Experimental study on the influence of river flow confluences on the open channel stage–discharge relationship

ABSTRACT

Accurate assessment of stage–discharge relationships in open channel flows is important to the design and management of hydraulic structures and engineering. Flow junctions commonly occur at the confluence of natural rivers or streams. The effect of flow junctions on the stage–discharge relationship at mountain river confluences was found by measuring velocity fields and water levels in experimental models. The results show that the backwater and accumulation–separation at flow junctions affect the flow structures and patterns in the channel; also, flow confluences may induce complex flow characteristics of backwater and flow separation at river junctions, indicating potential submerged flooding disasters within the confluence zone. The impacts of flow junctions on the stage–discharge relationship are investigated for two physical confluence models built from river confluence prototype systems in southwest China. The results show that the presence of tributary river inflows tends to increase the water level of the main river. This is important for flood control, flood-risk evaluation and engineering (e.g. hydropower station construction) in mountain rivers. Finally, a comparative quantitative analysis based on flow motion equations is conducted to evaluate the stage–discharge relationship in both uniform and regular confluence systems. The results indicate that more accurate prediction can be made when taking into account the flow non-uniformity induced by flow separation, backwater and distorted bed in the junction region.

KEYWORDS:

• river confluence
• stage–discharge relationship
• hydrodynamic influence
• backwater
• flow separation

Editor A. CastellarinGuest editor M. Borga

Editor A. CastellarinGuest editor M. Borga

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was financially supported by National Key R&D Program of China [2017YFC1502504], the National Natural Science Foundation of China [Grant nos 51639007, 51579163 and 41771543] and the Open Foundation of State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University [Grant no. SKHL1417].