Designing flows to resolve human and environmental water needs in a dam-regulated river

Abstract

Navigating trade-offs between meeting societal water needs and supporting functioning ecosystems is integral to river management policy. Emerging frameworks provide the opportunity to consider multiple river uses explicitly, but balancing multiple priorities remains challenging. Here we quantify relationships between hydrologic regimes and the abundance of multiple native and nonnative fish species over 18 years in a large, dryland river basin in southwestern United States. These models were incorporated into a multi-objective optimization framework to design dam operation releases that balance human water needs with the dual conservation targets of benefiting native fishes while disadvantaging nonnative fishes. Predicted designer flow prescriptions indicate significant opportunities to favor native over nonnative fishes while rarely, if ever, encroaching on human water needs. The predicted benefits surpass those generated by natural flow mimicry, and were retained across periods of heightened drought. We provide a quantitative illustration of theoretical predictions that designer flows can offer multiple ecological and societal benefits in human-altered rivers.

The Brisbane Declaration and Global Action Agenda on Environmental Flows (2018)

“…However, judicious use of water to better balance human and ecological needs can support biodiversity, resilient ecosystems, and socially-valued ecological services, including those provided by modified and novel aquatic ecosystems (Acreman et al, 2014b;Poff et al, 2016). There is ample evidence that concerted efforts to provide environmental flows can lead to societal and ecological outcomes that are socially acceptable and economically beneficial (e.g., King and Brown, 2010;Hermoso et al, 2012;Chen and Olden, 2017;Harwood et al, 2017). Implementation of environmental flows requires a complementary suite of policy, legislative, regulatory, financial, scientific, and cultural norms and values that ensure effective delivery and beneficial ecological and societal outcomes (Hart, 2016a,b;Harwood et al, 2017;Horne et al, 2017c).…”

“…The renewed Action Agenda promotes leadership to implement governance processes for adapting environmental flow management to climate change and human use scenarios, innovation around existing and novel technologies, and further application of trade-off processes to balance ecological resilience and societal benefits, including those provided by ecosystems with modified water regimes (e.g., Hermoso et al, 2012;Poff et al, 2016;Cartwright et al, 2017;Chen and Olden, 2017). Finally, long-term studies of aquatic ecosystem adjustments and societal responses are recommended in climatic and environmental change hotspots using novel experimental designs, meta-data analysis and measurement of ecological variables that capture rates of change in relation to shifting environmental flows, water quality and human water use Arthington et al, 2018;Webb et al, 2018).…”

Managed spring runoff to improve nursery floodplain habitat for endangered Rio Grande silvery minnow

“…Many rivers in western North America have been modified by flood control, water use, and ongoing climate change, causing riverside floodplains to become delinked from the main channel and negatively affecting riparian habitats and associated species (Petts, ). Managed releases from dams and reservoirs have been implemented to simulate a natural hydrograph and restore floodplain connection to benefit fish species (Chen & Olden, ), but reduced river volume and channel degradation have necessitated mechanically lowering floodplain inundation levels and coordinated water releases (Holden, ; Patno, LaGory, Chart, & Bestgen, ; Valdez & Nelson, ).…”

The impact of a hydroelectric dam on Neotropical fish communities: A spatio‐temporal analysis of the Trophic Upsurge Hypothesis

“…Anticipating the response of riverine fishes to a hydropower dam requires the analysis of site-specific data. Impact assessment, mitigation strategies and cost-benefit trade-offs must be inferred from hypothesised scenarios and data extrapolation (Chen & Olden, 2017;Poff et al, 2016;Sabo et al, 2017). Yet with more than half the world's large rivers already affected by dams (Nilsson, Reidy, Dynesius, & Revenga, 2005), a holistic framework for ecological assessment remains wanting (Barbour et al, 2016;Halls & Moyle, 2018;Jager & Smith, 2008;Poff & Zimmerman, 2010;Williams, 2018).…”

“…The case for evidence-based policy in dam management has been boosted by the concept of designer flows (DF): tailoring (dam release) floodplain inundation to meet specific ecological criteria (Chen & Olden, 2017;Horne et al, 2017;Poff & Olden, 2017). The overarching objective to "maximise fisheries production" has led to a focus on total fish biomass, with DF models indicating the potential to increase fish harvests by regulated flooding (Sabo et al, 2017).…”