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Stormwater Management Programs


Basinwide Study Program (by “Priority Areas”)

In 1996 the Stormwater Management Division divided Cobb County into quadrants and commenced a county-wide storm drainage structure inventory; floodplain mapping update;  and a basin-by-basin hydrologic and hydraulic modeling effort.  A major objective of this program was to update the Federal Emergency Management Agency’s (FEMA’s) flood insurance study stream models (hydraulics and hydrology), many of which were over 25 years old, to reflect current levels of urbanization in the County, and to project floodplains reflective of future basin build  out conditions in 2030.

The initial effort to inventory and study these four quadrants (Priority Areas) of Cobb County has been completed. Some beneficial spin-off programs resulting from this effort included the:

  • County-wide Survey Benchmark Database;
  • County-wide updated floodplain mapping;
  • Noonday Creek Floodplain Acquisition Program;
  • Nickajack Creek Floodplain Acquisition Program;  
  • Flood Storage Volume Purchase Program for existing privately-owned lakes and dams;
  • Enhanced Stream Buffer Program;
  • Regional Stormwater Management Facility at Chastain Meadows Parkway;
  • Regional Stormwater Management Facility at Mark Avenue;
  • Stormwater’s Asset Management Program

Storm Drainage Infrastructure Maintenance Program

In 1994, the Cobb County Board of Commissioners allocated $1.6 million to the Cobb County Stormwater Management Division to operate and maintain existing dedicated structural stormwater infrastructure. This budget has been increased each year to its current level of $5 million annually. The Stormwater Management Division has not been authorized or funded to maintain open channels, or other undedicated, unaccepted storm drainage structures on private property. Per Section 50-111 of the Official Code of Cobb County “The county shall not be responsible for aesthetic maintenance”.

Floodplain Mapping Update Program

One main objective of the Priority Area Basin Plans was to update the Federal Emergency Management Agency (FEMA) flood insurance study map to reflect existing levels of watershed urbanization; to estimate future (full basin build-out conditions) floodplain levels and limits; and to regulate new development away from these areas.

FEMA Community Rating System (CRS) Program

This is a Federal Emergency Management Agency (FEMA) program in which Cobb County is currently participating. In exchange for reductions in flood hazard potential and elimination of repetitive flood loss property, FEMA promises to lower flood insurance study premiums. Cobb County has currently been assigned a CRS “Level 8” which affords premium holders a 10% reduction in their flood insurance rates.

Flood Storage Volume Purchase Program (i.e. existing dam retrofit)

This program was one recommendation in the first Priority Area basin study completed in 1998.  New in-stream impoundments are difficult to permit through the Section 404 Wetlands Permitting Program. To address this situation, the concept to acquire, create, and/or purchase significant new storage volume areas in existing impoundments emerged to at least partially offset increased stormwater volumes resulting from urbanization. Additional stormwater flood storage volumes can most easily be created on the surface of existing impoundments, by simply lowering the normal pool level of the lake. Dropping the normal pool level in these existing impoundments creates more “freeboard” (which also promotes dam safety). Purchasing the created flood storage volumes pays for the public benefit while simultaneously providing the dam owners revenue to perform necessary maintenance or upgrades on their dam(s) and/or lake(s).

Floodplain Acquisition Program

The Cobb County Board of Commissioners (BOC) has authorized the purchase of floodplain along the following major creeks.

  • Noonday Creek
  • Nickajack Creek
  • Powder Springs Creek
  • Sweetwater Creek
  • Butler Creek
  • Rubes Creek

It is believed that these floodplain areas provide some of the best natural, self-sustaining flood mitigation and water quality improvements within the County. As people continue to move into Cobb County, the pressure to develop even what was previously considered to be “unsuitable land” increases. These floodplain areas provide an irreplaceable public benefit in terms of flood control, wildlife sanctuary, passive recreation, and natural assimilation of non-point source pollutants. The preservation of these major floodplain areas by fee- simple ownership, and the creation of riparian canopied “Town Forests” along these major streams, is a critical long-range goal of the Stormwater Management Program.

Total Maximum Daily Load (TMDL) Implementation Plan Program

Currently, Cobb County is following the directives of Georgia Environmental Protection Division (GAEPD) and of Atlanta Regional Commission (ARC) to comply with rules and regulations regarding Total Maximum Daily Load (TMDL) implementation. To date, all of Cobb County 303d-listed streams are on the list due to fecal coliform levels that are higher than the State standard (200 colonies per 100 milliliters). TMDL implementation plans to both the Chattahoochee and Etowah basins in Cobb County have been submitted to the District.  These plans are contained in this website and detail the preventative programs Cobb County has implemented to address non-point source pollutants identified on GAEPD 303(d) list of impaired waters.

National Pollutant Discharge Elimination System (NPDES) Program

Cobb County maintains a five year municipal separate storm sewer system (MS4) permit with United States Environmental Protection Agency (USEPA) which grants Cobb County the right to discharge stormwater from municipal stormwater management facilities into waters of the State.

