Water Erosion and Sediment Production Status in Iran: Statistical and Comparative Analyses

The erosion data collected by plots and Cs137 methods as well as gauged river sediment yields (about 1000 places countrywide) were studied. Due to the large differences in the range of recorded data within each method and between the methods and the limited data compared to the large size and diversity of the country, it was necessary to find a suitable technique for scientific interpretation of these results. The median was selected as the most appropriate erosion/sedimentation measure of center. The median sediment yield rate of the measuring sites, which are mainly located in the mountainous areas of the country, was estimated at 336 t/km2/y. Using EPM estimates corrected by the observed sediment yield data, the country's total annual erosion is approximately 900 million tonnes (550 t/km2). Whereas, soil losses of about 300 plots in the rangelands, forests and drylands are often much less than 100 t/km2/y. In contrast, up to about 3,500 t/km2/y were measured on marl formations. Due to the large differences between erosion in plots and river sediment yields, it is likely that sensitive formations, dryfarming, gullies, landslides and streambank erosion have a greater role in sediment production. Limited sediment source studies also confirm the greater contribution of deep erosion features. Finally, by examining worldwide erosion/sediment yield maps and some global data, it was shown that despite the presence of erosion hot spots and basins with high sediment production in Iran, there are areas with much more critical conditions in Asia and the world.