Boundaries can move for a number of reasons, some of which are as a result of the forces of nature rather than a naughty neighbour moving the fence whilst you are away on holiday. Flooding is one such example which is very much on the minds of many property owners across the country at the moment.
We all appreciate the fact that where land is ‘bounded’ by water, there are likely to be changes between the land and the water. Normally, we would expect these changes to be gradual and almost unnoticeable as the watercourse (and hence the boundary) changes with time. It’s generally accepted that a gently flowing river and the land either side can gain a bit or lose a bit as it meanders by.
The technical terms used are Accretion, which may be explained as a natural increase or advantage, as in accrue, and Diluvion, the advance of water, or erosion, as in dilution.
Flood waters will often rise from non-tidal rivers and streams. Where properties are separated by waters of this type, the presumption is that the boundary follows the centre line of the water so that each owner has half of the bed.
If the course gradually changes over a period of time, the position of the boundary will change accordingly. Where there is a sudden but permanent change in the course of the stream, whether or not it is due to natural causes, the boundary will remain along the centre line of the former bed. So when the flood waters have subsided, the boundary remains. The only time that this does not apply is when neighbours have reached an agreement over how natural changes operate and have registered that agreement, which is rare.
If you live on the coast then your boundary which adjoins the sea lies at the top of the foreshore, which is the land lying between the high and low water-marks. As with non-tidal rivers and streams, the boundary may move gradually as the line of the high water mark moves naturally over the years. However, when nature causes a sudden impact, the ownership of the area of land affected will not change.
So, once the flood waters have subsided or the sea waves have calmed a little, the boundary remains. For more details on this and boundaries in general, see our guidance on boundaries (Practice Guide 40 Supplement 3).