Optimising Denil fishways for passage of small and large fishes

Optimising Denil fishways for passage of small andlarge fishes

M . M A L L E N - C O O P E R & I . G . S T U A R T *

New South Wales Department of Primary Industries, PO Box 21, Cronulla, New South Wales 2230, Australia

Abstract An 8-m long experimental fishway was trialled at three different slopes [8.3% (1:12), 14.3% (1:7) and20% (1:5)] to examine the potential of the single-plane Denil fishway for the passage of small- and large-bodiednative fishes in Australia. Fish between 45 and 630 mm ascended the fishway. The lowest slope enabled the full sizerange of bony herring Nematalosa erebi (Gunther), from 45 to 350 mm fork length, to ascend the fishwaysuccessfully as well as a higher numerical proportion; 88% at the 8.3% slope compared with 31% at the 20% slope(fish numbers per trial ¼ 33–3936). These results dispel the notion that Denil fishways are inherently poor forsmall fishes. Manipulating the design parameters of slope, length, width and possibly depth-over-breadth ratioenables Denil fishways to pass a wide size range of fish, which may greatly extend their present application andenable them to make a greater contribution to the rehabilitation of diverse fish communities.

KEYWORDS : Australia, bony herring, Denil, fish passage, fishways, potamodromous migration.

Introduction

The restoration of fish passage has historically con-centrated on obligate migratory species with strongcommercial value, and the passage of other species hasoften been considered incidental (Northcote 1998).However, the objective of providing fish passage isdeveloping towards the restoration of stream continu-ity and whole fish communities (Jungwirth, Schmutz &Weiss 1998; Northcote 1998; Mallen-Cooper 1999). Inthis context, accommodating all movements of a widerange of species and sizes of fishes, and other aquaticfauna, is becoming increasingly important in fishwaydesign. A significant challenge of this objective isenabling passage of small fishes with poor swimmingabilities while also passing larger fishes, but at anacceptable capital cost. This challenge is highlighted inAustralian rivers where there is a wide size range ofmigrating fishes, anadromy is rare and there are nonative salmonids.In Australian coastal rivers, catadromy and am-

phidromy are common life-history strategies for fresh-water fishes (Harris 1984) with small life stages of 20–100 mm total length (TL) migrating upstream, as well

as adult fishes of 300–650 mm TL (Harris, Thorncraft& Wem 1998; Stuart & Mallen-Cooper 1999). Innorth-eastern coastal rivers there is also one species,the Australian lungfish, Neoceratodus forsteri (Krefft),which is up to 1200 mm TL that migrates upstream(Stuart & Berghuis 2002).

In the middle reaches of the extensive, semi-aridMurray-Darling river system, the subject of this study,almost all migratory species are potamodromous, withadult fishes (250–600 mm TL), yearling and sub-adultfishes (80–250 mm TL), and some small bodied species(15–60 mm) (Harris et al. 1998; Mallen-Cooper 1999)recorded moving upstream. Large adult Murray cod,Maccullochella peelii peelii (Mitchell), up to 1400 mmTL, may also move considerable distances upstreamand downstream (Koehn & Nicol 1998).

The main fishway options for these fish at low-levelweirs, which are the most common stream barrier, arepool-type fishways, Denil fishways, and �nature-like�bypass channels or rock-ramp fishways (Clay 1995;Lucas & Baras 2001). A major advantage of Denilfishways is that they can be built on steeper slopes thanother fishways and hence are shorter and cheaper (Clay1995). Typically, they are on slopes of 25% to 15%,

Correspondence: Dr Martin Mallen-Cooper, Fishway Consulting Services, 8 Tudor Place, St Ives Chase, NSW 2075, Australia

(e-mail: [email protected])

*Present address: Arthur Rylah Institute for Environmental Research, Post Office Box 137, Heidelberg, Victoria 3084, Australia

(e-mail: [email protected])

Fisheries Management and Ecology, 2007, 14, 61–71

� 2007 The Authors. Journal compilation � 2007 Blackwell Publishing Ltd 61

but occasionally used at lower slopes of 10% (Schwa-lme, Mackay & Lindner 1985; Laine, Kamula & Hooli1998; Haro, Odeh, Castro-Santos & Norieka 1999).This compares with pool-type and nature-like fishwayswhich typically have slopes less than 10% and 5%,respectively (Jungwirth et al. 1998).

Denil fishways have been predominantly used in thenorthern hemisphere for anadromous large-bodiedsalmonid and clupeid fishes, and at some sites withpotamodromous species such as white suckers, Cato-stomus commersoni (Lacepede), smallmouth bass,Micropterus dolomieu (Lacepede) and walleye, Sandervitreus (Mitchill) (Schwalme et al. 1985; Katopodis,Derksen & Christensen 1991; Laine et al. 1998; Bryant,Frenette & McCurdy 1999; Bunt, Katopodis &McKinley 1999; Haro et al. 1999; Bunt, Cooke &McKinley 2000; Laine, Jokivirta & Katopodis 2002).The size of fishes using these fishways is usually greaterthan 300 mm and, although the potential for passageof small fishes in Denil fishways with small baffles isrecognised (Larinier, Travade & Porcher 2002), thedesign is generally considered unsuitable for fish lessthan 250–300 mm TL.

