Evaluation of the Watershed Management Structures in Sediment Deposition in Khor-Sefidarak, Fashand and Azimiyeh Watersheds of Alborz Province

The aim of the current study is to evaluate the effectiveness of the watershed management operations by using the quantitative values obtained from the field survey in Khor-Sefidarak, Fashand, and Azimiyeh watersheds, and indicating a clear result of deposited sedimentation rate and vegetation improvement in reservoir tank of the structures. Field evaluation of watershed management structures showed that since 1991, a total of 652 gabion structures, 20 masonry structures, 533 small stone structures, and 15 embankment dams have been implemented in Khor-Sefidarak, Fashand, and Azimiyeh watersheds of Alborz province. A study of the stability of the structures showed that masonry structures had the most stability with the least need for restoration (92% of them). Also, 80% of gabion structures and 83% of small stone structures in the studied watersheds were stable. The study of sediment deposition in reservoirs tanks of structures in the study area showed that a total of 332,100 m3 of sediment has been deposited and stabilized by the structures and has prevented its transferring to rural and urban residential areas. Of this amount, 45960 m3 have been deposited by embankment dams and 286140 m3 by masonry structures, gabion and small stone structures. Sediment volume to structure volume index showed that it was 4.4, 15.3, and 1 for gabion, masonry, and small stone structures, respectively. Evaluation of vegetation and tree cover development of whining reservoirs tanks of watershed structures showed that 4880 trees and seedlings (97% of all them) have been grown and developed in the reservoirs of gabion structures. If the gabion structures are constructed, it is suggested that they be constructed in non-stone beds, and cement cover be used to prevent their destruction.