The Apalachicola-Chattahoochee-Flint River basin (ACF) is a large watershed in the southeastern United States. In 2012, the basin experienced the second year of a severe drought and the third multi-year drought in the last 15 years. During severe droughts, low reservoir and river levels can cause economic and ecological impacts to the reservoir, river, and estuarine ecosystems. During drought, augmenting Apalachicola River discharge through upstream reservoir releases and demand management are intuitive and often-suggested solutions to minimizing downstream effects. We assessed whether the existing reservoir system could be operated to minimize drought impacts on downstream water users and ecosystems through flow augmentation. Our analysis finds that in extreme drought such as observed during 2012, increases in water releases from reservoir storage are insufficient to even increase Apalachicola River discharge to levels observed in the 2007 drought. This suggests that there is simply not enough water available in managed storage to offset extreme drought events. Because drought frequency and intensity is predicted to increase under a variety of climate forecasts, our results demonstrate the need for a critical assessment of how water managers will meet increasing water demands in the ACF. Key uncertainties that should be addressed include (1) identifying the factors that led to extremely low Flint River discharge in 2012, and (2) determining how water "saved" via demand management is allocated to storage or passed to downstream ecosystem needs as part of the ongoing revisions to the ACF Water Control Manual by the US Army Corps of Engineers.
Stakeholders in river systems often target larger upstream water consumers as an intuitive solution for increasing flows for downstream ecological needs. Within regulated river systems, simplistic panaceas may have unexpected and unintended results at a watershed level. The
Apalachicola-Chattahoochee-Flint River Basin is a large watershed in the south-eastern UnitedStates whose management has been the source of conflict for several decades. This paper tests
This paper describes the development of a stakeholder-derived, water system model for the Apalachicola-Chattahoochee-Flint (ACF) basin (ACF-STELLA) and directly compares simulated daily outputs with a more complex model (HEC-ResSim) used by the U.S. Army Corps of Engineers to formally evaluate alternative basin management options. The two models were compared using 70 years of daily output (1939-2008; n = 25,668) for eight different ACF sites: five flow stations and three reservoir elevations. The comparison between models showed a strong match (p \ 0.01 rejection significance) between the daily outputs for six of the eight sites, with median Nash-Sutcliffe coefficient of efficiency ranging from 0.732 to 0.979. In the two sites where daily comparisons were less successful, additional analysis was conducted to explore where simulated results diverged. At the Lake Lanier outflow site, a 7-day moving average comparison provided a successful match with a Nash-Sutcliffe coefficient of efficiency of 0.788 (p \ 0.01 rejection significance). At the Walter F. George Lake elevation site, comparisons showed that a primary source of disagreement stemmed from a period where HEC-ResSim model outputs were significantly greater than historically observed reservoir elevations. Given the satisfactory model comparison as well as the significantly increased simulation speeds of ACF-STELLA, it was concluded that the ACF-STELLA model could be a useful tool in water policy planning activities to explore alternative basin management scenarios for expanded simulation by the more complex HEC-ResSim model. The use of multiple models in a river basin should not necessarily be interpreted as competitive, but instead can be seen as part of a collaborative effort to empower all stakeholders to systematically engage with their limited water resources.
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