Reza Ghafoorian; Hossein Sanaeinejhad; Najafgholi Ghiasi; Abolghasem Dadrasi; Javad Eizi
Abstract
Determination of mean slope of a watershed area is an essential parameter in most of the water resources projects. There are many methods for determining this parameter. The methods frequently used can be listed as Justin, Networking, Horton, Eight points, Average slope curve and a Geographic Information ...
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Determination of mean slope of a watershed area is an essential parameter in most of the water resources projects. There are many methods for determining this parameter. The methods frequently used can be listed as Justin, Networking, Horton, Eight points, Average slope curve and a Geographic Information System (GIS). Generally experts based on their experiences use one of the mentioned methods. Investigations in some watershed areas showed that the results of applying the various methods are considerable different in a given area. In order to obtain the most accurate method, it is necessary to compare the results of experimental methods with the mean slope which is directly measured in the field, namely direct method. In this study, three regions were selected in different parts of Khorasan Province. For these regions topographic maps with large scales of 1:1000 to 1:3000 were prepared. Afterward seven mountain slopes were chosen in the regions and mean slope was computed for the slopes using the above mentioned methods. The mean slope was directly measured in the field for all seven mountain slopes as well. The obtained results from the various methods have been compared with the direct method by Paired-Samples T test. Analysis showed that the Horton method is the most accurate method with respect to the others. Justin and GIS methods are in next order of accuracy in comparison with the direct method.
Abolghasem Dadrasi; Shahrokh Hakimkhani; Abdolsaleh Ranghavar
Volume 1, Issue 4 , February 2010, , Pages 227-239
Abstract
The fact that there are so many erosion models makes it necessary to critically select one of them as all have some limitations. Models are formulations of processes and logics as represented by the modeler. The formulations may be representations of either simple processes or complicated ones as the ...
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The fact that there are so many erosion models makes it necessary to critically select one of them as all have some limitations. Models are formulations of processes and logics as represented by the modeler. The formulations may be representations of either simple processes or complicated ones as the modeler deems necessary to solve a specific problem. These variables must be derived by a procedure of calibration for a specific case. The Soil erosion model of Morgan, Morgan and Finny (1982) from a large list of soil erosion models, have been applied to test the validity of the model in Sanganeh research station, Mashhad, Iran. After a field survey, plots with sheet erosion, were selected and their data was collected. Rainfall, slope and soil data were derived from station archive, vegetation cover and root depths were determined from field observations and some other parameters were tested on site. Soil loss was calculated by using overland flow for each plot after each rainfall and the measured records were compared with model estimations. The results show that in most plots, predictions deviated from the observations and in 28.21% of plots the results seem acceptable. The final result of present research shows that the model performs reasonably well for plots with lower density of vegetation cover (less than 20%), steep area with more than 40 percent, and soil depths of less than 10 centimeter.
