17,000 to 25,000 cu yds/year toward the south, indicating a net northerly 

 drift rate of from 18,000 to 30,000 cu yds/year. Other Maine beaches exhibit 

 long-term growth to the south, however, and the data from Wells should only be 

 considered as an indication of possible drift rates. 



Tides influence the vertical range over which waves act on a sand beach, hence 

 the thickness of beach deposit. Within the characterization area, mean tide 

 ranges vary from 9.0 feet (2.7 m) at Portland to 18.2 feet (5.5 m) at Eastport 

 (U.S. Department of Commerce, Yearly ) . 



Winds play a major role in moving sand on the back beach and dune areas. 

 Depending upon a number of factors (grain size, sorting, plant cover), winds 

 begin to transport dry sand at velocities of about 11 mph (18 km/hour) 

 (Bagnold 1954). The greatest amount of sand moved by wind occurs on 

 desiccated portions of the beach and vegetated dunes. 



Sand is transported by wind from the top of the beach berm to the foredune and 

 accumulates as a wedge against the foredune scarp (Timson and Kale 1977). 

 Continual movement and accumulation occurs during the sutraner and fall months, 

 increasing the width of the foredune and, in some areas, the height. Most of 

 this accujnulation occurs under the influence of southerly winds. 



Timson ( unpublished ) has found that some landward transport of sand occurs 

 during the northeast or east northeast winds onto and beyond the foredune. 

 Sand transport behind the foredune is relatively minor where dune vegetation 

 occurs; but devegetated areas are heavily affected by northwest winds. 

 Deflation of bare areas by northwest winds creates parabolic dunes, which 

 enlarge and migrate seaward towards the foredune ridge. Continued growth of 

 the parabolic dune and transport of sand may force the dune to breach in the 

 foredune ridge, through which storm waves may overwash and intrude into the 

 dune field. 



Sand beaches have only a very limited primary production. Due to the fine 

 grain size on sand beaches and wave action that continually moves the 

 sediments, macroalgal vegetation does not develop. A discussion of the unique 

 plant communities associated with sand beaches and dunes is found at the end 

 of this chapter. Depending upon the degree of exposure of the beach microalgal 

 colonization of pebbles and interstitial spaces below the surface may be a 

 source of organic matter production. Other heterotrophic microorganisms 

 (bacteria and fungi) coexist and provide a sink for organic matter produced by 

 photosynthesis . 



Low organic carbon and total nitrogen concentrations are reported by Croker 

 and coworkers (1975) on western Maine and New Hampshire beaches. These 

 authors also found unsystematic (i.e., without a pattern) seasonal differences 

 in the mean concentrations of these elements. The high values of the 

 carbon/nitrogen ratios indicate a large percentage of plant material, in the 

 form of shredded and detached macrophytic algae and smaller algae, is attached 

 to sand grains (Croker et al. 1975). This work suggests that imported 

 material and diatoms are the sources of energy (i.e., food) for the 

 invertebrate faunas of sand beaches. 



4-87 



10-80 



