In mountainous country, torrents pose a considerable threat to human beings, their living and settled areas, as well as important traffic and supply routes. Dangers arise through the rapidly swelling flood-wave that results from heavy rain, and also through the gravel, rubble (bed load) and wood it carries with it.
In the case of steep torrents with large accumulations of loose stone, debris flows of water, mud and rubble often occur, which move into settlement areas with great speed and high pressure, and are able to damage or even destroy buildings there.
In torrent catchments, severe ero¬sion and landslides often occur, which carry large amounts of bed load into the torrent. Due to the long, steep slope, the torrent itself is subject to severe erosion of its banks and stream bed.
also arises due to the penetration of floodwater into a building, to the erosion of the banks by the water, or to the accumulation of bed load and wood outside the stream bed. A severe risk is posed by the clogging of bridges (wood and bed load alter the course of the stream).
In Alpine valleys, old settlements are often located on the alluvial fans (debris cone with a cone-shaped deposit zone at the valley mouth) of the large torrents. Earlier, human beings depended on water supplies from streams, and these areas offered the only dry building sites on a valley floor otherwise occupied by moist meadows.
Over the centuries, the mountain population has learned to live with the dangers posed by torrents and has often implemented protective measures itself. Since the end of the 19th century, the state has assumed the task of protecting people from torrents in most countries, through making danger zone plans as a basis for preventive spatial planning and supporting active protective measures.
Torrent control primarily consists of retaining constructions, which stabilize torrent beds or serve to hold back or control bed load and logs. In settled areas, the stream bed must be secured (regulated), in order to divert the floodwater through the endangered area without any damage.
Over the past few years, new technology has been increasingly applied in torrent protection, e.g. various measuring and warning systems. Organizational protective measures are also gaining in significance. If flooding occurs, emergency operations at the torrent are concentrated on keeping the stream bed free from silted-up deposits and on clearing clogging at bridges.
The important thing immediately following a disaster is to secure the fresh area of erosion and to clear areas of silted-up deposit for succeeding flood waves.
One of the most important tasks is control of torrent catchment areas. Only the consistent clearing of deposits from the stream course and the timely discovery of any new hazard sources can help to prevent future damage in settlement areas.
Interpraevent