Field tests of a sled system for beach profile measurement and of bed load sampler at T-shaped observation pier

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The in situ measurement of the bottom topography and the rate of sediment transport under storm wave conditions have been studied with T-shaped observation pier(TOP) at Ogata Wave Observatory, DPRI, Kyoto University. First of all, a bottom profiler equipped with a pressure sensor could be developed and secondly a bed load sampler was made on the basis of the ideas of local scour around the sampler and discharge of water from the opening. The principal conclusions are as follows:1. It is possible to get an accurate three dimensional bottom topotraphy with the profiler at TOP, even if under storm wave conditions.2. The beach processes around the pier is as same as those on the Ogata Coast. the dip and shoal are nearly stable year by year and this feature is well fixed under storm waves in winter. Moreover, the offshore sediment transport generated by the reflected waves due to concrete armor units lined up along the shoreline leads to loss of sediment in the shallow water area and increment of water depth. Especially, at the east end of the offshore wing of the pier, a strong undertow can be detected under swell wave conditions.3. The bed load sampler can trap the rate of sediment transport during a half wave period. The local scour around the lower hopper part of the sampler can fix it at the same position. The intake of sea water through the elbow pipe whose entrance is at the height of 50cm from the sea bottom can spread out during another half wave period.4. The data of bed load transport are fairly good agreement with the present formula of sediment transport by waves which is theoretically derived by the author.