Sea-level rise will increase the risks associated with coastal hazards of flooding and erosion. Along the active tectonic margin of California, the diversity in coastal morphology complicates the evaluation of future coastal hazards. In this study, we estimate future coastal hazards based on two scenarios generated from a downscaled regional global climate model. We apply new methodologies using statewide data sets to evaluate potential erosion hazards. The erosion method relates shoreline change rates to coastal geology then applies changes in total water levels in exceedance of the toe elevation to predict future erosion hazards. Results predict 214 km 2 of land eroded by 2100 under a 1.4 m sea level rise scenario. Average erosion distances range from 170 m along dune backed shorelines, to a maximum of 600 m. For cliff backed shorelines, potential erosion is projected to average 33 m, with a maximum potential erosion distance of up to 400 m. Erosion along the seacliff backed shorelines was highest in the geologic units of Cretaceous marine (K) and Franciscan complex (KJf). 100-year future flood elevations were estimated using two different methods, a base flood elevation approach extrapolated from existing FEMA flood maps, and a total water level approach based on calculations of astronomical tides and wave run-up. Comparison between the flooding methods shows an average difference of about 1.2 m with the total water level method being routinely lower with wider variability alongshore. While the level of risk (actual amount of future hazards) may vary from projected, this methodology provides coastal managers with a planning tool and actionable information to guide adaptation strategies.

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Crenulate bay theory is well developed and natural examples of this type of bay are evident along many coasts. Case studies are presented here in which this theory has been applied and adapted at different scales to address the needs of management and coastal communities. In many places, these needs are not currently met because coastal protection is constraining landward shoreline movement, leading to erosion and consequential loss of property, infrastructure, public access and amenity value.Abereiddy, in west Wales has a small locally important beach backed by a seawall. With no intervention, seawall collapse will lead to realignment and a more natural beach form, but a reduction in car parking area. Crenulate bay theory was applied to understand what shoreline shape would result if the seawall was lost. Coyote Point, in San Francisco Bay, California is a popular recreation area. Coastal defence structures are failing, leading to erosion of the coastal path and beach loss. In order to develop an innovative sustainable solution to the erosion problem, whilst maintaining recreational functions and good public access, crenulate bay setback options were examined.These local examples can be set within the wider context of integrated coastal zone management. Axiomatic principles, such as crenulate bay theory, assist in interpreting existing broader-scale erosion monitoring in the context of geomorphological control. Examples are provided demonstrating regional benefits of the approach by taking a landscape-scale view of coastal evolution.

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