FISHY BUSINESS: A MULTI-OBJECTIVE APPROACH TO CULVERT AND DAM DECISIONS FOR IMPROVED INFRASTRUCTURE, ECOSYSTEMS, AND COST

People rely on tens of thousands of culverts to connect their communities through public and private roads. Many of these culverts are at risk of failure, due to their degrading condition as they age or because they are undersized for increasingly larger floods and bank erosion caused by climate change and urban development. Dams are another form of infrastructure often targeted for removal to restore river ecosystems. Many of these dams have long outlived their original purpose and now pose downstream safety risks. Underperforming culverts and dams also prevent many sea-run fish from reaching their natal habitat, cascading negative impacts into freshwater and marine ecosystems in ways that also diminish cultural, sustenance, and economic values held by local communities.

Underperforming culverts must be replaced under current federal standards that emphasize infrastructural and ecological longevity, but replacement is costly. Governmental agencies responsible for maintaining the safety and reliability of highways use limited budgets to prioritize replacement of critically degraded culverts on heavily used roads. In parallel many non-governmental organizations replace culverts on municipal and private roads, with the objective of prioritizing freshwater connectivity to restore freshwater ecosystems. Dam removal decisions are also challenging and multivariate because the benefits of hazard reduction and ecological restoration are potentially offset by the loss of hydroelectricity production, water supply, and other important services. A surprising range of stakeholders are impacted by these decisions, making it difficult to identify a single acceptable decision.

We use a multi-objective approach to combine the diverse priorities of stakeholders and examine a wide array of trade-offs and synergies involved with coordinated culvert replacement and dam removal at multiple spatial scales in Maine rivers. We find that increasing the scale of decision-making improves the efficiency of trade-offs among infrastructure improvements, ecosystem restoration, and economic costs, but this may lead to heterogeneous and less equitable local-scale outcomes. Our model may help facilitate multilateral funding, policy, and stakeholder agreements by analyzing the trade-offs of coordinated river infrastructure decisions, including net benefit alternatives to dam removal, at scales that satisfy these agreements. These benefits reveal significant potential synergies between disparate stakeholder preferences.