Regional analysis of groundwater droughts using hydrograph classification

Groundwater drought is a spatially and temporally variable phenomenon. Here we describe the development of a method to regionally analyse and quantify groundwater drought. The method uses a cluster analysis technique (non-hierarchical k-means) to classify standardised groundwater level hydrographs (the standardised groundwater level index, SGI) prior to analysis of their groundwater drought characteristics, and has been tested using 74 groundwater level time series from Lincolnshire, UK. Using the test data set, six clusters of hydrographs have been identified. For each cluster a correlation can be established between the mean SGI and a mean standardised precipitation index (SPI), where each cluster is associated with a different SPI accumulation period. Based on a comparison of SPI time series for each cluster and for the study area as a whole, it is inferred that the clusters are independent of the driving meteorology and are primarily a function of catchment and hydrogeological factors. This inference is supported by the observation that the majority of sites in each cluster are associated with one of the principal aquifers in the study region. The groundwater drought characteristics of the three largest clusters, which constitute ~ 80 % of the sites, have been analysed. There are differences in the distributions of drought duration, magnitude and intensity of groundwater drought events between the three clusters as a function of autocorrelation of the mean SGI time series for each cluster. In addition, there are differences between the clusters in their response to three major multi-annual droughts that occurred during the analysis period. For example, sites in the cluster with the longest SGI autocorrelation experience the greatest-magnitude droughts and are the slowest to recover from major droughts, with groundwater drought conditions typically persisting at least 6 months longer than at sites in the other clusters. Membership of the clusters is shown to be related to unsaturated zone thickness at individual boreholes. This last observation emphasises the importance of catchment and aquifer characteristics as (non-trivial) controls on groundwater drought hydrographs. The method of analysis is flexible and can be adapted to a wide range of hydrogeological settings while enabling a consistent approach to the quantification of regional differences in response of groundwater to meteorological drought

Regionalisation of groundwater droughts using hydrograph classification

Groundwater drought is a spatially and temporally variable phenomenon. Here we describe the development and application of a method to regionalize and quantify groundwater drought based on categorisation of Standardised Groundwater level Index (SGI) time series. The categorisation scheme uses non-hierarchical k-means cluster analysis. This has been applied to 74 SGI time series for the period January 1983 to August 2012 for a case study from Lincolnshire, UK. Six SGI time series clusters have been identified. For each cluster a correlation can be established between the mean SGI and a mean Standardised Precipitation Index (SPI) associated with an optimal SPI accumulation period, qmax. Based on a comparison of SPI time series for each cluster and SPI estimated for the whole study area, it is inferred that the clusters are largely independent of heterogeneity in the diving meteorology across the study region and are primarily a function of catchment and hydrogeological factors. This inference is supported by the observation that the majority of sites in each cluster are associated with one of three principal aquifers in the study region. The groundwater drought characteristics of the three largest clusters (CL1, CL2 and CL4 that constitute ~80% of the sites) have been analyzed. There is a common linear relationship between drought magnitude and duration for each of three clusters. However, there are differences in the character of the groundwater drought events between the three clusters as a function of autocorrelation of the mean SGI time series for each cluster. For example, CL1 has a relatively short period of significant SGI autocorrelation compared with CL2 (15 and 23 months respectively); CL1 has more than twice the number of drought episodes (39 episodes) than CL2 (15 episodes), and the average and maximum duration of droughts in CL1 (4.6 and 27 months) are less than half those of CL2 (11.3 and 61 months). The drought characteristics of CL4 are intermediate between those of CL1 and CL2. Differences in characteristics between the three clusters are also seen in their response to three major multi-annual droughts that occurred during the analysis period. For example, sites in CL2 with the longest SGI autocorrelation experience the greatest magnitude droughts and are the slowest to recover from drought, with groundwater drought conditions typically persisting at least six months longer than at sites in the other two clusters. Membership of the clusters reflects differences in the autocorrelation of the SGI time series that in turn is shown to be related to unsaturated zone thickness at individual boreholes. This last observation emphasises the importance of catchment and aquifer characteristics as (non-trivial) controls on groundwater drought hydrographs

The development of linked databases and environmental modelling systems for decision-making in London

A basic requirement for a city's growth is the availability of land, raw material and water. For continued and sustainable development of today’s cities we must be able to meet these basic requirements whilst being mindful of the environment and its relationship with anthropogenic activity. The heterogeneous and complex nature of urban systems where there are obvious environmental and anthropogenic inter-dependencies necessitates a more holistic approach to decision-making. New developments such as linked databases of environmental data and integrated environmental modelling systems provide new ways of organising cross-disciplinary information and a means to apply this to explain, explore and predict the urban systems response to environmental change. In this paper we show how, accessibility to linked databases, detailed understanding of the geology and integrated environmental modelling solutions has the potential to provide decision-makers and policy developers with the science based information needed to understand and address these challenges

From geological complexity to hydrogeological understanding using an integrated 3D conceptual modelling approach : insights from the Cotswolds, UK

