Water Supply and springs in Central Italy.

In central Italy, a large percentage of the water supply comes from mountain springs in calcareous areas. For example, roughly 70% of the water supply of Rome comes from springs in the Apennines. This is due to the fact that spring water is of good quality (the recharge zones are located in mountain areas with few inhabitants), it is easily obtained and distribution costs are rather low, since the springs are often found at high elevation. Given that water needs continue to rise, and that the majority of alluvial aquifers are already over-utilized and are often polluted, the use of mountain carbonate aquifers and springs is steadily increasing. This leads to the drying up of many springs or to a decrease in the flow of many streams originating from the springs, with serious environmental consequences. There are essentially three systems for drawing spring water: drainage tunnels, vertical wells and sub-horizontal drains. The traditional system is that of drainage conduits, which have high initial costs but low maintenance costs. Wells, which are used especially for springs having small dynamic reserves in comparison with their geological reserves, have the advantage of providing practically constant flows: during periods of low natural flows, the wells draw from the geological reserves. However, if the mean amounts being drawn are not carefully regulated, the geological reserves are depleted in a relatively short period of time, and as a result the springs remain dry for long periods. Sub-horizontal drains consist of a chamber with a bottom lower than the elevation of the spring. Sub-horizontal drains sloping down radiate from this chamber towards the spring for a distance of 150 - 200 meters. The drains have valves for controlling the flow of water, which is collected in a reservoir and then distributed. These systems have a rather high initial cost but offer the following advantages: they draw water from below the water table, and thus it is always filtered and clear, even after heavy rains; no electricity is needed to draw the water from the aquifer; the water drawn cannot exceed the mean aquifer recharge; large land areas are not needed for well fields. Regardless of the system used for drawing water, the main problems connected with spring management are the following: a) the vulnerability to pollution: being fed by carbonate formations with permeability from fracturing, these springs are potentially very vulnerable; b) the difficulty of constructing reliable mathematical models: this is due to fact that data from pumping tests and potentiometric data are usually not available: also, because of the fracturing, it is difficult to estimate the real flow velocities and in calculating the protection zones.