Denis Peach

Developing interdisciplinary science for integrated catchment management : the UK lowland catchment research (LOCAR) programme

Across the European Union, the Water Framework Directive is a major driver for change in river basin management. However, its focus on integrated management and, in particular, on ecological quality raises major scientific and technical questions. In the UK, the focus of experimental hydrology has been on the uplands, and at small catchment scale (< 10 km2), whereas major management pressures lie in the lowlands, and for catchment management units of about 300–400 km2. Particular problems arise for permeable lowland catchments: the scientific understanding of the major UK aquifers (the Chalk and the Triassic Sandstone) is poor, and tools for the integrated modelling of surface water–groundwater interactions are limited. In response to these factors, the LOwland CAtchment Research programme (LOCAR) was conceived. A major objective of the programme is to develop new interdisciplinary science and improved modelling tools to meet the challenges of integrated catchment management. The paper describes the research programme and addresses the issues raised in designing and implementing a major interdisciplinary research initiative.

Recovering tracer test input functions from fluid electrical conductivity logging in fractured porous rocks

A radially convergent tracer test was carried out in an unconfined Chalk aquifer of Berkshire, United Kingdom. Fluorescent tracers were injected into two boreholes lying 32 m (PL10A) and 54 m (PL10B) from the abstraction hole. The tracers were also mixed with an NaCl solution so that vertical distributions of tracer within the injection wells could be monitored using fluid electrical conductivity (FEC) logging. The breakthrough curve (BTC) from PL10A was unimodal and had a first arrival time of 14 min. The BTC from PL10B exhibited two distinct peaks and a first arrival time of just 4 min. The tracer test input functions were derived by numerically modeling the observed FEC logs of the injection wells. These were then convoluted with a conventional, Fickian matrix diffusion dual-porosity model. The results suggested that the multiple peaks were due to the way in which the tracers left the injection wells and migrated into the aquifer. FEC log inversion proved to be an effective method for predicting borehole flow data obtained by flowmeters and recovering tracer test input functions for radially convergent tracer tests.

Advances in modelling groundwater behaviour in Chalk catchments

Abstract Groundwater in Chalk catchments is a major resource that also helps support internationally important habitats and ecosystems. Its dual porosity and dual permeability properties, coupled with large-scale structural features (such as hard rock layers and marls), produce a highly complex hydrogeological system. Recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers. Current work on near-surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates. In addition, karst-like features, sedimentary deposits and valley bottom processes govern stream–aquifer interaction and present a challenge in their representation in any modelling system. Methods that have, and are being, developed to incorporate these features, and their use in modelling Chalk catchments, are described. These are required in order to address major challenges, such as groundwater flooding and drought impacts, both of which could become more frequent and intense as a result of climate change.

Numerical testing of conceptual models of groundwater flow: a case study using the Dumfries Basin aquifer

Synopsis The current understanding of the groundwater flow regime in the Dumfries Basin aquifer has been developed over a number of years and encapsulated in a conceptual model. A numerical modelling study has been undertaken to test the confidence in this understanding. This study has included three activities: recharge estimation, water balance calculations and steady-state groundwater flow modelling. It has been confirmed that the highest recharge is found in the NW of the basin and that the peat and marine clay deposits limit direct recharge in the east and south. The water balance is dominated by surface water flow, in particular the River Nith brings over 3200 Ml day−1 onto the basin. Conceptualized flow directions were confirmed by the steady-state modelling. The understanding and model validity are severely constrained by a lack of flow data in the lower River Nith and scarcity of water level and aquifer property information. These knowledge gaps could be filled by flow gauging just above the tidal limit of the river and additional drilling and testing.

Use of seasonal trend decomposition to understand groundwater behaviour in the Permo-Triassic Sandstone aquifer, Eden Valley, UK

