TRIAL OF
DENIL-TYPE FISH LADDER
ON PACIFIC SALMON
Marine Biological Laboratory
WOODS HOLE, MASS.
SPECIAL SCIENTIFIC REPORT: FISHERIES No. 99
UNITED STATES DEPARTMENT OF THE INTERIOR '
FISH AND WILDLIFE SERVICE
Explanatory Note
The series embodies results of investigations, usually of
restricted scope, intended to aid or direct management or utilization
practices and as guides for administrative or legislative action. It
is issued in limited quantities for the official use of Federal, State
or cooperating Agencies and in processed form for economy and to avoid
delay in publication.
Washington, D.C.
May, 1953
United States Department of the Interior, Douglas McKay, Secretary
Fish and Wildlife Service, Albert M. Day, Director
TRIAL OF DENIL-TTPE FISH LADDER ON PACIFIC SALMDN
by
Leonard A. Fulton and Harold A. Gangmark
Fishery Biologists
and Scott H. Bair
Hydraulic Engineer
Special Scientific Reports Fisheries No. 99
CONTENTS
Page
History of the Denil-type ladder , 1
Design developments of the Denil-type 'ladder 3
General design features of the Denil-type ladder at
Dryden Dam 5
General design f eatures of the Pool-type ladder at
Dryden Dam. ... - 8
The exp erL raent .^ 10
Discussion 13
Summary and conclusions l5
ILLUSTRATIONS
Figure Page
1. Perspective of Denil-type fish ladder with
single-plane baffles 2
2. Pictorial representation of flow conditions in
Denil-tj'pe fish ladder, with direction of flow at the
various depths shown by position of thread banderoles.
{Redrawn from Furuskog 19Ui) 1;
3. Arrangment of structures at Dryden Dam. 6
ii. Pool-type fish ladder in 19^8 prior to construction of
the Denil-type ladder 7
5. The Denil and pool-type fish ladders in operation in
19U9. 7
6. General design of Denil-type fish ladder at Dryden Dam.... 9
In the Pacific Northwest the problem of safeguarding the passage
of upstream migrating fish at hydroelectric and irrigation developments
is becoming increasingly importanto
New types of fishways are being considered in the hope that more
efficient ones will be found, A design known as the Denil-type fishway,
used to some extent in Europe, has had favorable comment as an economical
yet efficient means of enabling fish to surmount barriers. New interest
was stimulated hy an article by Valter Furuskog (19U$) of Stockholm,
Sweden, concerning the design and construction of a "fish pass" for the
Herting power dam on the Atran fliver, near Falkenburg, Sweden. As a
result of this interest, an experiment was designed to compare the effective-
ness of the pool-type and Denil-type ladders as fish-passage devices.
Observations were made in a side-by-side installation at Dryden Dam
on the Wenatchee River approximately 17 miles above the confluence of the
Wenatchee and Columbia Rivers.
HISTORY OF THE DENIL-TYPE LADDER
The Denil-type fish ladder, "counter-current" in principle, was
developed by G, Denil of Brussels, Belgium who devised a system of
baffles in a channel whxich by nature of their shape and position im-
part a secondary outward circulation of flow, producing a momentum
transfer from the central portion of the channel toward the walls.
In a publication concerning "fish-pass" installations at the Meuse and
Orthe Dams on the Rhine River, Denil (1909) presented his fish-ladder
design in its original form, explained the ideas xirhich served as the
basis of his design, and described in detail the first fish ladders con-
structed with his principles. Work initiated by Denil in 1907 was con-
tinued over a period of 30 years. In his endeavor to develop a rational
basis for fish-ladder design, Denil (1936-38) conducted numerous experi-
ments on the hydraulics of "counter- current" fish ladders, the nature
and magnitude of resistance encountered by fish in various types of
ladders, and the^ility of fish to overcome those resistances.
Denil 's principles were further investigated by the Committee on
Fish Passes, British Institution of Civil Engineers, who during the
period 1936-38 carried out hydraulic experiments at the Imperial College
of Science and Technology to confirm Denil' s results and, by application
of his principles, to develop a simpler design of baffle than the some-
what complicated cup-shaped baffle utilized by Denil in his experiments.
