Geoscience Reference
In-Depth Information
4 the fact that most of the route of the road tra-
verses unstable Holocene and Pleistocene deposits
and passes through highly dynamic outwash
zones such as the Batura glacier terminus.
A general assessment of the highway under-
taken by Jones et al. (1983) showed the relative
significance (% of length) of different terrain and
material types along 129 km of the highway:
sediment related hazards in mountain regions.
This can be illustrated by considering examples
of hazard assessment and mapping techniques
and the role monitoring can play in the remedi-
ation of mountain sedimentation events.
2.5.1 Hazard assessment
In mountain environments geomorphological pro-
cesses are highly active and the terrain inherently
unstable (see section 2.1.2). Any move to develop
such areas results in a potential hazard. Moun-
tain hazards are on the increase due to increasing
development pressures and recent environmental
change. Mountain hazard mapping is therefore
becoming an increasingly important component
of regional and local land-use planning. Over the
past few decades understanding of mountain sedi-
ment systems has advanced considerably (Owens
& Slaymaker 2004), however, the problem of
ranking the importance of geomorphological
processes in terms of hazards is still problematic
because of difficulties in:
1 recognizing and understanding causal
mechanisms;
2 adequately characterizing the time-scale and
frequency over which processes operate;
3 accurately mapping the occurrence of such
phenomena.
Slope instability in mountainous terrain is a
natural occurrence. In many regions, however,
this represents an important hazard that needs
to be carefully assessed. In Switzerland, there
is a long history of landslide disasters and
genuine concern about whether future climatic
warming will lead to an increase in hazards,
for example greater frequency of debris flows
from the periglacial zone. This is a significant
problem because more than 6% of the country
is affected by hazards that are related to slope
instability (Raetzo et al. 2002). Examples of
specific events include the summer debris flows
of 1987 and the Randa rock avalanches of 1991
(see section 2.3.3). Following the devastating
events of the summer of 1987 in Switzerland
revisions were made to the Federal Flood Protec-
tion Law and the Federal Forest Law, which came
in to force in 1991 to protect the environment,
alluvial and outwash fan
40.6
rock fall and scree
20.7
rock
18.3
terrace deposits
9.4
river
0.4
till
10.6
Considering the dynamic nature of the terrain
types and unstable character of the materials it
is inevitable that despite best practice in design-
ing and building the road, sections of it will be
periodically destroyed during seismic events,
floods and debris flows. The only action is to
rebuild following these natural catastrophes
(Fig. 2.16). The value of environmental sediment-
ology in designing such a highway is in careful
planning of the alignment of the road in relation
to the geomorphology and terrain types; assess-
ment of slope instability types and likely hazards;
and siting of local engineering measures to mini-
mize risk from specific slope processes.
In more developed mountain countries road
and railway construction is a highly sophisticated
engineering practice involving the construction
of switchbacks, blasting to achieve preferred
alignments; elaborate bridges; protective struc-
tures from rock fall and avalanches; and tunnels.
In the Rhaetian Alps in Switzerland the railway
runs over a distance of 240 km and on this route
has 376 bridges and 76 tunnels (Price 1981). In
some cases tunnels pass completely through a
mountain such as the 12 km Mont Blanc Tunnel
(completed in 1965) between France and Italy.
2.5
MANAGEMENT AND REMEDIATION
Environmental sedimentology is an essential
element in the management and remediation of
Search WWH ::




Custom Search