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Hydrochemical and stable isotope (δ 18 O, δ 2 H) data were used to identify the recharge sources of major springs and the hydraulic interconnection between the volcanic aquifer and springs in the Gilgel Abay catchment and adjacent areas. The hydrochemical data analysis showed that all water samples of springs and shallow wells have freshwater chemistry, Ca HCO 3 to Ca Mg HCO 3 types. This is mainly controlled by dissolution/hydrolysis of silicate minerals. The analyzed stable isotope data indicate that springs water, except Dengel Mesk, Kurt Bahir and Bility springs, and well waters, except Dangila well, fall close to the LMWL. This clearly shows that the infiltrated rainwater did not undergo much evaporation and δ 18 O values for spring water and groundwater are nearly equal to the value of Ethiopian summer rainfall, which is −2.5‰. Therefore, generally both stable isotope and hydrochemical data show the recharge source to springs and shallow groundwater is primarily from precipitation. Furthermore, data suggest that rock-water interaction has remained relatively limited, pointing to relatively short residence times, and local recharge rather than regional recharge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Freshening is continuing in the deep aquifer having good hydrodynamic potential. • Deep aquifer is an alternative to the saline shallow aquifers, suitable for public water-supply. • The quality of water is good, but attention has to be paid to the increased sodium concentration. • It is important to examine each element concentration during the formulation of WQI of an aquifer. • The presence of saline water below 300 m depth indicates paleo-seawater. Maintaining the water quality of a coastal aquifer is very important for its sustainable development and management. The shallow aquifers in the southwest coast of Bangladesh are highly saline. This research was conducted to explore the hydrochemistry and potential of the deep aquifer using pumping test, hydrochemistry, multivariate statistics, and groundwater quality index. The groundwater is mostly of NaHCO 3 type (85%), but small amount of NaCl (15%) type waters are also present. Principal component analysis indicates four factors (73.43% of the total variance) controlling the composition of groundwater: paleo-seawater, cation exchange, mineral dissolution, and oxidizing conditions. Zonation of hydrogeochemical processes within the deep aquifer are well established by hierarchical cluster analysis. Seven clusters have been distinguished from this analysis: cluster 1 (paleo-saltwater), clusters 2 and 4 (freshwater influence), clusters 3 and 7 (freshwater invasion and mineral dissolution), cluster 5 (no specific geographical location) and cluster 6 (mixed water). The groundwater quality index shows that 88% sampled water is of excellent to good and only 3% is unsuitable for drinking purposes. However, 53% of water has Na+ concentration above drinking standard. This parameter has very little contribution in groundwater quality index calculation, which we consider a shortage. Pumping tests revealed that transmissivity of deep aquifer has a median value of 888 m2/day and a hydraulic conductivity of around 15 m/d, indicating a good hydrodynamic potential. The overall water quality is good, except in the southwest corner of the study area. It is, therefore, recommended to exploit groundwater from the deep aquifer. [ABSTRACT FROM AUTHOR]

People in the southwestern (SW) coastal part of Bangladesh are suffering from a severe freshwater crisis due to saline groundwater at a shallow depth. Fresh groundwater below a 200 m depth is an option, but it is costly to construct deep tubewells for the local inhabitants. The processes of salinization and freshening were previously identified using conventional methods. In this study, we brought new insight into these processes by analyzing existing datasets using multivariate statistics to identify the factors affecting groundwater chemistry. Cluster analysis (CA) revealed three major clusters. Cluster A corresponded to saline (NaCl-type) water. Cluster B was also saline (NaCl-type) water but showed mixing effects. Cluster C was fresh groundwater (NaHCO3-type) and isolated. The hydrochemical characteristics of clusters A, B and C compared remarkably well with the groundwaters from the upper shallow aquifer (USA), lower shallow aquifer (LSA) and deep aquifer (DA), respectively. Factor analysis (FA) showed that 75% of the total variance was influenced by evaporate dissolution, carbonate dissolution/precipitation, cation exchange and anthropogenic pollution to some extent. Therefore, the integrated approach showed the validity of applying multivariate statistical techniques to infer the dominant hydrochemistry and to characterize and understand a complicated hydrogeological system. [ABSTRACT FROM AUTHOR]

The major springs in the Infranz catchment are a significant source of water for Bahir Dar City and nearby villages, while sustaining the Infranz River and the downstream wetlands. The aim of the research was to understand the hydrogeological conditions of these high-discharge springs and the recharge–discharge relations in the Infranz catchment. The Infranz catchment is covered by highly pervious and young quaternary volcanic rocks, consisting of blocky, fractured, and strongly vesicular scoriaceous basalt. At the surface, these rocks crop out as lineaments forming ridges, delimiting closed depressions in which water accumulates during the rainy season without causing surface runoff. Geology and geomorphology thus combine to produce very favorable conditions for groundwater recharge. Three groundwater recharge methods were applied to estimate groundwater recharge and the results were compared. Groundwater recharge was calculated to be 30% to 51% of rainfall. Rapid replenishment raises the groundwater level during the rainfall period, followed by a rapid decline during the dry season. Shallow local flow paths discharge at seasonal springs and streams, while more regional and deeper flow systems downstream sustain the high-discharge springs and perennial Infranz River. The uptake of 75% of spring water for the water supply of Bahir Dar City, local extraction for domestic and small-scale irrigation use from springs, rivers and hand-dug wells, encroaching farming, and overgrazing are exacerbating wetland degradation. [ABSTRACT FROM AUTHOR]

In the coastal region of Bangladesh, groundwater is mainly used for domestic and agricultural purposes, but salinization of many groundwater resources limits its suitability for human consumption and practical application. This paper reports the results of a study that has mapped the salinity distribution in different aquifer layers up to a depth of 300 m in a region bordering the Bay of Bengal based on the main hydrochemistry and has investigated the origin of the salinity using Cl/Br ratios of the samples. The subsurface consists of a sequence of deltaic sediments with an alternation of more sandy and clayey sections in which several aquifer layers can be recognized. The main hydrochemistry shows different main water types in the different aquifers, indicating varying stages of freshening or salinization processes. The most freshwater, soft NaHCO3-type water with Cl concentrations mostly below 100 mg/l, is found in the deepest aquifer at 200-300 m below ground level (b.g.l.), in which the fresh/saltwater interface is pushed far to the south. Salinity is a main problem in the shallow aquifer systems, where Cl concentrations rise to nearly 8000 mg/l and the groundwater is mostly brackish NaCl water. Investigation of the Cl/Br ratios has shown that the source of the salinity in the deep aquifer is mixing with old connate seawater and that the saline waters in the more shallow aquifers do not originate from old connate water or direct seawater intrusion, but are derived from the dissolution of evaporite salts. These must have been formed in a tidal flat under influence of a strong seasonal precipitation pattern. Long dry seasons with high evaporation rates have evaporated seawater from inundated gullies and depressions, leading to salt precipitation, while subsequent heavy monsoon rains have dissolved the formed salts, and the solution has infiltrated in the subsoil, recharging groundwater. [ABSTRACT FROM AUTHOR]