Photo courtesy of Santa Cruz Sentinel
When USGS’s Curt Storlazzi was standing near Moran Lake on the east side of Santa Cruz in January 1998, he witnessed waves from an epic storm wash onto the roadway and broadside a bus, hitting the bus hard enough to push it into the oncoming lane. Luckily no one was hurt, but the village of Capitola a few miles away suffered hundreds of thousands of dollars in damage from waves and wave-driven logs bursting through the ocean-facing windows of restaurants and businesses. Normally a huge protective barrier of beach exists between the Capitola Esplanade and the ocean. But in that El Niño year, much of the beach had already been eroded by earlier winter storms before this big storm hit.
Winter storms modified by future climate changes, including sea-level rise, could mean costly damage to harbors, beaches, and businesses, especially during El Niño years, when atmospheric conditions bring heavy rains to the central California coast. The biggest storms tend to hit later in the year when beaches have already been heavily battered. In a populated area that relies on its coastline for much of its revenue—from people such as surfers, beach goers, sailors, kite surfers, divers, and fisherman—there is a great need to understand how big storms can shape and affect the coast. Perhaps storms will alter an important snowy plover habitat, shift a surf break, or erode natural beach protection for waterfront businesses such as those in Capitola. USGS scientists in Santa Cruz have a rare opportunity to work on these issues close to home and collect data that can affect a range of people and businesses within the Monterey Bay region. Studying these changes now will help researchers create models of future climatic changes that will erode and shape our coasts—a valuable tool for city planners, conservationists, and the tourism industry.
USGS scientists started baseline mapping from all-terrain vehicles (ATVs), personal watercraft, and by foot from October 20–24, 2014. They used high-precision GPS receivers carried on foot and mounted on ATVs to measure beach and swash-zone elevations (topography). They used GPS receivers and 200-kilohertz echosounders mounted on personal watercraft to measure underwater elevations (bathymetry) along transects roughly two kilometers long and perpendicular to the shore. This initial fieldwork collected a total of 513 kilometers of trackline data along the coast: 219 kilometers of personal-watercraft data, 210 kilometers of ATV data, and 84 kilometers of backpack data, from the famous Santa Cruz Lighthouse/Surfing Museum to Moss Landing.
Multiple surveys are planned for the 2015 winter season, and regular surveys will occur in the fall and spring of subsequent years to capture seasonal fluctuations and extreme events such as flooding from the San Lorenzo River.
USGS scientists will also create beach maps from video captured during flyovers, and will attach time-lapse cameras and tide and wave gauges to local piers for a multi-dimensional view of what’s changing along the coast now, and over time.
Above: Photographs are of the Santa Cruz Main Beach before and after the December 11, 2014, “Super Soaker” storm that brought 2.5 inches of rain in just a few hours to Santa Cruz and 9 inches to Boulder Creek, along with big waves and swell. While the human eye may notice changes to the beach, ground-based lidar can create surface maps of precise elevation changes over time.
Lidar stands for Light Detection and Ranging. It is similar to radar but uses laser light instead of radio waves. This instrument rotates 360 degrees and bounces a low-power laser beam safe for the naked eye off everything around it. By measuring the length of time it takes for the light to bounce off an object and return to the scanner, the scanner can capture an accurate three-dimensional measurement of the surrounding surfaces. It is capable of doing this as fast as 122,000 times each second and produces about 10 million points of data in a single rotation.
The scanner is also capable of capturing digital images of its surroundings, which can be overlaid on the points to produce a photo-realistic three-dimensional image comprising millions of points.
These millions of points make up a “point cloud” that must be translated into geographic coordinates so that USGS can create a “map” showing super-fine detail of the area it surveyed. To enable this translation, special reflectors placed in different spots on the ground with known GPS coordinates are “seen” by the instrument as it scans. By matching up the scanned reflectors to their real-world coordinates, researchers are able to rotate the entire cloud of points to its real-life layout.
Lidar sees what the human eye can see—up to about a distance of 1,400 meters. At greater distances the measurement process is slower since it takes longer for the light to return. Like the human eye, the scanner can’t see around corners or behind objects so the equipment has to be moved to different spots to create a continous map without large gaps or shadows.
The painstaking process of producing elevation maps from multiple scans and millions of points is most time-consuming when filtering out objects such as buildings, trees, and even seabirds, so they don’t show up as false elevation peaks on the beach. Since the team wants to know how the beach and its elevation changes over time, they can overlay images produced in subsequent years or after large storms to measure the differences.
Lidar has many advantages for gathering fine-scale detail to see, for example, the effects of erosion over time, but sometimes the instrument has difficulty in registering wet objects close to the ground or in the surf zone. To overcome this, the lidar data can be combined with elevation data collected using the other techniques, such as the walking surveys, ATV surveys, and bathymetry surveys. By combining all of these data, researchers can create a continuous snapshot of the bluffs, beach, surf zone, and offshore.
Above: Once the point data from lidar are processed and overlaid with digital images, one can virtually “fly” through the scanned area. Landmarks like the Santa Cruz Main Beach volleyball nets, the Santa Cruz Beach Boardwalk, and the mouth of the San Lorenzo River are visible. Video by Josh Logan, USGS.
To learn more about USGS surveys along Santa Cruz beaches, please read:
“El Niño and La Niña Will Exacerbate Coastal Hazards across Entire Pacific”
USGS Newsroom, September 2015
“Climate change may flatten Santa Cruz’s famed surfing waves”
San Jose Mercury News, February 2015
“Climate change may flatten Santa Cruz’s famed waves”
Santa Cruz Sentinel, February 2015
“Mapping Coastal Changes Along Northern Monterey Bay, California, to Aid Planning for Future Storms”
Sound Waves, November/December 2014
“Survey charts Santa Cruz beaches, sandbars”
Santa Cruz Sentinel, November 2014
“Mapping Changes In Beach Landscapes In Our Backyard”
USGS Newsroom Media Advisory, October 2014
Coastal vulnerability across the Pacific dominated by El Niño /Southern Oscillation
Nature Geoscience Advance Online Publication, September 2015