Measuring Coastal Bluff Recession Rates Throughout the Puget Sound Region
border|left|300pxThis project, led by Coastal Geologic Services, aimed to better understand the range and drivers of coastal bluff erosion in the Puget Sound region. Coastal bluff recession supplies the majority of sediment on Puget Sound beaches (Keuler 1988, Finlayson 2006). However, there is considerable variability in bluff form, geology, stratigraphy, wave exposure, landslides, and erosion (recession) rates along the 660+ miles of bluff shore. Very little research has analyzed the variability and range of erosion rates (Shipman 2004, 1995). Most of the bluff recession rates measured in the region are from the most rapidly eroding bluffs, with far fewer documented rates from the more slowly eroding bluffs in central and southern Puget Sound. These slowly eroding bluffs account for considerable lengths of Puget Sound shores. A common disconnect between the perceived and actual need for shore protection (armor) due to coastal erosion has been documented among Puget Sound coastal landowners. Measuring bluff recession from only these most rapidly eroding bluffs simply compounds this erroneous perception. Better understanding of the range of bluff erosion rates can also aid in the development of capital projects that aim to restore beach systems. Regional bluff erosion rates have been used by CGS to identify feasible feeder bluff armor removal sites and to assess sea level rise vulnerability in San Juan County. Land use decisions, including setback distances and the installation of shore armor, rarely reflect regional variability in bluff recession rates. This project will increase understanding of the range and dominant drivers of coastal bluff erosion rates throughout the Puget Sound region to inform management, regulations, restoration, and ultimately will aid in preserving feeder bluff function.
The hypothesis for this proposed project is that building and analyzing a database of historical bluff erosion rates throughout the Sound and identifying the dominant drivers of bluff recession will advance understanding and inform management, restoration, research, and preservation. The results of these analyses can also be used to justify better management decisions (such as setback distances) and, importantly, prevent shore armor where unnecessary by allowing for informed application of risk measures in the Marine Shoreline Design Guidelines (Johannessen et al. 2014). These data can be used to direct capital project policy relating to site selection, feasibility, restoration, and protection. For a recent project, CGS paired setback distance data with extrapolated bluff recession data from 39 bluffs in Island and Jefferson Counties to screen out infeasible armor removal projects. The same erosion rate data was used together with bluff height data (from LIDAR) to quantify the potentially restored sediment volume resulting from restoration. These data could also be used to help determine whether relocating a road or other infrastructure is a preferred solution due to ongoing threat of erosion. This information can be used to make better long-term investments and informed management decisions of Puget Sound bluffs.
Relationships
- broader: beach food webs and biodiversity
Source: Measuring Coastal Bluff Recession Rates Throughout the Puget Sound Region on Salish Sea Wiki