Prioritizing Stream Barrier Removal to Maximize Connected Aquatic Habitat and Minimize Water Scarcity

Abstract

Research Impact Statement: Prioritizing stream barrier removal using dual-objective optimization quantifies tradeoffs between quality-weighted, connected fish habitat and water scarcity costs of reduced water deliveries.ABSTRACT: Instream barriers, such as dams, culverts, and diversions, alter hydrologic processes and aquatic habitat. Removing uneconomical and aging instream barriers is increasingly used for river restoration. Historically, selection of barrier removal projects used score-and-rank techniques, ignoring cumulative change and the spatial structure of stream networks. Likewise, most water supply models prioritize either human water uses or aquatic habitat, failing to incorporate both human and environmental water use benefits. Here, a dual-objective optimization model identifies barriers to remove that maximize connected aquatic habitat and minimize water scarcity. Aquatic habitat is measured using monthly average streamflow, temperature, channel gradient, and geomorphic condition as indicators of aquatic habitat suitability. Water scarcity costs are minimized using economic penalty functions while a budget constraint specifies the money available to remove barriers. We demonstrate the approach using a case study in Utah's Weber Basin to prioritize removal of instream barriers for Bonneville cutthroat trout, while maintaining human water uses. Removing 54 instream barriers reconnects about 160 km of quality-weighted habitat and costs approximately US$10 M. After this point, the cost-effectiveness of removing barriers to connect river habitat decreases. The modeling approach expands barrier removal optimization methods by explicitly including both economic and environmental water uses.(

A Meta-Analysis of Environmental Tradeoffs of Hydropower Dams in the Sekong, Sesan, and Srepok (3S) Rivers of the Lower Mekong Basin

“…Foregoing the proposed Sekong, Sambor, and Stung Treng dams would maintain one free-flowing tributary for much of its length, while providing hydropower from dam cascades in other tributaries. Giving up Sekong Dam supports research showing that building dams in the downstream reaches of tributaries should be avoided [47], and that managing rivers for either human or environmental benefits can provide greater economic and environmental benefits than managing for both human and environmental benefits simultaneously on multiple rivers [6,58]. A handful of papers made a compelling case for decision-making that better recognized environmental impacts in LMB because they creatively incorporated ecological objectives of rivers [3,11,22] or because they provided strategic sequencing of dam development [7].…”

Pareto Optimality and Compromise for Environmental Water Management

“…Where a fixed amount of water is to be allocated among water users, the Pareto frontier could shift outward with small environmental water transfers that provide overbank flows and connect rivers to floodplains (Figure S1 in Supporting Information S1) (Jeffres et al, 2008;Zeug & Winemiller, 2008) or through a change in management policies (Homa et al, 2005). Additional examples include managed aquifer recharge that increases summer baseflows for downstream fish or improves stream temperatures (water quality) for fish (Van Kirk et al, 2020), streamflow thresholds that connect stream reach habitats (Kraft et al, 2019), or reaches with favorable conditions for instream recreation (Génova et al, 2019). In some cases, the resulting Pareto frontier will be compound (Figure 2b), concave at the large scale, but with local convex regions.…”

“…Environmental and human water management often involves conflicts and tradeoffs (Jager et al., 2015; Lund & Palmer, 1997). Pareto optimality is a core concept for efficient multi‐objective management (Castelletti et al., 2013; Cohon, 1978/2004; Reed et al., 2013) and is often used to quantify and analyze tradeoffs among human and environmental objectives (Génova et al., 2019; Homa et al., 2005; Kraft et al., 2019; Null & Lund, 2012; Olivares et al., 2015; Shiau & Wu, 2007; Vogel et al., 2007). The mathematical characteristics of tradeoffs can help infer whether cooperation is likely, identify promising regions for compromise, establish the relative intractability of conflicts, and suggest strategies for reducing conflicts.…”

Featured Collection Introduction: The Emerging Science of Aquatic System Connectivity I

“…() explored the spatial relationship of wetlands and levee systems across a large river basin in the midwestern U.S.; and Kraft et al. () and Martin () examined barriers to biological connectivity along the river corridor in the western and eastern U.S., respectively. Further, at the downstream terminus, Marcarelli et al.…”

“…Kraft et al. () presented a barrier removal optimization model to prioritize restoration at a regional scale using stakeholder and expert opinion. Their approach is unique in that it considers both human and environmental water use benefits in prioritization.…”