Total Groundwater Research Articles

Domestic water demand challenges in Qatar

Qatar is an arid country with limited water resources due to the low amount of rainfall it receives. With no surface water and an average annual rainfall of 80 mm per year, Qatar relies upon desalination to meet the increasing domestic water demand. The average annual rainfall recharge is around 60 million m3, whereas the total groundwater abstraction is 250 million m3 per year. As a result, groundwater level drops dramatically, thereby inducing brackish water upconing and saline water intrusion. Desalination provides 99% of domestic water demand, which increases continuously as a result of the influx of migrants into the country. The current capacity of desalination plants in Qatar is around 540 million m3 per year. Around 30% of this volume is being lost as a result of leakage in the water system network, and the rest is used for domestic purposes. This paper discusses three different scenarios of water demand until the year 2040. The results of these scenarios show water demand will vary between 516 and 2718 million m3 in the year 2040, depending upon the various trends in population growth, and assuming the current per capita of 500 l/day. The results of this study highlight the need for water rationing and conservation and may help the planners of future water demand.

Analytical approach for time‐dependent groundwater inflow into shield tunnel face in confined aquifer

SummaryPrediction of time‐dependent groundwater inflow into a shield tunnel is a significant task facing engineers. Published literature shows that there is no available method with which to predict time‐dependent groundwater inflow into a tunnel. This paper presents a prediction approach for time‐dependent groundwater inflow into a tunnel in both anisotropic and isotropic confined aquifers. The proposed solution can predict groundwater inrush from the tunnel cutting face. To obtain the time‐dependent groundwater flow quantity, the concept of a horizontal‐well pumping test based on the theory of a point source is adopted. Multiple factors, eg, drawdown, thickness of aquifer, conductivities, and specific storage, are taken into account. Both groundwater inflow to the cross section of a tunnel face in the y‐z plane and total tunnel inflow are obtained. Based on the proposed approach, the time‐dependent groundwater inflow to a tunnel can be classified as either a uniform or non‐uniform flow. The proposed approach is applied to analyse groundwater inflow of 2 field cases: (1) Metro line No. 7, Guangzhou City and (2) an underground tunnel in Huizhou, Guangdong Province. Results show that the proposed method can predict the measured values, and drawdown‐related curves are also derived. In addition, the calculated results also reveal that the effect of hydraulic conductivity kz on the total groundwater inflow differs from that of hydraulic conductivities kx and ky and the thickness of the aquifer.

Controlling factors of fluoride in groundwater in a part of South India

Fluoride (F−) is the most important element for human health. Hydrogeochemical survey was conducted to probe into the controlling factors of F− in the groundwater of a semi-arid part of South India. The study area comprises of F−-bearing minerals (hornblende, biotite, and apatite) in the Precambrian rocks, sandstones in the Upper Gondwana rocks, and clays in the Quaternary formations. Forty-seven percent of the total groundwater samples have the higher F− content than its permissible limit of 1.50 mg/L prescribed for drinking purpose. The chemical data of the groundwater is analyzed to assess the geochemical processes dominating the F−-bearing groundwater, using Piper and Gibbs diagrams, correlations, saturation indices, ionic ratios, and multivariate analysis. Piper diagram shows that the groundwater quality is characterized by Na+-HCO\( {}_3^{-} \) and Na+-Cl−types, while the Gibbs diagrams suggest that the groundwater chemistry is mainly controlled by water-rock interactions and is subsequently modified by human activities. The F− groundwater is positively correlated with pH, total dissolved solids, Mg2+, Na+, K+, HCO\( {}_3^{-} \), Cl−, SO\( {}_4^{2-} \), and NO\( {}_3^{-} \) and negatively with Ca2+, representing the influences of geogenic and anthropogenic origins on the groundwater system. Geochemical ratios and saturation indices indicate that the processes of mineral dissolution, ion exchange, and evaporation mainly govern the high F− groundwater, while the chemical fertilizers cause for the enrichment of F−in the groundwater. Cluster and principal component analyses further support the above findings.

