Dog River and Garrows Bend

Watershed Management Plan

Ambient Water Quality and

Pollutant Loading Estimates

Doug Robison, PWS

Management Measures Working Group

July 26, 2016

Stakeholder Water Quality Concerns

• Trash

• Sediment

• Sewer overflows

• Algae blooms

• Safe fishing & swimming

Water Quality Data Sources

• Alabama Department of Environmental Management

(routine ambient monitoring)

• Alabama Water Watch – Dog River Clearwater Revival

(volunteer monitoring)

• Mobile Area Water & Sewer System (special study)

• Geological Survey of Alabama (special study)

• Mobile Bay National Estuary Program (baseline survey)

• Dog River is a tidal river

estuary

• Sub-basins and major

tributaries

– Upper Dog River

• Eslava Creek

• Bolton Branch

– Halls Mill Creek

– Lower Dog River

• Rabbit Creek

• Garrows Bend sub-

basin flows directly to

Mobile Bay

Water Quality Parameters of Concern

• Dissolved oxygen

– Measure of organic enrichment

– Critical for healthy fish & shellfish

populations

• Chlorophyll-a

– Measure of algal production and

organic enrichment

– Driven by excessive nitrogen and/or

phosphorus

• Bacteria

– Measure of animal waste discharges

– Indicator of human pathogens

• Heavy metals

– More problematic in urban watersheds

– Toxic accumulation in sediments & food

chain

Upper Dog River

Halls Mill Creek

Lower Dog River

Garrows Bend

Water Quality Summary

Upper Dog

River

Halls Mill

Creek

Lower Dog

River

Garrow’s

Bend

Dis. Oxygen

Chlorophyll-a

Nutrients

Bacteria

Metals

Good Fair Poor No Data

Dog River Watershed - Impaired Water

Bodies

Tributary/Segment Impairments

Halls Mill Creek Siltation (303(d) list)

Bolton Branch Pathogens (approved TMDL)

Eslava Creek Pathogens (approved TMDL)

Rabbit Creek Organic Enrichment (approved TMDL)

Pathogens (approved TMDL)

Dog River Organic Enrichment (approved TMDL)

Pathogens (approved TMDL)

NPS Pollutant Loading Model

• GIS-based model

• Links key watershed parameters

– Topography

– Land use

– Soil types

• Applies actual rainfall data

• Calculates annual runoff pollutant loads

– Nutrients, sediment, and heavy metals

– Based on actual event mean concentration (EMC) data

measured in the southeastern U.S.

Watershed Topography

Watershed Land Use

Watershed Soils

Pollutant Loadings by Sub-Basin

• Greatest pollutant loads are from the Upper Dog River– Greatest hydrologic load

• Differential pollutant loads per unit area among sub-watersheds– Differences in land use and soils

Estimated Load (Pounds/Year)

WatershedArea

(Acres)

Runoff

Volume

(Ac-Ft)

TN TP BOD TSS Copper Lead Zinc

Garrow's

Bend4,221 8,372 31,511 4,609 106,845 571,822 171 51 779

Halls Mill

Creek20,863 28,486 76,622 11,352 242,496 1,272,934 406 114 1,729

Lower Dog

River16,996 35,842 58,759 8,771 188,409 1,007,041 310 91 1,366

Upper Dog

River21,798 39,480 138,492 20,394 472,764 2,517,176 751 224 3,399

Total 63,877 112,180 305,384 45,126 1,010,515 5,368,973 1,637 480 7,273

Highest Pollutant Loading Areas

Water Quality Recommendations

• Greatest needs are in the Upper Dog River

• Improve public education to reduce illicit

discharges and encourage urban BMPs

• Continue to identify and mitigate failing

wastewater infrastructure

– Severe Weather Attenuation Basins (SWABs)

• Identify potential stormwater treatment sites

– Floatable trash skimmers

– Attenuation/sedimentation basins

– Wetland treatment systems

Potential Treatment Areas

Offline Wetland Treatment System

Salt Barrier

Estuary

Low FlowDiversionStructure

Questions