Le risorgive nella pianura parmense e piacentina

Springs in the Parma and Piacenza plains

Abstract

Attention is drawn to spontaneously occurring water sources or underground springs in the W Emilia plain at a time when the safeguarding of fresh water is becoming a matter of increasing importance. The study is based on information concerning the Quaternary sediments constituting the subsoil of the plain. Factors responsible for the establishment of areas rich in springs are identified. The outflows (sometimes considerable) are quantified, and the chemical purity of the waters concerned in assessed. The throwing out of spring waters may be said to depend on three different causes: a) Uprising of deep water due to reduced permeability of downstream sediments; this is the most frequent situation. Springs formed in this way are distinguished by their relatively constant flow, comparable to that of deep aquifers that only display to effects of changes in precipitation after a long interval; constant temperature with no seasonal variations; chemical data within regional potability standards. b) Tectonic changes in the seafloor, with upheaval of nearly to the surface of impermeable formations that bar the progress of underground streams. c) A few groups covering very limited areas appear to be clearly associated with the “water table”. Here the outflow is inconstant and a function of precipitation; the temperature is also influenced by the outside environment. The substance and conclusions of this paper must necessarily be brought within the context of earlier work on the deep aquifers of the plain that has gone beyond schematic and theoretical determination of the geological features of the Quaternary alluvial cover. This stage of the investigation clarified both to dynamics of these underground waters and their feed mechanisms, and led to the abandonment of insufficiently checked and hence uncritically applied patterns. In particular, the concept of a water table as a continuous unit extending over a large area, and capable of interception by means of drilling to virtually a constant depth, has been rejected. The new model is the fruit of a huge quantity of geological, hydrological, and geophysical data. It presents aquifers whose geometry is completely lacking in regularity, due to the chaotic distribution of clasts in the alluvial cover. This detailed information made it unlikely from the outset that a single water table existed, and hence a wholly phreatic supply for the springs. The data made it increasingly evident that the classic model, in which springs are attributed to a simple intersection between a continuous water table and the topographical surface, was inapplicable to this type of alluvial plain. By contrast, the marked flow rates, slight seasonal variations, distinct degree of artesianism, temperature, and chemical characteristics of these waters combined to suggest that they were of deep origin. Lastly, it should be pointed out that, even in this restricted area, distinctions could be drawn between groups of springs whose local geological situations were so different that no correlations could be determined, nor could a single classification be worked out.