Investigating the rate of soil erosion and sediment production using the RUSLE model and the modified method PSIAC (case study: kal basin of Ismail , Shahrood city, Semnan province)

Soil erosion and production of sediment load in the watershed has become one of the important environmental problems today, and therefore, Preventing its occurrence is one of the most important factors for protecting natural resources. Increasing soil loss in watersheds Watershed is a continuous challenge that is caused by the increase in population and the pressure on natural resources and unsustainable cultivation in soils and lands Slope causes a decrease in production in the land (Ahmad Abadi, 2017). One of the most important factors of soil destruction and fertility reduction is soil erosion, which is increasing nowadays and leads to Loss of good agricultural soil.

which is called the RUSLE relationship and is a function of six factors as follows:A=R*K*L*S*C*P (2) A: average soil loss per surface unit (tons per hectare per year) R: rain erosion factor, K: soil erodibility factor, L: slope length, S: slope degree, C: management factor Vegetation, P: Factor of soil protection measures This model is still the best available erosion prediction model that can be easily applied at the local level area to be used. In this method, using the DEM map of the basin in the GIS environment and having the factors RKLSCP factors, raster maps are prepared and finally, with the correlation of these maps, the soil erosion map is obtained. In the GIS environment, rain erosibility index maps (R), soil erodibility index (K), slope length index (L), Slope degree index (S) is prepared. Also, Landsat satellite bands 1 and 7 are used to prepare the NDVI map, Vegetation index (C) is prepared. - Third step: modified PSIAC

In 1968, the American Water Management Committee presented the Psiak method qualitatively. This model is based on the sum of 9 factors (X1-9) Effective on erosion, it gives the sedimentation of the basin, according to which the erosion class of the basin can be determined. In the year 1982 Johnson and Wegbhart took these factors numerically (Y1-9) so that the model takes on a quantitative state and its accuracy to increase Factors affecting erosion in this model include: lithology, soil, climate, runoff, topography, vegetation, Land use, the current state of erosion and erosion of Khanhai River. - Fourth step: preparing the necessary invoices:As stated, the revised global equation of soil erosion is an empirical model of soil erosion estimation based on the global equation. Soil erosion is designed. This model, in addition to being able to use data such as the physical characteristics of the basin and Meteorological stations can estimate the amount of soil erosion, it also enables the spatial distribution of soil erosion.

In this regard, in order to calculate the average loss of soil per surface unit (tons per hectare per year), the following factors were examined and calculated and prepared:- Slope degree: S=L* H/A S =541781.94*20/144538670=0.074 S=0.074*100=7.4 - Slope length:Basin slope length 16.03 square kilometers were calculated. Then, the erosive factors of precipitation, soil erodibility, slope length, slope degree, vegetation cover and protective measures were calculated and put in relation to the global equation as follows:R=8.86*0.376*0.72*7.17*1 R=17.197 Also, 3 factors involved in the modified Psiak model were calculated as follows and placed in the relevant section as follows:Q = 0253e^(0/036R) Q = 0.253*〖2.718〗^2.641 0.253×14.02=3.54

In this research, by preparing different layers of information, the state of sediment erosion and the amount of sediment production were determined. According Based on the amount of sediment production calculated and comparing this number with the sediment determination table, it can be said that the basin In terms of sedimentation and erosion, Kal Ismail Dara is in Class I and among the areas with very low intensity of sedimentation. The studied basin has a maximum height of 2000 meters and a minimum height of 1320 meters and in terms of topography (82.38) percent of the region includes, as well as the mountainous region with an area of 25.43 square kilometers, 17.61 percent of the basin includes In this research, using the Revised Universal Equation of Soil Erosion (RUSLE) (sediment erosion rate in the basin) 17.197 tons per hectare per year was obtained in Kal Ismail Valley, and other researchers used the same model for basins.They have calculated different figures. So that Artman et al. (2011) in Navroud, the rate of sediment erosionSediment erosion is 0-100 tons per hectare per year, Mousavi (2015) (in Shahroud-Miami, Mohammadi et al.) (2016) Taaler, Mahmoudi and Naqshbandi (2019) (in Gavshan dam, Arman et al.(2015) in TengSarkh dam, Mozbani et al.( 2021) In Sikan, the amount of sediment erosion was calculated as 2.31-68.185, 0-92.01, 35.2 and 62.17 tons per hectare respectively.Other researchers have also provided different figures for different basins using the PSIAC method. Rostaminia and Safarlaki (2017) In the Cham Gardalan basin, Eylamra 9.6, Alipour et al. (2016) in the Iver basin, 2.95 and Divasalari et al. (2013) in Solqan Qom, Nasiri et al. (2021) in Bakhtar, Qochan and Ghafari et al. (2015) in Cannes, the amount of sediment erosion They calculated 19.85, 4.5-84.2, 4.6-4.17 and 72.78 tons per hectare respectively. The basin of Kal Ismail Dara has an elongated shape