40 



less shore-parallel orientation pointing in the direction of the longshore 

 current. Transverse bars are oriented perpendicular to shore and are attached 

 at beach protuberances. 



Process-response mechanisms in the beach and nearshore environment have 

 been integrated into a number of distinct morphological states, ranging from 

 dissipative to reflective with several transitional morphodynamic regimes 

 (Wright et al. 1979; Short 1979; Wright and Short 1983). The system 

 interrelates waves, currents, morphology, sediment size and sorting, and sedi- 

 ment transport (Figure 15). Dissipative profiles are characterized by low 

 gradients and wide surf zones, multiple parallel bars, and suspended load 

 transport. Reflective systems have steep beach faces with surging breakers, 

 edge waves and widespread cusps, bed load transport, and an absence of 

 nearshore bars and rip currents. Intermediate regimes incorporate elements of 

 both domains, progressing through the transitional intermediate states from 

 longshore bar and trough to rhythmic bar and trough, to traverse bar and rip, 

 to ridge and runnel. 



On predominantly sandy coastlines, beaches and the nearshore region con- 

 tinually respond to ever-changing winds, waves, tides, and currents by 

 showing adjustments in profile and morphologic features according to beach 

 type and environmental conditions. The day-to-day changes can be notable. 

 On the beach and nearshore, when wave energy is low or moderate, there is 

 overall net onshore transport and constructional activity. 



As energy increases, long-period, steep-profile storm waves may produce 

 considerable erosion of the beach and nearshore envirormient. Longshore 

 bars, for example, can shift position quickly, moving offshore at rates of 30 m 

 daily. In response to less steep waves, bars move more slowly (Birkemeier 

 1985; 1987). Many types of morphologic changes respond to tidal cycles. 

 One example is the migration of erosion and accumulation zones on a diurnal 

 or semidiurnal basis with tidally driven water table changes (Duncan 1964). 



In addition to the day-to-day fluctuations in beach morphology, longer term 

 cyclic and unidirectional effects occur on sandy beaches. The principal cyclic 

 effects are usually related to seasonal variations in dynamic factors, which in 

 turn create distinct cyclic changes in beach morphology and sediment char- 

 acteristics. Thus, survey data should ideally cover different seasons in order 

 to indicate the range of values that may be encountered during a year. 



During periods or seasons when frequent or severe storms occur, (typically 

 winter), sand is eroded from the beach, causing the profile to become lower 

 and narrower. Offshore bars may develop or enlarge due to the addition of 

 material from the beach. With the return of fair weather conditions, the beach 

 tends to recover and all or a part of the material in offshore bars may return 

 to the beach. Occasionally, overtopping and overwashing occur on sandy 

 coastal barriers, when water and sediment may pass over the barrier crest and 

 settle on the landward side. Overwashing events are generally noncyclic, 

 preventing the beach from recovering to its initial condition. It is rare that 



Chapters Variable Coastal Features 



