Engineers divide the submerged beach profile into two discrete zones.
The nearshore zone is sedimentologically active in this model, while the offshore zone is inactive with regard to beach dynamics. The hypothetical point dividing the two zones, usually at about 15 feet of depth, is called the depth of closure point. In the model, sand deeper than this point is unable to move any closer to shore. Likewise, sand that is shallower, within the closure zone, is unable to move offshore beyond closure depth. It is at the core of modern engineering practice and, consequently, regulatory policy.