Assessing the potential for significant and episodic recharge in southwestern Australia using rainfall data

Agricultural practices in semi-arid parts of southwestern Australia have increased recharge and raised groundwater levels. As a result, land salinization has occurred. Managers aim to address the problem by reducing recharge, but it is not known whether all recharge is regular and seasonal or whether a substantial component is episodic (i.e. occurs in irregular pulses). Approaches that reduce regular recharge may not be effective at reducing recharge that is episodic. Water balances were used to assess the potential for recharge to be episodic at 53 sites throughout Western Australia. The results show that, for the conditions modeled, a substantial proportion of the recharge in drier parts of the agricultural areas occurred episodically, and that direct episodic recharge could be as important in some semi-arid areas as in arid regions. Therefore, mean annual rainfall is not a strong predictor of the ratio of episodic to total recharge at a site. The model indicates that in agricultural areas, most significant and episodic recharge events occurred over just a few days in winter months, when rainfall was dominated by frontal systems. However, substantial episodic recharge also resulted from large storms during the months of January, February, and March. The implication is that it will be difficult to reduce recharge substantially, and thus control salinity, as long as agriculture relies heavily on shallow-rooted winter-growing plants. Electronic Publication     

GIS for the assessment of the groundwater recharge potential zone

Water resources in Taiwan are unevenly distributed in spatial and temporal domains. Effectively utilizing the water resources is an imperative task due to climate change. At present, groundwater contributes 34% of the total annual water supply and is an important fresh water resource. However, over-exploitation has decreased groundwater availability and has led to land subsidence. Assessing the potential zone of groundwater recharge is extremely important for the protection of water quality and the management of groundwater systems. The Chih-Pen Creek basin in eastern Taiwan is examined in this study to assess its groundwater resources potential. Remote sensing and the geographical information system (GIS) are used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The weights of factors contributing to the groundwater recharge are derived using aerial photos, geology maps, a land use database, and field verification. The resultant map of the groundwater potential zone demonstrates that the highest recharge potential area is located towards the downstream regions in the basin because of the high infiltration rates caused by gravelly sand and agricultural land use in these regions. In contrast, the least effective recharge potential area is in upstream regions due to the low infiltration of limestone.     

Groundwater resources in the Jabal Al Hass region,northwest Syria: an assessment of past use and future potential

In many cases, the development of groundwater resources to boost agricultural production in dry areas has led to a continuous decline in groundwater levels; this has called into question the sustainability of such exploitation. In developing countries, limited budgets and scarce hydrological data often do not allow groundwater resources to be assessed through groundwater modeling. A case study is presented of a low-cost water-balance approach to groundwater resource assessments in a 1,550 km² semi-arid region in northwestern Syria. The past development of irrigated agriculture and its effect on the groundwater system were studied by analysis of Landsat images and long-term groundwater level changes, respectively. All components of the groundwater balance were determined. Groundwater recharge was estimated using the chloride mass balance method. Over the past three decades, groundwater levels have declined, on average, 23 m, coinciding with a two-fold increase in the groundwater-irrigated area. Groundwater resources are currently depleted by a value that lies between 9.5×10⁶ and 118×10⁶ m³ year^?1, which is larger than can be compensated for by a future decrease in natural discharge or changes in boundary conditions. However, groundwater resources are likely to be sufficient to supply domestic and livestock needs in the area.     

Artificial recharge of groundwater: hydrogeology and engineering

Artificial recharge of groundwater is achieved by putting surface water in basins, furrows, ditches, or other facilities where it infiltrates into the soil and moves downward to recharge aquifers. Artificial recharge is increasingly used for short- or long-term underground storage, where it has several advantages over surface storage, and in water reuse. Artificial recharge requires permeable surface soils. Where these are not available, trenches or shafts in the unsaturated zone can be used, or water can be directly injected into aquifers through wells. To design a system for artificial recharge of groundwater, infiltration rates of the soil must be determined and the unsaturated zone between land surface and the aquifer must be checked for adequate permeability and absence of polluted areas. The aquifer should be sufficiently transmissive to avoid excessive buildup of groundwater mounds. Knowledge of these conditions requires field investigations and, if no fatal flaws are detected, test basins to predict system performance. Water-quality issues must be evaluated, especially with respect to formation of clogging layers on basin bottoms or other infiltration surfaces, and to geochemical reactions in the aquifer. Clogging layers are managed by desilting or other pretreatment of the water, and by remedial techniques in the infiltration system, such as drying, scraping, disking, ripping, or other tillage. Recharge wells should be pumped periodically to backwash clogging layers. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s10040-001-0182-4. Electronic Publication     