Investigation of fluoride contamination and its mobility in groundwater of Simlapal block of Bankura district, West Bengal, India

The occurrence of dental/skeletal fluorosis among the people in the study area provided the motivation to assess the distribution, severity and impact of fluoride contamination in groundwater of Bankura district at Simlapal block, West Bengal, India. To meet the desired objective, groundwater samples were collected from different locations of Laxmisagar, Machatora and Kusumkanali regions of Simlapal block at different depths of tube wells in both pre- and post-monsoon seasons. Geochemical results reveal that the groundwaters are mostly moderate- to hard-water type. Of total groundwater samples, 37% are situated mainly in relatively higher elevated region containing fluoride above 1.5 mg/L, indicating that host aquifers are severely affected by fluoride contamination. Machatora region is highly affected by fluoride contamination with maximum elevated concentration of 12.2 mg/L. Several symptoms of fluorosis among the different age-groups of people in Laxmisagar and Machatora areas are indicating consumption of fluoridated water for prolonged period. The groundwater samples were mainly Na–Ca–HCO3 type and rock dominance indicating the dissolution of minerals taking place. Ion exchange between OH− ion and F− ion present in fluoride-bearing mineral is the most dominant mechanism of fluoride leaching. High concentration of Na+ and HCO3 − increases the alkalinity of the water, providing a favorable condition for fluoride to leach into groundwater from its host rocks and minerals.

Retrieving Groundwater Depletion and Drought in the Tigris‐Euphrates Basin Between 2003 and 2015

Quantitative estimates of the groundwater depletion and droughts in the Tigris-Euphrates Basin (TEB) can be useful for sustainably managing its water resources. Here, data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission are used to infer the monthly changes in the total water storage of the TEB from January 2003 to December 2015. Additionally, the data of altimetry and output from land surface models are used to remove the contributions from lake water changes and other hydrological factors to obtain the total groundwater depletion (TGWD), human-driven groundwater depletion (HGWD), and climate-driven groundwater depletion. We conclude that an alarming rate of decrease in the total water storage and the loss of TGWD have an "accelerating" trend, as the trend during 2007 to 2015 was 3.6 times that during 2003 to 2006. Moreover, the HGWD is 116.09 Gt, which accounts for 98% of the TGWD. Finally, the total storage deficit index (TSDI) is derived from the GRACE data to characterize the drought of the TEB. The results show that TSDI agrees well with the actual drought rather than the Palmer drought severity index (PDSI) and that the TEB has been undergoing a severe drought since September 2007 according to both the TSDI and PDSI. The research in this study provides an effective and unique method for understanding the hydrological processes and sustainable use of water resources in regions or countries with little data, which is essential for more efficient, sustainable, and cross-boundary cooperative water resource management.

The groundwater budget: A tool for preliminary estimation of the hydraulic connection between neighboring aquifers

Groundwater management authorities usually use groundwater budget calculations to evaluate the sustainability of withdrawals for different purposes. The groundwater budget calculation does not always provide reliable information, and it must often be supported by further aquifer monitoring in the case of hydraulic connections between neighboring aquifers.The Riardo Plain aquifer is a strategic drinking resource for more than 100,000 people, water storage for 60 km2 of irrigated land, and the source of a mineral water bottling plant. Over a long period, the comparison between the direct recharge and the estimated natural outflow and withdrawals highlights a severe water deficit of approximately 40% of the total groundwater outflow. A groundwater budget deficit should be a clue to the aquifer depletion, but the results of long-term water level monitoring allowed the observation of the good condition of this aquifer. In fact, in the Riardo Plain, the calculated deficit is not comparable to the aquifer monitoring data acquired in the same period (1992–2014). The small oscillations of the groundwater level and the almost stable streambed spring discharge allows the presumption of an additional aquifer recharge source.The confined carbonate aquifer locally mixes with the above volcanic aquifer, providing an externally stable recharge that reduces the effects of the local rainfall variability.The combined approach of the groundwater budget results and long-term aquifer monitoring (spring discharge and/or hydraulic head oscillation) provides information about significant external groundwater exchanges, even if unidentified by field measurements, and supports the stakeholders in groundwater resource management.

