provide a good prediction of future rates. “The results show that if a cliff experienced a large of amount of erosion during one time period, it was followed by a time period with very little erosion, and the cliff could be relatively stabilized for a time,” Young said. “It will mobilize again, but we don’t know when and more research is needed to better understand the time cycles involved.” Young also found that cliffs with high erosion rates in recent times were often preceded by time periods with very little erosion. These are key findings because models predicting future cliff retreat are often based on projecting the historical rates. Young also introduced a new experimental measure to identify the riskiest precipices. Previous research had suggested that the difference between erosion rates of the cliff face compared to the cliff top could indicate instability — in short, the cliff steepness. When he applied this hazard index, Young identified worrisome spots along the California coast, including San Onofre State Beach, Big Sur, Martins Beach, and Daly City. A reality check for planners Young is currently working on a set of maps to be made available to the public, and he has presented the work at scientific conferences. “I hope that this study will help improve models that predict erosion, help identify hazardous areas, and assist policymakers who are working to protect our coast,” Young said.
The research has already caught the attention of planners at the California Coastal Commission, a state agency charged with preserving and protecting the coastline for current and future generations. “The study could be particularly useful for local governments looking to update their local coastal programs in light of climate change and sea level rise,” said Lesley Ewing, a senior coastal engineer for the commission. While the study does not provide projections for future erosion rates, researchers expect that sea-level rise will contribute to faster erosion rates and greater risk to public and private coastal property, and governments are working to plan for the impacts. “The coast of California is stacked with very expensive real estate — not to mention power plants, wastewater treatment facilities, and highways,” Ewing said. Some of this is already at risk — more than 100 miles of shoreline armory has been built to protect it, and more will be at risk in the future. “There’s so much opportunity to use this research; this could serve as a reality check for planners who often focus on specific regions and smaller scales,” Ewing said. The research was also supported by the California Department of Parks and Recreation, Division of Boating and Waterways.
Information provided by Scripps Institution of Oceanography (https://scripps.ucsd.edu).
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csengineermag.com
february 2018
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