PAK BENG HYDROPOWER PROJECT - Mekong River Commission€¦ · Pak Beng Hydropower Project is the first cascade of the hydropower ... A stilling basin with energy dissipation by hydraulic

PAK BENG HYDROPOWER PROJECT

Overall Hydraulic Physical Model Investigation of Pak Beng HPP

September 2015


i

CONTENTS

1 INTRODUCTION ...................................................................................................... 1

2 EXPERIMENTAL OBJECTIVES ............................................................................... 1

3 BASIC DATA ............................................................................................................. 1

3.1 HYDROLOGY ............................................................................................ 1

3.2 SEDIMENT ................................................................................................. 3

3.3 PROJECT LAYOUT AND HYDRAULIC STRUCTURES .......................... 4

4 MODEL DESIGN AND MAKING ............................................................................. 8

5 EXPERIMENTAL CASES .......................................................................................... 8

6 ENERGY DISSIPATION EXPERIMENT ................................................................ 10

6.1 FLOW PATTERN ...................................................................................... 10

6.2 FLOW VELOCITY DOWNSTREAM OF STILLING POOL ..................... 16

7 SEDIMENT DEPOSITION AND FLUSHING EXPERIMENT ................................ 18

7.1 EXPERIMENT OF SEDIMENT DEPOSITION ......................................... 18

7.2 SAND FLUSHING EXPERIMENT ........................................................... 21

7.3 SEDIMENT EXPERIMENT CONCLUSION ............................................. 27

8 FLOW CONDITION FOR ENTRANCE AREA OF APPROACH CHANNEL ........ 28

8.1 TESTING APPARATUS ........................................................................... 28

8.2 EXPERIMENTAL CASES ........................................................................ 28

8.3 EXPERIMENTAL RESULTS .................................................................... 29

8.3.1 Upstream Entrance Area ....................................................................... 29

8.3.2 Downstream Entrance Area .................................................................. 40

9 EXPERIMENTAL CONCLUSIONS ......................................................................... 50

9.1 CONCLUSIONS ........................................................................................ 50

9.2 SUGGESTIONS ........................................................................................ 50


ii

LIST OF TABLES

Table Title Page

Table 3.1-1 Design Flood at Dam Site .......................................................................... 2

Table 3.1-2 Rating Curve at Dam Site ........................................................................... 2

Table 3.1-3 Rating Curve at Entrance Areas of Approach Channel. ............................. 3

Table 5-1 Experimental Cases .................................................................................... 9

Table 6.2-1 Downstream Flow Pattern of Case 2 ........................................................ 16



Table 6.2-4 Downstream Flow Pattern of Case 11 ...................................................... 17

Table 6.2-5 Downstream Flow Pattern of Case 13 ...................................................... 18

Table 8.2-1 Test Cases of Navigable Hydraulics ......................................................... 29

Table 8.2-2 Flow Velocity Limit in Entrance Area of Approach Channel .................. 29


iii

LIST OF FIGURES

Figure Title Page

Fig. 3.2-1 Suspended Load Grading Curve ................................................................ 3

Fig. 3.2-2 Bed Load Grading Curve ........................................................................... 4

Fig. 3.3-1 Project Layout ............................................................................................ 5

Fig. 3.3-2 Discharge Sluices Layout ........................................................................... 6

Fig. 3.3-3 Profile of Discharge Sluices Zone 1 ........................................................... 6



Fig. 3.3-6 Navigation Discharge Sluice Profile .......................................................... 8

Fig. 6.1-1 Downstream Flow Pattern of Case 1 ........................................................ 10








Fig. 6.1-9 Downstream Flow Pattern of Case 11 ...................................................... 14




Fig. 7.1-1 Project Layout and the Position of Testing Profiles ................................. 19

Fig. 7.1-2 Sediment Deposition before Dam ............................................................ 20

Fig. 7.1-3 Sediment Deposition in front of Sand Barrier .......................................... 20

Fig. 7.2-1 Sediment Deposition at Section 1 ............................................................ 21




iv




Fig. 7.2-7 Sediment before Dam for Discharge 14900m3/s ...................................... 24

