Application of remote sensing data and GIS technology to mapping soil erosion in Lang Son province


Posted at: 09:07:52 05/07/2016 - Read: 229
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Land is an essential natural resource in the world. However, the strong impact of the natural and cultivation activities of human lead to land degradation. One of the main cauces of land degradation is soil erosion.

In earth science, erosion is the action of surface processes (such as water flow or wind) that remove soil, rock, or dissolved material from one location on the Earth's crust, then transport it away to another location. The particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Soil erosion caused serious impacts on the environment and human life such as loss of land, loss of nutrients and declining soil fertility. Soil erosion at a high level as landslides, mountain landslide phenomena associated with flash floods caused severe damage not only to the environment but also the human, and society. Therefore, the calculation, reducing soil erosion is one of the top concerns of the scientists not only in Vietnam but also around the world.

In the world, there are many researchs and projects about soil erosion, ; the first study was done in 1877 by German scientists. Many year later, Musgrave et al has develop an empirical equation called the Musgrave equation in 1947. In 1958, Wischmeier and Smith were researched and gave a fomular to calculate soil erosion which called universal soil loss equation (USLE). Until now, there are many model of calculating soil erosion was developed base on USLE equation.

Today, with the development of information technology, the use of GIS remote sensing technology to identify, assess the status of soil erosion is considered to be a new direction in solving the problem of soil erosion. In recent years, in Vietnam appeared numerous researchs and projects that applying GIS technology to research soil erosion such as: "The application of GIS in soil erosion estimates the soil erosion in Da- Ma Dong Nai Province" by Nguyen Kim Loi (2006); "Applications of remote sensing and GIS to assess soil erosion in Son La province " by Dinh Van Hung (2009); "Applications of remote sensing and GIS to assess the soil erosion in Tam Nong district, Phu Tho Province, " the authors Tran Quoc Vinh, Dang Hung Vo, Dao Chau Thu (2011) .... . Most recently, the Geoinforatics research center of Thai Nguyen University used GIS and remote sensing technology to research soil erosion in Lang Son province serve for the project: "Investigation land degradation in Lang Son province ".

The research using soil erosion map to calculate the amount of eroded soil cause by rainfall. The map was build by use modeling method in ArcGIS and the amount of eroded soil was calculate according to universal soil loss equation of  Wischmeier and Smith: A = R.K.L.S.C.P

A: The amount of average annual loss of land transfer to the foothills (kg / m2.nam)

R: coefficient of erosion caused by rain (KJ.mm/m2.h.năm)

K: Coefficient of soil erosion (kg.h / KJ.mm)

L: Coefficient of the slope length

S: Coefficient of slope

C: Coefficient of vegetation cover and land management

P: The coefficient measures applied by cultivation methods for land protection

Figure 1:  The mprocess of mapping soil erosion.

The factors in the soil loss equation of Wischmeier and Smith are expressed and calculated base on thematic maps as raster data.

Based on the results of measuring the average rainfall of the month/year from 2000-2015 of the meteorological station in Lang Son province. Applying the formula of calculating the coefficient R for each meteorological station, Fournier (Arnoldus 1977) and Nguyen Trong Ha. Performing interpolation method (Krigging; IDW) for the rainfall data in meteorological stations, we get the result is the map of soil erosion cause by rain with the continuous value in RASTER data.

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Figure 2: The map of soil erosion cause by rain in Lang Son (coefficient R)

From the result of analyze the soil surface, we have the a coefficients and we can determine the weight of M particle, then using the equation of Wischmeier and Smith (1978) to get the b,c coeficients. After that, calculate K value for each soil sample that was collected from fieldwork corresponding to the land parcel on the map. Using ArcGIS 10.2 software to calculate and process data, we get the result is the map of K coeficient.

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Figure 3: The map of K coeficient in Lang Son city.

 

LS coefficients characterize for the influence of geographical factors to soil erosion, so it can be calculated by the terrain information. From topographic maps were digitized with about 10m high, assigning the high value for to the contours and points. Then, using the interpolation algorithm of GIS (ArcGIS 10.2), interpolating the contours and points to build digital elevation map (DEM).

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Figure 4: The slope and slope length map (LS coefficient)

From Landsat 8 images, classifying the landsat mage according to Normalized Difference Vegetation Index (NDVI) by Envi software 5.0. Then use ArcGIS 10.2 software to process and calculate the formula C of De Jong. The result is Vegetation Index maps and coefficient C map, the Vegetation Index from 0-0,65.

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Figure 5: Land cover and soil management map (C coeficient) in Lang Son

The coeficient P characterize for erosion mitigation level by using cultivation methods. If people using contour farming method, it’s may reduce the soil erosion. The P coeficient shown mostly in agricultural lands erosion, actualy, the main cultivation model in Lang Son province is contour farming, so we calculate the coeficient P according to the equation of Wischmeier and Smith (1978). From the slope map, assigning P values, we can get the map of P coeficient.

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Figure 6: The map P coeficient in Lang Son

The annual soil lost of each parcel is calculated by overlay all thermatic maps of coefficients according to universal soil loss equation. From the thematic maps on, synthesis, overlay maps, we obtain as a result of soil erosion map of Lang Son.

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Figure 7: Soil erosion map of Lang Son Province 2015

From soil erosion map Lang Son province, researchers have calculated, statistics eroded land in each district of Lang Son province through the following statistics table.

                                                               Eroded land areas                                                     Unit: Ha

From the result of overlaying thematic maps, we can identify the erosion area in Lang Son is 471608,27 ha, account for 63,98% of total surveying area. Thereby, we can see that the soil erosion was fairly strong in Lang Son, especially in Binh Gia, Dinh Lap, Trang Dinh district. At the same time, studies show us the strongly benefits, effects of using remote sensing technology in research, evaluate the soil erosion.
Posted by: GIRC

GeoInformatics Center - Thai Nguyen University of Agriculture and Forestry

Address: Quyet Thang commune, Thai Nguyen city, Vietnam | Tel: +84904.031.103

Email: girc.tuaf@gmail.com | Website: www.girc.tuaf.edu.vn