Denil fishways would appear to be unsuitable for thesmall non-salmonid fishes in southern hemisphererivers. However, the results and assumptions of theperformance of this fishway design are based onoperating at steep slopes. The aim of this study wasto test a Denil fishway at these standard steep slopes,but also at a lower slope than commonly used to assessthe suitability of this design for Australian fishes andexamine the potential to pass small fishes (<250 mmTL).

Materials and methods

Site

Euston Weir (Lock 15) in the middle reaches of theregulated Murray River was selected to test a Denilfishway. The Murray River has a low gradient andEuston Weir is 1110 km from the sea but only 43 mabove sea level. There is a relatively long reach of riverof 232 km downstream to the next weir, potentiallyproviding a large population of fish that can bemigrating upstream.

Euston Weir was built in 1937, it is 4.9 m high and120 m wide and impounds 37 000 ML of water for100 km. Included within the weir was a 44.6 m longpool-type fishway within an open concrete channel.There are 15 pools within the channel, each 2.74 mlong, 1.83 m wide and 1.22 m deep (Fig. 1). Thefishway has 16 baffles, with alternate submerged-

orifices (0.3 high by 0.5 m wide) and is built on an11% slope. The head loss between pools is 0.305 mcreating a maximum water velocity of 2.4 m s)1 and anaverage turbulence of 125–143 W m)3.

The Euston fishway enables passage of relatively lownumbers of some large fishes, and individuals less than160 mm TL cannot fully ascend because of the highwater velocities and high turbulence (Mallen-Cooper1996). The fishway has a well-located entrance at thebase of the weir and prior trapping had recorded largenumbers (up to 3000 per day) of migrating fishes(Mallen-Cooper 1996). For the present experimentsthis entrance was used and the lower five baffles of thefishway removed to leave a clear rectangular concretechannel 14 m long, 1.83 m wide and 1.22 m deep.

Experimental Denil fishway

The experimental Denil fishway was built of marineplywood and was 8 m long. Standard single-planeDenil baffles angled upstream at 45� were used; thesehad external width (B) ¼ 0.560 m, internal width(b) ¼ 0.325 m, depth (D) ¼ 0.7 m, with the distance

0 5 10

metres

Flow

cone-trap

screen

B

AA

B

Weir

Denil fishwayinsert

0 30 60

metres

Section B - B

0 1 2

metres

Section A-A

bank

cone-trap

Figure 1. Layout of Euston Weir, old submerged-orifice fishway and

experimental Denil fishway.

M. MALLEN-COOPER & I. G. STUART62

� 2007 The Authors. Journal compilation � 2007 Blackwell Publishing Ltd

between baffles ¼ 0.375 m. These dimensions followedproportions from White & Nemenyi (1942) that are thesame as, or close to, those commonly used (e.g. Beach1984; Lonnebjerg 1990; Larinier et al. 2002) (Fig. 2).The fishway was made adjustable for slopes up to amaximum of 20% and the Denil fishway could slide upand down the concrete channel to adjust for tailwatervariation. The baffles and internal channel of thefishway were painted black as earlier trials with a lightcolour (olive green) inhibited fish from entering.

Experimental design and procedure

Three fishway slopes [8.3% (1:12), 14.3% (1:7) and20% (1:5)] were tested in a randomised block designwith four replicates of each slope. Fish were trappedwith single cone-traps (covered in 15-mm square wire

mesh) as they entered the main fishway entrancechannel from the river to approach the Denil fishwayand at the top of the Denil fishway (Fig. 1). The cone-trap at the main fishway entrance tapered from anopening of 1.8 by 1.8 m to an exit of 0.4 by 0.15 m overa distance of 2 m. The cone-trap at the top of the Denilfishway tapered from an opening of 0.75 by 0.6 m toan exit of 0.4 by 0.15 m over a distance of 0.6 m.Escapement rates for bony herring, Nematalosa erebi(Gunther), from single cone-traps are less than 5%(Mallen-Cooper 1999). There was no handling of fishuntil the end of each test and hence, the samplesize and species composition during each trial wasunknown.

At the beginning of each trial, the Denil fishwaysection was positioned in the concrete channel at thetest slope, with an equal depth at each end. The

breadth (b) 325 mm

375 mm

depth (d)

depth(d)

baffleinvert

Elevation

End view

(D)

263 mm134 mm

560 mm (B)

45O

700 mm

Figure 2. Dimensions of experimental Denil fishway.

SMALL AND LARGE FISHES IN DENIL FISHWAYS 63


entrance and exit cone traps were installed and a wiremesh screen was placed in the next pool upstream ofthe Denil fishway exit to contain fish. An a prioridecision was made that if the slope of the water surfacewithin the Denil fishway section exceeded the test slope(i.e. headwater > tailwater) at the end of the trial, thedata would not be used. Earlier experiments showedthis was an important factor in the function of theDenil fishway, as it is with all pool-type fishways (Clay1995). Water temperature (�C) and dissolved oxygen(mg L)1) were recorded at the beginning and end ofeach trial.

The experimental procedure was to: (1) start theDenil fishway operating at 18:00 h; (2) 17 h later, at11:00 h, the exit of the cone-trap in the concretechannel below the Denil fishway was covered with wiremesh, preventing more fish from entering from theriver; and (3) 4 h later, at 15:00 h, the cone-trap exit atthe top of the Denil fishway was covered with wiremesh. The whole fishway was then drained and fishupstream of the Denil section and from the concretechannel below the Denil fishway were collected,identified and measured. Fork length (FL) measure-ments were taken to the nearest millimetre for specieswith forked tails and total length for others.

