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Appendix 1 - Screening Irrigation Offtakes in the Murray-Darling Basin to Reduce Loss of Native Fish 79

Appendices

Appendix 1

Review paper not presented at the Workshop but included as a resource document

Screening Irrigation Offtakes in the Murray-Darling

Basin to Reduce Loss of Native Fish

Tim Blackley

30th May, 2003

EXECUTIVE SUMMARY

Fish protection screens are installed at irrigationdiversions to prevent the entrainment of fishinto the offtakes. Despite the heavy reliance ofirrigation in the Murray-Darling Basin, to datethere are no fish protection measures in place.This report identified different techniquesavailable to screen irrigation diversions, andhighlighted some of the important designelements. This included investigation of:

• Types and applications of fish screens

• Fish screen design

• Placement of fish screening structures

• Debris control measures

From these elements, recommendations on themost appropriate types of screens for irrigationdiversions in the Murray-Darling basin havebeen made. This project demonstrates theprocess by which the most appropriate fishprotection screen can be selected for a givensituation. While there is information to guidethe design of fish screens available, currentlythere is no information specific to the Murray-Darling Basin. There is a need to conduct acomprehensive study of native fish movementsand biomechanics in the Murray-Darling system,in order to develop a set of design guidelinesappropriate for the region. Without this, anypreliminary screening attempts may prove to beineffective.

ACKNOWLEDGMENTS

I would like to acknowledge and thank TonyLadson, of the Department of Civil Engineering,Monash University, for his guidance andsupervision in the undertaking of this project.His support has been invaluable, not only intechnical expertise but also in encouragementand motivation.

Ap

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dices

Appendix 1 - Screening Irrigation Offtakes in the Murray-Darling Basin to Reduce Loss of Native Fish80

Table of Contents

1. Introduction 81

2. Fish Screens – Types and Applications 82

2.1 Rotary Drum Screens 82

2.2 Vertical Fixed Plate Screen 84

2.3 Vertical Travelling Screens 85

2.4 Non-Vertical Fixed Plate Screens 85

2.5 Pump Intake Screens 87

2.6 Infiltration Galleries 89

2.7 Experimental Behavioural Devices 90

3. Fish Screen Design 90

3.1 Approach Velocity 90

3.2 Screen Size 92

3.3 Screen Materials 92

3.4 Sweeping Velocity and Screen Orientation 93

3.5 Fish Bypass System 94

4. Placement of Fish Screening Structures 96

4.1 Streams and Rivers 96

4.2 Canals 96

4.3 Lakes and Reservoirs 96

5. Debris Control 96

5.1 Trash Racks 97

5.2 Manual Screen Cleaning 97

5.3 Brush Cleaning 97

5.4 Jet Spray Cleaning 97

5.5 Air Burst Cleaning 97

5.6 Power Systems for Cleaning Systems 98

6. Conclusions 98

7. References 100


1. Introduction Fish protection screens are devices installed atsurface water diversions to physically precludepassage of fish into the intake (WDFW, 2000).Screening irrigations offtakes to prevent the lossof fish has been a priority in many irrigationdistricts around the world for many years inresponse to a serious decline in fish numbers. Todate however, fish screening practices have beennon-existent in Australia. This is despite the factthat due to our climate we rely heavily onirrigation for our agricultural industry. Thisreport seeks to identify different techniques

available to screen irrigation offtakes to reducethe loss of fish, highlight important elementsthat should be considered in the design of fishscreens and also to make recommendations onthe basis of these findings. The Murray-Darlingbasin covers more than one million squarekilometres, nearly one seventh of Australia, andis one of the largest catchments in the world.Approximately 80% of the flow in the Basin’srivers is diverted and currently there are nomechanisms associated with these diversions toprevent fish from leaving the rivers (MDBC,2002). Figure 1 shows the Murray-DarlingBasin and areas of major irrigation within it.

Figure 1 – Irrigation in the Murray-Darling Basin 1


Studies on fish movements in the Murray-Darling system have shown that many of thenative species are quite mobile, especially in thesummer months. Unfortunately, this coincideswith the major irrigation season where thegreatest volume of water is diverted intoirrigation channels. Radio tracking devices haveindicated that the native fish, and in particularjuveniles, have a tendency to ‘go with the flow’and follow the natural flow of the waterway. Ifthis flow happens to enter an irrigation offtakethen it is a fair assumption that any fish in thatsection of the water will all so enter the offtake.Research has concluded that, fish entrained intoagricultural and municipal water diversionsexperience 100 per cent mortality (NMFS,1994). To put this into perspective, it isestimated that of the native fish lost from theBasin’s rivers each year, two-thirds of these arein fact killed in irrigation offtakes (MDBC, 2002).

2. Fish Screens – Types andApplications A variety of different measures have beendeveloped to prevent movement of fish from theparent body of water into irrigation offtakes(WDFW, 2000). Fish screens must be designed toprotect the weakest swimming species of fish intheir most vulnerable stage of development. Thismeans that screens are designed to protectjuvenile fish, because if a juvenile cannot makeit past a screen then logically, a fully grown fishwill not make it past.

Three main causes of injury or loss of fish atwater intakes are; entrainment, impingementand predation.

• Entrainment – Occurs when as fish, eithervoluntary or involuntary, enters a waterdiversion

• Impingement – Where a fish comes intocontact with a screen, trash rack or debris atthe intake. This causes bruising, descaling andother injuries. If Impingement is prolonged oroccurs at high velocities it causes directmortality.

• Predation – Water intake increases predationby stressing fish and/or by providing habitatfor fish and bird predators.

The majority of techniques employed to prevententrainment, injury, or death of fish at irrigationofftakes involve the construction of a physical

barrier to prevent fish passage. In order toachieve this, it is necessary to have a set ofguidelines to which these structures mustconform. These design considerations will beidentified later in the report. This section aims toidentify the most common fish screens in useand to describe their typical applications andlimitations.

