Response to September 21, 2009 Flood Event Gwinnett County Stormwater Management

Abstract

In the eight-day period beginning at 8 am on September 14, 2009 through 8 am September 21, 2009, the National Weather Service reports that approximately 19-inches of rainfall fell in portions of the Yellow River Watershed near Lawrenceville, GA with approximately 8- inches in a 24-hour period ending September 21. With saturated soil conditions in place and 24-hour rainfall totals exceeding a 1-percent annual chance (100-year) event, Gwinnett County, like much of the Metro Atlanta Area, received a record flood beginning the morning of September 21, 2009. At approximately 8 AM on September 21, 2009, the auxiliary spillway for Yellow River Watershed Dam No. 15 (Y15) was observed flowing. That was the beginning of a series of events that included the auxiliary spillways for Yellow River Watershed Dam Nos. 14 (Y14), 16 (Y16), and 17 (Y17) engaging in addition to widespread flooding and multiple culvert failures Countywide. A total of six (6) demand contractors and seven (7) demand consultants were utilized to address stormwater infrastructure repairs and evaluate the flood event. The total capital cost is $7.5 million with a total operating cost of $0.75 million. This paper will discuss Gwinnett’s response to the flood event of September 21, 2009.