The initial 17 h of fishway operation enabled fishmigrating in different diel periods (dusk, night, dawn,day) to enter the fishway entrance channel and the latter4 h provided an opportunity for fish thatmight have justentered the fishway entrance channel to ascend theDenilfishway. Each 21-h trial provided two samples: one ofthe total fish entering the trial (samples for the top of theDenil fishway and the fishway entrance channel com-bined) and one of fish that successfully ascended theDenil fishway. These samples provided a direct com-parison of the proportions of fish ascending the Denilfishwaywithin each trial, which avoids daily fluctuationsin the numbers, species and size composition of migra-ting fishes. Four replicates of each of three trial slopesprovided sufficient independent samples for comparisonof fish length distribution with a Kolmogorov–Smirnovlarge sample, two-tailed test. This test computes theD-statistic, the largest difference between cumulativelength–frequency distributions at any increment (Siegel& Castellan 1988), which was used to detect if smallerfishes, with a corresponding poorer swimming ability,were unable to ascend the Denil fishway.

Results

The experiments were carried out in February andMarch (late summer and autumn) 1995. The watertemperature varied from 24.2 to 26.0 �C and the

dissolved oxygen from 6.0 to 7.9 mg L)1, but there wasno significant difference in these variables between thetreatments (ANOVA, P > 0.22). Data from one repli-cate at 20% slope and one at 8.3% slope werediscarded as upstream water depth in the Denil fishwaywas greater than the downstream water depth at theend of the trial. The depth (d) in the Denil fishway,measured vertically from the invert of the baffle(Fig. 2), ranged from 0.38 to 0.50 m in all experiments,providing a depth-over-breadth (d/b) ratio of 1.2–1.5.

Native fishes entering the fishway approach channelcomprised 8880 bony herring, 28 golden perch, Mac-quaria ambigua (Richardson), and three silver perch,Bidyanus bidyanus (Mitchell). The non-native fishescomprised 106 common carp Cyprinus carpio L., onegoldfish Carrasius auratus (L.) and one redfin perch,Perca fluviatilis (L.).

The proportion of bony herring ascending the Denilfishway was significantly different between the slopes(ANOVA, P ¼ 0.015). A post hoc test indicated thatsignificantly more bony herring ascended the lowestslope (8.3%) than the highest (20%) (Tukey HSD teststatistic ¼ 41.57, P ¼ < 0.05). There was increasingpassage with decreasing slope, with a maximum passageof 95% recorded for the lowest slope of 8.3% (Fig. 3).

The length range of the bony herring was 45–350 mm FL, but 94% of these were less than 120 mmFL. To compare the length distributions of bonyherring, two random replicates were chosen from eachtest slope and the length data of fish ascending theDenil fishway was pooled; the remaining replicateswere pooled to provide an independent sample of fishentering the fishway approach channel. At an 8.3%slope the size of bony herring entering the approachchannel and ascending the Denil fishway were similar

Slope

% a

scen

ding

0

20

40

60

80

100

8.3% 14.3% 20.0%

Figure 3. Proportion (mean ± SE) of bony herring ascending an

experimental Denil fishway at three slopes (N ¼ 3–4; n ¼ 33–3936).



(D1323,292 ¼ 0.040) (Fig. 4). By contrast, there weresignificant differences at the higher slopes of 14.3%and 20% (D1323,403 ¼ 0.329; D1323,97 ¼ 0.597); theproportion of smaller bony herring ascending theDenil fishway declined with increasing slope, althougha few small fishes (<75 mm FL) were still able toascend the fishway at the steepest slope.Of the small numbers of golden perch (195–338 mm

TL) and common carp (122–632 mm FL) that werecollected, almost the full size range ascended the Denilfishway (Fig. 5). However, there were too few commoncarp, golden perch, or silver perch (74–105 mm FL) ineach of the replicates to apply the Kolmogorov–Smirnov test.

Discussion

Effectiveness of the Denil fishway

Despite the long history of the use of Denil fishwaysfor medium-sized fish, particularly salmonids and

clupeids, there is a general perception that they areunsuitable for small fish. However, the present studydemonstrated that these fishways can be specificallydesigned for small fish (45–350 mm long) of onespecies (bony herring) and have significant potentialfor passing other small fishes. Initial results indicatedthat this function does not compromise passage ofmedium-sized fishes, such as cyprinids and percichth-yids. Supporting this are studies of Denil fishways ofvery similar width and depth passing medium-sizedfish (212–800 mm length) (Schwalme et al. 1985;Katopodis et al. 1991).

Reducing the slope of the Denil fishway to 8.3%,less than that normally used, enabled smaller fish andgreater numbers to ascend, and can be considered theoptimum for the small fish in the present study. Thepassage of some small fish at slopes of 14.3% and 20%was unexpected as it has not previously been recordedfor a Denil fishway of these dimensions. This reducedperformance at higher slopes may be acceptable at siteswith lower ecological performance standards.

14.3% slope

Fork length (mm)

Per

cent

freq

uenc

y (%

)

0

10

20 (n = 1323) (n = 403)

8.3% slope

Fork length (mm)40 50 60 70 80 90 100 110 120 130 140 150

40 50 60 70 80 90 100 110 120 130 140 150

40 50 60 70 80 90 100 110 120 130 140 150

0

10

20 (approaching fishway n = 1323)(ascending fishway n = 292)

20% slope

Fork length (mm)

0

10

20 (n = 1323)(n = 97)

150 350

150 350

150 350

Figure 4. Size distribution of bony herring approaching (grey bar) and ascending (solid bar) an experimental Denil fishway.



