Fisher, J. J., and Simpson, E. J. 1979. "Washover and Tidal Sedimentation 

 Rates as Environmental Factors in Development of a Transgressive Barrier 

 Shoreline," in Leatherman, S. P., ed., Barrier Islands: From the Gulf of St. 

 Lawrence to the Gulf of Mexico, Academic Press, New York, N.Y. , pp 127-148. 



Washover fans and tidal deltas are significant reservoirs of sediment in 

 barrier island systems. These backbarrier and lagoonal deposits also 

 represent important sediment sinks in the overall littoral sediment budget of 

 a shoreline. Along the 40-km-long Rhode Island south shore barrier beaches, 

 extensive washover fans, resulting from hurricanes, and several inlet 

 deposits are prevalent. A long-term quantitative analysis of the subtidal 

 and supratidal sedimentation of these units from 1939-1975 was conducted 

 using photogrammetric techniques. Backbarrier sedimentation features were 

 first identified in the field to develop "ground-truth" keys to identify the 

 features on the aerial photography. Sediment units were measured on each set 

 of aerial photographs by point-counting of grids. These photographic 

 measurements were scaled by using ground survey data. 



During the 36-year study period, the total areal sedimentation change of 

 the supratidal washover deposits was +522,790 m 2 . The subtidal washover 

 deposits amounted to +267,950 m 2 , for a total washover sedimentation 

 accumulation of 790,740 m . For the same time period, the total area change 

 of supratidal flood tidal deltas at the inlets was +188,240 m 2 , while that of 

 the subtidal tidal deposits was +862,320 m 2 for a total tidal delta 

 deposition of +1,050,560 m 2 . This analysis indicates that during this 

 36-year period, tidal delta sedimentation is 1-1/3 times more effective than 

 washover in the landward transportation, deposition, and storage of sediment. 



This barrier coast, in addition to transgressing, is eroding at the rate 

 of 0.7 m/yr. An inverse relationship exists between overwash occurrence and 

 barrier island width, which can be further related to beach erosion. 

 Measured beach erosion over the 36-year period is directly related to the 

 rate of overwash occurrences at different points along the coast. (Authors) 



Fisher, J. S. 1980. "Field and Laboratory Study of Storm Swash and Overwash 

 Dynamics," Final Report, US Army Research Office, Arlington, Va . 



Field studies at Assateague Island quantified the flux and frequency of 

 overwash. Repeated surveys at several washovers revealed that storm- 

 generated overwash transports sand landward up to 100 m past the beach crest 

 for storms characterized by 1-year return periods. Poststorm winds transport 

 this material seaward, past the frontal duneline. Thus, overwash of this 

 magnitude does not supply permanent sediment to the island interior or bay. 

 Very large storms could transport sediment to the bay, but this is the 

 exception at the study site. Laboratory and field studies show that back- 

 shore structures, e.g., dunes or seawalls, enhance the backwash, and thus 

 beach erosion. In the case of dunes, however, the dune erosion feeds the 

 storm beach and thus offsets the erosion potential. A separate laboratory 

 study demonstrated that heavy mineral washover laminations can be related to 

 the depth and velocity of individual overwash surges. 

 (Author) 



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