Experimental Studies on Sediment Flushing in the Upstream

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Experimental Studies on Sediment Flushing in the Upstream Powered By Docstoc
					Experimental Studies on
Sediment Flushing in the
Upstream Approaching Channel
of TGP


                Wang Ruiyu
          Main Contents
 Introduction
 Model Experiment
 Analysis of the Result
 Conclusion
      This is the satellite
      picture of the TGP.
          We are
          here


         Five-steps Ship
         Lock

         Ship Lift
         Flushing Sluice




         Protecting Dike

Dam
  The protecting dike is built to minimize the sedimentation in the navigation channel,
  and protect it from the fluctuation in the main channel, thus formed the approaching
  channel.
  The upstream approaching channel is 2674 m long, and 220 m wide at the
  entrance. The bottom elevation is 130m. The sediment deposition should not
  exceed 139m at the ship lock channel, and 140m at the ship lift channel.
                                                                     Downstream
                                                  Flushing tunnel
                                                                     approaching
Upstream                                                             channel
approaching
channel

       Upstream
       protecting dike


Flushing Sluice                                                       Downstream
                                                                      protecting dike
   This study focus on three points:
1. How high is the maximum flushing discharge
   under the conditions that the difference of the
   water levels on the two sides of the protecting
   dike does not exceed 2m.

2. What is the efficiency of sediment flushing.

3. How to minimize the waves in the navigation
  ffchannel induced by the shutdown of the flushing
  ffsluice.
          Main Contents
 Introduction
 Model Experiment
 Analysis of the Result
 Conclusion
Length scale    Time scale of   Time scale of     Scale of
                water flow      fluvial process   discharge

1:180           1:13.46         1:300             1:434691



   Water level, water velocity and deposition volume are to
    be measured during the experiment. Because the
    process is unsteady, the water level varies much with the
    time. An automatic measuring device was applied to
    precisely trace the change of water level. 7 sensors
    measure the water pressure, and then convert the
    pressure into water level.
The framework of the automatic
       measuring device

                     导管2
                    Pipe 2   Modulus-
                             接模数转换器
                             number
                             converter

                             隔水圆筒
                              Column
      Experiment
          试验河道
      al channel
              导管1
           Pipe 1            Sensor
                             压力传感器
                  Sensor 0
                             Sensor 1
                                    Sensor 2
                                          Sensor 3
                                                     Sensor 4



                                                                Sensor 5



Entrance
                                                                  Sensor 6

                                                                     Flushing
                                                                     tunnel


           Flushing Sluice
          Main Contents
 Introduction
 Model Experiment
 Analysis of the Result
 Conclusion
           Analysis of the Result of the
                   Experiment
   1.Flushing Discharge
     We have mentioned above that the maximum flushing discharge
    under the precondition that the difference of the water levels on the
    two sides of the protecting dike does not exceed 2 meters has to be
    studied.
     The water level of the Three Gorges Reservoir during the flood
    season is 145 meter. This relative low water depth could increase
    the flushing velocity and thus improve the flushing efficiency.
    Therefore we will first study the condition of 145m reservoir water
    level, and the sediment deposition reaches 139m-140m.
                                      O peni ng of t he
                                                                                       n
                                                                              Shut dow of t he f l ushi ng
                                      f l ushi ng sl ui ce and
                                                                              sl ui ce and f l ushi ng t unnel
                                      f l ushi ng t unnel


                                145
Pr ot ot ype w er l evel ( m)




                                                                        at
                                                                 The w er l evel at t he
                                144                              ent r ance of t he
                                                                 f l ushi ng sl ui ce
                                                21 m n
                                                    i                                 et
                                                                 decr eases over 2 m er s
                                143
              at




                                          Q=5000m3/s
                                142


                                141


                                140
                                   - 20         0          20          40         60         80         100
                                                                             e   i
                                                           Pr ot ot ype t i m ( m n)
     We conducted experiments under different conditions and generalized the
     following diagram. We can see that the higher the reservoir water level is,
     the less the water level at the entrance of the flushing sluice drops.
The variation of the water level
 at the entrance of the flushing