Improving Denil fishways for small fish

The success of small fishes ascending the Denil fishwayis due not only to the reduced slope but also thenarrow fishway width, low depth-over-breadth (d/b)ratio and short length of the fishway. It is illustrative toexamine the origins of these criteria and the fieldexperience in different countries to review how over-looking their influence on fishway performance has ledto the common perception that Denil fishways providepoor passage for small fishes. It also reveals how thisdesign can have wider application.

The single-plane Denil fishway baffle was developedby White & Nemenyi (1942), from Denil’s originalcurved design (Denil 1909), and they recommended aninternal width (or clear baffle spacing, b) of 0.533 mwith a 20% slope and with the baffles angled upstreamat 45�. These were expanded to 0.76 m with a slope of16% in Sweden in 1945 (Furuskog 1945, in Fulton,Gangmark & Bair 1953) and considered successful forsalmonids. The wider dimensions were then tested inWashington State by the US Fish and Wildlife Servicein 1949 (Fulton et al. 1953), which indicated thepotential for the passage of adult salmon and otherlarge-bodied species. These dimensions are close to themost common width (b ¼ 0.711) now used in the USwhere, for example, in the north-east there are over 150Denil fishways for salmonids and alosids (Ben Rizzo,US Fish & Wildlife Service, personal communication).

Design guidelines in the US, France, Denmark,Germany and the UK now recommend slopes of 20%

to 12.5% with b ¼ 0.45 to 0.70, where slope decreaseswith increasing width (Ben Rizzo, US Fish & WildlifeService, personal communication; Larinier 1983;Lonnebjerg 1990; FAO/DVWK 2002). Narrowerwidths (b ¼ 0.29) have been used in France for smalltrout species and cyprinids (Larinier et al. 2002) andlower slopes of 10% are used occasionally in the USfor weak swimming species (Ben Rizzo, US Fish &Wildlife Service, personal communication). The rangeof widths and slopes used by these countries havegenerally proved effective for medium-sized fish from250 to 740 mm (e.g. Baras, Lambert & Philipart 1994;Haro et al. 1999).

A functional advantage of a wider Denil fishway is agreater discharge and hence, greater fish attraction,which is important in rivers where the river flowgreatly exceeds fishway flow. However, wide Denilfishways do not pass small fish well because of the �sizeof helical currents [and] the distance between baffles�(Larinier et al. 2002). There is also an importantinteraction of width and slope where a wider Denilfishway requires a lower slope to maintain acceptablevelocities and turbulence (Larinier et al. 2002).

Ignoring the width and slope of Denil fishways inevaluating fish passage performance has probablycontributed the most to the perception in manycountries that these fishway do not pass small fishes(Pasche, Dauwe & Blank 1995; Larinier 1998; Lucas,Mercer, Armstrong, McGinty & Rycroft 1999; FAO/DVWK 2002). However, very narrow Denil fishways(b ¼ 0.19) are used in Japan to pass juvenile ayu,

Length (mm)0 100 200 300 400 500 600 700

Slope

common carp entering fishwaycommon carp ascending fishwaygolden perch entering fishwaygolden perch ascending fishway

20%

14.3%

8.3%common carp

golden perch

enteringascending

ascendingentering

n = 1n = 2

n = 4

n = 14

n = 3n = 3

n = 22n = 53

n = 17n = 23

n = 24n = 39

Figure 5. Length range of common carp (grey bar) and golden perch (white bar) entering the fishway approach channel (diagonal hatching) and the

sub-sample that ascended the Denil fishway (no pattern) on three slopes.



Plecoglossus altivelis altivelis (Temminck & Schlegel),75–140 mm long, suggesting that narrower Denilfishways may favour small fishes (Nakamura, Noda,Misawa & Nakahara 1995; Wada, Azuma & Shunroku2000).The limit to reducing Denil fishway width is the

minimum swimming space for the largest fish orbehavioural limitations of schooling species. Widthalso influences the capacity of the fishway to pass highbiomass, the attraction discharge of the fishway and theheadwater range (variation of upstreamwater level overwhich the fishway operates) as the maximum fishwaydepth is determined by the width and the maximumdepth-over-breadth ratio (Larinier et al. 2002).The effect of the depth-over-breadth ratio (d/b,

Fig. 2) on fish passage is not well quantified. Thecriterion originates from White & Nemenyi (1942) whorecommended a maximum d/b of 1.5, which is stillwidely used (e.g. UK, Lucas et al. 1999; Japan, Wadaet al. 2000; France, Larinier et al. 2002). The passageof adult clupeids is known to vary within the d/b rangeof 1.1–1.5 (Haro et al. 1999). Narrow Denil fishways inthe US and Canada are designed with higher d/bs, upto 5, and passage of fish 212–800 mm in length hasbeen recorded at d/b up to 3.3 (Katopodis et al. 1991).However, most field and laboratory studies record fishpassage within the standard d/b of less than 1.5 or,regrettably, do not record water depth in the fishway.As d/b rises from 0.8 to 3 there is a significant

