Читать книгу Canyoning in the Alps. Graded routes in Northern Italy and Ticino, Austria, Slovenia and the Valais Alps онлайн

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Snow and glacial melt

Melting snow and ice can lead to dangerously high water levels as the day heats up. This is mainly a problem of canyoning early or late in the season. Few canyons in this guidebook have significant snow fields present in their catchment areas during the summer months.

Presence of upstream dams

Many canyons in the Alps have hydroelectric constructions somewhere along their length. Surprisingly, given the growing popularity of canyoning as a sport, it is difficult to find definitive information on their purge/opening patterns. Put simply, there are three basic types of construction

 a grill in the stream bed which pipes away water to a nearby reservoir or power plant

 a small dam that traps water first before piping it away

 larger-scale dams, holding back millions of cubic metres of water, which is piped off to the power plant. Water may be piped into the reservoir from a number of sources.

When a single river intake closes (due to obstruction, malfunction or maintenance purposes), the water normally diverted away will return to the natural riverbed. Unless the river is large this is unlikely to cause problems for the canyoner. If the whole power plant needs to be shut down, or if rainfall is especially heavy, even the larger reservoirs fill and may be forced to open their overflow gates. A release of such vast amounts of water would be disastrous to unwary canyoners downstream. The smaller dams are also dangerous. They may be ‘purged’ after rainy periods to flush away sand and other debris that could otherwise harm the system. In short, the flow of a river below a hydroelectric installation may suddenly increase without warning, even in times of good weather.