| Popis: |
Sequential bar development involving, in order, multiple bars, ridge and runnels, transverse/ oblique bars, and meandering or crescentic shore-attached or detached bars of both outer and nested inner systems were delineated at HaHoterim beach, northern Israel. The concomitant wave data, including wave directions, energy spectrum, significant wave height, and length of the calm period showed strong correlation with the bar stages. There is a notable lack of correlation between bar stages and incident wave periods, which were quite variable, even on a daily basis. Two bar developmental sequences were delineated: one shore-normal and the other initially oblique but gradually rotating to shore-normal in the mature stage. Threshold conditions for the initial stage development of shore-normal crescentic systems were defined as H1/3 < 1.0 m, peak spectral density of < 1 m2/Hz, and swell directions within ± 7° from the normal. The outer crescentic systems formed within 1 to 2 weeks. The nested inner crescentic bar system formed under different wave conditions. Development of inner micro-cresentic bars required 3 to 7 weeks of calm waves (H1/3 < 0.3 m), except for a short initiating pulse of wave energy from waves of about i m in height. The double crescentic pattern indicates the optimal evolutiona y stage of crescentic systems. The residence time of bar types was determined by the frequency of crossing of these threshold conditions. The outer bars and the mega-rip channels composed the most stable inshore elements. Out-of-phase relationships between inner and outer bar systems resulted from the lag in response of the outer bars behind changes in wave direction. Among the inner crescentic bars and shore rhythms, phase-correlation was the was the rule. Regional aerial photography and wave data indicate that the bar/wave relationships at HaHoterim axe representative of the eastern flank of the Nile, including most of the Israeli coast. Although the bar types described from other coasts are similar to those mapped at HaHoterim and the threshold wave conditions for initiation of bar stage development appear to be similar, the frequency of occurrence of specific bar types appears to be different at HaHoterim. |
