Investigation of recharge dynamics and flow paths in a fractured crystalline aquifer in semi-arid India using borehole logs: implications for managed aquifer recharge

Groundwater, and its replenishment via recharge, is critical to livelihoods and poverty alleviation in drylands of sub-Saharan Africa and beyond, yet the processes by which groundwater is replenished remain inadequately observed and resolved. Here, we present three lines of evidence, from an extensively-monitored wellfield in central semi-arid Tanzania, indicating focused groundwater recharge occurring via leakage from episodic, ephemeral stream discharges. First, the duration of ephemeral streamflow observed from daily records from 2007 to 2016 correlates strongly (R2 = 0.85) with the magnitude of groundwater recharge events observed and estimated from piezometric observations. Second, high-resolution (hourly) monitoring of groundwater levels and stream stage, established in advance of the 2015-16 El Ni&#241;o, shows the formation and decay of groundwater mounds beneath episodically inundated adjacent streambeds. Third, stable-isotope ratios of O and H of groundwater and precipitation as well as perennial and ephemeral surface waters trace the origin of groundwater to ephemeral stream discharges. The identification and characterisation of focused groundwater recharge have important implications not only, locally, for protecting and potentially augmenting replenishment of a wellfield supplying the capital of Tanzania through Managed Aquifer Recharge but also, more widely, in understanding and modelling groundwater recharge in dryland environments.

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Hydrogeological controls on groundwater recharge in a weathered crystalline aquifer: A case study from the Makutapora groundwater basin, Tanzania

10.5194/egusphere-egu2020-19140 ◽

2020 ◽

Author(s):

Emanuel Zarate ◽

Alan MacDonald ◽

Russell Swift ◽

Jonathan Chambers ◽

Japhet Kashaigili ◽

...

Keyword(s):

Groundwater Recharge ◽

Crucial Role ◽

Numerical Models ◽

Groundwater Resources ◽

Crystalline Rock ◽

Aquifer Recharge ◽

Crystalline Aquifer ◽

Geophysical Surveys ◽

Groundwater Basin ◽

Semi Arid

Drylands (semi-arid/arid regions) represent >35% of the Earth&#8217;s surface, support a population of around 2 billion people, and are forecast to be increasingly water stressed in coming decades. Groundwater is the most reliable source of water in drylands, and it is likely that the structure and hydraulic properties of superficial geology play a crucial role in controlling groundwater recharge in these regions.&#160; However, the spatio-temporal hydrogeological controls on the rates of groundwater recharge, and their sensitivity to environmental change are poorly resolved.In the Makutapora groundwater basin (Tanzania), an analogue for semi-arid tropical areas underlain by weathered and fractured crystalline rock aquifers, we conducted a series of geophysical surveys using Electrical Resistivity Tomography (ERT) and frequency domain electromagnetic methods (FDEM). Using these data, in conjunction with borehole logs, we identify and delineate five major lithological units in the basin: 1) Superficial deposits of coarse sand (>200 &#937; m) 2) Highly conductive smectitic clays (1-10 &#937; m) 3) Decomposed pedolitic soils (30-100 &#937; m) 4) Weathered saprolite (100-700 &#937; m) and 5) Fractured granitic basement (>700 &#937; m). We also identify 10-50m wide zones of normal faulting extending across the basin and cutting through these units, interpreted with the aid of analysis of a digital elevation model alongside the geophysics data.These results are combined with existing long-term hydrological and hydrogeological records to build conceptual models of the processes governing recharge. We hypothesise that: 1) Zones of active faulting provide permeable pathways enabling greater recharge to occur; 2) Superficial sand deposits may act as collectors and stores that slowly feed recharge into these fault zones; 3) Windows within layers of smectitic clay underlying ephemeral streams may provide pathways for focused recharge via transmission losses; and 4) Overbank flooding during high-intensity precipitation events that inundate a greater area of the basin increases the probability of activating such permeable pathways.Our results suggest that configurations of superficial geology may play a crucial role in controlling patterns, rates and timing of groundwater recharge in dryland settings. They also provide a physical basis to improve numerical models of groundwater recharge in drylands, and a conceptual framework to evaluate strategies (e.g. Managed Aquifer Recharge) to artificially enhance the availability of groundwater resources in these regions.

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Identification of suitable sites for managed aquifer recharge under semi-arid conditions employing a combination of numerical and analytical techniques

Environmental Earth Sciences ◽

10.1007/s12665-021-09797-y ◽

2021 ◽

Vol 80 (17) ◽

Author(s):

Jafar Alkhatib ◽

Irina Engelhardt ◽

Martin Sauter

Keyword(s):

