Experimental Study On The Effect Of Vertical Fluctuating Pressure On The Entrainment Of Fluid Mud

Fluid mud, in a broad sense, is a kind of suspended load whose median sediment size is smaller than 0.07 mm. It has high mobility and exists widespread in nature. It could appear in estuary, bay, inland waterway and lake, etc. Fluid mud could result in harbor, waterway and reservoir siltation, the evolvement of estuary and coast. Sometimes it accumulates so rapidly that it exceeds the capacity of available dredges to keep the channel clear. The thicker layer, which is up to several meters deep, could severely impedes navigation, resulting in great economic loss. It could also affect water quality and biochemical processes, especially in shallow lake by transport of sorbed nutrients and light penetration. Furthermore, certain toxicant pollutants and nutrients can be easily adsorbed by fine sediments, transporting along with these sediments, which results in the expansion of polluted areas. Scholars have done extensive research on the characteristic, entrainment condition of fluid mud, and the vertical distribution of turbidiy. However, the effects of wind wave and current on the entrainment of fluid mud have not been fully understood.In many shallow lakes, the most important factor which determines sediment transport is wind wave, in which exists fluctuating hydro-pressure near the bed. In this study, the effects of vertical fluctuating hydro-pressure on the entrainment of fluid mud were explored through laboratory experiments and field investigation in order to enhance our understanding of the mechanism of the entrainment of fluid mud. In laboratory experiment, the variation of water turbidity in vertical profile was monitored as time goes under different working conditions in order to investigate the effects of water depth, the fluctuating frequency and the magnitude on the entrainment of fluid mud. In field investigation, the local entrainment of mud was explored in the West Lake. Through comparison with the results of laboratory experiment, the factors which affect the suspension of fluid mud was discussed. The results show that vertical fluctuating hydro-pressure induced by wind wave has great impact on the entrainment of fluid mud. There is a good correlation between the distribution of turbidity and fluctuating frequency, magnitude. Through this study, two patens for invention were applied, including the method of measuring bottom fluctuating hydro-pressure induced by wind wave in shallow lake, and the device to collecting near-bed suspended solids in lake.