Geomorphological Impact Assessment in the River Mincio Plain (Province of Mantua, Northern Italy).

The research takes into account the landscape modifications induced by man's activity in the past 40 years in the sector of the River Mincio plain located between the Pleistocene morainic hills of Lake Garda to the north and the Mantua lakes to the south. From the geomorphological standpoint the study area is comprised within a stretch of territory made up of the outwash plain deposited by the paleocourse of the River Mincio and the wide triangle-shaped depression cut by the Mincio itself, north of the city of Mantua. The morphological setting within this depression is characterised by several scarps of varying height, mainly developed in a N-S direction, which form various orders of terraces. The study includes a detailed bibliographical research, the examination of maps and of aerial photographs taken in different years and a morphological survey carried out in the present day. The plain sector considered has been subjected to intense quarrying activities since the beginning of this century, because the outcropping sediments have good characteristics as building materials. Indeed, the outwash plain and the terraces inside the Mincio erosional depression are mainly made up of rounded coarse gravels. From a petrographic viewpoint, carbonatic, magmatic and metamorphic rocks are present in various percentages. On the contrary, in the present R. Mincio alluvial plain sandy sediments with a dominant carbonatic component are found, which are the most recent deposits. The open quarries are classified as trench quarries exploited above the water table and trench quarries exploited below the water table. The first-type quarries are excavated only up to a depth of a few metres below the original ground surface and, in any case, up to about 1 m above the maximum level of the water table. When no longer in use, these quarries are reclaimed for farming after the laying of a pedogenised level of organic soil on their floor. The second-type quarries can reach a depth of up to 20 m and when no longer in use are abandoned or in some cases used as occasional dumping sites or equipped for recreational fishing. All these quarrying activities have caused relevant landscape changes. The trench quarries above the water table appear as large, deep rectangular holes, which impress an "artificial" look on the area affected; also the trench quarries below the water table have formed several small ponds which are extremely different in shape from natural bodies of water (moreover, the interception at ground level of the most superficial aquifer causes potential pollution hazards owing to the possible uncontrolled inflow of waste materials). More in general, quarrying activities have implied the partial or total obliteration of relict fluvial landforms, such as terraces and paleo-riverbeds. The reclamation of the quarrying areas implies their restitution to farming practices, according to management criteria based on the safeguard of natural assets and landscape values. Another aspect of man's activities during the past decades concerns the construction of important artificial canals (Scaricatore Pozzolo-Mincio and Diversivo Mincio) which, besides modifying the natural flow of both surface and sub-surface waters, have altered the natural morphological features of the areas affected. In this research a simple methodology for the assessment of the scientific quality of landforms was applied. According to this model, the scientific quality for each element of the landforms is given by the product of their intrinsic scientific value and their condition of preservation. The impact on the landscape is defined as the reduction in scientific quality due to the assessment of the degree of damage produced by man's activity in the past 40 years.