Tracing ancient hydrogeological fracture network age and compartmentalisation using noble gases

We show that fluid volumes residing within the Precambrian crystalline basement account for ca 30% of the total groundwater inventory of the Earth (> 30 million km3). The residence times and scientific importance of this groundwater are only now receiving attention with ancient fracture fluids identified in Canada and South Africa showing: (1) microbial life which has existed in isolation for millions of years; (2) significant hydrogen and hydrocarbon production via water–rock reactions; and (3) preserving noble gas components from the early atmosphere. Noble gas (He, Ne, Ar, Kr, Xe) abundance and isotopic compositions provide the primary evidence for fluid mean residence time (MRT). Here we extend the noble gas data from the Kidd Creek Mine in Timmins Ontario Canada, a volcanogenic massive sulfide (VMS) deposit formed at 2.7 Ga, in which fracture fluids with MRTs of 1.1–1.7 Ga were identified at 2.4 km depth (Holland et al., 2013); to fracture fluids at 2.9 km depth. We compare here the Kidd Creek Mine study with noble gas compositions determined in fracture fluids taken from two mines (Mine 1 & Mine 2) at 1.7 and 1.4 km depth below surface in the Sudbury Basin formed by a meteorite impact at 1.849 Ga.The 2.9 km samples at Kidd Creek Mine show the highest radiogenic isotopic ratios observed to date in free fluids (e.g. 21Ne/22Ne = 0.6 and 40Ar/36Ar = 102,000) and have MRTs of 1.0–2.2 Ga. In contrast, resampled 2.4 km fluids indicated a less ancient MRT (0.2–0.6 Ga) compared with the previous study (1.1–1.7 Ga). This is consistent with a change in the age distribution of fluids feeding the fractures as they drain, with a decreasing proportion of the most ancient end-member fluids. 129Xe/136Xe ratios for these fluids confirm that boreholes at 2.4 km versus 2.9 km are sourced from hydrogeologically distinct systems. In contrast, results for the Sudbury mines have MRTs of 0.2–0.6 and 0.2–0.9 Ga for Mines 1 and 2 respectively. While still old compared to almost all groundwaters reported in the literature to date, these younger residence times compared to Kidd Creek Mine are consistent with significant fracturing created by the impact event, facilitating more hydrogeologic connection and mixing of fluids in the basin. In all samples from both Kidd Creek Mine and Sudbury, a 124-128Xe excess is identified over modern air values. This is attributed to an early atmospheric xenon component, previously identified at Kidd Creek Mine but which has to date not been observed in fluids with a residence time as recent as 0.2–0.6 Ga. The temporal and spatial sampling at Kidd Creek Mine is also used to verify our proposed conceptual model which provides key constraints regarding distribution, volumes and residence times of fracture fluids on the smaller, regional, scale.

The relationship between contrasting ages of groundwater and streamflow

AbstractTracer data demonstrate that waters in aquifers are often much older than the stream waters that drain them. This contrast in water ages has lacked a general quantitative explanation. Here we show that under stationary conditions, the age distribution of water stored in a catchment can be directly estimated from the age distribution of its outflows, and vice versa. This in turn implies that the storage selection function, expressing the catchment's preference for the release or retention of waters of different ages, can be estimated directly from the age distribution of outflow under stationary conditions. Using gamma distributions of streamflow ages, we show that the mean age of stored water can range from half as old as the mean age of streamflow (for plug flow conditions) to almost infinitely older (for strongly preferential flow). Many streamflow age distributions have long upper tails, consistent with preferential flow and implying that storage ages are substantially older than streamflow ages. Mean streamflow ages reported in the literature imply that most streamflow originates from a thin veneer of total groundwater storage. This preferential release of young streamflow implies that most groundwater is exchanged only slowly with the surface and consequently is relatively old.

