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

Figures & data

Figure 1. Typical sketch of flow structures at a river confluence (adapted from Zhou 2014).

Figure 2. Experimental flume system: (a) measurement sketch and (b) experimental test photo.

Table 1. Flow conditions and test parameters of the flume experiment.

Main flume discharge (m^3/s)	Tributary flume discharge (m^3/s)	Total discharge (m^3/s)	Main flume		Tributary flume
			Width (m)	Slope	Width (m)	Slope
0.069	0.053	0.122	1.0	2‰	0.4	2%

Figure 3. Physical Model #1 – the river confluence between Baisha River and Shenxi River as the prototype: (a) model design, (b) prototype photo and (c) measurement section arrangement.

Table 2. Experimental test cases of flow discharges in Baisha River.

Test case	1	2	3	4
Prototype discharge, Qp (m^3/s)	266.2	203.6	144.6	89.7
Model discharge Qm (m^3/s)	0.149	0.114	0.081	0.050

Table 3. Experimental test cases of flow discharge in Baisha and Shenxi rivers. Q_p: prototype discharge, Q_m: model discharge.

		Test case
		5	6	7	8
Baisha River	Qp (m^3/s)	266.2	203.6	144.6	89.7
	Qm (m^3/s)	0.149	0.114	0.081	0.050
Shenxi River	Qp (m^3/s)	101.8	101.8	101.8	101.8
	Qm (m^3/s)	0.057	0.057	0.057	0.057

Figure 4. River confluence zone between Wahei River and Xianjia River as the prototype of physical Model #2: (a) sketch and (b) prototype photo.

Figure 5. Physical Model #2: (a) sketch of the measurement section arrangement and (b) photo of the experimental test.

Table 4. Settings and parameters of experimental test groups in physical Model #2. Q_wp, Q_xp prototype discharge; Q_wm, Q_xm: model discharge.

		Test group
		Group 1	Group 2	Group 3	Group 4	Group 5
Wahei River	Qwp (m^3/s)	554	1350	1220	1350	1540
	Qwm (m^3/s)	0.031	0.076	0.069	0.076	0.087
Xianjiapu River	Qxp (m^3/s)	159	712	796	886	1010
	Qxm (m^3/s)	0.009	0.040	0.045	0.050	0.057

Figure 6. Measured u–v vector fields at the confluence zone in the flume experimental tests: (a) near surface (Z* = 0.09), (b) middle layer (Z* = 0.05), and (c) near bed (Z* = 0.018).

Figure 7. Flow structures and patterns at the confluence zone in the flume experiment: (a) contour plots of measured velocity fields at near-surface (Z* = 0.09), middle (Z* = 0.05) and near-bed (Z* = 0.018) locations, and (b) contour plot of measured water depth.

Figure 8. Mean vertical velocity distributions in the confluence zone.

Figure 9. Measured stage–discharge relationships at different sections for physical Model #1 with and without tributary flows.

Figure 10. Longitudinal water level changes at the left bank of Baisha River for different inflows.

Table 5. Measured elevation of the water level (w.l.) and dyke at the test positions. Q_T: total discharge.

Group	Discharge (m^3/s)			Elevation (m)
	Qwp	Qxp	QT	P1		P3		P2		P4
				w.l.	Dyke	w.l.	Dyke	w.l.	Dyke	w.l.	Dyke
1	554	159	713	819.2	823.0	821.5	824.3	820.1	822.0	820.9	823.5
2	1220	796	2016	822.5		824.8		822.6		823.5
3	1350	712	2062	822.7		824.3		822.8		824.1
4	1350	886	2236	822.7		825.0		823.0		823.9
5	1540	1010	2550	824.0		825.65		823.9		824.8

Figure 11. Measured stage–discharge relationships for physical Model #2 with different inflows.

Figure 12. Characteristics of water level variations in the confluence zone: variation of (a) transverse water level at five typical sections, and (b) longitudinal water level at typical positions from sections m02# to mx04#.

Figure 14. Comparison of measured and predicted stage–discharge relationships for Model #1.

Figure 13. Comparison of measured and predicted stage–discharge relationships for the laboratory experiment flume. Q_c and Q_cr refer to the predicted discharge based on the frictional slope by the uniform part only and both uniform and non-uniform parts (Equation (2)).

Zhou, S.F., 2014. Study on flow pattern and disaster reduction method in river confluences. Master degree thesis. the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, China.

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