A well designed and operated fish exclusion screen will:
- Protect all life cycles of fish and other aquatic life
- Meet local regulation or guidelines in relation to fish protection
- Reduce pumping costs
- Improve diverted water quality
- Assist operators to follow best social and environmental practices
- Improve public image
- Require minimal maintenance
- Have low whole of life costs
If the fish exclusion screen is selected, designed and installed correctly the ongoing operation of a fish exclusion screen should NOT be onerous on labour requirements or cost.
A well designed and correctly selected fish exclusion screen should require very little maintenance and will enhance your operation by providing an intake screen that will remain clean, reducing head loss and therefore lowering pumping costs. It will also supply cleaner water, reducing the need for downstream filtering and reduces pump maintenance.
Like everything the better design and quality screens will offer the best outcomes particularly when continuously operating out of sight in a harsh environment underwater.
The material the screen is made out of is critical as is the method of cleaning. The cleaning cycle should be as slow as possible to reduce wear and tear.
As stated above a well-designed screen will require minimal maintenance, but like all machinery its operational life and performance will benefit from periodic maintenance. Different screen designs will require different maintenance regimes, below is a general guide.
What are the benefits of owning a Fish Screen?
Your fish exclusion screen means you will be operating as an environmentally sustainable water diverter, a fact you should be proud of. You will be seen as a socially responsible and environmentally focused leader in your industry sector.
If you are operating a pumped diversion it is very likely that your fish exclusion screen will reduce historical energy consumption as the inlet screen will always be clean, reducing head loss.
Diverted water quality will be improved, significantly reducing post screening/filtering processes and back washing. Also reducing nozzle blockages in sprinkler heads.
The native or sporting fish populations will grow in the natural water way producing recreational fishing and economic benefits as well as environmental benefits.
What's required to maintain a Fish Screen?
Maintenance requirements will differ from screen type and manufacturer.
The fish exclusion screen manufacturer should be able to provide you with a detailed operations and maintenance manual that will clearly articulate the scheduled and periodic maintenance required for a particular screen. Be aware that the nominated maintenance schedules must be maintained as directed/scheduled or maintenance costs will be significantly higher than expected, the screen may not be compliant and your diversion efficiency may be compromised.
A fish exclusion screen requiring regular maintenance is likely to become non-conforming to fish protection specification, reduce delivery efficiency, increase energy costs, have high maintenance costs, have high downtime, a reduced operating life expectancy and high labour input, all resulting in a high whole of life cost. Look for a quality screen with low maintenance requirements.
Prior to specification or purchase of a fish exclusion screen it is highly recommended that the specifier/purchaser seek end user feedback/references from the market to ensure they will receive the quality and support they require to obtain a high quality, low whole of life cost fish exclusion screen.
The key criteria of all screens is that they stay clean to ensure compliance with specified approach velocities and to maintain delivery efficiency (relating to energy costs when pumping and head loss with gravity diversions). The cleaning system is usually a mechanical process and where the majority of maintenance requirement is derived from. The other primary factor to monitor and mitigate is corrosion. Depending on the screening material, if it is not made of robust material it may also require maintenance or replacement.
There are two primary ways to ensure your screen is maintaining the performance criteria specified.
- Retrieve the screen and visibly inspect it for cleanliness of the screen surface and check for damage. The screen surface should never be contaminated (always clean).
- Monitor the diversion delivery efficiency by closely logging energy usage on pumped systems. An energy curve can be established using a known clean screen performance criteria against various flows vs energy use. This curve can be monitored to ensure energy use matches the ‘clean screen’ curve, if energy use increases it would indicate the screen is not clean and should be immediately inspected. On a gravity diversion, logging various flows vs head loss may also highlight potential restrictions.
Visual inspection at least every 12 months will assure the user and legislative authority that the screen integrity is intact (no orifices larger than specified) and that the screen is clean, indicating diversion velocities will be as designed and specified.
If there has been a major event in the water way such as extensive algal bloom, icing, unusually heavy debris, excessively high suspended solids, flood etc. then it would be advisable to inspect your screens immediacy post these events.
Depending on the auxiliary equipment supporting a viable fish exclusion screen there will be other maintenance considerations. They could include periodic:
- Debris removal after floods or other events
- Anode replacement (if fitted)
- Visual check of the mechanical components
- Inspection of wiring harnesses or hydraulic hoses
- Inspection and testing of any rotating components
- Checking for oil leaks, hydraulic drive or gearbox
- Any air or water hose pipe fittings
- Inspect for corrosion of any ferrous metal parts and coating integrity
- Physical damage
If oil is used in a gearbox or hydraulic drive system it should be an environmentally friendly oil. Ideally gearboxes should be grease filled.
If a screen is submersed deeper than 3m it may have an equalising bladder or some other arrangement on its gearbox to equalise internal pressures. This device is another item to check during maintenance.
Periodical maintenance: should be carried out at a minimum to the screen manufacturer's nominated schedules. It should also be wise to inspect a screen prior to a seasonal event or anytime that the screen has been non-operational for a prolonged period of time.
Flood events: Consider carrying out inspection and maintenance prior to flood event, if you plan on pumping during a flood event. Your screen will be challenged during a flood event due to higher surrounding velocities and changed hydraulic conditions, increased debris and suspended solids etc. It may be difficult to carry out inspection and maintenance during flood events so you want your screen in optimal operating condition during these times.
Retrieval systems: allow the screen to be raised to the surface for safe and efficient inspection. Retrieval systems can include submersible pontoons, track systems with winches or various other types. If well designed and manufactured, these retrieval systems will be virtually maintenance free due to the very low usage. Visual inspection of infrastructure including pipes, cables etc. once a year would be sufficient.
NOTE: If the screen system does not include a retrieval system and inspection/maintenance is required, divers would have to be used, or cranes brought in which is typically expensive and increases safety risk profiles. Again always refer to the fish exclusion screen operation and maintenance manual supplied by the screen manufacturer and always maintain the screen as per the scheduled maintenance. If you do this and you have purchased a quality screen in the first place you will have a low maintenance, low cost long service life from your screen.
