Modeling a Proposed Quarry Reservoir for Raw Water Storage in Atlanta, Georgia

Abstract

The City of Atlanta plans to convert a recently acquired urban quarry into Bellwood Quarry Reservoir (BQR), an off-stream supplemental water supply. CE-QUAL-W2, Version 3.5, was used to perform five-year water quality simulations of the reservoir. Nine inflow/outflow design and operation scenarios were evaluated for thermal stratification, dissolved oxygen (DO), algae, and iron (Fe) and manganese (Mn). For a perpetual storage scenario with no inflow and outflow and an operating scenario with monthly pump exercising flows, the model predicts ample reservoir DO to maintain an oxidizing environment in the hypolimnion and low dissolved Fe and Mn. A single portal near the bottom of the reservoir is recommended for alternating pump exercise inflows and outflows. Continuous flow-through operating scenarios do not improve predicted water quality. However, if selected, a mid-depth inflow and bottom outflow design configuration is recommended. A natural monomictic cycle is essential to maintain hypolimnetic DO. BQR’s relatively large mean depth (60 m) and low sediment surface area to volume ratio is consistent with other mesotrophic lakes of similar water quality.