The following types of fish screening devices areused extensively in the USA as well as otherparts of the world. As these devices have alreadyundergone a large degree of testing andimprovement, they will be the focus whenlooking at solutions to screening irrigationofftakes in the Murray-Darling Basin. Thesedevices are:

• Rotary Drum Screens

• Vertical Fixed Plate Screens

• Vertical Travelling Screens

• Non-Vertical Fixed Plate Screens

• Pump Screens

• Infiltration Galleries

• Experimental Behavioural Devices

2.1 Rotary Drum Screens The rotary drum screen is the most commonlyused physical barrier in service for the protectionof juvenile fish. It can be used for numerousapplications but the most common function is inopen channel flow situations, such as gravityirrigation channels. Using a single drum ormultiples, rotary drum screens can be used toscreen a wide range of diversions with flowsfrom as low as 0.05 m3/s up to 85 m3/s or more(WDFW, 2000). This type of screen hasundergone extensive biological testing, with theresults generally showing better than 98%survival of juvenile fish (Nordlund, 1996).Figure 2 shows a rotary drum screen inisometric view while Figure 3 shows it from aside elevation.

Water passes through screen mesh that covers arotating cylinder. The greatest advantage of arotary drum screen is that due to its rotation, itcontinually removes any debris that mayaccumulate. The debris is picked up by thescreen mesh and is deposited downstream sideof the screen, leaving the screen clean. It isimportant to note that large pieces of debris willnot necessarily be removed by this method andmay need to be manually removed from thevicinity of the screen face.


A rotary drum screen operates by utilising apower system to permanently rotate the drum.Screen rotation can be achieved by a number ofenergy sources. These include;

• Electric Motor

• Paddlewheel

• Solar Drive

• Hydraulic Motor

In order for a rotary drum screen to removedebris, it must be properly submerged. Becauseof this submergence becomes a major designparameter for this type of screen. For successfuloperation, the screen must always have between65% and 85% submergence (WDFW, 2000).This can be seen as a disadvantage of this type ofscreen as there is only a narrow range ofsubmergence required for acceptableperformance. Submergence greater than 85%dramatically increases the potential for fish

Figure 2 – Isometric View of Rotary Drum Screen (WDFW, 2000)

Figure 3 – Side Elevation of Rotary Drum Screen (WDFW, 2000)


entrainment and impingement on the screen. Ata submergence level less than the desiredminimum (65%), debris is not efficiently pickedup on the face of the screen. Once again thisgreatly increases the chance of impingement tooccur.

Another disadvantage of the rotary drum screenis that it requires on-going routine maintenance.Since the drum is continually rotating, wear onthe side and bottom seals must be closelymonitored, depending on site conditions. Siltaccumulations in front of a rotary drum screencan wear seals quickly, so sometimes a sedimentsill is incorporated into the design that allows fora deposition of sediment that can be removed onan annual basis (Nordlund, 1996). The failure(or leakage) of the seals can result in fishimpingement. The mesh also requires a regularinspection for signs of wear or damage. At somelocations it has been noted that mesh hasexperienced fouling due to algal growth. Theproblem of algae can be solved quite simply byusing a mesh with growth inhibitorcharacteristics, such as phosphor bronze, or byinstalling additional cleaning mechanisms suchas internal spray bars.

2.2 Vertical Fixed Plate Screen The vertical fixed plate screen is also one of themost common screens used in practice. Theyhave many diverse applications in that they are

used for industrial, domestic and irrigationintakes, at both pump and gravity diversions.Much of their popularity comes from the factthey are relatively simple to tightly seal becausethe mesh is fixed directly to the structural frame.There are also no moving parts or wear surfacesbetween the screen mesh and structural frameresulting in less maintenance. Figures 4 and 5show an example of a vertical fixed plate screenarrangement in both plan and side elevations.

A major advantage of the vertical fixed platescreen is that it can be built in a canal withmuch less blockage of the canal cross sectionand flow compared to a rotary drum screen. Thisis because narrow columns can suffice for thesupporting piers rather than having toaccommodate the drum diameter. Also, for smalldiversions, vertical fixed plate screens can beinstalled on the bank of a river and thereforerequire no bypass.

The disadvantage of a vertical fixed plate screenis that removal of debris may be more difficultthan with a rotary drum screen depending onthe type of debris present. Because of thisvertical fixed plate screens must incorporate amechanical cleaning system for the removal thisdebris. Two common mechanical cleaners forvertical fixed plate screens include travellingbrush cleaners and hydraulic back-spraysystems. The best brush cleaners produce a smalleddy behind the brush as it travels the length ofthe screen, allowing debris to be suspended until

Figure 4 – Plan Elevation of Vertical Fixed Plate Screen (WDFW, 2000)

Figure 5 – Side Elevation of a Vertical Fixed Plate Screen (WDFW, 2000)


it is passed of the downstream end of the screen(Nordlund, 1996). The operation of the cleaningsystem is activated by a timing mechanism, ahead loss detection unit or a combination ofboth.

2.3 Vertical Travelling Screens Vertical travelling screens are a widely usedscreening technique mainly utilised for pumpdiversions. There are two varieties of verticaltravelling screens commonly used; panel typeand belt type. The difference between the twotypes is in the screening mesh itself. Panel typescreens have many discrete mesh panels that arehinged together, while a belt type screen isconstructed of a continuous belt mesh. Similarly,both screens are driven by electric motorsthrough a drive shaft at the top and rotatearound a parallel idler shaft at the bottom(WDFW, 2000). This is illustrated in Figure 6.

The advantages of a vertical travelling screen aresimilar to those of a rotating drum screen in thatthe mesh rotates to remove debris to thedownstream side of the screen. Otheradvantages include:

• Scope for installation on a river bank(therefore requiring no bypass)

• Civil Works are relatively minimal

• They can be installed in deep water

Because the screen lifts vertically, there is nolimitation on minimum or maximum screensubmergence to be effective (WDFW, 2000).

