Groundwater supplies to island communities
Bardsey is a small island off the Welsh coast. Water supplies are drawn from spring sources but water shortages are experienced in summer. Sanitation depends on Elsan type toilets. There are limited groundwater resources in the Gwna Mélange, which is of Monian age, with groundwater transport controlled by fracture flow. There is evidence of some groundwater contamination.
Common to other small islands, water resource management is a critical issue on the Isles of Scilly, UK. This study examined the current practice of water management on the islands of St Martin’s and St Agnes in the Isles of Scilly so that a local water management plan could be formulated. The study commenced with a survey of water supplies which included locating wells, rainwater tanks and septic tanks and determining their connections and utility. Wellheads were level surveyed with respect to UK Ordnance Datum, allowing reduced groundwater levels to be monitored. Groundwater is abstracted from shallow dug wells in blown sand or Head deposits and deep wells bored into fractured granite. Hydraulic tests were conducted in seven wells to determine well and aquifer characteristics, although these tests were limited by the low yields of the wells. A geographical information system was used to collate and process information. MODFLOW and MODPATH models were constructed to help interpret the hydrogeology; to determine the impact and sustainability of groundwater abstractions; and to determine the possible extent of source protection zones around wells. The present rate of abstraction is sustainable but, due to large natural variations in the water table level, groundwater resources will always be vulnerable during periods of dry weather. The main threats to existing groundwater supplies are saline intrusion, elevated nutrient levels from agriculture and bacterial contamination from septic tanks.
Figures & Tables
Groundwater in the Celtic Regions: Studies in Hard Rock and Quaternary Hydrogeology
This book covers a diverse range of hydrogeological environments that occur in the Celtic regions of Britain and Ireland. These include hard rock aquifers of Lower Palaeozoic and Precambrian age, generally dominated by fracture flow within a shallow zone of weathering; Carboniferous Limestone aquifers, often characterized by conduit flows in karstic systems; dual-porosity Permo-Triassic sandstone aquifers; and Quaternary deposits, many of which form shallow granular aquifers. The papers presented here address a number of current issues common to the Celtic regions, including: groundwater protection policies, groundwater management in karst aquifers, groundwater development in Quaternary aquifers, groundwater evaluation in data-scarce aquifers and groundwater supplies to small island communities.