Majdi Mansour

Effectiveness of the Nitrate Sensitive Areas Scheme in reducing groundwater concentrations in England

The Nitrates Sensitive Areas (NSA) Scheme in England was a voluntary, compensated measure from 1990 to 2003 which aimed to reduce nitrate leaching from agricultural land to vulnerable groundwaters by modifying land use management. Measurements from 22 NSAs introduced in 1994/5 show an overall 34% decrease in the nitrate concentration of water leaching from the soils from 115 mg/l (1994/5-1995/6) to 76 mg/l (1998/9-1999/2000). This study looks at two NSAs in depth. The Old Chalford NSA consists of a small (81 km2) catchment with a series of spring sources in the Oolitic Limestone in Oxfordshire, whilst the Pollington NSA is the much larger (358 km2) catchment of three large public water supply sources (PWS) in the Sherwood Sandstone of North Yorkshire. Soil leaching model results suggest that the Scheme reduced root zone nitrate concentrations from 98 mg/l in 1994 to 69 mg/l in 1998 at Pollington NSA, and from 43 mg/l in 1990 to 37 mg/l in 1998 at Old Chalford NSA. These data served as inputs into flow modelling to quantify the effect of changes in the soil zone on groundwater concentration. At Old Chalford changes in the soil zone had a measurable effect at abstraction points after only two years, whereas Pollington NSA has shown little effect of the Scheme on abstracted groundwater concentration to date as the geology and geometry of the source catchment zones are expected to lead to a noticeable impact only after 30 years. Although results demonstrate the effectiveness of the Scheme in reducing root zone nitrate leaching, the timescales involved in groundwater responses mean that, in many areas, the impact of such pollution control measures will not be realized for several decades.

3D geological models and their hydrogeological applications : supporting urban development : a case study in Glasgow-Clyde, UK

Urban planners and developers in some parts of the United Kingdom can now access geodata in an easy-to-retrieve and understandable format. 3D attributed geological framework models and associated GIS outputs, developed by the British Geological Survey (BGS), provide a predictive tool for planning site investigations for some of the UKs largest regeneration projects in the Thames and Clyde River catchments. Using the 3D models, planners can get a 3D preview of properties of the subsurface using virtual cross-section and borehole tools in visualisation software, allowing critical decisions to be made before any expensive site investigation takes place, and potentially saving time and money. 3D models can integrate artificial and superficial deposits and bedrock geology, and can be used for recognition of major resources (such as water, thermal and sand and gravel), for example in buried valleys, groundwater modelling and assessing impacts of underground mining. A preliminary groundwater recharge and flow model for a pilot area in Glasgow has been developed using the 3D geological models as a framework. This paper focuses on the River Clyde and the Glasgow conurbation, and the BGSs Clyde Urban Super-Project (CUSP) in particular, which supports major regeneration projects in and around the City of Glasgow in the West of Scotland.

Tension over equitable allocation of water: estimating renewable groundwater resources beneath the West Bank and Israel

Abstract Competition for water resources between Palestine and Israel is an ongoing cause of tension. The Western Aquifer Basin forms a major part of the complex, largely karst, limestone system of the West Bank Mountain Aquifer. The aquifer crops out and is recharged solely in the semi-arid uplands of the West Bank and groundwater flows west beneath Israel to discharge at the Yarqon and Nahal Taninim springs near the Mediterranean coast. Annual recharge to the aquifer is not easy to quantify but lies within the range 270×106 to 455×106 m3 a−1, and current uncertainties do not support definition of a single value of long-term average recharge. The resource is heavily exploited and abstraction is directly controlled and apportioned between Israel and the West Bank by Israel. The key to equitable apportionment is the determination of the long-term average recharge to the basin, which also requires definition of the eastern boundary of the basin to confirm the recharge area. Calculations include empirical formulae and process-based models that are likely to constrain the best estimate provided that there is appropriate, ongoing monitoring. Improved understanding can then be fed back into the model.

Grid Refinement in Cartesian Coordinates for Groundwater Flow Models Using the Divergence Theorem and Taylor's Series

Grid refinement is introduced in a numerical groundwater model to increase the accuracy of the solution over local areas without compromising the run time of the model. Numerical methods developed for grid refinement suffered certain drawbacks, for example, deficiencies in the implemented interpolation technique; the non-reciprocity in head calculations or flow calculations; lack of accuracy resulting from high truncation errors, and numerical problems resulting from the construction of elongated meshes. A refinement scheme based on the divergence theorem and Taylors expansions is presented in this article. This scheme is based on the work of De Marsily (1986) but includes more terms of the Taylors series to improve the numerical solution. In this scheme, flow reciprocity is maintained and high order of refinement was achievable. The new numerical method is applied to simulate groundwater flows in homogeneous and heterogeneous confined aquifers. It produced results with acceptable degrees of accuracy. This method shows the potential for its application to solving groundwater heads over nested meshes with irregular shapes.