There have been a number of disadvantages ofthe vertical travelling screen that have becomeapparent. The main one stems from the fact thatthese screens were originally designed to keepdebris away from pump intakes rather thanprotect fish. Although this original design hasbeen modified, problems with current screensstill exist. Many installations of these screensshow high incidence of impingement andentrainment, due to improper alignment, meshsize and mesh seal problems (Nordlund, 1996).Mesh seal problems are difficult to identify, sincethe screen is often located in a sump.

2.4 Non-Vertical Fixed Plate Screens Fixed plate screens do not always have to beorientated in a vertical direction. Other possiblealignments include:

• Downward Sloping Flat Plate Screens

• Downward Sloping Contoured Plate Screens(Coanda Screens)

• Upward sloping Flat Plate Screens

Downward sloping screens can either beconstructed as a flat plate or a contoured platesuch as the Coanda screen. This design operatesby allowing a percentage of the flow over the

Figure 6 – Vertical Travelling Screen (WDFW, 2000)


screen to pass through it. The flow that passesthrough the screen falls into a canal situatedbelow the screen, where it is routed to where itis required. Any fish or debris that are present inthe original flow are passed over the screen withthe remainder of the flow. Figure 7 and Figure 8 detail the non-vertical fixed platescreen and the Coanda screen respectively.

In terms of fish passage, downward slopingscreens only function successfully if sufficientflow depth exists at the downstream end of thescreen. This allows debris to be moveddownstream where it won’t pose a hazard to fishpassing over the screen. The minimum flow overa screen face should be based on expectations ofsize and type of debris, size and condition of fish

Figure 7 - Downward Sloping Flat Plate Screen (WDFW, 2000)

Figure 8 - Downward Sloping Coanda Screen (WDFW, 2000)


passing, and potential changes in flow that couldreduce the depth to below the desired minimum(WDFW, 2000). For these prescribed minimums,substantial amounts of bypass flow is oftennecessary, and even the use of headgates toregulate flows. Downward sloping screens aregenerally used for gravity diversions howeverthey do require up to a metre of head to operatesuccessfully.

Downwards sloping flat plate screens can alsosuffer from non-uniform flow distribution acrossthe screen. This is due to the water depth of theupstream end being greater than that at thedownstream end. This non-uniform flow canmake transition across the screen difficult forfish that tend to avoid regions of variable flow.Traversing through non-uniform flow can alsodisorientate or stun juvenile fish, making theman easy target for predators. The contoured plateon a Coanda screen helps to minimise this effectas the head driving flow through the screen ismore uniform. However, the contour of thescreen will only be optimal for a certain flowrate and a variation of the flow magnitude willcreate problems similar to that of the flat platescreen.

Upward sloping screens are the opposite ofdownward sloping screens in that their profilerises in the direction of the flow as seen inFigure 9.

As can be seen in the diagram above, waterdrops over the downstream end of the screen

creating the fish and debris bypass. Anadvantage associated with this type of screen isthat there is generally uniform flow distributionthrough the screen due to a uniform headdifferential throughout its area (Nordlund,1996).

Unlike the downward sloping plate screen, theupward sloping flat plate screen does require anautomatic cleaning device that can addsignificantly to the cost of the screen. If thedoesn’t remain clean, the weight of debris buildup on the screen may cause structural failure.The operation of this screen is also very sensitiveto the minimum bypass depth. Typically a depthof at least 30 cm is required to keep fish fromrejecting the bypass (WDFW, 2000). This meansthat if the upstream water surface elevation isnot high enough, the minimum bypass depthwill not be achieved.

2.5 Pump Intake Screens Pump intake screens are basically a variety ofscreens built at the end of a pumping intake toprevent fish and debris from being sucked intothe pump. The most common design of thesescreens is either a box or cylinder, with the wallsconstructed from screen mesh and the suctionpipe entering into one of these walls.

An advantage of pump intake screens is thatthere are many different screen configurationsthat are commercially available meaning they do

Figure 9 - Upward Sloping Flat Plate Screen (WDFW, 2000)


not require custom construction. The flow rangeof these screens is approximately 0.03 m3/s toover 2 m3/s. The area of the screen must belarge enough so that the flow velocities enteringthe screen are not too great, to minimise thechance of fish impingement. For large flowintake applications, it is possible to place anumber of screens in series as demonstrated inFigure 10 to reduce the velocity at the screenface.

The disadvantage of pump intake screens is thatthey are quite susceptible to clogging fromdebris. Because of this there have been a

number of different systems developed toautomatically clear the screens of debris.

These include:

• Fixed spray bar, rotating screen

• Fixed screen, rotating spray bar

• Internal air burst

The first two of these cleaning systems arereasonably self explanatory. The internal airburst operates by backwashing the screen with aburst of air. This has been used with quite alarge degree of success but care needs to be

Figure 10 – Configurations of Pump Intake Screens (WDFW, 2000)

Figure 11 – Tee Configuration Pump Intake Screen (WDFW, 2000)


taken to ensure that it removes debrisaccumulation from the bottom of the screenwhich is sometimes overlooked.

Pump intake screens have the option of being apermanent submerged structure or they can bedesigned to be retractable for ease ofmaintenance. Either way they can be used in avariety of water depths, from shallow to verydeep. Regardless of the depth of installation it isadvantageous for there to be significant flow tocarry debris away from the pumping site. Thiswill increase the effectiveness of other the debrisremoval measures mentioned above. Figure 11shows a typical pumping site fitted with acylindrical tee pump intake screen.

