چكيده لاتين :
Introduction
Water and soil are the most important natural resources in the any country and considered base of sustainable development, especially in the agriculture category. All natural and human factors that threaten these resources are discussed as the soil erosion. Soil erosion is make soil the poorer and decreased fertility and caused to sedimentation in the streams, behind dams and etc. The effect and signs of erosion are seen in most areas of Iran. Director General of soil conservation and erosion control, estimates erosion amount of in the Iran country is 15 ton/hectare/year.
The study area is the Sulachai watershed with an area of 45 KM2 is situated in the east Sula village. In the study area, the problems such as: the development of the indiscriminate dry lands, tillage of nonsystematic (vertical on the contour of slope), livestock excessive grazing, excessive exploitation of the soil for agriculture and creation the communication network has exacerbated of soil erosion area and is necessary studies soil erosion and sedimentation
Methodology
The main objective of this research is the estimation of soil erosion and sedimentation in the Sulachai watershed with using WEPP and EPM models and assessment the effectiveness of each model in the study area. Therefore, considering the nature of the research subjects, its methods are the morphometric, fieldworks, experimental and laboratory. Therefore for doing that was performed the following four stages:
A. Collection and reviews of books, dissertations, papers and any subject related to research subject.
B. Observations and field surveys, collected samples, doing measurements and laboratory works.
C. Calculations, processing, analysis and data in computer.
D. The final provide reports
Results and Discussion
WEPP model has three methods which are slope, catchment area and flow-direction. Factors needed to calculate the erosion and deposition of any of the three methods are: climate, soil, management, topography and drainage. Parameters were examined for climate file including: monthly precipitation average, rainfall standard deviation, rainfall skewness coefficient, The probability of a wet day following a wet day, the probability of a wet day after a dry day, minimum temperature the average, minimum temperature standard deviation, maximum temperature the average, maximum temperature standard deviation. For soil factor were examined such as: clay percent, sand percent, rock percent, organic matter percent, catiuon exchange capacity, soil texture, effectively hydraulic conductivity, critical shear, rill erodibility, interrill erodibility, initial saturation level percent and albedo percent in soil samples.
Management and vegetation cover file is including a series of management practices, plant characteristics and tillage methods used in the region. To build this file were studied information related info the three parameters management and operations performed on, initial conditions and the physiological and phonological characteristics the most plant.
Drainage file also is contains information such as: the drainage soil, the drainage slope, drainage management and drainage type (drainage shape, the friction gradient, control section type in drainage output, edge slope and etc.
After the preparation of and entering data above files in software, was developed drainage and slopes leading to each drainage by the GEOWEPP software and was implemented WEPP model through GEOWEPP software. In the end erosion and sedimentation was obtained for methods to available at WEPP model.
The estimated the amount of sediment produced using EPM model, was performed in two stages: 1- The determination erosion intensity the coefficient and its qualitative classification and 2- Calculation shipped the sediment.
Conclusion
The amount produced special the sediment in Sulachai watershed by any of the methods available in WEPP model namely slope, catchment area and flow-direction Respectively Were estimated 0.213, 0.178 and 0.785 and so by EPM model were estimated 0.033 ton/hectare/year. The amount observed sediment also using the gradient discharge and sediment were estimated 0.241 ton/hectare/year. The results of comparison of WEPP model with observed sediment suggest that from among the methods available in WEPP model, initially slope method and then catchment area method is a closer to amount observed sediment and have offered a more acceptable results than to flow-direction method. But the flow-direction method is not suitable method because of the large variation with amount observed sediment. Also the results of sediment estimate with EPM model suggest that this model is very different with observed sediment. In sum, we conclude that the WEPP model have a higher performance than EPM model in the estimate erosion and sedimentation Sulachai watershed.
