Setbacks. All buildings and structures, except those needed for a water-dependent use, shall be set back from the mean high-tide line a minimum of 35 feet where there is a seawall, or 80 feet where there is no seawall, in order to create a continuous waterfront yard area around David's Island, unless a greater setback is needed to provide the previously mentioned horizontal hedge of vegetation and tree canopy. Structures permitted within a waterfront yard area shall be durable, nonobtrusive, harmonious, and unified in terms of color and materials, including exterior lighting, walkways, fences, benches, signs, piers, and docks.