Artificial recharge was carried out experimentally in north London by the Water Resources Board and the Metropolitan Water Board between 1953 and 1970(Boniface 1959). These trials were successful, although only small volumes of water were recharged. Research by Thames Water Authority continued between 1975 and 1984 at a larger scale in the north London area (Flavin & Hawnt 1979; Flavin & Joseph 1983).

Thames Water Utilities drilled and tested 14 new production boreholes for the Enfield-Haringey Scheme along the course of the New River in north London (Fig. l, opposite). These new boreholes, together with nine existing sites, are designed to increase the strategic groundwater resources of north London by 90 Ml/d by artificially recharging the Chalk and Thanet Sands aquifer beneath London (O'Shea 1994).

During an average year, demand for water is often lower than that available from the Coppermills Water Treatment Works and between 10 and 20 M1/d of this excess fully treated water can be gravity recharged to the aquifer. This will be by low-rate, trickle recharge ensuring that the volume of water stored in the aquifer is sufficient to sustain a prolonged drought abstraction for up to 200 days. When demand for water is high, as in drought conditions, groundwater can be pumped from the aquifer, using the same boreholes, directly into the New River which acts as an aqueduct taking the water back to Coppermills, via the East Reservoir at Stoke Newington for treatment and supply. The scheme will be used strategically in times of

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