Reason to Cheer: Detention Pond Offers Neighborhood Relief from Flooding
Inland Flooding 9/1/2009 DeKalb County
Atlanta, GA - The neighborhood of Drew Valley in DeKalb County is comprised of approximately 950 homes. The area initially was developed in the 1950s and has seen steady growth over time. As is often the case, the continued increase in development also brought an increase in floods and repeated damage to a number of homes in the neighborhood.
Drew Valley is crossed by two streams: Poplar Creek and a tributary of North Fork Peachtree Creek, both of which run through the neighborhood and pass near a number of residences. Over the years, during periods of especially high rainfall or tropical storm activity, these waterways have overflowed at least nine times, pushing water into many of the nearby homes. While most of these floods were relatively local in scale, they were still responsible for considerable costs in repairs and lost property.
“Most of the houses that flooded were not in the floodplain,” said Katie Oehler, chairwoman of the Drew Valley Civic Association’s Zoning and Land Use Committee. “There were a lot of damages from these smaller floods that weren’t covered because most of the people who lived in these areas didn’t have flood insurance.”
On June 16 and 17, 2003, Drew Valley experienced the worst flooding in the neighborhood’s history. In what has been referred to as a “25-year flood,” steady rain over the two-day period inundated more than 50 homes in the neighborhood. Oehler’s home was submerged in 5 1/2 feet of water.
Following the 2003 flood, the Drew Valley Civic Association decided it was time to do something about the ongoing problem. At the request of the association, DeKalb County hired a local engineering firm to perform a detailed study of the neighborhood. The study included a hydrologic and hydraulic analysis of the local waterways, an assessment of the culverts in the area, a review of prior flood levels, and an examination of threatened homes. The results of the study showed that improving six of the neighborhood culverts, acquiring and demolishing 23 properties in the most threatened areas of the neighborhood, and installing a detention pond would offer the best solutions.
The project began with the acquisition and removal of five homes from the area identified as the ideal location for the detention pond. Construction then began on the detention pond, its outlet culvert, and an additional culvert the engineers felt was responsible for repeated high-water problems. Unfortunately, before substantial progress could be made, Hurricane Ivan made landfall in September 2004, and created yet another flood situation for Drew Valley residents.
“The 2003 flood was the straw that ‘broke the camel’s back,’” said Oehler. “The 2004 flood was the log that fell on top of the camel.”
Construction of the detention pond was completed in April 2009. To fit in with the rest of the neighborhood’s aesthetics, the detention pond was designed to function as a semi-active wetland. When not serving its primary function of retaining floodwater, the detention pond serves as home to families of geese, ducks, and other wildlife. A variety of plant life, including azaleas, mountain laurels, and other aquatic vegetation, has been planted throughout the 1.6-acre area to beautify the normally austere appearance common to such structures. Additionally, a walkway has been constructed around the pond, giving the entire facility the feel of a nature preserve.
During a two-week period in September 2009, a low-pressure weather system hovered over northern and middle Georgia, dumping up to 20 inches of rain. In some areas, the flooding that resulted from these storms was off the charts, creating record water depths as great as 28 feet.
Amazingly, despite the fact that many communities throughout the affected areas were seeing the highest water levels on record, Drew Valley sustained mostly minor flooding to some residents’ yards. Only two of the remaining homes immediately downstream of the detention pond were reported as having been affected by the floodwater.
“Monday it was all coming down, and it seemed the whole world was flooding, a bunch of us former flood victims ended up over at the detention pond, watching it work,” said Oehler. “We just stood and cheered it.”
The Drew Valley detention pond was funded with a Federal Emergency Management Agency (FEMA) Pre-Disaster Mitigation (PDM) grant. The PDM grants provide federal funding up to 75 percent of the costs of a project that is designed to reduce or eliminate future disaster damages. Responsibility for the remaining 25 percent of a project’s costs comes from non-federal funding sources, such as local or state governments, or private homeowners. While the bulk of PDM funds do come from FEMA, the program is managed by the state. Local governments interested in applying for a PDM grant must submit an application to the state, which then chooses projects based on specific criteria, with an emphasis on the overall impact each project will have.
At the time of the September 2009 floods, the 23 acquisitions, the detention pond, and two of the six culvert improvements had been completed. Although four culverts had not yet been completed, the Drew Valley area experienced a significant reduction in flood levels.
“We consider the detention pond a miracle,” said Oehler. “It’s a miracle it was built during a two-year drought. And it’s a miracle it got completed right before we had the biggest flood this area has ever experienced. The fact that a bunch of neighbors were out here applauding a pond says it all. We stood on this wall cheering because we knew that if this pond hadn’t been here, all the water that was filling this thing would have been on top of us and in our homes, ruining our lives again.”