عنوان مقاله [English]
Regarding the importance of water resources in arid and semi-arid regions, and also, sediment and soil erosion problems, it is necessary to explain proper management. Soil erosion and sediment yield are among the major limitations in the use of water and soil resources. For this reason, the objective of this study evaluate MPSIAC and WEPP models in predicting erosion and sediment and one of the sub basins gojan chalnamad watersheds. In this study, at first, all of the factors of the both models were collected and measured in each of the land units. Then, the files of each of the parameters of the model were made and calculated special sediment load. Sediment amount was estimated by the WEPP and MPSIAC models respectively 4.14 and 9.1 tons per hectare per year. With the amount of sediment (5.27 tons per hectare per year) and in comparison with the amount of sediment estimated by two models and data analysis, the results showed that WEPP model With 21 percent relative error in the estimation of sediment, with less error is estimated and estimate the amount of sediment has closer special observation sediment and the MPSIAC model to estimate sediment 72% relative error, the error estimate is over. The overall results showed that the WEPP model is better than the MPSIAC model to estimate sediment.
Soil is formed complex processes that affect of the five main factors: climate, topography, parent material, vegetation and time. If the desirable of four main factors, long time is required for soil formation. Since, soil and water are the most important factors in ensuring human needs. The lack of maintenance of these will import damages. The main reason for degradation of water resources and soil disturbing the natural balance an area, it is the main cause of human manipulation and intervention. Since the soil erosion and sediment was one of the most natural complexes processes and many factors are involved, so it is very difficult an understanding of the factors in this process. MPSIAC model is an experimental model that the amount of erosion and sediment evaluated using the 9 key factors quantitatively. But this is not process model, while erosion and sediment yield for a process occurred. WEPP model is a new product of technology to estimate erosion, that in addition to abilities universal equation, it has been added many other capabilities.
The study was carried out in the gojan chal-namad watershed, in the Chahar-Mahal-va-Bakhtyari province in Iran located between latitudes 32°11´ 26´´ and 32°16´34´´ N and longitudes 50° 24´46´´ and 50°32´11´´E. The study area was about 330.6 hectares. The soil moisture and temperature regimes of the region determined by means of Newhall software are Xeric and Mesic, respectively. The soils were classified according to the USDA classification system as the orders of Entisols, and Inceptisols.
In this study, the homogeneous regions map was prepared in Arcgis software from geological, topography, and geomorphologic land forms layers, then data of WEPP and MPSAIC models have collected.
Results and discussion
The simulation results of erosion and sediment in the form of hillslope of watershed showed that the amount of special erosion, total erosion, and special sediment and total sediment using WEPP model with 7.7ton/hac/yr, 2535.8ton/yr, 4.4ton/hac/yr, and 1370.4ton/yr, respectively.
The amount of sediment estimated using the WEPP and MPSIAC models, 4.4ton/hac/yr and 9.4ton/hac/yr respectively.
A comparison of WEPP and MPSIAC models with the amount of sediment observation showed that WEPP and MPSIAC models have 21% and 78% error in estimating sediment respectively.
According to the results of this research, however MPSIAC model uses more variable to estimate sediment yield, but the estimate of this model 1.7 times the amount of observed sediment and it has about 72% error in the amount of observation sediment. Although WEPP model has about 21% error in the amount of observation sediment. Generally using the WEPP model to estimate the amount of erosion and sediment nearer to the observed results presented.