Mean annual rainfall for the entire basin is about 800 mm, which is higher than the mean annual rainfall of 775 mm over all of Sardinia. The rainiest months are November and December, and the most arid month is July. Precipitation patterns over the basin are non-uniform and highly correlated to topography, with 650 mm average rainfall below 200 m.a.s.l. and 1285 mm above 1000 m. The highest peak in the basin (and in Sardinia) is Bruncu Spina (Gennargentu) with 1829 m. The climate of the basin can be classified as humid Mediterranean above 500 m elevation and as sub-humid Mediterranean below 500 m. Losses are mainly due to evapotranspiration with low infiltration rate (due to the impermeability of the basin characterized by shaly rocks) and high runoff. In the figure below the max, min, average temperature, the humidity and solar radiation trends along one year are reported.

 

A characteristic element of Sardinian wildlife is the presence of the monk seal and the mouflon which, together with the Sardinian sparrow, are found only in this region. Vipers, badgers, wolves and bears do not exist and certain other animals, such as deer and foxes, have developed individual characteristics so diverse from the original species that they are to be regarded as purely Sardinian.

In Flumendosa basin, Gennargentu with its great forests and wild rugged morphology is an interesting environment that is almost unique in the Mediterranean, with vegetation that varies in accordance with the distance from the sea and the nature of the ground. Near Cagliari a wild impenetrable zone is famous for one of the last surviving herds of Sardinian fallow deer, found nowhere else in the world, and its wildlife includes wild boar, hares, foxes and the Sardinian wildcat, as well as rare birds, such as Bonelli's eagle, the golden eagle and the Sardinian partridge.

Sardinia is famous for its wetlands. Near Cagliari, Molentargius and Santa Gilla lagoons are wonderful examples of brackish ecosystems and are considered among the most important wetlands at international level, with an incredible concentration of variegate flora and fauna, in spite of the encroaching city. Water birds such as duck, waders and common species of brackish birds are present together with common gulls and the pink flamingos.

Sardinia is strongly influenced by the Mediterranean semiarid climate characterised by a long dry period followed by high rainfall intensities. In its water ecosystems, very sensitive to diffuse and point sources, every pollution event leads to a further reduction of water quality. The annual period of streamflow affect water quality of downstream water resources especially during the first flood events that follow the dry season. Floods can cause high transport of nutrients accumulated in the basin (overall particulate forms by erosion phenomena), that may cause eutrophication processes in recipient water bodies (reservoirs, lagoons). The results obtained by a recent survey (Sept 2003-Aug 2004) conducted by Hydrocontrol in the Mulargia basin (sub-basin of Flumendosa catchment) in the framework of TempQsim project (EU project, V framework programme), showed the importance of flood events in the sediment transport. Although, in terms of flow, the first flood represented only the 10% of the annual runoff, it resulted to transport into Mulargia reservoir more than the 30% of the total annual suspended solids load, while the total load was exported almost entirely during the episodic floods occurred in just 30 days a year. Active erosion in all basin favours an abundant accumulation of sediments in the reservoir. Materials accumulated include a major mineral fraction, from coarse gravel to silt and clay with associated nutrients, a minor organic fraction, including vegetal and animal debris, as well as an extremely various set of human products. Rythmic granulometric variations indicate cyclic water flow intensity variations, also related to seasonal migration of the “shoreline”, as well as with varying water depth.

The total storage capacity of all the hydraulic system of Flumendosa-Campidano is about 750 Mm³ and of this amount almost the 90% is stored in the Mulargia and Flumendosa reservoirs. The dams of the system and their storage capacity are reported below:

Water supplies structures:

The main features of the reservoirs of the system (regulating capacity, average runoff and average volume stored) are reported in the table below. It is possible to notice how the average stored volume of the dams is less than their regulating capacity.

The actual recharge of the aquifer in Muravera plain is mainly due to rainfall infiltration in the alluvial materials, with some more influx of lateral recharge. This phenomenon could be split into two components. The first one is direct lateral recharge from paleozoic rocks surrounding the plain, which constitute a low permeability aquifer but in which a groundwater flow system exist in the fracture system which characterize it. The second component is diffuse runoff on paleozoic rocks which cause infiltration of superficial water in areas in which alluvial deposits lay directly on it.

The main alluvial plain aquifer recharge, before upstream dams construction, was due to Flumendosa River, in particular when river flood interested the plain during high rainfall period in autumn and spring. After dams construction this phenomenon halted, causing overexploitation of groundwater coastal flow system, because groundwater abstraction at a high rate continued, being the aquifer the only water body available for drinking, irrigation and industrial water supply in the area, not supplied by reservoirs. No average groundwater recharge has been calculated so far for the Muravera-Villaputzu-San Vito plain alluvial aquifer. The only information available relates to groundwater abstractions for drinking supply (data from Genio civile, Regional Authority). In particular for Muavera Municipality the groundwater abstraction for civil uses is equal to 30 l/s, for Villaputzu is 50 l/s and for San Vito is 18 l/s. 

The main problems of surface water in Sardinia are linked to eutrophication phenomena due to their high sensitiveness to point and diffuse pollution sources which transport into the ecosystems high nutrient loads. In order to evaluate the degree of eutrophication surveillance monitoring is constantly carried out in the reservoirs. In the table below the yearly average values of the chemical and biological parameters analysed in the two main reservoirs of the basin (Flumendosa and Mulargia) are shown. The two reported values indicate the different concentrations in the surface and in the bottom of the reservoirs. From the analysis of the data below it is possible to highlight a eutrophic status for Mulargia while Flumendosa is meso-eutrophic. The presence of cyanophyceae blooms in Mulargia dam is an index of the possible presence of toxic microalgae.

As already explained, the aquifer recharge in Muravera plain, before upstream dams construction, was due to Flumendosa river, in particular when river flood interested the plain during high rainfall period. After the dams construction, this phenomenon halted, causing overexploitation of groundwater coastal flow system. Because of this lack of an important part of its previous recharge, the aquifer was interested in the last decades of sea water intrusion phenomena.

The water quality of the reservoirs of the hydraulic Flumendosa-Campidano system is checked constantly with the aim of classifying the water quality of resources used for drinking water purposes, in conformity with the law (152/99). The drinking water effluents treated in the potable plants are regularly analysed to check the conformity with the low 31/99 (which adopted the EU Directive 98/83).