The addition to land by the slow action of water.
Heavy rain, river or ocean action would have this effect by either washing up sand or soil or by a permanent retreat of the high water mark.
The sudden washing up of soil is often called avulsion although the latter term is but a variety of accretion, just as alluvion refers to the slow washing-up of soil or land.
In Clarke, Canada's Supreme Court wrote:
"(A)ccretion 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.
"The fact that the increase is brought about in whole or in part by the water, as the result of the employment of artificial means, does not prevent it from being a true accretion, provided the artificial means are employed lawfully and not with the intention of producing an accretion, for the doctrine of accretion applies to the result and not to the manner of its production."
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