Spatial relationship of groundwater arsenic distribution with regional topography and water-table fluctuations in the shallow aquifers in Bangladesh

The present study has examined the relationship of groundwater arsenic (As) levels in alluvial aquifers with topographic elevation, slope, and groundwater level on a large basinal-scale using high-resolution (90 m × 90 m) Shuttle Radar Topography Mission (SRTM) digital elevation model and water-table data in Bangladesh. Results show that high As (>50 μg/l) tubewells are located in low-lying areas, where mean surface elevation is approximately 10 m. Similarly, high As concentrations are found within extremely low slopes (<0.7°) in the country. Groundwater elevation (weekly measured by Bangladesh Water Development Board) was mapped using water-table data from 950 shallow (depth <100 m) piezometers distributed over the entire country. The minimum, maximum and mean groundwater elevation maps for 2003 were generated using Universal Kriging interpolation method. High As tubewells are located mainly in the Ganges–Brahmaputra–Meghna delta, Sylhet Trough, and recent floodplains, where groundwater elevation in shallow aquifers is low with a mean value of 4.5 m above the Public Works Datum (PWD) level. Extremely low groundwater gradients (0.01–0.001 m/km) within the GBM delta complex hinder groundwater flow and cause slow flushing of aquifers. Low elevation and gentle slope favor accumulation of finer sediments, As-carrying iron-oxyhydroxide minerals, and abundant organic matter within floodplains and alluvial deposits. At low horizontal hydraulic gradients and under reducing conditions, As is released in groundwater by microbial activity, causing widespread contamination in the low-lying deltaic and floodplain areas, where As is being recycled with time due to complex biogeochemical processes.     

Spatial and temporal distribution of groundwater recharge in northern Nigeria

Moisture samples obtained from unsaturated-zone profiles in sands from northern Nigeria were used to obtain recharge estimates using the chloride (Cl) mass-balance method and to produce records of past recharge and climatic events. Recharge rates range from 14–49 mm/year, on the basis of unsaturated-zone Cl values and rainfall chemistry measured over eight years at three local stations. The unsaturated-zone results also provide a record of the changing recharge and climatic events of the past 80 years; this record compares quite well with modelling results using precipitation data from Maiduguri, especially for the late 20th-century period of drought. The best fit for the model is made, however, by using a lower mean rainfall Cl (0.65 mg/l) than that obtained from the mean of the field results (1.77 mg/l Cl). This result implies that the measured rainfall Cl probably overestimates the depositional flux of Cl, although the lower value is comparable to the minimum of the measured rainfall Cl values (0.6 mg/l Cl). Recharge estimates made using these lower Cl values range from 16–30 mm/year. The spatial variability was then determined using results from 360 regional shallow wells over 18,000 km². Using the revised rainfall estimate, the Cl balance indicates a value of 43 mm for the regional recharge, suggesting that either additional preferential flow is taking place over and above that from the vadose one, or that the regional recharge represents inputs from earlier wetter periods. These recharge estimates compare favourably with those from hydraulic modelling in the same area and suggest that the recharge rates are much higher than values previously published for this area. High nitrate (NO₃) concentrations (NO₃-N>Cl) preserved under aerobic conditions in the vadose zone reflect secondary enrichment from N-fixing vegetation, as occurs elsewhere in the Sahel. Electronic Publication     

Agricultural groundwater use and rural livelihoods in sub-Saharan Africa: A first-cut assessment

The rapid expansion in agricultural groundwater use in the last few decades has transformed rural economies in large parts of the developing world, in particular South Asia and North China. There has been no such “Groundwater Revolution” in most of sub-Saharan Africa and little is known about the actual role of groundwater use in supporting agricultural livelihoods in the region or opportunities to expand this role in the future. Published literature has been reviewed to paint a preliminary, region-wide picture of the contribution groundwater makes to agriculture, and in turn to rural livelihoods, within sub-Saharan Africa. The findings indicate that groundwater is used on only 1–2 million hectares of cropped area, directly contributing to the livelihoods of 1.5–3% of the rural population. Groundwater also plays a critical role in the vital livestock sector as well as an important indirect role in the supply of domestic water to agricultural households. While data are lacking, these latter two roles likely surpass the direct importance of groundwater to crop production. This suggests that an understanding of the value of agricultural groundwater use in support of rural livelihoods in sub-Saharan Africa should be based on different models than have typically been applied in Asia.

