An Investigation on Different Theories of Longshore Sediment Transport (1997 - 2000)

The Longshore Sediment Transport Rate (L.ST.R) is usually an important factor to determine amount of erosion or accretion along a coast. Many scientists have tricd to find empirical methods for estimating L.S.T.R during the past decades. These methods have been calibrated and could be applied under limited conditions. The aim of this dissertation is to investigate the accuracy and validity of empirical methods for estimating L.S.T.R in the south coast of Caspian Sea. For this purpose, a filed measurement was conducted to measure L.S.T.R using sediment traps in Babolsar coast, North of Iran) during 15 days. The measured data were compared with those predicted by given empirical formulae. This measurement was done with 16 sediment traps in low-wave energy condition. In addition. another measurementwas carried out in order to calculate the irnpoundmenr sediment behind existing breakwater, which was deposited resulting from wave action and the beach. The latter measurement was done in order to estimate annual L.S.T.R. Data on beach profiles, wave height, and sediment properties were taken together with the transport rate. In both measurements, results were compared with six known empirical formulae. During first field measurement, the sea state was a low-wave energy condition with wave heights. less than 0.6 111. Results for this condition show that transport rates measured by sediment traps were considerably lower than rates predicted by empirical formulae. It was shown the predicted L.S.T.R. by Kamphuis (! 99]) form ula, which includes the effects of wave period. beach slope and sediment grain size. were about 5 times lower than the one predicted by C.E.R.C formula and closer to the measured values. In the second measurement. the results show that C.E.R.C formula with coefficient of 0.77 (recommended by shore protection manual 1984) was noticeably closer, to the . measured value. Also, Kamphuis (1991), Kraus (1982), Van der Meer (1990) formulae under estimate L.S.T.R. in comparison with measured data. Thus, these formulae could not be suitable for estimation of annual L.S.T.R. in 13abolsar coast. In addition to above, results of present work indicate that the linear correlation between wave energy flux factor and the total rate of longshore sediment transport contained the commonly used c.E.R.e predictive formula is supported. However. a lower value of the empirical coefficient. 0.057 instead of the 0.77. recommended by the Shore Protection Manual. was dctcnuiucd for the trap. data, which collected in a low-wave energy sea state.