2.6 Infiltration GalleriesInfiltration galleries consist of perforated pipemanifolds or single pipes buried perpendicularto the stream channel approximately onemetre below the stream bed (OFWO, 2002).Water infiltrates through the stream bed andinto the pipe system where it is drawn awayto be used. The pipes must be installed in asteep section of a river such as slight rapids,which is maintained free of fine sediment dueto the hydraulic action of the stream. Forexample they must be installed in a locationwhere the bed is regularly scoured andthereby cleaned, rather than in a depositionalarea such as an artificial pool. The section of

stream also needs to comprise very coarse bedmaterial to ensure adequate flow to permeate.Infiltration galleries are usually associatedwith pump diversions; though can be used atgravity diversions where there is adequatehead available to drive the flow (WDFW,2000).

The advantage of infiltration galleries is thatwhen they are successfully placed in the rightlocation, the stream hydraulics manages thedebris and sediment without the need for anexpensive cleaning system. They areextremely successful in screening fish as thescreen is simply made up of the stream bedwhich the fish cannot, and have no desire to,penetrate.

The disadvantage of infiltration galleries is therisk associated with them becoming cloggedwith sediment or other types of debris. Oncean infiltration gallery becomes clogged withsediment, it is very difficult maintain becauseit is buried in the stream bed. The bestmethod to maintain them is firstly by placingthem in the correct location in the stream tobegin with, and secondly to make allowancesfor the system to be reverse flushed witheither pressurised water or air.

The failure rate of infiltration galleries is high;approximately 50% (WDFW, 2000). Thisfailure rate is generally the result of poorunderstanding of the technical designrequirements of an infiltration gallery, coupled

Figure 12 – Layout of an Infiltration Gallery (WDFW, 2000)


with installation at an unsuitable location.Figure 12 shows the layout of an infiltrationgallery at a pump diversion.

2.7 Experimental BehaviouralDevices Fish behavioural devices have beenexperimented with since the 1960’s as asubstitute for physical barrier screens (EPRI,1986). This has been brought about by the highcost often associated with conventional screeningtechniques. At diversions of high flow (10-15 cubic metres per second or greater), thelow velocity requirement and structuralcomplexity can drive the cost for fish protectionand the associated civil works to over a milliondollars (NMFS,1994).

A behavioural device, as opposed to a physicalbarrier, requires a deliberate response on the partof the fish to avoid entrainment. The philosophybehind these devices is to either attract or repelfish, depending on the specific desire for the areain which the device is placed. This is achieved bythe device transmitting a signal to trigger abehavioural response from the fish, usuallynoticeable agitation. Unfortunately, to date usingthese startle investigations to develop effectivefish guidance systems has not been effective(NMFS, 1994).

Experiments show that there is a large variationin response between individual fish of the samesize and species. Because of this, it cannot bepredicted that a fish will always move towards oraway from a certain stimulus. Evidence alsoshows that even when such a movement isdesired by a fish, it often cannot distinguish thesource or direction of the signal and thereforemay not swim in the required direction.

One of the factors to explain the poorperformance of behavioural devices is that manydo not incorporate a controlled set of hydraulicconditions to assure fish guidance, as do thephysical screening systems. This means that thedevices can encourage fish movement indirections that actually contrast with theexpected natural response. Because of this, thefish gets mixed signals about what direction tomove. Another concern is that of repeatedexposure in that over a length of time a fish mayno longer react to a signal that initially was anattractant or repellent.

In addition to the unpredictable response of anindividual fish, it is expected that behaviourvariations will occur due to size, species, lifestage, and water quality conditions. In strong oraccelerating water flows, the swimming ability of

a fish may prevent it from responding to astimulus even if it attempts to do so.

The main motivation for choosing to installbehavioural devices is for the purpose of costsaving. This is because much of the cost inconventional systems is for the physical structureneeded to provide proper hydraulic conditions.Ironically, implementing a behavioural devicewith its own structural requirements may lessenmuch of its cost advantage.

Present scepticism over behavioural devices issupported by the fact that few are currentlybeing used in the field and those that have beeninstalled and evaluated seldom exhibit consistentguidance efficiencies above 60 per cent (NMFS,1994). Given this, until improved technology isobtainable it would be difficult to recommendthe use of this system.

3. Fish Screen Design In the design of fish screens, it is important tokeep the project in perspective and not loosesight of the main aims. Fish screening is an issuedue to the fact that people have to divert waterfor irrigation. Therefore, the primary designconsiderations of any fish protection device arebased upon hydraulics. The screen must allow asufficient quantity of water to pass through withminimal head loss, while still providingconditions that prevent entrainment,impingement, or predation of fish.

Protection criteria have been developed inaccordance to these requirements, and if carriedout correctly can successfully protect fish whilstposing no threat to the operation of the irrigationofftake. These criteria are quite conservative, andare based on protecting the weakest swimmingspecies, at their most vulnerable time, underadverse environmental conditions.

The most critical aspects of a successful fishprotection screen are based on control ofconditions around the screens. This section is toexamine the conditions from the perspective offish protection. These critical designconsiderations are:

• Approach Velocity

• Screen Size

• Screen Materials

• Sweeping Velocity and Screen Orientation

• Fish Bypass System


3.1 Approach Velocity The primary objective in the design of fish screensis to match the swimming ability and behaviourof fish, to the hydraulic characteristics of thescreen and civil works design, to minimise theprobability of contact with the screen (WDFW,2000). This means that the screen design mustensure that the velocity of the water flowingtowards the screen is low enough so that fish canvoluntarily prevent themselves becomingimpinged on the screen. Because of this, approachvelocity is one of the most critical characteristicswhen designing fish protection screens.

Before setting design limits on the approachvelocity, it is necessary to define what it actuallyis. The true water velocity approaching the screencan be broken up into vector components asshown in Figure 13. The approach velocity is thecomponent the flow perpendicular to theorientation of the screen. In other words, this isthe component of the flow that actually travelsthrough the screen. The other component flowsparallel to the screen face. This is known as thesweeping velocity and will be discussed later.