decrease in roughness (skin friction) and an increase inwater velocities (Rajaratnam & Katopodis 1984;Kamula & Barthel 2000; Larinier et al. 2002), whichsuggests there would be decreasing efficiency in passingsmall fish. Certainly the d/b range of 1.2–1.5 in thepresent study would have aided the passage of thesmall clupeids. Future work on quantifying fish pas-sage at high d/b ratios is important as it determines theheadwater range of the fishway and hence the appli-cability of the Denil fishway design to sites withvarying water levels.Length is known to influence fish passage perform-

ance of Denil fishways, but is also not well quantified.The original Denil fishways were conceived withresting pools every 1.83–2.44 m in vertical rise (White& Nemenyi 1942), which is the criterion still used today(Larinier et al. 2002; Ben Rizzo, US Fish & WildlifeService, personal communication). In long fishwaysthis generally results in continuous lengths of less than10 m, and 6–8 m is common. Observations in anangular Denil fishway (Alaskan steeppass) showed thatnon-salmonids such as common carp and Americanshad, Alosa sapidissima (Wilson) could ascend 7.9 m oflength but had restricted passage over 15 m and no

passage over 20 m (Slatick & Basham 1985). However,these results were on steep slopes of 28.7% to 23.3%and there seems to be no other research in this area,either on the single-plane or angular Denil fishways.There are field observations of small westslope cut-throat trout, Oncorhynchus clarki lewisi (Suckley),(mean length 106 mm) using short (2.4–3.6 m) Denilfishways on standard slopes (15.8–16.4%) indicatingthat length may have a important influence on passageof small fish (Schmetterling, Pierce & Liermann 2002).Larinier et al. (2002) considered that small fisheswould not be able to ascend Denil fishways of standarddimensions for more than a few metres and suggeststhis would make the fishway impractical, but notedthat changing the dimensions would likely extend thelength that small fishes can ascend. The present studyconfirmed that small fishes can ascend 8 m of Denilfishway, but further work is needed to examine theinteraction of length and slope on fish passage,especially for small fishes in low-slope Denil fishways.

In summary, the initial application of the Denilfishway for adult salmonids and later for adult clupeidsand similar-sized warmwater species led to designcriteria that optimised attraction and passage of largefish but inadvertently inhibited the passage of small(<250 mm long) sizes of fish. Without a full apprecia-tion of the interactions of width, slope, d/b and length,the poor passage of small fishes has been considered aninherent characteristic of Denil fishways. In reviewingthe literature these significant design parameters areoften not described, especially width and water depth,and hence d/b. To enable interpretation of fish passageperformance, it is recommended that these parametersare included in future papers on Denil fishways, as wellas the more commonly reported aspects of baffledesign.

The present results and interpreting the literaturesuggest that narrow, low-slope Denil fishways aresuitable for small fishes. The limitations of reducingthese design variables are that they reduce the head-water range and passage of larger fish, and dischargefor attracting fishes, but manipulating these designparameters opens up a range of possibilities for thewider application of Denil fishways and their use inpassing small- and large-bodied fish communities.

Application of low-slope Denil fishways for smallfishes

The immediate application is the use of the dimensionsof the Denil fishway in the present experiment, at an8.3% slope, with the objective of passing 45–630-mmfish. Using a resting pool criterion of 10 times the



internal channel width (Larinier et al. 2002), thepresent fishway would need 3.25 m long resting pools,and hence the total slope would be 5.9%. This raisesthe question of whether there is any functional or costadvantage over a pool-type fishway, such as a vertical-slot, on the same total slope. A comparison can beprovided with a vertical-slot fishway on a tidal weir onthe Fitzroy River in north-eastern Australia (Stuart &Mallen-Cooper 1999). The fishway is on a slope of 5%and passes a very similar size range of fish and uses asimilar discharge. The channel width of the vertical-slot fishway is over three times that of the Denilfishway used in the present experiment and it cannot benarrower as the pool volume is needed to maintain alow turbulence (40 W m)3) for passage of small fishes.The reduced width of the Denil fishway suggests thereis a significant cost advantage for a similar fish passageperformance. An additional construction and costadvantage of the Denil design, particularly at remotesites, is that it can be easily pre-fabricated. However, atremote fishways there are maintenance considerations,such as blockage by debris, and well-designed trashracks and debris booms are necessary.

Functionally, the Denil design is more limited in theheadwater range where the vertical-slot is unlimited ifheadwater and tailwater rise and fall in phase. Vertical-slot fishways have the capacity to pass a high fishbiomass (Andrew 1990), whereas Denil fishways haveless capacity, which can mainly be improved by addinganother fishway (e.g. Blackett 1987). Migratory bio-mass has not been quantified in Australian streams,although a maximum of 150 kg h)1 was recorded inthe tidal vertical-slot fishway mentioned above (Stuart1999). The single-plane Denil fishway design may alsobe poorer at passing surface-dwelling species as the lowwater velocities for fish passage are located at the baseof the baffle (Rajaratnam & Katopodis 1984). AngularDenil fishways (Alaskan steeppass) offer a potentialalternative here as the low velocity zone for fishpassage is at the surface (Rajaratnam & Katopodis1991; Wada et al. 2000).

