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Cob Malltraeth.

Cob Malltraeth.

The two Ariel photographs taken by Hamish Fenton on the 12th June 2012 are an excellent illustration of the project undertaken between 1788 and 1812. The reclamation of about 4200 acres of land known as Malltraeth Marsh or Cors Ddyga was first proposed in 1754. The proposal was that an embankment be built accross the estuary at Malltraeth, and the meandering river Cefni be straightened and canalised for the six mile tidal section between Malltraeth and the outskirts of the town of Llangefni.


The works were authorised by Parliament in 1788 and work on the scheme started immediately. Hundreds of men and some women were employed in the building of the main sea defence embankment across the estuary, the Cob, and the banks to contain and canalise the river, using earth, sand, turf and timber. A severe storm on the night of the 17th October 1789 damaged the sea defence bank and the works were suspended due to financial difficulties. Further legislation passed in April 1790 authorised the appointment of Commissioners with powers to raise monies to complete the works.

Another storm in February 1796 caused a large breach in the Cob. Some landowners hadn't paid the Commissioners for three years and the project was again in financial difficulties and the works were abandoned.

The breach was left open until a third Act of Parliament was passed in 1811. This Act gave the Commissioners greater powers to ensure that the landowners paid their contributions and their arrears. The famous engineers Thomas Telford and John Rennie were commissioned to report on the works and how to improve them. Based on their recommendations and designs, work began immediately using some 300 to 500 men to repair the storm damage using timber and stone. The hulk of a ship was sunk in the main breach and covered to effect a full repair. Work on the sea embankment [the Cob] was completed in 1812 and the embankment has not been breached since.

Telford Tidal doors on the Malltraeth Drain with the sill visible.

A key feature of the whole project were the Telford designed "Tidal Doors" which were located in sluice chambers built at the mouth of the two Cefni side drains, the Malltraeth drain on the north side and the Menai drain to the south. No land drainage enters the river Cefni shortly after it passes through the town of Llangefni, but drains into the two channels that run alongside the embankments of the canalised main river. When the tide is out water drains freely into the estuary, but as the tide raises twice daily the design of these doors results in them closing automatically as the weight of water on the seaward side increases, sealing the two side drains preventing the entry of the tidal waters and retaining the land drainage on the other side. The tide is able to rise freely within the embankments of the main river as far as the outskirts of Llangefni. As soon as the tide falls the weight of water behind the doors causes them to open, thus allowing the free drainage of the land. This ingenious "door design" has resulted in approximately 4200 acres of land to be reclaimed from the sea.

Completion of the works enabled Telford to construct the A5 turnpike road to Holyhead, completed in 1826 and the development of the various coal workings on the marsh. The bridge built at Malltraeth circa 1812 allowed for the construction of the road to Newborough, the estuary having been previously crossed using fords at low water, the two main ones being Rhyd Maen Du at Malltraeth and Rhyd Aber Hocwn at the bottom of the lane from the village of Hermon. The Chester and Holyhead railway was built over the reclaimed land with the river and its side drains crossed by the 19 arch stone viaducts opened in 1848.

Work underway to replace the doors in the north oulet of the Menai drain by William Hughes & Sons - 2010
The frame to support the new doors under construction.

The sluice chambers at the mouth of the land drains have all been modified over the years, with the exception of the northern outlet of the Menai drain which is virtually as built in 1812. The last set of tidal doors on this outlet which were to the original design and specification of 1812, though not the original set was removed in 2010. Their replacements which were constructed at Amlwch by Gareth Gadsby Joinery are exact copies, but using EKKI, an African hardwood  timber and stainless steel fixings, rather than the Green Heart timber used previously and wrought iron and mild steel fittings. The installation works were carried out by William Hughes and Sons of Bodffordd on behalf of the Environment Agency. The doors removed in 2010 were donated to the local regeneration group, Malltraeth Ymlaen by the Environment Agency.

New doors in situ with canopy visible - 2010
New Ekki timber doors - 2010.


Malltraeth Ymlaen formulated a project to mount these historic objects on the Cob at Malltraeth. An application for funding under the "Adfywio Pentrefol" scheme, administered by Menter Mon as part of the Rural Development Plan, Axis 3, and Business Plan 2 was submitted in October 2011. The application was approved on the 28th March 2012 and a grant award in the sum of £19153-18 was offered and accepted. Planning permission for the scheme was sought with the assistance and support of the Bodorgan Community Council. Work on the project commenced on the 14th June 2012 and was completed on the 16th August 2012 despite the atrocious weather experienced during this time.

Work starts 14th June 2012.
Main cross beam in position.

Stone work in progress.
Plinth for mounting three interpretation panels under construction.
Pathways laid and new bench seats.


The historical tidal doors can now be seen on the site together with three interpretation panels. One panel outlines the history of the building of the Cob, another shows photographs of what can be seen in the locality, the third panel which is the work of two local artists shows the Snowdonia peaks visible from the site with their name and height, and examples of the wildlife that can be seen in the immediate vicinity.

Interpretation Panels & Slate Plaque.
Completed works - August 2012.
Completion marked on the 20th October 2012.
(L-R) Jackie Lewis, Menter Mon;Bryn Jones-Chair,Menter Mon; Cllr Robert Ll Hughes;Elfyn Roberts,Menter Mon; David Jones,Chair, Malltraeth Ymlaen

Funding Acknowledged.

Malltraeth Ymlaen wish to place on record their thanks to the two local artists Christine Garwood and Philip Snow for their work which can be seen on one of the panels, and to Rachel Sayer for the design of another panel. We also thank Mrs Jackie Lewis, the Community Projects Manager at Menter Mon and her colleagues Community Development Officers Mr Elfyn Roberts and Mrs Rhian Jones for their support and assistance.The works on site were carried out by H R Hughes & Sons, Aberffraw, bench seats by Annog 'cyf' of Llangefni, the frames by Dave North of Valley Forge, the panels and artwork by Xpose Media Ltd of Mona, and slate plaques by R Hughes & Son, Llangefni; the stone is
from Aber Quarry at Moelfre - all local Anglesey companies.