Effect of inclined jet screen on turbidity current

Figures & data

Figure 1 Screen of upward inclined water jets as technical measure to control turbidity currents and location of sediment deposits in reservoir

Figure 2 Schematic view of experimental installation with

test flume with jet screen and downstream weir,

constant head stilling box with gate and tranquilizer outlet,

mixing tank and

outlet tank with sediment filter

Figure 3 (a) Flume inlet with tranquilizer box, (b) water jet injection apparatus, (c) UVP transducer, bottom (small dots) and longitudinal reference electrodes for sediment layer thickness measurements

Table 1 Experimental parameters of turbidity currents influenced by inclined jet screen (series E) and for comparison with Test A06 involving comparable initial conditions than Test E01, h ₀ is equal to gate opening of 4.5 cm

Test	S o (%)	Δρ (g/cm^3)	c s (%)	Δρ/ρ f (%)	g′ 0 (cm/s^2)	U 0 (cm/s)	q 0 (cm^2/s)	B 0 (cm^3/s^3)
A06	4.64	3.53	2.610	0.353	3.53	7.0	31.62	109.5
E01	4.64	4.06	2.990	0.406	3.99	11.2	28.68	114.3
E02	4.64	3.78	2.785	0.378	3.71	9.6	24.26	90.0
E03	0.00	3.92	2.890	0.392	3.85	9.1	26.47	101.9
E04	0.00	3.78	2.790	0.378	3.71	10.8	27.94	103.7

Table 2 Test parameters of inclined jet diffuser

Test	Q j0 (cm^3/s)	A j (cm^2)	U j0 (cm/s)	M j0 (cm^4/s^2)
E01	107	1.026	104.3	11,159
E02	163	1.026	158.9	25,896
E03	105	1.026	102.3	10,746
E04	98	1.026	95.5	9361

Table 3 Characteristics of inclined jet screen related to approach flow turbidity currents

Test	Jet		Turbidity current
	q j0 (cm^2/s)	m j 0x (g/cm^3)	Q (cm^2/s)	h (cm)	m (cm^3/s^2)	q j0/q 0	m j 0x /m	l M (cm)
E01	3.96	290	50.41	9.53	267	0.08	1.09	10.37
E02	5.99	673	43.34	9.32	202	0.14	3.34	31.13
E03	3.86	279	40.99	9.17	183	0.09	1.52	13.98
E04	3.60	243	48.71	10.59	224	0.07	1.09	11.50

Figure 4 Locations of five velocity profiles taken using UVP transducers, with dimensions in (m)

Figure 5 Physical modelling of turbidity current flowing down incline of S _o  = 4.64%, passing through 45° upward inclined water jet screen, at t = 140 s (Test E01, see also Fig. 9), resulting in a bore propagating upstream

Figure 6 Sequence of turbidity current flowing through inclined jet screen, time intervals 10 s, Test E04

Figure 7 Vertical velocity profiles of turbidity current for Test A06 (a)–(f), continuous turbidity current without obstacle and Test E01 (g)–(k), with jet screen at x = 515 cm

Figure 8 Evolution of non-dimensional turbidity current (□) velocity U/U ₀ and (Δ) height h/h ₀ along flume up- and downstream of jet screen for E series. For comparison, the values for Test A06 are also shown. Lines for E series represent average of all height and velocity data, respectively

Figure 9 Measured turbidity current front positions of series E with jet screen at x = 515 cm. Test E01 had a clearly defined reflection bore, Test E02 was completely blocked by jet screen, Tests E03 and E04 went through the screen with a slight decrease in velocity

Figure 10 Measured evolution of sediment deposit of turbidity current partially blocked by 45° upward inclined water jet screen, Test (a) E01 and (b) E03. Note the considerable reduction of downstream sediment deposit depth d _b (in log scale)

Figure 11 Comparison of ratios q _s /q _s0 for (a) Test E01 with a sloping bottom and (b) Test E03 with a horizontal bottom