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    1. Erosion Control
    2. Vegetation Management

    Mapping the Changes

    Nov. 1, 2003
    One of the questions the National Oceanic and Atmospheric Administration (NOAA) regularly fields from the public is, apparently, why the government isn’t doing more to prevent hurricanes. Suggestions range from dropping moisture-absorbing gel into the storm to coating the ocean’s surface with some sort of substance that prevents water from evaporating, and from seeding the clouds with silver iodide (this one was actually attempted) to blowing the storms away from shore with giant windmills. While we might not be close to preventing them, we can predict hurricanes earlier than ever before, and we can also measure their effects with greater precision – particularly the extent of coastal erosion they cause. Storm damage can be all too apparent to those whose homes and livelihoods lie in the path of a hurricane, but the larger effects and the long-term changes to the shoreline have not always been clear from the ground. Assessing how the coast is holding up can dictate what steps to take next, and it has immense economic implications. For example, cities that have undertaken beach replenishment projects – adding sand to widen the beaches – were especially anxious after Hurricane Isabel in September to know the current shape of their shorelines.

    Hurricane Isabel close to making landfill; image taken September 18, 2003, at 7:53 a.m. EDTThe practice has always been controversial; many argue that beach replenishment, or beach nourishment as it’s sometimes called, simply washes away money, because the processes of erosion that are stealing the beach in the first place will inevitably claim the added sand as well. Others, such as engineers in Virginia Beach who watched as Isabel threatened to remove much of the sand they’d recently spent $125 million to place in front of hotels and tourist spots, view the practice as an insurance policy.The newly expanded beaches, rather than the expensive real estate behind them, absorbed the brunt of Isabel’s waves. In the past, storms have sometimes left such severe destruction that it was difficult for those assessing the aftermath to identify landmarks and damaged structures, or even to hazard a guess as to where some manmade structures had been located; GPS and GIS technology allow far better orientation.

    Comparison of the new inlet created by Hurricane Isabel near Cape Hatteras Village, NC. The back-and-white images was taken in 1998. The color image as taken September 19, 2003, by a NOAA aircraft.Vastly improved mapping technologies, too, are allowing us to track – and sometimes to predict – not only the violent and sudden changes from a Hugo or an Isabel but also more subtle patterns of long-term erosion and water-level changes. Ideally, seeing these trends can help guide land-use planning and new development. It also allows time for erosion control measures to be implemented for existing structures that are threatened. LiDAR (light detection and ranging) and other technologies are being used extensively to create baseline maps for just these reasons. (See “Shoreline Mapping Along the Great Lakes” in the March/April 2003 issue.)NOAA, using a new aircraft-mounted digital sensor system camera that it acquired just weeks before Isabel, can carry out long-term mapping projects and was also able to document within hours a new inlet that the hurricane created near Cape Hatteras. Remote-sensing technologies such as synthetic aperture radar, which can obtain shoreline imagery even through dense clouds, and Airborne Visible and Infrared Imaging System hyperspectral imaging are also being used for mapping shorelines and tracking coastal changes. For EC practitioners, this ability to have more data sooner – whether it helps predict sudden damage or slow change – is a significant planning tool and a boost to credibility as well, as it can visually demonstrate to planners the prudence of investing in erosion control measures – or in relocation of assets, as the case might be. Incidentally, NOAA actually addresses the feasibility of each of the hurricane-dissipating suggestions on its Web site (www.aoml.noaa.gov), including the results of Project Stormfury, the cloud-seeding effort, in the 1960s and ’70s.