Coupling a radial model of the Darcy-Forchheimer equation with a regional groundwater model to simulate drawdown at supply boreholes

Assessing the short and long-term risks to a groundwater source is a critical part of water resource management. In the UK, public water supply companies apply the term Deployable Output (DO) to describe the yield of a groundwater source under drought conditions. DO is constrained by the physical properties of an aquifer and operational factors such as licence conditions, water quality, and pumping and treatment capacity. A robust assessment of groundwater DO should be informed by numerical modeling. This requires the groundwater level in a supply borehole to be accurately simulated within its regional hydrogeological context. A 3D radial flow model of the Darcy-Forchheimer equation is presented for simulating drawdown at a borehole. The Darcy-Forchheimer Radial Flow Model (DFRFM) represents linear and non-linear flows around the borehole; confined and unconfined conditions; vertical heterogeneity in the aquifer and borehole storage. The DFRFM is coupled with a regional groundwater model which represents the large-scale groundwater system, including lateral and vertical aquifer heterogeneity, rivers, and spatially varying recharge. The model has been applied to a supply borehole located in the dual permeability Chalk aquifer, which forms the principal aquifer in the UK and provides 40-70% of the total public water supply in southern and eastern England. The application demonstrates the potential for the coupled model to be used to inform DO assessments and to assess the long-term risk to sources under climate change scenarios

Environmental governance on the street : towards an expanded research agenda on street-level bureaucrats

Funding: Scottish Government Hydro Nation Scholars Programme (KH).Research on environmental governance would benefit from greater attention to the practices, agency and subjectivities of the frontline civil servants who implement and shape environmental policies and interventions on the ground. These actors conduct the everyday work of bringing global agreements and state policies into being. In doing so, they influence how citizens experience the state and environmental governance. In this review paper, we provide a brief overview of existing literature on ‘street-level bureaucrats’ (SLBs). We then suggest three key research areas through which insights into the role of SLBs in environmental governance could be further developed, including (i) the nature of SLBs agency and practice as they enact global and national environmental agendas, (ii) the subjectivities of SLBs and how they affect environmental governance and (iii) the outcomes of the activities of SLBs on state-citizen relations. This research agenda has explanatory power in understanding existing and desired environmental governance.Publisher PDFPeer reviewe

Groundwater's contribution to water security in Africa

Achieving water security for Africa presents a challenge, particularly given the increasing pressures on water resources related to population growth, climate change, rising living standards and land use change. Water security can be defined as the availability of an acceptable quantity and quality of water for health, livelihoods, ecosystems and production, coupled with an acceptable level of water-related risks to people, environments and economies (Grey & Sadoff, 2007). Groundwater – the fresh water naturally stored in rocks beneath the ground surface – makes a significant contribution to the security of water supplies for both domestic and productive uses across the African continent. Its importance and use are increasing markedly. Groundwater can help achieve universal and equitable access to resilient water services for both rural and urban populations in Africa. With the relevant methods and expertise, groundwater can be found across much of Africa, with even the least productive aquifers often capable of providing sufficient yields to supply communities with handpumps or low-intensity, small-scale irrigation schemes. The volume of water stored underground in Africa – estimated to be 20 times more than the freshwater stored in lakes and reservoirs – can also provide a critical buffer against short-term rainfall variability, making groundwater reserves less vulnerable than surface waters to drought. Groundwater is also less vulnerable to contamination. The implications of resilient, safe, and sustainable water services for all, where groundwater forms a critical part of an integrated approach to water resource management, are significant and wide-reaching in terms of national growth, economic development and poverty reduction. Groundwater development is not, however, without risks. Securing equitable access to groundwater for both domestic and productive uses across rural and urban Africa requires a detailed understanding of groundwater resources coupled with adequate governance arrangements so that the potential gains of groundwater investment can be balanced against the associated risks for people, the environment, and the economy. This paper has been prepared by researchers within the UPGro (Unlocking the Potential of Groundwater for the Poor) Programme, along with colleagues from the International Association of Hydrogeologists, Africa Groundwater Network, and GRIPP. It is intended as a working paper, presenting a summary of our current understanding of groundwater in Africa along four themes: (1) urban water security, (2) socially inclusive and sustainable rural water services, (3) groundwater for agricultural growth and transformation, and (4) groundwater resources and renewability

Relative influence of changes in hydraulic conductivity with depth and climate change on estimations of borehole yields