Adequate hydrogeological conceptualisation of structurally complex fractured aquifers requires the support of detailed geological mapping and three dimensional understanding. With a geological framework in place uncertainties in hydrological understanding and irregularities in hydraulic observations may be rationalised. Using the Cotswold of southern England, which are underlain by the ooidal limestone-dominated Middle Jurassic Inferior Oolite and Great Oolite groups, 3D modelling software GSI3D and Geographical Information Systems (GIS) have been used to integrate observed hydraulic behaviours with the 3D geological framework. In this way a conceptual model is developed to assist simulation of groundwater flow and the predicted response of groundwater levels and river flows to climatic extremes. The structural and lithological complexity of the bedrock results in sub-catchments which exhibit individual hydraulic responses and a hydrogeological setting dominated by shallow rapid fracture pathways and copious spring discharge

Groundwater resilience Nepal: preliminary findings from a case study in the Middle Hills

Groundwater resources in the Middle Hills of Nepal perform a major role in supplying domestic and irrigation water and in regulating river flows. However, there has been little systematic study of groundwater within the region, making it difficult to evaluate how water supplies and river flows may change in response to climatic and anthropogenic change. To begin to build an evidence base, two catchments in the Middle Hills were investigated. The aim of the study was to characterise the hydrogeology of the catchments, assess water supplies and water usage and evaluate how resilient groundwater may be to change. Two contrasting sub-catchments within the Kali Gandaki River catchment were chosen: Ramche Village Development Committee (VDC), at an elevation of 2000 – 3000 m, with subsistence terraced farming and highly forested slopes, and Madanpokhara VDC which is largely below 1000 m, with expanding commercial agriculture. Groundwater sampling was undertaken during the post-monsoon season 2013 and pre-monsoon season 2014. Springs, tube wells and rivers across the two catchments were investigated using a combination of surveys, flow measurements, and sampling for inorganic chemistry, stable isotopes, groundwater residence time indicators (CFC and SF6) and noble gases. In addition, 12 months of weekly hydrological monitoring and monthly water usage surveys were undertaken at several sites. There is a heavy reliance on springs for water supply in Ramche. The springs are typically perennial but with significantly reduced flows during the winter and pre-monsoon season. The springs have bicarbonate groundwater chemistry and generally low overall mineralisation. Springs issuing from the higher slopes are reliant on seasonal monsoon rainfall and snow to sustain higher flows, but baseflows are sustained by groundwater storage within the weathered aquifer and will therefore have some inter-annual storage. Discrete springs issuing from lower slopes are most likely to be fed from groundwater storage within the fractured aquifer network. Groundwater residence time indicators (CFC and SF6) suggest a mean residence time of 10-20 years for pre-monsoon groundwater, implying inter-annual storage and therefore some built in resilience. However the general low storage of the groundwater environment suggests that none of the springs would be resilient to a long term reduction in precipitation. In the lower catchment of Madanpokhara where floodplain and outwash deposits are present, many hand-drilled shallow tubewells have been installed in the last 5-10 years, decreasing the reliance on springs. The development of groundwater resources has resulted in a thriving agricultural co-operative, inward migration and a growing population. These shallow tubewells have increased the resilience of the water supplies to change but are potentially vulnerable to over-exploitation as a result of the rapid increase in abstraction. Groundwater sampled in tubewells along the margin of the floodplain is modern (~20 yrs Mean Residence Time (MRT)) with bicarbonate groundwater chemistry and no significant water quality concerns. Groundwater sampled from tubewells towards the centre of the floodplain appears to be older (~50 yrs MRT) with elevated concentrations of iron, manganese, zinc and arsenic detected at some sites. With a growing recognition of the importance of groundwater storage in the Middle Hills there is significant potential to further advance the characterisation of groundwater systems and investigate the resilience of groundwater supplies to change. Systematic monitoring of groundwater, as springs flows, groundwater levels and chemistry would give a much better understanding of emerging trends. Likewise, monitoring current yields of springs and comparing to historic values at installation may allow some conclusions to be drawn about the trajectory of springflow. There are several groundwater-related initiatives underway within organisations in Nepal; the lessons learned from this current research, the methodologies used and the preliminary findings will be of value to these

Accounting for groundwater in future city visions

City planners, urban innovators and researchers are increasingly working on ‘future city’ initiatives to investigate the physical, social and political aspects of harmonized urban living. Despite this, sustainability principles and the importance of urban groundwater are lacking in future city visions. Using London as a case study, the importance of groundwater for cities is highlighted and a range of future city interventions may impact on groundwater are reviewed. Using data from water resource plans and city planning strategies, changes in the groundwater balance which may occur as a result of city interventions are calculated for two future city scenarios: a ‘strategic’ future informed by organisational policy and an ‘aspirational’ future guided by sustainability principles. For London, under a strategic future, preferential investment in industry-scale technologies such as wastewater treatment and groundwater storage would occur. Acknowledgement that behaviour change offers the potential for a faster rate of transformation than innovation technologies is ignored. The capacity of community-led action and smart-home technologies to deliver sustainable water use under an aspirational future is evident, with a measurable impact on urban groundwater. These methods may be used to inform city interventions that consider the social context in addition to environmental constraints and business drivers

