A Method of Sediment Transportation
by Special Ejector Pump System in the Dam Reservoir
Yuji Nakamura,, Toshio Okabe, & Toshiyuki Temmyo, Dr. Eng.
Hazama Corporation, Japan
nakamurayu@hazama.co.jp

Tokujiro Yamashita, Mutsuhiro Kaku & Yuya Yamagami
Kyushu Electric Power Corporation, Japan

Osami KurokiWest Japan Engineering Consultants, Japan

Tetsuya Sumi, Dr. Eng. , Sameh Ahmad Kantoush, Dr. Eng. & Mohammad Meshkati
Disaster Prevention Research Institute, Kyoto University, Japan
ABSTRACT:
Several techniques have been applied to reduce the sedimentation problems in the reservoirs such as: flushing, bypassing, density
current venting and dredging, which practiced successfully and found to be inexpensive in some cases. This paper mainly deals withthe filed case studies of a dredger system that newly developed in Japan. This system is composed of Special Ejector and that is why
named Special Ejector Pump System (SEPS). The SEPS has two specific applications. One is called Suction-SEPS, which sucks
deposit sediment up from the bottom of reservoir and then transports them to the downstream area. The other one is called
Hopper-SEPS, which transports sediment from a specific site to a disposal site without any suction, called Hopper-SEPS. For
Suction-SEPS tests, the sediment suction and transportation rate was approximately 35 m3/h. While, for Hopper-SEPS, the measured
sediment transport rate was approximately 50 m3/h and 30 m3/h for 600 m and 1000 m transport length respectively.
Keywords: Sediment Management Strategy, Sedimentation, Dredging, Ejector Pump

1. INTRODUCTION
For reducing the drastic consequences of sedimentationin the reservoirs and sustaining its long-term useful lifeof a reservoir, de-siltation has received worldwide
attention owing to the lack of suitable dam sites, the highcost of dam construction, strict environmental regulations
and resident’s resistance. Therefore, it is necessary todevelop ingenious solutions for integrated sediment andwater management; otherwise the human being will lose
the struggle to enhance the available water resources andecological environment.
Several techniques have been proposed by researches tosolve the problems of sedimentation in reservoirs;
including flushing, bypassing, density current venting,dredging and etc, which all can play an important role inextending the useful life of dams. Nowadays, dredging
method is commonly utilizing in dam reservoirs. This
technique is considerably efficient; because it can dredge
sediment from reservoir continuously without any stop.
However, usual dredging pump with impeller is hard to
excavate the deposit sediment at the bottom of reservoir
due to the large number of big size gravels and rubbish
accumulated there. To solve the problem of usual dredger
pump and enhance the efficiency of sediment removal inthis method, a Special Ejector Pump System (SEPS) has
been developed by authors. This system is composed ofspecial ejector and that is why named SEPS. Fig. 1
shows the schematic side view of special ejector inSEPS.
The SEPS is designed, to be able to utilize for two main
purposes: first to suck deposit sediment up from thebottom of reservoir and then transport them to thedownstream area, called Suction-SEPS; and second, totransport sediment from a specific site to a disposal site
without any suction, called Hopper-SEPS.

NozzleAir controller inlet

Discharge

Jet water

Inner pipeSuctionFigure 1. Schematic Side View of Special Ejector

In previous field tests, the maximum size of gravel thatremoved by SEPS was around 150 mm. However,commercial version of SEPS needs to be applicable forremoving coarser sediment larger than 150 mm. Thus,
new filed tests trials were conducted aim to enhance theefficiency of SEPS, to be able to remove coarser
materials from reservoir.

2. SUMMARY OF APPARATUS
The SEPS is distinguished by several unique innovations
for its special ejector as well as its structurally simple
and easy to maintain design. In contrary to usual dredger
system, there is no rotary part (impeller wheel) inside of
the special ejector. The energy to vacuum sediment isprovided by differential pressure between inside of
special ejector and bottom of reservoir. The commercial
SEPS includes five distinct sections: high pressure pump,special ejector, air compressor, suction section andtransport section. The details about each section and theirfunction were given below.

Figure 2. High Pressure Pump

2.1. High Pressure Pump
A high pressure pump supplies water jet with highvelocity into the special ejector in the pump system. This
unit run with 220kW power engine aims to create apressure equivalent with 1.5MPa (5 m3/minute flow rate).
The high pressure pump used in this field test was shownin Fig. 2.