Fig. 7.2-8 Upstream River Sediment for Discharge 14900m3/s ............................... 25

Fig. 7.2-9 Sediment before Dam for Discharge 11600m3/s ...................................... 26

Fig. 7.2-10 Sediment before Dam for Discharge 8000m3/s ........................................ 27

Fig. 8.1-1 Vectrino-Plus Current Meter with Point Type .......................................... 28

Fig. 8.3-1 Velocity in Entrance Area of Upstream Approach Channel for

Discharge of 865m3/s ............................................................................... 32


Discharge 1500 m3/s. ................................................................................ 33


Discharge 3160 m3/s. ................................................................................ 34


Discharge 5440 m3/s. ................................................................................ 35


Discharge 8000 m3/s. ................................................................................ 36


Discharge 10000 m3/s. .............................................................................. 37


Discharge 11600 m3/s. .............................................................................. 38


Discharge 13200 m3/s. .............................................................................. 39

Fig. 8.3-9 Velocity in Entrance Area of Downstream Approach Channel for

Discharge 865 m3/s. .................................................................................. 42


Discharge 1500 m3/s. ................................................................................ 43


Discharge 3160 m3/s. ................................................................................ 44



v

Discharge 5440 m3/s. ................................................................................ 45


Discharge 8000 m3/s. ................................................................................ 46


Discharge 10000 m3/s. .............................................................................. 47


Discharge 11600 m3/s. .............................................................................. 48


Discharge 13200 m3/s ............................................................................... 49


1

1 INTRODUCTION

Pak Beng Hydropower Project is the first cascade of the hydropower development scheme for

the Mekong River, and its installed capacity and normal water level are 9120MW and 340m

respectively. It is located in the upper reaches of the Mekong River in Pak Beng District in

Oudomxay province of northern Laos.

Runoff type development is applied to this project, while a run-of-river powerhouse is

designed. The complex structures consist of water retaining structures, flood release structures,

powerhouse, navigation and fish way.

The flood release structures consist of discharging sluices and sand outlets. The discharge

sluices and navigation discharge sluice are located on the right flood land with fourteen

15m×23m (width×height) openings. A stilling basin with energy dissipation by hydraulic

jump is designed behind the sluices. The sand outlets are designed on the powerhouse section,

and a sand outlet with the opening dimension of 2.5m×5m (width×height) is constructed

between every two generating units, and eight sand outlets are designed.

2 EXPERIMENTAL OBJECTIVES

The objective of hydraulic experimental is to research the hydraulic characteristics as follow:

(1) Discharge capacity of the sluices;

(2) The flow condition in the entrance of approaching channel both upstream and

downstream;

(3) The energy dissipation efficiency of the stilling pool of sluices;

(4) Pattern of sediment deposit at upstream and downstream area of the dam;

(5) Sediment flushing efficiency of discharge sluices and navigation discharge sluice;

(6) Optimize the layout of hydraulic complex by experiment.

3 BASIC DATA

3.1 HYDROLOGY

(1) Flood

Design flood at dam site refers to Table 3.1-1.


2

Table 3.1-1 Design Flood at Dam Site

Flood frequency (%) 50 33.33 20 10 5 3.33 2

Return period (year) 2 3 5 10 20 30 50

Peak discharge (m3/s) 11600 13200 14900 17000 18900 20000 21400

Flood frequency (%) 1 0.5 0.33 0.2 0.1 0.05

Return period (year) 100 200 300 500 1000 2000

Peak discharge (m3/s) 23100 24800 25800 27000 28700 30200

(2) Rating Curve

Rating curve at dam site refers to Table 3.1-2, and rating curve at entrance area of

approach channel refers to Table 3.1-3.

