scholarly journals Deep Groundwater Recharge Mechanism in the Sedimentary and Crystalline Terrains of Sri Lanka: A Study Based on Environmental Isotopic and Chemical Signatures of Spring Water

2020 ◽  
Author(s):  
Sakhila Priyadarshanee ◽  
Zhonghe Pang ◽  
Viraj Edirisinghe ◽  
H.A. Dharmagunawardhane ◽  
H.M.T.G.A. Pitawala ◽  
...  
Keyword(s):  
Sri Lanka ◽  
Geochemical Characteristics ◽  
Thermal Springs ◽  
Thermal Waters ◽  
Deep Groundwater ◽  
Flow Paths ◽  
Water Interaction ◽  
Deep Aquifers ◽  
Regional Flow ◽  
Rock Water Interaction

In many instances, dynamic, potential status and geochemical characteristics of groundwater discharging through natural springs are not well known. Present study has assessed the deep groundwater in the form of thermal and non-thermal spring in artesian condition in the selected zones in Sri Lanka, using isotope and geochemical characteristics. The results revealed that evaporation-fractional crystallization and cation-exchange in the sedimentary aquifers while rock-water interaction in crystalline deep aquifers, are the significant mechanism that control the groundwater chemistry. All the deep groundwater recharged from meteoric water at different elevations and further influenced by either evaporation or rock-water interaction during the subsurface flow. Artesian aquifers in the sedimentary terrain in the north-western coastal zones showed the recharging elevation as from 100 to 200 m amsl. They are not mixed with sea water and slightly impacted by the locally evaporated surface waters. Almost all these waters are comparatively old; indicating slow movement along the regional flow paths. Considering the recharge and discharge conditions of artesian non-thermal waters in the Southern lowlands of crystalline terrain can be classified as non-mixed, non-evaporated and young groundwater with higher elevation recharge. The artesian non-thermal waters in the East North Central lowlands, have shown the same characteristics but with evaporated conditions. All artesian thermal waters are tritium free, hence they are older and deep percolated. Intensive rock-water interaction and higher altitude origin were observed in some thermal springs. Some spring clusters in the weathered overburden have shown significant mixing with recent local rains. Non-mixed, non-evaporated and less rock-water interacted nature is a significant in two thermal springs that emerges through (chemically inert) quartzite bed rock. Both thermal and non-thermal water with artesian condition have clearly indicated that they are originated from a common recharge source but with different flow paths in different penetration depths and travel distances, resulting different chemical characteristics. Fresh water springs are mostly young and recharged from local rains followed with shallow percolation.

Modeling of groundwater flow velocity and aquifer recharge in a Cenozoic multi-aquifer system – a case study from Eastern Brandenburg (Germany)

2020 ◽  
Author(s):  
Silvio Janetz ◽  
Christoph Jahnke ◽  
Frank Wendland ◽  
Hans-Jürgen Voigt
Keyword(s):  
Groundwater Flow ◽  
Groundwater Resources ◽  
Turnover Time ◽  
Aquifer Recharge ◽  
Deep Groundwater ◽  
Near Surface ◽  
Aquifer System ◽  
Deep Aquifers ◽  
Regional Flow ◽  
Flow Processes

<p>In recent years, deep aquifers (> 50 m below ground level) have become increasingly interesting for the supply of drinking and irrigation water or geothermal use. Understanding the regional flow processes between near-surface and deep aquifer systems is an important criterion for the sustainable management of deep groundwater resources. However, hydrogeological conditions, regional flow rates and aquifer recharge in deep aquifers are largely unknown in many cases. The aims of the present study are therefore to determine (i) groundwater flow velocities in a Cenozoic multi-aquifer system, and (ii) proportion of aquifer recharge into the individual Cenozoic aquifers and timescales to completely replace water in the Cenozoic aquifers (turnover time).  </p><p>The numerical study was carried out in three adjacent groundwater catchment areas in the region of Eastern Brandenburg. In a first step, a hydrogeological 3D model of the entire Cenozoic aquifer system (85 km × 73 km and down to a depth of 0.5 km) was developed, which comprises up to 12 unconsolidated sandy aquifers and 10 confining units (glacial tills, silts and clays). In a second step, a steady-state flow modelling was performed including calibration using natural hydraulic head data from both regional main and deep aquifers.</p><p>The modeling results show that the average groundwater flow velocities decrease from 20-50 m/a in the near-surface Pleistocene main aquifers to 1-2 m/a in the deep Oligocene aquifers. At the same time, the aquifer recharge in the aquifer system decreases substantially with increasing depth. Depending on the catchment geology, the Pleistocene main aquifers are recharged by 65-70 % of infiltration water, while the aquifer recharge of the deep Oligocene aquifers is only 4.5-9.5 %. The calculations of turnover time indicate that the time periods to completely flush the deep aquifers are very long (approx. between 90 and 4600 years). The results thus allow a first quantification of the flow processes between near-surface and deep aquifers as well as the identification of flow paths to develop a utilization concept for deep groundwater resources in the region of Eastern Brandenburg.</p>

scholarly journals Understanding wetland sub-surface hydrology using geologic and isotopic signatures

2009 ◽  
Vol 13 (7) ◽  
pp. 1313-1323 ◽  
Author(s):  
P. K. Sikdar ◽  
P. Sahu
Keyword(s):  
Surface Water ◽  
Urban Areas ◽  
Isotope Composition ◽  
Operation Time ◽  
Freshwater Wetland ◽  
Bengal Basin ◽  
Silty Clay ◽  
Deep Groundwater ◽  
Deep Aquifer ◽  
Deep Aquifers

Abstract. This paper attempts to utilize hydrogeology and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) – a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater of the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. At few places the top silty clay layer is absent due to scouring action of past channels. In these areas sand is present throughout the geological column and the areas are vulnerable to groundwater pollution. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deep groundwater with very low tritium is recharged mainly from distant areas. At places the deep aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminium, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution. In the area south of ECW isotope data indicates no interaction between shallow and deep aquifer and hence this area may be a better location to treat sewage water than within ECW. To reduce the threat of pollution in ECW's aquifer, surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificial recharging of the aquifer.

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