TIME-LAPSE SALINITY INTRUSION STUDIES IN DISTRICT KARAK USING REMOTE SENSING (LANDSAT DATA 1990-2020) AND ELECTRICAL RESISTIVITY SURVEYS

Abstract

Data of 19 VES points are collected through Electrical Resistivity Survey. The apparent resistivity values which are taken from these points are then used to find true values. Interpretation of the electrical resistivity survey was made with the help of different software and available literature. Different VES points are developed in IPI2WIN software. Each VES point gives subsurface lithology image in the form of pseudosection on the basis of resistivity values. Interpretation results show variation in lithology from alluvial sediments, sand mixed with gravel, sandstones, clays, and water saturated sand beds. Interpreted cross sections of these pseudosection is prepared which indicate change in lithology at different depth interval, pseudosections along all the VES points show sandstone and clays in the subsurface and water concentration zone at various points in depth. In order to analyse the lateral salinity intrusion on the soil surface for the prior 30 years, from 1990 to 2020, for district Karak, remote sensing data from Landset4-5, Landset7, and Landset8 were acquired from USGS Earth Explorer. The data was evaluated using Arc GIS 2.7.1 and the following method of NDSI computation that is used in the industry. According to the study, the soil's surface becomes more salinized over time. But study also revealed that before constructing a dams i.e. water reservoirs the salinity was very high at flood plan area, This happens after significant rain fall in mountain places because the Bakhader Saline Series, which is mostly composed of Bakhader Khel salt and gypsum, may quickly dissolve in rains and run into streams and on flood plan areas where it precipitated. The water bodies have been in a heavily salinized zone since 2005, when several dams were constructed across these streams, and the flood strategy has been changed to account for intermediate salt levels. Following are the some highlights of the present research work. The alluvium, thin top layer, aquifer, and bedrock were the four subsurface Geoelectrical layers identified by VES experiments.The aquifer's bedrock exhibits varying resistivity values as a result of the various types of bedrock.The aquifer thickness increases towards the south, the regional direction of increasing deposition in the basin. The boundary of the aquifer has been determined and zones with high yield potential estimated for future development in the aquifer and for choosing the drilling site. The resistivity survey reflected that the lithology of the study area is almost homogeneous with three prominent layers as top 3m fill material, the middle layer of about 5m to 10m thickness was a dense alluvium followed by a saturated layer of soil.