G. Gabert: Integration of LANDSAT TM Data and SPOT Digital Elevation Model
173
The ridges and valleys have steep slopes of 30 to 50 degrees and are intensively
dissected by a drainage pattern of gullies; the ridges have a thin residual soil cover,
while their flanks are made up of colluvium, debris and talus fans. The extensive
erosion on the ridge slopes indicates their surface instability which is proven by
frequent old, new and reactivated landslides of varying dimensions; they, in turn,
have affected the overburden and the bedrock. Half of the study area shows a high
risk potential and comprises, in addition, protected forest areas.
It was thus evident that from the geotechnical point of view, a geo-hazard map had
to be established. In a first step, this was done by the interpretation of LANDSAT
TM false colour composites using an ARC/INFO workstation, and by combining
the digitized results with data from a digitized landslide map of the DMG, based
on airphoto interpretation and field mapping. In a second step, tectonic data were
added which were derived from lineament interpretation of the same LANDSAT
TM false colour composites, on colour prints at 1: 125 000 scale. Two main
lineament systems were identified striking NNE - SSW and N - S. They represent a
neotectonic fault pattern which dissects the entire project area, and to which some
earthquake risk potential is connected.
2.3 Hazard mapping for water supply project
All the hazard data are displayed in a geo-hazard map from which "hazard values"
or hazard parameters were derived. To this end, the following factors had to be
considered: presence of landslides and erosion gullies, steepness of slopes, status of
vegetation cover, nature of land-use, geological and hydrogeological conditions.
For the solution of the geotechnical problems, regarding the determination of an
optimal route for the planned water transfer (Fig. 2), adequate criteria had to be
taken into account concerning the:
natural conditions (extreme morphology, difficult accessibility)
engineering conditions (geo-hazards, availability of building material)
environmental conditions (protected areas, different forms of land-use,
population density).
Using GIS overlay techniques, specific parameters for hazards, elevation, landslides
and accessibility were introduced in order to optimize the route for the planned
water transfer. To this end, a path-finding algorithm was used with the following
constraints:
gravity-driven water flow at moderate slope conditions
minimum of natural obstacles
minimum of the overall costs.
3 CONCLUSION
By means of network analysis and a path-finding program of ARC/INFO, an
optimal route for a channel, with a few short tunnels in places, could thus be
determined, and the water intake site could be moved from a high-hazard to a
medium-hazard area (Fig. 3); potential tunnel routes were identified for follow-up
ground checks. By minimizing the crossing of protected areas, forests and arable
land, the environmental impact of the planned channel/tunnel combination will be
greatly reduced (Fig. 4).
173
The ridges and valleys have steep slopes of 30 to 50 degrees and are intensively
dissected by a drainage pattern of gullies; the ridges have a thin residual soil cover,
while their flanks are made up of colluvium, debris and talus fans. The extensive
erosion on the ridge slopes indicates their surface instability which is proven by
frequent old, new and reactivated landslides of varying dimensions; they, in turn,
have affected the overburden and the bedrock. Half of the study area shows a high
risk potential and comprises, in addition, protected forest areas.
It was thus evident that from the geotechnical point of view, a geo-hazard map had
to be established. In a first step, this was done by the interpretation of LANDSAT
TM false colour composites using an ARC/INFO workstation, and by combining
the digitized results with data from a digitized landslide map of the DMG, based
on airphoto interpretation and field mapping. In a second step, tectonic data were
added which were derived from lineament interpretation of the same LANDSAT
TM false colour composites, on colour prints at 1: 125 000 scale. Two main
lineament systems were identified striking NNE - SSW and N - S. They represent a
neotectonic fault pattern which dissects the entire project area, and to which some
earthquake risk potential is connected.
2.3 Hazard mapping for water supply project
All the hazard data are displayed in a geo-hazard map from which "hazard values"
or hazard parameters were derived. To this end, the following factors had to be
considered: presence of landslides and erosion gullies, steepness of slopes, status of
vegetation cover, nature of land-use, geological and hydrogeological conditions.
For the solution of the geotechnical problems, regarding the determination of an
optimal route for the planned water transfer (Fig. 2), adequate criteria had to be
taken into account concerning the:
natural conditions (extreme morphology, difficult accessibility)
engineering conditions (geo-hazards, availability of building material)
environmental conditions (protected areas, different forms of land-use,
population density).
Using GIS overlay techniques, specific parameters for hazards, elevation, landslides
and accessibility were introduced in order to optimize the route for the planned
water transfer. To this end, a path-finding algorithm was used with the following
constraints:
gravity-driven water flow at moderate slope conditions
minimum of natural obstacles
minimum of the overall costs.
3 CONCLUSION
By means of network analysis and a path-finding program of ARC/INFO, an
optimal route for a channel, with a few short tunnels in places, could thus be
determined, and the water intake site could be moved from a high-hazard to a
medium-hazard area (Fig. 3); potential tunnel routes were identified for follow-up
ground checks. By minimizing the crossing of protected areas, forests and arable
land, the environmental impact of the planned channel/tunnel combination will be
greatly reduced (Fig. 4).