L'uso di modelli digitali del terreno come strumento per lo studio dell'evoluzione morfologica dei corsi d'acqua: proposte metodologiche e primi risultati

Abstract

Lollino G. et al., DTMs comparison methodology as a tool for studying morphological river evolution (IT ISSN 0394-3356,
2008).
The availability of new instruments for large area survey activities such as LIDAR gives, perhaps for the first time, the possibility to make Digital Terrain Model (DTM) of rivers and other geomorphological contexts. The high geomorphological complexity of rivers and the necessity to also carry out surveys of the submerged zone, make this context very complex.
For this reason the exclusive LIDAR use is not always enough and often the use of other survey instrumentation is necessary to obtain a high resolution (2 - 8 point per meter) river DTM. As for other recent instrumentation, also for LIDAR standard survey methodology is
still not available. From this point of view, there is probably the necessity to try to define possible relationships between survey
methods and morphological river characteristics, for example, at Po Basin scale. The experience conducted by the CNR IRPI of Turin
in this field has so far allowed us to recognize a possible relationship between river morphology and surveying methods. Such a
hypothesis, until now experimental, has been made due to years of experience in the field of stream surveying using such techniques
and this data typology. When a DTM is calculated, it is then in fact possible to use different applications: starting from the more simple
such as topographical river section extraction, to arrive at the most complex, such as a digital model comparison carried out at different times on the same river bed areas. The goal of such comparisons is to recognize and measure variations which occurred, through the creation of a management and treatment data methodology that implies specific knowledge in both topographical and in the geo- morphologic field. The comparison process here proposed is not in fact a simple computational exercise but a path based on a series of steps where a control and validation from a geomorphologic point of view, through a digital ortophoto analysis, is taken during the LIDAR survey. In this way it is maybe possible to place along side the studies conducted using topographical sections, a new areal approach (through regular grids with a footstep of 1m2), that takes into consideration the whole river bed.
In the light of collected results and partly shown, such methodology seems to be able to underline recent variations of a water course with an high degree of reliability and to create a new study methodology to commonly combine those already used by the scientific
community. The use of geographic information systems, thus, also allows us to create an unambiguous database in which, keeping in
mind the enormous differences, data coming from the historical cartographies, with the variations which occurred in the last 3-4 years, can be imputed; the final goal is to create a more exhaustive scenery using all the available information from a multidisciplinary analysis point of view of a river domain. The aim of this research is not only to define the DTM comparison methodology, but also to evaluate the best way to do them: the necessity to use not only the LIDAR but also some instrumentation to carry out the DTM of submerged areas (single beam, multibeam, side scan sonar) required the possibility to define a survey methodology that assigns the relationship between river morphology and survey activity.