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About Stormwater Management

Historical Perspective

2011 August 29– HMGP 1858-0013 amended to include t more homes in Unincorporated Cobb County within the effective 100-year (baseflood) floodplain which sustained “substantial damage” as the result of the September 21, 2009 flood.

2011 July 31– Construction of the Chastain Meadows Regional Stormwater Management Facility completed.

2011 May 1– Construction of Mark Avenue Regional Stormwater Management Facility begins.

2010 October 6– Property Acquisition Grant under Hazard Mitigation Grant Program (HMGP) 1858-0014 awarded to Cobb County and executed for the purchased demolition and removal of 16 residential homes in the City of Powder Springs within the effective 100-year (baseflood) floodplain which sustained “substantial damage” as the result of the September 21, 2009 flood.

2010 October 6– Property Acquisition Grant under Hazard Mitigation Grant Program (HMGP) 1858-0013 awarded to Cobb County and executed for the purchased demolition and removal of 34 residential homes in Unincorporated Cobb County within the effective 100-year (baseflood) floodplain which sustained “substantial damage” as the result of the September 21, 2009 flood.

2010 March 10- Construction on the Chastain Meadows Regional Stormwater Management Facility begins.

2009 November 13– Public Partnership Agreement with the Mobile District signed with the U.S. Army Corps of Engineers Mobile District

2009 September 21– Catastrophic flooding in Cobb County in which some 1600 homes were flooded countywide. Close to 100 homes in Unincorporated Cobb; over 84 homes in the City of Austell and over 16 homes in the City of Powder Springs sustained “substantial damage”.  Southwestern portions of the county in and around the City of Austell at the Paulding – Douglas – Cobb County line received rainfalls in excess of 20 inches within a 24 hour period.  USGS estimated this storm was well above the 500-year recurrence interval. NWS straight-line projections put this storm at the 10,000-year recurrence interval.

2008 September 26- Final Design Place, Specifications, and Geotechnical Report for the Chastain Meadows Regional Stormwater Management Facility resubmitted to Georgia Environmental Protection Division (GAEPD) for approval.

2007 November 28- Digital Flood Insurance Rate Maps (DFIRM) Drafts for Cobb County Update submitted to Federal Emergency Management Agency (FEMA).  DFIRM scheduled to become effective on December 21, 2008.

2007 September 26- Design Plans and Specifications of Chastain Meadows Regional Stormwater Management Facility resubmitted to Georgia Environmental Protection Division (GAEPD) for approval.

2007 August- Pilot study completed for Storm Drainage Structure Inventory, Northeast Cobb County.

2006 April 6- Georgia Emergency Management Agency (GEMA) flood mitigation assistance grant number FMA-PJ-04-GA-FY2006-007 awarded to Cobb County for the buyout of 1 home on Rio Montana Drive.

2006 November 6- Stream Buffer Variance received from Georgia Environmental Protection Division (GAEPD) for Chastain Meadows and Mark Avenue Regional Stormwater Management Facilities (Noonday Creek Watershed).

2006 October 27- Georgia Emergency Management Agency (GEMA) flood mitigation assistance grant number FMA-PJ-04-GA-FY2006-006 awarded to Cobb County for the buyout of 2 homes on Rio Montana Drive.

2006 April 6- District Authorization for Section 404 Individual Permits for Chastain Meadows and Mark Avenue Regional Stormwater Management Facilities (Noonday Creek Watershed).

2005 July 11- Hurricane Dennis hits Cobb County and drops 12–14 inches of rainfall in southwestern Cobb County. Approximately 400 properties were flooded and over 70 homes were damaged. Two Georgia Emergency Management Agency (GEMA) Flood Hazard Mitigation grants were obtained to buy-out 26 homes which sustained “substantial damage”.