Some aspects of South Asia's groundwater irrigation economy: analyses from a survey in India, Pakistan, Nepal Terai and Bangladesh

Since 1960, South Asia has emerged as the largest user of groundwater in irrigation in the world. Yet, little is known about this burgeoning economy, now the mainstay of the region's agriculture, food security and livelihoods. Results from the first socio-economic survey of its kind, involving 2,629 well-owners from 278 villages from India, Pakistan, Nepal Terai and Bangladesh, show that groundwater is used in over 75% of the irrigated areas in the sample villages, far more than secondary estimates suggest. Thanks to the pervasive use of groundwater in irrigation, rain-fed farming regions are a rarity although rain-fed plots within villages abound. Groundwater irrigation is quintessentially supplemental and used mostly on water-economical inferior cereals and pulses, while a water-intensive wheat and rice system dominates canal areas. Subsidies on electricity and canal irrigation shape the sub-continental irrigation economy, but it is the diesel pump that drives it. Pervasive markets in tubewell irrigation services enhance irrigation access to the poor. Most farmers interviewed reported resource depletion and deterioration, but expressed more concern over the high cost and poor reliability of energy supply for groundwater irrigation, which has become the fulcrum of their survival strategy.

Hydrochemical characteristics and the effects of irrigation on groundwater quality in Harran Plain,GAP Project,Turkey

Improper design, faulty planning, mismanagement and incorrect operation of irrigation schemes are the principle reasons for the deterioration of groundwater quality in a large number of countries, in particular in semi-arid and arid regions. The aim of this study is to determine the dimensions of groundwater quality after surface irrigation was begun in the semi-arid Harran Plain. Physical and chemical parameters of the groundwater including pH, temperature, electrical conductivity (EC), sodium, potassium, calcium, magnesium, chloride, bicarbonate, sulphate, nitrate, nitrite, ammonium, total phosphorus, total organic carbon and turbidity were determined monthly during the 2006 water year. The quality of the groundwater in the study area was assessed hydrochemically in order to determine its suitability for human consumption and agricultural purposes. In the general plain, the EC values measured were considerably above the guide level of 650 μS/cm, while nitrate in particular was found in almost all groundwater samples to be significantly above the maximum admissible concentration of 50 mg/l for the quality of water intended for human consumption as per the international and national standards. Total hardness reveals that a majority of the groundwater samples fall in the very hard water category. Interpretation of analytical data shows that Ca–HCO₃ and Ca–SO₄ are the dominant hydrochemical facies in the study area.     

The use of infiltration field tests for groundwater artificial recharge

 When using surface infiltration as a method of recharge, infiltration testing is considered an important additional data input along with other hydrogeologic data into the recharge decision. As part of an investigation into the potential for groundwater recharge, two desert basins in Jordan (Wadi Madoneh and Wadi Butum) were investigated to determine the possibility of recharge using floodwater retention structures. For each area, short-duration (up to 7-h) infiltration tests were conducted to estimate surface infiltration capacity of the upper soil layers in order to present to the authorities preliminary information which could be used along with other factors to aid in the selection of the best site for a pilot recharge project. Given the highly fractured rock formations that constitute the underlying aquifers in the two areas, it was assumed that the upper alluvium layers are the limiting factors in transmitting water to target aquifers. The infiltration tests conducted to estimate the recharge characteristics of the recharge sites yielded test results that indicated a representative infiltration rate of 0.44 m/day for the Wadi Madoneh site and 0.197 m/day for the Wadi Butum site. The data input was used subsequently with other decision factors to select the most promising site for the pilot project. Received: 9 January 1998 · Accepted: 27 April 1998     

Preliminary evidence of a link between surface soil properties and the arsenic content of shallow groundwater in Bangladesh

