Cooling the London Underground: Evaluating the use of groundwater and subterranean river water

One of the most salient current engineering challenges facing sub-surface rail networks is overheating of stations during increasingly warm summer months. Reducing temperatures is a complex proposition in older networks like the London Underground (Tube): overheating poses important risks from both public health and engineering perspectives. Here we critically examine the use of two potential water sources - subterranean river flow and pumped groundwater from the Chalk aquifer - to supply pumped water-heat exchanger systems to cool the London Underground network. First, suitable localities were identified using GIS. Secondly, a proxy for subterranean rivers was used to compare methods of estimating discharge, which was then converted to cooling capacities over an annual hydrological cycle. Groundwater flow was simulated to determine the influence of pumping on the water table at two field sites. Finally, an economic and environmental analysis was undertaken. An average central London subterranean river can provide up to 19 MW cooling capacity, increasing discharged water temperature by 3 degrees C, but also exceeding peak cooling demands. Though groundwater pumping rates (similar to 50 l s(-1)) prove unsustainable during summer months, water table recovery is observed as cooling demands are relieved. Our proposed scheme could contribute to smarter, healthier, low-carbon transportation systems elsewhere.