Impacts of climate change on small island hydrology : a literature review

This report comprises a review of literature relating to the impacts of climate change on small islands. Given the diversity of material presented on climate change studies this review has intentionally focussed on small island hydrogeology, the impacts of climate change specifically on small islands and finally a review of impacts associated with extreme events. The small islands and climate change literature is abundant. It assesses and predicts change and associated impacts. Perhaps the greatest uncertainty relates to manifestation of climate change impacts and their attribution to natural or anthropogenic causes. Many researchers also highlight the interdependencies between environmental, social and economic determinants. An assessment of impacts of climate change across the various types of small islands is highlighted by the Inter-governmental Panel on Climate Change (IPCC) as an area requiring consideration that is lacking within the literature and would benefit from further research

Project progress report 2010-11 : groundwater monitoring in urban areas : a pilot study in Glasgow, UK

The work described in this progress report is part of ongoing efforts to develop a better conceptual understanding of the groundwater system in Glasgow. It is also aimed at developing protocols for improved groundwater monitoring in urban areas, which is a key step in improving hydrogeological understanding. In 2009 BGS started a pilot project to examine the potential for the development of a long-term urban groundwater monitoring network in Glasgow, using existing monitoring boreholes. The project has close links to a number of BGS projects: the Clyde Urban Super Project (CUSP) and the Industrial Legacies project; a project being carried out jointly between Glasgow City Council (GCC) and BGS under the Local Authorities and Research Councils Initiative (LARCI); and wider research into groundwater monitoring and sustainable drainage systems (SuDS) within the BGS Urban Development and Groundwater Systems and Monitoring teams. Project aims Identify and collate existing groundwater monitoring data (groundwater level and chemistry data) for Glasgow Design, develop and populate a dedicated database to store the groundwater monitoring data (and associated borehole data), and make it easily available for analysis and interpretation Interpret the collated data, in conjunction with related datasets (e.g. 3D geological models), and so develop an improved conceptual model of the shallow (superficial deposits) groundwater regime in Glasgow Use the collated data and hydrogeological interpretation to design a pilot groundwater monitoring network in a selected area in Glasgow, using existing monitoring boreholes, and specify a monitoring regime and protocol. Make recommendations for a future longer-term (>10 yrs) and larger scale (Glasgowwide) groundwater monitoring network. Why monitor groundwater in Glasgow? Drivers for long-term groundwater monitoring in Glasgow have been identified in consultation with stakeholders, in particular GCC and the Scottish Environment Protection Agency (SEPA). There is a wide range of groundwater issues, each of which requires slightly different hydrogeological information to properly address. Any one groundwater monitoring network cannot capture data to address all of these issues. It is important, therefore, that monitoring is targeted to one or two key drivers is essential so that the monitoring network can capture data that is both representative of the groundwater system and appropriate to the monitoring need. The two key drivers identified are: the need to address the existing gaps in basic hydrogeological data for Glasgow, which currently limit our understanding of the groundwater system; and the need to understand the effects of urban regeneration and development on the groundwater system, and in particular the effect of sustainable drainage schemes (SuDs). Other related drivers for monitoring groundwater across Glasgow are: the requirement of stakeholders for assistance in regulating impacts on the groundwater system and meeting Water Framework Directive (WFD) and other regulatory requirements the need to better understand the impact of contaminated land on groundwater the need to understand the impact of heat engineering schemes and existing groundwater abstractions on the groundwater system the need to understand the role of groundwater in flooding

Some relationships between lithology, basin form and hydrology : a case study from the Thames Basin, UK

The role of lithology in influencing basin form and function is explored empirically by investigating correlations between a range of catchment variables, where the spatial unit of analysis is not surface catchments but lithologically coherent groundwater units. Using the Thames basin, UK, as a case study, nine groundwater units have been identified. Values for 11 hydrological and geomorphological variables, including rainfall, drainage density, Baseflow Index, aquifer porosity, storage coefficient and log-hydraulic conductivity, aquifer and drainage elevation, river incision, and hypsometric integral have been estimated for each of the groundwater units in the basin, and Pearson correlation coefficients calculated for all pairs of variables. Seven of the correlation coefficients are found to be significant at a confidence level of > 99%. Negative correlations between drainage density and log aquifer hydraulic conductivity, and between drainage density and river incision, and positive correlations between log-hydraulic conductivity and river incision, log-hydraulic conductivity and Baseflow Index, and between Baseflow Index and river incision are inferred to have consistent causal explanations. For example, incision of rivers into aquifers leads to relative increases in hydraulic gradients in the vicinity of rivers which, in turn, promotes the development of secondary porosity increasing both aquifer hydraulic conductivity and, hence, Baseflow Index. The implication of this interpretation is that the geomorphological evolution of basins is intimately linked to the evolution of hydraulic conductivity of the underlying aquifers. This is consistent with, and supports the notion of a coupled complexly evolving surface water-groundwater system