Stormwater Pond Program

Cobb County inspects commercial and industrial ponds throughout the county to ensure compliance with Cobb County Code Section 50-112a, Maintenance of Stormwater Facilities-Commercial/Industrial. The Stormwater Environmental Compliance Section inspects, issues violations, and provides education on the design, function, and maintenance of ponds in the county.

Stream Monitoring Program

Non-point Source pollutants

The outfall monitoring program (performed twice a year) has been changed to a new watershed “in-stream monitoring” approach with more comprehensive chemical and biological screening through Cobb County’s Stream Monitoring Program. Tests are conducted under Cobb County’s chemical screening program for pH, temperature, conductivity, heavy metals (copper, cadmium, lead), phenols, surfactants, fecal coliform, biochemical oxygen demand (BOD), dissolved oxygen (DO), chemical oxygen demand (COD), nutrients, and turbidity.

Biological Monitoring

The biological monitoring aspect of the program provides a more comprehensive and accurate understanding of a stream’s health as it reflects acute changes and long term trends in the watershed. A more comprehensive assessment of stream health can be gained through periodic assessments (sample monitoring) of biological diversity in the stream. Cobb County staff members perform in-stream monitoring twice a year and annual biological assessments for all of our major streams.

West Nile Vector Control Program

The Cobb County Water System currently funds several part-time positions for the Health Department for the West Nile Vector Control Program. Cobb County Stormwater Management Division follows directives from the Health Department in the application of larvicide. Currently Stormwater Management treats areas within 900 feet of County-operated Senior Citizens Centers, in County Parks, and within 900 feet of infected birds.

Flood Hazard Mitigation (GEMA Grants) Floodplain Property Buyouts

Hazard Mitigation Grant Program (HMGP)

In 1999, Georgia Emergency Management Agency (GEMA) awarded Cobb County a 75/25 matching grant to purchase 16 homes in the Noonday Creek floodplain. The grant was later amended to include 16 additional homes located along Leasa Court. All of these homes have now been purchased and removed from the floodplain. This grant was later amended again in 2004 to include the purchase of 10 homes on Rio Montana. (42 homes total)

Flood Mitigation Assistance (FMA) Grants

In 2002, GEMA awarded Cobb County a 75/25 matching grant to purchase 3 homes in the Little Noonday Creek regulatory floodway located on Leasa Court. These homes have been purchased and removed from the floodplain. (3 homes total)

Disaster Relief Grants (DR1554) and (DR1560)

On July 11, 2005 Hurricane Dennis struck Cobb County and hit hardest in the southwestern corner of the County in and around Cities of Austell and Powder Springs. Over 70 homes sustained significant damage from the flooding resulting from 12-14 inches of rainfall over a 24 hour period. The flood stage of record (22 feet) was recorded at the United States Geological Survey (USGS) streamflow gage on Sweetwater Creek near Austell. Unfortunately a federal disaster was not declared for Hurricane Dennis. To assist Cobb County with local relief efforts, GEMA and Federal Emergency Management Agency (FEMA) made disaster relief funds available from previous Hurricane Disasters (Hurricane Francis – September 7, 2004 and Hurricane Ivan – September 16, 2004). In February 2006, Cobb County was awarded two Flood Hazard Mitigation Grants (FHMG) from GEMA and FEMA to purchase, demolish and remove 26 homes that sustained substantial damage from Hurricane Dennis. (26 homes total)

Hazard Mitigation Grant Program (HMGP 1686-0005)

On July 14, 2007, an intense thunderstorm moved across central portions of Cobb County and dropped over 4 inches of rainfall over a 2 hour period in Red Oak Park in the vicinity of Crockett Drive, Little John Trial, Sunny Lane and Princess Lane. Cobb County submitted an application to acquire 5 homes in this neighborhood as well as 2 homes along Rio Montana Drive. Subsequent to Cobb County’s application for federal assistance made in September 2007 GEMA and FEMA awarded a property acquisition grant to Cobb County to acquire demolish and remove 7 properties. Ultimately 3 property owners withdrew from the program and 4 were purchased, demolished, and removed . (7 homes total)

Hazard Mitigation Grant Program (HMGP 1858-0013)

Following catastrophic flooding on September 21, 2009, during which portions of Cobb County in and around the City of Austell received rainfall amounts in excess of 20 inches over a 24 hour period of time, on January 19, 2010 Cobb County submitted a property acquisition application for 34 substantially damaged homes within the 100-year floodplain. This grant was subsequently awarded to Cobb County in late September 2010.

Hazard Mitigation Grant Program (HMGP 1858-0014)

Following catastrophic flooding on September 21, 2009, during which portions of Cobb County in and around the City of Austell received rainfall amounts in excess of 20 inches over a 24 hour period of time, on January 19, 2010 Cobb County submitted a property acquisition application for 34 substantially damaged homes within the 100-year floodplain. This grant was subsequently awarded to Cobb County in late September 2010. The City of Powder Springs entered into and Intergovernmental Agreement with Cobb County to reimburse Cobb County for the portions of the expenditures not covered by the federal and state sponsors.