Groundwater age in the Wairarapa

Mapping Intimacies ◽

10.26686/wgtn.17008315.v1 ◽

2021 ◽

Author(s):

◽

Ryan David Evison

Keyword(s):

Land Use ◽

Drinking Water ◽

New Zealand ◽

Groundwater Flow ◽

Groundwater Age ◽

Groundwater Resources ◽

Age Distribution ◽

Transport Processes ◽

Age Assessment ◽

The Mean

This dissertation focuses on the catchment-scale evaluation of groundwater age as a function of space and time in the 270 km² Middle Wairarapa catchment. The simulation of the mean age and point distribution of ages, contributing to a regional age estimate, is a novel demonstration of the recently developed groundwater software, Cornaton (2012). The Wairarapa is in the southern North Island of New Zealand and is a dynamic water catchment exhibiting complex interactions between its rivers and shallow aquifers. Groundwater has been widely utilized since the 1980s for agriculture, horticulture and drinking water; increasing land use development (i.e. irrigation and nutrient application) requires effective regional management of both the quantity and quality of water resources. Groundwater age provides insights into groundwater flow and transport processes and thus enables better management of groundwater resources. Subsurface water age information enables the interpretation of recharge influence, zones of sensitivity for sustainable abstraction, as well as contamination risk from land-use intensification to drinking water supplies. It is accepted that groundwater is composed of a mixture of water with different ages, however, until very recently mean age has been the primary indicator for groundwater age assessment. Mean age alone can misrepresent the potential for contamination from young water; for example, a groundwater sample with an old mean age may still contain a significant fraction of young water; therefore, a fuller understanding of the age distribution in both time and space is important for groundwater management. The ability to simulate the full distribution of groundwater age within transient numerical groundwater models has only been very recently enabled, through implementation of the time-marching Laplace transform Galerkin technique (TMLTGT), and is demonstrated in this dissertation. A transient finite-element groundwater flow model originally developed by Greater Wellington Regional Council was converted to simulate transport of the age tracer tritium and groundwater age using the Ground Water (GW) software. Observed tritium concentrations were utilized in the calibration using the Monte Carlo and Gauss-Marquardt-Levenberg methods. Following the calibration of the transport model the GW software was then used to derive pumping well capture zones and directly simulate age throughout the Middle Wairarapa Valley catchment. The advective dispersive equation and the TMLTGT were used for transient mean-age and transient simulations of the full distribution of groundwater age. The results are presented as maps and graphs of both mean age and age distributions throughout the Middle Valley, covering a 15 year simulation period. The mean-age simulations indicated the groundwater age in the valley was strongly influenced by seasonal changes and extreme climatic events. Significant variations existed, from high rainfall recharge percolating young water throughout the domain, to dry extended droughts limiting recharge and increasing the age throughout large sections of the Middle Valley. Age distributions were shown to be strongly influenced by abstraction pressures, depth and geology. Abstractions were shown to skew the age distribution, creating both older and younger mean-ages depending on the location of the observation point, and several simulations indicated the potential misrepresentation of young (potentially contaminated) water quantified as old by mean-age assessment. These results show the dynamic nature of the Middle Valley groundwater system and its inherent vulnerabilities. The Wairarapa transient age distributions are one of the first such examples in New Zealand, and they demonstrate the potential of the information interpreted from age estimates to more effectively manage groundwater resources.

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Groundwater age in the Wairarapa

10.26686/wgtn.17008315 ◽

2021 ◽

Author(s):

◽

Ryan David Evison

Keyword(s):

Land Use ◽

Drinking Water ◽

New Zealand ◽

Groundwater Flow ◽

Groundwater Age ◽

Groundwater Resources ◽

Age Distribution ◽

Transport Processes ◽

Age Assessment ◽

The Mean

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A multi-environmental tracer study to determine groundwater residence times and recharge in a structurally complex multi-aquifer system

Hydrology and Earth System Sciences ◽

10.5194/hess-24-249-2020 ◽

2020 ◽

Vol 24 (1) ◽

pp. 249-267 ◽

Cited By ~ 1

Author(s):

Cornelia Wilske ◽

Axel Suckow ◽

Ulf Mallast ◽

Christiane Meier ◽

Silke Merchel ◽

...