Juvenile fish must be able to swim at a speedequal to or greater than the approach velocity foran extended length of time to avoid impingementon the screen (WDWF, 2000). It is thereforenecessary that a study on fish biomechanics beconducted in order to determine the sustainedswimming speed of the weakest swimmingspecies of fish present, to use at a designparameter. This study would be quite complex as

there are a number of factors apart fromindividual fish species that affect their speeds.Some of these factors include; water temperature,fish size, dissolved oxygen content, and waterquality. This study is beyond the context of thisproject.

To give an estimate of the allowable magnitude ofthe approach velocity, a comparison is made to afish species found in the USA. In the case ofjuvenile pacific salmonoids, nearly 100% of fry(fish less than 40mm in length) are protected ifapproach velocity is less than 0.122 metres persecond (Nordlund, 1996). This value is theaccepted design value for most parts of the world.The only time this varies, is if studies prove thatfish of this size and swimming ability are neverpresent near a particular offtake, and that onlystronger swimming species are present.

To determine the approach velocity, simpletrigonometric relationships are applied to the flowvelocity of the canal and the vector componentsare determined.

This is shown in Equation 1 below.

Figure 13 – Velocity Vector Components (WDFW, 2000)

Equation 1 – Approach Velocity

Va = V sine Ø

Where: Va = Approach Velocity (m/s)

V = Canal Velocity (m/s)

Ø = Angle between Screen Face and Canal Flow Line


3.2 Screen Size The size of the screen is one of the mostimportant factors to consider when designingfish screens. It is screen size that dictates whatthe approach velocity on a canal will be basedon a particular design flow rate. The relationshipbetween approach velocity, screen size and flowrate is shown in Equation 2 below.

A = Q/ Va

Where: Va = Approach Velocity (m/s)

Q = Design Flow Rate (m3/s)

A = Effective Screen Area (m2)

As Equation 2 showed, the screen areacalculated is the effective area. This takes intoaccount the area covered by seals and otherpotential obstructions and any area that is not

submerged. The effective area is therefore thegross area of the screen, not the open area of themesh. Because of this it is important that thedesign considers the area of submerged screenthroughout the entire range of diverted flows.Design must also consider the possibility of apercentage of the screen face becomingineffective due to blockages caused by debris.

There are some situations where the water levelof the canal must be raised as it approaches afish screen in order to provide sufficient screensubmergence. An example of this is in the use ofrotary drum screens that have a low tolerance ofsubmergence levels as mentioned earlier.

3.3 Screen Materials Many different types of materials have beendeveloped for the use for fish protection screens.This report will focus on the three most commonmaterials; perforated plate, profile bar and wovenwire. For each of these materials, design criteriahave been established based on protecting

Equation 2 – Required Screen Area

Fry Criteria (Fish less than 60mm)

Fingerling Criteria(Fish greater than 60mm)

Perforated Plate (maximum opening

diameter or slot width) 2.38mm 6.35mm

Profile Bar (maximum width opening)

1.75mm 6.35mm

Woven Wire (maximum opening in the

narrow direction) 2.38mm 6.35mm

Minimum Open Area % 27 40

Table 1 – Criteria for Screen Face Material Based on Juvenile Fish Size (WDFW, 2000)

Figure 14 - Perforated Plate


juvenile fish. These criteria relate to themaximum opening dimensions to prevententrainment as well as minimum open areas toensure that water can pass freely through thematerial. Table 1 presents these criteria.

Perforated plate is constructed from sheet metal,with a number of holes or slots drilled into it. Theplate is generally either stainless steel oraluminium for corrosion protection and can comein a variety of thicknesses. Thick plate is generallyused when there is a high probability of largedebris striking the screen, however as the plategets thicker, the head loss across it becomesgreater. Figure 14 shows two differentconfigurations of perforated plate.

Profile bar is constructed of parallel stainless steelbars welded to a structural backing. It is thestrongest of all the screen materials, but also themost expensive. Profile bar is a commoncommercial product with a variety of bargeometries, sizes, and slot widths between thebars (WDFW, 2000). Profile bar can also beconstructed in a cylindrical arrangement for usein pump screen applications.

In use, profile bar can be orientated eithervertically or horizontally, depending on the type

of cleaning system used in conjunction with it.For example, if a brush cleaner was utilised toclean the profile bar, then it would have to travelin at same direction as the orientation of the bars.Figure 15 shows a schematic of the profile bar.

Woven wire mesh, as the name suggests, isconstructed from wire that has been woventogether to form a permeable mesh. It is quiteversatile and because of this is one of the mostcommon screen materials used. It versatilitycomes from its ability to be constructed out ofvarying gauge wire depending on conditions. Ifthere is only small debris present at a screen sitethen the mesh can be of fine grade. Conversely,if large sized debris is present, a more heavy dutygauge of wire may be necessary. An example of awoven wire mesh can be found in Figure 16.

3.4 Sweeping Velocity and ScreenOrientation As mentioned previously, the water flow in acanal can be separated into two directionalvectors. The sweeping velocity is the componentof the true water velocity that runs parallel tothe screen face as seen in Figure 13. This

Figure 15 - Profile Bar

Figure 16 - Woven Wire Mesh


sweeping velocity is extremely important as it isresponsible for guiding fish across the face of thescreen to the bypass. To guide fish to a bypass,the sweeping velocity component should be asleast as great as the approach velocity (WDFW,2000).

Sweeping velocity is determined by theorientation of the screen relative to the directionof the true water flow in the canal. Therefore, inorder to meet the criteria of sweeping velocitybeing at least equal to approach velocity, thescreen should have a maximum angle of 45 degrees to the canal flow. If the angle of thescreen is reduced to below 45 degrees, then thesweeping velocity component becomes largerthan the approach velocity. This is sometimes arequirement depending on the conditions of thesite and the type of fish being screened.