The type of baffle selected ty the British investigators as the most
practical was a single-plane baffle (see Figure 1) which is more readily
constructed than the cup-shaped baffle used by Denil.
Figure 1.— Perspective of Denil-type fish ladder with single-plane baffles
2
In March 19ii3j further investigations were made by Swedish fishery-
interests at Stockholm, of experimental fish ladders constructed in
accordance with the recommendations of the Committee on Fish Passes.
Based on the results of these experiments ^ a Denil-type ladder was de-
signed by Furuskog for the Herting power dam in Swedeno Furuskog's
design represented a modification of the design recommended by the
Committee on Fish Passes, involving an increase in linear dimensions
and a decrease in bottom slope of the channel.
Further comparative experiments of models of the Herting fish
ladder were undertaken in May 19^3 "under the guidance of Professor
Hellstrom of the Royal Technical University of Stockholm. One of the
models was sawed down the middle, and one of the halves was placed
against the glass wall of a test flume, so that observations could be
made of currents inside the fish-ladder model„ By use of a wire with
thread banderoles attached, it was found that the currents near the
bottom of the channel were nearly vertically upward with the higher
velocities in a longitudinal direction occurring near the water surface
(see Figure 2) . The baffles being placed at an angle with the floor of
the channel catch the faster-flowing water near the water surface, forc-
ing the flow downward to the floor where it is directed upward in such a
manner that it slows down the current in a longitudinal direction. Ex-
periments utilizing small fish gave no indication of their being disturbed
by the vertical currents.
The Herting fish ladder was completed in May, 19hS ^ and counting
observations were initiated in September of the same year. According
to Furuskog (19U5), Sh Atlantic salmon i^eighing up to 20 pounds and 6
sea-run trout negotiated the new fish ladder during one 3-hour period.
The success of the Denil-type ladder at the Herting power dam was con-
sidered proved, although the information furnished by Furuskog gives
no indication of the size of run involved.
i DESICM DEVELOPMENTS OF THE DENIL-TYPE LADDER
Based on experiments conducted by the British investigators during
the period 1936-38, a practical Denil-type fish ladder as defined by the
Committee on Fish Passes (19^2) would have a channel width of 3 feet,
with single-plane baffles spaced at a distance of two-thirds the c hannel
width and laid sloping upstream at a h5=-degree angle with the channel
floor. As further defined by the Committee, a practical Denil-type fish
ladder would have a clear opening between the upright portions of the
individual baffles of 1 foot 9 inches 5 the channel would have a bottom-
slope not exceeding 1 on U, and resting pools would be provided at verti-
cal intervals of 6 to 8 feet. A bottom slope of 1 on 5 was, however,
recommended where a channel length of 30 feet is provided between resting
pools.
FiFure 2.— Pictorial representation of flow conditions in Denil-type fish
ladder, -ith direction of flow at the various depths shown by
position of thread banderoles. (Redrawn from Furuskog 19A5;.
Effective operating depth, as recommended by the Committee, varies
between the limits of 2 to 3 feet above the floor of the channel. At a
depth of 2 feet J approximately 10 second-feet (cubic feet per second)
of flow would be required for operation of the defined practical Denil-
type ladder^ and at a 3-foot depth, flow requirements would be increased
to about 21 second-feet.
As described by Furuskog (19h5) , the Denil-type ladder at the Herting
power dam represents a modification of the design recommended by the Com-
mittee on Fish Passes, involving a linear enlargement of about lU2 percent
and a decrease in bottom slope of the channel to 1 on 6. The channel width
was increased to 1,30 meters (i; feet 3-I/I4 inches), with a clear opening
between the upright portions of the individual baffles of O.76 meters (2
feet 6 inches) . The slope of the baffles was maintained at hS degrees
with respect to the floor of the channel, and the spacing of baffles was
maintained at two-thirds the channel width. The greatest channel dis-
tance between successive resting pools in 9*02 meters (29 feet 7-1/8
inches'^ .
