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3 NATURE AND SIGNIFICANCE OF IMPACTS 
3.1 Consumable resources 
The nature of impacts a motorway can produce on consumable geomorphological resources is essentially of an 
economic nature. Although these materials have a low unitary value and are usually abundant, in certain areas they may 
be scarce. If they are destroyed or sterilised, supply from alternative, distant sources may be necessary, with the 
consequent cost increase. In the case of widely used materials, such as sand and gravel, this could represent an increase 
of costs for all construction activities, for many years to come. The overall impact could thus be considerable. 
3.2 Sites of geomorphological interest 
These sites are part of the natural and cultural heritage (Poli, 1999); they contain essential information for the 
interpretation of geomorphological processes and history and have a potential for scientific, educational or tourism use. 
They can be totally destroyed or partly damaged by motorway construction. 
3.3 Valuable natural units 
Certain land units present a combination of geomorphological (landform, deposits, processes, soil) and other 
characteristics (land cover, heritage sites) that confers them a high natural value. In other cases their interest is due to a 
high natural or potential productivity (wetlands, high quality soils). Again, these units can be damaged or destroyed 
during motorway construction. 
3.4 Land units with high utilisation potential 
Some land units have geomorphological (landform, deposits, absence of hazards) and other characteristics (location) 
which make them especially suitable for intensive uses. The occupation of these units by a motorway represents the loss 
of a resource which may be scarce, as is the case in the study area. 
3.5 Visual landscape 
Visual quality (intrinsic merit of a unit from a perceptual point of view) and fragility (sensitivity to visual intrusion from 
human activities) of landscape are determined mainly by three groups of factors: geomorphology (relief, shape, rock 
type), vegetation, and land use (especially impacting elements such as prominent constructions); presence of water is 
also important. The introduction of new large structures such as a motorway represents a visual intrusion which may 
reduce visual quality. This reduction ( intensity of the impact) is related to the degree of modification; that is, contrast 
in size, shape, colour and texture between the structure and the pre-existing landscape. The magnitude of the impact 
can be considered to depend on the number of people and/or extent of the area affected. 
4 IMPACT MEASUREMENT AND EVALUATION 
The procedure to assess impacts on these resources rests on the application of a GIS-based database consisting of a 
number of thematic layers that represent natural and human characteristics of the study area. The following steps are 
involved: 
- Identification of suitable impact indicators 
- Establishment of the procedure to measure and/or predict the effects of the new motorway on those indicators 
- Determination of data input necessary for measurement/prediction 
- Selection, modification or creation of the necessary thematic layers in the GIS-based database 
- Implementation of procedure 
- Translation of the initial indicators into terms that are significant for comparisons and impact evaluation. 
These steps are briefly presented below for the different types of geomorphological resources considered. 
4.1 Consumable resources 
and value of the material lost or sterilised. The geomorphological 
Indicators used to express impacts are the volume 
deposits map and associated database provide the information to determine volume and value of the individual deposits 
affected (Fig.3; Table 1). 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 245