Groundwater potential of the eastern Kalahari region of South Africa

Abstract An integrated approach involving geological, borehole data, hydrogeochemical and environmental isotope analyses was used to determine the groundwater potential of the eastern Kalahari region of South Africa, an area to the west of Mahikeng that stretches northward from the Orange River into Botswana. The total groundwater resource potential for the eastern Kalahari region of South Africa is estimated at 10127 Mm3/a, with the Kalahari Group aquifer showing the greatest potential, comprising 51% of the total resource. The storage capacity of the Kalahari Group aquifer (7130 Mm3) is also impressive, estimated to be more than twice that of the dolomite aquifer (2728 Mm3). Despite having such great potential, the aquifer is not actively recharged and is often associated with very saline water that is not suitable for human and livestock consumption. The limestone and dolomite aquifers of the Campbell Rand Subgroup, as well as the weathered granitic rocks of the Archaean basement, are considered as the most prospective water bearing formations, with a groundwater resource potential estimate of 1981 Mm3/a and 1845 Mm3/a, respectively. Aquifers with the least potential in the project area comprise the fractured basement rocks of the Kraaipan - Amalia greenstone belt, with a groundwater resource potential of 26 Mm3/a, and the fractured sedimentary rocks of the Asbestos Hills Subgroup, with a groundwater resource potential of 108 Mm3/a. The calculated groundwater storage and resource potential in the eastern Kalahari region of South Africa satisfies a large proportion of the water demand in the region.

A quantitative assessment of groundwater resources in the Middle East and North Africa region

The Middle East and North Africa (MENA) region is the world’s most water-stressed region, with its countries constituting 12 of the 15 most water-stressed countries globally. Because of data paucity, comprehensive regional-scale assessments of groundwater resources in the MENA region have been lacking. The presented study addresses this issue by using a distributed ArcGIS model, parametrized with gridded data sets, to estimate groundwater storage reserves in the region based on generated aquifer saturated thickness and effective porosity estimates. Furthermore, monthly gravimetric datasets (GRACE) and land surface parameters (GLDAS) were used to quantify changes in groundwater storage between 2003 and 2014. Total groundwater reserves in the region were estimated at 1.28 × 106 cubic kilometers (km3) with an uncertainty range between 816,000 and 1.93 × 106 km3. Most of the reserves are located within large sedimentary basins in North Africa and the Arabian Peninsula, with Algeria, Libya, Egypt, and Saudi Arabia accounting for approximately 75% of the region’s total freshwater reserves. Alternatively, small groundwater reserves were found in fractured Precambrian basement exposures. As for groundwater changes between 2003 and 2014, all MENA countries except for Morocco exhibited declines in groundwater storage. However, given the region’s large groundwater reserves, groundwater changes between 2003 and 2014 are minimal and represent no immediate short-term threat to the MENA region, with some exceptions. Notwithstanding this, the study recommends the development of sustainable and efficient groundwater management policies to optimally utilize the region’s groundwater resources, especially in the face of climate change, demographic expansion, and socio-economic development.

Annual safe groundwater yield in a semiarid basin using combination of water balance equation and water table fluctuation

The safe groundwater yield plays a major role in the appropriate management of groundwater systems, particularly in (semi-)arid areas like Iran. This study incorporates both the water balance equation and the water table fluctuation to estimate the annual safe yield of the unconfined aquifer in the eastern part of the Kaftar Lake, an Iranian semiarid region. Firstly, the water balance year 2002–03, owing same water table elevation at the beginning and year-end, was chosen from the monthly representative groundwater hydrograph of the aquifer to be taken into account as a basic water year for determining the safe yield. Then the ratio of the total groundwater pumping to the annual groundwater recharge in the selected water balance year together with the quantity of total recharge occurred in the wet period (October to May) of the year of interest were applied to evaluate the annual safe yield at the initiation of the dry period (June to September) of the year of interest. Knowing the annual safe groundwater withdrawal rate at the initiation of each dry period could be helpful to decision makers in managing groundwater resources conservation. Analysis results indicate that to develop a safe management strategy in the aquifer; the ratio of the annual groundwater withdrawal to the annually recharged volume should not exceed 0.69. In the water year 2003–04 where the ratio is equal to 0.52, the water table raised up (about 0.48 m) while the groundwater level significantly declined (about 1.54 m) over the water year 2007–08 where the ratio of the annual groundwater withdrawal to the annually recharged volume (i.e., 2.76) is larger than 0.69.