For screens installed directly on the river bank atthe entrance of a diversion, it is the natural flowdirection in the river that provides the sweepingvelocity. However, at time of low flow or highwater extraction, the flow of the river can varyto the point where the majority of the flow isactually in the direction of the approach velocity.If a screen is susceptible to this occurrence, aguide wall may have to be constructed to creategeometry similar to that on an angled screen ina canal. This will alter the sweeping velocity toconform to the guidelines mentioned above.

3.5 Fish Bypass System A fish bypass system is a flow route designed totransport both juvenile and adult fish from theface of the screen back to the river and isnecessary if the screen is not located in the riveritself (WDFW, 2000). Screens located in on thebank at an offtake diversion do not require abypass system, as the fish always remain in themain waterway. While the actual design of a fishbypass can be quite complicated, the diagramsshown in Figures 17 and 18 illustrate the majorcomponents of a system in a straightforwardmanner. This example shown is for a drumscreen installation.

There are a number of design considerations thatmust be taken into account if the bypass systemis to operate successfully by returning fish backto the main waterway at a safe location, withminimum risk of injury. These major designconsiderations can be summarised into thefollowing points:

• Entrance Geometry

• Entrance Velocity

• Bypass Conduit

• Return Delivery

The geometry of the entrance to the bypasssystem is one of the most important and criticalcomponent of the entire screening system. This

Figure 17 – Plan View of Fish Bypass System at Drum Screen Installation (WDFW, 2000)


is because every fish that enters the offtakeand is successfully screened must enter thebypass system in order to get back to the mainstream. The entrance must be designed so thatfish freely enter the bypass without delay. Toachieve this, the geometry of the screen mustbe carefully designed so that adverse hydraulicconditions are not present that may hamperfish passage.

Juvenile fish often delay or avoid passingthrough areas where the velocity decreases orincreases rapidly (WDFW, 2000). Because ofthis the entrance velocity of the bypass mustbe considered carefully in design. It is widelyaccepted that for optimum performance of thebypass, the velocity of the flow at the entranceshould be about 10% greater than the truevelocity approaching the screen. This must bethe case for all flow rates experienced in theofftake. Despite the need for this additionalvelocity, the increase must be gradual if thefish are to fully accept the bypass.

The bypass conduit is responsible fortransporting any fish and debris present backto the river. The conduit can comprise of pipesor channels with the emphasis on creating anenvironment free from turbulent flow.Additional criteria as specified by in fish screenprotection guidelines (WDFW, 2000) include:

• Bypass hydraulics should be open channelflow; bypass pipes should not be pressurised

• Depth of flow in a bypass must be greater than230 mm

• Minimum bypass pipe diameter of 600 mm

• There should be no extreme bends in the pipes

• Bypass system sampling stations should notimpair normal operations of the screen facility.

The final component of a bypass system is theoutlet where fish are returned to the mainwaterway. The outlet should protect fish fromtwo factors; direct injury due to the impact whenthey enter the water, and predation. The impactvelocity is the velocity of the bypass pipe as itstrikes the water in the river. If this is too great,then shear occurs between the fish and thereceiving water, and descaling can occur.

The outlet must be located in designed in such away that it deters predators. The selection of anoutlet site is based on their being suitable velocityin the receiving stream to enable fish to movequickly away from predators. Care needs to betaken to find a balance between helpful velocityand turbulent flow that can disorientate fish,allowing them to become easy prey.

If a bypass is designed to these above designconsiderations, then there is every chance that itwill be successful and accepted by the fish.

Figure 18 – Elevation View of Fish Bypass System at Drum Screen Installation (WDFW, 2000)


4. Placement of FishScreening Structures The choice of location for an irrigation diversionis generally based on the convenience of theirrigator. In many cases this chosen location canmake it difficult for screening. Considerationsmay include whether to screen water directlyfrom the river or in a canal diverted from theriver. This is because the point of withdrawal isimportant for the hydraulic aspects of thescreen, as well as for the protection of juvenilefish.

This section is going to look at the placement ofscreening structures at the following locations:

• Streams and Rivers

• Canals

• Lakes and Reservoirs

4.1 Streams and Rivers Optimally, and where physically practical, thescreen should be constructed at the diversionentrance with the screen face parallel to thestream flow (NMFS, 1997). The foremost reasonbehind this is that it causes the minimalinterference with the fish, and thus the greatestsurvival rates. Another reason is that it isgenerally the most economic solution asalternative screening systems requirecomplicated bypass systems to return fishentrained into the offtake back to the river.

There are a number of factors that may preventthe installation of a fish protection screen at adiversion entrance. The most common reasonsinclude excess river gradient, the potential fordamage by large debris (for example logs duringa flood), large amounts of sedimentation, orinappropriate flow conditions (WDFW, 2000).The screen face must be aligned with theadjacent bank, which in some cases may requireminor works to achieve this. This is done toprevent eddies in front, upstream, anddownstream of the screen. While it is preferableto locate the fish screen at the diversionentrance, if the conditions are not suitable thenin the long term it is better not to try and forcethis placement as the screens will not workeffectively.

4.2 Canals If it is impractical to locate the fish screen on thebank at the diversion then a screen can be

installed in the diversion offtake. Because theflow into the offtake is taken directly from themain stream, screens located in canals require abypass system to collect entrained fish and safelyreturn them to the river. Due to the need forthis bypass it is necessary to locate the fishprotection screen as close as practical to thediversion entrance to minimise the time fishspend in the bypass. To prevent impingement offish onto the screens, the angle of the screen tothe flow should be adequate to guide fishtowards the bypass entrance (NMFS, 1997).

4.3 Lakes and Reservoirs Observations and research have shown thatwhen in lakes or reservoirs, juvenile fish spendthe majority of their time in shallow water nearthe shore. On the basis of this, the most practicaldiversion outlets should be located offshore andat reasonable depth where there are the leastnumber of fish present. Where possible, intakesshould be located in areas with sufficientsweeping velocity to minimise sedimentaccumulation in or around the screen and tofacilitate debris removal and fish movementaway from the screen face (NMFS, 1997).

