河口区斜压梯度对余水位的累积影响及其机制探讨

余水位（即潮平均水位）是河口区径潮相互作用的典型结果，研究其形成演变机制对探讨河口区的水资源高效开发利用具有重要科学意义。本文基于不同径潮边界条件下的三维斜压水动力数值模拟及切比雪夫机制分解，初步探讨了概化地形条件下斜压梯度对余水位沿程变化的影响。数值模拟结果表明:河口区余水位的沿程变化明显受径流量、潮波振幅、辐聚地形及斜压梯度等因素的共同影响，斜压梯度对余水位的影响是一种累积效应且影响区域集中在回水区，同时其影响强度具有明显的大小潮变化、洪枯季变化。利用数值模型提供的水位及流速场信息，通过切比雪夫分解非线性摩擦项分离出控制余水位变化的3个主要因素，即径流、潮流和径潮相互作用因子，并与斜压梯度产生的余水位进行对比分析，结果表明:回水区域余水位主要以径潮相互作用因子为主导；斜压梯度对余水位影响主要体现在小潮期间，有可能成为影响余水位变化的主控因子。

Cumulative effect of baroclinic gradient on the residual water level in estuaries and its underlying mechanism

Residual water level (i.e. the tidally averaged water level) is mainly controlled by the tide-river interaction, and understanding its formation and evolution is important with regard to water resources management in estuaries. In this study, based on the three-dimensional baroclinic hydrodynamic numerical results under different tide-river conditions and the Chebyshev polynomial decomposition approach, the impact of the baroclinic gradient on residual water level variation was explored for given idealized geometry with a convergent width and a linear bed slope. Model results show that the variation of residual water level along the estuary axis is determined by freshwater discharge, tidal amplitude, convergent topography and baroclinic gradient. In particular, the influence of the baroclinic gradient on the residual water level is featured by an accumulative effect over the whole backwater zone, with a significant spring-neap and wet-dry changes. Information of water level and velocity field are provided by numerical model, making use of Chebyshev polynomial decomposition, it is possible to decompose the residual water level into different components, linking to tide, river and tide-river interaction, respectively. When compared with the residual water level induced by baroclinic gradient, it is shown that, the residual water level in backwater zone is primarily controlled by the tide-river interaction. Effect of baroclinic gradient on the residual water level becomes important during the neap tide and may become the dominant factor on the residual water level.