Managed Aquifer Recharge Using Stormwater as a Drought Mitigation Strategy in London

Managed Aquifer Recharge (MAR) involves artificially recharging and storing water into an aquifer to recover it during times of drought. This water can also serve to raise local water table levels in aquifers connected to rivers, thus having the potential to augment low river levels through baseflow. Considering that a significant proportion of rainfall falling over urban environments is converted into runoff, it is worth exploring the opportunity and feasibility of using MAR with urban runoff as the recharge water source. In this process, stormwater must be captured, stored and pre-treated before it is recharged into the subsurface. Sustainable Drainage Systems (SuDS) are ideal for this purpose and, therefore, a SuDS/MAR scheme can be envisaged in an urban setting. Barriers and opportunities arising from implementing such a scheme are explored for the Cray catchment, South London. The analysis follows a stepwise methodology examining whether (i) sufficient quantity can be captured, (ii) a suitable aquifer is found locally, (iii) there is sufficient space for SuDS development and (iv) water quality constraints can be dealt with given aquifer protection regulation. Given the relative temporal distribution of rainfall, groundwater levels and river flow, results indicate there is some potential benefit for river flow augmentation. However, the insufficient thickness of the utilized unconfined aquifer limits the recharge flow rate. Controlling the rate ensures no groundwater flood risk. Although benefits are limited in the present study, schemes under more favorable conditions might become increasingly needed in a context of future climate uncertainty where the marginal environmental and economic costs for additional storage capacity in surface reservoirs are expected to rise sharply.