Often there is a requirement for very large flowsto be diverted out of lakes and reservoirs, as thisis the reason many of them were constructed inthe first place. This must be taken into accountwhen designing an appropriate fish protectionscreen to ensure that the effective screen area islarge enough so that screen velocities areminimised. If this is not done, fish impingementonto the screens may become a large issue.Using very large, but low velocity, offtakes canalso help maintain the high flows required in anenvironment when there is often very little headavailable.

5. Debris Control Debris found in the natural waterway can havea large impact on the effectiveness and operationof a fish screen. The debris can be large such astree branches or as small as sediment or algae. Itis important both for the protection of fish andthe hydraulic performance of the irrigationofftake, that an adequate cleaning system is inplace to remove debris efficiently and completelyfrom the screen mesh. Failure to incorporate anadequate mesh cleaning system can causecatastrophic failure of the screen assembly(Nordlund, 1996).


The primary concern of inadequate screencleaning is that debris may build up on thescreen face. This reduces the effective area of thescreen resulting in an increased flow throughthe remainder of the screen. Increased flowleads to higher approach velocities and a greaterchance of impingement on the screen. A secondconcern is that debris build-up in the trashracks, fish bypass, and screen face change thehydraulics of the system. Irrigators do notreceive as much water due to these blockagesand fish have a higher mortality rate due toincreased velocities and impingement with thescreen face and debris.

To prevent this from taking place, a number offish screen cleaning systems have beendeveloped. The most common of these include:

• Trash Racks

• Manual Screen Cleaning

• Brush Cleaning

• Jet Spray Cleaning

• Air Burst Cleaning

5.1 Trash Racks Trash racks are placed upstream of fish screensto collect larger debris that might damage thescreen or get blocked in the bypass system.Typically, a trash rack is a frame of bars slantedvertically at approximately 45 degrees to theflow, with bars spacings of 150-250mm (WDFW,2000).

Juvenile fish require a bar spacing of at least100mm to safely pass through the trash rack, sothis forms the minimum allowable bar spacing.It is important to remember that the role of thetrash rack is to prevent large debris damagingthe screens, not to prevent passage of fish. If thebar spacings are too small them they will collectmore debris, not only enhancing the problems offish passage, but also having a negative impactof the hydraulics of the intake.

Trash racks must be cleaned and have any debrisremoved on a regular basis. At screening sitesthat are very large, it may be necessary to usetrash racks with an automatic rack cleaningdevice. These devices are quite commonplace,even in Australia, where they are currentlyutilised in most waste water treatment plants toclean the primary screens.

5.2 Manual Screen CleaningManual screen cleaning is generally used for

small screens or in instances where there isinsufficient debris load to require an automatedcleaning system. Manual cleaning involvesremoving debris from bypass entrances and trashracks, as well as the screen face itself.

If a manually cleaned screening system is to beinstalled, it is important to take this into accountin the screen design stage. Because the screen isonly getting cleaned at specific times, it isinevitable that a degree of debris build-up willtake place. Due to this, the total screen areashould be larger than normally required to takeinto consideration the loss of effective area dueto blockage. If this is not done, increasedvelocities due to reduced flow area can causejuvenile fish to become impinged onto thescreen face.

5.3 Brush Cleaning Brush cleaning systems are similar to themechanical rakes used to remove debris fromthe trash racks. They consist of a series ofbrushes that continually travel over the screenon a conveyor system. It is important to ensurethat the brushes are orientated so they efficientclean the entire screen. For an effective clean,the brushes must also travel in the direction thatthe screen is orientated. For example, for avertical fixed plate screen, brushes must travel ina vertical direction or parallel to the screen face.Brush cleaners are one of the most commoncleaning systems used in practice and have agood reputation for performance. Adisadvantage with them is because theyencompass moving parts, they also require acertain degree of maintenance.

5.4 Jet Spray Cleaning Jet spray, or water jet, cleaning systems havebeen used with success for fixed plate screens,pump intake screens, vertical travelling screensand as additional cleaners for drum screens atsites with particularly heavy debris load(Nordlund, 1996). They work by spraying highpressure water onto the back side of the screen,dislodging any debris present. Depending on thetype and amount of debris present, different jetpressures are required. A standard range ofpressures commonly used is 200-700 kPa.

5.5 Air Burst Cleaning Air burst cleaning systems are similar to jet spraysystems only they use compressed air rather thatwater to blow the debris off the screen. Since


being developed, it has mainly been used as thecleaning system for pump intake screens. Airburst systems have a variable record, workingvery well in some sites, less so in others. Themain criticism with this system is that it has atendency to only clean the upper portion of thescreen. This makes sense as after release, the airbubbles will naturally and quickly raise towardsthe surface.

5.6 Power Systems for CleaningSystems Apart from manually cleaned screens, anymechanical cleaning system is going to require apower source in order to operate. The type ofpower system used for a particular site should bebased on the physical constraints that the sitepossesses. The main priorities of any powersystem are that it must be capable if deliveringthe required amount of power, in the most costefficient manner, with a very high degree ofreliability. The most common power systemsinclude;

• Electric Motors

• Paddle Wheels

• Hydraulic Motors

• Solar Power

Electric motors are the most preferred option forpower systems. This is because they are by farthe most reliable, and are reasonableinexpensive to run and maintain. Unfortunatelyhowever, many screening sites are situated inremote areas, thus a significant distance fromthe power grid. It is under these conditions thatalternative sources of power are required.

Paddle wheels or water wheels are a reliablesource of power in many locations. They aredependent on the flow of the water foroperation so are only suited to certain locations.An advantage of using a paddle wheel is thatafter construction there in very little costassociated with operation. Hydraulic motors arealso powered by paddle wheels but have theadvantage that the paddle wheel can be placedaway from the screen. For example it can beinstalled in a location where there are higherflows and therefore better operating conditions.With hydraulic motors, hydraulic lines connectthe motor to the screen.