The limitations of the single-plane Denil fishwaydesign need to be considered on a site-specific basis.There are many sites in eastern Australia that havestable headwater (often needed for irrigation ordomestic water supply offtakes), low migratory bio-mass, with no specialist surface-dwelling fishes. Theheadwater range of Denil fishways is often seen as themajor limitation, but there are options to improve thisaspect. In the US north-east the headwater range ofDenil fishways has been expanded by having lift-outbaffles at the upstream end which are removed as theheadwater lowers (Ben Rizzo, US Fish & Wildlife

Service, personal communication). In one Australianapplication, the upstream end of the Denil fishway haslift-out channel sections to shorten the fishway asheadwater lowers. The limitation of these options isthey need to be manually adjusted and are unsuitablefor unmanned remote sites. Rajaratnam, Katopodis &Flint-Petersen (1987) suggested stacking Denil chan-nels to expand the headwater range. Although thiswould need to be configured to avoid a tunnel thatwould inhibit passage of some species (Mallen-Cooper1999), the principle of having separate Denil fishwaysfor different headwater and tailwater levels is asolution that needs no manual adjustment.

The other immediate application of the results ofthis study is to retrofit Denil fishways into steep pool-type fishway channels. Three such Denil fishways havebeen applied to existing Australian fishways, includingthe one in this study, and others on sub-tropicalcoastal rivers. The new full-length Denil fishway atEuston Weir is on a 15% slope with three resting pools2.0 m long with 3.5 m3 or greater, fitting into the old11% slope channel. The relatively steep slope andsmall resting pools of the Denil fishway reflected a costsaving decision and further work will be needed toquantify the extent that small-bodied native fish areable to ascend.

In achieving the most effective cost–benefit for afishway, the major design variables that are examinedare the river levels over which the fishway will operate,the entrance location and the size range of fish. Lowriver flow conditions determine the maximum headdifferential and the high river flows determine theheight of the fishway walls and influence the need formultiple entrances. The hydraulic conditions below theweir influence the entrance location and its ability toattract fish. The minimum fish size reflects the weakestswimming fish and determines the maximum watervelocity while the maximum fish size determines theminimum space (width, depth) needed. These differingfish passage functions are usually accommodated inone fishway. The present study suggests an opportun-ity to separate these functions and potentially providegreater fish passage at less cost.

One option is to use a small Denil fishway for smallfish, optimising the design variables identified in thepresent study, and use either a large Denil or vertical-slot fishway for large fish. On the Murray River,vertical-slot fishways on a gradient of 3.1% (1:32) withlarge pools of 3 m by 2 m are being constructed to pass50–1000 mm long fish (Barrett & Mallen-Cooper,2006). Costings suggest that a twin-fishway option,with a 5.5% (1:18) vertical-slot fishway to pass largespecies 100–1000 mm in length (e.g. Mallen-Cooper



1999) and a small Denil fishway to pass small species50–100 mm in length is cheaper because the vertical-slot fishway is half the length. Research on thesuitability of the small Denil fishway would be neededbefore such an application.A second option is to use a Denil fishway to separate

the function of fish passage at high and low flows. At a3.2 m high weir approximately 286 km downstream ofEuston Weir (Wentworth Weir, Lock 10), two fishwayswere completed in mid-2006; a 96 m long 3.1% slopevertical-slot fishway optimised for small and largefishers for low to medium flows and a short 6 m long15% slope Denil fishway operating for large fish athigh flows. This configuration saved cost on the heightof the concrete wall of the vertical-slot fishway andresulted in two fishways being cheaper than one. Thedesign decisions were driven by fish ecology, where inthe extensive semi-arid reaches of the Murray-Darlingriver system large fishes tend to dominate the upstreammigratory population at high flows and small fishesdominate at low flows.A similar migratory ecology may apply to tidal

barriers, which would present another option for usinga Denil fishway. Tidal barriers present a particular fishpassage issue with small catadromous juveniles as wellas adults migrating upstream. There are some ecolog-ical observations to suggest that the juveniles of somespecies move upstream at low flows (Harris 1983;Mallen-Cooper 1992; Stuart & Mallen-Cooper 1999),while the adults move upstream at low and high flows(Stuart & Mallen-Cooper 1999). In this situation asingle Denil fishway with a dual function could beused. The effect of d/b on fish passage could be used sothat at low flows the fishway operates with a low d/b(e.g. 0.5) optimised for small fishes with some large fishpassage, and at high flows with higher headwater levelsit would have a higher d/b (e.g. 1.5), which would beoptimised for large fishes but would compromisepassage of small fishes. A Denil fishway at low depthalso uses little water, which would make this conceptcompatible with other water uses in streams where asemi-arid hydrology and long periods of very low floware typical. It would also use more water for fishattraction when it was available at higher flows andheadwater levels.The present study dispels the long-held assumption

that Denil fishways are inherently poor for the passageof small fish. Denil fishways on a low slope havepotential to pass a wide size range of fishes, whichgreatly extends their present application. Separatingthe biological and hydrological functions of fishpassage further extends the application of Denilfishways. Although there is a general understanding

of the influence of slope, length, width and d/b on fishpassage in Denil fishways, further experimentation isneeded to quantify these aspects for small fishes. As thetrend in fish passage moves increasingly towards amore holistic view (Jungwirth et al. 1998; Northcote1998) Denil fishways are likely to have much broaderpotential than previously recognised to contribute toimproved passage of whole fish communities.

Acknowledgments

The Murray-Darling Basin Commission funded con-struction of the experimental Denil fishway and jointlyfunded the assessment with the NSW Department ofPrimary Industries. We are grateful to Graeme White,NSW Department of Primary Industries and RayMcMaster, NSW State Water, for assistance on site.

