The hydrogeology of the Enfield-Haringey artificial recharge scheme, north London

Abstract

The Enfield-Haringey artificial recharge scheme comprises 23 abstraction/recharge boreholes located between Enfield and Haringey in north London. It is a strategic groundwater development aimed at increasing drought yields to meet the 'target level of service' defined by OFWAT for availability of water resources. The hydrogeology of the scheme, revealed by the drilling and testing of 15 new production boreholes is described and its strategic use summarized. The hydrochemistry of the groundwater in the Chalk and Basal Sands aquifer is briefly considered and the likely effects of re-saturation after recharge on the quality of the pumped groundwater is commented on. This and previous studies have led to a better understanding of the aquifer system and the hydraulic relationship between the Basal Sands and the underlying Chalk. Intensive exploitation in the past led to some dewatering but reduction in abstraction since the 1950s has allowed water levels to recover, a process that is continuing. In most of the Enfield-Haringey area the aquifer is still only partially saturated, hence the potential for artificial recharge. The Chalk aquifer has been found to be typically anisotropic and heterogeneous with the upper 30–40 m being productive. Acidization was found to produce significant increases in well yields. Chalk groundwaters are mainly of a calcium bicarbonate type while those of the overlying Basal Sands are dominated by sulphate. Both groundwaters become progressively richer in sodium at the expense of calcium from north to south, in the direction of groundwater flow and towards more deeply confining conditions.

The Unified Scale of Natural Waters

“…In 1972 a pilot experiment was carried out at two sites in the Lea Valley. It proved impossible to predict the effects of artificial recharge on groundwater quality over a regional scale, so a prototype scheme was carried out intermittently between 1977 and 1980 (Flavin and Joseph, 1983;O'Shea et al, 1995). Modelling by Gale et al (1991) suggested that oxidation of FeS 2 in the Palaeogene sands by atmospheric O 2 could generate increased concentrations of SO 4 and Fe (see Box 3.1), although the effects were likely to be localised.…”

Exploitation of Satellite A-DInSAR Time Series for Detection, Characterization and Modelling of Land Subsidence

“…Thus, the EA implemented an observation borehole network within the basin in order to monitor and manage changes in groundwater levels. Furthermore, an artificial recharge scheme was licensed in North London, NLARS (North London Artificial Recharge Scheme; [46]) to support the groundwater levels control [49,50]. The available scenes were processed using the GAMMA SAR and Interferometry software (Gamma Remote Sensing, Bern, Switzerland) and, in particular, the Interferometric Point Target Analysis (IPTA) algorithm [52].…”

Assessment of Managed Aquifer Recharge Potential Using Ensembles of Local Models

“…comm. (2005), 8 Heisig and Prince (1993) , 9 Ross Schmidt et al (2007) , 10 Passow (1996) , 11 Johnston (1993) , 12 O’Shea et al (1995) , 13 Brothers and Katzer (1990) , 14 Dillon et al (1997) , 15 Lacombe (1996) , 16 Reeder et al (1976) .…”

“…Large hydraulic loads can also be achieved using large basins with smaller infiltration rates, for example, 83 ML/d at Leaky Acres with infiltration rate 0.17 m/d and basin area 47 ha (Nightingale and Bianchi 1973). Large injected hydraulic loads are generally achieved using large capacity wells in aquifers with large transmissivity, for example, 48 ML/d at Enfield-Haringley using 13 wells injecting at 43 L/s each into a fissured chalk aquifer with transmissivity around 1300 m 2 /d (O'Shea et al 1995).…”