太湖水环境模型关键参数曼宁系数的水槽试验

FLUME EXPERIMENT STUDY ON MANNING COEFFICIENT, A KEY PARAMETER OF WATER ENVIRONMENT MODEL OF THE TAIHU LAKE

曼宁系数是在水流计算和实际工程中应用最广泛的水流阻力系数,是河湖阻力研究中的重要方向。基于室内循环水槽,利用三维声学多普勒流速仪,研究了不同沉水植株密度和水体流速下曼宁系数的变化特性。根据摩阻力相似原理、实际曼宁系数和试验曼宁系数换算公式,计算得到不同工况下的太湖曼宁系数;并通过回归拟合,得到太湖曼宁系数与植株密度、株高和水体流速的最优拟合方程式。结果表明:当湖底植株状况一定时,太湖曼宁系数与水体流速呈明显的单调递减幂函数关系;当植株密度≤200株/m^(2),水体流速和株高一定时,太湖曼宁系数与植株密度呈单调递增关系;当水体流速与植株密度一定时,太湖曼宁系数与植株株高呈单调递增关系。通过试验模拟得到太湖实际曼宁系数,对沉积物-水界面氮磷营养盐的迁移转化研究、富营养改善及湖泊长效管理具有重要意义。

Manning coefficient is the most widely used water flow resistance coefficient in water flow calculation and practical engineering, and it is an important direction in the research of river and lake resistance. Based on the indoor circulating flume, the variation characteristics of the Manning coefficient under different submerged plant densities and water flow rates were studied with a three-dimensional acoustic Doppler velocimeter. According to the similarity principle of friction resistance, the conversion formula of the actual equivalent and the experimental Manning coefficient values, the Manning coefficient of the Taihu Lake under different conditions were calculated. Through regression fitting, the optimal fitting equation of the Manning coefficients of the Taihu Lake with plant density, plant height and water velocity were obtained. The results showed that when the plants’ condition at the bottom of the lake was constant, the Manning coefficient of the Taihu Lake and the water velocity presented an obvious monotonic decreasing power function. When the plant density was no more than 200 plants/m^(2), water velocity and plant height were constant, the Manning coefficient of the Taihu Lake increased slightly with the increase of plant density. In addition, when the water velocity and plant density were constant, the Manning coefficient of the Taihu Lake was monotonically increasing with plant height. The actual Manning coefficient of the Taihu Lake obtained through experiments was of great significance to the study of the migration and transformation of nitrogen and phosphorus nutrients at the sediment-water interface, the improvement of eutrophication, and the long-term management of the lake.