FIGURE 26.-NOS index map of tidal bench marks for the State of Maine. Indexes are available for other coastal States.

2/18/76

SOUTH CAROLINA

U.S. DEPARTMENT OF COMMERCE

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL OCEAN SURVEY

The difference between the National Geodetic Vertical Datum (NGVD) 1929 (formerly Sea Level Datum 1929) and the mean low water (MLW) for each location where the tidal bench marks and the geodetic bench marks of the National Geodetic Network have been connected by differential levels is given below.

Bench mark elevations above the National Geodetic Vertical Datum (1929) may be obtained by applying the tabular difference to the published elevations above mean low water, subtracting the difference when positive and adding the difference when negative.

9

39A

40

42

Georgetown, Sampit River Entrance..

Fort Johnson, South Channel, Charleston Harbor.
Charleston (Custonhouse Wharf), Cooper River Entrance..
Cainhoy, Wando River....

1.03

2.22

2.65**

2.81

53

Virginia-Carolina Chemical Company Wharf, Ashley River.

2.45

90

Marine Training Station, Parris Island, Beaufort River.

3.51

BENCH MARK 1 (U.S.E.) is a chiseled cross in the top and near north end of bottom step of east entrance of customhouse at intersection of Market and Conrad Streets. Elevation: 11.95 feet above Charleston low-water datum.

BENCH MARK 5 = 9 (U.S.G.S.) (1918) is a standard disk, stamped "9.311 1918," set in top and near north end of bottom step at east entrance of customhouse. It is 1/2 foot south of Bench Mark 1 (U.S.E.). Elevation: 11.97 feet above Charleston low-water datum.

BENCH MARK 7 (1921) is a standard disk, stamped "7 1921 ELEV. 13.612 FT," set in top of east end of ledge of second basement window west of southeast corner of east wing of customhouse, and about 5 feet above ground. Elevation: 16.28 feet above Charleston low-water datum.

Elevations of other tide planes referred to *Charleston low-water datum are based on 19 years of records, 1941-1959 and are as follows:

*CHARLESTON LOW-WATER DATUM. This datum has been in use by the National Ocean Survey since 1905. It was officially adopted by the Corps of Engineers, U.S. Army and the U.S. Coast and Geodetic Survey in May 1929, and is defined as being 11.95 feet below Bench Mark 1 (U.S.E.) at the Customhouse Wharf at Charleston.

FIGURE 28.-Charleston, S.C., tidal bench mark descriptions. Descriptions are available for NOS tide gages shown on State indexes (app. fig. 26).

HEIGHTS ARE RECKONED FROM THE DATUM OF SOUNDINGS ON CHARTS OF THE LOCALITY WHICH IS MEAN LOW WATER.

FIGURE 29.-Charleston, S.C., times and heights of high and low waters. This table is taken from

the Tide Tables published annually by NOS.

FIGURE 30.-James Island, S.C., 1:250,000-scale geodetic control diagram. These NOS/NGS diagrams are drawn on USGS base maps. They show horizontal control lines and monuments established by NGS and USGS. This general area is also shown in appendix figures 17, 18, 19, 21, and 34.