Sediment Dynamic Processes And Evolution Of Small Tidal Inlet Systems

Tidal inlets are a common feature along littoral drift shores all over the world. Located in the eastern Shandong Peninsula. China, Yuehu is a small tidal inlet system with great values in terms of fish culture, tourism, environment and scientific research. Generally, the environment in the Yuehu area was stable before the 1 970s, but some inappropriate development activities (e.g. the artificial closure of the entrance in 1979, and reclamation of a large part of the intertidal land of 0.59 km2 within the tidal basin since 1986) have resulted in high deposition rate, degeneration of water quality and deterioration of the lagoon ecosystem. This indicates that this coastal embayment is fragile and sensitive to external forcing; the environment and ecosystem damage caused by human activities is difficult to recover naturally. Several aspects of the Yuehu Inlet system are of scientific research significance. First, as a typical tidal inlet system with special hydrodynamics characteristics, this system is an excellent case for sediment dynamics study. Moreover, the latest 20 years saw fast and disastrous environmental changes happening in Yuehu. Such changes deserve extensive research focusing on the interaction between human activities and physical environment evolution. Two phases of hydrodynamic observation and sediment sampling were undertaken in winter 1998 (from November 12 to December 11) and summer 1999 (from August 12 to September 9), respectively. During each period of fieldwork, tidal water levels of 29 days were recorded at the lagoon center using an Aanderaa Water-Level Recorder (Model 7 for winter and 8 for summer). Spring and neap tidal cycle measurements of the current velocity, tidal water level and suspended sediment concentrations were carried out within the entrance to the tidal basin. Further, 130 surficial sediment samples and 9 short cores were collected. During the sampling, the position was fixed using a (Magellan 2000XL) portable GPS. In the laboratory, grain size analysis was undertaken for the sediment samples using a CILAS 940L laser grain size analyzer and sieves, and grain size trends overthe lagoon were computed using the Gao-Collins model (Gao and Collins, 1991). Four short cores were selected for analysis of depoaition rate ( 0Pb method) and one for organic carbon content (using a Perkin-Elmer 240C Elemental Analyzer). Water level records were processed with TIRA (a program for harmonic analysis), and tidal currents within the inlet entrance were calculated on the basis of the law of conservation of mass and a method proposed by Gao and Collins (1994). Furthermore, bedload and suspended sediment transport rates at the inlet mouth were calculated. Historical data from scientific journals, maps and aerophotos were also collated in order to understand the evolution of the Yuehu Inlet. Yuehu has a small lagoon of 4.94 km2 in area and an average water depth of 1.0 m. The lagoon was separated from the open sea by a send spit. An entrance channel of 132 m (measured at MSL) in width connects the lagoon with the open sea. Five small rivers discharge seasonally into the lagoon; the catcbment basin, 15.2 km2 in area. is characterized by low hills. Longshore drift along the beach on the open sea side is relatively weak. The lagoon is generally dominated by fine-grained material, and mud and sandy mud account for about 40% of the lagoon area. The central part of the tidal basin is covered with muddy se...