in tidal surface. Along our southern Atlantic coast the present mean tide 
level is about 0.3 foot above the 1929 datum. Differences from 0.2 to 0.8 
foot occur at other locations, and the MIL at Astoria, Oregon, is 1.5 feet 
above the geodetic datum. The geodetic bench marks should never be used 
directly as a reference for mean sea level. The relation between geodetic 
and tidal bench marks must be determined locally for the current epoch. 
The contours on 1:24,000-scale maps are based on the 1929 geodetic datum, 
which has been denoted (until 1973) by the margin statement "datum is mean sea 
level.” To avoid possible confusion with local mean sea level, NOS (and USGS 
in turn) adopted the new datum name, "National Geodetic Vertical Datum of 1929." 
Even if a new vertical adjustment is performed, the compilation of new contours e 
may not be practical except during a complete revision of the map. While map 
contours can be used only as a guide in defining a coastal zone or coastal 
wetland, the value of using a specified contour line for reconnaissance or 
regulatory purposes should not be overlooked. Because of their defined 
accuracy on existing maps, contours offer a quick pragmatic solution until 
other measurements can be obtained. 
INTERPRETING THE COASTAL WETLANDS 
There have been a number of studies that have attempted to relate mean 
high water lines to vegetative boundaries. The change between high vigor 
spartina slterniflora which results from a daily flooding by saline water 
and a lower vigor form that is only flooded occasionally has appeared to 
indicate a "biological mean high water line." A similar effect has been 
noted between red and black mangrove. This close relationship is probably 
correct in many areas, but it is deficient in two operational criteria. 
First, establishing cadastral boundaries by engineering tidal surveys is 
an accepted legal procedure, and a biological survey may be supportive but 
not sufficient evidence in court. Second, the wetlands as defined by the e 
growth of several species of vegetation often extend above the mean high 
water line. The regulation of wetlands is an exercise in the government's 
authority to zone land and control use regardless of ownership. Therefore 
the time, expense, and difficult ground surveying that may be required to 
relate a vegetation boundary to & tidal datum appear unwarranted. If the 
purpose of the mapping is to delineate the wetlands for regulatory action, 
then vegetative boundaries are appropriate. A cadastral survey requires a 
tidal datum. 
Although several general regulatory acts have been proposed at the 
Federal level, and the U.S. Army Corps of Engineers grants permits for 
dredge and fill operations, primary control of coastal wetlands rests with 
the States. The Coastal Zone Management Act of 1972, Public Law 92-585, 
provides Federal grants to coastal States (including those bordering the 
Great Lakes) for planning, mapping, and managing the coastal zone. À 
uniform definition of the shoreward limits of the coastal zone or the 
coastal wetlands is not part of this law. The zone may extend inland 
only to the extent necessary to control the shoreland uses that have a 
direct and significent effect on coastal waters. For administrative pur- e 
poses a town or county boundary or a road may be the most effective inland 
limit of the coastal zone. It is strongly implied that the States should