Death time estimation of water heritages in Gonabad Plain, Iran

摘要

A Qanat is a hydraulic structure for the extraction of the groundwater using only gravity force without need to apply external force through pumping. The deepest and oldest Qanats in the world are located in the Gonabad Plain in the Razavi Khorasan Province, east of Iran. Qanats have been the most important approach for groundwater extraction and survive in arid region such as the study area for thousands of years, but they are disappearing because of climate and human factors. In the present research, descending trends of flow rate of four historical Qanats (i.e., Rahn, Baidokht, Kheshuie and Qasabeh) of the Gonabad Plain have been studied and analyzed using discharge values of the Qanats over the last 33 years. Effective factors on discharge values of these Qanats have also been discussed. The analysis indicated that the amount of precipitation in the study area and its mountains has decreased significantly since 2000. Moreover, because of drinking demand and traditional agriculture consumptions, the amount of annual groundwater extraction through deep wells has increased since 1960 and its amount reached 12 million cubic meters. As the groundwater drawdown increases, the water-bearing zone of the Qanats will decrease and the Qanats will dry gradually. The annual groundwater level drawdown in the Gonabad Plain is 0.1 m per year. The discharges of the different Qanats in the Gonabad Plain have been dropped from 38 to 9 L/s during the last 33 years. The results indicated that the discharge reduction of the Qanats is 4-14 L/s due to one meter groundwater level drawdown. As the groundwater drawdown continues with the current rate in the Gonabad Plain, these valuable water heritages will perish over 9-157 next years for the aforementioned Qanats. To prevent the destruction of the Qanats, it is suggested to reduce 7.2 MCM of groundwater extracted through wells by optimal use of water and prevent the development of agriculture and industries that need water in the Gonabad Plain.