De-culverting the stream in the Wood
The concrete pipes (culverts) which originally ran from the north west of the bandstand area to Pymmes Brook were continually blocked by debris. So in 2018 the London Wildlife Trust (LWT) proposed to create a surface stream with wetlands instead. They secured funding from the Greater London Authority and Environment Agency, and worked with Barnet Council on the project.
It was not intended to try to prevent Pymmes Brook from flooding its flood plain (see below). Water retained by flooding onto the grass plain helps to reduce the risk of the brook over-topping its banks further downstream where it would flood houses (for example in West Walk).
The original design was for the new stream to flow on the surface all the way into Pymmes Brook. But as LWT wrote in August 2018:
"Unfortunately, due to the limitations of the presence of a gas pipeline we have been restricted by where we can make interventions. The ability to carry out excavations/ground works near gas pipelines is severely limited, and any work within about 20m would require additional permissions, significantly driving up the costs, making the project undeliverable.
We have investigated the feasibility of utilising existing culverts along the brook (there are several disused ones along the river bank), and the only one that is workable and allows the stream to connect into the pymmes brook is using the current culvert/location of the ditch.
Therefore, we have worked up a design that utilises the existing culvert, whilst working within the confines of the topographical limitations to ensure the newly dug stream can function properly, and goes where we want it to."
Matthew Frith, Head of conservation at London Wildlife Trust gave a virtual talk to The London Natural History Society. You can see the section about Oak Hill Park on the Media page.
The Flood Plain
This map is from the Government's flood risk database at flood-map-for-planning.service.gov.uk
