Development and comparison of integrated river/reservoir models in the Apalachicola–Chattahoochee–Flint basin, USA

Abstract

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.

Simulating system‐wide effects of reducing irrigation withdrawals in a disputed river basin

“…As the flow dataset was developed using historically observed flows, it includes both surface and groundwater sources and accounts for climatic water inputs to the basin from precipitation. Additional details of routing, evaporation, and precipitation at reservoirs and consumptive demands are described in Leitman and Kiker ().…”

“…These reductions reflect findings that SBR may reduce the need for irrigation by 50% to 75% on peanut and cotton as well as other crops adaptable to the system during drought events (Dourte, Bartel, George, Marois, & Wright, ); low‐pressure drop nozzle retrofits can reduce irrigation water use on pivot or similar systems by up to 22.5%, VRI by an average of 15%, advanced irrigation scheduling by up to 15%, and conservation tillage by up to 15% (Perry & Yager, ). The set of scenarios to modify the agricultural effects on streamflow include (a) Increased Demands: a 25% increase to effects on streamflow due to expansion of irrigation practices and production areas, (b) Current Demands: 2012 agricultural effects on streamflow (Leitman & Kiker, ), (c) Moderate Decrease: a 25% decrease due to widespread adoption of SBR, VRI, and related water‐saving technologies (Dourte et al, ; Perry & Yager, ; Wright et al . , ), (d) Large Decrease: a 50% decrease due to an even larger scale adoption of the water saving conservation practices, and (e) Rain‐fed: a 100% decrease (or removal) of demands.…”

“…This paper tests the hypothesis that reductions in consumptive losses to stream flow through the introduction of efficient irrigation practices will have a positive effect on downstream flows and ecosystem services to the Apalachicola River. To evaluate the effects of reducing irrigation demands in the ACF basin, an existing water systems model (Leitman & Kiker, ) was used to simulate reach flows and reservoir dynamics under a variety of irrigation scenarios. This model was selected because it has been shown to be consistent with the USACE HEC‐ResSim model and because of model's flexibility and fast run‐time (Leitman & Kiker, ).…”

“…To evaluate the effects of reducing irrigation demands in the ACF basin, an existing water systems model (Leitman & Kiker, ) was used to simulate reach flows and reservoir dynamics under a variety of irrigation scenarios. This model was selected because it has been shown to be consistent with the USACE HEC‐ResSim model and because of model's flexibility and fast run‐time (Leitman & Kiker, ). The resulting downstream flows were analysed for flow changes and potential ecosystem service effects as well as the upstream effects on reservoir levels in the regulated portion of the ACF basin.…”

Editorial

“…Tzoumis et al (2015) explore the historical use of the presidential executive order as an environmental policy tool. Finally, Kiker and Leitman (2015) compare the results of two hydrological models in the context of basin management alternatives.…”