2004 September 7- Hurricane Francis. Received Federal Disaster Declaration. Minimal flooding to Cobb County.

2004 September 16- Hurricane Ivan causes widespread flooding in central and northeast Cobb County. Flooding of numerous roads in Cobb County after dropping 4 -8 inches of rainfall in Cobb County over a 2 hour period.

2004 September 28- Hurricane Jean brushes by Cobb County causing minor flooding.

2004 Jordan Jones and Goulding Inc. submits updated Hydrologic and Hydraulic Modeling Results for “Priority Area 4” (PA4) which includes: Sope Creek, Sewell Mill Creek, Rubes Creek, and Trickum Creek watersheds.

2004 AMEC Inc. submits updated Hydrologic and Hydraulic Modeling Results for “Priority Area 3” (PA3) which includes: Nickajack Creek, Rottenwood Creek, and Olley Creek Watersheds.

2003 Receipt of two 75/25 matching Georgia Emergency Management Agency (GEMA) grants, Cobb County Water System is able to buy out (and move out) a record number (45) floodplain homes, including homes along areas of chronic flooding on Leasa Court and on Cynthia Court.

2003 AMEC Inc. retained to evaluate current level and extent of stormwater management services offered in Cobb County and whether a compelling case exists (created by state and/or federal government mandates; changing legal precedents or increasing citizen demands) to augment (or curtail) the current level of stormwater management services.

2001 Cobb County’s enhanced Stream Buffer Ordinance revised to require restrictive easements is recorded for all enhanced stream buffers within new developments.

2001 June 28- A series of three concentrated thunderstorms pass over northeast Cobb County in rapid succession dumping almost 4 inches of rainfall within a 2 hour period of time resulting in the flooding of 34 homes in the vicinity of Trickum and Steinhauer Roads.

2001 Kucera Inc. completes two-foot contour interval digital mapping for the entire county.

2000 October 10- The Disaster Mitigation Act of 2000 (DMA 2000) was put into motion. President signs the Act (Public Law 106-390). This legislation reinforces the importance of mitigation planning and emphasizes planning for disasters before they occur. As such, the Act establishes a pre-disaster hazard mitigation program and new requirements for the national post-disaster Hazard Mitigation Grant Program (HMGP).

2000 Cobb County Board of Commissioners approved limiting impervious surface coverage in Regional Activity Centers (80% for commercial, 70% for residential, 70% for Community Activity Centers, and 70% for Neighborhood Activity Centers) where the property contains one or more streams or floodplains. Streams and floodplains must be identified as open space.

1999 October 1- Enhanced stream buffer ordinance goes into effect. Minimum stream buffer width is now 50 feet. Buffer widths increase up to 200 feet, depending upon drainage intercepted and the stream involved.

1999 Cobb County Board of Commissioners enacts an Open Space Community (“OSC”) Zoning overlay district to encourage the set aside of Flood Hazard Areas as open space not to be developed. The OSC Overlay District ( Cobb County Code §134-198.1) is designed to protect land and water by limiting land disturbance, decreasing impervious surfaces and permanently protecting contiguous open space in perpetuity via mandatory covenants.

1999 Cobb County Board of Commissioners approves Countywide Watershed Assessment and Protection Plan Program.

1999 June 30- A concentrated thunderstorm stalls near the City of Powder Springs dumps some 5 inches of rainfall over a 2 hour period, resulting in the flooding of 144 homes.

1999 April- Mayes Sudderth and Etheredge Inc. and Parsons E/S Inc. submit Final Report for “Priority Area 2” (PA2) which includes: Allatoona Creek, Little Allatoona Creek, Butler Creek, Proctor Creek, and Tanyard Creek watersheds. Recommended Plan as proposed in this study cannot be implemented due to the presence of an endangered species, the Cherokee Snail Darter, on Proctor, Butler and Allatoona Creeks.

1998 Greenhorne and O’Mara Inc. submit the Recommended Plan for “Priority Area 1” (PA1) drainage basins to the Cobb County Board of Commissioners. PA1 includes Noonday Creek, Noses Creek, Mud Creek, John Ward Creek, and Powder Springs Creek watersheds.

