uav + surveying
Two LiDAR data sets recorded 11 years apart were used to analyze cliff changes along the California coast.
aerial surveys — which were used to create detailed 3D elevation maps. Existing cliff erosion studies are often small scale, use a variety of techniques, and often rely on lower-quality data sources, providing a patchwork across the state. “What’s unique about this study is that it applies a consistent methodology across a very large area using accurate high-resolution laser data,” Young said. While some of the basic causes of coastal cliff erosion — such as rainfall and waves — are clear, this has not translated into a simple way to predict future erosion rates or identify areas at risk. Variation in cliff geology, beach protection, exposure to weather, and other factors also complicate predicting erosion rates. Previous research has identified clear correlations between rainfall and coastal erosion in southern California, but the impact of storm waves has been more elusive. “It’s difficult to measure,” Young said. “We lack field observations because with powerful waves crashing against the cliff, it is not an easy place to make measurements.” Variation in cliff geology, beach protection, exposure to weather, and other factors also complicate predicting erosion rates. Understanding erosion, preventing disaster To create a consistent analysis of recent cliff changes, Young compared two massive LiDAR data sets — 3D maps of the California coastline recorded 11 years apart. The greatest cliff erosion rates were found in San Onofre, Portuguese Bend, Palos Verdes, Big Sur, Martins Beach, Daly City, Double Point, and Point Reyes. Young then compared the recent cliff erosion maps to historical records from 1932 and 1934. By comparing the different maps, he built an analysis for the majority of the state’s coastline, showing both recent and historical erosion rates. The study shows that the historical cliff erosion rate does not always
Study provides the largest analysis of cliff erosion throughout California and provides a new hazard index for determining areas at most risk. LiDAR helps identify unstable cliffs
Yellow warning signs — Danger: Unstable Cliffs - Stay Back — that pepper coastal cliffs from northern California to the U.S.-Mexico border may seem overly dramatic to the casual observer. But actively eroding cliffs make up the majority of the California coastline, and sudden landslides and collapses have caused injuries and several fatalities in recent years. In addition, eroding cliffs currently threaten highways, houses, businesses, military bases, parks, power plants, and other critical facilities — billions of dollars of development. Research suggests that erosion rates will increase as sea level rises, further exacerbating these problems. “It is critical we study current and historical cliff retreat so we can better plan for the future,” said Adam Young, a researcher at Scripps Institution of Oceanography at the University of California San Diego, who recently published a large-scale analysis of coastal cliff erosion in California. The study, published in the journal Geomorphology, and funded by California Sea Grant, provides accurate erosion rates for 680 miles of the California coast, from the U.S.-Mexico border to Bodega Head in Sonoma County. It identifies areas that have eroded faster than others, and introduces a new experimental hazard scale to identify areas that may be at greater risk of impending collapse. It is the first such large-scale study in California using LiDAR data — laser elevation data recorded in
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february 2018
csengineermag.com
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