Where a landowner is in possession of land shown at HM Land Registry as abutting a non-tidal river, the question may arise as to what happens if the course of the river changes so that the boundaries on the ground no longer reflect what is recorded at the Land Registry (or indeed on the plans to the original Conveyance or Transfer by which the land was acquired).
The answer will, in the first instance, depend on how the movement of the river occurred.
If the change in the course of the river is caused by a sudden, one-off event, such as a large flood or storm resulting in a permanent alteration to the river’s route, the doctrine of avulsion will apply. This doctrine provides that the boundaries remain as recorded at the Land Registry, in spite of the fact that the river is now in a different place. Whilst some landowners will not be affected by this if their boundary still abuts the river after the change has taken place, others will find themselves left with no river boundary and will consequently lose their presumed ownership of half the soil of the river-bed (under what is known as the ‘medium filum’ rule) and the benefit of the fishing rights associated with this.
If, however, as is perhaps more common, the change to the course of the river has taken place steadily over a period of time, and has been ‘gradual and imperceptible’, the doctrine of accretion and diluvion will apply. This doctrine, described by Lord Wilberforce in Southern Centre of Theosophy Inc v State of South Australia  AC 706, 716, provides that where a river boundary moves gradually, the boundary of a landowner’s title will be deemed to move with the river, meaning that the extent of the landowner’s title may increase or decrease, but the river will always define the boundary. The landowner will also always be deemed under the medium filum rule to own half the soil of the river-bed and will be free to exercise the fishing rights attaching to that portion of the river (unless they have previously been severed) or to sell or lease these to a third party.
A further question arises where the position on the ground after a change in the course of the river does not match the presumption. What happens, for example, where one landowner has owned the land to the east of the river and a neighbouring landowner has owned the land to the west. The river has moved, increasing the extent of land to the east of the river. Under the doctrine of accretion and diluvion, this additional land is deemed to belong to the eastern landowner. In practice, however, the western landowner has occupied this additional land, with no objection from the eastern landowner.
In these circumstances, the eastern and western landowners would be well advised to record the fact that the presumption of accretion and diluvion does not apply and that the land is in fact deemed to comprise part of the western landowner’s title. This can be recorded by way of an agreement, registered on both their titles at the Land Registry. Without any such agreement, issues may arise when one of the landowners comes to sell or if the land changes hands for any other reason. Whilst a potential buyer may be prepared to take a view on the basis of the circumstances on the ground, the legal presumption would be that the land comprises part of the eastern landowner’s title, and with no evidence of agreement to the contrary, it would be more difficult to establish that the presumption does
not apply were someone to try and argue the point.
The agreed ownership of the fishing rights should also be recorded – again, the presumption would be that the owner of the river-bank owns the soil to the middle of the river-bed, but if the fishing rights were previously severed by the eastern landowner for the benefit of a third party, the western landowner should agree that his ownership of the additional land will be subject to these rights and he should acknowledge that he is not free to exercise them himself or to sell or lease them to a third party.
As in all cases, wherever there is scope for uncertainty or dispute, agreement is always best and landowners should take all necessary steps to ensure the position on the ground is correctly registered at the Land Registry.