Quantifying Tradeoffs Associated with Hydrologic Environmental Flow Methods

Abstract

Freshwater management requires balancing and tradingoff multiple objectives, many of which may be competing. Ecological needs for freshwater are often described in terms of environmental flow recommendations (e.g., minimum flows), and there are many techniques for developing these recommendations, which range from hydrologic rules to multidisciplinary analyses supported by large teams of subject matter experts. Although hydrologic rules are well acknowledged as overly simplified, these techniques remain the state-of-the-practice in many locations. This article seeks to add complexity to the application of these techniques by studying the emergent properties of hydrologic environmental flow methodologies. Two hydrologic rules are applied: minimum flow criteria and sustainability boundaries. Objectives and metrics associated with withdrawal rate and similarity to natural flow regimes are used to tradeoff economic and environmental needs, respectively, over a range of flow thresholds and value judgments. A case study of hypothetical water withdrawals on the Middle Oconee River near Athens, Georgia is applied to demonstrate these techniques. For this case study, sustainability boundaries emerge as preferable relative to both environmental and economic outcomes. Methods applied here provide a mechanism for examining the role of stakeholder values and tradeoffs in application of hydrologic rules for environmental flows.

Habitat provision associated with environmental flows

“…This study contributes to a growing body of information about the effects of river flow regimes on the Middle Oconee River ecosystem (e.g., Nelson and Scott 1962, Grubaugh and Wallace 1995, Katz and Freeman 2015, McKay 2015, McKay et al 2016. A number of these studies have focused on the consequences of different environmental flow alternatives, and this body of evidence suggests that overall, percent-of-flow approaches appear to have fewer ecological impacts than minimum flow approaches.…”

“…A number of these studies have focused on the consequences of different environmental flow alternatives, and this body of evidence suggests that overall, percent-of-flow approaches appear to have fewer ecological impacts than minimum flow approaches. However, results shift slightly depending on the process investigated, and in some scenarios minimum flow approaches are functionally equivalent to percent-of-flow approaches (McKay 2015, McKay et al 2016. Although some outcomes are highly sensitive to changes in low flow conditions, many of the species in the river exhibit remarkable resilience to drought and low flows (Katz and Freeman 2015).…”

Proctor Creek Ecological Model (PCEM) : Phase 1 - site screening

“…However, the applicability to other streams in the region is high, and the basic structure could potentially be adapted for other watershed scale restoration projects. (Poff et al 1997, Baker et al 2004, McKay 2015. Table B1.…”

Monitoring and Management of Inland Waters: Insights from the Most Inhabited Italian Region

“…It is based on hydrological data series, without properly considering the requirements of the aquatic communities. E-flow recommendations based on simple hydrologic rules [80,81] have been widely recognized to be inadequate for sustaining the biological structures and the functionality of aquatic ecosystems [82]. Current state-of the-art approaches, e.g., [83][84][85][86], specifically advocate that e-flow recommendations should be based on the mechanistic relationships between flows and ecological outcomes.…”