Cleaning systems driven off solar power arebecoming increasingly popular as solartechnology progresses. As solar energy can onlybe collected during daylight, these systems usesolar energy to charge batteries that operate the

cleaning systems. Battery charging systems arereadily available for reasonable costs that allowoperations for up to 48 hours without sunlight.

It is important to note that the above mentionedpower systems are not just restricted tooperating the cleaning systems. In manyinstances these systems are used to power theoperation of mechanical screens as well as thecleaning systems.

6. Conclusions As the report detailed, there have been anumber of different solutions designed toprevent fish becoming entrained into irrigationofftakes. Each of these solutions has theiradvantages and disadvantages, and there is noone screen that can be used universally. Theenvironment in the Murray-Darling basin isnot ideal for the screening of fish. The waterhas a high degree of turbidity and possesses alarge quantity of fine sediment that will easilyclog fine grade screens. Despite this, there area number of screens that could be adapted tosuit the conditions. Table 2, gives thesuitability of each of the screening methodsdescribed in the report, and offers suggestionsas to what measures need to be taken toensure they work successfully.

Not only does the type of screen need to beconsidered when determining a course ofaction, but careful thought must also takeplace on the design of these fish protectionscreens. At present there is limited informationto guide this design for Australian conditions.There is a need to conduct a comprehensivestudy of the movements and biomechanics ofnative fish in the Murray-Darling Basin. It isonly on the outcomes of this study, that a setof guidelines and design parameters bedetermined for the effective screening of fish.Without these guidelines, any future fishprotections works may not be as effective asthey potentially could.

There is a need for public education toenhance awareness on the topic of screeningirrigation offtakes for the purpose of protectingfish. As studies in this report have pointed out,there is a large problem of fish mortality inthese offtakes. Despite this, when the Murray-Darling Basin Commission approved a fishmanagement plan that listed its objectives todeal with the problem of depleting native fishpopulations, screening irrigation offtakes wasnot mentioned.


The project was also able to identify somelimitations of the screens recommended.Properly designed, they are quite capable ofscreening both adult fish and juveniles down toabout 40mm in length. However, some of thenative fish spend a portion their life cycles asfloating eggs or tiny larvae, which even in a

screened offtake would experience entrainment.This is another example of where research needsto be conducted so that conclusions can bedrawn on the best practices to extract water,while protecting all stages of the fish’s lifecycle.

The problem of screening offtakes in theMurray-Darling is quite unique due to the

Pump Intake

Very suitable.Pump diversions do not alter environmentalconditions as much as surface diversions. Requires automated cleaning system.

Infiltration Galleries

Not suitable in the majority of the Murray-Darling system due to sediment and unsuitable flow conditions. May be used in some tributary streams in thehigh country where sediment loads are low and appropriate hydraulic conditions prevalent.

Experimental Behaviour Devices Not recommended due to testing evaluations showing poor performance in screening fish.

Screen Type Suitability for use in the Murray-Darling Basin

Rotary Drum

Very Suitable .One of the most commonly used screens, therefore large amount of technical informationavailable for design purposes. May not require a separate cleaning system.Can handle quite large flows (80 + m3/s)Suitable for use in canals or directly at diversion.

Vertical Fixed Plate

Very Suitable.Simple design and construction. Requires automated cleaning systemSuitable for use in canals or directly at diversion.

Vertical Travelling

Suitable for use at pumping sites, especially fordeep extraction. Better alternatives available for gravity surface diversions.Maintenance can be difficult due to access to screen.

Non-Vertical Fixed Plate

Average suitability. Require a significant amount of head. Upward sloping screens require mechanicalcleaning system.Fine sediment build up may occur in drop canal below screen face.

Table 2 – Conclusions on Screen Suitability


diversity of flow situations that occur. They varyfrom small diversions to service a single farm tothe offtake at Mulwala that has a maximum flowrate of up to 115m3/s. To date, fish screens haveonly be developed for flow rates a little over 80 m3/s so there are a lot of opportunities foradvancement in this field.

Looking into the future, water demands forirrigation are not going to decrease. In fact, aspeople strive to increase agricultural productivity,the requirement for water is likely to increase.This increase in water demand is only going toadd to the pressures already experienced by ournative fish populations. The technology isavailable to successfully screen irrigation offtakesin the Murray-Darling Basin to reduce the loss ofour native fish, but without implementation thebenefits of this technology will never beappreciated.

7. References EPRI (Electric Power Research Institute), 1986,Assessment of Downstream Migrant Fish ProtectionTechnologies for Hydroelectric Application, EPRI, PaloAlto, CA

Koehn, J. Nicol, S, 1998, Habitat and MovementRequirements of Fish in Riverine Environment Forum,MDBC

MDBC (Murray-Darling Basin CommissionMinisterial Council), 2002, Native Fish Strategy for theMurray-Darling Basin, MDBC

NMFS (National Marine Fisheries Service), 1994,NMFS Southwest Region Position Paper on ExperimentalTechnology for Managing Downstream Salmonid Passage,http://swr.ucsd.edu/hcd/expert.htm

NMFS (National Marine Fisheries Service), 1997,Juvenile Fish Screen Criteria, NMFS,http://swr.nmfs.noaa.gov/hcd/fishscrn.pdf

Nordlund, Bryan, 1996, Designing Fish Screens for FishProtection at Water Diversions, NMFS,www.nwr.noaa.gov/1hydrop/hydroweb/docs/usfws_97.htm

OFWO (Oregon Fish and Wildlife Office), 2002,Sucker Creek Fish Enhancement, US Fish and WildlifeService, http://pacific.fws.gov/jobs/orojitw/proj-info/josephine/ summary/26-9502.htm

WDFW (Washington Department of Fish andWildlife), 2000, Fish Protection Screen Guidelines,WDFWhttp://www.wa.gov/wdfw/hab/ahg/screen51.pdf

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