A HISTORICAL REVIEW ON THE QANATS AND HISTORIC HYDRAULIC STRUCTURES OF IRAN SINCE THE FIRST MILLENNIUM B.C

In order to review the situation of Qanats and Historic Hydraulic Structures in the course of the Iranian history, this paper explores some documents on these structures from the first historical records to the present ones. To do so, we try to review the situation of qanats and historic hydraulic structures keeping pace with the history of kings and governments. First of all, it seems necessary to take up some facts on the geographical and climatological conditions of Iran, for the natural infrastructures had an important role in creating and developing the qanat systems. Suffice to say Iran has a variable climate, and In general, this country has an arid climate in which most of the relatively scant annual precipitation falls from October through April. In most of the country, yearly precipitation averages 250 millimeters or less. The major exceptions are the higher mountain valleys of the Zagros and the Caspian coastal plain, where precipitation averages at least 500 millimeters annually. In the western part of the Caspian, rainfall exceeds 1000 millimeters annually and is distributed relatively evenly throughout the year. This contrasts with some basins of the Central Plateau that receive 100 millimeters or less of precipitation annually.