Surface and groundwater flow modeling for calibrating steady state using MODFLOW in Colorado River Delta, Baja California, Mexico

This study presents the data-scarce and hydro-geologically important surface and groundwater system of Colorado river delta, Mexico, with the aim of understanding dynamics of surface–groundwater interactions in the Delta aquifers applying hydrological conceptual model into integrated hydrological numerical model for Colorado river delta (MCRD) aquifer, calibrated based on averages of daily basis data throughout 8-year period. The model was developed using MODFLOW-OWHM code under the ModelMuse Graphical User Interface, where surface–groundwater interactions through unsaturated zone were simulated using River package (RIV) and Unsaturated-Zone Flow (UZF1) MODFLOW packages under data scare conditions. In the steady-state calibration: gross recharge, contributed 93.3%, lateral inflow 3.2% and stream leakage 3.4% of the total groundwater inflow. The groundwater outflow consisted of groundwater evapotranspiration 87.5%, stream leakage 3.1%, groundwater pumping 3.09% and lateral outflow 6.31%. Processes encountered in the calibrated parameterizations show groundwater flows axially from almost all directions of the model towards the golf of California at the south border of the model, match the course of the Colorado River and laterally towards new river (Rio Nuevo) in the North-west, with a larger portion flowing out southward than north-west ward. Though this study shows Groundwater and surface water interactions in MCRD, cannot be embedded in operational water management yet, it provides a means to assess focal areas for future data collection and model improvements.

Challenges for creating a site-specific groundwater-use record for the Ozark Plateaus aquifer system (central USA) from 1900 to 2010

Hydrologic budgets to determine groundwater availability are important tools for water-resource managers. One challenging component for developing hydrologic budgets is quantifying water use through time because historical and site-specific water-use data can be sparse or poorly documented. This research developed a groundwater-use record for the Ozark Plateaus aquifer system (central USA) from 1900 to 2010 that related county-level aggregated water-use data to site-specific well locations and aquifer units. A simple population-based linear model, constrained to 0 million liters per day in 1900, provided the best means to extrapolate groundwater-withdrawal rates pre-1950s when there was a paucity of water-use data. To disaggregate county-level data to individual wells across a regional aquifer system, a programmatic hierarchical process was developed, based on the level of confidence that a well pumped groundwater for a specific use during a specific year. Statistical models tested on a subset of the best-available site-specific water-use data provided a mechanism to bracket historic groundwater use, such that groundwater-withdrawal rates ranged, on average, plus or minus 38% from modeled values. Groundwater withdrawn for public supply and domestic use accounted for between 48 and 74% of total groundwater use since 1901, highlighting that groundwater provides an important drinking-water resource. The compilation, analysis, and spatial and temporal extrapolation of water-use data remain a challenging task for water scientists, but is of paramount importance to better quantify groundwater use and availability.

Developing a Multi-Objective Conflict-Resolution Model for Optimal Groundwater Management Based on Fallback Bargaining Models and Social Choice Rules: a Case Study

Conflict-resolution models can be used as practical approaches to consider the contradictions and trade-offs between the involved stakeholders in integrated water resource management. These models are utilized to reach an optimal solution considering agents interactions. In this paper, a new methodology is developed based on multi-objective optimization model (NSGA-II), groundwater simulation model, M5P model tree, fallback bargaining procedures and social choice rules to determine the optimal groundwater management policies with an emphasis on resolving conflicts between stakeholders. By incorporating the multi-objective simulation-optimization model and bargaining methods, the optimal groundwater allocation policies are determined and the preferences of the stakeholders as well as social criteria such as justice are also considered. The obtained data set, based on Monte Carlo analysis of calibrated MODFLOW model, is used for training and validating the M5P meta-models. The validated M5P meta-models are linked with NSGA-II to determine the trade-off curve (Pareto front) for the objectives. Social choice rule and fallback bargaining methods, as conflict-resolution models, are applied to determine the best socio-optimal solution among stakeholders, and their results are compared. The effectiveness of the proposed methodology is verified in a case study of Darian aquifer, Fars province, Iran. Results indicated that the solutions obtained by the proposed conflict-resolution approaches have an appropriate applicability. Total groundwater withdrawal, after applying the optimal groundwater allocations, reduced to 20.85 MCM, resulting in a 4.62 m increase in the mean groundwater level throughout the aquifer.

