In only two days a small group of adult learners were to design and build a raingarden. A further intention was to inspire and empower the participants to build their own or help others build them. Situated in a small "pop-up" park in the centre of Stroud, it was also an opportunity to demonstrate to the community how they can help reduce flooding and improve water quality by building simple raingardens.
Before the first training day we dug trial holes to determine the nature of the ground build-up and carried out infiltration tests.
Infiltration was good but the trial hole found compacted hardcore containing asbestos. For this reason we advised that the course should build a fully raised raingarden over the existing ground.
On the first day, we introduced the learners to the concepts and principles of raingarden design, including calculating volumes and sizes, and took them to our St Peter's School raingardens to see different planting themes.
The learners then produced a design for the new raingarden which was to include a concave angle along one side to allow people to sit on the edge and be sociable.
Before the day of the build we sourced redundant hardwood pallets, a soil/sand mix and wildflower turf and designed the structure of the raised garden to utilise the hardwood slats from the pallets.
On the day of the build we worked closely with the adult learners and Stroud Valleys Project staff and volunteers to build the raingarden with much of the day spent preparing the pallet wood and building the raised walls.
At around 4 o'clock in the afternoon, the soil was prepared and the wildflower turf rolled out to give an instant vegetated meadow appearance at the end of an exhausting but thoroughly enjoyable day.
We had built a raingarden in just one day!
Rain is diverted from a rainwater pipe into the raingarden which is sized to accommodate the 1 in 2 year return period rain event at a water depth of 150mm.
The shallow raingarden basin is covered with meadow turf over 150-200mm depth sandy loam topsoil incorporating 50mm coarse compost to create a free-draining growing medium. Had the existing ground been more favourable or had we been planting more ornamental garden plants we would have created a more generous soil depth of up to 450mm.
The recycled pallet walls to the raingarden are lined with a butyl pond liner whilst the base is free to drain into the existing ground. The benefits of a raised raingarden are less digging, less material to dispose of and the greater ease of carrying overflows back to the sewer at the surface. The overflow pipe in this case discharges over a small retaining wall to be collected by the existing channel drain.