Keyword(s):

Groundwater Flow ◽

Groundwater Recharge ◽

Groundwater Age ◽

Age Distribution ◽

Dead Sea ◽

Artificial Sweetener ◽

Environmental Tracers ◽

Jordan Valley ◽

Aquifer System ◽

Lumped Parameter

Abstract. Despite being the main drinking water resource for over 5 million people, the water balance of the Eastern Mountain Aquifer system on the western side of the Dead Sea is poorly understood. The regional aquifer consists of fractured and karstified limestone – aquifers of Cretaceous age, and it can be separated into a Cenomanian aquifer (upper aquifer) and Albian aquifer (lower aquifer). Both aquifers are exposed along the mountain ridge around Jerusalem, which is the main recharge area. From here, the recharged groundwater flows in a highly karstified aquifer system towards the east and discharges in springs in the lower Jordan Valley and Dead Sea region. We investigated the Eastern Mountain Aquifer system for groundwater flow, groundwater age and potential mixtures, and groundwater recharge. We combined 36Cl ∕ Cl, tritium, and the anthropogenic gases SF6, CFC-12 (chlorofluorocarbon) and CFC-11, while using CFC-113 as “dating” tracers to estimate the young water components inside the Eastern Mountain Aquifer system. By application of lumped parameter models, we verified young groundwater components from the last 10 to 30 years and an admixture of a groundwater component older than about 70 years. Concentrations of nitrate, simazine (pesticide), acesulfame K (ACE-K; artificial sweetener) and naproxen (NAP; drug) in the groundwater were further indications of infiltration during the last 30 years. The combination of multiple environmental tracers and lumped parameter modelling helped to understand the groundwater age distribution and to estimate recharge despite scarce data in this very complex hydrogeological setting. Our groundwater recharge rates support groundwater management of this politically difficult area and can be used to inform and calibrate ongoing groundwater flow models.

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Nitrate transfer in the Critical zone view through N & O isotopes of NO3 and CFC-SF6 groundwater residence time assessment

10.5194/egusphere-egu2020-17524 ◽

2020 ◽

Author(s):

Emmanuelle Petelet-Giraud ◽

Nicole Baran ◽

Virginie Vergnaud ◽

Flora Lucassou ◽

Jean-Michel Schroetter

Keyword(s):

Drinking Water ◽

Residence Time ◽

Rural Areas ◽

Groundwater Resources ◽

Major Elements ◽

Critical Zone ◽

Basin Scale ◽

Nitrate Concentrations ◽

The Mean ◽

Gas Measurements

Drinking water quality in agricultural rural areas remains locally a challenge even all the effort made by local authorities to restore the groundwater resources quality, especially regarding nitrates. In Plourhan, a ~2000 inhabitants, about 10 km from the sea, NW France, the drinking water is pumped in a natural spring emerging from the Brioverian basement. The nitrate concentrations exceed the 50 mg/L standard for drinking water supply, and thus needs to be diluted to be delivered to the population. Over the last 15 years, a large programme of measures was undertaken in order to reduce the NO3 concentration, including the purchase of agricultural parcels around the spring, moving progressively from mixed farming and livestock to fallows and meadows, and thus drastically change the local land use. Despite all these efforts, nitrate concentrations only decrease very slowly and remain above the 50 mg/L standard.In this context, the objective of this study is to better understand the transfer of nitrates at the basin scale, by studying flow paths, geochemical reactions, transit times that are key parameters to estimate the vulnerability and the recovery-time of the critical zone. In that way, a geochemical and isotopic approach is applied at the basin scale. Major elements analysis of the groundwater reflect the drained contrasted lithologies as metasediments (pelites & sandstones) and amphibolite, with a large spatial heterogeneity of the NO3 concentrations, ranging from a few mg/L to more than 50 mg/L. Nitrogen and oxygen isotopes of nitrates (&#948;15N-NO3 and &#948;18O-NO3) suggest that denitrification can occur locally in some wells presenting low or intermediate &#160;NO3 contents, whereas other wells present high or low NO3 concentrations without any evidence of denitrification processes. The mean residence time of groundwater is assessed through CFCs and SF6 dissolved gas measurements. Some wells preferentially in amphibolite, present water with low recharge temperature (around 6&#176;C while the mean recharge temperature in Britany is 11-12&#176;C) correlated with low CFCs/SF6 values indicating that some very old groundwater (last glaciation :&#160; -19/17 k yrs) exists in the reservoir. Other ones in metasediments have modern water or a mixing between an old and a present day recharge. These results, together with structural and lithological detailed geological field mapping, help to draw up the conceptual model of the aquifer functioning regarding nitrates transfer in the critical zone.&#160;&#160;This work is part of the POLDIFF study that benefits from the funding of BRGM and the French Loire-Bretagne water Agency.

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Towards aquifer deformation models integrating SAR remote sensing: preliminary land subsidence results using GEP tools

10.5194/egusphere-egu21-12806 ◽

2021 ◽

Author(s):

Guadalupe Bru ◽

Pablo Ezqerro ◽

Carolina Guardiola-Albert ◽

Marta Béjar-Pizarro ◽

Gerardo Herrera ◽

...

