VII. BEACH PROFILE CLASSIFICATION AND CHARACTERISTICS 



Based on the original classification of beach profiles by Hayes and 

 Boothroyd (1969), and detailed observations of beach morphology between 

 June and August 19 71 and during January and February 1972, a modified 

 scheme is proposed for the classification of beach profiles. 



1. Early Preweld or Poststorm Profile (duration dependent upon severity 

 of storm). . 



A flat, concave, upward beach profile with heavy mineral concentra- 

 tion (garnet, hornblende, and magnetite) near the distal end of the storm 

 swash is commonly at the base of the dune scarp. The grain size is uni- 

 formly medium sand (Hayes and Boothroyd, 1969). Small ridges (amplitude 

 <20 centimeters) appear in 1 day to 1 week after the storm passes and 

 move quickly across the low tide terrace. A beach step is rarely pre- 

 sent. The gradient of the high tide beach face varies between 4° and 6° 

 (Fig. 68). 



2. Late Preweld Accretional Profile (up to 6 weeks after storm) . 



Late preweld beach profiles characteristically have small neap berms 

 with beach cusps. A wide low tide terrace is present where ridge and 

 runnel systems migrate (Fig. 69). The sand is generally uniformly fine 

 on the low tide terrace (1.5 to 1.9 phi), with a coarse zone (often bi- 

 modal, -0.4 to +0.8 phi) at the beach step. Mean grain-size measurements 

 for the high tide beach face vary between 0.5 and 1.0 phi, with a zone of 

 coarser sediment at the berm crest and finer sediment on the neap berm 

 (1.1 to 1.6 phi). Coarse eolian ripples formed by strong offshore winds 

 may exist on the berm and the beach face. Zones of coarse sediment may 

 also occur in other areas of higher swash energy such as at the base of 

 cusp bays. Large runoff channels between the ridge and runnel systems 

 are also prevalent. As the landward-migrating ridges weld onto the back- 

 shore and form wide berms, the early postweld stage is reached. 



3. Early Postweld (2 to 5 days to several weeks after welding) . 



After the large berm has formed by ridge migration and welding of the 

 ridges to the backshore, there is a period during which the active high 

 tide beach face is landward of the berm (Fig. 70). Small ridges may still 

 migrate across the berm surface and weld onto the backshore. The gradient 

 during the early postweld period is steeper on the high tide beach face 

 than on the seaward side of the berm ridge. 



4. Late Postweld . 



Late postweld takes place after the active high tide beach face is 

 no longer landward of the berm, but exists on a former ridge beach face. 

 High tide swash does not overtop the berm crest during late maturity 

 (Fig. 71). 



84 



