FIGURE 3-8 



CONCEPTUAL MODEL OF A HIGH-SCENARIO SEA LEVEL RISE IN THE GREAT 



BAY BOULEVARD MARSH (Tidal Range = 3.18 ft) 



Transition 

 2075 

 Highland <1% 



2075 

 <1% 



High Marsh 



2075 



<1% 



2 



g 



< 

 S 



a 

 > 



a 



z 



Water 



20 7 5 2075 (+ 4.5 ft.) 



_.?!* 2075 (+ 3.3 ft.) 



2075 (+ 1.8 ft.) 

 2075 (+ 0.7 ft.) 



Highland 

 1980 

 2% 



'/////// £&&* 



imenialio.i Smm/yr '// 

 - C I ( 



1980 +1.8 



1980 + 0.7 



Transition 

 - 1980 

 1% 



High Marsh 

 1980 



25% 



_V 2075 MSL 



T High Scenario 



1980 MSL 



'Axis on left shows NGVD elevation; spot elevations are relative to 1980 or 2075 mean sea level. 



suggesting that shore-protection measures would be considered in both study areas to protect 

 existing developed land at marginal elevations above the marsh transition zone. The critical 

 highland elevations in Charleston are between 2.0 m and 3.0 m (6.5 ft and 10 ft), compared to 

 between 1.5 and 2.6 m (5.0 ft and 8.5 ft) in New Jersey. This difference, of course, is attributable 

 to the lower tidal range in New Jersey. 



Normalized Elevations 



The absolute modal elevation for each species is site-specific for the two marsh areas near 

 Tuckerton. Presuming that the zonation is controlled primarily by tidal inundation, it is possible 

 to normalize the data for variable tidal ranges based on frequency curves for each water level. 

 Figure 3-9 contains a tide probability curve for Atlantic City, New Jersey, near the study area, 

 based on detailed statistics of Atlantic Coast water levels given in Ebersole (1982). The left axis 

 gives the absolute elevation with respect to local MSL, and the right axis has normalized the data 

 as a function of the tidal range. Note that MHW and MLW, the average high and low water levels, 

 respectively, plot at ±0.50 ft on the right-hand axis. This curve has been transformed in Figure 

 3-10 into a cumulative probability curve which is a measure of the relative duration of flooding at 

 various tide levels. 



The data are also normalized for the two specific tidal range areas in the New Jersey study 

 area. Superimposed on the curves are the normalized modal elevations for key wetland species. 

 The relative position of each species is the same, but note the displacement of the entire suite to 

 higher levels in the 2.0-ft (61-cm) tidal range marsh. Tall S. altemiflora occurs at predicted MHW 

 in the Great Bay Boulevard marsh (elevation /tidal range = 0.50), but at a much higher relative 

 elevation in the Tuckerton fringing marsh (elevation /tidal range - 1.20 ft [36.6 cm])— a 

 difference of 0.7 ft (21 cm). Similarly, short S. altemiflora is displaced by an elevation /tidal range 

 ratio of approximately 0.7. 



If marsh vegetation depends primarily on duration of inundation, one or both sets of these 

 data would be immediately suspect. Therefore, we reviewed the data to determine possible 

 sources of error. First, we compared the results with a similar curve for Charleston (Kana, Baca, 

 and Williams, 1986, Figure 2-7B). The Charleston results are in good agreement with the Great 

 Bay Boulevard marsh (96.9 cm [3.18 ft] tidal range) area. Tall 5. altemiflora in New Jersey and 

 low marsh S. altemiflora in Charleston both plotted at MHW. The cumulative duration of 

 inundation (probability percentage) in both areas is 10-14 percent. This is very close, given the 

 limit of accuracy in the surveys. 



79 



