Document Type : Research Paper
Authors
Soil Science Dep., Faculty of Agriculture, University of Tehran, Karaj, Iran
Abstract
Keywords
Main Subjects
EXTENDED ABSTRACT
One of the most important problems in the field of soil erosion research is the dependency of measurements and estimates on the scale. In recent years, several studies have been conducted in the field of soil erosion scaling, which resulted in development of some different models. This research was conducted to investigate the changes in sediment concentration and detachment rate in rills with different lengths under various flow rates in the field conditions.
The research was carried out at the Educational and Research Farm of the University of Tehran located in Karaj (35°48' N latitude and 50°57' E longitude). The average annual temperature and precipitation of the area are 14.2°C and 256 mm, respectively. The soil was a calcareous sandy loam with weak aggregate stability. The rills of 1 to 8 meters lengths and 5 cm width were artificially created in a plot with an area of 140 square meters and a slope of 5 percent after plowing and leveling. The experiments were conducted under two flow rates of 0.12 and 0.25 liters per second. Sediment concentration and flow rate were measured periodically for 30 minutes. The changes with time in sediment concentration were evaluated for different rills and under both flow rate. To scale rill erosion, the changes with rill length of the mean sediment concentration and particle detachment rate, both at three initial unsteady, final steady and total event conditions, were evaluated and modeled.
The sediment concentration was generally decreased exponentially with time from an initial relatively high level reached to an almost steady level. The initial flashing out of fine and pre-detached particles, and development of a deposited layer are the eventual reasons for decreasing sediment concentration. The changes with time in sediment concentration affected by both flow rate and rill length. The average sediment concentration increased linearly with rill length (spatial changes) at lower flow rate, and exponentially (reaching a certain limit) under the higher flow rate in all three conditions of initial unsteady, final steady and whole event. On the other hand, the particle detachment rate decreased exponentially with rill length under both flow rates in all three cases of unsteady, steady and total event averages. The particle detachment rate induced by flow decreases with increasing sediment concentration, mainly due to consumption of flow energy for transportation. The scaling equation developed by Ban and Lei (2002) was reasonably fitted to the data.
Soil erosion processes in rills are complex and dynamic affected by several factors such as soil type, flow rate and slope steepness, and as well by rill length. In general, the results of the current study confirmed the models and theories in which particle detachment rate in rills decreases exponentially with length.
Conceptualization, H.A., S.A. and A.D.M.; methodology, H.A. and S.A.; software, A.D.M.; validation, A.D.M and H.A.; formal analysis, A.D.M., S.A. and H.A.; investigation, S.A.; resources, H. A.; data curation, S.A.; writing—original draft preparation, S.A. and A.D.M.; writing—review and editing, H.A. and A.D.M.; visualization, A.D.M.; supervision, H.A.; project administration, H.A.; funding acquisition, H.A.
All authors have read and agreed to the published version of the manuscript.
Data is available on reasonable request from the authors.
The authors would like to thank University of Tehran for providing all the needed facilities.
The authors avoided data fabrication, falsification, plagiarism, and misconduct.
The authors declare no conflict of interest.
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