The John Lewis Rain Garden
The John Lewis rain garden is Central London’s first street-side rain garden. It is located on Victoria Street, at the head offices of the John Lewis Group, just around the corner from Victoria Station. The site is immediately outside the main entrance to the building, on the street and pavement, and adjacent to the portico that provides a dry drop-off point for visitors. Previously the site was completely paved and cobbled, apart from two poorly shaped trees. Indeed, the whole immediate and adjacent area is devoid of trees and green space. This lack of green, combined with the flood-prone nature of Victoria, made the John Lewis site the prime choice for the creation of a new rain garden. The rain garden has been funded by the Victoria Business Improvement District (Victoria BID) as part of their Green Infrastructure Audit process, whereby suitable sites for retro-fitting green features that promote biodiversity, flood prevention, and human enjoyment are identified and supported.
The John Lewis rain garden is a prime example of turning ‘Grey to Green’ and of retrofitting Green Infrastructure. But it also contains several examples of a climate-change adapted landscape: the rain garden itself; a storm water planter; and minimal irrigation urban planters. A landscape adapted for both extreme rainfall events, and for droughts and lack of water.
Design: Nigel Dunnett & The Landscape Agency. Construction: Landform UK. Completion: Spring 2015
All images © Nigel Dunnett & The Landscape Agency
John Lewis Rain Garden
The site previously was totally paved, apart from two small spaces for trees, and contributed to the problems in the area of excessive rainwater runoff.
How the rain garden works
An analysis of rainfall runoff patterns and main directions of flow is essential for rain garden design. The John Lewis rain garden will capture rainwater runoff from the adjacent road and pavement, as well as absorbing rain that fall directly on it. But the rain garden also collects rainwater that runs from the roof of the portico, by disconnecting the down pipe and feeding the rainwater runoff into the garden instead.
The objective is to absorb and hold back that rainwater runoff. Rain gardens can be effective in both reducing the total amount of runoff that enters the drains, and that in a storm can contribute to overloading of that drainage system. But they also reduce the amount of surface water runoff (and the speed at which it collects) that can cause surface flash flooding after heavy rainfall.
They function through the combined effects of soil and vegetation replicating the sort of processes that would happen to rainfall in a natural landscape, as opposed to what happens with the predominantly ‘sealed’ and hard surfaces of the urban environment. As well as the rain garden itself, the scheme includes a ‘storm water planter’ that first captures the rainwater from the roof, and climate-change adapted planting around the building that replaces former irrigation-dependent planters.
If, in the highly unlikely event, that the rain garden fills completely with water, any excess can overspill into the existing street drain.
Planting the Rain Garden
The rain garden includes two new trees. These are Italian Alders, Alnus cordata. It was important to choose a very resilient tree, tolerant of exposed urban conditions, and Italian Alders are tough trees. In addition they have fantastic displays of catkins in the spring, hold onto their leaves until late in the year, and being an alder, they are very tolerant of the alternating wet and dry conditions within a rain garden.
The main area of the rain garden is planted with a naturalistic mix of grasses and perennials to deliver a low-maintenance, beautiful and long-season visual effect. Promoting biodiversity is a key objective, and there is a wealth of flowering plants to support pollinating insects in this predominantly ‘grey’ part of the city. The rain garden is sited in a typical ‘urban canyon’ on the street: windy and exposed. The chosen plants need to be hardy in these conditions. Although the plants will need to cope with periodic wet conditions, in a street-side location in Central London, there are also likely to be prolonged dry, and potentially very hot conditions. It is important to emphasise therefore that in such conditions, a rain garden is not a ‘wetland’. The chosen species are therefore tolerant of a wide range of environmental conditions. Some native UK species are used, but so also are a wide range of plants from elsewhere.
It was extremely important to the building users that the rain garden presents a clean, neat and tidy image that looks effective throughout the year, as befits the head offices of a major company. Therefore, there is a solid and regular structure of evergreen hedges (Sarcococca, which is highly scented when flowering in the winter and early spring) within the garden to provide a sense of order and formality amongst the naturalistic planting. And the plantings are established within a silver-grey granite gravel mulch that matches the colour of the building. The mulch creates a clean and neat surface that will look effective in the winter, although the intention is that during the growing season, the vegetation will cover the mulch completely. But the mulch also acts as a weed control, and creates a stable surface should the rain garden fill with water.
Below: the layout of the garden, with dividing hedges amongst the perennials Below: early concept visualisation for the rain garden
Constructing and Planting the John Lewis Rain Garden
Construction and planting was undertaken in early spring 2015. The existing trees were removed and the existing hard surfaces removed. The site was excavated carefully by hand (because of the complexity of buried services), and the site backfilled with a free draining artificial substrate or growing medium. A layer of more organic rich planting medium was placed above this. Plants were set into a granite stone gravel mulch.
The Storm Water Planter
The storm water planter captures rainwater runoff that flows directly off the roof of the portico. Previously, the runoff flowed to a down pipe that ran through one of the supporting columns of the portico, and then emptied directly into the conventional drainage system. The new scheme disconnects that down pipe from the drainage system, and diverts the flow instead, through a new spout, into the raised planter. The water can infiltrate down through the planter, and any excess can flow out through outlets in the base into the rain garden. However, should the planter completely fill with water in an exceptionally severe downpour, then there are overspill spouts that enable any excess to empty directly into the rain garden.
The storm water planter is therefore the first step in the rainwater management process in this scheme. Combined with the rain garden itself, it starts to form a ‘rainwater chain’ of features, that between them can account for most of the rainfall entering the system. The initial concept for the scheme also included a green roof for the portico, which would have been the starting point for that storm water chain. However, subsequent structural analysis proved the portico to be unsuitable for supporting a green roof.
Climate-change Adapted Planters
The planters around the main entrance area to the John Lewis Head Office on Victoria Street were previously planted with a low diversity of evergreen shrubs which were dependent on regular irrigation for their survival. The new scheme replaces these with a more diverse mix of perennials and grasses, with some evergreen smaller shrubs, that will provide for year-round interest, and which, crucially, will require far less support, maintenance and irrigation than the previous scheme, while delivering greater visual interest, seasonal change, scent, and flowers for pollinators.
The images below show the previous condition, and the newly established diverse, low-irrigation planters