YARNER WOOD CULVERT

January – April 2018

BRIEF DESCRIPTION

Yarner Wood is an existing Dartmoor Nature Reserve and is a classified Area of Outstanding Natural Beauty (AONB).

The river during normal flows runs across the existing ground before entering a 375mm pipe that runs under the access road before spilling downstream. Under heavy flows, the river however flows up and over the access road and floods the gardens and land of the downstream properties.

The works required by Natural England were to install a meandering upstream channel with a culvert structure with wing walls and a large retaining headwall, with a downstream rip rap system of large boulders that would both store more water and convey the flow in a more consistent fashion.

SCOPE OF WORK

MDA firstly carried out environmental surveys on the area and set up the required protection zones. There was a 13T weight restriction in place that limited the plant and materials we could import or export. There was also only a single width access track into and out of Yarner Wood which serviced three businesses and two residential properties so everything had to be co-ordinated around this.

The first stage of the construction works was to install the overpumping. MDA deemed it a requirement to have 24/7 overpumping to dry out the existing ground and also to keep the working area dry. Once the two 8” high flow pumps were installed upstream and the 200m of pipework was placed outside of the working area, works could commence. We firstly removed the existing steel cattle grid and gate. Once this was removed, we could begin to excavate the embankment and remove the made ground that would not be suitable to backfill the new structure with.

Once excavated down to the foundation level, we needed to install the downstream works as access would be cut off by the main works. Once the downstream channel was constructed and the rip-rap and rock armour placed, we could construct the large reinforced concrete structure consisting of a rock armour bedding, toe beam and deep foundation slab with a 3.5m high upstand headwall.

With the main structure completed, the backfill needed to be completed to a certain level before access could be gained to the upstream channel. The upstream section of the works had to be completed on the way out of the works to ensure the plant could be removed without cutting off access to the rest of the works.

Upon completion of the structure and backfill, MDA constructed a new reinforced concrete road, incorporating the old cattle gate and fence. We then installed new fencing along the length of the road to complete the works.

The works were carried out to the usual MDA standard, without accident or incident, ahead of schedule. We encountered heavy flooding, snow and high winds but worked together to compete the works. Natural England were extremely please with the finished product and the local residents, businesses and walkers were equally impressed.

This was one of MDA’s most logistically challenging schemes but we enjoyed the overcoming the challenge.

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