Keyword(s):

Remote Sensing ◽

Drinking Water ◽

Groundwater Flow ◽

Land Subsidence ◽

Surface Deformation ◽

Salt Water ◽

Groundwater Resources ◽

Groundwater Depletion ◽

Web Tool ◽

Aquifer Systems

Groundwater is a critical resource that provides fresh drinking water to at least 50% of the global population and accounts for 43% of all of the water used for irrigation (Siebert et al., 2010; UNESCO, 2012). A main consequence of groundwater depletion in overexploited aquifers is land subsidence, which ensues other impacts, such as increasing flooding risk (specially in coastal areas), damages to infrastructures and reduction of storage capacity in aquifer systems. Aquifer deformation and groundwater flow models are essential to design sustainable management strategies. In this context, A-DInSAR techniques provide valuable surface displacement data to understand the deformational behaviour of the aquifer and to characterise its properties.RESERVOIR project, which is part of the PRIMA programme supported by the European Union, aims to provide new products and services for a sustainable groundwater management model to be developed and tested in four water-stressed Mediterranean pilot sites. Each of them is representative of a different aquifer system flow scheme. They are located in Italy (coastal aquifer of Comacchio), Spain (Alto Guadalent&#237;n Basin), Turkey (Gediz River Basin) and Jordan (Azraq Wetland Reserve). The water usages of these aquifers are irrigation, drinking water and/or power generation. Each site is prone to different issues such as land subsidence, salt water intrusion, water pollution, over-exploitation and insufficient recharge.One of the primary objectives of the project is the use of advanced satellite-based Earth Observation (EO) techniques for the hydrogeological characterization and their integration into numerical groundwater flow and geomechanical models. This will lead to improve the knowledge about the current capacity to store water and the future response of aquifer systems to natural and human-induced stresses. Free Sentinel-1 SAR acquisitions available at the Copernicus Open Access Hub will be used to perform A-DInSAR processing in representative areas of each pilot site. Additionally, the InSAR processing tools of the Geohazards Exploitation Platform (GEP) funded by the European Space Agency, will be used for a first assessment of ground deformation. In this work we present the preliminary results obtained with Sentinel-1 images using the P-SBAS web tool on GEP (De Luca et al., 2015) at the four pilot sites.&#160;De Luca, C., Cuccu, R., Elefante, S., Zinno, I., Manunta, M., Casola, V., Rivolta, G., Lanari, R., and Casu, F., 2015, An on-demand web tool for the unsupervised retrieval of earth&#8217;s surface deformation from SAR data: The P-SBAS service within the ESA G-POD environment: Remote Sensing, v. 7, no. 11, p. 15630-15650.Siebert, S., Burke, J., Faures, J.-M., Frenken, K., Hoogeveen, J., D&#246;ll, P., and Portmann, F. T., 2010, Groundwater use for irrigation&#8212;a global inventory: Hydrology and earth system sciences, v. 14, no. 10, p. 1863-1880.UNESCO, 2012, World&#8217;s Groundwater Resources Are Suffering from Poor Governance, UNESCO Publishing: Paris, France, UNESCO Publishing.

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Distributions of Groundwater Age under Climate Change of Thailand’s Lower Chao Phraya Basin

Water ◽

10.3390/w12123474 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3474

Author(s):

Pinit Tanachaichoksirikun ◽

Uma Seeboonruang

Keyword(s):

Climate Change ◽

Groundwater Age ◽

Human Life ◽

Age Distribution ◽

Co2 Concentration ◽

Shallow Aquifers ◽

Groundwater Velocity ◽

Lower Velocity ◽

Deep Aquifers ◽

The Mean

Groundwater is important for daily life, because it is the largest freshwater source for domestic use and industrial consumption. Sustainable groundwater depends on many parameters: climate change is one factor, which leads to floods and droughts. Distribution of groundwater age indicates groundwater velocity, recharge rate and risk assessment. We developed transient 3D mathematical models, i.e., MODFLOW and MODPATH, to measure the distributions of groundwater age, impacted by climate change (IPSL-CM5A-MR), based on representative concentration pathways, defined in terms of atmospheric CO2 concentration, e.g., 2.6 to 8.5, for the periods 2020 to 2099. The distributions of groundwater age varied from 100 to 100,000 years, with the mean groundwater age ~11,000 years, generated by climate led change in recharge to and pumping from the groundwater. Interestingly, under increasing recharge scenarios, the mean age, in the groundwater age distribution, decreased slightly in the shallow aquifers, but increased in deep aquifers, indicating that the new water was in shallow aquifers. On the other hand, under decreasing recharge scenarios, groundwater age increased significantly, both shallow and deep aquifers, because the decrease in recharge caused longer residence times and lower velocity flows. However, the overall mean groundwater age gradually increased, because the groundwater mixed in both shallow and deep aquifers. Decreased recharge, in simulation, led to increased groundwater age; thus groundwater may become a nonrenewable groundwater. Nonrenewable groundwater should be carefully managed, because, if old groundwater is pumped, it cannot be restored, with a detriment to human life.

