.93 mg/L

TKN 2.1 mg/L

Total P 0.11 mg/L

Diss. P 1415

Sealants reapplied Sealants reapplied every few years. every few years. About 600,000 About 600,000 gallons of sealant gallons of sealant are applied are applied annually in Austin. annually in Austin.

coal-tar-coal-tar-emulsion-emulsion-sealedsealed

asphalt-asphalt-emulsion-emulsion-sealedsealed

unsealed unsealed asphalt or asphalt or concreteconcrete

Other Sources of PollutantsOther Sources of Pollutants

Sewer Lines in Creeks – Tannehill Branch

Sewer Lines in Creeks – Tannehill Branch

Algae bloomsAlgae bloomsMarch 2, 2002March 2, 2002

Barton Creek Wastewater Leak

Barton Creek Wastewater Leak

Regulatory StrategiesRegulatory Strategies

• Do nothing

• Do something (structural)

• Meet a performance standard

• Meet water quality standards

• Do nothing

• Do something (structural)

• Meet a performance standard

• Meet water quality standards

Local RequirementsLocal Requirements

• Austin – Achieve pollutant reduction comparable to a sand filter system, or “no discharge” of stormwater.

• LCRA – Reduce TSS, TP, and O&G by 75%

• TCEQ – Reduce the increase in TSS discharged by 80%.

• Houston – Do something

• Austin – Achieve pollutant reduction comparable to a sand filter system, or “no discharge” of stormwater.

• LCRA – Reduce TSS, TP, and O&G by 75%

• TCEQ – Reduce the increase in TSS discharged by 80%.

• Houston – Do something

Filter System – Lamar & Loop 360Filter System – Lamar & Loop 360

Uniform Distributed Small-scale Controls

Maintaining Natural Hydrology Functions Maintaining Natural Hydrology Functions