Generally speaking, the Region Friuli Venezia Giulia can be divided into three different bents that characterize its hydrological structure:

1. pre-alpine and alpine zone (thah includes the Alps, the Eastern Hills/Colli Orientali, and the Western part of the Karst/Carso Occidentale)
2. middle-high plan (mainly determined by large river conoids)
3. low plain (characterized by alternating river, lagoon and marine sediments, and including the lagoon areas)

In the pre-alpine and alpine zone it is present a diversified system of water bodies. It includes a developed underground hydrographic system, associated to karstic phenomena. Water bodies are mainly fed by superficial water and springs. And there are also some relatively small lakes, both natural and artificial. Water composition is quite variable, due to great lithological differences characterizing the several mountain basins.

The middle plan zone shows a large and very permeable gravel cover, fading to the north-east into the morenic apparatus of the Tagliamento River, and to the south into the lagoon and marine sediments. The gravel bed - that can be thick/deep as much as 700 meters - comes from the rapid erosion of the mountain basins that took place during the last glaciation. Deeply under this gravel bed there is a unique groundwater, that emerges to surface in the "spring water area" (area delle risorgive), where underground layers of impermeable clay force water masses to rise.

The low plain is a uniform flattened area. Its northern geographical border is represented by the "resurgence water area" - see photogallery - (area delle risorgive) (very much suggestive, in this respect, a visit to the resurgence waters and land within the Park of Villa Ottelio, just in front of the ETP aquarium, in Ariis di Rivignano), and the waters from the "risorgeve" bring to surface large amounts of water that feed streams, canals, trunks, and rivers.