Study Of Water Quality Evolvement At Early Stage Of Muguandao Reservoir

Muguandao Reservoir is a coastal reservoir with sediments filled with saline water.The special geology and water environment determine the salt release from intertidal sediments to overlying freshwater and will affect the water quality and normal function of the reservoir, so the reserch on the spatial-temperial profile of salt plays a great role in construction of the reservoir.On the basis of field investigation and drilling,three typical sediments of silty clay,pelitic silt and medium-fine sand and freshwater are sampled around Muguandao Reservoir. Static column and dynamic flume experiments are conducted to inquire the interaction law between sediments and water, then to calculate the salt flux across the sediment-water interface.A quasi-three-dimension model which can reflect the effects of salt release from sediments on the water quality is developed.The variations of salt concentration at the early stage of Muguandao Reservoir are simulated in flood,mean and dry period respectively, especially the dynamic distribution of salt concention are simulated in different hydrological year.At last the feasibility of regulation and control measures are simulated. Some new understanding and conclusions are drawn.(1) The experiments indicate that salt release from sediments are of obvious impact on overlying water. In column experiment the salt release flux from different sediment can be expressed as a negative exponential function and decrease in the order of silty clay,medium-fine sand and pelitic silt. Pumping the salty water near the interface is efficient to decrease the salt concentration of overlying water.(2) According to the flume experiment, under wind blowing a boundary layer is situated above the sediment-water interface with a mean thickness of 3 cm, which limits the salt exchange between sediment and water. wind accelerates salt mixture, and makes salt concentration homogeneous above the boundary layer.(3) The numerical simulation results reflect the influence of different sediment on water quality.If impounding time is in flood period ,the water will meet the demand of quality ;Impounding in mean period,if the water entered the reservoir in the first two months is discharged ,the water can be used directly;Impounding in dry period, water level will rise to only one meter,but the water quality can not meet the standard. Discharged the impounding water in dry period ,if the next year is mean period ,the water will meet the need of quality.