Groundwater management of the upper Venetian plain. Improvement of monitoring network and geo-structural model through numerical simulations.

Abstract:

In this work we present a study dealing with the spatio-temporal behavior of a regional aquifer in north-eastern Italy, with the aim of obtaining a tool suggesting appropriate policies for the management of water resources affected by a changing environment.

The high quality of the water makes it suitable for human consumption. Consequently, hundreds of wells have been drilled for this purpose by both water service companies and private bodies. Moreover, the area is widely exploited for agricultural purposes (more than 60% of the surface), and the dense network of ditches that guarantees the agricultural requirements by border irrigation, is being converted to pressurized systems (sprinkler and drip). This conversion shows positive effects, reducing the requirement of water diverted from rivers and granting the respect of the Ecological Flows but, on the other hand, the infiltrating volumes that contribute to the groundwater recharge since centuries ago, are decreasing.

The study area (900 km²) develops north to south from the Prealps to the middle of the plain, between Brenta River (west) and Piave River (east), about 50 km far from Venice. Evidences from geological surveys show a sand and gravel aquifer extending from uplands in the north piedmont region to the southern one where a layered system of nine aquifers can be recognized. The beginning of the layered aquifer is usually assumed to overlap alluvial springs that origin the rivers Sile and Dese, that act as drains for the phreatic aquifer.

The 3D finite element model of the system has been developed using Feflow® by DHI. The spatial extent was chosen according to the availability of data – piezometric levels and/or fluxes – on the boundaries. A simple approach based on knowledge of piezometric levels and gradients in the artesian aquifers, together with boreholes’ data, was implemented to build a reasonable geo-structural model (Occam’s razor). Rainfall, irrigation, evapotranspiration and water withdrawal from wells or springs, and the flow exchange with rivers, are the considered forcing.

The numerical model makes us capable to provide preliminary indications on the management of water resources and to identify new measurement positions, improving the monitoring network and refining the geo-structural model also by topographical and geophysical surveys.