(A Dam Operation Method Using Only Reservoir Water Table) · - The timing to start flood discharge is the time the operation transfers from water supply stage to Pre-flood regulation

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A GATE OPERATION METHOD FOR DAMS WITHOUT SUPPORT FACILITY

(A Dam Operation Method Using Only Reservoir Water Table)

Please contact with Dr. Nguyen Son Hung for details

[email protected]

April 2016

mailto:[email protected]

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A GATE OPERATION METHOD FOR DAMS WITHOUT SUPPORT FACILITY

(A Dam Operation Method Using Only Reservoir Water Table)

(1) There are a lot of earthdams with spillway gates, but no budget to build an operation

support system that measures /calculates inflow, discharge etc. and guides gate operators

how to do when floods come.

(2) There is in short supply of experienced experts/engineers for dam operation.

(3) Due to lack of experience, dam operators sometimes have caused very rapid discharges

that brought on serious damages of human and asset to the downstream. Namely, the dam

operations have caused human -made disasters.

(4) Dambreaks by poor operation have happened due to top dam overflows.

(5) Dam operation rules and regulations define the reservoir water levels or rules to be kept

with but they have no description for how to do to achieve them.

(1) Dam operator may operate easily and effectively with using only reservoir level and

diagrams already prepared based on the actual rules and regulations of dam operation and

the hydrological and hydraulic features of reservoir, its catchment and downstream river

channel.

(2) Rapid discharges will be avoided and anybody who operates will have the same result.

Namely, it does not require any skill or experience of the operators. Therefore, the

operators will have not any mental stress due to dam operation.

Figure 1 shows an example of the method (herein, we call as Imamura method) used in the

case dam has no operation support system, namely, using only reservoir water level with its

diagram to operate spillway gates.

The main gate operation to large floods may be sepetated into the following four stages: (1)

Pre-flood regulation stage, (2) Flood regulation stage, (3) Pre-emergency stage and (4)

Emergency stage. The diagram is used to operate for the four operation stages as follows:

-Pre-flood regulation stage-

Role and difficulty: The crucial roles of this stage are (1) Not starting flood discharge too

early to advoid waste water discharge, and (2) Not delaying the appropriate timing to start to

flood discharge to avoid afterward having to implement very rapid flood discharge so the users

of downstream river have no enough time to evacuate from its river water level increase due to

the flow discharge from the dam. Because these two roles conflict with each other, it is difficult

to determine the appropriate timing to start flood discharge.

Solution:

-The light blue vertical line in Figure 1 shows the stage of water supply (domestic and

irrigation or power generation), the supply flow is always constant.

DO YOU/YOUR ORGANIZATIONS FACE THE FOLLOWING ISSUES?

WHAT IS THIS METHOD USEFUL FOR?

AN EXAMPLE OF DIAGRAM USED TO OPERATE SPILLWAY GATES

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- The black dashed cuves shows the candidate relationships between discharge and reservoir

water level (herein call the Qo-H relationship) of dam operation, namely, each curve of them

defines the flow to discharge for corresponding revervoir water level, in the Pre-flood regulation

stage.

- The timing to start flood discharge is the time the operation transfers from water supply

stage to Pre-flood regulation stage, namely, traferring from the light blue vertical line to a curve

of the black dashed curves.

- To define the transfer timing, the reservoir water level increment △H in the given time

interval △t will be used. Namely, when the point describring a pair of reservoir water level and

its increment, namely (H, △H) approaches nearly to one of intersections of light blue vertical

line and black dashed cuves, the transfer shall be done. In Figure 1, the transfer timing and the

Qo-H relationship after being transferred are respectively described by the point and curve of

purple color. By this method, the opearation will avoid the very rapid flood discharge and

transfer to the Flood regulation stage without delaying.

Pre-flood control operation stage

-Flood regulation stage-

Role and difficulty: The crucial roles of this stage are (1) Not starting the Pre-emergency

stage too early in order to positively decrease discharge flowing to the downstream river, and (2)

Not delaying the appropriate timing to start the Pre-emergency stage to assure enough time for

downstream people to evacuate from flooding and to avoid the top dam overflow that will cause

dambreak. Because these two roles conflict with each other, it is difficult to determine the

appropriate timing to start the Pre-emergency stage.

Solution:

- Using the blue curve to operate spillway gates in the Flood regulation stage.

- The black dashed cuve group in the Pre-emergency stage of Figure 1 shows the candidate

Qo-H curves in this stage.

