scholarly journals Quantifying freshwater resource in coastal barriers: the joint use of transient electromagnetic and magnetic resonance soundings

2012 ◽  
Vol 9 (4) ◽  
pp. 5261-5294
Author(s):  
J.-M. Vouillamoz ◽  
J. Hoareau ◽  
M. Grammare ◽  
D. Caron ◽  
L. Nandagiri ◽  
...  

Abstract. Many human communities living in coastal areas in Africa and Asia rely on thin fresh water lenses for their domestic supply. Population growth together with change in rainfall patterns and sea level will probably impact these vulnerable groundwater resources. A spatial knowledge of the aquifer properties and the use of groundwater model are required for the sustainable management of the resource. This paper presents a ready-to-use methodology for estimating the key aquifer properties based on the joint use of two non-invasive geophysical tools together with common hydrological measurements. We applied the proposed methodology on a coastal sandy barrier in South-Western India. We found that the joint use of magnetic resonance and transient electromagnetic soundings allows to map the fresh water lens and to estimate the specific yield, the hydraulic conductivity, the water salinity and the water table recharge. From the geophysical results, we estimate the fresh water reserve to range between 400 and 700 l m−2 of surface area according to the location and to the season. Using time lapse geophysical measurements and common groundwater monitoring, we also estimate the recharge of a rainy event to be about 100% of the rain, and the net recharge at the end of the monsoon to be less than 10% of the rain. Thus, we conclude that a change in rainfall patterns will probably not impact the groundwater resource since most of the rain water recharging the aquifer is flowing towards the sea and the river. However, a change in sea level will impact both the groundwater reserve and net recharge.

2012 ◽  
Vol 16 (11) ◽  
pp. 4387-4400 ◽  
Author(s):  
J.-M. Vouillamoz ◽  
J. Hoareau ◽  
M. Grammare ◽  
D. Caron ◽  
L. Nandagiri ◽  
...  

Abstract. Many human communities living in coastal areas in Africa and Asia rely on thin freshwater lenses for their domestic supply. Population growth together with change in rainfall patterns and sea level will probably impact these vulnerable groundwater resources. Spatial knowledge of the aquifer properties and creation of a groundwater model are required for achieving a sustainable management of the resource. This paper presents a ready-to-use methodology for estimating the key aquifer properties and the freshwater resource based on the joint use of two non-invasive geophysical tools together with common hydrological measurements. We applied the proposed methodology in an unconfined aquifer of a coastal sandy barrier in South-Western India. We jointly used magnetic resonance and transient electromagnetic soundings and we monitored rainfall, groundwater level and groundwater electrical conductivity. The combined interpretation of geophysical and hydrological results allowed estimating the aquifer properties and mapping the freshwater lens. Depending on the location and season, we estimate the freshwater reserve to range between 400 and 700 L m−2 of surface area (± 50%). We also estimate the recharge using time lapse geophysical measurements with hydrological monitoring. After a rainy event close to 100% of the rain is reaching the water table, but the net recharge at the end of the monsoon is less than 10% of the rain. Thus, we conclude that a change in rainfall patterns will probably not impact the groundwater resource since most of the rain water recharging the aquifer is flowing towards the sea and the river. However, a change in sea level will impact both the groundwater reserve and net recharge.


2018 ◽  
Vol 54 (4B) ◽  
pp. 260
Author(s):  
Nguyen Viet Ky

Ho Chi Minh City has 7 aquifers with different distributions, ascending from the east, western-north to eastern-southeast with total potential reserves of about 1.65 million mP3P of fresh water/day, potential reserves of underground water brackish-salty approximately 2.25 million mP3P/day. This resource is invaluable for the development of the city today and the future. However, groundwater resources are at risk of depletion of reserves, quality under the impact of climate change and sea level rise. In this paper, the authors focus on evaluating the impact of rising sea levels to shift the boundaries of the aquifer salinity, which narrow the area of fresh water and diminishing reserves of fresh water . To assess, first based on climate change scenarios and sea level rise has been Vietnam announced in 2012, at the same time as the underground water is exploited more constant (the maximum amount of water extraction in 2015 basis), the authors conducted for running surface flow model to get the water level data at some point to put into models of groundwater flow. Thanks to model groundwater flow, the authors showed that the sea level rise significantly shift the boundaries of the aquifer salinity toward the inner city. The area contains fresh water and reduced water reserves only light compared with present reserves.


2021 ◽  
Author(s):  
Uwe Morgenstern ◽  
Zara Rawlinson

<p>Geologic data to provide information on the functioning of aquifers is often scars. For the aquifers underlying the Heretaunga Plains, Hawkes Bay, one of New Zealand’s most important groundwater systems, we used groundwater age (tritium, SF6, 14C) to inform the geologic model and to provide information on groundwater flow through alternating strata of permeable river gravel beds and fine impermeable beds that form an interconnected unconfined–confined aquifer system with complex groundwater flow processes.</p><p>The aquifers are a result of geological processes responding to climate change cycles from cold glacial when sea level was more than 100m below present sea level, to warm interglacial periods with sea level similar to present day. Glacial climate strata are river gravel, sand and silt deposits and include the artesian aquifers. The interglacial strata form the aquicludes and are marine sand, silt, and clay deposits with interbedded estuarine, swamp and coastal fluvial silt, clay, peat and gravel deposits.</p><p>We have re-visited tracer data sampled during the drilling of multi-level observation well in the early 1990s, and collected new samples from these multi-level bores in order to understand in 3D the groundwater recharge sources, groundwater recharge and flow rates, connection to the rivers, and potential groundwater discharge out to sea. Consistently young water (c. 25 years) at depth greater than 100m indicates preferential flow paths, likely related to paleo-river channels. The flow pattern obtained from the water tracer data improves the geologic information from the drill-holes, and fits with information from recent airborne transient electromagnetic (SkyTEM) geophysical surveys.</p>