Understanding the impact of climate change on borehole yields from fractured aquifers is essential for future management of groundwater resources. Although the impact of changes in hydraulic conductivity with depth (VKD) on groundwater levels is well established, the relative significance of climate change and VKD on borehole yield estimates is poorly understood. We hypothesize that VKD exerts a significant additional control on borehole yields under climate change which has not been considered in yield assessments to date. We developed a radial groundwater flow model of an idealised pumping borehole in the fractured Chalk aquifer of south-east England, and applied 11 VKD profiles based on a simple conceptual representation of variability in hydraulic conductivity with depth in the Chalk. For each VKD profile, we applied 20 climate scenarios and six constant pumping rates for the period 1962 – 2014. We then estimated borehole yields based on the derived lowest pumping water levels during key drought years (e.g. 1976). We show that VKD is more significant (p 0.1) in controlling lowest pumping groundwater levels. Hydraulic conductivity is as significant a control as climate on borehole yields, although responses are highly non-linear associated with pumping water level-pumping rate curves intersecting key yield constraints (e.g. pump intake depth, major inflow horizons). It is recommended that variations in hydraulic conductivity with depth are taken into consideration in future assessments of borehole yields under climate change when developing integrated water resources management plans. The approach presented is generic and can be applied across different aquifers where vertical heterogeneity is present

Africa Groundwater Atlas: Making African groundwater information more visible and accessible

Groundwater information and data is vital to sustainably developing groundwater resources, and to hydrogeological research, in Africa. But robust groundwater information for Africa is often not visible, available and/or accessible. The online Africa Groundwater Atlas is a major initiative involving hydrogeologists across Africa, coordinated by the British Geological Survey and funded by the UK UPGro programme. The Atlas provides a systematic overview of the hydrogeology and groundwater resources of 51 African countries, and a gateway for those wishing to learn more. Alongside geology and hydrogeology maps and descriptions for each country, the Atlas includes supporting information on rainfall, soils and surface waters; and on groundwater status and management. So far, 25 detailed country profiles have been developed in collaboration with 58 hydrogeological specialists for the relevant country, including members of IAH and AGW-Net. The remaining country pages include the same maps and supporting data, but have been produced without input as yet from country experts and so have more limited information. These will be updated in Phase 2 of the project, which began in May 2017. The Atlas has been developed in parallel with the online Africa Groundwater Literature Archive, which so far indexes nearly 7000 references related to African groundwater. These can be searched spatially or by thematic keyword, and as many as possibly are freely available as digital downloads. This initiative grew out of the publication of quantitative groundwater maps for Africa in 2012, which renewed interest amongst donors in the key role that groundwater resources can have in shaping Africa’s future, and highlighted the need for more information at a country scale, to better support the sustainable, integrated development of groundwater resources. The Africa Groundwater Atlas and Literature Archive provide a readily updateable platform to highlight and improve access to the wealth of groundwater information and expertise that already exists in Africa

The impact of across-slope forest strips on hillslope subsurface hydrological dynamics

Forest cover has a significant effect on hillslope hydrological processes through its influence on the water balance and flow paths. However, knowledge of how spatial patterns of forest plots control hillslope hydrological dynamics is still poor. The aim of this study was to examine the impact of an across-slope forest strip on sub-surface soil moisture and groundwater dynamics, to give insights into how the structure and orientation of forest cover influences hillslope hydrology. Soil moisture and groundwater dynamics were compared on two transects spanning the same elevation on a 9° hillslope in a temperate UK upland catchment. One transect was located on improved grassland; the other was also on improved grassland but included a 14 m wide strip of 27-year-old mixed forest. Sub-surface moisture dynamics were investigated upslope, underneath and downslope of the forest over 2 years at seasonal and rainfall event timescales. Continuous data from point-based soil moisture sensors and piezometers installed at 0.15, 0.6 and 2.5 m depth were combined with seasonal (~bi-monthly) time-lapse electrical resistivity tomography (ERT) surveys. Significant differences were identified in sub-surface moisture dynamics underneath the forest strip over seasonal timescales: drying of the forest soils was greater, and extended deeper and for longer into the autumn compared to the adjacent grassland soils. Water table levels were also persistently lower in the forest and the forest soils responded less frequently to rainfall events. Downslope of the forest, soil moisture dynamics were similar to those in other grassland areas and no significant differences were observed beyond 15 m downslope, suggesting minimal impact of the forest at shallow depths downslope. Groundwater levels were lower downslope of the forest compared to other grassland areas, but during the wettest conditions there was evidence of upslope-downslope water table connectivity beneath the forest. The results indicate that forest strips in this environment provide only limited additional sub-surface storage of rainfall inputs in flood events after dry conditions in this temperate catchment setting