Architectural Units and Groundwater Resource Quantity Evaluation of Cretaceous Sandstones in the Ordos Basin, China

Sandstone is a common lithology in a number of groundwater reservoirs. Studying the skeleton sandstone architectural units, therefore, lays the basis for characterizing aquifer systems, groundwater quality, and resource evaluation. This comprehensive analysis of Cretaceous aquiferous sandstones in the Ordos basin, China, shows that there exists a basin-scale skeleton sandstone in the Luohe Formation which contains 11 isolated barrier beds, 12 small skeleton sandstone bodies in Huanhe Formation, and 3 in the Luohandong Formation. The spatial structure and superimposed relationship as well as the medium properties of these skeleton sandstones and isolated barrier beds can be shown by 3D visualization models. Simultaneously, resource quantity can be evaluated with the 3D inquiry functions. The comparison between property models and structural models indicates that the salinity of groundwater of the Luohe Formation has a close connection with the locations of isolated barrier beds that contain abundant gypsum. Through quantitative calculation, groundwater resource of the Cretaceous Luohe and Luohandong formations is estimated to be 1.6×1012 m3, and the total groundwater resource of the Cretaceous system in the Ordos basin is more than 2×1012 m3.

Evaluation of groundwater recharge in Poland using the infiltration coefficient method

Variable methods and results are reported on groundwater recharge in Poland. The evaluation of recharge on a small scale requires the use of a single method. In order to evaluate these outcomes and their distribution, the authors have decided to verify different approaches and select the infiltration coefficient by comparison. The article is an extension of the studies on groundwater recharge conducted by the authors. The main goal is to verify previously designed values of the infiltration coefficient based on groundwater runoff from additional river basins in Poland. Total groundwater recharge from precipitation in Poland was calculated at 34,118 km 3 per year, which equals 109.3 mm of water column. The obtained value is close to the average multi-year value of the groundwater runoff. Recharge constituted 18.6% of average precipitation in Poland, which was calculated at 588.5 mm. The estimated groundwater recharge value was verified referring to groundwater runoff from 37 river basins with known discharge rates in the years 1976–2005. Differences in mean groundwater runoff for the entire area (37 river basins) obtained by the infiltration coefficient method and by the use of Wundt’s method amounts to only 0.7%. Despite the simplified calculation methods, the results obtained on a small scale are more accurate than other calculations, which are based on data pertaining to precipitation, soil type, land use, topography of the area, and depth to the groundwater.

Globalization and the sustainable exploitation of scarce groundwater in coastal Peru

Trade in agricultural and food products has increased sharply since the 1980s, but links and trade-offs between socio-economic benefits and environmental impacts of this trend have hardly been studied. The empirical analysis of this article focuses on the Ica province in Peru, where agricultural export production has led to huge economic growth and employment generation at the expense of unsustainable aquifer depletion. Building on the concept of ecosystem and societal metabolism (MuSIASEM), a model of the province including groundwater use, added value generation and employment creation is built. Absolute and relative differences between crop production for auto-consumption and national markets, and for export markets are assessed at different societal levels. Moreover, the impact of two land use scenarios aiming to reduce total groundwater extraction is explored. The analysis draws a picture of a system which is highly dependent on the use of natural resources. Export agriculture generates considerably more value added and employment while extracting more than five times more water from the aquifer than local crop production. The scenarios show that although being more efficient regarding intensive indicators, a reduction of groundwater use for export activities is indispensable to sustain environmentally sustainable agricultural production in the long run. Several policy measures aiming at mitigating groundwater depletion are discussed.

