Cendrero, Antonio
4.4 Land units with high utilisation potential
The loss of land resources can be best expressed in terms of
absolute and relative area of such units occupied or degraded
by the motorway. Utilisation potential of homogeneous
morphodynamic units (Cendrero et al., 1993) is established on
the basis of: slope gradient, size and shape of units, potential
hazards and geotechnical conditions, location with respect to
roads and inhabited areas. Figure 5 shows the distribution of
morphodynamic units; only units with the optimum conditions
for the criteria indicated above have been highlighted. Land
units within the service perimeter of the motorway (25m on
each side of the axis) are totally lost for other uses. An
additional 50m on each side of the road are considered to be
affected by a 50% reduction of their potential.
Ty
oads (red) ai
igh potential for use
rbanisalion = ef ;
ZIP AT UN À Ns
Figure 5. Map of homogeneous land units. For
greater clarity the colour code has been
eliminated, except for units with high
potential for use.
Impacts can easily expressed as area destroyed or affected or by means of the equivalent monetary value (Table 3).
Area lost Value |Total value Area Value |Total value Total
Alternative! (m^ |?*6 |(€/m?)| (€) laffected (m^) % (€m^)| (© impact (€)
1 z T = = - - - -
2 5,125 [1.51| 54,57 [279,671.25 5,125 1.51| 27,29 |139,861.25 419,532.50
Table 3. Example of application of SGIs database to impact calculation.
(EURO values are conservative estimates and do not intend to reflect actual land prices).
In the example considered, only alternative 2 produces an impact on this resource and it is not very significant.
4.5 Visual landscape
Indicators of impact magnitude can be the total
area from which the new structure (or individual
sectors of it) can be seen or the number of people
affected. A measure of intensity can be obtained
by defining the level of visual intrusion in
sensitive units (those with high visual quality or
fragility) on the basis of different degrees of
contrast with the new structure, presented by
means of photographs or images. The procedure
to follow for assessing visual impacts starts with
the definition of landscape units directly affected
by the new road. Visual quality of units can be
assessed on the basis of: relief (difference
between maximum and minimum altitude);
general shape (convexity, concavity, etc); Be
landform (irregularity, ruggedness);
geomorphological diversity (No. of
geomorphological elements in unit); vegetation
(rank of vegetation type); land use (intensity of
human modification); water bodies/courses.
Figure 6a. Visual basin. Figure 6b. Areas of great
visual effect
The magnitude of impacts is expressed as the intersection (Fig. 6c) between visual basins of individual motorway
sectors (Fig. 6a) and areas of great visual effect or buffers around population centers and main roads (F ig. 6b).
This can be performed using standard GIS tools. Realistic views (RV, Fig. 7) are then simulated for each motorway
sector.
248 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.
