Investigating the Effects of Hanna Dam Construction on Long-Term Land Use/ Cover Changes

This study aimed to evaluate the effects of Hana’s dam (constructed in 1996) on land use and cover changes using Landsat satellite images. Three images over 35 years (taken in 1976، 1998، and 2011) were obtained and geometric، atmospheric and topographic corrections were applied. The dam’s affected area was selected based on the interpretation of satellite imagery and local expert knowledge. Maximum likelihood and post-classification techniques were used to detect land use/ cover changes and their accuracy then was assessed using field works. The overall classification accuracy and Kappa statistics for all the maps were more than 83% and 79%، respectively. The classification map of year 1998 indicated that about 703 hectares of rangelands and agricultural lands were destroyed due to Hanna dam construction. In year 1998، the agricultural irrigated lands increased about100% due to Hanna dam construction in 1996 but in 2011 their extent decreased up to 69% and 36% in comparison with year 1998 and 1976، respectively. There was also a decrease about 10 percent in rangeland land use from 1976 (195906 ha) to 2011 (176827ha). The results of 2011 classified map revealed that 425 hectares of the water reservoir has changed to bare land because of severe drought conditions and over-exploitation in recent years. Overall، the results confirmed that in a short period of time after dam construction، the extent of agricultural irrigated lands has been increased، but a sharp decline was observed in agricultural areas after 15 years which can be as a result of population growth and water consumption in residential، commercial and industrial sectors in the region.