Soil erosion mapping using Remote Sensing data and Geographic Information System
Manu Omakupt
Land use planning division
Land development department
Ministry of Agriculture and Cooperatives
Abstract
The study area coverage an area of 60 km x 60 km in the chiang mai basin and the surrounding hilly area in the northern Thailand.
The method used consists of interpretation of SPOT and Land sat data which enables units characteristics by combination geographical units and land use pattern .Field measurements of universal soil loss equation factor field measurements of universal soil erodibility slope steepness and length vegetation cover and conservation practice allowed the productions of an erosion map. the integration of these five erosion factors was performed on the spatial analysis system data base .Digital terrain model DTM and satellite image data were electronically transferred from the MERIDIAN image processing system . The processing and or interpretation work involved to derive each factor and the final soil erosion susceptibility map are produced.
The study showed that maximum erosion risk as expected occurs in the mountains regions where the forest has been cleared to make place for the cultivations of field crops all tree plantation mostly pine control practices as many exbhit a seeding pattern parallel to the directions of the slope that a measure that is very prone to erosion.
Introduction
Thailand is like many other developing countries situated ina tropical environment the problem of all soil erosion is of major concern from study carried area out in the 1985 by the bank it was estimated that 39% of the total area of designed forest land had been encroached deforestation in hilly areas where the risks of soil erosion are high has reached disturbing proportions even only in the last decade.
The sixth national plan emphasizes the importance of the proper utilization of renewable natural resources .Among the numbers agencies involved in the with the aspects related to the development of land resources including land use planning soil and water conversation and land improvement..
LDD is responsible for identifying areas requiring programmes of soil conservation and processing the measures to implement these being aware of this the mapping of erosion susceptibility is a suitable information for soil and water conservations work.
Back ground
Remote sensing techniques have been used as an aid soil survey Thailand since the early most of the research dealing with the use the satellite images for erosion studies has been done in the context of soil surveying a well Known parametric equation the universal soil loss equation is currently used to assess soil loss due to water erosion. It is written as:
A = RKLSCP
This equation explained inn detail is Wish Meier and smith describes soil loss a as a function of rain fall R its amount and intensity soil erodibility related to the texture percentage organic matter structure and permeability of the soil topography especially the slope gradient and the length of the slope the vegetative cover and the erosion control practices (p).
Because of its simplicity the relative ease of evaluating each factor and because in most parts of the world it gives acceptable results a number of authors have used this equation to evaluate soil loss due to water erosion easily adapted to many different scales it has been used by arnoldus for morocco E1 scarify in Hawaii say ago for a region in Argentina brail et al for a small sector in the province of Quebec such as the food and agricultural organization and the land directorate of the Canadian Ministry of Environment.
