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| Calculation tool of topographic factors |
| Fu Suhua1,Liu Baoyuan1,Zhou Guiyun2,Sun Zhongxuan2,Zhu Xiaoli1 |
| 1. State Key Laboratory of Earth Surface Processes and Resource Ecology, School of Geography, Beijing Normal University, 100875, Beijing, China;2. School of Resources and Environment, University of Electronic Science and Technology of China, 611731,Chengdu, China |
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Abstract Topographic (slope length and slope gradient) factors (LS) are important parameters in the soil erosion model, for example, universal soil loss equation (USLE) and Chinese soil loss equation (CSLE ). The LS factor was usually computed using digital elevation models (DEM) for basin-wide application of the USLE and CSLE. The calculating process is very complicated and is difficult to be directly calculated using common GIS software such as ArcMap software. In this paper, an LS tool software is developed on the platform of Visual Studio 2010 software. Source codes are written using C+ +
language. The C+ + language is used to obtain the window of the software. This tool is easy to use with a friendly interface. To extend the tool suitability, the slope gradient factor equation at steep slope is added in the algorithms. An equation considering segmented slope situation is used to calculate the value of slope length factor. The calculation progress includes the following six steps: 1) filling topographical depression, 2) calculating flow direction, 3) extracting gully net, 4) calculating non-cumulative slope length (NCSL) of each grid cell, 5) calculating the cumulating slope length of each grid cell and 6) calculating LS factors of each grid cell. The above six steps are described in detail in this paper. The cutoff slope factor and gully net are used to stop the cumulating slope length. The input file is a DEM file with *. aux, *. xml or *. tif format. The outputs include slope gradient, slope gradient factor, gully, slope length and slope length factor etc. . The parameters of threshold values including slope gradient, slope length, slope cutoff factor, channel initiation and gully length are optional of user input. Maduo county located in Qinghai Province was used as an example to test the application of the software. The area of the county is 25 000 km2. The DEM with 30 m resolution includes 7 500 rows and 6 080 columns. The run time was less than 2 min on the computer with the 32-bit operating system to finish calculating. The application results show that the software has a high calculation capacity and runs efficiently. For the 32-bit operating system, the software can be used to calculate the LS factors of a region with 10 000 rows and 10 000 columns; for a 64-bit operating system, it can be used for a region with 40 000 rows and 40 000 columns. This tool can be used as a sub-model to evaluate soil loss and to plan the soil conservation practice at a region scale.
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Received: 18 March 2015
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