Although the model is intended for regional forecasts it does not treat effects on subsurface 

 freshwater supplies or storm-surge effects. 



Application. The use of the model may be best understood through application to a 

 particular site. Because Tuckerton, New Jersey, was used as a case study (Kana et al. 1988 and 

 Chapter 3, this report), it is used as an example here. We simulated the change in square- 

 kilometer cells; three representative cells are emphasized in the following discussion. These are 

 shown in Figure 4-9. 



The open-ocean and inland tidal ranges of 3 feet and 2 feet were taken directly from the 

 map. The area was not designated as deltaic, although a small delta is adjacent to the area. 



Cell A contains part of a barrier island and adjacent bay and open ocean. Because the 

 barrier island is the dominant element, the cell is encoded as "beach," ignoring the fact that 

 water constitutes almost 40 percent of the area. (The portion of the barrier island immediately to 

 the north does not constitute the dominant element in either of two cells, so both cells are 

 encoded as water.) The average elevation of the island in cell A is estimated to be 1.0 m; with a 

 contour interval of 10 feet and only the dunes shown as exceeding 10 feet, the determination of 

 elevation is admittedly imprecise. Furthermore, the elevation of the dominant category is used, 

 rather than the average elevation for the cell; otherwise, a conflict might arise between the 

 category elevation and the cell elevation used in the simulation. 



Cell B is approximately 50 percent marsh and 50 percent developed lowland; it is 

 categorized as marsh. Inspection of the map indicates that this "worst case" occurrence of two 

 equally distributed categories is uncommon. More often cells are dominated by a single category. 

 Furthermore, over large areas, error compensation would be expected. Based on a linear inter- 

 polation, the average elevation is assumed to be 0.5 m. It is not possible to tell from the 

 topographic map whether cell B is salt marsh or fresh marsh, but, given the elevation and the 

 tidal range, we assume it would be salt marsh. Although the cell is developed, because it is salt 

 marsh the development is ignored in the simulation (the assumption being that developed marsh 

 is not valuable enough to be protected). 



Cell C is partly developed lowland, partly marsh, and partly undeveloped upland; it is 

 categorized as developed lowland. The elevation varies from near sea level to over 20 feet; it is 

 given as 1.0 m. 



We begin the simulation with the year 1975. The datum for mean sea level is 0.00 m. 

 Because the percentage of marsh is greater than 5 percent and less than 25 percent, we assumed 

 that accretion would be at 5 mm/yr; because the area is not deltaic, we assumed the sedimenta- 

 tion rate to be half that of marsh accretion (2.5 mm/yr). The rates were assumed to be half the 

 natural rates, due to engineering projects diverting sediment on rivers. It might have been 

 reasonable to change this default and double the rates. 



Based on an interpolation for the high scenario, the initial rate of sea level rise would be 5 

 mm/yr; therefore, by 1980, mean sea level is modeled as 0.03 m above the datum. This rise has 

 no effect on the distribution of cell categories in the Tuckerton area. In fact, not until 2030, 

 when sea level is close to 0.5 m above the 1975 datum, is a change observed (0.3 percent of the 

 upland, which was originally 4.0 m in elevation, is converted to lowland). Meanwhile, by 2000 the 

 rate of sea level rise has increased to 10.44 mm/yr; by 2025 it has increased to 15.72 mm/yr. 



In 2035, due to the position of the spring high water level, the fresh marshes are converted 

 to salt marshes, with mean sea level 0.55 m above the 1975 datum. In 2060, with mean sea level 

 at 1.02 m, several changes take place. Undeveloped upland loses 0.1 percent to undeveloped 

 lowland, and 7.3 percent of salt marsh and 0.1 percent of tidal flat are converted to sheltered 

 water. These cells, originally 0.5 m in elevation, are now inundated even at low tide. With 

 wetlands decreasing to below 5 percent of the map area, accretion of marsh drops to 2.0 mm/yr 

 and sedimentation drops to 1.0 mm/yr, mimicking sedimentation further upstream in estuaries 

 rather than along the coast. 



106 