1997 The Cobb County Development Standards completely revised for the first time since the early 1980’s. Significant upgrading of floodplain protection elements included dam design regulations.

1994 Stormwater Management Division implements Unit Price Contract Program. Program is initially funded with an annual budget of $1.6 million thereafter to increase 20% per year for five years.

1993 Stormwater Management Division Transferred from Community Development Agency to the Cobb County Water System.

1992 August 18- The Cobb County Flood Insurance Study is reissued. Restudies of the hydrology for: Noonday Creek, Little Noonday Creek, Morgan Lake Tributary, Noonday Creek Tributary 3, Noonday Creek Tributary 4, Rubes Creek, Trickum Creek, Olley Creek, and upper reach of Rottenwood Creek were performed. Previous floodplain analyses for the other streams studied in Cobb County were copied onto this flood insurance study update.

1989 July 6 & 7- Torrential thunderstorm stalls over northeast Cobb dumping 9 inches of rainfall in 13 hours over portions of Cobb County (Tate Creek, Noonday Creek, Trickum Creek, and Rubes Creek watersheds). Several roads flood. Wooten Lake Road washes out. Significant damage to Wooten Lake Dam occurs, but Cobb County’s Regional Flood Control facility located immediately downstream on Tate Creek, survives with minimal damage. Emergency spillways at the SCS watershed control structures at Frey Lake and at Burruss Lake both engage. Extrapolations on probability paper place this storm to be almost a 1500-year recurrence interval flooding event.

1989 Congress enacts George C. Bush’s “No Net Loss in Wetlands” policy.

1989 February- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1988 October 11- Cobb County’s Flood Damage Prevention Ordinance revised per Federal Emergency Management Agency (FEMA) guidelines.

1988 March- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1987 October- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1986 July 21- Final Report, “Cobb County Drainage Study”, submitted to David Hankerson by Connelly Sanders, Jr., P.E.

1986 April- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1982 Using Federal Emergency Management Agency (FEMA) funds, Cobb County Water System purchased and removed 14 homes along Sope Creek which had suffered repeated flooding.

1980 Cobb County’s population rises to 297,718 persons.

1979 December 11- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1978 October 1978- “Section A, Requirements for Plan Review for Cobb County” REVISED.

1978 Federal Emergency Management Agency (FEMA) issues the first Flood Insurance Study for Cobb County, which include Flood Insurance Rate Maps (FIRMs), and Floodway - Flood Hazard Boundary Maps. Prior to the issuance of these maps, property owners in Cobb County could utilize the United States Department of Agriculture's (USDA) SCS Soils Maps and the U.S. Housing and Urban Development’s Preliminary Flood Hazard Maps to get a rough idea about flood hazard potential for their respective properties.

1975 July 28- "Section A, Requirements for Plan Review for Cobb County” AMENDED.

1975 Georgia Sediment and Erosion Control Act enacted.

1974 March 6- “Section A, Requirements for Plan Review for Cobb County” AMENDED.

1974 November 12- “Section A, Requirements for Plan Review for Cobb County” ISSUED.

1972 Congress Enacts the United States Clean Water Act (USCWA).

1968 Congress authorizes the Federal Flood Control Act which ultimately leads to the creation of the National Flood Insurance Program (NFIP).

Goals and Objectives

  • To continuously update the limits, magnitude and frequency of the 100-year frequency flood hazard in the County; to determine the extent that flood hazards areas have been augmented by human activity (i.e. dams and urbanization); to exclude future development from these areas; and to publicly own, preserve and reclaim major floodplains as natural flood storage areas to the maximum extent practicable. 
  • To comply with federal and state mandates regarding clean water laws and regulations; to monitor a wide spectrum of non-point source pollutants within the major streams in Cobb County; to implement plans to improve the aquatic habitat and quality of streams; and to monitor the biological diversity of our stream as an indicator of the long-term water quality health of our major streams. 
  • To maintain stormwater infrastructure dedicated to and accepted by Cobb County for perpetual maintenance according to our current County Code.

