We are currently in the middle of two adjacent contracts constructing quays on the edge of the Fal estuary in Cornwall. When we first quoted and tried to gather as much information about quay construction as possible it was difficult to discover much at all. The BS information is based largely on more modern standard construction and concentrates predominantly on the waterproofing qualities of the materials. Using drystone negates much of this and yet has been largely superceeded nowadays despite being very well suited to both marine and riparian constructions.
Using large stones >25kg, (it is necessary that every single stone is of sufficient weight), each stone is selected for an even weight along its length which is placed to allow a narrow face. The stones need to be placed vertically as much as possible, (an uneven pattern can also work), this is due to horizontal stones effectively being able to float on a strong current. The back fill is loose and with an amount of gaps the water can simply flow in and out of the whole base of structure.
Estuarine locations are by far the easiest locations in which to construct on the foreshore. The full force of the sea is usually tempered and flooding is not constricted and as such not fast flowing. Despite this it is essential to ensure the face is able to withstand very strong forces indeed. However the back of the wall face is under a much greater pressure - on high tides, particularly spring tides, the whole of quay becomes waterlogged and the pressure downwards and onto the rear of the facing stone is immense as the tide falls.
The work is incredibly labour intensive, although the localities make up for the hard work. The photos are of the first quay in construction, 46 metres long, which is in an AONB and surrounded by National Trust land; as such the design has to be traditional and the final finish needs to look in tune with the much older quays in the vicinty. A random pattern to the face allows for this easily.BEFORE:
The total cost for the above job came in below £5000.00, and as such it would be impossible to build a timber or concrete construction for the same price. Dry stone is becoming increasingly more fashionable as the prices for the stone become increasingly more competitive against prefabricated products. The sustainability factor cannot be beaten either, the stone for the above came from less than 20 miles away and all other materials were recycled.What is very amusing is to see the different species which utilise the quays in comparison to the dry stone walls.Crabs vs Toads. The final touch is a specialist seed mix for estuarine riparian and coastal headland, with strong rapid establishing grass seeds it is a mix that hardly suits any other type of lawn but will assist greatly in erosion preventative vegetative measures and remediation, (EPV) thus ensuring the longevity of the structure.
Dry Stone walls in Cornwallwww.paysagedurable.com