Aug 172013

James Taylor, Surrey County Council Senior Countryside Management Officer, has provided an update to this article, and some additional information, for which thanks.

Mytchett Lake worksThe embankment to the lake at Mytchett retains the Basingstoke Canal as well as acting as a dam for the lake. Even though the lake itself belongs to the MOD, the Canal and embankment is owned by Surrey County Council, and so SCC have the
responsibility for its maintenance. Since the lake is subject to the provisions of the Reservoirs Act 1975, it is regularly inspected by an independent Inspecting Engineer, and the Environment Agency require the owners to act upon the recommendations arising from these inspections.

The last principal inspection in 2009 required that the stability of the embankment be improved to meet modern standards by December 2014, and its effective height be increased to minimise the possibility of overtopping in extreme weather conditions. The stability of the bank is being adversely affected by water penetration from the Canal (evident from water collecting at the bottom of the slope), so one of the key recommendations is to reduce this flow. The work has to be completed with the Canal and lake “in water”, so a scheme of works have been devised by Surrey County Council’s engineers to stabilise the dam with 6.5 – 8.5m long steel sheet piles driven hydraulically by a 32 ton state-of-the-art rig mounted on a floating platform (see above).

The Basingstoke Canal is one of the highest corporate risks that the Surrey and Hampshire Counties have to manage, and their primary concern is that a breach does not take place. If the Canal were to break its banks, then a flood situation could quickly ensue and the effects upon the surrounding conurbations could be disastrous. Hence the importance of completing the works at Mytchett Lake.

Mytchett Lake Reptile trapIn response to an earlier reservoir inspection, several trees were cut down along the embankment about 3 years ago, as it was believed these could have a destabilising effect. More recently, an ecological and reptile survey of the embankment slope and foot was carried out – as a consequence, a reptile enclosure (left)  was installed around the slope and the flat area at the bottom to keep protected species away from the works. And, in the middle of August, the reinforcement work, being undertaken by contractor Dyer and Butler, started in earnest. The Secretary of the Society, Gareth Jones, lives close to the embankment and can attest that piling is going on, since his house is getting a jolly good rattling….

Mychett Lake Diagram

The diagram above shows the planned reinforcement works, which will include the following:

  • Sheet piling extending below the “toe” of the embankment will be installed along its length of around 130m, to prevent water penetrating the bank
  • The towpath will be raised by around 0.5m, and will be surfaced with limestone chips in a tar surface, to prevent water penetration.
  • A 1m concrete wall will be built along the back edge of the towpath, rising around 0.5m above it, as an additional overtopping protection. This wall will be hidden from view by being concealed under soil at the rear, and the front will be faced with timber

A towpath closure and diversion for around 8 weeks (ie to around mid October) will be necessary while these works are going on. Boaters please be aware: The navigation will remain open, but there will be temporary restrictions, as follows:

  • Boats navigating the Canal must sound their horn at the entry of the work zone (Mytchett Lake Road to Mytchett Lake Rail bridges) and proceed at tick-over only, being prepared to stop – there is no mooing or stopping within the work-zone and the towpath is of course closed.
  • During operating hours (Monday to Saturday 08.00-18.00) all unpowered craft must stop at the entry to the work-zone and seek authority from the foreman to proceed.

When the work is completed, rubbing strip and bollards will be installed, and so the embankment will provide new temporary moorings for visiting boats, within a short walk of the Canal Centre, pubs and local shop.