References

Andrew F.J. (1990) The use of vertical-slot fishways in

British Columbia, Canada. In: S. Komura (ed.) Proceed-

ings of the International Symposium on Fishways �90 in

Gifu. Gifu, Japan: Publications Committee of the Inter-

national Symposium on Fishways �90, pp. 267–274.Baras E., Lambert H. & Philipart J. (1994) A comprehensive

assessment of the failure of Barbus barbus spawning mi-

grations through a fish pass in the channelized River

Meuse (Belgium). Aquatic Living Resources 7, 181–189.

Barrett J. & Mallen-Cooper M. (2006) The Murray River’s

�Sea to Hume Dam� fish passage program: progress to date

and lessons learned. Ecological Management and Restor-

ation, 7, 173–183.

Beach M.H. (1984) Fish Pass Designs – Criteria for the

Design and Approval of Fish Passes and Other Structures to

Facilitate the Passage of Migratory Fish in Rivers. Fisheries

Research Technical Report, Lowestoft, England, No. 78,

46 pp.

Blackett R.F. (1987) Development and performance of an

Alaska steeppass fishway for sockeye salmon (Oncorhyn-

chus nerka). Canadian Journal of Fisheries and Aquatic

Sciences 44, 66–76.

Bryant M.D., Frenette B.J. & McCurdy S.J. (1999) Coloni-

zation of a watershed by anadromous salmonids following

installation of a fish ladder in Margaret Creek, southeast

Alaska. North American Journal of Fisheries Management

19, 1129–1136.

Bunt C.M., Katopodis C. & McKinley R.S. (1999) Attrac-

tion and passage efficiency of white suckers and small-

mouth bass by two Denil fishways. North American

Journal of Fisheries Management 19, 793–803.

Bunt C.M., Cooke S.J. & McKinley R.S. (2000) Assessment

of the Dunnville Fishway for passage of walleyes from



Lake Eyrie to the Grand River, Ontario. Journal of Great

Lakes Research 26, 482–488.

Clay C.H. (1995) Design of Fishways and Other Fish Facilit-

ies. Boca Raton: Lewis Publishers, CRC Press Inc., 248 pp.

Denil G. (1909) Les echelles a poissons et leur application

aux barrage de Meuse et d’Ourthe (Fishpasses and their

application at the Meuse and Ourthe dams). Annales des

Travaux Publics de Belgique, 150 (5 plates).

FAO/DVWK (2002) Fish Passes – Design, Dimensions and

Monitoring. Rome: FAO, 119 pp.

Fulton L.A., Gangmark H.A. & Bair S.H. (1953) Trial of a

Denil-type Fish Ladder on Pacific Salmon. U.S. Fish and

Wildlife Service Special Scientific Report – Fisheries, No.

99, 16 pp.

Furuskog V. (1945) En ny laxtrappa (A new salmon pass).

Sartryck ur Svensk Fiskeri Tidskrift 11, 236–239 (in

Swedish).

Haro A., Odeh M., Castro-Santos T. & Norieka J. (1999)

Effect of slope and headpond on passage of American shad

and blueback herring through simple Denil and deepened

Alaska steeppass fishways. North American Journal of

Fisheries Management 19, 51–58.

Harris J.H. (1983) The Australian bass, Macquaria novema-

culeata. PhD Thesis. Sydney: University of New South

Wales, 260 pp.

Harris J.H. (1984) Impoundment of coastal drainages of

south-eastern Australia, and a review of its relevance to

fish migrations. Australian Zoologist 21, 235–250.

Harris J.H., Thorncraft G.A. & Wem P. (1998) Evaluation of

rock-ramp fishways in Australia. In: M. Jungwirth,

S. Schmutz & S. Weiss (eds) Fish Migration and Fish

Bypasses. Oxford: Fishing News Books, pp. 331–347.

Jungwirth M., Schmutz S. & Weiss S. (eds) (1998) Fish

Migration and Fish Bypasses. Oxford: Fishing News

Books, Blackwell Science, 438 pp.

Kamula R. & Barthel J. (2000) Effects of modifications on

the hydraulics of Denil fishways. Boreal Environment

Research 5, 67–79.

Katopodis C., Derksen A.J. & Christensen B.L. (1991)

Assessment of two Denil fishways for passage of fresh-

water species. American Fisheries Society Symposium 10,

306–324.

Koehn J. & Nicol S. (1998) Habitat and movement

requirements of fish. In: R.J. Banens & R. Lehane (eds)

Proceedings of the 1996 Riverine Environment Forum,

Brisbane. Canberra: Murray Darling Basin Commission,

pp. 1–6.

Laine A., Kamula R. & Hooli J. (1998) Fish and lamprey

passage in a combined Denil and vertical slot fishway.

Fisheries Management and Ecology 5, 31–44.

Laine A., Jokivirta T. & Katopodis C. (2002) Atlantic sal-

mon, Salmo salar L., and sea trout, Salmo trutta L., pas-

sage in a regulated northern river – fishway efficiency, fish

entrance and environmental factors. Fisheries Management

and Ecology 9, 65–77.

Larinier M. (1983) Guide pour la conception des dispositifs

de franchissement des barrage pour les poisson migrateurs.

Bulletin Francais Peche et Pisciculture 39, 29pp.

Larinier M. (1998) Upstream and downstream fish passage

experience in France. In: M. Jungwirth, S. Schmutz & S.