Our Approach

We lead by example. Our progressive Stormwater Management program serves as a model in eliminating non-point source pollution. Our goals are to maintain stormwater infrastructure, control flooding and preserve water quality now and for future generations.

Non-point source pollution is a major contributor to pollution of surface water. Watershed protection is the best long-range solution to guarantee the quality of drinking water. 

Most people are unaware that rainwater running off lawns, streets and parking lots ultimately flows back into our lakes and rivers. Grease, oils, and gasoline that wash off paved surfaces; bird droppings washed off rooftops; and sedimentation from erosion contribute to pollution which is often referred to as “non-point source" pollution because it is not from a single point but from the entire watershed. Impervious (roofs and paved) surfaces not only increase the amount of rainfall that becomes runoff but also the amount of pollutants that enter our streams.

The challenge remains how to balance the inevitable results of development in our watershed while maintaining the highest water quality standards.

The Water System is working to ensure that watershed protection is as basic as our traditional infrastructure program. The Cobb County Board of Commissioners' visionary direction has brought about beneficial changes in stream buffer ordinances. Minimum fifty-foot wide buffers are now required for all streams, increasing to as much as 200 feet depending on the contributing drainage area. This increase in buffers around the streams and rivers throughout the County means that deep-rooted trees and shrubs can “naturally” hold a bank in place to reduce runoff volume and filter pollutants.

Basin studies conducted by the Water System have shown that regional detention planning greatly contributes to watershed protection. Large-scale detention ponds or “holding” ponds serve the watershed by collecting runoff. Flows are stored and “bled” out over time thereby reducing downstream flooding. The Stormwater Management Division has constructed three regional facilities within the county. The Echo Mill Regional Detention facility in West Cobb serves 1,000 acres of watershed development and the Chestnut Hill Regional Detention Facility serves 640 acres in North Cobb. The area surrounding County Services Parkway is also served by a regional detention facility.


The county has begun an aggressive program to acquire floodplain land along major waterways. An acquisition of 265 acres of floodplain land in north/central Cobb gives Noonday Creek a very large buffer of 300-400 feet through much of its length. This not only preserves water quality and wildlife habitat but provides our citizens recreational opportunities in an area protected from future commercial development.

Stormwater Education

The goal of the Stormwater Education Program is to inform citizens about the environmental impact of stormwater runoff and increase their knowledge about methods to reduce that impact. We educate our citizens about obtaining flood insurance, determining whether they are in a floodplain, and identifying and reporting surface water pollution. Through our participation in the Federal Emergency Management Agency Community Rating System these outreach efforts help ensure that our citizens retain the lowest flood insurance rates possible.

Stormwater Environmental Compliance

The Stormwater Environmental Compliance Section protects the health and beauty of Cobb County's creeks by monitoring impacts to the creeks due to excess stormwater runoff from urbanization, illicit discharges, lack of maintenance to stormwater structures, failed Best Management Practices (BMPs), and poor housekeeping on, around, or in stormwater facilities and the creeks they drain into.

Major Areas of Stormwater Environmental Compliance:

 •  Water Quality Compliance

  1. Water Quality Compliance Creek located off Heather Road in Smyrna. A sewer overflow was running straight into the creek that resulted in large fecal results, discoloration, and odor. Repair was done and creek now runs clear with normal fecal results.
  2. Previous location of Jordan Auto in Mableton. Carwash discharge into the storm system. Water from carwashes carries dirt, grease, oil, brake dust, and other materials that are picked up from environments where the vehicles are driven. The wash was running into the storm system and into nearest creek.

