Soil and Groundwater Salinization Problems in the Khorat Plateau, NE Thailand - Integrated Study of Remote Sensing, Geophysical and Field Data

Transcription

1 Soil and Groundwater Salinization Problems in the Khorat Plateau, NE Thailand - Integrated Study of Remote Sensing, Geophysical and Field Data Probleme der Boden- und Grundwasserversalzung in der Khorat Hochebene, NE Thailand - Studie mit Fernerkundung, Geophysik und Geländekartierung Dissertation zur Erlangung des akademischen Grades doctor rerum naturalium (Dr.rer.nat.) am Fachbereich Geowissenschaften der Freien Universität Berlin vorgelegt von Akkhapun Wannakomol, Berlin, Juni 2005

2 Angefertigt mit Genehmigung des Fachbereiches Geowissenschaften der Freien Universität Berlin Tag der Disputation: 14. Juli 2005 Gutachter: Prof. Dr. Franz K. List (1. Gutachter) Freie Universität Berlin, Fachbereich Geowissenschaften Dr. Friedrich Kühn (2. Gutachter) Bundesanstalt für Geowissenschaften und Rohstoffe, Referat Fernerkundung 2

3 Acknowledgements This work was funded by the German Academic Exchange Services (Deutscher Akademischer Austauschdienst, DAAD) during the years 2002 to Remote sensing data and a computer-based remote sensing working place was provided at the Freie Universität Berlin (FUB), the Germany Federal Institute for Geosciences and Natural Resources (BGR), and at the Department of Mineral Resources (DMR), Thailand. The Suranaree University of Technology (SUT) in Nakhon Ratchasima Province provided the required geophysical data and instruments. All of them are gratefully acknowledged. I am greatly indebted to Prof. Dr. F. K. List for his guidance and invaluable discussions on this work. I also would like to express my sincere thanks and gratitude to Dr. F. Kühn for his initiation and guidance at all stages of the work. I am greatly indebted to Dr. K. Munier for her invaluable advice on GIS and remote sensing software used in the work. Also I would like to thank Mr. Dirk Büter, Mr. Jörn Levenhagen, and Mr. Sami El Khidir, colleagues and friends at FUB, for their supporting ideas and help. I do gratefully thank my parents and special thank to my wife for her supporting and encouragement. 3

4 4

5 Abstract The study area is located in the western part of the Khorat basin, a sub basin of the Khorat Plateau, northeastern Thailand. The aims of the study are to map the distribution of saline soil at the surface of the study area, to correlate presumably saltrelated features visible in the remote sensing data with information/indications provided by geophysics or other sources of data, to develop tentative assumptions on relationships between typical salt-related features in the remote sensing imagery and corresponding subsurface conditions, to outline concepts on the development of soil salinity, depending on lithological and structural conditions, and to investigate the differentiation between saline and non-saline soil by differences of their spectral properties. The non-remotely-sensed data, e.g. geophysics, groundwater, borehole logs and GIS data were employed to study the distribution, depth and shape of the rock salt members of the Maha Sarakham Formation, which are supposed to be the major sources of the salinity in this region. Results from geophysical investigations by conducting seismic reflection, resistivity and microgravity investigation indicate that the rock salt beneath the moderately to the severely salt-affected areas is present at a depths range from 80 to 100 m. The rock salt has a relatively flat to broadly anticlinal surface. These results also imply that beneath the elevated areas the rock salt is situated at greater depths than under the low-lying areas, troughs or swampy areas, e.g. in the vicinity of the Khong District, Nakhon Ratchasima Province. Remotely sensed data including Landsat 5 (TM), Landsat 7 (ETM+) and ASTER covering the study area were used to map the land use and salinity in the study area by means of visual interpretation and digital classification. Based on visual interpretation of land use and existing saline soil maps and two additional field trips investigating the amount of salt crust present at the surface, salt-affected areas in the study area could be categorized into three major types: severely, moderately and slightly salt-affected. Land use classifications of Landsat 7 and ASTER data showed good results in differentiating salt-affected from non salt-affected areas. Especially ASTER data gave high accuracy. Soil salinity classification derived from Landsat 7 by Band Math techniques gave poor results, particularly, when differentiating saline areas from bare ground, while those derived from ASTER data gave higher accuracy. Processing and interpreting ASTER data made it possible to effectively differentiate saline areas from bare ground. The total area of classified salt-affected areas in the study area is 495 km 2. Results from reflectance spectra measurements showed that salt crust covering saline areas has specific spectral absorption feature at nm wavelength. It is notable that most of the salt affected areas are located where lineaments occur. The dissolved salt rises to the surface using increased permeability along fault and fracture planes which are featured by lineaments on satellite images; salt crusts accumulate along these features and cause salinity later on. Based on hydrogeology, geology and topography, this study classifies the salinity in the study area into three main types: 1) Salinity along weak zones including salinity along a rock boundary, salinity along a lineament and a river course, 2) salinity in depression areas, and 3) salinity affected by reservoir and irrigation systems. 5

