SHAHROOD (IRAN) AND ITS WATER SUPPLY TROUGH THE QANATS

Shahrood is a city located on the northern border of Kavir desert (altitude 1345 m a.s.l.), along one of the main Silk Road paths, in the North-West of Iran, within the Province of Semnan (Fig. 1). Even if ,nowadays, water is supplied by a modern system of drilled wells and aqueducts, in the recent past, it was ensured by a complex qanats system; a part of it is still working and supplies more than one third of the water needs of Shahrood population (about 210?000 inhabitants). The part of the qanat still operational (Fig. 2) has a length of approximately 25 km; it is subdivided in two branches (Tash e Mojen), in the upper recharge area, each one has a length of about 5 km, then the two tunnels merge in a single main gallery, in which a pipeline has been placed to avoid stability problems and to safeguard water supply of the town (Fig. 3a). The hydraulic system was excaveted inside alluvial and eluvio-colluvial deposits along the valley, while the final part of the qanat crosses limestone rocks. At the qanat outlet, the original comb-like structure was preserved, it was used to split water flow among different users (Fig. 3b). Today, waters, downstream the outlet, are sent to the drinking water treatment plant, before entering urban pipelines. In the areas crossed by the qanat, there are several similar hydraulic structures, realized at different depths and along other directions in order to drain underground water as efficiently as possible. Along the last section of the qanat, where it exits from the main valley and enters a secondary one, it is possible to see several shafts, which directions are transversal to the one of the main qanat, converging toward a morphological notch in the limestone reliefs, that divides this valley from the plain where Shahrood lies (Fig 4a). These qanats were probably intended for agricultural water supply. The importance of this system, now abandoned, is justified by the presence of a large adobe building, probably erected to control the mentioned shafts and qanats(Fig. 4b). While the secondary valley is still of strategic relevance, since four water wells have been drilled to support qanat flow during drought periods. The large use of drilled wells, in the last decades, has driven into crisis the ancient sub-horizontal underground drainage system.