15.20.350 Filling of Land Below Elevation 70, National Geodetic Vertical Datum (NGVD).
Where fill is to be placed on land below Elevation 70, NGVD, the following requirements, in addition to the other provisions of this chapter, shall be met:
A. Minimum Elevation. The minimum elevation after ultimate settlement shall be as follows:
1. 70 – Streets, lot pads, driveways, parking areas and other specified areas.
2. 80 – Finished floor of structures.
These minimum elevations apply to areas immediately adjacent to tidal influence which are unaffected by stormwater run-off. Where stormwater run-off, wind action and wave action are a factor, the above minimum elevations shall be increased and a reasonable freeboard provided.
B. Ultimate Settlement. Ultimate settlement means that settlement which is predicted to occur over a thirty-year period, commencing with the completion of all fill operations.
C. Normal Drainage. The street grades and storm drainage system shall be designed for the maximum design storm flowing against a one-hundred-year tide elevation of 63 NGVD. The system must be designed so that gravity drainage will be adequate after ultimate settlement has occurred.
1. Major waterways having a drainage area of four (4) square miles, or more, shall be designed for an average recurrence interval of one hundred (100) years.
2. All other waterways less than four (4) square miles shall be designed for an average recurrence interval of twenty-five (25) years.
D. Special Drainage. In those cases where the tributary drainage system entering the area to be filled cannot be made to comply with subsection (C) of this section, then one (1) of the following alternates shall be provided:
1. Within each such project a holding pond or interconnecting ponds shall be provided. The combined areas of such ponds shall be not less than one-twentieth of the total area drained, including any outside tributary area. The bottom elevation of the ponds shall be not higher than minus three (3) feet.
2. The culverts draining such holding ponds shall be at least twelve (12) inches in diameter, be equipped with tide gates at the discharge ends and shall have a minimum combined cross-sectional area in square feet equal to eight-one-hundredths times the total number of acres drained, including outside tributary area.
3. In lieu of the holding ponds, pumps may be provided to handle surface water runoff during the time the discharge end of drain lines is below water. The pumps shall meet the following requirements:
a. Capacity shall be adequate to handle maximum runoff for the fifty-year storm from area, including any tributary areas.
b. Discharge from pump shall be to a tidal channel and, if below water, shall be provided with necessary check valves.
c. Pumps shall operate automatically when the gravity drain lines stop functioning. (Ord. 696 § 1 (part), 1983; Ord. 288 § 6G, 1962)