Monitoring seawater intrusion into the fractured UK Chalk aquifer using measurements of self-potential (SP)

Using laboratory, numerical and field experiments this study investigated whether borehole measurements of self-potential (SP) can be used to monitor seawater intrusion into the fractured UK Chalk aquifer. The SP, a natural voltage, arises in water saturated fractured porous media due to gradients in pressure (electrokinetic (EK) potential) and concentration (exclusion-diffusion (EED) potential), both features of seawater intrusion. An electrode array was installed in a monitoring borehole c.1.7 km from the coast, in Saltdean, East Sussex, and c.1.3 km from an active abstraction borehole. Head fluctuations in the monitoring borehole were controlled by tidal processes and seasonal changes in inland head. SP monitoring over 1.5 years revealed tidal SP signals. The fluctuations (c.600 μV) were two orders of magnitude larger than those observed at an inland site in the same aquifer, near Reading in Berkshire. Numerical simulation, supported by laboratory measurements, of the coupled hydrodynamic and electrical processes in the coastal aquifer suggested that the EK potential generated by tidal processes was one order of magnitude too small to be responsible for the tidal SP fluctuations. Instead, SP was caused by the EED potential that arose due to the concentration gradient between groundwater and seawater across the saline front (i.e. the 1000 mg/l isoline) some distance from the borehole. The saline front moved through a fracture at the base of the borehole in response to tides. A vertical SP gradient (c.0.22 mV/m), only present in the coastal borehole, was also observed. Modelling suggested that the gradient was due to the close proximity of the saline front (c.4 m) below the borehole and was caused by the EED potential. In August 2013 and 2014, tides and a decline in inland head caused saline water to enter the borehole. Fluid electrical conductivity logging showed that entry was via the fracture. Prior to each occurrence of saline breakthrough, an increase in the SP of c.300 μV was observed, commencing c.7 days before saline water was detected in the borehole. Although this study focused on a monitoring borehole, SP arrays could be installed in abstraction boreholes. The results suggest that SP monitoring may be used to provide early warning of saline water breakthrough, allowing for improved management of groundwater resources in coastal aquifers.Open Acces

The tidyverse : manipulating and visualising large datasets

Manipulating and visualising large datasets using tidyverse: a demonstration, using an example from the Ethiopian drought in 2015-16, of the power of Tidyverse, to clean and manipulate data, and produce striking, clear, reproducible and high impact visualisations using the dplyr and ggplot2 packages

A Hidden Crisis: unravelling current failures for future success in rural groundwater supply

Hand-pumped borehole (HPB) supplies are the main type of rural water supply in Africa, but high rates of failure, and poor performance has been a persistent problem over recent decades. The first survey of the Hidden Crisis project assessed 600 HPBs in three African countries (Ethiopia, Malawi and Uganda). The HPBs were selected using a two stage randomised stratified sampling approach and functionality was assessed using a new tiered definition. The results indicate that at any one time around 70 to 80% of HPBs provide some water, but only one third reliably provide sufficient water of good quality year-round. The reasons for these poor statistics are multifaceted, and relate not simply to poor construction or a changing climate, but are the result of a wide set of inter-related issues. Phase two of the project examined in detail a subset of 150 of the original 600 HPBs. The investigations included dismantling each HPB in order to conduct a rigorous assessments of the underlying causes of poor functionality. At each HPB detailed engineering inspections of pump components, pumping tests, water quality and residence time sampling and downhole CCTV inspections were conducted. Communities were asked detailed questions about their experience of the pump and sanitary and geological surveys were conducted. This presentation will provide an overview of the methods used in the field and analysis. The project aims to understand the underlying causual factors relating to borehole functionality, and both statistical approaches and systems thinking has been applied to investigate the relationship and influence of both the physical and social factors underlying poor borehole functionality

Resilience of rural groundwater supplies during drought in Ethiopia

As a result of climate change, sub-Saharan Africa, is expected to experience more frequent and extreme droughts, contributing to greater water insecurity. Droughts affect the reliability, quantity and quality of water available, potentially undermining recent gains in drinking water access and making it difficult to extend services. Ethiopia, in particular, is highly vulnerable to drought. Since 1965, Ethiopia has experienced 15 severe droughts affecting more than 65 million people and causing serious economic damage. Most recently, in 2015 and 2016, Ethiopia suffered a harsh drought, linked to El Nino, which forced more than 10 million people to rely on emergency aid due to crop and water supply failures. During the 2015-16 drought significant effort was made to monitor and understand the performance and use of rural water points. Drawing on two recently published studies we demonstrate that with adequate monitoring and maintenance rural groundwater points can deliver a consistent and safe water supply during drought. The first study monitored a total of 5196 water points (hand-pumps, motorized boreholes, springs, open-sources) and the success of a maintenance programme, every week for 12 weeks in early 2016. Enumerators used questionnaires on mobile phones to gather quantitative and qualitative data from those responsible for water points. The second study involved monitoring 51 groundwater points (hand-pumps, springs, hand-dug wells) over an 18 month period. Water sources were equipped with water level loggers and water was tested monthly for Thermo-tolerant Coliforms (TTCs). All sources were put under considerable strain during drought. Most demand was placed on motorised boreholes in lowland areas. Increases in functionality for motorised boreholes, as a result of the maintenance programme, lagged behind those of hand-pumped boreholes. More complex technologies have longer downtimes due to a lack of appropriate and/or accessible maintenance skills. Real time-monitoring and effective information flow helped facilitate responsive and proactive maintenance of infrastructure, and ensured demand was spread across a larger infrastructure portfolio reducing pressure on individual sources during the drought. Water level monitoring showed that shallow boreholes equipped with handpumps recovered quickly from daily abstraction. Recovery rates of hand-dug-wells and springs was longer. All sources were contaminated during the rains marking drought cessation but boreholes were least affected. We conclude that prioritising access to groundwater via multiple improved sources and a portfolio of technologies, such as hand-pumped and motorised boreholes, supported by responsive and proactive maintenance, increases rural water supply resilience to drought and climate change

The evolution of long-term groundwater storage in the north-western IGB aquifer

• Introduction to BGS and our groundwater work • BGS work in India • Groundwater in the IGB • Long-term changes in groundwater in the north-western IGB aquifer • Quantifying the relative influence of recharge sources in the north-western IGB aquife