Abstract: This synthesis on groundwater recharge targets the Southern African region as a result of the dependence of the community and economic sector on the groundwater resource. Several literature based recharge studies were collected and assessed in order to find out the main controls to the occurrence of recharge. The Water Table Fluctuation and Base flow separation methods have been tested in the catchment that drains crystalline basement rocks and dolostones close to the city of Johannesburg, South Africa. Based on the assessed data the Chloride Mass Balance method resulted in groundwater recharge of less than 4% of the rainfall, while it reaches 20%, when rainfall exceeds 600mm. For the classical water balance method, recharge proportion is less than 3% of rainfall as a result of very high ambient temperature in the region. Based on the Saturated Volume Fluctuation and Water Table Fluctuation methods, recharge could be less than 6% for annual rainfall of less than 600mm. Observational results further suggest that sporadic recharge from high intensity rainfall has important contribution to the groundwater recharge in the region, owing to the presence of permeable geological cover, which could not be fully captured by most of the recharge estimation methods. This study further documents an evaluation of the most reliable recharge estimation methods in the area such as the chloride mass balance, saturated volume fluctuation and water table fluctuation methods in order to successfully manage the groundwater resource.

Abstract: Competing commercial demands on water resources need to be balanced as the world’s population rises. Generally, groundwater is raised by subsurface dams. In this paper, the geographic information system (GIS) software and a decision-making method were applied. As the first step, the limitations that affect the establishment of the subsurface dam were identified using eliminating criteria by the Boolean logic. Regarding the second step, the most appropriate axis was determined for subsurface dam construction in each of the limits. The analytical hierarchy process (AHP) was applied according to the evaluation criteria in this study. The aim of using AHP was to weigh and prioritize the criteria of the groundwater dam for recognizing appropriate sites. Among various places and regarding the subsurface dam construction, AHP was conducted using a hierarchy process for finding the most suitable sites in the third stage of the decision-making method. Finally, among the ten appropriate sites, cross comparison was drawn by using Decision Expert (DEX), Evaluation based on Distance from Average Solution (EDAS), and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Compared together (as a process of decision-making), DEX, TOPSIS, and EDAS methods assisted in ranking the most appropriate sites in the final step of subsurface dam pre-selection. A and C axes obtained scores between 1 and 2, among 10 axes according to the numerically ranked locations. Regarding the water shortage issue and better management of the underground water at certain levels, the findings of this study could be useful for the residents of Kajbid-Balaqly Watershed in the dry season. Further, water managers can use the above-mentioned methods for their decisions regarding the proper subsurface dam establishment.

Abstract: In the present study, the ground water quality parameters were monitored during pre- and post-monsoon seasons across Narmada district, Gujarat, India. Monitoring was done in 89 drinking water samples collected by grid sampling method from the study area. Uranium and fluoride were analyzed along with associated parameters such as pH, dissolved oxygen, Cl−, NO3−, F−, SO42−, total alkalinity, total dissolved solids and hardness. In 4% samples the fluoride content was found to be above WHO permissible limits of 1.5 mg/L (2.36 mg/L in Undaimandava, 1.55 mg/L in Shira, 3.04 mg/L in Fatehpur and 1.83 mg/L in Dholivav) during pre-monsoon season (PRM) and 4.74 mg/L, 2.41 mg/L, 2.34 mg/L and 3.99 mg/L respectively in Bantawadi, Shira, Undai Mandava and Fatepur villages during post-monsoon (POM). The uranium level was within WHO limits in both POM and PRM seasons. The quality of the water was evaluated by Principal Component and Pearson Correlation statistical analysis techniques. The PRM and POM correlation study indicated a strong correlation of TDS with EC, Chloride, total alkalinity and bicarbonate and U while moderately strong correlation of TDS with fluoride were observed indicating that chloride, total alkalinity, bicarbonate, U and fluoride contributed to TDS and EC. Principal component analysis was applied for 14 variables, from which 3 factors were extracted during PRM and POM seasons. The extracted components, contributed 84.391% and 83.315%, to variation during PRM and POM seasons respectively. The study indicated that the analyzed water samples in Narmada district were safe for drinking purpose. However, Tilakwada tehsil groundwater was observed to be unsustainable for drinking, without further water treatment, but was appropriate for agricultural purposes. The study will help the residents of the district to understand the present water quality status and will also help in future management to protect the ground water of Narmada district.

