Integrated modelling of cost‐effective siting and operation of flow‐control infrastructure for river ecosystem conservation

Abstract

[1] Wetland and floodplain ecosystems along many regulated rivers are highly stressed, primarily due to a lack of environmental flows of appropriate magnitude, frequency, duration, and timing to support ecological functions. In the absence of increased environmental flows, the ecological health of river ecosystems can be enhanced by the operation of existing and new flow-control infrastructure (weirs and regulators) to return more natural environmental flow regimes to specific areas. However, determining the optimal investment and operation strategies over time is a complex task due to several factors including the multiple environmental values attached to wetlands, spatial and temporal heterogeneity and dependencies, nonlinearity, and time-dependent decisions. This makes for a very large number of decision variables over a long planning horizon. The focus of this paper is the development of a nonlinear integer programming model that accommodates these complexities. The mathematical objective aims to return the natural flow regime of key components of river ecosystems in terms of flood timing, flood duration, and interflood period. We applied a 2-stage recursive heuristic using tabu search to solve the model and tested it on the entire South Australian River Murray floodplain. We conclude that modern meta-heuristics can be used to solve the very complex nonlinear problems with spatial and temporal dependencies typical of environmental flow allocation in regulated river ecosystems. The model has been used to inform the investment in, and operation of, flow-control infrastructure in the South Australian River Murray.

Ecohydrological and socioeconomic integration for the operational management of environmental flows

“…We used mixed methods to develop, apply, and link a variety of models and data to create the suite of information to support integrated modeling for environmental flow management. While we present an illustrative application here, the full optimization model and its innovative solution strategies have been published in detail elsewhere (Higgins et al 2011).…”

“…The model includes water balance and flow equations, and a key variable in the model is the volume of water in each ecohydrological unit polygon in each month. Inundation depends on the flow at the SA border, weir heights, the commence-to-fill flow rate of ecohydrological units, whether regulators are built and how they are operated, and water losses through evaporation and infiltration (Higgins et al 2011).…”

“…For such a large combined investment and operational decision problem, finding a guaranteed optimal solution is currently impossible. We solved the problem using the Tabu search heuristic strategy, which has been found to produce good solutions within a reasonable time (Higgins et al 2011).…”

“…Without a spatial approach, linking hydrological flow rates with environmental flow metrics for specific areas of river ecosystem types is not possible and the ability of the model to capture key ecohydrological processes is limited. Some recent studies have incorporated high-resolution spatial hydrological data in integrated models (e.g., Schluter et al 2006, Higgins et al 2011. Ecological responses to natural flow regimes have often been specified based on single species/ ecosystems (e.g., Overton et al 2006, Schluter et al 2006 or ecosystem-wide generalizations (Yin and Yang 2011).…”

“…7 E-mail: brett.bryan@csiro.au Bednarek and Hart 2005, Rood et al 2005, Richter and Thomas 2007, Higgins et al 2011, Watts et al 2011. Compatible, high-quality (i.e., accurate, precise), and high-resolution (i.e., landscape spatial scale and daily/ monthly temporal scales) ecohydrological and socioeconomic information is required to support operational environmental flow management decisions that efficiently achieve both ecological and socioeconomic objectives (Hillman and Brierley 2002, Cai 2008, de Lange et al 2010.…”