用一维水力学方程求取泻湖水位及潮汐汊道断面流速——以海南陵水新村港为例

本文通过一维水力学运动方程及连续性方程,得出一个反映泻湖水位变化的二阶非线性有阻尼的强迫振动方程,采用龙格-库特四步格式进行求解,并以海南陵水新村港为例,计算了泻湖水位及潮汐汊道的断面流速.研究结果表明:(1)一维水力学方程可容易地求得泻湖-潮汐汊道体系中泻湖内的水位及汊道的断面流速,计算简单快捷.(2)一维水力学方程可分析潮汐汊道体系中的一些基本现象.如潮汐汊道对潮波的"过滤器"特征;由于泻湖-潮汐汊道体系的阻尼系数较大所导致的潮波自外向泻湖传播时衰减剧烈;径流对泻湖水位及汊道流速产生有利于落潮优势的影响;风可使泻湖水位抬升或下降等.(3)无论是否考虑泻湖与潮汐汊道面积随水位的变化,一维水力学方程都具有相当大的缺陷.由于其不能反映泻湖内地形的空间变化,也不能解决漫滩与归槽等过程,在外海潮波无次生波的情况下,它本身不能产生次生潮波,因而不能正确地反映潮汐汊道体系的涨落潮历时与流速不对称,从而不能分析泥沙的净输运及潮汐汊道的稳定性问题.(4)新村港泻湖-潮汐汊道体系中潮汐汊道的断面面积大小对整个体系的稳定性及演变趋势起着控制作用.

Obtaining water elevation in the lagoon and cross-sectionally averaged velocity of the tidal inlet by using one-dimensional hydraulic equation——a case study in Xincun Inlet Linshui, Hainan, China

Through one-dimensional hydraulic momentum and continuity equation,this paper established a second-order nonlinear forced oscillation equation representing the water level variation in lagoon,which can be solved by four-step Runge-Kutta method.A case application to get the water level in lagoon and cross-section velocity at inlet was conducted at Xincun Inlet,Linshui,Hainan.The study shows following results.(1) The water level in lagoon and cross-sectionally averaged velocity at inlet can be easily obtained by this method.(2)Some basic characteristics of the lagoon-inlet system can be represented by this method,such as the 'filter' effect of the inlet to offshore tidal wave,the strong dissipation of tidal wave due to large impedance,the effect of river discharge in producing ebb-dominant tidal asymmetry and the water level setup or set-down at the lagoon by winds.(3)Relatively large shortcoming appears whether the method takes the factor of variation of lagoon and inlet areas with water level into account.It can not resolve the spatial in-uniformity in the lagoon,simulate the wetting and drying processes of tidal flat,and produce overtides by forced with primary tidal waves at the offshore boundary,thus it is not able to resolve the tidal duration and velocity asymmetry at inlet and to be used to analyze the net sediment transport and stability of the lagoon-inlet system.(4) The narrow inlet cross-section area seems to play a dominant role in controlling the stability and the evolution trend of the system.