Flow requirements of the Denil-type fish ladder at the Herting
power dam was reported by Furuskog to be normally l.k cubic meters per
second (li9 second-feet) , although the figure is not particularly sig-
nificant in that the operating depth within t he channel was not
specified.
GENERAL DESIGN FEATURES OF THE DENIL-TYPE LADDER
AT DRYDEN DAM
The apoarent success of the Herting fish-ladder installation
designed by Furuskog, encouraged the Fish and Wildlife Service to con-
struct a Denil-type ladder side by side with an overflow weir pool-
type ladder. In this way the efficiency of the two types could be
compared under similar operating conditions and with the same species
of fish. The site at Dryden Dam (see Figure 3j on the Wenatchee River
was selected, inasmuch as it was a relatively low dam where concentra-
tions of salmon could be assured. The location was oarticularly advan-
tageous, since, as the r esult of reconstruction work at Dryden Dam to
replace sections of the dam damaged by high water in the spring of 19li3,
a temporary earthfill cofferdam made it possible to construct the Denil
fish-ladder in the existing pool-type ladder while the latter was
unwateredo The work was thus facilitated and resulted in a more econom-
ical installation than otherwise could have been effected.
Construction of the Denil-type ladder reduced the width of the pool-
type ladder to approximately one-half of its original width of 10 feet
as shown in Figures h and 5. The two ladders could then be compared to
determine inhich was preferred by the fish. Work on the Denil-type
installation was initiated during the fall of I9U8 and was completed in
the spring of I9U9.
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Fi^re I. — Pool-type fish ladder in 19A^ prior to construction of
the Denil-type ladder.
Figure 5. — The Denil and pool- type fish ladders in operation in 1949,
Design of the Denil-type ladder at Dryden Dam was patterned after
the Herting installation and varied therefrom only to the extent that no
weirs were provided at the upper end for regulation of ladder flows with
accompanying forebay fluctuations. However, flow regulation c an be
effected to a small degree by the insertion of one or more stop-logs in
the guides provided at the upper end of the ladder for unwatering pur-
poses. The Dryden installation (see Figure 6) consists of a channel 1;
feet 3 inches in width, with 10 U-shaped wooden baffles spaced 2 feet
10 inches on centers along the floor of the channel and set at & h^-
degrse angle thereto. Clear ooening between the upright portions of
the individual baffles is 1 foot 9 inches, and the bottom slope of the
channel is 1 on 6, The ladder is d^ '. c^ned for a maximiun difference in
elevation betxreen forebay and tail. if approximately 5 feet 9 inches,
Flow through the ladder was experimentally adjusted between 20 and
30 second-feet during the tests. According to the British Committee on
Fish Passes, minimum operating depth^ for, the Denil-type ladder with a
channel 3 feet in width was indicated to be 2 feet above the channel
floor. Observations made at Dryden Dam showed that fish could readily
negotiate the ladder at a lesser depth.
The maximum operating depth was based on the assumption that the
maximum depth (3 feet) prescribed by the Committee on Fish Passes for
the channel 3 feet in width could be increased by U2 percent. The U2
percent represents the increase in linear dimensions of the Denil-type
ladder at Dryden Dam over that recommended by the Committee on Fish
Passes. From actual observations, the most suitable operating depth
appeared to be 3 feet. At this depth flow through the Dryden installa-
tion was computed from current-meter readings to be approximately 30
second-feet.
GENERAL DESIGN FEATURES OF THE POOL- TYPE LADDER
AT DRYDEN DAM
As previously mentioned, the width of the pool-type ladder was
reduced to about one-half of the original width (10 feet) as a result
of construction of the Denil-type ladder. The pool-type ladder con-
sisted of h pools each 5 feet wide and 6 feet long. This made 5 steps
of approximately 1 foot drop. Flows were regulated at from 9 to 12
second-feet.
Tne pool-type ladder was damaged by high waber in the spring of
1950 when the lowest weir supports were vrashed out. This reduced the
number of ladder pools to three and created a short entrance channel
to the ladder from the tailwater area below the dam. This change in
the number of pools apparently did not affect fish passage. More fish
ascended the ladder in 19^1 than in 19ii9.