Groundwater discharge and hydrologic partition of the lakes in desert environment: Insights from stable 18O/2H and radium isotopes

Studies of isotope characteristics of lake water in a desert can provide important information on groundwater discharge and hydrologic partition of the lakes in the desert. This paper presents the investigation of 18O and 2H stable isotopes and radiogenic radium of different water endmembers in three representative lakes of Badain-E, Badain-W and Sumujilin-S in the Badain Jaran Desert (BJD), the fourth largest desert in the world. A stable 18O and 2H isotopic buildup model is constructed to classify the hydrologic conditions of the desert lakes by estimating the ratio between groundwater discharge rate (Fin) and lake surface evaporation (E). Then the radium mass balance models are developed to quantify Fin. Based on the obtained Fin/E and Fin, Badain-E, Badain-W and Sumujilin-S are classified as flowing through, terminal and desiccating lakes, respectively, and their hydrologic partition is obtained. The groundwater discharge rate of Badain-E, Badain-W and Sumujilin-S, is estimated to be 8–10mmd−1, 4–5mmd−1, and 7–8mmd−1, respectively. The total groundwater discharge to the lake areas in the BJD is about 1.68×105m3d−1. The flow-through condition explains the existence of the fresh lakes, while the terminal and desiccating conditions lead to the lake salinization over time. This study represents the first attempt to couple both stable and radium isotopic approaches to investigate the groundwater discharge and hydrologic partition of desert lakes in the BJD and is instructional to lake studies in other deserts in the world.

Constraining the annual groundwater contribution to the water balance of an agricultural floodplain using radon: The importance of floods

AbstractThe water balance of drained floodplains is highly dynamic with complex groundwater–surface water interactions operating over varying spatial and temporal scales. Here we hypothesize that the majority of groundwater discharge will follow flood events in a modified wetland. To test this hypothesis, we developed a detailed water balance that quantifies the contribution of groundwater discharge to the annual water budget of an extensively drained agricultural floodplain. A clear relationship between surface water radon measurements and groundwater level indicated alternating connection–disconnection dynamics between the drains and shallow groundwater. This relationship was used to develop a radon mass balance to quantitatively model groundwater discharge continuously throughout the year. Groundwater discharge varied by four orders of magnitude over the study period, with daily average rates ranging from 0 to 27,200 m3 d−1, peaking just a few hours after floods receded. Flood events occurred only 12% of the time yet contributed 72–76% of the total groundwater discharge. During flood recession periods, aerial groundwater discharge rates reached up to 325 cm d−1 which were some of the highest rates ever estimated. We proposed that the high drainage density of this site (12.4 km constructed drains km−2 catchment area) enhanced groundwater discharge during wet periods due to increased connectivity with the soil. Overall, groundwater discharge contributed 30–80% to the total surface water discharge. This study offers insight into the dynamic behavior of groundwater within an extensively drained floodplain, and the importance of capturing flood events to quantify total groundwater contribution to floodplain water balances.

Wypływy wód podziemnych w dnach mis jeziornych na przykładzie Jeziora Raduńskiego Górnego (Pojezierze Kaszubskie)

The aim of the study was to locate and describe groundwater outflows in a selected lake basin. The second aim was to measure spring discharge and measure physical characteristics of the studied waters ( temperature, conductivity ). The time scope of the work comprised the period from January 2011 to September 2012. The spatial scope of the work included the area of Lake Radunskie Gorne located in the Kashubian Lake District in northern Poland. The study consisted mostly of fieldwork and reviewing archived materials. Four groundwater outflows were located in the course of the study. Their total discharge was 4.6 l·s-1 and ranged between 0.5 and 2.5 l·s-1. This produces an annual yield of about 145,000 m3·yr-1. This value is comparable to that for other lakes in the world. In effect, Lake Radunskie Gorne receives about 0.15% of its water from under-lake springs. This is a minute value in comparison with the lake’s total groundwater recharge ( 97 mln m3 per year ). However, it must be assumed that the actual number of under-lake springs is many times greater than that identified in the course of this study, which means that the share of water supplied in this manner is likely much higher and its effect on water chemistry and water levels in the lake is also likely much more pronounced.