Table 3.1-2 Rating Curve at Dam Site

Water

Level (m)

Discharge

(m3/s)

Water

Level (m)

Discharge

(m3/s)

Water

Level (m)

Discharge

(m3/s)

304.15 496 316.46 3870 330.29 13200

305.11 660 317.46 4270 331.28 14200

306.10 840 318.39 4670 332.43 15500

307.02 1020 319.40 5100 333.34 16700

307.98 1200 320.26 5540 334.38 18100

308.98 1410 321.14 6040 335.33 19400

309.90 1620 322.13 6630 336.35 20800

310.86 1860 323.17 7270 337.37 22200

311.82 2120 324.25 7960 338.45 23700

312.67 2380 325.27 8700 339.43 25100

313.33 2620 326.33 9530 340.39 26500

313.99 2880 327.35 10400 341.33 27900

314.67 3160 328.19 11200 342.20 29200

315.51 3500 329.14 12100 343.05 30500


3

Table 3.1-3 Rating Curve at Entrance Areas of Approach Channel.

Water

Level (m)

Discharge

(m3/s)

Water

Level (m)

Discharge

(m3/s)

Water

Level (m)

Discharge

(m3/s) 496 303.50 3870 315.81 13200 329.64 660 304.46 4270 316.81 14200 330.63 840 305.45 4670 317.74 15500 331.78

1020 306.37 5100 318.75 16700 332.69 1200 307.33 5540 319.61 18100 333.73 1410 308.33 6040 320.49 19400 334.68 1620 309.25 6630 321.48 20800 335.70 1860 310.21 7270 322.52 22200 336.72 2120 311.17 7960 323.60 23700 337.80 2380 312.02 8700 324.62 25100 338.78 2620 312.68 9530 325.68 26500 339.74 2880 313.34 10400 326.70 27900 340.68 3160 314.02 11200 327.54 29200 341.55 3500 314.86 12100 328.49 30500 342.40

3.2 SEDIMENT

(1) Grading of Suspended Load

The median particle diameter (d50) is 0.0077mm, mean particle diameter (dm) is

0.0224mm; the maximum diameter is 2.45mm. The grading curve of suspended load is

shown in Fig.3.2-1.

0

10

20

30

40

50

60

70

80

90

100

0.0010.010.1110particle diameter (mm)

sedi

men

t wei

ght p

erce

nt (

%)

d50=0.0077mm dm=0.0224mm

Fig. 3.2-1 Suspended Load Grading Curve


4

(2) Grading of Bed Load

The median particle diameter (D50) is 16.9mm, the mean particle diameter (Dm) is

28.0mm, and the maximum diameter is 180mm. The grading curve of bed load may

refer to Fig.3.2-2.

0

10

20

30

40

50

60

70

80

90

100

0.11101001000particle diameter (mm)

sedi

men

t wei

ght p

erce

nt (

%)

D50=16.9mm Dm=28.0mm

Fig. 3.2-2 Bed Load Grading Curve

3.3 PROJECT LAYOUT AND HYDRAULIC STRUCTURES

(1) Complex Layout

The complex structures consist of water retaining structures, flood release structures,

powerhouse, ship lock and fish way. The project layout refers to Fig.3.3-1.

(2) Discharge Sluices Layout

The flood release structures consist of thirteen discharge sluices, one navigation

discharge sluice and eight sand outlets. The discharge sluices and navigation discharge

sluice are located on the right flood land with fourteen 15m×23m (width×height)

openings. Stilling pool with energy dissipation by hydraulic jump is designed behind

the sluices. The sand outlets are designed on the powerhouse section, and a sand outlet

with the opening dimension of 2.5m×5m (width×height) is constructed between every

two generating units.

Discharge sluices and navigation discharge sluice layout refer to Fig.3.3-2.


5

Fig. 3.3-1 Project Layout


6

Fig. 3.3-2 Discharge Sluices Layout

1# discharge sluice is located at left side of ship lock, its main function is to

wash the sediment deposited on access channel, and it can be used as

discharge sluice when ship lock is closed, and it was named as navigation

discharge sluice.

The 13 sluices (from 2# to 14#) are the main discharge sluices of spillway;

they are named as discharge sluices and divided into three zones as follows.

Zone 1 is on the left, it consisted of three sluices (from 12# to 14#), and the

bottom elevation of the stilling basin is 310m.

