Tower of London moat to become wetland after £70m upgrade approved
Victorian drainage tunnel will be converted into an underground water tank to sustain the new habitat
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The Tower of London’s moat will be transformed into a wetland habitat after Historic Royal Palaces received permission for a £70 million upgrade. The project will repurpose a Victorian drainage tunnel beneath the western moat into an underground water storage tank to sustain the new ecosystem.
The moat, built in the 1270s under King Edward I, was originally a defensive feature filled with water. By the 1840s, it had become a sewer, prompting the Duke of Wellington, then Constable of the Tower, to order its drainage. It has remained largely dry since, except for occasional flooding.
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Why the moat needs water storage
Previous attempts to reintroduce water to the moat faced challenges. A large water tank installed in recent years failed to store enough water to keep ponds topped up during heatwaves. The stone walls surrounding the moat also trap heat, making it difficult for plants to thrive.
The solution lies in the moat’s existing drainage system. When the moat was drained, Victorian engineers installed tunnels to remove rainwater and groundwater. These tunnels still function, though a section was damaged by a Second World War bomb. The remaining culverts collect stormwater and must be manually emptied in sync with the Thames’ tidal cycle.
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The western culvert will now be converted into a large underground storage tank. This will allow Historic Royal Palaces to maintain water levels in the moat, supporting the new wetland. A borehole will also be drilled to supplement water supplies during dry periods.
Trials and archaeological findings
A small wetland patch has already been tested in the moat. The results will inform the creation of larger wetland areas along the moat’s perimeter. Archaeological work has revealed that, before full drainage, the moat supported a diverse range of native plants and animals during periods when it held water.
The project aims to restore a habitat similar to what existed before the moat was drained, though without the sewage that plagued it in the 19th century. The upgrade is part of broader efforts to modernise the Tower’s facilities while preserving its historical character.
What happens next
Historic Royal Palaces has not announced a start date for the work. The £70 million upgrade includes this project alongside other improvements to the Tower’s infrastructure. Residents and visitors will see changes to the moat’s appearance as the wetland develops, though no disruption to public access has been detailed.
Questions this report answers
+Why is the Tower of London’s moat being turned into a wetland?
The moat will become a wetland to restore a habitat last seen before it was drained in the 1840s. The project aims to support wildlife and improve plant growth, using a Victorian drainage tunnel for water storage. Historic Royal Palaces leads the effort as part of a £70 million upgrade.
+How will the moat stay filled with water?
A Victorian drainage tunnel beneath the western moat will be converted into an underground water storage tank. This will collect stormwater and groundwater, keeping the moat topped up. A borehole will also be drilled to supply additional water during heatwaves or dry periods.
+What did archaeologists find in the moat?
Archaeological work revealed that the moat once supported native plants and animals when it held water. This was before full drainage in the 1840s, though it often dried out at low tide. The findings are guiding the wetland restoration project.
+When will the work on the moat start?
Historic Royal Palaces has not announced a start date for the moat conversion. The £70 million upgrade includes this project alongside other improvements to the Tower’s facilities. No details on public access disruptions have been provided.
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