Floods occur when water covers land which is normally dry. Floods in Australia range from localised flash flooding as a result of thunderstorms, to more widespread flooding following heavy rain over the catchment areas of river systems. Flooding is also a regular seasonal phenomenon in Northern Australia. Australian towns were built on floodplains despite warnings from local Aborigines. Nyngan (meaning flood in its local Aboriginal language) was severely flooded on 23 April 1990.

Gundagai was rebuilt on a new site after a flood in 1852 wiped out 71 buildings, and 89 of the town’s 250 inhabitants died. More people would have perished were it not for the heroism of local Aborigine Yarri of the Wiradjuri people and his mate Jackie, who saved more than 40 people using a simple bark canoe.

Recently, town councils and shires have started mapping the 100-year flood areas so that the extent of the flood plain can be mapped for town planning, building regulations and zoning for land use to avoid building on flood-prone areas. Regional flood mitigation programs have been initiated by the Australian Government to work with state and territory governments.

In a cooperative research program, the U.S. Geological Survey, NASA and the U.S. Army Corps of Engineers have been mapping the coastlines of the United States using airborne laser altimeters, or lidar (light detection and ranging). The laser altimeter scans a several hundred meter wide swath of the earth’s surface acquiring an estimate of ground elevation every few square meters. Baseline surveys conducted during periods of calm weather are compared to surveys collected following extreme storm events in order to quantify the resulting coastal change.

Two instruments are currently used for the majority of our surveying efforts: NASA’s EAARL and the U.S. Army Corps’ CHARTS. These instruments survey hundreds of kilometers of coast in a single day with data densities that cannot be achieved with traditional survey technologies. Specifications for the lidar instruments can be found on the individual websites for NASA’s EAARL and U.S. Army Corps’ CHARTS.

Airborne scanning laser surveys are providing unprecedented data to investigate the magnitude and causes of coastal changes that occur during severe storms.