Abstract: Five sediment cores (<200 cm) and twenty-two sea-bottom surface sediment samples have been collected in Caofeidian coastal area of Bohai Bay during field work in 2008. Grain size and ²¹⁰Pb data as welll as underwater topographic section (carried out in 2006) have been used to analyze modern sedimentation of tidal inlet in Caofeidian coastal area of Bohai Bay. The results indicate that the sea bottom sediments are mainly composed of silty sand and their particle sizes are getting finer and finer from nearshore to offshore areas. The underwater topographic section has shown that the Laolonggou tidal channel was eroded by 213 cm from 1997 to 2006 on an average. On a decade scale, the Laolonggou channel is quite stable. According to ²¹⁰Pb data, the accumulation rates in the river mouth and shallow lagoon area are between ca.0.9 cm/a and ca.1.5 cm/a.
The results have shown the river mouth area has been greatly disturbed by human activities, such as digging and reclamation. This will positively increase the navigational channel silting and harbor silting. The water depth of Laolonggou tidal channel has been greatly attributed to the strong tidal currents, so in the harbor planning and navigational channel construction the tidal prism should be taken into account.