MORPHODYNAMIC SYSTEM AND THE EVOLUTION OF LAOLONGGOU TIDAL INLET

Laolonggou is a typical tidal inlet as a part of the barrier-lagoon system of the north Bohai bay. The threshold of the inlet is 2.1 km wide and over 20m deep, and the maximum flood current or ebb current through the threshold may be over 1 m/s. A dendritic tidal drainage system is well developed on the flood delta with little sediment accumulation. According to the morphology of terminal shoal, the edge of the ebb tidal delta is located around -11 m of water depth. A main ebb tidal passage is developed on the east side of ebb tidal delta, in which ebb jet dominates. A swash platform with gentle slope is on the west side of the delta, on which the tidal dynamics is the weakest and the sediment the finest. On the shoal of terminal lobe and segmented sand bar, because of secondary sorting by breaking wave, silty sand and sand with shelly fraction deposited. The geomorphological evolution during 1945-2006 shows that both the tide and incident wave control the evolution of the morphological system of the Laolonggou tidal inlet. The main ebb passage swung westward due to the change of ebb jet under the influence of the movement of segmented sand bar and offshore barrier islands. The migration of the bar and islands was driven by the east and south incident wave. Most of sediment trapped at the tidal inlet is supplied by the longshore sand drift. Most of the sediment deposited on the ebb tidal delta, except part deposited on the intertidal flat around the Laolonggou lagoon.