Abstract: Apart from some notable exceptions, the sound governance of transboundary aquifers (coupled or uncoupled to rivers) is seriously lacking in most regions of the world, despite a highly successful 20-year ISARM initiative. The distinction between regions of water abundance (as in the Haute Savoie–Geneva aquifers) and those of water scarcity (\textless1000 m3/an/capita), as in the Rum-Saq aquifer, ought to be a driver for the urgency in adopting sound governance. In the latter regions, however, such an urgent response faces too many hurdles (institutional, financial, and weak capacity). Climate change, one of the global megatrends (among demography, economic shift, resources stress, urbanization, and novel viruses such as COVID-19), will exacerbate the problem in the coming decade and beyond. This chapter provides an critical perspective on the status of this subsurface asset in 570 or so, domestic and transboundary aquifers of the world (self-identified by country experts), while taking full account of their interconnections, or not, with surface waters. This critical perspective will be grounded in two important factors, first the hiatus in adoption by countries of the evolving international water law and guidance on transboundary aquifers (the Draft Articles, which provide legal pathways for collaboration or eventually dispute resolution), and second the framework of the sustainable development goals (SDG) 6 (clean water and sanitation), which countries have committed themselves to with reference to transboundary waters. The critical perspective finds that despite the lack of momentum in adopting formal global norms, sporadic cooperation and collaboration is continuing and is well received, when delivered methodically through the support of international agencies. The findings of the critical perspective are that even if water-related SDGs will have been achieved across the world, it would contribute precious little to meaningful enhancement of governance of transboundary aquifers, unless they have been explicitly addressed in terms that are tangible to decision makers, such as the impact of disregarding them on the current or future national GDP. The onset of a “new socioeconomic normal” in the aftermath of COVID-19 could further defer meaningful progress, taking the example of Latin America, where a 5% decline has been forecast for 2020. With such declines in the finances of governments, attention to shared aquifer resources may well decline even further. Urgent wise reaction to this possibility must be a priority for the professional science-policy community.

Abstract: Floods are one of the most common natural disasters, resulting in the extensive destruction of infrastructure, property, and human life. The destructive potential of a flood depends on numerous factors, including the size of the flood, the rate of flooding, the time it takes for the water to move through a given area, the river’s planform and cross-section geometry, and other similar factors. The present study is a unique analysis of flood mapping that was accomplished with the help of the Analytical Hierarchy Process (AHP), Frequency Ratio (FR), and hydrogeomorphic response to floods by integrating geospatial analysis and unit stream power modeling. The Indus catchment region of Pakistan is where the subject topic is put into practice. According to the hydrologic analysis of the yearly peak discharge, the hydro-station in Gilgit-Baltistan can move boulders measuring up to 0.5 m in height during significant flooding. On the other hand, there will be no change to the geometry of the cross-section throughout 1980–2020 in Gilgit-Baltistan. The flood susceptibility map is constructed using data from twelve influencing parameters, including elevation, proximity to the drainage network, slope, drainage density, geomorphology, rainfall, the curvature of the topography, flow accumulation, geology, land use, Topographic Wetness Index (TWI), and Stream Power Index (SPI). The area under the curve (AUC) approach, which demonstrates a substantial degree of accuracy (85% and 83%), is utilized to evaluate the effectiveness of the AHP and FR. The current study fills the gaps between the geospatial approach and the hydrogeomorphic assessment of flood to determine flood susceptibility.