’Sky Garden’ wetlands which can help stop flooding
Now here’s a question for you! Is it possible to make habitat for bees and dragonflies on rooftops whilst
helping to stop flooding at the same time? Surprisingly the answer is yes, and apparently it’s not difficult
to do. Recently, the Victoria and Albert Museum created London’s first wetland green roof as part of a
rooftop ‘wilderness’ project. Installed during a heatwave in July, the rooftop wetland has already been a
hit with the museums honey bees, and has seen dragonflies and damselflies regularly stopping to visit.
This tiny green roof takes up a very small area,
but every inch of it provides multiple benefits,
both to flood management and to wildlife. In its
own small way, this rooftop is helping to
reduce flooding by ‘taking out’ and using
rainwater run off which would otherwise flow
off the roof, contributing to urban surface
water floods. At the same time it creates
valuable wetland, shingle and meadow habitat
for a whole range of wildlife species including
birds, insects, dragonflies and bees. Just imagine
how much flood run off we could remove if
every rooftop in Sussex had a rooftop wetland?
As the native wildflower plants take root, and the miniature pond develops, spring will herald a small
oasis of wildlife in the heart of the Royal Borough of Chelsea and Kensington.
To make this sky high mini nature reserve, the Green Roof Consultancy (GRC) helped enhance the
innate characteristics of the roof by using a 150mm deep central gully which usually drains rainwater. A
small ‘dam’ either end of this gully allowed a 150mm narrow pond to be created in between the roofs,
whilst still allowing the roof to drain. Moisture protection layers help capillary action, spreading water
across the rest of the roof, helping to keep meadow vegetation alive.
Either side of the mini wetland, two steep pitched roofs dispense their rain water onto the Sky garden.
To dissipate the force of this water and to provide an interface between the green roof and the edge of
the building a narrow shingle run was installed. There are plans to feed the wetland roof with water
discharged from nearby air conditioning units, which will be of particular importance during heat waves
and droughts when there would otherwise be no water to feed the pond and the
plants.
So, storing rainwater, creating nature and reusing water are all part of the ongoing story of London’s
first wetland roof. The GRC is looking forward to telling the Sky garden story as it unfolds, and we hope
that sometime soon we will be able to tell you about the first Sky garden nature reserve in Sussex too.
Image by Dusty Gedge, Green Roof Consultancy