London needs to double sustainable drainage ambition to avoid flood risk

London needs to double its drainage ambition and “significantly” increase funding for sustainable drainage systems (SuDS) to protect the capital from future flood events, a scrutiny body has said.

The London Assembly outlined water resource needs and wastewater management in its Water and London rivers report,  as well as mitigations for surface water flooding.

The London Assembly called on Thames Water to set more ambitious leakage reduction targets and promote water efficiency, backed with novel tariff structures and smart metering across London.

It said the water company should work with mayor of London Sadiq Khan on campaigns to promote reductions in water consumption and expand smart metering to inform customers about usage.

It suggested that Thames and Ofwat consult on tariff options for the upcoming AMP8 from 2025 with options to link charging structure to water use, as well as social tariffs.

The National Infrastructure Commission recently identified surface water flooding as a significant but not-well understood threat to urban areas.

“The Mayor should significantly scale up funding and installation of sustainable drainage systems (SuDS) and scale up the resources available for local boroughs and other landowners to increase their own SuDS installation,” the paper states.

To address runoff from roads, the paper recommended doubling the target in the Mayor of London Transport Strategy to 100,000 square meters a year of roads to drain into SuDS; secondly that Transport for London should double its SuDS installation target to 10,000 square meters per year.

Thames Water called out the need for a major increase in SuDS across the city to avoid surface water flooding risks. The water company suggested 7,000 hectares of SuDS was required to aid natural drainage and reduce impacts on sewer networks at times of heavy rainfall.

The report recommends that the Department for environment (Defra) establishes a need-based fund for London boroughs to access simple and long-term funding for SUDS, and for it to also “significantly increase funding available for SuDS installation”.

To ensure the sewer networks have the capacity to deal with intense rainfall, the report said Thames should “accelerate investment in its wider sewer infrastructure” in parts of the capital not covered by the Thames Tideway tunnel.

The paper was written following investigations by the Committee into the impacts of climate change, flood risk, sewage pollution, the potential to reduce emissions and how to safeguard future water resources in London.

It said stakeholders, including citizens, have a role to play in ensuring plentiful supplies of water are available now and for future generations and acknowledged the three-pronged approach of cutting leakage, managing demand and adding novel resources, as outlined in Thames’ water resource management plan.