MONITORING GEOMORPHIC CHANGES OF TIDAL FLAT AND TIDAL CREEKS SYSTEM IN RESPONSE TO RECLAMATION IN THE YANGTZE ESTUARY

摘要

Quasi real-time simulations were made to determine flow and sediment transports in Texel inlet (with a focus on the ebb-tidal delta). Validation of the model results with observations showed that the model is able to simulate the dominant features in the flow and transport patterns even in the complexity of the ebb-tidal delta domain. Analysis of the model data provides valuable information on governing flow and sediment transport patterns in the instrumented and the un-instrumented areas, and allows for identification of the dominant processes by systematically checking mechanisms. Both observational data and model results show that the present morphological developments on the ebb-tidal delta are dictated by sediment redistribution on the ebb-delta, and sediment exchange between ebb-delta and basin; sediment is eroded from the ebb-delta (including adjacent shorelines) and deposited in the basin. Sediment import into the basin (mainly due to tides and setup) is estimated to range between 5 to 6 Mm~3/year. Three basic requirements are identified to explain the sediment influx: (1) Sediment demand; Reanalysis of the basin volume changes shows that the western Wadden Sea still needs sediment to compensate for the effects of Closure of the Zuiderzee and relative sea-level rise. (2) Sediment availability; Noorderhaaks can be considered as an abundant source of sediment originating from the pre-closure situation conveniently located in front of the inlet, feeding the main inlet circulation with sediments. (3) Sediment transport capacity; Sediment transport capacity is present in the form of the large tidal prisms and associated tidal currents in the inlet gorge and proximal part of the ebb delta channels (main inlet circulation). The presence of the supra-tidal Noorderhaaks and Helderse Zeewering, and segregation in ebb- and flood velocities dominated zones form a crucial role in the flood-dominant transport capacity of the main inlet circulation.