Proceedings of the Symposium on Global and Environmental Monitoring: Proceedings of the Symposium on Global and Environmental Monitoring

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Multivolume work

Persistent identifier:: 856665355

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts ; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856665355

Language:: English

Document type:: Multivolume work

Volume

Persistent identifier:: 856669164

Title:: Proceedings of the Symposium on Global and Environmental Monitoring

Sub title:: techniques and impacts; September 17 - 21, 1990, Victoria Conference Centre, Victoria, British Columbia, Canada

Scope:: XIV, 912 Seiten

Year of publication:: 1990

Place of publication:: Victoria, BC

Publisher of the original:: [Verlag nicht ermittelbar]

Identifier (digital):: 856669164

Illustration:: Illustrationen, Diagramme, Karten

Signature of the source:: ZS 312(28,7,1)

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: International Society for Photogrammetry and Remote Sensing, Commission of Photographic and Remote Sensing Data

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [TP-4 SOILS]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: EROSION RISK MAPPING IN THE TROPICS. J. D. Flach, S. M.White, W. G.Collins, T. R. E. Chidley

Document type:: Multivolume work

Structure type:: Chapter

130 EROSION RISK MAPPING IN THE TROPICS J.D.Flach 1 , S.M.White 2 , W.G.Collins 3 , T.R.E.Chidley 3 1. Image Technology Systems, Aston Science Park, Aston Triangle, Birmingham, UK. 2. NERC Water Resources Systems Research Unit, Dept. Civil Engineering, The University, Newcastle.u.Tyne, UK. formerly: ODU, Hydraulics Research Ltd, Wallingford, Oxfordshire, UK. 3. Dept. Civil Engineering, Aston University, Aston Triangle, Birmingham, UK. ABSTRACT This paper investigates the use of remote sensing and Spatial Information Systems as a decision support tool in river basin management; providing information for input to regional hydrological models. The test case highlights a study undertaken in the Philipinnes to determine areas of a river catchment that would benefit most from a re-forestation project. The integration of various types of data into the model is discussed along with the generation of an erosion risk map for the catchment. The use of weather satellites for areal rainfall estimation as input to the model is also discussed. KEY WORDS: Erosion Risk, Hydrological Modelling, Spatial Information Systems. 1. INTRODUCTION Soil erosion is a major problem in many third world countries. The response to rising food demand has often been met by increased agricultural production in marginal lands, and the world trade in timber has caused the destruction of many forested upland areas. In many cases this has led to accelerated erosion rates, total degradation of the land, high sediment loads in rivers and canals, and a reduction in water available for irrigation. Ultimately sediment deposition in reservoirs can mean a drastic reduction in operating life. Unfortunately the modelling of hydrological processes, in particular the prediction of sediment yield, in developing countries is often a subjective task, hampered by lack of data. This paper describes the basis for a remote sensing based hydrological information system (Ragan and Fellows, 1979), (Allewijn, 1988), and its application in the creation of a database of useful information for input to distributed hydrologic models. 1.1. The Study Area The study area used as a test case for developing a methodology was the 4123 km 2 Magat River Catchment in Luzon, Philippines. Problems of high localised erosion and rapid sedimentation in the reservoir at the catchment outlet have resulted in plans for re-forestation of parts of the catchment. It was neccesary to identify those areas of the catchment, which if re-forested, would give most return in terms of reduction of soil loss at the site and reduction in sediment yield to the reservoir. This study and subsequent monitoring of the effects of catchment management policies is being undertaken by the Overseas Development Unit of Hydraulics Research Ltd, Wallingford, UK. 2. EROSION RISK MODELLING The prediction of sediment yield in developing countries is often a subjective task, and has in the past often proved to be extremely unreliable. Numerous examples exist where sediment yields predicted at the feasibility stages of an irrigation project are found to underestimate the real yields by a factor of ten or more. One of the contributory factors to these unreliable predictions is the preponderance of simplistic or inappropriate predictive techniques. Formulae are either simple, relying on only one or two factors, or extremely complex and data-hungry. Most formulae have been developed in climatic and geomorphic zones which are very different from those found in the tropics where many developing countries are located. This does not stop people from using them! The processes of erosion and sediment transport are dependent on many factors, whose inter-relationships are complex. Prediction of erosion and sediment yield is therefore achieved by combining the various causative and resistive forces for the area under consideration. Prime examples of this type of approach are the Universal Soil Loss Equation (Wischmeier and Smith, 1978) for individual plots of land, and catchment scale models that average data over the entire catchment (Fleming, 1969). Development of computer based distributed models allow the catchment to be modelled on a grid cell or sub-catchment basis (Beasley, 1960), (Fleming and Walker, 1976). Distributed models of this nature require sediment routing algorithms to account for movement through and between model cells. Data requirements for distributed models are clearly high which normally precludes their use in developing countries. Remote Sensing and Spatial Information Systems provide a possible source of data for these models. As a basis for modelling erosion risk a modified version of the SLEMSA model, originally developed and used for a study in the SADCC region (Stocking 1987), was investigated. This model takes into account a number of factors: 1. Erosive power of rain 2. Interception by plant cover 3. Topography (slope, etc.) 4. Resistance of soil to erosion. Given these as required inputs to the model a fine mesh database was required. Remote sensing and spatial information systems provided the key to creating a database from satellite digital data and thematic cartographic data.

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