The extremely heterogeneous distribution of As in Bangladesh groundwater has hampered efforts to identify with certainty the mechanisms that lead to extensive mobilization of this metalloid in reducing aquifers. We show here on the basis of a high-resolution transect of soil and aquifer properties collected in Araihazar, Bangladesh, that revealing tractable associations between As concentrations in shallow (< 20 m) groundwater with other geological, hydrological, and geochemical features requires a lateral sampling resolution of 10–100 m. Variations in the electromagnetic conductivity of surface soils (5–40 mS/m) within a 500 m × 200 m area are documented with 560 EM31 measurements. The results are compared with a detailed section of groundwater As concentrations (5–150 μg/L) and other aquifer properties obtained with a simple sampling device, “the needle-sampler”, that builds on the local drilling technology. By invoking complementary observations obtained in the same area and in other regions of Bangladesh, we postulate that local groundwater recharge throughout permeable sandy soils plays a major role in regulating the As content of shallow aquifers by diluting the flux of As released from reducing sediments.     

Groundwater irrigation and its implications for water policy in semiarid countries: the Spanish experience

Over the last decades, groundwater irrigation has become commonplace in many arid and semiarid regions worldwide, including Spain. This is largely a consequence of the advances in drilling and pumping technologies, and of the development of Hydrogeology. Compared with traditional surface water irrigation systems, groundwater irrigation offers more reliable supplies, lesser vulnerability to droughts, and ready accessibility for individual users. Economic forces influence the groundwater irrigation sector and its development. In Spain's Mediterranean regions, abstraction costs often amount to a very small fraction of the value of crops. In the inner areas, groundwater irrigation supports a more stable flow of farm income than rainfed agriculture. The social (jobs/m³) and economic (€/m³) value of groundwater irrigation generally exceeds that of surface water irrigation systems. However, poor groundwater management and legal controversies are currently at the base of Spain's social disputes over water. A thorough and transparent assessment of the relative socio-economic value of groundwater in relation to surface water irrigation might contribute to mitigate or avoid potential future conflicts. Enforcement of the European Union's Water Framework Directive may deliver better groundwater governance and a more sustainable use.

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Resumen Durante las últimas décadas, la irrigación con agua subterránea se ha vuelto común en muchas regiones áridas y semiáridas alrededor del mundo, incluyendo a España. Ésta es en gran medida una consecuencia de los adelantos en las tecnologías de perforación y bombeo, y del desarrollo de la Hidrogeología. Comparada con los sistemas tradicionales de irrigación con agua superficial, la irrigación con agua subterránea ofrece suministros más fiables, la vulnerabilidad es menor a las sequías, y posee accesibilidad inmediata para los usuarios individuales. Las fuerzas económicas influyen el sector de irrigación con agua subterránea y su desarrollo. En las regiones mediterráneas de España, los costos de extracción suman a menudo una parte muy pequeña del valor de las cosechas. En las áreas internas, la irrigación con agua subterránea constituye un flujo más estable de ingresos para la granja, que la agricultura dependiente del agua lluvia. El valor social (empleos/m³) y económico (€/m³) de la irrigación con agua subterránea, generalmente excede a aquél con sistemas de irrigación de agua superficial. Sin embargo, la gestión pobre del agua subterránea y las controversias legales están actualmente en la base de las disputas sociales en España acerca del agua. Una evaluación completa y transparente del valor socio-económico relativo de agua subterránea respecto a la irrigación con agua superficial, podría contribuir mitigar o evitar los conflictos potenciales del futuro. La entrada en vigor del Marco Reglamentario de Agua de la Unión Europea, puede conllevar a una administración mejor del agua subterránea y a un uso más sostenible.

