中文摘要：

平原河网地区河道纵横交错，平交口门区（“＋”型交汇区）水流受交汇河道共同影响，水动力特征复杂。以新沟河三山港一武进港与京杭运河平交口门区为例，对其水动力特征进行了试验研究，并探讨了不同边界条件下的变化规律。受三山港吸流影响，京杭运河来流流至三山港口门时水流明显左偏并进人三山港，出现一定范围的横流区；受武进港出流顶托作用，位于武进港出口上游的运河右侧出现一较大范围的回流区，其范围随着武进港出流流速的减小而减小。河道边界对口门区水动力特征存在明显影响，流速较大一侧边界条件的改变对水动力特征的影响最明显。在类似平交口门区，需改变流速分布时，可优先考虑调整流速较大侧边界。

英文摘要：

Usually in the plain a river which has separated into a number of entwined channels called the plain river network areas, where the flow concentration region is a common occurrence. Hydrodynamic characteristics of flow structure in the level crossing entrance area （i. e. ＋-shaped river confluence ） are very complex due to common impacts given by crossing fiver channels. In this study, model tests on the hydrodynamic characteristics of the flow structure have been carried out and the law of variation under different boundary conditions is investigated, taking the level crossing entrance, where the Sanshan port-Wujin port is located at the Xingou River across the Beijing- Hangzhou Grand Canal, as a study example. Affected by suction flow of the Sanshan port, the current obviously flows towards the left side and flows into the Sanshan port during the inflow from the Beijing-Hangzhou Grand Canal to the Sanshan port entrance area, which results in a transverse-current area with in a certain range; affected by the Wujin port outflow＇s backwater effect, the reverse current zone with a larger range appears along the right side of the Grand Canal located on the upstream outlet of the Wujin port, and the range of the reverse current zone decreases with the decrease of flow velocity from the Wujin port. The river channel boundaries have significant impacts upon the hydrodynamic characteristics of the entrance area and the change in the boundary conditions of the larger side where flow velocity is higher, which has the most obvious impacts upon the hydrodynamic characteristics. In the similar level crossing entrance area, regulation of the boundary conditions of the larger side where flow velocity is higher should taken into account when the velocity distribution is in need of change, especially for the boundary with larger flow velocity.