The Thames Barrier closed four times in the 1980s, 35 times in the 1990s, and 50 times in the year 2014. Is this because of climate change and sea level rise? No. Is it because London’s rainfall has increased? No. Is it because too little has been done about sustainable urban drainage (SuDS)? Yes.

The area of impermeable surfacing in London keeps increasing, and the volume of surface water discharge increases with it. Half the Barrier closures are now at low tide – to keep the water out of London so that the tideway can be used as a stormwater detention facility. This is required because impermeable surfacing and new drains are accelerating surface water runoff throughout the Thames catchement. The worsening of London’s flood problem is caused by bad planning and bad design, mostly by architects and engineers on development projects.

So what can be done? In a lecture to the London Parks and Gardens Association on 21 June 2017, I made the following suggestions:

Better flood management facilities in parks

Parks should have many more rain gardens, storm detention areas and storm infiltration areas installed as income-generating facilities. Spending flood defence money in this way is much better than spending it on madcap projects like the Thames Tideway Tunnel. Even the chair of the panel that recommended the Tideway Tunnel now sees it as a waste of money. The best example of storm detention I know of in a public open space in London is Sutcliffe Park in Greenwich, designed by landscape architects working for the National Rivers Authority, which became the Environment Agency and implemented the project.

Green roofs

Cities with flood problems should adopt ambitious Green Roof Strategies. The US Environmental Protection Agency has found that green roofs can ‘remove 50% of annual rainfall runoff volume through retention and evapo-transpiration’ and that ‘rainfall not retained is detained, effectively increasing the time to peak, and slowing peak flows for a watershed’. Green roofs are a public good (as well as being private goods) and the creation of public goods is one of the distinguishing characteristics of the landscape profession.

Olympic Park flood detention

The Queen Elizabeth II Olympic Park could have a large flood detention facility, learning from the Grüner See (Green Lake) in Styria, Austria, which gets 10 metres deeper in spring. Such was the popularity of the lake, particularly with scuba divers, that all watersports are prohibited to prevent damage to the environment.

Better flood storage in the Thames Path

A landscape strategy to increase the flood storage capacity of the Thames Tideway should be developed and implemented. Sections of the Thames Path can be allowed to flood, as can public open spaces beside the river. Owners of riverside homes in high flood-risk areas should be encouraged to flood-proof their own houses and gardens, as the residents of Richmond and Strand on the Green already do. The advantages of this policy, compared with flood walls and berms, are that they do much less damage to the capacity of flood plains than bunds, and they do not have to be funded by taxing people who have not chosen to live in flood plains.

Landscape professionals should publicise the fact that while engineers want to get water off the land, we want to keep water on the land. We need to work closely with RTPI members on this. Planners have the power to persuade landowners and developers to create public goods. Engineers tend to be single-minded, and architects tend to work on projects that create private goods. Landscape professionals often have two clients: the landowner and the wider community.