Discharge of spillways R

eser

vo

ir W

ater

Lev

el

Qi

Qo

H1

QoS

Q

t QoS Qo

Spillway crest

Normal WL in flood term

WL of 1/200 flood

WL of 1/100 flood

QoS Water supply

H1

Hn

Spillway crest

QoS Water supply


WL of 1/200 flood

WL of 1/100 flood

QoS

Q

t

Normal WL

△H

Hn

Discharge of spillways QoS QoC

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- To define transfer timing to the Pre-emergency stage, the reservoir water level increment △H

in the given time interval △t will be used. Namely, when the point describring a pair of

reservoir water level and its increment, namely (H, △H) approach nearly to one of intersections

of the blue curve and black dashed cuves, the transfer shall be done. In Figure 1, the transfer

timing and the Qo-H relationship after being transferred are respectively described by the point

and curve of orange color. By this method, the opearation will avoid the very rapid discharge

and transfer to Emergency stage without delaying.

Flood control operation stage

-Pre-emergency and Emergency stages-

Roles: Avoiding the top dam overflow that will cause dambreak.

Solution: Operating with using the orange and red curves of Qo-H relationship.

Pre-emergency and Emergency operation stages

In the case the actual operation rules may be changed or there is a budget to install operation

support system, we may propose new rules and systems based on the high-level Imamura method

to use more effectively existing reservoir based on our professional experiences.

FOR MORE EFFECTIVE USE OF RESERVOIR STORAGE

WL of 1/100 flood

WL of 1/200 flood

Normal WL

Hpe

Qof Qope

QoD

△H

Discharge of spillways

QoC

QoS

Q

t

QoS Water supply

Spillway crest


Hpe

WL of 1/100 flood

WL of 1/200 flood

QoD

QoI

WL of 1/200 flood

Normal WL

He

Qoe

Qope

QoC


WL of 1/200 flood


Spillway crest

He

QoS Water supply

QoS

t

Q

WL of 1/200 flood

Normal WL

WL of 1/100 flood

Hf

Qof QoD


QoC

QoS

Q

t

Hf

Spillway crest


QoS Water supply

WL of 1/100 flood

4

WL of 1/200 flood


Res

ervo

ir W

ater

Lev

el

Qi

Qo

H1

QoS

Q

t QoS Qo

Spillway crest


WL of 1/200 flood

WL of 1/100 flood

QoS Water supply

H1

Hn

Spillway crest

QoS Water supply


WL of 1/200 flood

WL of 1/100 flood

QoS

Q

t

Normal WL

△H

Hn

Discharge of spillways QoS QoC

Normal WL

WL of 1/100 flood

Hf

Qof QoD


QoC

QoS

Q

t

Hf

Spillway crest


QoS Water supply

WL of 1/100 flood

WL of 1/100 flood

WL of 1/200 flood

Normal WL

Hpe

Qof Qope

QoD

△H


QoC

QoS

Q

t

QoS Water supply

Spillway crest


Hpe

WL of 1/100 flood

WL of 1/200 flood

QoD

QoI

WL of 1/200 flood

Normal WL

He

Qoe

Qope

QoC


WL of 1/200 flood


Spillway crest

He

QoS Water supply

QoS

t

Q

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FIGURE 1 GATE OPERATION WITH RESERVOIR WATER LEVEL

42.5

43

43.5

44

44.5

45

45.5

46

46.5

47

47.5

48

48.5

49

0 200 400 600 800 1000 1200 1400 1600

Re

se

rvo

ir w

ate

r le

vel (

m)

Discharge of spillways (m3/s)

Water supply

PRE-FLOOD REGULATION OPERATION

FLOOD REGULATION OPERATION

PRE-EMERGENCY OPERATION

Discharge curve (Free flow) of Spillway No.1

Discharge curve (Free flow) of Spillways No.1 &

No.2 EMERGENCY OPERATION

QoS

Water Level (Flood 1/100)

QoDmax

Water Level (Flood 1/200)

Normal water in Flood Term

QoC QoImax

△H=0.02 m

PRE-FLOOD REGULATION OPERATION STAGE:

+ Water supply with the light blue curve

+ Based on H & △H to determine the timing to begin

the flood discharge

+ After that operate with the purple curve.

Note:

+ H: Reservoir water level

+ △H: Reservoir water level rise in the given time

interval (herein 30 minutes)

EMERGENCY OPERATION STAGE: open all gates

PRE-EMERGENCY OPERATION STAGE: + Operate with the orengy curve

Gate openings of spillway No.2

Gate openings of spillway No.1

FLOOD REGULATION OPERATION STAGE: + Operate with the blue curve

+ Based on H & △H to determine the timing to transfer to PRE-EMERGENCY OPERATION

Normal water level in No Flood Term

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(A Dam Operation Method Using Only Reservoir Water Table) · - The timing to start flood discharge is the time the operation transfers from water supply stage to Pre-flood regulation