Empirical Equation ◽

Surface Characteristics ◽

Managed Aquifer Recharge ◽

Specific Yield ◽

Multiple Model ◽

Aquifer Recharge ◽

Suitability Maps ◽

Aquifer Characteristics ◽

Groundwater Mound ◽

Semi Arid

AbstractOverpumping or overexploitation of groundwater is one of the major threats for aquifer systems in arid and semi-arid areas. Managed aquifer recharge (MAR) has been suggested by many researchers as a sustainable and effective method to alleviate negative impacts of overpumping. Optimizing artificial recharge considers the selection of suitable MAR sites in terms of surface and subsurface characteristics. While surface characteristics at potential MAR sites could be modified (e.g. slope, soil texture, etc.), subsurface characteristics cannot be changed through engineering work. Characteristics of the aquifer, such as depth to groundwater, play an important role in determining the capability of an aquifer to store a specific volume of infiltrated water. Currently, only a limited number of quoted researches are available that consider factors related to aquifer characteristics and the range of these factors to identify optimal MAR sites. In this study, a new approach is presented, that employs numerical groundwater modeling to generate MAR suitability maps considering sub-surface characteristics, such as depth-to-groundwater, aquifer transmissivity and specific yield. Multiple model-runs are conducted to simulate groundwater table response with respect to the volume of infiltrated water. Simulation results are used to calibrate a groundwater mound empirical equation that calculates the groundwater level increase as a function of the transmissivity and infiltrated water volume for a given value of aquifer’ specific yield, range of vertical hydraulic conductivities and a specific design and operation conditions of the MAR system. The empirical equation is employed in GIS to spatially calculate the height of groundwater mound beneath a hypothetical MAR site and to generate, based on that, suitability maps for MAR implementation. Assuming that MAR structures capture the median of monthly surface runoff rates at the respective wadi (catchment area), suitability maps are generated for different configurations/scenarios of aquifer hydraulic conductivity in a parameter study. The results highlight the importance of integrating aquifer characteristics (geometry and hydraulic parameters) and expected magnitudes and fluxes of infiltration water in delineating suitable sites for MAR.

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Managed aquifer recharge (MAR) by the construction of subsurface dams in the semi-arid regions: A case study of the Kalangi river basin, Andhra Pradesh

Journal of the Geological Society of India ◽

10.1007/s12594-013-0204-6 ◽

2013 ◽

Vol 82 (6) ◽

pp. 657-665 ◽

Cited By ~ 13

Author(s):

N. Janardhana Raju ◽

T. V. K. Reddy ◽

P. Muniratnam ◽

Wolfgang Gossel ◽

Peter Wycisk

Keyword(s):

River Basin ◽

Andhra Pradesh ◽

Arid Regions ◽

Managed Aquifer Recharge ◽

Aquifer Recharge ◽

Semi Arid

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Contamination risk and drinking water protection for a large-scale managed aquifer recharge site in a semi-arid karst region, Jordan

Hydrogeology Journal ◽

10.1007/s10040-017-1586-0 ◽

2017 ◽

Vol 25 (6) ◽

pp. 1795-1809 ◽

Cited By ~ 5

Author(s):

Julian Xanke ◽

Tanja Liesch ◽

Nadine Goeppert ◽

Jochen Klinger ◽

Niklas Gassen ◽

...

Keyword(s):

Drinking Water ◽

Large Scale ◽

Managed Aquifer Recharge ◽

Karst Region ◽

Water Protection ◽

Aquifer Recharge ◽

Contamination Risk ◽

Semi Arid

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Evaluation of MAR Methods for Semi-Arid, Cold Regions

Water ◽

10.3390/w11122548 ◽

2019 ◽

Vol 11 (12) ◽

pp. 2548 ◽

Cited By ~ 1

Author(s):

Nasanbayar Narantsogt ◽

Ulf Mohrlok

Keyword(s):

Water Reservoir ◽

Managed Aquifer Recharge ◽

Capital City ◽

Ice Storage ◽

Aquifer Recharge ◽

Dry Period ◽

Groundwater Aquifer ◽

Recharge Rates ◽

Semi Arid ◽

Natural Recharge

Mongolia is a semi-arid, highly continental region with highly variable precipitation and river discharge. The groundwater aquifer located near Ulaanbaatar, the capital city of Mongolia, is the only one source for city water supply consumption, and it is important to ensure that groundwater is available now and in the future. The main watercourse near the capital city is the Tuul River, fed by precipitation in the Khentii Mountains. The semi-arid and cold environment shows high variability in precipitation and river discharge. However, due to absence of precipitation in winter and spring, the riverbed usually runs dry during these times of the year, and weather observations show that the dry period has been extending in recent years. However, in parallel with urban development, the extended groundwater aquifer has shown a clear decline, and the groundwater levels have dropped significantly. Therefore, a groundwater management system based on managed aquifer recharge is proposed, and a strategy to implement these measures in the Tuul River valley is presented in this paper. This strategy consists of the enhancement of natural recharge rates during the wet summer from the northern drainage canal, an additional increase in groundwater recharge through melting the ice storage in the dry period, as well as the construction of underground dams to accumulate groundwater and a surface water reservoir that releases a constant discharge in the outlet. To increase natural recharge rates of groundwater during the early dry period through the melting ice storage period, the MATLAB icing code, which was written for ice storage for limited and unlimited areas, was considered through finite element subsurface FLOW (FEFLOW) simulation scenarios as a water source in ice form on the surface. A study of the artificial permafrost of underground as an ice dam was processed in FEFLOW simulation scenarios for accumulating groundwater resources. The results of these artificial recharging methods were individually calculated, combined, and compared with the surface reservoir, which releases a constant discharge through the dam. In this paper, new ideas are presented involving managed aquifer recharge—MAR methods, and include application to aufeis, a mass of layered ice for groundwater recharge by melting. Additionally, the accumulation of groundwater using artificial permafrost is used as an underground dam. In addition, was considered recharging scenario only with constant release water amount from water reservoir also with all MAR methods together with reservoir combination.

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