Optimizing stream infrastructure and ecosystem services through transformative partnerships: watershed coordination of dam and culvert management decisions

Dam removal is now common practice for restoring connectivity in rivers with well-documented benefits for migratory fish with freshwater and marine habitat requirements. That said, dams are not the only type of infrastructure barring movements in nontidal stream systems, and aquatic organisms other than sea-run fish can also benefit from improvements to connectivity within nontidal tributary networks. Barriers created from road culverts, dikes, and levees can constrain intended goals of stream ecosystem restoration efforts. We explore collaborative opportunities for combining dam removals and road culvert improvements to improve the costs and restoration benefits related to infrastructure projects affecting connectively in nontidal stream systems. Culverts are more pervasive than dams in developed landscapes and can have impacts on instream movements if they are not designed to have hydraulic conditions commensurate with the surrounding stream environment. Meanwhile, there are important roadway safety and cost considerations that factor into design improvements, including those responding to forecast climate changes and implications to freshwater flows. The dual benefits of improved ecological connectivity and infrastructure resilience can help fulfill the objectives of conservation organizations and transportation agencies, providing an opportunity to pool resources and achieve a greater overall impact across both objectives. Several case studies from New England are used to demonstrate these benefits. We find that, when compared to dam management decisions only, coordinating dam and culvert management decisions can lead to greater improvements in habitat connectivity for a wider diversity of diadromous fish species, with the added value of improved road safety. We also demonstrate how coordinating these decisions at greater spatial scales may enhance synergistic collaborations and dramatically improve the cost-effectiveness of restoration efforts now and under future climate predictions.