The daily groundwater level (GWL) response in the Permo-Triassic Sandstone aquifers in the Eden Valley, England (UK), has been studied using the seasonal trend decomposition by LOESS (STL) technique. The hydrographs from 18 boreholes in the Permo-Triassic Sandstone were decomposed into three components: seasonality, general trend and remainder. The decomposition was analysed first visually, then using tools involving a variance ratio, time-series hierarchical clustering and correlation analysis. Differences and similarities in decomposition pattern were explained using the physical and hydrogeological information associated with each borehole. The Penrith Sandstone exhibits vertical and horizontal heterogeneity, whereas the more homogeneous St Bees Sandstone groundwater hydrographs characterize a well-identified seasonality; however, exceptions can be identified. A stronger trend component is obtained in the silicified parts of the northern Penrith Sandstone, while the southern Penrith, containing Brockram (breccias) Formation, shows a greater relative variability of the seasonal component. Other boreholes drilled as shallow/deep pairs show differences in responses, revealing the potential vertical heterogeneities within the Penrith Sandstone. The differences in bedrock characteristics between and within the Penrith and St Bees Sandstone formations appear to influence the GWL response. The de-seasonalized and de-trended GWL time series were then used to characterize the response, for example in terms of memory effect (autocorrelation analysis). By applying the STL method, it is possible to analyse GWL hydrographs leading to better conceptual understanding of the groundwater flow. Thus, variation in groundwater response can be used to gain insight into the aquifer physical properties and understand differences in groundwater behaviour.RésuméL’évolution journalière des niveaux piézométriques au sein de l’aquifère des grès Permo-Triassique dans l’Eden Valley, Angleterre (Royaume-Uni), a été étudiée à l’aide de la technique de décomposition « seasonal trend by LOESS (STL). Les hydrographes provenant de 18 piézomètres situés dans les grès Permo-Triassique ont été décomposés en trois composantes: saisonnalité, tendance générale et restant (ou résidu). Les résultats de ces décompositions ont été analysés d’abord visuellement, puis à l’aide d’une variété d’outils tels qu’un ratio de variances, une classification hiérarchique adaptée aux séries temporelles et des analyses corrélatoires. Les différences et similarités en termes de décomposition ont été interprétées à l’aide des caractéristiques physiques et hydrogéologiques associées à chacun des piézomètres. Les grès de Penrith manifestent une hétérogénéité aussi bien verticale qu’horizontale, tandis que les grès de St Bees, plus homogènes, sont caractérisés par des hydrographes possédant une saisonnalité clairement identifiable. Il existe toutefois des exceptions au sein même de ces groupes. Au sein des grès de Penrith, une forte composante de tendance à long terme domine les hydrographes pour les zones silicifiées du Nord, alors que la composante de saisonnalité se manifeste plus intensément dans les zones situées au Sud et comportant des formations bréchiques de Brockram. Trois paires de piézomètres profonds/superficiels permettent de mettre en évidence des réponses distinctes, mettant en évidence des hétérogénéités verticales au sein des grès de Penrith. Les différences géologiques (lithologie, etc.) entre les formations gréseuses de Penrith et de St Bees, mais également les variations au sein même de ces formations exercent une influence sur la réponse piézométrique. Les séries résiduelles, après soustraction des composantes de saisonnalité et de tendance, ont été ensuite utilisées pour caractériser la réponse notamment en termes d’effet mémoire (analyse d’autocorrélation). L’application de la méthode STL permet ainsi d’analyser l’évolution temporelle des niveaux piézométriques afin d’améliorer la compréhension conceptuelle des écoulements souterrains. De ce fait, les variations en termes de réponse piézométriques peuvent être exploitées afin de proposer une première approximation des propriétés physiques des aquifères et de comprendre les différences de comportement des eaux souterraines.ResumenSe estudió la respuesta diaria del nivel freático (GWL) en los acuíferos de la Arenisca del Pérmico-Triásico en el Valle Edén, Inglaterra (Reino Unido), mediante el uso de la descomposición tendencia estacional por la