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A multi-environmental tracer study to determine groundwater residence times and recharge in a structurally complex multi-aquifer system

10.5194/hess-2019-451 ◽

2019 ◽

Author(s):

Cornelia Wilske ◽

Axel Suckow ◽

Ulf Mallast ◽

Christiane Meier ◽

Silke Merchel ◽

...

Keyword(s):

Groundwater Flow ◽

Groundwater Recharge ◽

Groundwater Age ◽

Age Distribution ◽

Dead Sea ◽

Artificial Sweetener ◽

Environmental Tracers ◽

Jordan Valley ◽

Aquifer System ◽

Lumped Parameter

Abstract. Despite being the main drinking water resource for over five million people, the water balance of the Eastern Mountain Aquifer system on the western side of the Dead Sea is poorly understood. The regional aquifer consists of fractured and karstified limestone – aquifers of Cretaceous age and can be separated in Cenomanian aquifer (upper aquifer) and Albian aquifer (lower aquifer). Both aquifers are exposed along the mountain ridge around Jerusalem, which is the main recharge area. From here, the recharged groundwater flows in a highly karstified aquifer system towards the east, to discharge in springs in the Lower Jordan Valley and Dead Sea region. We investigated the Eastern Mountain Aquifer system on groundwater flow, groundwater age and potential mixtures, and groundwater recharge. We combined 36Cl/Cl, tritium and the anthropogenic gases SF6, CFC-12 and CFC-11, CFC-113 as dating tracers to estimate the young water components inside the Eastern Mountain Aquifer system. By application of lumped parameter models, we verified young groundwater components from the last 10 to 30 years and an admixture of a groundwater component older than about 70 years. Concentrations of nitrate, Simazine® (Pesticide), Acesulfame K® (artificial sweetener) and Naproxen® (drug) in the groundwater were further indications of infiltration during the last 30 years. The combination of multiple environmental tracers and lumped parameter modelling helped to understand the groundwater age distribution and to estimate recharge despite scarce data in this very complex hydrogeological setting. Our groundwater recharge rates support groundwater management of this politically difficult area and can be used to inform and calibrate ongoing groundwater flow models.

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A New Normalized Groundwater Age-Based Index for Quantitative Evaluation of the Vulnerability to Seawater Intrusion in Coastal Aquifers: Implications for Management and Risk Assessments

Water ◽

10.3390/w13182496 ◽

2021 ◽

Vol 13 (18) ◽

pp. 2496

Author(s):

Mohammed Adil Sbai ◽

Abdelkader Larabi ◽

Marwan Fahs ◽

Joanna Doummar

Keyword(s):

Steady State ◽

Seawater Intrusion ◽

Coastal Aquifers ◽

Groundwater Age ◽

Groundwater Resources ◽

Age Distribution ◽

Flow Simulation ◽

Risk Assessments ◽

Henry Problem ◽

Variable Density Flow

The vulnerability of coastal aquifers to seawater intrusion has been largely relying on data-driven indexing approaches despite their shortcomings to depict the complex processes of groundwater flow and mass transport under variable velocity conditions. This paper introduces a modelling-based alternative technique relying on a normalized saltwater age vulnerability index post-processed from results of a variable density flow simulation. This distributed index is obtained from the steady-state distribution of the salinity and a restriction of the mean groundwater age to a mean saltwater age distribution. This approach provides a novel way to shift from the concentration space into a vulnerability assessment space to evaluate the threats to coastal aquifers. The method requires only a sequential numerical solution of two steady state sets of equations. Several variants of the hypothetical Henry problem and a case study in Lebanon are selected for demonstration. Results highlight this approach ability to rank, compare, and validate different scenarios for coastal water resources management. A novel concept of zero-vulnerability line/surface delineating the coastal area threatened by seawater intrusion has shown to be relevant for optimal management of coastal aquifers and risk assessments. Hence, this work provides a new tool to sustainably manage and protect coastal groundwater resources.