Figure 3. Special Ejector

2.2 Air Compressor
In order to transport sediment effectively, air wasinjected into the system by air compressors, which wasinstalled at the beginning of transport pipeline just after
special ejector.
2.3. Special Ejector
The special ejector is known as heart of SEPS. As
mentioned above, pressure gradient between inside of
special ejector and bottom of reservoir leads to sediment
suck up to the system. To create a negative pressuredomain inside of special ejector, the high pressure pumpshould discharge water jet with high velocity into thespecial ejector through a tiny nozzle. Then, the pressure
gradient between the entrance of suction pipeline andinside of special ejector vacuums the mixture of sedimentand water into the system. Thereafter, the sediment will
be pushed forward into the inner pipeline and finallytransports to the downstream area.
It notes worthy to mention, special ejector is also
equipped by two specific accessories: air controller inletand a straight inner pipeline. Both tow above mentioned
accessories are very effective to preserve special ejector
against the cavitations and abrasion resistance of thepump. By changing the combination of diameter ofFigure 4. Screw Crusher

Figure 5. Screw Crusher with Long Armed Excavatornozzle, diameter of inner pipeline, the suction rate ofSEPS can easily be adjusted. The outside view of special
ejector is shown in Fig. 3.
2.4. Suction Section
The suction section includes an excavator arm, a screw
crusher and a suction pipeline. The excavator arm wasused to bring down the suction pipeline deep inside thereservoir and keep its entrance close to the sedimentsurface. A screw crusher was also attached to theexcavator arm to crush deposit gravels and ease theirsuction by SEPS. The screw crusher’s shaft was conicalshape, which could crush the gravels placed between
conical shaft and lining plates in the shell. The gravels
with maximum size of 300 mm could be crushed withscrew crusher’s shaft. The used screw crusher and long
excavator arm are shown in Fig. 4 and Fig. 5,respectively.

Sediment

2.5. Transport Section
The transport section was consisted of pieces of pipewith 6m length and 400mm diameter, which connected toeach other by rubber pipe with 1m length. To make thetransport pipeline float on water surface, 2 sets of float
tube were attached to the each individual tube.

3. FIELD TESTS PROCEDURE
Field tests were conducted for both two type of SEPS,
Suction-SEPS and Hopper-SEPS. In this part, the tests
procedure was given in details. The image of the system
is shown in Fig.6.
3.1. Test Procedure for Suction-SEPS
Several places in the reservoir area were considered as atarget site for dredging with different water depth< Hopper-SEPS >HopperSuctionBelt conveyor

Pressure WaterCompressor
High pressure pump

P1

P3
P2

Special Ejector
High pressure pump

Dispenser
Outlet transportation pipe,
400 mm in diameter

Q1

Dam Reservoir

Excavator withScrew Crusher
Q2< Suction-SEPS >Figure 6. System Image of the SEPS

Figure 7. Overall view of Suction-SEPS

ranging from 4 to 9 m. Also, different suction pipeline
length (5, 10, 15 and 20 m) was used to check theperformances for suction of sediment.
Overall view of Suction-SEPS and dredging shipboard isshown in Fig.7 and Fig. 8 respectively. High pressure
pump and air compressor (18 m3/min) were set to injectdifferent values of water and air rate into the system,
respectively from 1 to 3 set of high pressure pumps and 0
to 1 set of air compressor. When the target place fordredging was deeper than 10m, to suck up sediment
effectively, the special ejector was tried to install under
the water. These tests were executed with some extra
modifications and adjustments. The total numbers of test
cases was 58.

Figure 8. Shipboard of Suction-SEPS

3.2. Test Procedure for Hopper-SEPSIn Hopper-SEPS tests, sediment was fed into the systemthrough a hopper installed above special ejector. The
used Shipboard of Hopper-SEPS in this field test isshown in Fig. 9. As can be see in Fig. 9, the hopper, belt
conveyor and SEPS was mounted on the shipboard.
In this case, the maximum transportation length wasconsidered 1000 m. To transport sediment in longer
distance, considerable amount of air was injected into thetransportation pipeline to assist the sediment through it.
In order to release the transported sediment into thereservoir, as shown in Fig. 10, a distributor is set at theend of transport pipeline. Silt fences of 5m in depth areinstalled to avoid water pollution.

Figure 9. Shipboard of Hopper-SEPS

Since Hopper-SEPS test is executed nearby the test fieldfor Suction-SEPS, the characteristics of both of thesediment are almost same. However, since original
sediment included big size gravels, it was screened by asieve with 120 mm and 80mm mesh, which are called D150 mm and D 100 mm respectively. The sediment grain
size curve is shown in Fig. 11. The tests were conductedusing various transport length, different sediment grainsize, dissimilar diameter of the nozzle and inner pipeline.

4. PARAMETERS & MEASUREMENT DEVICES

1) Initial discharge (Q1, m3/min) measured by flow
meter.
2) Initial pressure of water (P1, MPa) measured bypressure gauges (which both initial discharge andinitial water pressure were supplied by high pressurepump).
3) The negative pressure in the special ejector (P3, MPa).
4) The pressure at the initial point of the outlet pipeline(P2, MPa).
4) Flow rate of suction pipeline (Q2, m3/min).
5) Air injected concentration into the transport pipeline

100
Original

80
Passing Percentage（％）

The main parameters and used measurement devices are
as follow:

Figure 10. Shipboard of Distributor

D=150mm
D=100mm60
40
2000.010.1

1
10Sieve Size （mm）

1001000

Figure 11. Grading Distribution of the Sediment(A, m3/min) which measured by air flow meter.
The locations of the each instrumentation are shown inFig. 6.
50

