دانلود تحقیق آماده قالب pdf با عنوان مقالات انگلیسی خاک 13 ص

دانلود تحقیق آماده قالب pdf با عنوان مقالات انگلیسی خاک 13 صفحه

Iranian Journal of Science & Technology, Transaction B, Engineering, Vol. 30, No. B4

Printed in The Islamic Republic of Iran, 2006 

© Shiraz University 

INCORPORATING ROCK FRAGMENTS IN SOIL EROSION MODELS: A 

CASE STUDY, THE ANSWERS MODEL*

S. AMIN1** AND S. H. AHMADI2

1

 

Dept. of Irrigation, College of Agriculture, Shiraz University, Shiraz, I. R. of Iran 

Email: [e-mail] 2

Agricultural Research and Education Organization, Agricultural Eng. Research Institute, Shiraz, I. R. of Iran 

Abstract– Many researchers have incorporated the effects of rock fragments in soil erosion studies 

to improve the prediction of erosion by raindrop impact and overland flow. According to the Box-

Simanton approach, the effect of rock fragments should be incorporated into the crop factor of 

USLE, C, whereas the Poesen-McCormack and Sepaskhah et al. approaches include the rock 

fragments in the soil erodibility factor K. For this study we investigated which approach was most 

suitable for our research basins. This study is based on a comparison of observed sediment 

concentration data out of a representative agricultural watershed in the south of Iran with the 

output of ANSWERS model. Preliminary results reveal that there is no meaningful statistical 

difference between the Poesen-McCormack and Box-Simanton approaches. Nevertheless, when 

the runoff coefficient exceeded 0.3, the Poesen-McCormack approach was more accurate, but 

under high antecedent soil moisture conditions, the Box-Simanton approach gave more accurate 

results. Finally, a comparison of the Sepaskhah et al. approach with other methods showed that, in 

general, the Sepaskhah et al. method is more practical and reliable than the other approaches. 

Keywords – Rock fragments, ANSWERS, soil erosion, erodibility factor (K), crop and management factor (C), 

USLE 

1. INTRODUCTION 

In most soil erosion studies, particles larger than 5 mm are considered rock fragments [1, 2]. The role of 

rock fragments in protecting the soil surface against raindrop impacts is well known and has been well 

documented since 1943 [3, 4]. Rock fragments in the soil and on soil surfaces significantly influence 

infiltration, runoff, moisture storage, and land use [5-7]. Rock fragments protect a soil surface by 1) a 

reduction in soil erodibility by protecting the soil surface against raindrop impact and overland flow 

detachment, 2) a reduction of soil surface sealing, and 3) retardation of overland flow which results in 

lowering its shear stress and transport capacity [8]. Therefore, it is necessary to incorporate the role of 

rock fragments in soil erosion models, increasing the accuracy of the estimation of soil loss from arable 

lands and watersheds. 

2. BACKGROUND 

The removal of rock fragments caused increase of both runoff volume and rate and soil loss of a watershed 

[3, 4, 9]. Nyssen et al. [1] found that reducing surface rock fragments cover from 20% to 0% resulted in a 

threefold increase of soil loss. 

Several studies have been carried out to investigate how size [10], shape [11], and position [12] of

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