|UNDERGROUND CATCHMENT TUNNELS
Definition characters description and diffusion
Underground water devices, drainage tunnels which thanks to their horizontal development, they tap the microflows seeping through the rocks and when is it possible they drain off the upper part of the groundwater. Thus, they do not convey water from the springs or underground pools but create free waters acting as production systems. The technique of drainage tunnels dates back thousands of years and is adopted over a very large area stretching from China as far as Latin America, throughout Persia, Arabian Peninsula, Saharan desert, Spain, and Italy. This technique is very similar to the khottara of Morocco, the quanat or kariz of Persia, the madjirat of Andalusia, the falaj of Arabia and the magara of Jorden, although they have different characteristics. Very similar water systems have been found in Peru and in Mexico within pre-Columbian farm units called hoyas (Soldi, 1982).
General characters description and diffusion
The different depth, dimension, and integration of this technique with the open-air systems as well as its different use as water catchment or supply system especially depend on the geomorphology of the sites. The first documentary inscriptions on this technique date back to the Assyrian King Sargon II in the 7th century BC. The Greek historian Polybius (2nd cetury BC) refers to underground wells and canals dug out in the desert of Asia Minor and Vitruvius (1st century BC) describes, among 'the techniques to find water', the one based on the airing wells connected to each other by underground pipes. It is difficult to exactly establish if these systems come from knowledge dissemination or from reinventing processes in areas with the same physical characteristics. As a matter of fact, the construction of many ancient towns (Qana, Jericho, Jerusalem, Marrakech, etc.) was based on the building of these systems which allowed people coming from inhospitable lands to live and develop. In Italy, these systems have been discovered in Palermo, in Gravina di Puglia, in Laterza, in Taranto and in Tuscania. The tunnels that are dug parallel to the ground do not go down as far as the groundwater, byt they drain off the upper part. Thus, they prevent the aquifer from lowering and absorb the right quantity of water for the replenishment of the aquifer itself. Thanks to the heat excursion during the day, these tunnels function as pumps which attract vapor-laden air and produce water from atmosphere as air sources. In the past, this specialized and expensive technique employed a lot of labour in very hard work conditions. However, its spread and efficacy astonish still now and, in fact, is the only source of sustainable water supply in many areas.
Advantages and sustainability
This catchment of ground water through microflows and other sources is vital to human processes which make up communities and help communities survive.