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Résumé Depuis les dernières décennies, l’irrigation avec l’eau souterraine est devenue commune dans plusieurs régions arides et semi-arides, incluant l’Espagne. Ceci est largement une conséquence due à l’avancement aux technologies de forages et des pompages, et au développement de l’Hydrogéologie. Comparé avec des systèmes traditionnels d’irrigation utilisant l’eau de surface, l’irrigation avec l’eau souterraine offre une technique d’alimentation plus fiable, une vulnérabilité à la sécheresse moins grande, et une accessibilité plus aisée pour chaque utilisateur. Les forces économiques influencent le secteur de l’irrigation par l’eau souterraine et son développement. Dans les régions de l’Espagne Méditerranéenne, les coûts d’exploitation représentent toujours une petite fraction de la valeur des cultures. Dans les régions intérieures, l’irrigation par l’eau souterraine supporte une agriculture plus stable et continue qu’une agriculture reposant sur l’eau de pluie. La valeur sociale (emploi/m³) et économique (€/m³) de l’irrigation avec l’eau souterraine, excède généralement celle des systèmes d’irrigation avec l’eau de surface. Néanmoins, des gestions pauvres de l’eau souterraine et des controverses légales sont couramment à la base de disputes sociales sur l’eau. Un bilan transparent et minutieux des valeurs relatives socio-économiques de l’eau souterraine en relation avec l’eau de surface d’irrigation, devrait contribuer à éviter de potentiels et futurs conflits. Un renforcement de la Directive Cadre de l’Union Européenne devrait apporter une meilleure gouvernance et un usage plus durable.

     

Estimating impacts of changed land use on recharge: review of modelling and other approaches appropriate for management of dryland salinity

To manage dryland salinity, one needs to know how changed land use affects groundwater recharge. Few techniques are available for comparing 'deep drainage' under different land uses. Soil-tracer methods, although good for replication and remote field sites, are subject to spatial variability. Lysimeters are good for comparisons but are difficult for drier areas and sloping land. Agronomic water-balance studies, where appropriate soil-water measurements exist, may be used with a soil-vegetation model to estimate long-term deep drainage. Complex models are required to analyze specific land-use differences, such as perenniality and root and leaf area dynamics, but models require intensive and extensive data for calibration. This approach is time-consuming, labour-intensive, and difficult in remote locations. Because of the one-dimensionality of most soil-vegetation models and the small fraction of the total water balance that is deep drainage, little success has occurred in extrapolating beyond the research plot, or to spatially heterogeneous systems such as alley farming. Some 'top-down' modelling and landscape disaggregation approaches have been partially successful in making catchment or regional-scale predictions. The direction for further work depends on the level of recharge reduction that is required for most groundwater systems and difficulties that it imposes. Electronic Publication     

The evolution of groundwater rights and groundwater management in New Mexico and the western United States

Historically, rights in water originated as public property and only later became individualized rights to utilize the public resource, in a manner consistent with the public welfare needs of society, but protected by principles of property law. Five basic regulatory systems for rights in groundwater in the United States have evolved to date. The problems raised by the hydrologic differences between groundwater hydraulically connected to stream systems and groundwater in non-replenished aquifers have been resolved to some extent by a couple of leading court cases. Numerical modeling and other technical methodologies have also evolved to evaluate the scientific issues raised by the different hydrologic conditions, but these are not immune from criticism. The current role of aquifers is evolving into that of storage facilities for recycled water, and their utilization in this manner may be expanded even further in the future. The policy implications of the choices relating to joint management of ground and surface water cannot be overstated. As this paper demonstrates, proactive administration of future groundwater depletions that affect stream systems is essential to the ultimate ability to plan for exploitation, management and utilization of water resources in a rational way that coordinates present and future demand with the reality of scarcity of supply. The examples utilized in this paper demonstrate the need for capacity building, not just to develop good measurement techniques, or to train talented lawyers and judges to write good laws, but also for practical professional water managers to keep the process on a rational course, avoiding limitless exploitation of the resource as well as conservative protectionism that forever precludes its use.

Declining groundwater level and aquifer dewatering in Dhaka metropolitan area,Bangladesh: causes and quantification

Large abstraction by water-wells has been causing a linear to exponential drop in groundwater level and substantial aquifer dewatering in Dhaka, Bangladesh. The city is almost entirely dependent on groundwater, which occurs beneath the area in an unconsolidated Plio-Pleistocene sandy aquifer. Analysis shows that the pattern of water-level change largely replicates the patterns of change in the rate of groundwater abstraction. Contribution of the aquifer storage to the abstraction is estimated to be more than 15% in the year 2002. This abstraction has caused a sharp drop in water level throughout the city and turned into two cones of depression in the water level. Upper parts of the aquifer are already dewatered throughout the area, with the exception of part of the northeast and southeast corner of the city. It is calculated that about 41 million cubic metres (MCM) of the aquifer dewatered by the year 1988, which increased to 2,272 MCM in the year 2002. Water-level decline may increase non-linearly due to limiting vertical recharge in areas where the aquifer is dewatered and may severely threaten the sustainability of the aquifer.     

