Extensive torrent control works, such as grade-control dams, debris basins, deflecting walls,
etc. have been implemented in the European Alps since the last decades of 19th century.
These structural measures, aimed at stabilizing channels and to control sediment transport,
are also widespread in Japan and are increasingly present in other mountain regions. As
debris flows are one of the most destructive processes in steep mountain channels,
hydraulic works are often intended to attenuate debris-flow hazard. Multi-temporal
aerial photos and historic records permit evaluating the long term effects of torrent
control works on the morphological settings of the channels and the delivery of
sediment.
The experience arising from over one century of torrent control works in debris-flow
channels of the Alps permits also to improve the management of steep headwater
catchments.
A basic issue in the management of debris-flow channels is the recognition of success
versus failure of engineering control works. Successful debris-flow control works provide
benchmarks for further implementations, whereas the failure in reducing debris-flow hazard
may lead to refinements in planning and design of control works or to the choice of preferring
non-structural measures for coping with debris flows. Data from historical archives on
debris-flow occurrence and on the performance of control works are the basic sources of
information for these analyses.
Moreover, when dealing with hydraulic structures for debris-flow control, it should be
reminded that the artificial morphology resulting from the construction of check
dams provides only a temporary stability to the channel and adjacent banks. This
stresses the importance of evaluating the state of conservation and the effectiveness of
control works and implies the need for their careful and continuous maintenance.
Inventories of hydraulic structures, coupled with detailed data on catchment and
channel topography, sediment sources and supply processes, are required for taking
decisions about maintenance and possible upgrade of debris-flow control works. |