Profile of discharge sluices zone 1 refers to Fig.3.3-3.

Fig. 3.3-3 Profile of Discharge Sluices Zone 1


7

Zone 2 is on the right side of zone 1, it consisted of three sluices also (from 9#

to 11#), and the bottom elevation of the stilling basin is 312.5m.



Zone 3 is on the right side of zone 2, it consisted of seven sluices (from 2# to

8#), and the bottom elevation of the stilling basin is 317m.



Sluices of zone 1 and 2 are chiefly opened for frequent flood discharge, when

floods are larger, all discharge sluices will open for discharging.

Profile of navigation discharge sluice profile refers to Fig.3.3-6.


8

Fig. 3.3-6 Navigation Discharge Sluice Profile

4 MODEL DESIGN AND MAKING

The physical model includes all structures in the hydropower station, and is made

according to gravity similarity.

The model scale λL=70.

The total length of simulated river channel in physical model is 4200m, including the

upstream reach of 2500m and downstream reach of 2000m.

5 EXPERIMENTAL CASES

The experimental cases are showed in Table.5-1.


9

Table 5-1 Experimental Cases

Case No

Flood Frequency（%）

Reservoir Water

Level (m)

Total Discharge

(m3/s）

Opening of Discharge Sluices, Navigation Discharge Sluice and Sand Outlets（Unit：m） Turbine

Discharge

(m3/s)

Downstream Water Level

(m) Zone1 Zone2 Zone3 Navigation

Discharge Sluice

Sand Outlets1# 2# 3# 4# 5# 6# 7# 8# 9# 10# 11# 12# 13#

1 340 5000 3 3 3 full 3212 318.96

2 340 5000 3 3 3 full 3212 318.96

3 340 5000 10 full 3212 318.96

4 340 8000 6 6 6 2.5 2.5 2.5 full 3212 324.31

5 340 8000 4 4 4 4 4 4 full 3212 324.31

6 340 8000 9 9 9 full 3212 324.31

7 340 8000 9 9 9 full 3212 324.31

8 340 10000 10.5 10.5 10.5 2 2 2 2 full 3212 326.89

9 340 10000 7 7 7 5.5 5.5 5.5 full 3212 326.89

10 340 10000 full 10.5 full full 3212 326.89

11 50 340 11600 full full full 4.5 full 4.5 full 3212 328.30

12 50 340 11600 7.5 7.5 7.5 7.5 7.5 7.5 3 3 3 3 3 3 3 full 3212 328.30

13 33.33 340 13200 8.5 8.5 8.5 8.5 8.5 8.5 4 4 4 4 4 4 4 full 3212 329.99

14 33.33 340 13200 full 6 full full full full full 3212 329.99

15 5 335.03 18900 full full full full full full full full full full full full full full 334.82

16 0.2 341.26 27000 full full full full full full full full full full full full full full 340.59

17 0.05 343.7 30200 full full full full full full full full full full full full full full 342.86


10

6 ENERGY DISSIPATION EXPERIMENT

6.1 FLOW PATTERN

Flow pattern for experimental cases are shown in Fig. 6.1-1~6.1-12.

Fig. 6.1-1 Downstream Flow Pattern of Case 1



11




12



Flow pattern at the end of


13




14




15




16

The figures of flow pattern show that when all of sluices are used to release the flood,

flow pattern in the downstream of the sluices are good.

6.2 FLOW VELOCITY DOWNSTREAM OF STILLING POOL

Flow velocity of experimental cases downstream of stilling pool are shown in Table

6.2-1~6.2-5.

Table 6.2-1 Downstream Flow Pattern of Case 2

Stake

No

Distance from partition wall

(m)

Velocity

(m/s) Stake No


(m)

Velocity

(m/s)

D0+160.

00

7.50 7.61

D0+220.0

0

11.75 6.74 26.00 8.31 30.50 3.87 44.50 6.34 60.50 3.33 64.50 5.73 98.00 3.58 83.00 3.54 143.00 2.46 121.50 0.46 158.00 0.29 177.00 0.29 248.00 0.31

D0+287.

