Calculation and Analysis of Momentum Coefficients in the Changjiang River Estuary

Based on the field data of velocity profile observed at 23 measuring sites distributed over the Changjiang River Estuary in March and September, 1996, the momentum coefficients are calculated and their temporal and spatial distribution characteristics are obtained through statistical analysis. For different typical time interval and different places in the Changjiang River Estuary, the results of linear regression show that the momentum coefficients are larger for flood flow than for ebb flow, and for flood season than for dry season, that they increase from spring tide, mean tide to neap tide on temporal distribution, and that they increase from the outside the mouth to inside the mouth for the North Branch, and increase at first and then decrease from outside the mouth to inside the mouth for the South Branch together with the North Passage and the South Passage, the maximum value appearing near the mouth where fresh water meets salt water on spatial distribution. Through analysis, the feature of frictional resistance in the motion of tide is better understood, and an easy approach is provideed for choosing the Manning coefficient for numerical simulation of plane 2-D tidal flow.