Dry stone causeways
Practical Action
Reasons for design
It has already been
explained why the
causeway should be built
to a good width. This
makes it extremely
heavy, and resistant to
damage by floods. What
other factors are
involved?
The stepped design
Figure 7: Cross section of finished causeway
guides the water over the
causeway smoothly, instead of acting as a dam. On the downstream side, the water does not
fall straight down, but it flows gently, helping to prevent erosion.
Because the boulders are touching each other and locking together, the force of the water
cannot move individual stones. The causeway is locked together as one unit, weighing
perhaps 200 tonnes.
The action of the water is also reduced in other ways. A percentage will flow through the large
drain section, and more will trickle through the causeway itself. The drain also prevents
siltation. The causeway must be level because then the flow of water is spread evenly all the
way along it. If the causeway slopes one way or the other, the force of the floodwater will
concentrate at the lowest point and the possibility of damage will increase markedly.
It does not help to cement or concrete the boulders into place. It is expensive, and if the
causeway is damaged during severe flooding, then large slabs will be removed rather than one
or two boulders, and concreted stones cannot be re-used.
Although a great deal of labour is required, it is only for a short time, and then all the
advantages of a dry crossing for traffic can be enjoyed by everyone in the community. The
causeway is unlikely to be entirely maintenance free, and it is important that this is
understood. With particularly heavy flooding, some of the stones may be moved, although not
necessarily so. If this happens it is most important that the causeway is repaired the moment
the water recedes enough to permit working. There needs to be immediate action by the
community elders to organise the repairs, because there is a tendency for such matters to be
ignored. Repairs have to be done before further flooding, for the next time the damage could
be severe. Provided this precaution if followed, the causeway will give a great many years of
service, and will stand as a tribute to the organisation and efforts of the people who built it.
Richard Tufnell is the International Coordinator of the Dry Stone Walling Association of Great
Britain. He has written a number of booklets and produced training videos about stone
walling. All drawings in this article are by Bill Holmes.
Richard Tufnell Construction World-wide
100 Mill Street, Ottery St Mary
Devon, EX11 1AF
United Kingdom
E-mail: drystoneuk@aol.com
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