50

11.75 5.57

D0+362.5

0

11.75 3.06 30.50 3.70 30.50 1.77 60.50 3.04 60.50 2.43 98.00 3.45 98.00 2.46 143.00 2.21 143.00 2.64 195.50 0.88 195.50 1.04 255.50 0.17 255.50 2.41


Stake No Distance from partition wall

(m)

Velocity

(m/s) Stake No


(m)

Velocity

(m/s)

D0+160.0

0

7.50 10.46

D0+220.0

0

11.75 12.10 26.00 14.39 30.50 12.68 44.50 12.36 60.50 7.44 64.50 4.25 98.00 2.46 101.50 0.00 143.00 5.37 140.00 -1.25 195.50 3.66 214.00 -1.31 248.00 1.96

D0+287.5

0

11.75 7.53

D0+362.5

0

11.75 7.69 30.50 7.03 30.50 6.20 60.50 5.62 60.50 4.78 98.00 3.00 98.00 3.79 143.00 3.37 143.00 3.46 195.50 5.82 195.50 3.29 255.50 2.08 255.50 1.50


17


Stake

No


(m)

Velocity

(m/s) Stake No


(m)

Velocity

(m/s)

D0+160.

00

7.50 6.41

D0+220.0

0

8.00 4.53 26.00 6.28 23.00 3.53 44.50 5.49 38.00 3.62 64.50 4.17 60.50 2.95 83.00 3.98 79.25 2.79 101.50 4.36 94.25 3.62 121.50 0.41 128.00 1.96 158.50 0.36 165.50 0.58 214.00 0.00 218.00 0.67

D0+287.

50

44.50 5.49

D0+362.5

0

60.50 2.95 64.50 4.17 79.25 2.79 83.00 3.98 94.25 3.62 101.50 4.36 128.00 1.96 121.50 0.59 165.50 0.58 158.50 0.50 218.00 0.67 214.00 0.25 -82.00 0.67


Stake

No


(m)

Velocity

(m/s) Stake No


(m)

Velocity

(m/s)

D0+160.

00

7.50 9.07

D0+220.0

0

11.75 3.87 26.00 2.39 30.50 1.04 44.50 4.78 60.50 0.21 64.50 4.95 98.00 2.21 83.00 0.32 143.00 6.95 101.50 -1.10 195.50 6.95 140.00 7.94 248.00 5.04

D0+287.

50

11.75 4.78

D0+362.5

0

11.75 4.29 30.50 4.99 30.50 2.88 60.50 0.34 60.50 0.67 98.00 1.55 98.00 2.12 143.00 7.94 143.00 0.29 195.50 8.24 195.50 0.25 248.00 6.95 248.00 0.46


18


Stake

No


(m)

Velocity

(m/s) Stake No


(m)）

Velocity

(m/s)

D0+81.0

0

121.50 3.79

D0+160.0

0

7.50 8.77 140.00 4.04 26.00 8.36 158.50 3.87 44.50 9.61 177.00 4.69 64.50 3.79 195.50 5.49 83.00 4.04 214.00 3.53 101.50 3.87 232.50 4.20 140.00 4.69

D0+220.

00

11.75 4.41

D0+287.5

0

11.75 4.74 45.50 4.02 45.50 4.24 75.50 4.20 75.50 4.24 113.00 2.83 113.00 4.33 143.00 1.78 143.00 2.29 173.00 1.77 173.00 2.08 210.50 1.78 210.50 2.25

7 SEDIMENT DEPOSITION AND FLUSHING EXPERIMENT

7.1 EXPERIMENT OF SEDIMENT DEPOSITION

The water release structures, the topography of dam site and the position of testing

profiles are shown in Fig.7.1-1.

The discharge of experiment is 2-year return period flood. The accumulated time of

experiment is 30 hours, and the corresponding time of prototype is about 260 hours.

The topography of sediments in front of the dam after the experiment is shown in Fig.

7.1-2, and sediment deposition in front of sand barrier is shown in Fig. 7.1-3.