Towards a policy for sustainable use of groundwater by non-governmental organisations in Afghanistan

A 'first pass' groundwater management policy has been developed for use by non-governmental organisations (NGOs) in Afghanistan, designed to prevent derogation of existing traditional water sources, aquifer over-abstraction and chemical deterioration of soil and groundwater quality. Key elements include (1) continuing promotion of groundwater as a drinking water source, (2) a presumption against use of motorised pumps to abstract groundwater for irrigation unless other options (surface water, qanats) are not available, (3) the use of groundwater for irrigation as a temporary alternative to surface water (i.e. a strategy for drought survival) rather than as a long-term development policy, (4) limiting groundwater abstraction to a long-term average of 1 l s^–1 km^–2, (5) siting irrigation wells at least 500 m from other groundwater sources and (6) analysing irrigation groundwater for electrical conductivity, sodium absorption ratio, boron and residual sodium carbonate alkalinity. Analyses of these parameters indicate that groundwater from some areas is of dubious suitability for irrigation. In some villages and towns, groundwater contains elevated nitrate and faecal bacteria concentrations, probably derived from latrines, sewage or animal wastes. Electronic Publication     

Radon distribution in groundwater of Taiwan

Radon levels were surveyed in 517 monitoring wells constructed in five major groundwater areas of Taiwan. The radon concentration in groundwater samples varied in a wide range from below the detection limit of 18 pCi/L up to 1,100 pCi/L. A worldwide comparison of reported groundwater radon levels was conducted. Overall radon levels in Taiwan groundwater are relatively low compared to other countries because the geology of Taiwan is mainly comprised of sedimentary rocks. Among the 517 wells monitored, only five wells were found with radon concentrations higher than 500 pCi/L. These five wells are all located near the Chaochou Fault in the Pingtung Plain. This study suggests that well sites near the Chaochou Fault could be good locations to monitor radon anomalies for earthquake prediction and should be avoided for developing domestic water supply. In the recharge area near the Chaochou Fault, the radon concentration in groundwater from shallow wells was approximately 1/2 to 1/4 of that from deep wells in the same cluster.

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Resumen Se investigaron los niveles de radón en 517 pozos de monitoreo, construidos en las cinco mayores áreas de agua subterránea de Taiwan. La concentración de radón en las muestras de agua subterránea varía en un rango amplio, desde inferior al límite de detección que es 18 pCi/L hasta 1,100 pCi/L. Se realizó una comparación a escala mundial de los niveles de radón reportados en agua subterránea. En general los niveles de radón presente en el agua subterránea de Taiwan, son relativamente bajos comparados con otros países, puesto que la geología de Taiwan está compuesta de rocas sedimentarias. Entre los 517 pozos monitoreados, solamente en cinco se encontraron concentraciones de radón mayores a 500 pCi/L. Estos cinco pozos están todos localizados cerca de la falla ChaoChou en la Planicie de PingTung. El presente estudio sugiere que los pozos cercanos a la falla Chaochou, podrían ser buenos sitios para monitorear anomalías de radón para la predicción de terremotos y deberían evitarse para los desarrollos de abastecimiento de agua potable. En la zona de recarga cerca de la falla Chaochou, la concentración de radón en agua subterránea obtenida en pozos someros, fue aproximadamente de &frac; a &frac; de aquella en pozos profundos ubicados en el mismo sector.

