Introduction

The depletion of aquifers by excessive pumping is one of the prominent global sustainability issues in the field of water resources. It is mainly caused by the water needs of irrigated agriculture. The North China Plain is a global hotspot of groundwater overexploitation.

Study of water salinity in the Chtouka plain (Morocco) using TEM geophysical method, chemical and isotopes tracers

<p>The Chtouka plain in Morocco suffers from groundwater overexploitation and a significant increase in water salinity. In this study, a multidisciplinary approach combining water chemistry, stable isotopes of water (18O, 2H) and Transient Electromagnetic (TEM) method was used. The main objective was to identify the water salinity sources and the extension of the marine intrusion. Water samples were collected from wells and boreholes, springs, the Massa river and the main source of freshwater in the region, the Youssef Ibn Tachfine Dam. Geophysical (TEM) measurements (12 profiles comprising 83 measurement points) were carried out along the coastal zone and around the northern bank of the Massa river. The results show a spatial variability of water salinity, indicating rock-water interaction, seawater intrusion and anthropogenic influence. The interpretation of the TEM soundings allow to draw the front line of the marine intrusion in the aquifer. The results, compared to previous numerical simulations, show a significant progress of the marine intrusion into the coastal aquifer. The intrusion indeed reaches a distance of 2.5 km from the coast, far beyond models’ predictions. The local water authorities can use these results to improve their monitoring network and better assess the progress of the seawater intrusion.<br>Keywords: Water salinity, TEM geophysical method, chemical and isotopes tracers, marine intrusion</p>

Morphometric analysis of the terrain over time to characterize subsidence. Case study: Mexico City, Mexico.

<p>It is well known that groundwater overexploitation can generate land subsidence due to the compaction of compressible aquitards. Mexico City's soils are an important example of highly compressible lake sediments in compaction due to groundwater extraction that have significantly damaged the urban and commercial building structures. Previous studies indicate that there is annual subsidence of 15 to 25 cm in the Mexico City International Airport, 10 cm in downtown, and between 10 to 15 cm in the Southeast Mexico City area. Soil fracturing is an indicator of differential subsidence that has damaged buildings and infrastructure, including hydraulic pipes, sidewalks, and pavements. For this reason, it is necessary to carry out specific studies related to topographic deformation. This talk presents a characterization of the terrain changes over time and a zoning map for Mexico City subsidence susceptibility. To this end, free access elevation models generated from 2000 to 2018 by different sensors and methodologies were compared. The resulting model is validated by mapping information from active GPS stations, whose data is also freely available. Besides, a spatial comparison of land subsidence areas and sites previously identified as flooding and aquifer overexploitation areas is presented. The results will serve as a basis for future monitoring to be carried out in the area with high-resolution tools.</p>

Assessment and analysis of groundwater overexploitation in China

As an important water resource, groundwater has been unreasonably developed for a long time in our country, causing a lot of problems. This paper combines the data from the national groundwater monitoring stations and the groundwater depth data collected locally to statistics and analysis of groundwater overexploitation across the country. Especially in key plains, through the water level variation method. The research results are compared and verified with national authoritative data such as Groundwater Dynamics Monthly Report and predecessors’ records in the literature, revealing the current key areas of groundwater overexploitation, and clarifying the importance and urgency of groundwater governance in the future. This study also put forward some suggestions of groundwater overexploitation.

Quantifying Ground Subsidence Associated with Aquifer Overexploitation Using Space-Borne Radar Interferometry in Kabul, Afghanistan

Rapid population growth combined with recent drought events and decades of political instability have left the residents of Kabul facing water scarcity, significantly relying on groundwater. Groundwater overexploitation might have induced various magnitudes of ground subsidence, however, to date, no comprehensive study of ground subsidence in Kabul has been conducted. In this study, we investigated the spatio-temporal evolution of ground deformation phenomena and its main governing processes in Kabul from 2014 to 2019 using C-Band Sentinel-1 derived Interferometric Synthetic Aperture Radar (InSAR) time-series from both ascending and descending orbits to extract the two-dimensional (2D) surface displacement field. Four subsidence bowls were distinguished with highly variable spatial extents and deformation magnitudes over four separate aquifer basins, with the maximum value of −5.3 cm/year observed in the Upper Kabul aquifer basin. A wavelet analysis suggests that there is a strong correlation between the groundwater level variations and subsidence. Investigation of hydrogeological data further reveals that the observed subsidence could be attributed to the presence of highly compressible clayey soils. This detailed space-borne regional survey provides new insights into the main governing mechanism of land subsidence in Kabul and may direct better mitigation plans of potential hazards.