213 



20% inorganic ash. If Delaware marshes could retain 60% of their total 

 production, they could be maintained in the face of sea level rises as 

 great as 0.7 cm/yr . 



Table A. 2. Required Sedimentation (g/m'^/yr) by Marsh Grass Alone 

 To Maintain Surface for Various Sea Level Rises 



You might also want to add, either to Sect. 10 or to Sect. 11, as 

 appropriate: 



Often, protected estuarine shorelines consist of marsh without barrier 

 beaches. These marshy shorelines frequently exhibit high rates of erosion. 

 We often assume, as the shoreline retreats under the influence of rising 

 sea level, that new marsh is created at the landward edge of the 

 transgressing surface. Phillips (1986) has studied the relation between 

 erosion rate, marsh surface accretion, and the slope of the surface being 

 transgressed. He has found that the determination of whether the marsh 

 area will be maintained depends critically on the slope of the surface 

 being transgressed (Fig. 1 in Phillips, 1986). Clearly, the upland slope 

 must be very low (0.2°) and the rate of marsh retreat must be small 

 (0.3 m/yr) to maintain marsh areas, because accretion rates seldom exceed 

 10 mm/yr (Table 10.1) . 