técnica LOESS (STL). Los hidrogramas de 18 pozos en la Arenisca Pérmico-Triásico se descompusieron en tres componentes: la estacionalidad, la tendencia general y el resto. La descomposición se analizó en primer lugar, visualmente, a continuación, utilizando herramientas que implican una relación de varianza, de series de tiempo de agrupación jerárquica y análisis de correlación. Se explicaron las diferencias y similitudes en el patrón de descomposición mediante la información física e hidrogeológico asociado a cada pozo. La Arenisca Penrith exhibe heterogeneidad vertical y horizontal, mientras que los hidrogramas más homogéneos de agua subterránea en la Arenisca St. Bees caracterizan una estacionalidad bien identificada. Sin embargo, las excepciones pueden ser identificadas. Una componente de tendencia más fuerte se obtiene en las partes silicificadas del norte de la Arenisca de Penrith, mientras que el sur de Penrith, que contiene la Formación Brockram (brechas), muestra una mayor variabilidad relativa de la componente estacional. Otros pozos perforados en pares poco profundos / profundos muestran diferencias en las respuestas, que revelan las posibles heterogeneidades verticales dentro de la Arenisca de Penrith. Las diferencias en las características de la roca de base entre y dentro de las formaciones de la Arenisca Abejas Penrith y St parecen influir en la respuesta del GWL. El GWL de la serie sin estacionalizar y sin tendencia de tiempo se utilizaron para caracterizar la respuesta, por ejemplo, en términos de efecto de memoria (análisis de autocorrelación). Al aplicar el método de STL es posible analizar hidrogramas GWL que conducen a una mejor comprensión conceptual del flujo de agua subterránea. Por lo tanto, la variación en la respuesta de las aguas subterráneas se puede utilizar para obtener una perspectiva de las propiedades físicas del acuífero y comprender las diferencias en el comportamiento del agua subterránea.摘要通过LOESS (STL)技术利用季节性倾向分解研究了英国伊顿谷二叠-三叠纪砂岩含水层中日常地下水位的响应。二叠-三叠纪砂岩中18个钻孔的水位图被分解为三个分量:季节性、一般趋势和其它。首先在外观上对分解进行分析,然后采用包括方差比、时间序列分级群聚和相关分析等再次对分解进行分析。采用每个钻孔的物理和水文地质信息解释了分解模式的差异和相似之处。Penrith砂岩层显示出了垂向和横向非均质性,而比较均匀的St Bees砂岩层地下水水位图表现出经水井鉴定出的季节性。然而,例外可以辨别出来。在Penrith砂岩层北部硅化部分获得了更强的趋势分量,而在包含着砂泥石灰角砾岩地层的Penrith砂岩层南部,显示出季节分量更大的相对变异性。作为浅层/深层双井的其他钻孔显示出响应的差异,揭示了Penrith砂岩层内潜在的垂向非均质性。Penrith砂岩层和St Bees砂岩层内及两者之间的基岩特征差异似乎影响着地下水水位的响应。然后利用除季节化的和除倾向化的地下水水位时间序列描述响应的特征,例如在记忆效应方面(自相关分析)。通过应用LOESS (STL)方法,分析地下水水位图,更好地概念上理解地下水水流是可能的。因此,利用地下水响应的变化情况可深入了解含水层物理特性及地下水状态的差异。ResumoA resposta diária dos níveis de águas subterrâneas (NAS) nos aquíferos de arenito Permo-Triássico no Vale do Éden, Inglaterra (Reino Unido), foi estudada utilizando a decomposição sazonal de tendência através da técnica LOESS (STL). Os hidrogramas de 18 poços no arenito Permo-Triássico foram decompostos em três componentes: sazonalidade, tendência geral e remanescente. Em primeiro lugar, a decomposição foi analisada visualmente, em seguida, com ferramentas que envolvem variância, agrupamento hierárquico de séries temporais e análise de correlação. As diferenças e similaridades nos padrões de decomposição foram explicadas usando informações físicas e hidrogeológicas associadas a cada poço. O Arenito Penrith apresenta heterogeneidade vertical e horizontal, ao passo que os hidrogramas mais homogêneos de água subterrânea do Aretino St. Bees caracterizam uma sazonalidade bem definida. No entanto, exceções podem ser identificadas. Uma forte componente de tendência é obtida nas partes silicificadas ao norte do Arenito Penrith, enquanto que ao sul de Penrith, contendo a Formação Brockram (breccias), mostra uma maior variabilidade relativa ao componente sazonal. Outros poços perfurados em pares rasos/profundos mostram diferenças nas respostas, revelando potenciais heterogeneidades verticais dentro do Arenito Penrith. As diferenças nas características dos leitos rochosos, entre e dentro, das formações de arenito St Bees e Penrith parecem influenciar a resposta dos NAS. As séries temporais dessazonalizadas e sem tendências de NAS foram usadas para caracterizar a resposta, por exemplo, em termos de efeito de memória (análise de autocorrelação). Por meio da aplicação do método STL, é possível analisar os hidrogramas de NAS, o que conduz a uma melhor compreensão conceitual dos fluxos de águas subterrênas. Assim, a variação na resposta das águas subterrâneas pode ser utilizada para obter informações sobre as propriedades físicas do aquífero e compreender as diferenças no comportamento das águas subterrâneas.

