Reservoir Design in Georgia's Piedmont
Reservoirs for water supply in Georgia must be designed to allow a water supply manager to meet demands during a design drought without reducing streamflow when flows are less than the Non-Depletable Flow (NDF), normally the 7Q10 flow. The design drought is typically either a 50 or 100 year drought or a specific drought such as the 1954-55 or 1986-88 drought This requirement is based on the Georgia Water Quality Control Act (O.C.G.A. Par. 12-5-31, et seq.) and related Water Quality Control regulations 319-3- 6-.07. This paper compares reservoir storage to meet these requirements as calculated by two methods: a probability based design using monthly streamflow data, as compared to daily time series computations using streamflows from a specific drought period. The stream gage with a long history of observation used is the Oostanaula gage near Resaca, Georgia. This gage has a 100 year history, beginning in January of 1893. This particular comparison showed that the reservoir storage volume calculated by analysis of daily data from the 1954-57 drought was larger that the storage calculated using monthly streamflow data for a 100 year drought.