The built environment can significantly impact ecosystem services, especially where built infrastructure (e.g., road and rail systems) is designed without full consideration of stream ecology and the migratory nature of anadromous species. In the Pacific Northwest, salmon are not only keystone species, but are also culturally and economically critical, supporting large tribal, commercial, and recreational fishing industries. Modifying stream crossing infrastructure to restore salmon access to inland habitat is a major (albeit expensive) priority throughout the region. Progress towards this goal will require more diverse funding options and broader stakeholder support. We must expand our understanding of the value of replacing poorly designed and degraded stream crossings to include not only ecological costs, but also conventional risks (e.g., localized flooding, transportation disruptions) arising from disruptions to hydrological processes. Our team has developed innovative, scalable geospatial techniques for identifying conventional risks associated with blocked and degraded stream crossings. Including these values will strengthen the benefit-cost rationale for pursuing habitat access restoration, expanding such efforts. We are also developing more nuanced assessments of the marginal contribution that restoring access to inland habitat for the goods and services produced by those ecosystems.
Results/Conclusions
Our initial case study focused on 250 degraded stream crossings in the Mat-Su borough of southcentral Alaska. Of these, we identified 103 crossings (41 percent) with non-zero conventional cost (risk), 50 of which (20 percent of the total) were found to achieve a benefit-cost ratio (BCR) of 1.0 or greater based solely on conventional risks ($21.5M, in 2016 dollars). Inclusion of ecosystem services increased the total to 54 crossings (21 percent). Of these, just 5 crossings (2 percent) presented localized flooding risks to nearby buildings ($2.3M). Fully 46 crossings (18 percent) had the potential to isolate households following a road washout ($4.2M in risk to public safety). All 53 degraded stream crossings in the regional rail system (21 percent) presented a risk of disruption ($14.9M). The total contribution to ecosystem goods and services flowing the restoration of access to inland habitat was limited by treating each crossing in isolation. Analyzing restoration projects at the stream level is likely to result in higher aggregate gains to habitat and ecosystem goods and services. Our team is currently expanding this work in the Chehalis basin of southwest Washington state; results of that work will be reported at the conference.