Basement hydrogeology and fortification of the Channel Islands: legacies of British and German military engineering

Abstract

The islands of Jersey, Guernsey, Alderney and Sark lie close to the Normandy coast of France. They expose a largely Precambrian crystalline basement of metamorphic and igneous rocks – Jersey and Alderney also expose some early Palaeozoic clastic sediments – and all have a thin but widespread Quaternary sedimentary cover. The three largest islands were progressively fortified by the British between the early 13th and mid-19th centuries, and by German forces during occupation in World War II, a legacy illustrated by the castles, forts and numerous German coastal fortifications that still adorn them. A German military geologist based on Jersey from mid-1941 to mid-1944, and a military geological team on Guernsey and Alderney during 1942, generated hydrogeological maps and reports that were then in advance of understanding of crystalline basement aquifers elsewhere in the British Isles. All the major documents have now been found in Germany, the USA and UK, although none survived on the islands themselves. Geological mapping and hydrogeological studies postwar under the auspices of the British Geological Survey were completed without access to German data. However, German and British data together now facilitate an appraisal of the heavily stressed aquifers on these small, hard-rock islands over an unusually long (65 year) timespan.

The groundwater invertebrate fauna of the Channel Islands

“…The Environment Department of the States of Jersey Government carries out a programme of biological monitoring of the island's surface waters and also monitors groundwater levels and chemistry in Figure 1. The location of the Channel Islands in the English Channel (map from Robins et al 2012). a network of wells and boreholes across the island but no study of groundwater fauna has ever been undertaken.…”

“…The islands of Jersey, Guernsey, Alderney and Sark constitute part of the eroded remnants of the Armorican Massif, which is more extensively exposed in Brittany and western Normandy (Robins et al 2012). The islands largely consist of Precambrian crystalline metamorphic and igneous rocks, together with early Palaeozoic clastic sediments that outcrop on Jersey and Alderney.…”

Integrating aerial geophysical data in multiple-point statistics simulations to assist groundwater flow models

“…The Lagan Valley Aquifer has been studied for many decades (Bennett 1976;Cronin et al 2000Cronin et al , 2005Hartley 1935;Kalin and Roberts 1997;Kalin et al 1998;Manning et al 1970;McNeill et al 2000;Robins 1996;Yang et al 2004) and the region is well documented to contain Tertiary dykes. The effect of dykes on groundwater flow is acknowledged by previous authors as acting as relative barriers to flow: the hydraulic effect is described in Bennett (1976), Kalin and Roberts (1997), Burns et al (2010), Wilson (2011) and numerous consultancy studies involving hydraulic testing.…”

Military aspects of hydrogeology: an introduction and overview

“…Mather (2012a) describes such an example, in which the water supply to British garrisons on both sides of the Thames estuary was enhanced, at considerable expense, to improve the defences of London against amphibious attack from Dutch and later French forces in the 18th century. Robins et al (2012) include a reference to another notable example, Fort Regent on the Channel Island of Jersey, where a well was excavated through granite to a depth of 72 m in 1806-1808, yielding a supposedly inexhaustible supply of water. Later in the 19th century 'Palmerston Forts', built on the recommendation of a Royal Commission in 1860 to protect important Royal Navy bases from attack (Crick 2012), were typically provided with their own wells or storage tanks, holding water from civilian sources, sufficient for a 14-day supply.…”

“…It was calculated initially that 75 trucks each carrying 85 jerry cans with a capacity of 20 l were required for transporting the daily requirements of just one army division between water supply points. However, both British and German forces came to make significant use of drilled boreholes to reduce the need for longdistance water transport, and wells sited with geologist guidance were progressively developed as the conflict oscillated across North Africa (Rose 2012b;Willig & Häusler 2012b Robins et al 2012;Rose 2012b;Willig & Häusler 2012b) and subsequent conflicts (Dow & Rose 2012;Gellasch 2012;Willig 2012).…”