 •  Commercial Stormwater Pond Compliance

  1. Detention pond with unwanted vegetation. Volume capacity could be impacted as well due to trees that are growing in the pond. Too many trees and other unwanted vegetation do not allow for the wanted vegetation to grow correctly and can also cause erosion issues. Trees and other woody vegetation damage the structures in the pond if left unmaintained.
  2. With unwanted vegetation removed, water flow is allowed to move through the pond as originally designed. Vegetation that should be in the pond (grasses) will grow and provide filtration of sediments and pollutants before water leaves the pond. The wanted vegetation will also stabilize the embankments and help prevent erosion from occurring.

The Cobb County Stormwater Management (CCSWM) is a Division of the Cobb County Water System and is currently divided into four Sections: 


The Operations Section of the Stormwater Management Division is responsible for maintaining stormwater infrastructure in unincorporated Cobb County which has been formally dedicated to and accepted by Cobb County for perpetual maintenance. Most commonly, this formal dedication and acceptance process is handled through the recordation of a Final Plat. The maintenance of dedicated stormwater infrastructure is currently limited to the structural components of the stormwater conveyance system (i.e. pipes and ponds) and does not include maintenance activities related to open drainage systems, such as streams, creeks ditches and/or other open drainage easements [refer to Section 110-61 (f) in the Cobb County Code or online]. 

Currently, the Operations Section is staffed by thirteen people. 

Plan Review

Plan Review is one of the two regulatory sections of the Stormwater Management Division. This section is responsible for: 

  •  Reviewing the Stormwater Management aspects of new development and redevelopment proposals in the County. 
  •  Ensure compliance with the Cobb County Code, the Cobb County Development Standards and specific stipulations set by the Cobb County Board of Commissioners relative to property rezoning. 
  •  Review all Rezoning and Variance applications to ensure compliance with all Federal, State and local requirements pertaining to flood mitigation and water quality protection. 

Currently, the Plan Review Section is staffed by three people.

Water Quality (Stormwater Environmental Compliance)

Water Quality is another regulatory branch of the Stormwater Management Division. This Section is responsible for: 

  • Maintaining Cobb County’s compliance with: 
    • The federal and state mandated National Pollution Discharge Elimination System (NPDES) MS4 permit; with the Metropolitan North Georgia Water Planning District (i.e. “the District) requirements pursuant to O.C.G.A. § 12-5-582(a). 
    • The Federal Emergency Management Agency (FEMA) Community Rating System (CRS) for setting flood insurance premiums. 
  • Collect samples and perform dry weather screening inspections as required under the provisions of Cobb County’s NPDES permit. 
  • Perform property flood damage assessments. 
  • Educate and train the community on stormwater pollution prevention. 
  • Issue water quality violations. 
  • Work with the offending parties to have violations of the Clean Water Act corrected. 

Currently, the Water Quality Section is staffed by three people. 

Basin Planning

Basin Planning is the section of CCSWM responsible for performing storm drainage design; in concert with the Operations and Maintenance Section, compiling the comprehensive countywide storm drainage structure inventory database; updating and expanding countywide floodplain mapping; and preparing long-term comprehensive basin-wide stormwater management capital improvement master plans for Cobb County. 

This Section is responsible for: 

  • Updating the FEMA flood insurance study maps for Cobb County. 
  • Planning structural and non-structural Capital Improvements to Cobb County’s Stormwater Master Plan. 
  • Updating CCSWM’s hydrologic (HEC-1) and hydraulic (HEC-2 or HEC-RAS) basin simulation models. 
  • Creating and improving CCSWM’s planning maps, including
    • Stream buffer maps 
    • Monitoring station location maps 
    • Rain gage maps 
    • Floodplain purchase tracking maps 
  • Performing hydrologic and hydraulic basin studies to independently evaluate the effect of urbanization on downstream properties. 
  • Designing storm drainage pipe upgrades to Cobb County’s stormwater management infrastructure. 

Currently, the Basin Planning Section is staffed by one person.