1. Operations, Maintenance & Testing
Importance of Gate Reliability
Ensure safe passage of floods
Allow emergency dewatering of reservoir
Permit control of storage level
Provide supply to downstream users
For dams that have spillway gates, they will most likely play a critical role in operating and ensuring the safety of the dam. This is because they may be required to:
Ensure the safe passage of flood waters
Dewater the reservoir in emergency situations (e.g. for significant earthquakes), and to
Manage reservoir levels through controlled releases.
Gates by their very nature have inherent reliability issues and a gate may sit idle for long periods of time and then be expected to work flawlessly during a sudden flood event.
Critical gates are therefore required to have a high level of operational readiness and reliability.

2. Important O&M aspects to achieve desired reliability
Operations
Operating procedures
Operations Plan
Inspections
Training
Maintenance
Testing & Exercising
To ensure the desired levels of reliability it is important that appropriate operation and maintenance measures are put in place such as:
an Operations Plan and relevant procedures for:
Inspections
Training of operators and other relevant personnel in all aspects of the equipment
Maintenance, and for
Testing and Exercising.
Evidence of poor maintenance

3. Spillway Gate reliability processes and components
SPILLWAY GATE RELIABILITY REQUIREMENTS
SPILLWAY GATE COMPONENTS
Data System
Acquisition
Data
Processing
Control &
Comm.
Power
Supply
Hoist
Unit
Gates
Support
Structures
KEY PROCESSES
Design
Ensure designed to a standard for the acceptable level of risk
Supply & Construction
Is in accordance with design drawings and to an adequate standard of quality
Maintenance
Regular preventative maintenance
Inspection
Periodic audit of equipment
Operation
Gate operation in accordance with clearly defined procedures
Testing
Periodic testing of all equipment and systems
Training
Regular training of all staff involved in gate operation
As an example, this table from a document produced by the NSW Dams Safety Committee in Australia shows the key processes and components of spillway gates that they recommend for ensuring a reliable system.
NSW Dams Safety Committee: DSC3D Reliability of Spillway Flow Control Systems. June 2010

4. O&M challenges Limited ability to inspect parts of gate
Out in the open weather
Made of corrosive materials
Infrequent use
Requirement for high reliability
Need to be always available for floods
Expectations for long service life
Was the gate designed and constructed properly
What condition is the equipment really in
What is the chance of the gate sticking open
Here is a list of some of the challenges we face in having to deal with operating and maintaining gated dams.
Spillway gates are normally exposed to inclement weather and are usually constructed of materials that are subject to corrosion. We expect them to have a long service life but in some cases they would normally only be required to operate infrequently but when we do want them to operate we expect them to do so properly. This requires a big ask and therefore we need to do the things that will provide them with a high level of reliability.
In addition, there may be limited information available about their original design and construction and as parts of the gate may have limited ability for inspection do we really know what condition all the equipment is in.

5. Responsibilities Dam Owners Engineers and other specialists Operators
In regard to responsibilities, dam owners have the ultimate responsibility for the safe operation of their dams under all circumstances so as to protect the downstream population from adverse consequences resulting from gate mal- operation or a dam failure.
Owners are therefore required to ensure that appropriate procedures and practices and suitably trained and skilled resources are available to operate the dam safely under all conditions.
Engineers would assist in the development of procedures and maintenance practices and would be involved in the witnessing of gate inspections and testing and in reviewing performance monitoring data.
Operators are obviously responsible for operating the gates and for the initial identification of problems should they occur. They need to be fully conversant with gate operations and should be adequately trained and experienced in gate operations during both normal and unusual events.
Poor maintenance showing lack of greasing

6. Inspection of Gate Equipment - Planning
Plan well in advance
Obtain relevant checklists
Identify critical areas to inspect
Consider equipment criticality, frequency of inspections
How to access? (dewatering, disassembly, divers)
Review drawings
Consider performance history
Talk to Operators, the experience of the operators is invaluable
Determine what to monitor
Determine resource requirements
As listed on this slide, before an inspection or exercising of a gate it is very important that proper planning takes place. This should involve all relevant personnel and should include a review of all available information including a gate’s performance history.
The team needs to decide exactly what is to be done, how it is to be done and what is to be inspected and monitored. Appropriate procedures and checklists should be made available.
Sometimes access or ability to operate can be difficult

7. Operational Documentation
Operations Plan
Operating procedures
Clearly defined responsibilities
Records
Gate operating procedures should be well written and easy to understand and should be regularly reviewed and updated.
Operational procedures should cover all three types of events, namely:
Normal operations
Unusual events such as floods, and
Extreme or Emergency events such as dewatering following a damaging earthquake.
A set of gate operating rules should be established for flood events to define the factors and logic that shall be used to determine gate opening rates. This should involve hydrologists, flood and dam safety engineers and operational staff.
Where responsibilities are shared, the Operations Plan should clearly identify these responsibilities to avoid confusion. The contents and level of detail of an Operations Plan would depend on the nature of the dam and the criticality of the equipment.
Need well documented procedures for such works