6 6

7 Soil and Groundwater Salinization Problems in the Khorat Plateau, Thailand- Integrated Study of Remote Sensing, Geophysical and Field Data Contents Page Acknowledgements... 3 Abstract. 5 Contents Introduction 1.1 Problems of Soil and Groundwater in the Khorat Plateau Objectives of the Study The Study Area Previous Work Geological Studies Soil and Groundwater Salinity Remote Sensing Data and Equipment Remotely Sensed Data Other Data Computer Software and Other Equipment Methods of Investigation Laboratory Methods Field Methods Geology 2.1 General Geology Regional Plate Tectonic Development Structural Framework Lithostratigraphy and Sedimentology Pre-Caledonian Megasequence Pre-Variscan Megasequence Pre-Indosinian I Megasequence The Saraburi Group The Wang Saphung Group Pre-Indosinian II Megasequence Pre-Himalayan Megasequence The Khorat Group The Maha Sarakham Formation The Phu Tok Formation Post-Himalayan Megasequence Rock Salts in the Khorat Plateau General Overview Salt Structure Salt Flowage Mechanism Salt Structure Developments Recent Surface Topographic Features Subsurface Geology

8 Page 3. Soil and Groundwater Salinization in the Khorat Plateau 3.1 Soil and Groundwater Salinity Hydrogeology Meteorological Conditions of the Study Area Groundwater Conditions of the Study Area Aquifer Systems Depth to Groundwater Recharge and Discharge Conditions Groundwater Types Causes of Soil and Groundwater Salinization in the Khorat Plateau Salinity Caused by Natural Causes Salinity Caused by Human Activities Salinity Classification Salinity along Weak Zones Salinity in Depression Areas Salinity affected by Reservoir and Irrigation Systems Remote Sensing and GIS Investigation 4.1 General Background Remote Sensing Data Used Landsat 5 (TM) and Landsat 7 (ETM+) Data ASTER SRTM Image Processing Image Registration Image Enhancements Image Mosaicking Lineament Analysis Previous Work on Lineament Analysis in the Khorat Plateau Methodology Drainage Pattern Analysis Saline Soil Mapping Land Use Classification Salinity Index and Vegetation Index GIS Data and Maps Geophysical Investigation 5.1 Geophysical Investigations and Rock Salt Electric Resistivity Investigation Seismic Investigation Microgravity Investigation Results of the Study and Recommendations 6.1 Distribution of Rock Salt and Soil Salinity in the Study Area Overview Results from Present Work 119 8

9 Page Results from Borehole Logs Study Results from Geophysical Investigations Salinization Features and Remote Sensing Results from Visual Interpretation Drainage Pattern in the Study Area Lineament Detection on Satellite Images Distribution of the Salt-affected Areas on Satellite Images Results from Digital Classification Results from Unsupervised Classification Results from Supervised Classification Results from Indices Analysis Conceptual Model of Soil and Groundwater Salinization in the Khorat Plateau Causes of Salinity in the Study Area Salinity Caused by Natural Causes Salinity Caused by Human Activities Salinity Types in the Study Area Salinity along Weak Zones Salinity in Depression Areas Salinity affected by Reservoir and Irrigation Systems Salinity Classification of the Study Area Recommendations Recommendations for Future Work Recommendations for Salinity Problems Management References Appendices 199 Enclosure 1. False Color Composite Image Landsat 7 ETM+ ( ) Western Khorat Plateau, NE Thailand, Bands 4, 3, 2 as red, green, blue Scale 1: Classification of salt-affected areas on the western Khorat Plateau, NE Thailand Scale 1:

10 10