19

Fig. 7.1-1 Project Layout and the Position of Testing Profiles


20

Fig. 7.1-2 Sediment Deposition before Dam

Fig. 7.1-3 Sediment Deposition in front of Sand Barrier


21

7.2 SAND FLUSHING EXPERIMENT

(1) Sand Flushing Experiment for 5-Year Return Period Flood

Sand flushing discharging is 14900 m3/s, and all of 14 discharge sluices are

opened fully.

The profiles of sediment before dam after sand flushing are shown in Fig.

7.2-1~7.2-6. Experiments show that after sand flushing, sediment deposition

cannot be found in the area no more than 100 m before dam, the sediment will

deposit 100~120m away from the dam.

Fig. 7.2-1 Sediment Deposition at Section 1


22




23




24


The sediment deposition before dam and the upstream river bed are shown in

Fig.7.2-7 and Fig.7.2-8 respectively.

Fig. 7.2-7 Sediment before Dam for Discharge 14900m3/s


25

Fig. 7.2-8 Upstream River Sediment for Discharge 14900m3/s

Basing on the sand flushing experiments, it can be seen that sediments in the

upstream move obviously to dam due to sand flushing. Moreover, most of

sediments in front of discharge sluices of zones 1 and 2 have been washed

downstream, and riverbed is exposed. Sand flushing effect of zone 3 is a bit

poor compared with the zone 1 and zone 2. In zone 3, there is a small amount

of sediment deposition in front of the sluices.

Due to the high terrain of upstream navigation channel, the sand flushing

effect in this area is good, and almost no sediment deposits.

As to the upstream river bed, because it is convex towards the right side,

sediment deposition mainly in the middle part and the left bank.

(2) Sand Flushing Experiment for 2-Year Return Period Flood

For 2-year return period flood, the sediment deposition before dam is shown in

Fig.7.2-9.


26


When the discharge sluices of zone 1, 2 and 3 open fully to discharge 2-year

return period flood 11600m3/s, almost no sediment deposits in front of dam.

Due to the training wall in zone 1, the sand flushing effect in this area is best;

it is not so good in zone 2. The original elevation of zone 3 is relatively high,

so the sediment is relatively thin and the original terrain is exposed after

flushing.

(3) Sand Flushing Experiment for Frequent Flood

For flood of 8000m3/s with all sluices opening fully, the sediment deposition

before dam is shown in Fig. 7.2-10. With the discharge of frequent flood, it

has great effect on sweeping the deposition before discharge sluices, when the

discharge sluices of zone 1, 2 and 3 are opened fully.


27


7.3 SEDIMENT EXPERIMENT CONCLUSION

The experiment results show that:

(1) As for the 2-year return period flood, opening the discharge sluices fully can

ensure there is almost no sediment deposition in the area no more than 100m

before the discharge sluices;

(2) For 5-year to 2-year return period flood, and the frequent flood, it can wash up

sediments in the range of 150m~200m before the discharge sluices, when

discharge sluices of all the three zones open fully. Meanwhile, the sediments in

reservoir move simultaneously to dam site. This can help to relieve deposition in

the reservoir.

(3) Due to the bend of the upstream river, the sediments coming from the upstream

will not deposit too much near the sand barrier, a longitudinal dune will form on

the upstream and right side of the sand barrier, so bed loads cannot climb over

the sand barrier, and reach the intake of power station.

(4) Due to the high original terrain in approach entrance area of navigation channel

upstream, sediment at this part of river bed can be washed up if sluices of zone 3

open fully for a certain period of time.


28

8 FLOW CONDITION FOR ENTRANCE AREA OF

APPROACH CHANNEL

8.1 TESTING APPARATUS

In order to measure the flow velocity, the current meter with point type basing on

acoustic Doppler has been used in experiments. The current meter is developed by

Nortek Company, and named Vectrino-plus (shown in Fig.8.1-1). It is based on

acoustic Doppler, and its point type has high precision. This current meter is used to

measure the three-dimensional flow velocity of entrance area of approach channel.

