Soil and Water Conservation for Desertification Control in Iran - Combating Desertification in Asia, Africa and the Middle East - page 364

Fig. 18.1 Iran has a large arid zone. It borders on the Caspian Sea, the Persian Gulf and several
Central Asian Countries to the east
surface geology, soils, climate, runoff, topography, ground cover, land use, upland
erosion and channel erosion was employed to estimate erosion and sediment yields
for watersheds without gauging stations. The results show that watersheds under
study have an average annual sediment yield of 750 t/km 2 and an erosion yield of
2,500 t/km 2 . The Karkheh, Sefid-rood, maroon, Hirmand and Zohreh watersheds
had the highest annual sediment yields with 1,409, 967, 779, 722, and 704 t/km 2
respectively. It is estimated that the average annual erosion rate in watersheds of
Iran is 20-30 times of the acceptable level. Intense erosion and sedimentation has
been primarily caused by: (i) over grazing (estimated 76 million sheep currently
being grazed on a land area with sustainable carrying capacity of only 26 million),
(ii) dry farming on steep slopes and deforestation (Fig. 18.2 ).
Available information indicates that 59 % from 17 watersheds of major dams in
Iran (about 8.8 Mha) are badly degraded. Further detailed studies are recommended
for soil erosion estimation in different regions of Iran.