A rapid model for estimating the depletion in river flows due to groundwater abstraction

Abstract The Environment Agency of England and Wales uses its calibrated regional models to estimate the reduction in river flows resulting from proposed groundwater abstractions. Where there is no regional model, analytical equations can produce quick initial estimates of river flow depletion. However, users often want more confidence in their estimates by representing more faithfully their understanding of the real river–aquifer system. This paper shows that, when using a numerical model designed to predict river flow depletion, it is important to include adjacent catchments and intermittent streams and less important to include river elevations and variations in transmissivity with groundwater head. Recharge does not usually need to be included unless part of the river becomes disconnected or dry. Therefore, for rivers where stream length is constant and transmissivity variations are small, it is valid to use a ‘no-recharge’ depletion model, which can be built quickly (within a month). A case study on the River Leith in NW England illustrates the use of such a model to assess the ecological impact of two groundwater abstraction licences under the European Union Habitats Directive.

The role of numerical modelling in understanding groundwater flow in Scottish alluvial aquifers

Abstract Groundwater in Scotland has been, until recently, an under-rated resource given the abundance of surface water resources. In the last decade, a number of new abstractions have been developed and existing ones enhanced. Implementing groundwater abstraction licensing through the Scottish Water Environment (Controlled Activities) Regulations (2005) has accelerated the need to understand such schemes. Simulating the groundwater systems, which are generally small in area, with an immature understanding and where subsurface data are often sparse, is a challenge. This challenge is amplified when groundwater abstraction is proposed from previously unexploited gravel valley deposits in close proximity to large rivers. Examples of recent work undertaken for Scottish Water illustrate the important role that groundwater models have in testing and refining conceptual understanding as well as convincing regulators of the suitability of the groundwater abstraction.

Estimation of spatially distributed groundwater potential recharge for the United Kingdom

The calculation of distributed recharge is necessary to drive numerical groundwater models used to manage and protect groundwater resources, to assess the impact of anthropogenic stresses and climate change, and to study the viability of technologies, such as exploiting the heat stored in the ground. A national-scale model allows policymakers and governmental decision-makers to set policy within the correct geographical context. However, many challenges are associated with building large-scale models, for example, the representation of processes on coarse grid resolution. This study presents distributed potential recharge values, calculated using the modified Environment Agency (EA)/Food and Agriculture Organization recharge algorithm. The model calibration is presented and the simulated potential recharge values and soil moisture deficit values are compared with estimates provided by the EA and the Meteorological Office (Met Office). Long-term average potential recharge values are very small in the east of the UK but they increase significantly towards the west and north, reaching values as high as 8 mm day−1 over the hills of Wales and Scotland. While this study highlights the need for further model refinement, the presented results are useful for assessing the potential recharge values at a national scale and for undertaking water resource studies, especially in catchments with unconfined/near-surface aquifers.

Impact of model complexity and multi-scale data integration on the estimation of hydrogeological parameters in a dual-porosity aquifer

