感潮河段交汇区水流特性数值模拟——以宁波三江口为例

Numerical simulation of flow characteristics in a tidal river confluence——A case study of Sanjiangkou in Ningbo City

河流交汇为城市的发展提供了便利,对区域防洪、航运及河道演变影响重大。针对感潮河段交汇区域特有的非恒定往复流条件,以宁波三江口为例,运用Delft-3D建立二维水动力数学模型。基于实测水文和地形资料,引入四种评估参数对模型进行了率定与验证。重点分析了洪、枯两季涨、落急时刻,交汇区流速分布及水面形态等水流特性。结果表明:涨潮时,交汇区流场可类比分叉水流;落潮时,则为交汇水流;交汇区顶点及左支入汇侧下游存在两个低流速区,并可形成分离区;汇流区流速整体呈落潮大于涨潮的趋势,洪、枯季间最大流速相近。此外,涨、落急时刻典型特征断面水面呈单一横比降,且落急时刻比降明显大于涨急时刻;落急时,交汇口水面呈混合层附近高,两侧低的"马鞍形"分布。

River confluence provides convenience for the development of cities and has significant influence on the region′s flood control,inland navigation,and fluvial processes.Aiming at the unidirectional flows in a tidal river confluence(Sanjiangkou,Ningbo city),we established a two-dimensional hydrodynamic mathematical model using Delft-3D.Based on the measured hydrological and topographic data,we applied four commonly used parameters to calibrate and validate the model results,focusing on such flow characteristics as the tidal current fields,velocity distribution and horizontal water level changes at the maximum flood and ebb tides in wet and dry seasons.The results showed that the flow field in the confluence area is analogous to the distributary flow during the flood tide,and is the confluence flow during the ebb tide.There are two low-velocity regions in the confluence vertex and the downstream of the left branch confluence area and they can form a separation region.The confluence flow velocity during the ebb tide is generally larger than that during the flood tide.The maximum flow velocities in the wet and dry seasons are close.In addition,the water surface of the three typical cross-sections shows a single transverse slope during the maximum flood and ebb tides.the water surface slope at the maximum ebb tide is greater than that at the maximum flood tide.At the maximum ebb tide,the water surface of the confluence area is high near the mixed layer and low at its two sides,showing a"saddle shape".