Chapter 4 One-dimensional reservoir venting experiments
4.3 Ultrasound acoustic imaging of the turbidity current
As we used this technique to observe the cavity formation and getting good enough result. Again we used ultrasound acoustic for observing entering turbidity flood; from Figure 4-8. the sequences picture realize that we can observe shape of turbidity very clearly. Those prove that using ultrasound for observing underwater structure, turbidity and other phenomena, is one of the successful tools.
Figure 4-8. Observation of turbidity current by ultrasound acoustic.
79
4.4 inlet and outlet Measurements
For those experiments we used two types of measurements: the first type is measure incoming
and outgoing concentration by weight, and the second is to measure incoming and out going flow rate in interval 10 minutes for getting more precise results.
Measuring Concentration by weight
Three runs of scenario A’s experiment, we realize that amount of sediment going out from surface outlet is very low and similar for three runs during flood event. This is expectable. Table 4-1 and Figure 4.9. Shows the concentration by weights of each run.
Table 4-1 concentration by weight of scenario A’s runs.
Run C-in C-bottom outlet C-surface outlet 1 0.027604 Not applicable 0.003033 2 0.035357 Not applicable 0.010595 3 0.035759 Not applicable 0.011788
80
Figure 4-9. Concentration by weight of scenario A’s runs.
Three runs of scenario B’s experiment, we realize that amount of sediment going out from bottom-venting outlet is almost half of incoming amount during flood events. Table 4-2 and Figure 4-10. Shows the concentrations by weights of each run.
Table 4-2 concentration by weight of scenario B’s runs.
Run C-in C-bottom outlet C-surface outlet
1 0.034445 0.018779 0.002
81
Figure 4-10. Concentration by weight of scenario B’s runs.
Three runs of scenario C’s experiment, we observe and realize the application of jet–trenching in remaining or even decreasing bed level during dispersing bed soil and flushing out from bottom-venting outlet during flood events, different in concentrations amount, depends on the hardness level of the bed, but in conclusion we observed that amount of sediment going out from dam area is almost twice bigger than incoming sediment’s concentration. Table 4-3 and Figure 4-11.
Table 4-3 concentration by weight of scenario C’s runs.
Run C-in C-bottom outlet C-surface outlet
1 0.029668 0.064584 0.0044
82
Figure 4-11. Concentration by weight of scenario C’s runs.
Measuring Sediment discharge
Collecting inlet and outlet sediment discharge for 10 minutes interval time for each runs of experiments, following figures and tables shows incoming and out coming sediment discharge of runs of each scenario.
These different colors of rectangular boxes indicating entering, bottom outlet and surface outlet sediment discharge.
Percentage Concentration by Weight
Run
Scenario C
C-in
C-surface outlet C-bottom outlet
83 Scenario A
Figure 4-12. sediment discharge of three runs of scenario A.
0
84 Scenario B
Figure 4-13. sediment discharge of three runs of scenario B.
0
85 Scenario C
Figure 4-14. sediment discharge of three runs of scenarios C.
0
86
Table 4-4 sediment discharge of scenario A’s runs.
Run
Table 4-5 sediment discharge of scenario B’s runs.
Run
Table 4-6 sediment discharge of scenario C’s runs.
Run
87
4.5 Comparison and discussion
From concentration by weight and sediment discharge, we can compare the efficiency of three scenarios. Bottom outlet Concentration by weight for scenario C is bigger than scenario B and A.
from other side measurement by sediment discharge, we can get similar results. Therefore after clicking in the long profile of the bed level for each scenario, we observe that for scenario A flood event causing rising on bed level. Figure 4-15. For scenario B, however bottom outlet is open, but still there rising on bed level. Figure 4-16. Scenario C gave us optimizing result. Figure 4-17. Because of dispersing bed sediment and flushing it out from bottom outlet during flood event, then bed level remain the same or even decrease.
In conclusions the ratio of sediment discharge going out from dam area to entering sediment
88
Figure 4-15. Different on bed level before and after flood event for Scenario A.
89
90
Figure 4-16. Different on bed level before and after flood event for Scenario B.
91
Figure 4-17. Different on bed level before and after point jet dispersing and flood event for Scenario C.
92
Chapter 5 Venting Experiments with a Scale Model of Wu-She Reservoir
In the previous chapters, we tested jetting and venting in very idealized condition (narrow flume).In this chapter, we present the more realistic tests conducted with a distorted scale model of Wu-She Reservoir. The model is a faithfully reproduces the topography of Wu-Wu-She Reservoir at scale 1:1000 in the horizontal direction and 1:100 in the vertical direction. The model was conducted at the Nanshijiao laboratory operated by the team of Dr. J. S. Lai of the Hydrotech Research Institute, and was kindly made available for the present thesis research.
93
5.1 Experiment set-up
Figure 5-1. Shows Small scale Laboratory experiment tank of 1/1000 Wu-she reservoir’s scale factor, its length width and depth individually are 5 m, 1.5 m and 50 cm. made by several thin flat layers of wood, cut by laser for making the same shape of Wu-she Reservoir. Using advantage of wood layers is loosing water and compact soil in the bed of the small scale reservoir.
Figure 5-1. Experiment model.
For mixing cohesive soil and getting homogenous material, we used high-speed agitator and then sieving the muddy material for avoiding coarse or wooden material, again agitating the material by small agitator. Then preparing several pail of the muddy well-stirring material, taking concentration from each pail for defining concentration percentage. Figure 5-2.
94
Figure 5-2. Process for preparing experiment’s sediment.
95
Set-upping and preparing point jet technique for scenario C experiment; we used single point jet extending it by steel tube, Connecting jetting tube which resisting high pressure to the high pressure 0.5 HP pump, then adjusting jetting power. Jet tools carried by a track, which can move in both X and Y direction. Figure 5-3.
Figure 5-3. Process for setting up point jet tools.
96