2021 ◽  
pp. 132-141
Author(s):  
Ashish Kumar Jangid

The Short-tailed ground agama or Hardwicke’s bloodsucker Calotes minor (Hardwicke & Gray, 1827) is known to occur in the Indian subcontinent and is largely confined to arid to semiarid environments, such as hard barren desert and abandoned fields. The precise distribution of this species is largely unknown to date, with few locality records spread biogeographically across Eastern Pakistan, Central and Western India. To improve on the existing spatial knowledge on this species and assess the ability to predict species distributions for taxa with few locality records, we studied the distribution of C. minor using a species distribution modelling framework. Our study allowed us to predict the distribution range of C. minor and help define a niche for this habitat-specific species. Highly probable habitats for C. minor were arid and semi-arid dryland habitats, characterised by plains or less rugged terrain with moderately narrow temperature range, lower aridity index, moderate to low vegetation index, and wide precipitation range. Furthermore, we report four additional occurrence records of C. minor from central Rajasthan.


2003 ◽  
Vol 47 (7-8) ◽  
pp. 259-265 ◽  
Author(s):  
P. Literathy ◽  
M. Quinn ◽  
M. Al-Rashed

The only natural freshwater resource of Kuwait occurs as lenses floating on the saline groundwater in the northern part of the country, near to the oil fields. Rainwater is the only means of recharge of this limited groundwater resource. This groundwater is used as bottled drinking water and the fresh groundwater aquifer is considered as a strategic drinking water reserve for Kuwait. As a result of the 1991 Gulf War, the upper soil layer has been widely contaminated with crude oil and crude oil combustion products, which are potential pollutants likely affecting the groundwater resources. Significant efforts have been made to assess this pollution. These included: (a) a soil survey for assessing the soil contamination, and (b) leaching experiments to characterise the mobilization of the soil-associated pollutants. Fluorescence measurement techniques were used during field surveys as well as for laboratory testing. In addition, determination of the total extractable matter (TEM), total petroleum hydrocarbons (TPH), and GC/MS measurement of polyaromatic hydrocarbons (PAHs) were performed for the assessments. The laser induced fluorescence (LIF) measurement, having good correlation with the other laboratory measurements, was proved to provide necessary information for the assessment of the oil-contamination level in the desert soil. The subsequent leaching test with water demonstrated the mobilization of the fluorescing compounds (e.g. PAHs), and the alteration in the leaching characteristics of the contamination during the long-term environmental weathering of the oil.


Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. WB33-WB48 ◽  
Author(s):  
Denys Grombacher ◽  
Mike Müller-Petke ◽  
Rosemary Knight

To produce reliable estimates of aquifer properties using surface nuclear magnetic resonance (NMR), an accurate forward model is required. The standard surface NMR forward model assumes that excitation occurs through a process called on-resonance excitation, which occurs when the transmit frequency is set to the Larmor frequency. However, this condition is often difficult to satisfy in practice due to the challenge of accurately determining the Larmor frequency within the entire volume of investigation. As such, in situations where an undesired offset is present between the assumed and true Larmor frequency, the accuracy of the forward model is degraded. This is because the undesired offset leads to a condition called off-resonance excitation, which impacts the signal amplitude, phase, and spatial distribution in the subsurface, subsequently reducing the accuracy of surface NMR estimated aquifer properties. Our aim was to reduce the impact of an undesired offset between the assumed and true Larmor frequency to ensure an accurate forward model in the presence of an uncertain Larmor frequency estimate. We have developed a methodology where data are collected using two different transmit frequencies, each an equal magnitude above and below the assumed Larmor frequency. These data are combined, through a method we refer to as frequency cycling, in a manner that allow the component well-described by our estimate of the Larmor frequency to be stacked coherently, whereas the component related to the presence of an undesired offset is combined destructively. In synthetic and field studies, we have determined that frequency cycling is able to mitigate the influence of an undesired offset providing more accurate estimates of aquifer properties. Furthermore, the frequency-cycling method stabilized the complex inversion of surface NMR data, allowing advantages associated with complex inversion to be exploited.


Author(s):  
K. Furuno ◽  
A. Kagawa ◽  
O. Kazaoka ◽  
T. Kusuda ◽  
H. Nirei

Abstract. Over 40 million people live on and exploit the groundwater resources of the Kanto Plain. The Plain encompasses metropolitan Tokyo and much of Chiba Prefecture. Useable groundwater extends to the base of the Kanto Plain, some 2500 to 3000 m below sea level. Much of the Kanto Plain surface is at sea level. By the early 1970s, with increasing urbanization and industrial expansion, local overdraft of groundwater resources caused major ground subsidence and damage to commercial and residential structures as well as to local and regional infrastructure. Parts of the lowlands around Tokyo subsided to 4.0 m below sea level; particularly affected were the suburbs of Funabashi and Gyotoku in western Chiba. In the southern Kanto Plain, regulations, mainly by local government and later by regional agencies, led to installation of about 500 monitoring wells and almost 5000 bench marks by the 1990's. Many of them are still working with new monitoring system. Long-term monitoring is important. The monitoring systems are costly, but the resulting data provide continuous measurement of the "health" of the Kanto Groundwater Basin, and thus permit sustainable use of the groundwater resource.


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