Hydrodynamic characteristics of staggering peak flows at the confluence section of Yiluo River

The hydrodynamic characteristics of staggering peak flows at the Y-shaped confluence of Yiluo River are systemically investigated for the planning and design of a flood-prevention project. A two-dimensional hydrodynamic model is applied to the Y-shaped confluence to simulate staggering peak flows. The hydrodynamic characteristics of staggering peak flows can thus be analyzed including water levels and flow patterns, as well as the interaction of two tributary flows. Results show that model simulations agree well with observations. The surface-water flow pattern in the confluence section shows a saddle-shaped surface moving downstream with an increase in discharge.The overbank flow caused by the stronger tributary flow can obstruct the weaker one during the course of staggering peak flows. The hydrodynamic characteristics in the confluence section are significantly associated with the ratio of stronger tributary flow to the weaker one. The structure and direction of rotation of spiral induced flow downstream of the confluent point are determined by the stronger tributary flow. The variation of water level with time exhibits a quadratic curve with three line segments during the course of staggering peak flows, and the duration of high water levels can be 5 to 7 times longer than that occurred during the course of a single peak flow or a single flow with the equivalent peak value. The stage-discharge relation graph can be fitted with a forked curved line. The latter has two inflection points in the vicinity of the two flood peaks.