                                      0                                       Condition 1:
                                                                              reservoir water
                                   -0.5
                                                                              level 145m, sediment
                                     -1                                       deposition reaches
                                                                              139-140m
            sluice(m)




                                   -1.5                                       Condition 2:
                                                                              reservoir water
                                     -2                                       level 147m","
                                                                              sediment deposition
                                   -2.5                                       reaches 142.7m
                                                                              Condition 3:
                                     -3                                       reservoir water
                                                                              level 150m, sediment
                                   -3.5                                       depositon reaches
                                      2000   3000    4000       5000   6000   142.7m
                                                            3
                                                Discharge(m /s)
             Analysis of the Result of the
                     Experiment
    2. Flushing efficiency
    Number    Reservoir water   Height of sediment Flushing           Flushed Sediment
              level (m)         deposition (m)     Discharge (m3/s)   Volume(m3)
    8         145               139-140            4000               231631
    12        147               142.7              4000               427519
    15        147               142.7              5000               818408

    The result show that: Compared with experiment 8, the reservoir water level
    of experiment 12 is 2m higher, and the flushed sediment volume has nearly
    doubled.
    The flushing discharge of experiment 15 is 1000 m3/s more than that of
    experiment 12, and the flushed sediment volume has again nearly doubled.
    The result show that increasing flushing discharge and raising reservoir
    water level are effective methods to improve flushing efficiency.
                                3
  Average Flushing Depth(m)


                              2.5                                                       Result of
                                                                                        experiment
                                2                                                       15
                                                                                        Result of
                              1.5
                                                                                        experiment
                                                                                        12
                                1
                                                                                        Result of
                              0.5                                                       experiment
                                                                                        8
                                0
                                    0       500         1000        1500        2000
                               Distance to the entrance of the approaching channel(m)

It can be seen that the flushing intensity at 500-600m from the entrance of the
approaching channel is the highest. In the downstream part the flushing intensity
is relatively low.
         Analysis of the Result of the
                 Experiment
3. Fluctuation in the upstream approaching channel
   To safeguard the navigation, the water flow condition in the
    upstream approaching channel should satisfy the following
    requirements: the longitudinal flow velocity<2m/s,
    transverse flow velocity<0.5m/s, wave height<0.5m,
    converse flow velocity<0.4m/s.Otherwise the safety of
    the navigation will be compromised. Therefore it is
    necessary to study the fluctuation in the approaching
    channel induced by the shutdown of the flushing sluice.
                                                                                         Initial fluctuation amplitude
                                                                                                                         1.8
Duration of the fluctuation




                              200
                                                                                                                         1.6
   in prototype time(min)




                              180
                              160                                                                                        1.4
                              140                                                                                        1.2
                              120                                                                                          1




                                                                                                      (m)
                              100                                                                                        0.8
                               80
                                                                                                                         0.6
                               60
                               40                                                                                        0.4
                               20                                                                                        0.2
                                0                                                                                          0
                                    0            5         10         15            20                                         0        5         10        15        20
                                        Water depth of the approaching channel(m)                                              Water depth of the approaching channel(m)



              These two diagrams are based on 4 experiments, all conducted with a discharge
              of 5000m3/s, but the water depths of the approaching channel of each experiment
              are different. We can see that both the duration of the fluctuation and the initial
              fluctuation amplitude has a good linear relationship with the water depth of the
              approaching channel.
              Although higher reservoir water level and thus greater water depth could improve
              the flushing efficiency, it may cause more turbulent fluctuation, and thus prolong
              the intermittence of navigation.
          Main Contents
 Introduction
 Model Experiment
 Analysis of the Result
 Conclusion
     Conclusion
    Sediment flushing plays a vital part in the navigation facilities
     management in the Three Gorges Project. Aperiodic flushing is
     an efficient way to lower the upstream approaching channel bed.
     The result of the experiments shows that:
1.   for the reservoir water level 145m, the flushing discharge should
     not exceed 3700m3/s for the safety of the dike; to increase the
     flushing discharge to 5000m3/s, the reservoir water level must
     be enhanced.
2.   The higher is the flushing discharge the larger is the volume of
     scoured sediment.
3.   The amplitude and duration of the waves induced by shutdown
     of the flushing gate in the approaching channel increase along
     with the water depth.