STUDY ON THE BEHAVIORS OF COHESIVE SEDIMENT IN THE YANGTZE ESTUARY

Abstract

In order to study the deposition and erosion behaviors of the cohesive sediment in the navigation channel through the bar of the Yangtze Estuary, a series of experiments have been made with a standard settling tube and Ubbelodhe viscometer. The tests show that the flocculation and rheological behaviors of the cohesive sediment differ from the clay mineral contained in the fine sediments. Different clay mineral aggregates or floes have their apparent volume due to the thin layer of water surrounding the aggregates or water entrained in the floes. The Bingham relative viscosity and yield stress are obtained: nr = (l-KCv)"zo, ty =0. 13Kexp (7kcv). The suspended load transport rate and depositional behavior of the cohesive sediment have been studied with rotating annular channel. It is shown that there is a certain silt carrying capacity for a certain flow condition. The equilibrium silt concentration can be expressed; Coq=A(t b- T i) and the concentration-time relation is C=Coq+(C0 -CBq) exp (-a wt/2H). Using the above formulas and tidal velocity analysis the yearly average dredging amount in the the navigation channel can be calculated.