Weiss (eds) Fish Migration and Fish Bypasses. Oxford:

Fishing News Books, Blackwell Science, pp. 127–145.

Larinier M., Travade F. & Porcher J.P. (2002) Fishways:

biological basis, design criteria and monitoring. Bulletin

Francais Peche et Pisciculture 364(Suppl.), 208.

Lonnebjerg N. (1990) Fishways in Denmark. In: S. Komura

(ed.) Proceedings of the International Symposium on Fish-

ways �90 in Gifu. Gifu, Japan: Publications Committee of

the International Symposium on Fishways �90, pp. 253–259.

Lucas M.C. & Baras E. (2001) Migration of Freshwater

Fishes. Oxford: Blackwell Science, 420 pp.

Lucas M.C., Mercer T., Armstrong J.D., McGinty S. &

Rycroft P. (1999) Use of a flat-bed passive integrated

transponder antenna array to study the migration and

behaviour of lowland river fishes at a fish pass. Fisheries

Research 44, 183–191.

Mallen-Cooper M. (1992) Swimming ability of juvenile

Australian bass, Macquaria novemaculeata (Steindachner),

and juvenile barramundi, Lates calcarifer (Bloch), in an

experimental vertical-slot fishway. Australian Journal of

Marine and Freshwater Research 43, 823–834.

Mallen-Cooper M. (1996) Fishways and freshwater fish

migration in south-eastern Australia. PhD Thesis. Sydney:

University of Technology, 377 pp.

Mallen-Cooper M. (1999) Developing fishways for nonsal-

monid fishes: a case study from the Murray River in

Australia. In: M. Odeh (ed.) Innovations in Fish Passage

Technology. Bethesda, MD: American Fisheries Society,

pp. 173–195.

Nakamura S., Noda M., Misawa H. & Nakahara Y. (1995)

Temporarily installed long, steep Denil fishway on the

OhkohchiSabo-Damin theAbe-GawaRiver. In:S.Komura

(ed.) Proceedings of the International Symposium on Fish-

ways �95 in Gifu. Gifu, Japan: Publications Committee of

the International Symposium onFishways �90, pp. 155–162.Northcote T.G. (1998) Migratory behaviour of fish and its

significance to movement through riverine passage facilit-

ies. In: M. Jungwirth, S. Schmutz & S. Weiss (eds)

Migration and Fish Bypasses. Oxford: Fishing News

Books, Blackwell Science, pp. 3–18.

Pasche E., Dauwe L. & Blank M. (1995) New design prin-

ciples of fishways. In: S. Komura (ed.) Proceedings of the

International Symposium on Fishways �95 in Gifu. Gifu,

Japan: Publications Committee of the International Sym-

posium on Fishways �90, pp. 113–120.



Rajaratnam N. & Katopodis C. (1984) Hydraulics of Denil

fishways. Journal of Hydraulic Engineering 110, 1219–1233.

Rajaratnam N. & Katopodis C. (1991) Hydraulics of steep-

pass fishways. Canadian Journal of Civil Engineering 18,

1024–1032.

Rajaratnam N., Katopodis C. & Flint-Petersen L. (1987)

Hydraulics of two-level Denil fishways. Journal of Hy-

draulic Engineering 113, 670–674.

Schmetterling D.A., Pierce R.W. & Liermann B.W. (2002)

Efficacy of three Denil fish ladders for low-flow fish pas-

sage in two tributaries to the Blackfoot River, Montana.

North American Journal of Fisheries Management 22, 929–

933.

Schwalme K., Mackay W.C. & Lindner D. (1985) Suitability

of vertical slot and Denil fishways for passing north-tem-

perate, non-salmonid fish. Canadian Journal of Fisheries

and Aquatic Sciences 42, 1815–1822.

Siegel S. & Castellan N. (1988) Nonparametric Statistics for

the Behavioural Sciences, 2nd edn. New York: McGraw-

Hill, 399 pp.

Slatick E. & Basham L.R. (1985) The effect of Denil fishway

length on passage of some nonsalmonid fishes. US

National Marine Fisheries Service Marine Fisheries Review

47, 83–85.

Stuart I.G. (1999) Assessment of a vertical-slot fishway for

non-salmonid fish at a tidal barrier on the sub-tropical

Fitzroy River, Queensland. MSc Thesis. Rockhampton:

Central Queensland University, 208 pp.

Stuart I.G. & Berghuis A.P. (2002) Upstream passage of fish

through a vertical-slot fishway in an Australian subtropical

river. Fisheries Management and Ecology 9, 111–122.

Stuart I.G. & Mallen-Cooper M. (1999) An assessment of the

effectiveness of a vertical-slot fishway for non-salmonid

fish at a tidal barrier on a large tropical/sub-tropical river.

Regulated Rivers: Research and Management 15, 575–590.

Wada K., Azuma N. & Shunroku N. (2000) Migratory

behavior of juvenile Ayu in Denil and Steeppass fishways

in Japan. In: M. Odeh (ed.) Advances in Fish Passage

Technology. Bethesda, MD: American Fisheries Society,

pp. 103–114.

White C.M. & Nemenyi P. (1942) Report on Hydraulic

Research on Fish-passes. Appendix of the Report of the

Committee on Fish-Passes. Institution of Civil Engineers.

London: William Clowes and Sons, pp. 32–59.



Optimising Denil fishways for passage of small and large fishes

Documents

Transcript of Optimising Denil fishways for passage of small and large fishes