(a) No person shall construct or erect any structure or construct, erect, conduct, or engage in any shoreline engineering activity or engage in any land alteration which alters the natural topography or vegetation of any area within the jurisdiction of this part, except in accordance with the terms and conditions of a permit therefor issued in accordance with this part. A permit may authorize the construction or maintenance of the project proposed in an application. After construction of a project pursuant to a permit, the project may be maintained without a permit so long as it does not further alter the natural topography or vegetation of the site or increase the size or scope of the project.

(b) No permit shall be required for a structure, shoreline engineering activity, or land alteration which exists as of July 1, 1979, provided that a permit must be obtained for any modification which will have a greater adverse effect on the sand-sharing system or for any addition to or extension of such shoreline engineering activity, structure, or land alteration; provided, further, that, if any structure, shoreline engineering activity, or land alteration is more than 80 percent destroyed by wind, water, or erosion as determined by an appraisal of the fair market value by a real estate appraiser certified pursuant to Chapter 39A of Title 43, a permit is required for reconstruction.