Subsidence hazard assessment as a basis for planning guidance in Ripon

Abstract The Ripon area of North Yorkshire provides a well-documented example of subsidence problems caused by the natural dissolution of gypsum deposits. This paper summarizes the findings of a programme of research, commissioned by the former Department of the Environment, which has aimed to assess the degree of hazard associated with this particular form of subsidence and to develop appropriate planning and engineering responses which might be applicable both to Ripon and to other affected areas. The paper draws attention to the sensitive nature of the problem and to the conflict which exists between the benefits of using hazard assessment to minimize the risk to future development within an area, and the possible disbenefits of widely publicizing the existence of a land instability problem. In Ripon, the potential consequences of gypsum-related subsidence, in terms of building damage and road closures, can be significant. In addition, there may be a small risk of personal injury. It is therefore important that the planning of future development in the area should be guided by the results of the hazard assessment carried out in this study and that such development should be subject to controls and mitigation measures, where appropriate. However, the probability of this form of subsidence occurring at any given site is very low and the risk to individual properties is therefore generally very small, especially from the statistical viewpoint normally adopted by insurers. Taking account of these facts, forward planning and development control procedures have been recommended for use by the local planning authority.

The hydrochemistry of a Chalk aquifer during recovery from drought

Chalk groundwater levels typically decline markedly in response to drought, and rebound strongly when the drought breaks. Chalk streams, largely groundwater-fed, are of ecological importance but little research has been conducted on possible water-quality effects accompanying fluctuations in groundwater level. This study monitored springs, boreholes and surface water in the Pang and Lambourn catchments in southern England during a major recovery in 2006–2008. Hydrochemistry, stable isotopes and age indicators were used to characterize the waters. Perennial springs showed little change in water quality over the monitoring period, and even seasonal springs soon became consistent in their hydrochemistry. A similar lack of change was observed in borehole waters and in the River Lambourn. Stable isotopes demonstrated the high degree of damping relative to rainfall inputs, and residence time indicators showed that Chalk groundwater is basically a mixture with an ‘old’ (pre-1950s) component of ≥50%. This being the case, any water quality changes owing to water level fluctuations would inevitably become diluted. Therefore, although future climate predictions for southern Britain include greater extremes in rainfall and temperature, and consequently water level changes of greater amplitude, the buffering effect of the Chalk aquifer should protect the quality of Chalk springs and streams.

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.

Using stable isotopes and continuous meltwater river monitoring to investigate the hydrology of a rapidly retreating Icelandic outlet glacier

ABSTRACT Virkisjökull is a rapidly retreating outlet glacier draining the western flanks of Öræfajökull in SE Iceland. Since 2011 there have been continuous measurements of flow in the proglacial meltwater channel and regular campaigns to sample stable isotopes δ2H and δ18O from the river, ice, moraine springs and groundwater. The stable isotopes provide reliable end members for glacial ice and shallow groundwater. Analysis of data from 2011 to 2014 indicates that although ice and snowmelt dominate summer riverflow (mean 5.3–7.9 m3 s−1), significant flow is also observed in winter (mean 1.6–2.4 m3 s−1) due primarily to ongoing glacier icemelt. The stable isotope data demonstrate that the influence of groundwater discharge from moraines and the sandur aquifer increases during winter and forms a small (15–20%) consistent source of baseflow to the river. The similarity of hydrological response across seasons reflects a highly efficient glacial drainage system, which makes use of a series of permanent englacial channels within active and buried ice throughout the year. The study has shown that the development of an efficient year round drainage network within the lower part of the glacier has been coincident with the stagnation and subsequent rapid retreat of the glacier.

Model fusion at the British Geological Survey: experiences and future trends

Abstract The British Geological Survey (BGS) is developing integrated environmental models to address the grand challenges that face society. Here we describe the BGS vision for an Environmental Modelling Platform (BGS 2009) that will allow integrated models to be built, and describe case studies of emerging models in the United Kingdom. This Environmental Modelling Platform will be founded on the data and information that the BGS holds. This will have to be made as accessible and interoperable as possible to both the academic and stakeholder decision-making community. The geological models that have been built in an ad hoc way over the last 5–10 years will be encompassed in a National Geological Model that will be multi-scaled, beginning with onshore UK and eventually including the offshore continental shelf. The future will be characterized by the routine delivery of 3D model products from a multi-scaled and scalable 3D geological model of the UK that can be dynamically updated. The deployment of this model will generate further significant requirements across the Information and Knowledge Exchange spectrum, from applications development (database, GIS, web and mobile device), data management, information product development, to delivery to a growing number of publics and stakeholders.