Observation of hydrographic and sedimentary processes over an intertidal flat based on ADP-XR and OBS-3A Taking Hongdao Island intertidal flat in the north of Jiaozhou Bay as an example

Turbidity,horizontal and vertical current speeds,echointensity,water depth,salinity and temperature were observed using OBS-3A and ADP-XR during a spring-neap period,on 17~24 August 2004.Meanwhile,suspended and bed sediments were sampled for grain size analysis.On the basis of calibration of turbidity with in situ sediment samples and regression between the turbidity and the echointensity,the turbidity and the echointensity were converted to a suspended sediment concentration (SSC).The SSC is found to be generally low.For most of the tidal duration,the near bottom(30 cm abovebed)SSC is less than 30 m g/dm³.Because mud grains are abundant in the bed sediments,the low SSC is mainly at tributed to low water energy especially weak currents.The near bottom current speed is generally less than 15 cm/s due to the narrow ness of the intertidal zone(500 m in width).However,the high SSC ranging f rom 100 mg/dm³ to greater than 1 000 mg/dm³ occurs during the shallow and short stages mainly due to the action of waves.As a result,the time series of near-bottom SSC is "U"-shaped during each tidal cycle.The vertical stratification of SSC tends to occurduring deep stages and calm weathers.The SSC does not show spring-neap cyclicity,which is at tributed to the int erference of waves.It is concluded that resuspension/settling over the study intertidal flat is governed by waves.