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Using groundwater age to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-11-9907-2014 ◽

2014 ◽

Vol 11 (8) ◽

pp. 9907-9960 ◽

Cited By ~ 2

Author(s):

U. Morgenstern ◽

C. J. Daughney ◽

G. Leonard ◽

D. Gordon ◽

F. M. Donath ◽

...

Keyword(s):

Water Quality ◽

Land Use ◽

Agricultural Land ◽

Root Zone ◽

Groundwater Age ◽

Age Distribution ◽

Series Data ◽

Delayed Response ◽

Groundwater System ◽

Historic Land Use

Abstract. The water quality of Lake Rotorua has declined continuously over the past 50 yr despite mitigation efforts over recent decades. Delayed response of the groundwater discharges to historic land-use intensification 50 yr ago was the reason suggested by early tritium measurements, which indicated large transit times through the groundwater system. We use the isotopic and chemistry signature of the groundwater for detailed understanding of the origin, fate, flow pathways, lag times, and future loads of contaminants. A unique set of high-quality tritium data over more than four decades, encompassing the time when the tritium spike from nuclear weapons testing moved through the groundwater system, allows us to determine detailed age distribution parameters of the water discharging into Lake Rotorua. The Rotorua volcanic groundwater system is complicated due to the highly complex geology that has evolved through volcanic activity. Vertical and steeply-inclined geological contacts preclude a simple flow model. The extent of the Lake Rotorua groundwater catchment is difficult to establish due to the deep water table in large areas, combined with inhomogeneous groundwater flow patterns. Hierarchical cluster analysis of the water chemistry parameters provided evidence of the recharge source of the large springs near the lake shore, with discharge from the Mamaku ignimbrite through lake sediment layers. Groundwater chemistry and age data show clearly the source of nutrients that cause lake eutrophication, nitrate from agricultural activities and phosphate from geologic sources. With a naturally high phosphate load reaching the lake continuously via all streams, the only effective way to limit algae blooms and improve lake water quality in such environments is by limiting the nitrate load. The groundwater in the Rotorua catchment, once it has passed through the soil zone, shows no further decrease in dissolved oxygen, indicating absence of electron donors in the aquifer that could facilitate microbial denitrification reactions. Nitrate from land-use activities that leaches out of the root zone of agricultural land into the deeper part of the groundwater system must be expected to travel with the groundwater to the lake. The old age and the highly mixed nature of the water discharges imply a very slow and lagged response of the streams and the lake to anthropogenic contaminants in the catchment, such as nitrate. Using the age distribution as deduced from tritium time series data measured in the stream discharges into the lake allows prediction of future nutrient loads from historic land-use activities 50 yr ago. For Hamurana Stream, the largest stream to Lake Rotorua, it takes more than a hundred years for the groundwater-dominated stream discharge to adjust to changes in land-use activities. These time scales apply to activities that cause contamination, but also to remediation action.

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Application of Visual MODFLOW to the Analysis of Boundary Conditions for a Phreatic Porous Aquifer Using Limited Available Information: A Case Study

Anuário do Instituto de Geociências - UFRJ ◽

10.11137/1982-3908_2021_44_39646 ◽

2021 ◽

Vol 44 ◽

Author(s):

Milena Stefany Lage Almeida ◽

JOSÉ AUGUSTO COSTA GONÇALVES

Keyword(s):

Boundary Conditions ◽

Groundwater Flow ◽

Root Mean Square ◽

Flow Behavior ◽

Groundwater Resources ◽

Absolute Error ◽

Mean Square ◽

Visual Modflow ◽

Porous Aquifer ◽

The Mean

The increasing water demand, especially in developing regions, continuously puts pressure on groundwater resources both quantitatively and qualitatively. Hydrogeological modeling is a tool used in planning and management of groundwater resources. The factors that interfere in groundwater flow dynamics can be determined by developing a conceptual model and they can be validated via a numerical model. The objective of the manuscript is the hydrogeological groundwater flow modeling of the phreatic porous aquifer of the Ribeirão Candidópolis catchment in the Itabira municipality, State of Minas Gerais (Brazil). The software used in this study is GMS: MODFLOW, which enabled a steady state flow regime modeling by means of the Finite Difference Method (FDM) and the parameters calibration from a semi-transient approach. To assess the performance of the model, the Mean Error (ME), the Mean Absolute Error (MAE), and the Root Mean Square Error (RMSE) were calculated. The results proved to be compatible with the values observed in the field. After several adjustments of the boundary conditions, a Normalized Root Mean Square (NRMS) of 9.648% and a correlation coefficient of 0.993 were obtained. Despite the economic importance of the study area, studies made available on groundwater flow behavior are rare. The results obtained via modeling are in accordance with the data observed in the field and consequently our model can be used in the study of water level changes.

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