8. Inspections and routine operations
Involve all aspects & critical components
Involve all modes of operation
Inspection types
Routine (operators)
Intermediate (e.g. annual)
Periodic
Training
Access arrangements
Regular inspections and periodic gate operations are critical activities:
To provide confidence that the gates will operate when required
To improve gate reliability, and
To improve operator’s knowledge and capability for all events.
These measures should involve all aspects of the gates (i.e. all critical components and modes of operation). To improve gate reliability it is very important that a suitable number of back-up operating systems are available and that the potential for common cause failures is minimised.
Gate inspection types can consist of:
routine
intermediate (e.g. annual), and
periodic that would involve more detailed inspections.
It is desirable to have good access to all parts of a gate, as can be seen in the photo, as this facilitates better inspections.
The equipment itself and human factors can both affect gate reliability. Training is therefore very important. Major floods may occur very infrequently for some dams. Operators therefore may not have experienced a major flood event and so it would be important to run simulation exercises as well.
A recent worldwide trend has been a reduction in the manning levels at dams and greater reliance on remote operations. Such decisions must be made in light of their impact on gate reliability and the safety of the dam particularly during flood events.
Example of good access arrangements

9. Preventive Maintenance Schedule - Crest Gates Equipment
Maintenance manual and procedures
Types
routine preventative (e.g. periodic or condition based)
corrective
Condition Monitoring
Documentation of results
Critical spares
Preventive Maintenance Schedule - Crest Gates Equipment
Equipment Item
Location
PM No
Type
Frequency
DIESEL GENERATOR
Emergency Generator, Portable
M061
MINOR INSPECTION, CLEAN & LOAD CHECK 1
SWITCHBOARD, 415V
Dam Crest East
E049
INSPECTION 12
MOTOR, 415V – INSPECTION
Pier - Lower Chamber
E052
RADIAL GATE – INSPECTION
Dam Crest - Access Shaft
M118
OPERATOR INSPECTION
RADIAL GATE – LUBRICATION
M180
INSPECTION AND LUBRICATION 6
LEVEL TRANSMITTER
Pier 16 Middle Chamber
E122
It is important to have a Maintenance Manual and/or System that contains all appropriate maintenance procedures and checklists for monitoring gate performance.
Maintenance ranges from routine preventative maintenance involving check inspections, adjustments, lubrication etc. through to the less frequent major overhauls. Corrective Maintenance is undertaken where problems arise or where performance monitoring dictates.
A schedule, as per the sample shown here, should be prepared for all routine and preventative maintenance activities. Records should be kept of all maintenance activities, repairs and condition monitoring data.
The non-routine and more complex tasks would normally be undertaken by skilled maintenance persons however there is benefit in operations staff being involved and witnessing maintenance exercising.
The availability of adequate critical spare parts is another important aspect in ensuring operational readiness of equipment.

10. Exercising/Testing Extent of operation (i.e. opening range, head)
Frequency
At least once/year
Monthly for critical equipment
Full test every 5-10 years
Procedures
Documentation of results
Gate tests must demonstrate the reliability of the complete system
Measure vital statistics:
Unusual noise or vibration
Motor currents
Trunnion friction
Clearances and movements
Hoist loads
Periodic testing and exercising of gates is another very important activity and such testing could identify issues requiring non-scheduled maintenance or repairs. It is better to identify such issues during a planned test rather than during an actual flood when staff are under far more pressure with little time available to resolve and correct faults.
It would be ideal to operate gates through their full range of travel under maximum loading conditions and utilising all normal and back-up modes of operation. In many cases this may not be practical for a number of reasons but it is recommended that gates should still be operated under full head for a small range of opening (say 300 to 600mm) and also for their full travel in the dry.
The type and frequency of exercising of gates would depend on:
the type and function of the gate
its criticality to the safety of the dam, and
the consequences of miss-operation or non-operation of the gate.
A higher frequency should be applied for dams that critically depend on the spillway gates to pass floods and are required to be in a continuous state of operational readiness. Some sample frequencies for important gates are provided on the slide.
Exercising and testing of gates should:
Have the planned tests discussed amongst all involved personnel
Have their performance monitoring recorded and compared to historical values and trends
Be used as a means of training of resources
Be witnessed by all appropriate resources
Include the testing of all critical gate operating and control systems.
The proposed ICOLD bulletin will provide guidance on typical inspection, exercising and testing frequencies for spillway gates.
Access to enable up-close detailed inspection

11. Conclusions Importance Benefits We want to prevent this!
In conclusion, as I have described, appropriate inspections, operation and testing of gates will result in an improved level of reliability and should be given the upmost level of attention.
Historically, mechanical and electrical equipment may not have been given the degree of attention that it should have in comparison to concerns about the dam itself and with the possible misconception that the gates will always operate as intended. This is more likely to be the case where the gates have operated far less often.
Several actual cases have shown that by increasing the frequency and extent of exercising, the number of identified gate incidents has initially increased demonstrating that the gates were not as reliable as first thought.
However, by having identified and fixed these issues under controlled conditions future reliability was shown to have improved.
We want to prevent this!