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Résumé On a mesuré les taux de Rn dans 517 forages ouverts dans cinq aquifères majeures de Taiwan. Les concentrations en Rn couvrent un domaine très large, à partir de valeurs très basses, au dessous de la limite de détection de 18pCi/l jusquaux valeurs assez grandes de 1100pCi/l. On a mené une analyse comparative avec des valeurs mentionnées en littérature. Par report aux valeurs mesurées en autres pays, les concentrations en Rn en Taiwan sont asses basses, compte que la structure géologique de Taiwan est constituée surtout par des roches sedimentaires. On a trouvé des concentrations au desuss de 500pCi/l seulement en cinq de 517 forages investigués. Tous ces cinq forages se trouvent au voisinage de la faille de Chaochou dans la plaine de Pingtung. Cet étude suggere que les forages situés près de la faille de Chaochou peuvent bien monitoriser les anomalie de Rn pour la prédiction des séismes mais doivent être évités lorsqil sagit de lalimentation en eau potable. Dans la zone de recharge près de la faille de Chaochou les concentrations en Rn mesurées dans les puits peu profondes representent 1/2-1/4 de ceux mesurées dans les forages de profondeur.

     

Modeling the impact of groundwater harvesting on the hydro-salinity of a saline catchment in southeastern Australia

Recharge to a saline, unconfined shallow-water-table aquifer is normally considered as an irrecoverable loss of water, but such thinking could be reviewed empirically. The use of an appropriate groundwater harvesting system does not only provide an opportunity to recover this lost water, but can also help in catchment salinity management and improvement. Agricultural-based land-drainage systems such as those that use serial biological concentration (SBC) of salts, provide examples of such harvesting methods. The impact of groundwater harvesting has been assessed on the hydro-salinity of a saline catchment in southeastern Australia through modeling. For both the below average rainfall and very wet years, the “do nothing” scenario resulted in increasing salinization in the catchment. However, after introducing a SBC system, groundwater salinity showed a decreasing trend while hydraulic heads tended to stabilize around the depth of subsurface collector wells. However, for a successful groundwater harvesting system, proper understanding of the groundwater flows and salt mobilization associated with a catchment is necessary. The outcomes of this modelling study have the potential to address similar issues (salinization) and/or needs (water harvesting) existing elsewhere in the world, particularly in semi-arid regions.

Optimizing groundwater development strategies by genetic algorithm: a case study for balancing the needs for agricultural irrigation and environmental protection in northern China

Gaoqing Plain is a major agriculture center of Shandong Province in northern China. Over the last 30 years, the diversion of Yellow River water for intensive irrigation in Gaoqing Plain has led to elevation of the water table and increased evaporation, and subsequently, a dramatic increase in salt content in soil and rapid degradation of crop productivity. Optimal strategies have been explored, that will balance the need to extract sufficient groundwater for irrigation (to ease the pressure on diverting Yellow River water) with the need to improve the local environment by appropriately lowering the water table. Two simulation-optimization models have been formulated and a genetic algorithm (GA) is applied to search for the optimal groundwater development strategies in Gaoqing Plain, while keeping the adverse environmental impacts in check. Compared with the trial-and-error approach of previous studies, the optimization results demonstrate that using an optimization model coupled with a GA search is both effective and efficient. The optimal solutions identified by the GA will provide Gaoqing Plain with the blueprints for developing sustainable groundwater abstraction plans to support local economic development and improve its environmental quality. Li Zheng is currently a visiting scientist in the Mathematical Modeling and Analysis Group, Los Alamos National Laboratory, New Mexico, USA.     

Rainfall and irrigation controls on groundwater rise and salinity risk in the Ord River Irrigation Area,northern Australia

Groundwater beneath the Ord River Irrigation Area (ORIA) in northern Australia has risen in elevation by 10–20 m during the past 40 years with attendant concerns about water logging and soil salinization. Persistent groundwater accession has been attributed to excessive irrigation and surface water leakage; however, analysis of daily water-table records from the past 10 years yielded a contrary result. On a seasonal basis, water-table elevation typically fell during irrigation (dry) seasons and rose during fallow (wet) seasons, conflicting with the conventional view that irrigation and not rainfall must be the dominant control on groundwater accession. Previous investigations of unexpectedly large infiltration losses through the cracking clay soils provide a plausible explanation for the apparent conundrum. Because rainfall is uncontrolled and occurs independently of the soil moisture condition, there is greater opportunity for incipient ponding and rapid infiltration through preferred flow pathways. In contrast, irrigation is scheduled when needed and applications are stopped after soil wetting is achieved. Contemporary groundwater management in the ORIA is focused on improving irrigation efficiency during dry seasons but additional opportunities may exist to improve groundwater conditions and salinity risk through giving equal attention to the wet-season water balance.