Estimation and Zoning of Soil Erodibility Factor in Aliabad Watershed, Roodbar, Guilan Province

Soil erosion in upstream areas has an important role in sediment entry to dams. Sediment accumulation result in decreases of dam service life, environmental problems, and acceleration of floods. In addition to climate, topography, vegetation cover and land management, soil erosion amount depends on soil characteristics and its erodibility.  In this research, soil erodibility factor and its special distribution was assessed by using of various pedotransfer functions including KUSLE, KEPIC and KDg in a part of Aliabad watershed of Roodbar, located at upstream of Sefidrood dam. The soil samples were collected from 0-10 cm depth and size distribution of soil primary particles, organic carbon content, and aggregates stability were measured. The KUSLE was calculated in two ways without codes of soil structure and permeability, and with respective codes, named as KUSLEi, and KUSLEf, respectively. The results showed that studied soils generally had coarse texture, and KUSLEi was estimated low to moderate in range of 0.11 to 0.040 ton h MJ-1 mm-1. The least soil erodibility factor belongs to KDg, which was significantly lower than the soil erodibility factors calculated by other pedotransfer functions. All of the calculated erodibility factors had significant negative correlation with mean weight diameter of aggregates which KUSLEi and KDg showed the most and least correlation with MWD, respectively. All of the erodibility factors had moderate spatial dependence, however KUSLEi showed strong spatial dependence. Therfore, it generally can be concluded that zoning map of KUSLEi  generated via kriging can be a suitable indicator of the studied soils erodibility.