UCL installs biodiverse rain planters for nature-based climate adaptation

A collaboration between The Bartlett School of Architecture, Sustainable UCL and UCL Estates has led to the installation of two rain planters on campus to pilot a new prevention method for flooding.

Following the success of Medawar Gardens, a student-led initiative to plant a scented, relaxing wellbeing garden on campus, Blanche Cameron who leads the Greening Cities module at the Bartlett School of Architecture, and Hannah Biggs, Wild Bloomsbury lead from Sustainable UCL, had the idea to capture rainwater from the roof of the nearby quiet contemplation room to water the Medawar Gardens’ plants.  

As well as a rainwater collection tank, the idea was developed to also install rain planters to demonstrate how nature-based solutions can help reduce flooding, energy demand and costs, as well as provide biodiverse habitats for nature. 

The rain planters were designed by Wendy Allen, an award-winning garden designer specialising in creative rain gardens and Sustainable Drainage Systems (SuDS), with input from John Little, a leading expert on biodiverse public realm landscapes and habitats, and Susanna Grant, expert on shade-loving plants.  

The principle of a rain planter is to slow and temporarily store rainwater before it enters our drains, preventing the likelihood of surface-level flooding. This is done by channelling water from a downpipe (a pipe which collects water from the roof or a building), into a planter before entering the drain. 

This project is part of UCL’s Living Laboratory programme, an initiative which enables students and staff to help solve UCL’s sustainability challenges through research and teaching.

UCL students Anya Blanchfield, Mihaela Suciu and Motong Yang from Blanche’s Greening Cities module and Aude Vuilliomenet, PhD candidate in urban green infrastructure at The Bartlett’s Centre for Advanced Spatial Analysis, joined Wendy Allen for her workshop on rain planters and the installation, enabling them to get hands-on learning about rain planters’ design and function.  

As the interpretation board on the planters explain, the two rain planters have a different order of substrate layers, to find out whether one performs better than the other. We welcome students and staff to head down to the rain planters to view them and find out more. 

The project also received vital help from UCL Facilities Management and maintenance teams, Andy Norton at Sodexo, Stan, Jamie and Dan at Tivoli, and the logistics team especially Ian Porter – thank you all! 

Benefits of rain planters 

• Helping to reduce flooding on campus: climate change is bringing more intense summer storms and rain events (as well as droughts), and the drainage system cannot cope with the amount of water falling so quickly.

• Intercepting rainwater for our nearby Medawar Garden: London is a water-stressed city and water is a scarce resource, with embodied CO2e. By attaching a rain water collection tank to the planter, we can capture water instead of sending it down the drain. 

• Reducing demands on resources: water, carbon, maintenance time and cost: We used shade-loving plants which can tolerate brief periods of both saturated soil (wet periods) and drought, meaning that once plants are established, maintenance time, costs, water and carbon are reduced. 

• Cooling our increasingly hot campus: Plants and soils/substrates cool the local microclimate through evapotranspiration (breathing out moisture) and can provide nice shady spots to escape the heat and connect with nature. 

• Increasing biodiversity: Using a mixture of native and non-native plants will give biodiverse habitats for bees, beetles and butterflies all year round. 

• Reducing sewage overflows: Most of the rain that falls onto an impermeable surface rushes down the nearest drain, collecting pollutants on the way. If rain falls quickly, it can create flash flooding, and overload our sewage system, causing raw sewage to overflow into our rivers. The Environment Agency and the 'State of Our Rivers Report' by the Rivers Trust reveals that just 14% of the UK's rivers are of good ecological standard and none are of good chemical standard. By taking water away from the drains we can prevent this? 

What are we researching? 

Each 600mm depth rain planter uses the same layers but in a different order, to allow students to consider what processes are occurring.  

Identical plants were used in both rain planters so that the different layer order in each planter is the only variable element. Each planter has a 40mm overflow and drains to a 40mm drilled waste pipe inside the base layer. 

Rain Planter 1 (RP1) – Inverted Rain Planer layers: (from top) 100mm void space; 50mm gravel mulch; 200mm Leca clay granules (10-20mm size); 50mm sharp sand; 200mm sandy loam blended topsoil Bourne Amenity TS6 

Rain Planter 2 (RP2) – Standard Rain Planter layers: (from top) 100mm void space; 50mm gravel mulch; 200mm sandy loam blended topsoil Bourne Amenity TS6; 50mm sharp sand; 200mm Leca clay granules (10-20mm size). 

Students will assess each rain planter in terms of: 

1. Do both rain planters prevent the first flush (5mm) of rainwater from reaching the drainage system? 

2. Is the maximum rain planter storage potential reached before overflow occurs? Compare this as plant roots establish over time. 

3. After establishing watering period, monitor the condition of plants. Are some better suited to the free draining later at the top of rain planter 1? Which prefer soil layer uppermost in rain planter 2? 

4. Discuss how soil horizons might affect infiltration in each rain planter. 

What did we plant? 

The following plants were chosen, due to their ability to survive in fluctuating soil moisture and to provide year-round interest to species, despite the small space.  

Ajuga reptans ‘Black Scallop’, Anemone x hybrida ‘Honorine Jobert’, Brunnera macrophylla ‘Jack Frost’, Carex oshimensis ‘Everest’, Geranium macrorrhizum ‘White Ness’, Luzula sylvatica 'Marginata', Polypodium vulgare, Polystichum setiferum, Sarcococca hookeriana var. digyna 'Purple Stem', Tiarella ‘Pink Skyrocket’, Saxifraga x urbium, Vinca difformis ‘Ruby Baker’. 

How can I learn about Green Infrastructure?

‘Cities are hot, dry, polluted, impermeable and lacking in nature,’ (Gary Grant). This makes them vulnerable to heatwaves, rainstorms and other climate impacts, as well as being unpleasant and unhealthy for people to live and work in. 

The Greening Cities module (BARC0172), led by lecturer Blanche Cameron at the Bartlett School of Architecture, explores how integrating biodiverse nature-based solutions into the urban fabric can help to cool buildings and neighbourhoods, reduce flooding, filter water pollution, reduce carbon emissions, reduce energy and costs, and improve people’s health and sense of wellbeing. 

Biodiverse green infrastructure includes interventions like Wendy Allen’s lovely rain planters, as well as green roofs, green walls, Stockholm tree pits, vegetated gravel turf, rain gardens and so on. 

Leading biodiverse green infrastructure practitioners contribute to the module, including Dusty Gedge, Gary Grant, John Little, Wendy Allen, Chris Bridgman and Peter Massini. 

The Greening Cities module is an elective on the Bartlett’s BSc Architectural & Interdisciplinary Studies, available also to students across UCL.