Fig. 8.1-1 Vectrino-Plus Current Meter with Point Type

8.2 EXPERIMENTAL CASES

The navigation hydraulic experiments cases and the requirements are showed in Table

8.2-1 and Table 8.2-2 respectively.


29

Table 8.2-1 Test Cases of Navigable Hydraulics

Case No

Discharge (m3/s)

Upstream Water Level

(m)

Downstream Water Level

(m) Remarks

1 865 340/335 306.23 minimum navigable discharge

2 1500 340/335 309.38 average discharge of dry season

3 3160 340/335 314.67 average annual flow discharge

4 5440 340 320.07 average discharge of flood season

5 8000 340 324.31 frequent flood 6 10000 340 326.89 frequent flood 7 11600 340 328.30 2-year return period flood 8 12200 340 329.99 9 13200 340 329.99 3-year return period flood

10 14900 331.68 5-year return period flood, gates opened fully

11 17000 333.34 10-year return period flood, gates opened fully

Table 8.2-2 Flow Velocity Limit in Entrance Area of Approach

Channel

Longitudinal velocity (m/s)

Transverse velocity (m/s)

Back velocity (m/s)

≤2.0 ≤0.30 ≤0.4

8.3 EXPERIMENTAL RESULTS

8.3.1 Upstream Entrance Area

The flow velocities of entrance area of upstream approach channel are shown in

Fig.8.3-1~8.3-8. In which, the red dashed line is the main route, and the scope

between two solid red lines means that it meets the navigable requirements.

It can be seen that the flow velocity of entrance area of upstream approach channel

could satisfy the navigation requirement.

(1) Experiment Results of Discharge 865m3/s

The experimental results of discharge 865m3/s are shown in Fig.8.3-1.


30

The maximum longitudinal velocity is 0.26m/s, most of the transverse flow

velocity is below 0.15m/s, and the maximum velocity of back flow is 0.03m/s.


In the case of discharge 1500 m3/s, the experimental results are shown in

Fig.8.3-2.

The maximum longitudinal velocity is 0.15m/s, most of the longitudinal

velocity is below 0.1m/s, the maximum transverse velocity is 0.2m/s, and most

of them are between 0.01~0.1 m/s. Small back velocity is found near the right

bank, and the maximum velocity of back flow is 0.09m/s.


In the case of discharge of 3160 m3/s, the experimental results are shown in

Fig.3.3-3.

The maximum longitudinal velocity is 0.23m/s, the maximum transverse

velocity is 0.18m/s.



Fig.8.3-4.

The maximum longitudinal velocity is 0.22m/s, most of the longitudinal

velocity is below 0.1m/s. The maximum transverse velocity is 0.19m/s, and

most of them are between 0.10 m/s. The obvious back flow area is found near

the right bank, and the maximum velocity of back flow is 0.12m/s.



Fig.8.3-5.


velocity is 0.22m/s, and most of them are between 0.10 ~0.20m/s. No obvious

back flow area is found in this case, and the maximum velocity of back flow is

0.06m/s.



Fig.8.3-6.


31

It can be seen that the maximum longitudinal velocity is 0.64m/s, the

maximum transverse velocity is 0.29m/s, and the maximum velocity of back

flow is 0.12m/s. The location of maximum back flow is near bank.


In the case of 2- year return period flood of 11600 m3/s, the experimental

results are shown in Fig.8.3-7.


velocity is 0.27m/s, and the maximum velocity of back flow is 0.12m/s.

(8) Experiment Results of discharge 13200m3/s

In the case of 3- year return period flood of discharge 13200 m3/s, the

experimental results are shown in Fig.8.3-8.


velocity is 0.28m/s, and the maximum velocity of back flow is 0.13m/s.


32

Fig. 8.3-1 Velocity in Entrance Area of Upstream Approach Channel for Discharge of 865m3/s


33

Fig. 8.3-2 Velocity in Entrance Area of Upstream Approach Channel for Discharge 1500 m3/s.


34



35



36

Fig 8-6



37



38

Fig 8-8



39



40

8.3.2 Downstream Entrance Area

The flow velocities of entrance area of approach channel are shown in Fig.8.3-9~16.

