Pareto‐optimal solutions for environmental flow schemes incorporating the intra‐annual and interannual variability of the natural flow regime

Abstract

[1] The temporal variations of natural flows are essential elements for preserving the ecological health of a river which are addressed in this paper by the environmental flow schemes that incorporate the intra-annual and interannual variability of the natural flow regime. We present an optimization framework to find the Pareto-optimal solutions for various flow schemes. The proposed framework integrates (1) the range of variability approach for evaluating the hydrologic alterations; (2) the standardized precipitation index approach for establishing the variation criteria for the wet, normal, and dry years; (3) a weir operation model for simulating the system of flows; and (4) a multiobjective optimization genetic algorithm for search of the Pareto-optimal solutions. The proposed framework is applied to the Kaoping diversion weir in Taiwan. The results reveal that the time-varying schemes incorporating the intra-annual variability in the environmental flow prescriptions promote the ecosystem and human needs fitness. Incorporation of the interannual flow variability using different criteria established for three types of water year further promotes both fitnesses. The merit of incorporating the interannual variability may be superimposed on that of incorporating only the intra-annual flow variability. The Pareto-optimal solutions searched with a limited range of flows replicate satisfactorily those obtained with a full search range. The limited-range Pareto front may be used as a surrogate of the full-range one if feasible prescriptions are to be found among the regular flows.Citation: Shiau, J.-T., and F.-C. Wu (2007), Pareto-optimal solutions for environmental flow schemes incorporating the intra-annual and interannual variability of the natural flow regime, Water Resour. Res., 43, W06433,

A dual active‐restrictive approach to incorporating environmental flow targets into existing reservoir operation rules

“…There is now a consensus among scientists and river managers that to protect freshwater biodiversity and maintain the ecological services that rivers can provide, managed releases of water from reservoirs, termed environmental flows, are needed to mimic the components of natural flow variability, which include the magnitude, frequency, timing, duration, rate of change, and predictability of extreme events such as floods and droughts [Arthington et al, 2006]. This may explain why, over the past three decades, the scientific field of environmental flows prospered to generate >200 methods for specifying the minimum instream flows or quantifying flow regimes required to sustain the riverine ecosystems and their valued features [Tharme, 2003;Shiau and Wu, 2004a, 2004b, 2007a, 2007b, 2008, 2009. It has also become increasingly clear that failure to meet the environmental flow requirements would lead to adverse consequences for the river users, including the downstream ecosystems and the communities that rely upon them [Arthington and Pusey, 2003].…”

Analysis of Hydrologic Alteration Due to River Diversion

“…Once alteration indexes AI are computed for each N variables, overall hydrologic alteration can be estimated using the index proposed in Shiau & Wu (2007a). The Index…”

“…To this end, great effort has been focused on the use of optimization models (Shiau & Wu, 2004, 2007a, 2007bSuen & Eheart, 2006).…”

“…The RVA is a milestone in the hydrologic alteration assessment and has been widely utilised (e.g. : Galat & Lipkin, 2000;Irwin & Freeman, 2002;Shiau & Wu, 2004, 2007a, 2007b. Zolezzi et al (2009) combined the RVA with a wavelet transform analysis in order to separate the scales of variability and investigate their alterations independently.…”

Quantitative Assessment of Flow Regime Alteration Using a Revised Range of Variability Methods

“…Hence, several studies have attempted to revise the RVA method. For example, Shiau et al [29] combined the RVA with compromise programming to identify the optimal solution of the object function, aggregating multiple water allocation criteria in the Kaoping diversion weir. Yin et al [30] used the Euclidean distance method to account for the type of hydrological year, showing that changes in the order of hydrological year type are a major factor in river ecosystem alteration.…”