Alkema, Dinand 
  
Data preparation 
A geomorphologic map was made both by using fieldwork data (raw data) and stereo-photo interpretation. A landcover 
map was derived from the satellite images and the aerophotos (Genelletti 2000) (fig. 6). The topographic map was used 
to obtain an infrastructure map together with additional information from the Urban Planning Office of the 
Autonomous Province of Trento (P.A.T.). Digital stereo-photo processing techniques were used to reconstruct a DTM. 
The geomorphologic map was used in several ways to obtain the required input data for the model. Firstly it was used to 
derive the dyke failure hazard map, based on the considerations that the dyke failure (of a dyke of uniform quality) is 
most likely to happen for the following reasons: 
e just after a curve where water with the maximum velocity hits the outer bank (where erosion is usually severest); 
e where the dykes cross paleo-riverbeds; these are infamous sites for piping (a subsurface process that may cause 
dyke-instability); 
e at the confluence of two rivers. 
Secondly it was used to derive an indicative infiltration map. It is indicative because it is based on the assumption that 
geomorphologic units, that have a common genesis, will have similar hydrologic properties. Furthermore, the 
infiltration rates are estimated values. It allows to estimate the interaction between surficial floodwater and 
groundwater. Thirdly is was used to create a detailed DTM, together with data from the coarser DTM derived from the 
aerophotos. The Digital Terrain Model was further modified to reach a satisfactory level of detail by adding information 
of the infrastructure, to include the available cross-section of the river Adige and to add the height and sizes of all build- 
up structures (houses and industry) (see fig. 7). 
Fig 6. The landcover map was derived from a satellite image, using aerophotos to delineate suitable segments 
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The landcover map was used to derive the bottom friction map. This map shows the spatial distribution of Manning’s 
friction parameter (Selby 1989). It is a measure of the resistance that the various land-cover elements pose on the 
floodwater propagation. 
The infiltration map is considered as a water-loss map. Per time step a certain amount of water is taken from the vertical 
waterbalance of each pixel. Temporal variation of the infiltration loss (because the soil eventually will become 
saturated) is not taken into account due to limitations of the software. 
Infiltration allows to link the flood process with the water table. Floods may cause the uncontrolled distribution of 
hazardous materials, and thus, through infiltration, important aquifers may be polluted. 
The discharge and waterlevel data were used to retrieve the Q-h relation (waterlevel as function of the discharge) using 
data of the Hydraulics Service of the P.A.T. (fig. 8). 
1966 vs. 1997 
Data with the specific lay-out of the new motorway are not yet available. 
Therefore the present infrastructure is used as a training set. For the simulations the hydrologic conditions of November 
5th 1966 were used, when large parts of the studied area were flooded. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 59