Flumendosa river basin (1824 Km²) is located in the central-eastern part of the Island of Sardinia. It includes three interconnected reservoirs (Flumineddu-Flumendosa-Mulargia) which together with other interconnected reservoirs, located outside the basin, constitute the Flumendosa-Campidano hydraulic system (Figure 2‑2), the most important and complex in Sardinia. The reservoir system supplies water resources for civil, agricultural, industrial and hydroelectric purposes not only inside the basin but mainly outside in Campidano plain (Southern Sardinia), including the biggest City of Cagliari.
The soils of the basin are generally of modest thickness with frequent rocky relief due also to erosive phenomena. Soil humidity, as well as rainfall, is highly spatially and temporally variable, and in the driest months the soil wetness in large parts of the basin reaches residual values. These soils have been characterised in detail (Figure 2‑3).
As for geomorphology, shaly rocks characterise the basin almost entirely, determining scarce permeability, low infiltration losses and high runoff.
Flumendosa reservoir, which crosses the central part of Sardinia, has a sharply elongated form, with a length of about 17 km and a maximum width of about 500 m, reflecting the canyon morphology of the Flumendosa valley; accordingly, this artificial lake has an average depth of 35 m and its maximum capacity is 316M m3. Flumendosa reservoir is the most important water collector of the system and receives water from Flumineddu reservoir by means of an artificial tunnel. A few main tributaries and small streams cut the steep flanks of the valley along the entire reservoir, and drain several rock complexes of different ages and lithologies. These complexes include a Palaeozoic crystalline bedrock covered by Mesozoic and Tertiary marine sediments, as well as by Quaternary basalts. Palaeozoic terrains comprise terrigenous sequences, with interbedded carbonate lenses and calc-alkaline acidic volcanics (“porphyroids” AUCT), intruded by Hercynian granites. All sedimentary and volcanic sequences suffered folding and regional metamorphism, as well as thermometamorphism induced by granite intrusions with formation of shales, micaschists, gneisses, marbles, hornfelses, and skarns. Permian terrains locally cover this metamorphic complex. The Mesozoic series includes basal conglomerates, clays, and a thick carbonatic complex. At the southern borders of the basin, Eocene conglomerates and limestones occur discontinuously, followed by a continuous cover of Miocene sandstones, marls, and limestones. Ore mineral occurrences in Palaeozoic terrains include skarn-related, mixed-sulphide and magnetite occurrences, sulphide disseminations in “porphyroids”, and quartz veins containing variable amounts of sulphides and barite. Minor concentrations of pyrite, with traces of other sulphides, occur irregularly in the Mesozoic clays associated with plant remnants.
Sulphide minerals include base-metal sulphides and minor sulphosalts; magnetite-rich ores also include variable amounts of sulphides, as well as minor quantities of hematite. Small amounts of tin and tungsten minerals also occur in skarn-related mineralizations.
Near the outlet of Flumendosa river in the Thyrrene sea, the presence of an alluvial plain (Muravera plain) with porous aquifers allow groundwater withdrawal for civil and agricultural purposes. The Muravera plain is formed mainly by layered horizons of gravels, sands (from silty to coarse) clay and silt, interbedded in a very chaotic way. The plain morphology is characterized by a sub – horizontal surface, somewhere slightly sloping into the east direction towards the sea. In the vicinity of the coastal line a canal of 7 km of length is located and some other small canals (called foxi) cut the topographic surface getting inside the plain, representing the old mouths of the Flumendosa River. The plain is bordered by the sea in the East direction, and in all other directions mainly by paleozoic metamorphic and sedimentary outcrops. The thickness of the alluvial deposits of the plane ranges between a few metres near the border with the paleozoic formations and 50 – 60 metres in the coastal sector. As said before, the plain is interested by the presence of a multilayered aquifer. It is possible to identify a shallow unconfined part of the aquifer and a deeper portion of the groundwater flow field, which is characterized of semi – confined to confined conditions. The confinement conditions of the aquifer in its deepest portion vary greatly in function of the local presence and stratigraphic continuity of the clay and silt horizons, and the presence of wells drilled and conditioned not to assure the complete separation of the deepest confined layers of the aquifer from the shallow unconfined ones.
Land use is largely influenced by grazing: natural pastures have great extension to satisfy large sheep requirements and a lot of cultivated lands are dedicated to the production of pasture for breeding. Many areas have been reforested and in the northern parts of the basin, natural vegetation cover is still present with a mixture of bare soil, grassland, shrubs, and forests.
The Flumendosa and Mulargia reservoirs are fed by Flumendosa River and Mulargia stream which are characterised by rapid changes in water flow due to the particular climate trend.
Inside the basin there are no protected areas. As for wetlands there is the San Giovanni lagoon near the Tyrrhene Sea which is exploited for fishing. Outside the basin in Campidano plain there are two very important lagoons Molentargius and Santa Gilla which are protected by the RAMSAR convention.