Mother Nature will occasionally use water to effect changes in the location of land bordering on water courses. The term which applies to the gradual increase or acquisition of land by the imperceptible action of natural forces washing up sand, soil, or silt from the water course is "accretion". A gradual eroding or washing away is referred to as "reliction". Any increase of soil or sand to land adjacent or contiguous to a water course formed by Accretion becomes the possession of the riparian or littoral owner. Likewise, any erosion or reliction due to the gradual actions of nature become lands lost by the riparian or littoral owner.

By contrast, the sudden and perceptible change formed by nature is referred to avulsion. Examples of this are frequented on New England by winter storms. The violence of a storm may suddenly change the flow or construction of a water course or the lands abutting thereon. Unlike with accretion, land so divided by avulsion remains the property of the original owner as if the water course had not been moved.

Accretion and avulsion are principals of common law which go far back into English legal heritage. Since these situations are rarely encountered, when they do arise, the local office should be consulted. Factors which will be considered in determining the underwriting will be: what caused the change in the water course; how much land has been added, removed, or changed; who are the abutters; and, what is the size and nature of the water course involved (i.e. navigable or unnavigable stream, ocean, pond, or lake). Based upon the answers to these questions, the local office will make an underwriting decision as to what land should be included in the description of the insured parcel and whether any specific exceptions need to be added to the policy.