It can be seen that the flow velocity of entrance area of downstream approach channel

could satisfy the navigation requirement.

(1) Experiment Results of discharge 865m3/s

In the case of minimum navigable discharge 865 m3/s, the experimental results

are shown in Fig.8.3-9.

The maximum longitudinal velocity is 0.64 m/s, the maximum transverse

velocity is 0.26 m/s.



Fig.8.3-10.


velocity is 0.27 m/s, and the back flow velocity is below 0.04 m/s.



Fig.8.3-11.





Fig.8.3-12.





Fig.8.3-13.


velocity is 0.29 m/s, and the maximum back flow velocity is 0.04 m/s.



41

In the case of flood 10000 m3/s, the experimental results are shown in

Fig.8.3-14.


velocity is 0.22 m/s, and the maximum back flow velocity is 0.21m/s.


In the case of 2-year return period flood 11600m3/s, the experimental results

are shown in Figure8.3-15.





Fig.8.3-16.



For downstream entrance area of approach channel, when discharge sluices

open for releasing flood, the main stream towards the left river bank, so the

flow in the entrance area of approach channel is relatively stable. All of the

flow velocities meet the requirement of corresponding specification, and there

is no bad effect on navigation.


42

Fig. 8.3-9 Velocity in Entrance Area of Downstream Approach Channel for Discharge 865 m3/s.


43



44



45



46



47



48



49

Fig. 8.3-16 Velocity in Entrance Area of Downstream Approach Channel for Discharge 13200 m3/s


50

9 EXPERIMENTAL CONCLUSIONS

9.1 CONCLUSIONS

Basing on the above study, the main conclusions can be drawn as follows:

(1) Dividing the discharge sluices into different zones will improve the flexible

operation of hydropower project.

(2) The sluices should be open uniformly to discharge flood. In these cases, flow

pattern of releasing flood is good, scouring in the downstream is light.

(3) The sediment deposition is far from the entrance area of navigation channel, so

its impact is little. For flood less than 3-year return period flood, flow pattern in

the entrance area of navigation channel is good and the flow velocity meets the

design requirements, if the discharge sluices open properly.

(4) There is no obvious sediment accumulation in the area no more than 100m

upstream of the discharge sluices, most of sediment will be washed away by flow,

if the sluices are opened fully to flush frequently. All sluices of zone 1, 2 and 3

have to be used together to clean up the sediment in front of zone 3.

(5) Due to the sand barrier and the training wall, the effect of sand flushing of 14#

discharge sluice is better.

(6) Basing on flush experiments with sluices opening fully for 5-year return period

flood, 2-year return period flood, as well as frequent flood, it can be seen that

sediment can be cleaned up around 150m~200m before sluices, meanwhile

sediment in the reservoir will move towards downstream, that will relieve the

reservoir deposition.

(7) Due to the bend of the upstream river, the sediment will not deposit too much

near the sand barrier, they will deposit on the right and upstream of sand

barrier to form longitudinal dunes, but dunes will low than sand barrier, and bed

loads cannot climb up the sand barrier and get into the intake of power station.

(8) Due to the high original terrain of upstream approach entrance area, as long as

sluices of zone 3 open fully regularly, sediment in this area can be wash away.

9.2 SUGGESTIONS

(1) It is suggested to set anti-scour trenches in the end of stilling basin for all sluices.

The anti-scour trenches are also suggested for right side foundation of partition


51

wall, and the length of anti-scour trench is suggested to be more than 20m.

(2) Because the sluices will be used to flush opening fully, it is not suitable to set

auxiliary energy dissipater and differential end sill.

(3) During the flood season, lower the upstream water level and open sluices fully to

flush sand, sediment can be washed away effectively. The proposed critical

discharge for opening fully is 8000m3/s.

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PAK BENG HYDROPOWER PROJECT - Mekong River Commission€¦ · Pak Beng Hydropower Project is the first cascade of the hydropower ... A stilling basin with energy dissipation by hydraulic