Choosing a Future Shoreline for the San Francisco Bay: Strategic Coastal Adaptation Insights from Cost Estimation

Abstract

Abstract:In metropolitan regions made up of multiple independent jurisdictions, adaptation to increased coastal flooding due to sea level rise requires coordinated strategic planning of the physical and organizational approaches to be adopted. Here, we explore a flexible method for estimating physical adaptation costs along the San Francisco Bay shoreline. Our goal is to identify uncertainties that can hinder cooperation and decision-making. We categorized shoreline data, estimated the height of exceedance for sea level rise scenarios, and developed a set of unit costs for raising current infrastructure to meet future water levels. Using these cost estimates, we explored critical strategic planning questions, including shoreline positions, design heights, and infrastructure types. For shoreline position, we found that while the shortest line is in fact the least costly, building the future shoreline at today's transition from saltwater to freshwater vegetation is similar in cost but allows for the added possibility of conserving saltwater wetlands. Regulations requiring a specific infrastructure design height above the water level had a large impact on physical construction costs, increasing them by as much as 200%. Finally, our results show that the costs of raising existing walls may represent 70% to 90% of the total regional costs, suggesting that a shift to earthen terraces and levees will reduce adaptation costs significantly.

Adapting to Sea Level Rise: Insights from a New Evaluation Framework of Physical Design Projects

“…The pre-development conditions of the projects are all less than 50% dynamic by shoreline length as well, with the exception of the Aramburu Project (#1). When compared to the Bay-wide conditions, the pre-development conditions are representative of the conditions of the larger region, which is currently comprised of predominantly static landforms (69% of the entire SF Bay edge), typically including an earthen slope or berm with a riprap edge (Hirschfeld and Hill 2017).…”

“…Approach 1 is based on a typology of coastal infrastructure and typologies are known to be valuable heuristic tools in decision theory (Mees et al 2014). Researchers in the San Francisco Bay have used this typology to understand missing design strategies (Hill 2013), and the costs of future adaptation (Hirschfeld and Hill 2017). Most recently the typology was applied to coastal adaptation planning in Denmark (Aarhus School of Architecture 2019).…”

“…our assessment is shown in Figures 3 and 4. materials is significant because walls are associated with significantly higher costs (Hirschfeld and Hill 2017;Jonkman et al 2013) and represent a reduction in future flexibility, since the footings of walls are designed for a limited height. If the designed height of a wall must be exceeded in the future to respond to higher sea levels, the entire structure and its footings must be removed and replaced at significant expense.…”

“…First, we used the reclassification scheme shown in Table 3 to align the shoreline data from SFEI to the shoreline typology (Hirschfeld and Hill 2017). Next, each project's boundary was used to clip the SFEI data and generate specific pre-development conditions for each case study.…”

Coastal Sea Levels, Impacts and Adaptation

“…Understanding how to respond to shoreline change is important, and the study by Hirschfield and Hill [21] is an example of how adaptation and decision-making, at the local scale in urban areas, is addressed. They analyse the San Francisco Bay shoreline and estimate unit costs for raising current infrastructure, taking into account the shoreline position and design heights, as well as the range of shoreline infrastructure.…”