Monitoring and assessing waterlogged and salt-affected areas in the Eastern Nile Delta region, Egypt, using remotely sensed multi-temporal data and GIS

摘要

Waterlogged and salt-affected soils are serious environmental hazard indicators for wasteland problems in arid and semi-arid regions of the World. Similarly human activities in agricultural and urban sustainable developments have also led to the development of waterlogging and subsequent salinization of soils leading to many geo-environmental problems. Thus, it is important to be able to monitor, assess and map waterlogged and salt-affected areas at an early stage to develop an effective soil reclamation programme that helps to reduce and prevent a future increase in areas of wasteland. Remote sensing and GIS tools and techniques have been found to outperform more traditional methods for assessing the impact of soil salinity and waterlogging, thereby providing extremely useful, informative, and professional rapid assessment techniques for monitoring and accurate mapping and the quantification of waterlogged areas and salt-affected soils. This study applies digital image processing and GIS tools to monitor, assess, and map the waterlogged and salt-affected areas, to establish the main causes that lead to widespread wastelands, and to suggest approaches to mitigation in the eastern Nile Delta region in Egypt. Multi-temporal Landsat 5, 7 and 8 data for 1984, 2000, 2006 and 2013 and ASTER GDEM were selected to monitor, assess and map the waterlogged and salt-affected areas, and to determine and map the rate of change of land-use/land-cover, the status of wasteland, and the use of geomorphological terrain analyses based on enhanced digital images processing and field verification. Image band combinations, PCA, change detection, and image classification techniques, together with many indices such as NDVI, NDSI, NDWI and NDBI were applied, together with statistical analysis, to construct various thematic and spatial distribution change maps of the wasteland hazard indicators. Spatial distribution maps of waterlogging, salt-affected areas, permanent and temporarily waterlogged areas, surface changes, and their rate of change in addition to integrated relationships between terrain analyses, water table, depth to water and landform maps over a timespan of 29 years based on the analysis and interpretation results of image processing, field investigation and ancillary geological and hydrogeological data. The results reveal that changes to land-cover caused by human activities - particularly irrigated agriculture and land reclamation as well as urban expansion - will lead to a serious deterioration in the environment through waterlogging and salinization presenting future difficulties for any sustainable development of the study area. In addition; the existence of natural factors such as areas of low-lying land, topographic depressions, and rising water tables will increase the threat of waterlogging and salinization. It is concluded that it is essential for planners and decision makers to seriously consider taking appropriate action now concerning the recommended mitigation measurements from this study to avoid serious future problems in these areas.