What is the common law doctrine of accretion?

It may be helpful at this point to reiterate the common law doctrine of accretion. The description of the doctrine is easily made but difficult to apply. In Clarke v. Canada (Attorney General), 1929 CanLII 38 (SCC), [1930] S.C.R. 137, Lamont J. defined the doctrine as follows, at 144: The term “accretion” denotes the increase which land bordering on a river or on the sea undergoes through the silting up of soil, sand or other substance, or the permanent retiral of the waters. This increase must be formed by a process so slow and gradual as to be, in a practical sense, imperceptible, by which is meant that the addition cannot be observed in its actual progress from moment to moment or from hour to hour, although, after a certain period, it can be observed that there has been a fresh addition to the shore line. The increase must also result from the action of the water in the ordinary course of the operations of nature and not from some unusual or unnatural action by which a considerable quantity of soil is suddenly swept from the land of one man and deposited on, or annexed to, the land of another.