This study investigates the impact of model complexity and multi-scale prior hydrogeological data on the interpretation of pumping test data in a dual-porosity aquifer (the Chalk aquifer in England, UK). In order to characterize the hydrogeological properties, different approaches ranging from a traditional analytical solution (Theis approach) to more sophisticated numerical models with automatically calibrated input parameters are applied. Comparisons of results from the different approaches show that neither traditional analytical solutions nor a numerical model assuming a homogenous and isotropic aquifer can adequately explain the observed drawdowns. A better reproduction of the observed drawdowns in all seven monitoring locations is instead achieved when medium and local-scale prior information about the vertical hydraulic conductivity (K) distribution is used to constrain the model calibration process. In particular, the integration of medium-scale vertical K variations based on flowmeter measurements lead to an improvement in the goodness-of-fit of the simulated drawdowns of about 30%. Further improvements (up to 70%) were observed when a simple upscaling approach was used to integrate small-scale K data to constrain the automatic calibration process of the numerical model. Although the analysis focuses on a specific case study, these results provide insights about the representativeness of the estimates of hydrogeological properties based on different interpretations of pumping test data, and promote the integration of multi-scale data for the characterization of heterogeneous aquifers in complex hydrogeological settings.RésuméCette étude étudie l’impact de la complexité du modèle et des données hydrogéologiques préalables multi-échelles sur l’interprétation des données de pompage d’essai dans un aquifère à double porosité (l’aquifère de la craie en Angleterre, Royaume -Uni). Afin de caractériser les propriétés hydrogéologiques, différentes approches s’étendant d’une solution analytique traditionnelle (approche de Theis) à des modèles numériques plus sophistiqués avec des paramètres d’entrées automatiquement calibrés sont appliquées. Les comparaisons des résultats des différentes approches prouvent que ni les solutions analytiques traditionnelles ni un modèle numérique supposant une couche aquifère homogène et isotrope ne peuvent expliquer convenablement les rabattements observés. Au contraire, une meilleure reproduction des rabattements observés dans chacun des sept endroits de suivi est obtenue quand le milieu et des informations préalables à l’échelle locale sur la distribution de la conductivité hydraulique verticale (K) sont employées pour contraindre le procédé de calage du modèle. En particulier, l’intégration des variations verticales de K à une échelle moyenne basées sur des mesures de débitmètre mène à une amélioration de la qualité de l’ajustement des rabattements simulés d’environ 30%. On a observé d’autres améliorations (jusqu’à 70%) quand une approche de mise à l’échelle (upscaling) simple a été employée pour intégrer des données de K à petite échelle pour contraindre le procédé automatique de calage du modèle numérique. Bien que l’analyze se concentre sur une étude de cas spécifique, ces résultats fournissent un éclairage sur la représentativité des évaluations des propriétés hydrogéologiques basées sur différentes interprétations des données de pompage d’essai, et favorisent l’intégration de données multi-échelles pour la caractérisation des aquifères hétérogènes dans les systèmes hydrogéologiques complexes.ResumenEste estudio investiga el impacto de la complejidad del modelo y de los datos hidrogeológicos previos de múltiples escalas en la interpretación de los datos de ensayos de bombeo en un acuífero de doble porosidad (el acuífero Chalk en Inglaterra, Reino Unido). Para caracterizar las propiedades hidrogeológicas, se aplican diferentes enfoques que van desde una solución analítica tradicional (enfoque de Theis) hasta modelos numéricos más sofisticados con parámetros de entrada calibrados automáticamente. Las comparaciones de los resultados de los diferentes enfoques muestran que ni las soluciones analíticas tradicionales ni un modelo numérico que asuma un acuífero homogéneo e isotrópico pueden explicar adecuadamente las depresiones observadas. En cambio, se logra una mejor reproducción de las depresiones observadas en las siete ubicaciones de monitoreo cuando se usa información previa a escala local y media sobre la distribución vertical de conductividad hidráulica (K) para restringir el proceso de calibración del modelo. En particular, la integración de las variaciones verticales de K a escala media basadas en mediciones de flujo conduce a una mejora en la bondad de ajuste de las depresiones simuladas de aproximadamente 30%. Se observaron mejoras adicionales (hasta 70%) cuando se utilizó un enfoque de escalamiento simple para integrar datos de K a pequeña escala para restringir el proceso de calibración automática del modelo numérico. Aunque el análisis se centra en un estudio de caso específico, estos resultados proporcionan información sobre la representatividad de las estimaciones de propiedades hidrogeológicas basadas en diferentes interpretaciones de los datos de ensayos de bombeo y promueven la integración de datos a múltiples escalas para la caracterización de acuíferos heterogéneos en configuraciones hidrogeológicas complejas.摘要本研究调查了模型复杂性及先前多尺度水文地质数据对(英国英格兰白垩含水层)双重孔隙介质含水层抽水试验数据解译的影响。为了描述水文地质特性,应用了从传统解析方法(Theis方法)到更复杂的具有自动校准输入参数的数值模型等不同方法。不同方法的比较结果显示,假定是均质及各向同性含水层,无论是传统解析方法还是数值模型都不能充分解释观测到的水位下降。当采用有关垂直水力传导率(K)分布的介质及局部尺度的先前信息约束模型校准过程时,反而在七个观测点能够再现观测到的水位下降。特别是,基于流量计测量结果的介质尺度垂直K变化的整合可提高模拟水位下降的拟合优度大约30%。当采用简单粗化方法综合小尺度K数据约束数值模型的自动校准过程时,可观测到进一步的提高(达70%)。尽管分析集中在一个特殊的研究实例,但这些结果有助于人们根据抽水试验数据的解译深入了解水文地质特性估算值代表性,促进多尺度数据的整合以描述复杂水文地质背景下异质含水层的特征。ResumoEsse estudo investiga o impacto da complexidade do modelo e dados hidrogeológicos anteriores multiescala na interpretação dos dados do teste de bombeamento em aquífero de porosidade dual (o aquífero Chalk na Inglaterra, Reino Unido). Para caracterizar as propriedades hidrogeológicas, são aplicadas diferentes abordagens variando de uma solução analítica tradicional (abordagem de Theis) a modelos numéricos mais sofisticados com parâmetros de entrada calibrada automaticamente. Comparações dos resultados das abordagens diferentes mostram que nem soluções analíticas tradicionais nem modelos numéricos assumindo um aquífero isotrópico e homogêneo podem explicar adequadamente os rebaixamentos observados. Uma melhor reprodução dos rebaixamentos observados em todos os sete locais de monitoramento é ao invés atingido quando informações anteriores em escala local e média escala sobre a distribuição da condutividade hidráulica vertical (K) são utilizadas para restringir o processo de calibração do modelo. Em particular, a integração de variações K verticais em média escala baseadas nas medidas do medidor de fluxo levaram à melhora na qualidade dos ajustes dos rebaixamentos simulados em torno de 30%. Melhoramentos futuros (acima de 70%) foram observados quando uma abordagem refinada foi utilizada para integrar dados K de pequena escala para restringir o processo de calibração automática do modelo numérico. Embora o foco da análise seja em um estudo de caso especifico, esses resultados trazem compreensões sobre a representatividade das estimativas de propriedades hidrogeológicas baseadas nas diferentes interpretações de dados de teste de bombeamento, e promovem a integração de dados de em multiescala para a caracterização de aquíferos heterogêneos em configurações hidrogeológicas complexas.