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In figure 2 the methodological sequence is presented, accompanied by its application to a concrete case study. Impacts have 
been considered for two distinct phases: construction and operation of the highway, but only the first phase is represented in 
the figure. During the construction phase land cover destruction, soil perturbation and excavation and accumulation 
elsewhere will alter infiltration and runoff. This will have consequences for discharge, which in turn may affect flood hazard. 
  
  
[rm mm nm 
I 
Main steps| | Methodological steps | Case study - Vitoria-Eibar motorway — ' 
  
  
  
  
1) Project VE E ERE 1 
  
  
2) Expected impacts = W@W | 442222000 DEM a 
  
  
4) Runoff generation (hydraulic conductivity, 1 
I 
I 
£ ' 
1 
Bo ! modification of local relief) 
3) Relevant impacts (concerns) 
  
  
4) Relevant processes for concerns 
  
  
  
5) Relationships between runoff, infiltration — i 
and erosion are defined conceptually 
5) Conceptual model Pr AE 
  
  
| 6) Relationships are described mathematically 
A enin e m m en an am m tam no I 
  
  
6) Mathematical model 
  
  
  
  
   
  
  
  
|. 7) No information on storage capacity of soils 
| is available. Based on superficial lithology an 
|: approximation is introduced in 6) 
1 
7) Is required data available 
or can it be obtained? 
  
  
8) Calibration & validation or aa ae a ver ve mk Su eH po ee 
satisfactory? 9) Infiltration characteristics are altered. Flow 
1 
i 
I 
- | is modelled separately for flat surface (motor- 
9) Model is modified for the | way) and slopes. 7) is repeated: no detailed in- 
1 
1 
I 
1 
I 
  
  
  
  
  
  
presence of infrastructure formation on local slope modification is avail- 
able and a solution will have to be incorpora- 
ep 7) is repeate ted in 5) and 6) 
10) Qualitative reasoning OCIICDITODESEIIDOCIOCOOIOEDODOOÓE 
Do predictions make sense? 11) Predictions are translated from soil loss in 
I 
1 
! grams per modelled time interval to useful agri-i 
! cultural life of a plot in years. 
  
  
  
  
  
  
  
  
  
  
  
C 11) Translation of impacts 
  
  
  
  
  
Figure 3. Methodological sequence for the development of an EIA specific hydrological model(the numbers between 
parenthesis in the text correspond to the boxes in the figure) 
Land disturbance and runoff will affect soil erosion and the consequent change in channel sediment load. This effect is likely 
to be enhanced by channel erosion, which could increase directly as a result of modifications by roadworks and indirectly by 
the increase in streamflow. The net result will be alteration of suspended load in channel, with the consequent decrease in 
water quality for aquatic life. Changes in sediment load will affect channel and reservoir siltation. Chemical pollution of 
surface waters is also likely to occur, due to operation of machinery and use of a variety of chemical substances during the 
construction period. Most of the effects described are likely to disappear when the construction phase is over. 
During the operational phase, the main impact will probably be increase and diversion of runoff (a significant area will be 
covered with asphalt). Overland flow will be diverted, either by the construction of ditches and gutters, or indirectly due to 
landform changes which introduce barriers, depressions, small valleys, etc. The pattern of runoff and channel discharge will 
be altered. Although overall discharge of main water courses is unlikely to be significantly affected, changes could be 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII Part B7. Amsterdam 2000. 179