3Sediment Transportation Rate S （m /h）Ejector is on the ship
Ejector is on the ship (at the end of dredging)
Ejector is under the water

5. RESULTS AND DISCUSSION
5.1. Results of field test on Suction-SEPS
Two sets of high pressure pump were used in this field
test. Although some instrumentations were partially outof order, the initial water pressure provided by highpressure pump ranged from 1.40 MPa to 1.55 MPa, anddischarge flow rate ranged from 10 m3/min to 11 m3/min.
Additionally, P2, P3 and Q2 were set to be in the range of0.08 MPa to 0.18 MPa, -0.04 MPa to -0.08 MPa and 7.9m3/min to 12.0 m3/min respectively.
The relationship between water depth and sedimenttransportation rate taken from all data was plotted in Fig.
12. Sediment transportation rate is defined as the volumeof landed sediment from the bottom of the reservoir per
one hour. When Suction-SEPS tried to suck up sedimentfrom a deeper area in reservoir, the suction rate wassignificantly reduced. For instance, in case of suction
pipeline with 20 m length when the sediment discharge
was equal to 25m3/min, blockage in the system has often
happened. The reasons why transported rate of system
was reduced by increasing suction pipeline length are
discussed below:

4030201000246810Water Depth H （m）

Figure 12. Water Depth and Sediment Transportation Rate(1) Initial Stage

1) A longer suction pipeline length causes more lose ofenergy and consequently less transported rate value.
2) Since fine sediment is easily transported and coarse
gravel is tend to remain on the reservoir bed, as the resultof the continuous dredging works, the sediment grading
size has changed. Namely, the big pieces of gravel areconcentrated in the bottom of the reservoir, and theyobstructed continuous dredging as shown in Fig. 13. The
performance of dredging works is substantially depended
on the condition of the bottom of reservoir.
Fig. 12 depicts that when special ejector was installed
under the water surface, the greater values oftransportation rate was measured. It proves that theshorter suction pipeline can provide more advantages forthe system.

(2) Middle Stage(3) Final Stage
Figure 13. Bottom of the Reservoir during Dredging

Fig. 14 shows the representative sediment grain size andrubbishes, which was sucked and transported by
Suction-SEPS to the disposal site. The Suction-SEPS
was able to remove gravels with maximum 200 mm
diameter and woods with 500 mm length.
5.2. Results of field test on Hopper-SEPS
Fig. 15 shows the pressure at the beginning of thepipeline versus transportation rate of Hopper-SEPS withdifferent transportation length. Sediment transportation

Figure 14. Sucked Gravels and Debris

3Sediment Transportation Rate（m /h）

8060
40200m20600m
1000m

00.00

0.10

0.20

0.30

Pressure P2 （MPa）

Figure 15. Pressure at the Beginning of the Pipeline
versus Sediment Transportation Rate

1003The air concentration injected into the transportation
pipeline was equal to 36 Nm3/min and 54 Nm3/min for
600 m 1000 m transport pipeline, respectively. Since theinitial water discharge into the system set around 10m3/min, then the injected air concentration in system wasapproximately 3 to 6 times of water discharge. The
measured transportation rate was around 30 m3/h and 50
m3/h for 600 m and 1000 m transport pipeline length,
respectively.

100Sediment Transportation Rate S （m /h）rate is proportional to pressure, P2 by each transportation
length. When the pressure at the beginning of pipeline ishigher, transportation rate is higher. On the other hand,
the relation between the pressure at the beginning of thepipeline divided by transportation length (P2/L) andsediment transportation rate (S) is shown in Fig.16.
Sediment transportation is also proportional to P2/L. The
transportation rate is inversely proportional to thetransportation length. It is found that to transport
sediment long distance and to increase the transportation
rate, enough pressure at the beginning is important.

6. CONCLUSION
The sediment suction and transportation rate by
Suction-SEPS were approximately 35m3/h, and thesediment transportation rate by Hopper-SEPS was
30m3/h and 50m3/h for 600 m and 1000 m transport
length respectively. Above mentioned sediment dredging
and transportation system can be effectively used at damsites without any interruption in their daily operations.
Field research efforts show that this system could beeffectively applicable as a countermeasure to solve thesediment problem in reservoirs. At last but not least, theauthors hope that this newly upgraded system contributes
to the supply of sediment at downstream area ofreservoirs, and is considered as a positive jump forenvironmental remediation of rivers.
REFERENCES
Temmyo, T. et al., (2009): Enhancement of Hydrological
Safety of Dams by New Sediment Transportation System“SAND STORM”, International Symposium for the 6thEADC, pp.183-190.

80

60

40

200
0.0

0.2

0.4

0.6

0.8

1.0Pressure P2 / Length L （MPa/km）

Figure 16. Pressure at the Beginning of the Pipeline
Divided by Transportation Length versus SedimentTransportation Rate