of marsh accretion will depend on proximity to tidal channels (sediment sources) and density of 

 plants (baffling effect and detritus), we believe these published rates are reasonably representative 

 for the case study area. Thus, for purposes of modeling, we assumed a sedimentation rate of 

 5 mm (.2 in) per year. Obviously, the actual rate will vary across any wetland transect, so this 

 assumed value represents an average. Lacking sufficient quantitative data and considering the 

 broad application of our model, we found it was more feasible to apply a constant rate for the 

 entire study area, even though this assumption may overestimate the rate of vertical accretion in 

 the irregularly flooded transition zone between low marsh and terrestrial highland. 



Elevation Zones. Transformation of wetland environments under various sea level rise and 

 sedimentation scenarios also required assumptions regarding existing elevation zonations. The 

 field transects provided criteria for delineating the upper and lower limits of several subenviron- 

 ments that could be considered as discrete zones for area estimation. 



We assumed the cutoff elevation for highland around Tuckerton is 1.5 m (5.0 ft) NGVD, 

 based on results of the transects and observations in the field. In general, this area is free of 

 yearly flooding and tends to mark the transition from salt-tolerant species to terrestrial 

 vegetation. Although terrestrial vegetation occurs at lower elevations that are impounded 

 between dikes or ridges, this situation is less relevant for sea level rise modeling. The zone of 

 concern is the area bordering tidal waterways where slopes are assumed to rise continuously 

 without intermediate depressions (see composite transects in Figures 3-3 and 34). 



The transition zone is defined as a salt-tolerant area between predominant, high-marsh 

 species and terrestrial vegetation. This area is above the limit of fortnightly (spring) tides, but is 

 generally subject to tidal and storm flooding several times each year. The indicator species for 

 this zone were found to be Panicum spp. and Phragmites communis in the low-tidal-range 

 Tuckerton marsh and 5. patens and Iva frutescens in the Great Bay Boulevard marsh. 



High marsh is defined for the study areas by variable elevation ranges of 70 to 120 cm 

 (2.3-3.8 ft) for the Great Bay Boulevard marsh and 76 to 101 cm (2.5-3.3 ft) for the Tuckerton 

 marsh, based on the transects. Dominant specie^ include short S. altemiflora at 93.0 cm 

 (3.05 ft), Limonium carolinianum at 92 cm (3.0 ft), &id Salicomia spp. at 89.9 cm (2.95 ft) for 

 the Great Bay Boulevard marsh and S. patens at 107 cm (3.5 ft) and short S. altemiflora at 99.1 

 cm (3.25 ft) for the Tuckerton marsh. 



Low marsh ranges from +31 to + 76 cm (1.0 to 2.5 ft) based on results of the transects, with 

 a narrower range of elevations (37 to 70 cm [1.2-2.3 ft]) in the higher tidal-range Great Bay 

 Boulevard marsh. The principal indicator species, tall S. altemiflora, occurred at 48.5 and 

 73.2 cm (1.59 and 2.40 ft), respectively, in the Great Bay Boulevard and Tuckerton marshes. 

 Sheltered tidal flats actually occur between mean low water and mean high water but were found 

 to be more common in the elevation range of zero to 31 or 37 cm (1.0 or 1.2 ft). 



Results for Central New Jersey 



From these scenarios and the sedimentation rate of 5mm (.2 in) per year, we computed the 

 net substrate elevation change for the year 2075, as shown in Table 3-3. Note in Table 3-3 that 

 the combined sea level rise scenarios and sedimentation rate yield a positive change in substrate 

 elevation for the baseline and a negative change for the low and high scenarios. The results of 

 the scenario models for the New Jersey study area are given in Tables 34 and 3-5. Table 34 

 divides the number of acres in the study area and the percent of the area they cover according to 

 principal zones. It shows existing coverage (1980) and the predicted coverage for the baseline, 

 low, and high scenarios for the year 2075. Table 3-5 lists the net change in acres for each 

 scenario compared with the coverage in 1980. The baseline 2075 results are a projection of 

 recent historical trends in sea level rise. 



74 