The average depth of water in the pools of the ladder was calcu-
lated to be $o5 feet for the h pools in 19h9 and U.U feet for the 3
pools as operated during 19.^1 «
THE EXPERIMENT
V/ith the completion of the Denil-type ladder at Dryden Dam
in the spring of 19l;95 plans were formulated for fish-passage obser-
vations at both the Denil-type and pool-type ladders, in connection
with the migration of blueback salmon (Oncorhynchus nerka) and chinook
salmon (Oncorhynchus tshawytscha) on their way to their spawning grounds.
The method used for making comparative counts of fish utilizing the
individual ladders was for the observer to alternate his attention from
one ladder to the other for approximately equal periods. When two observers
were available, fish were counted simultaneously in both ladders.
During the 19li9 migration, llU hours 20 minutes of observa'' ions were
made, with a total of 260 fish being counted through the ladders. However,
not as many fish were tallied as had been anticipated, since, as the result
of flow conditions over this relatively low dam, a great many were able to
negotiate the dam without using the ladders. Fish other than salmon seen
ascending the Dryden ladders were rainbow or steehead trout (Salmo
gairdenrii) , Dolly Varden trout (Salvelinus malma) , suckers (Catostomus
so.) and Squawfish (Ptychocheilus oregonensis) .
In I9L9, a total of 259 fish was counted through the Denil-type ladder
in 6U hours and $ minutes, while only one fish was observed passing
through the pool-type ladder in 50 hours l5 minutes of observation. Data
concerning these observations are listed in Table 1. The observations
were extended to the 19^0 season, but were soon abandoned after no fish
were seen using the ladders over a period of several days. High water
conditions resulted in the fish finding other means of negotiating the
dam than by the ladders.
From the standpoint of the experimental observationo, water levels
during the 19^1 season were more satisfactory and salmon used the fish
ladders to a greater extent. Both the Denil-type and pool-type ladders
were observed for a total of U6 hours IiO minutes during which time l^SS^
fish ascended the Denil-type ladder and 225 fish were counted through the
pool-type ladder. The data on 195l observations can be found in Table 2.
Thus in the total time that counting was conducted in 19^9 and 19^1 (207
hours ho minutes, 89 percent of the fish used the Denil-type ladder and
11 percent used the pool-type ladder. As will be noted from Tables 1 and
2, a larger percentage of fish negotiated the dam in 195l by use of the
pool-type than in I9U9.
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DISCUSSION
In an experiment of this type^ it is difficult to eliminate all
influences which might have an effect on the final outcome. Results of
the experiment would have been more conclusive, had it been possible to
alternate the position of the two ladders. However, the importance of
position is minimized to a degree at least by two conditions: (1) the
small flow requirement for each of the ladders as compared to the total
flow over the dair gave both ladders a relatively equal attraction to
salmon approaching from either shore ;, and (2) despite the fact that sal-
mon are sometimes known to follow the shorelines in their upstream migra-
tion^, our experience at other damSj such as Tumwater Dam further upstream^
indicates that the greatest numbers of fish do not always use the entrance
situated nearest the shore.
Another question which arisen is v:hether or not the pool-type ladder
at Dryden Dam was a good example of that type. That is, were the pools of
adequate dimensions and was the entrance most suitably located with respect
to the downstream face of the dam? Also, might not the pool-type ladder
have been more effective had it been possible to provide submerged orifices
in the weirs? Short ladder pools ( 6 feet) precluded the use of submerged
orifices, //hile the pool-type ladder at Dryden Dam is not suggested as
being the best exam.ple of that type ladder, it is a typical example of
the ladders constructed at low-head dams on the tributary streams through-
out the Columbia River basin.
It appeared from observations made in connection with the experiment
that the foremost advantage of the Denil-type ladder is the attractive
entrance condition created by the nozzle-like flow from the ladder entrance.
In the case of the pool-type ladder, the effect of the nappe of flow over
the entrance weir is quickly dissipated as it plunges into the deeper water
below the dam, whereas the effect of the jet of flow from the Denil-type
ladder extends downstream a considerable distance from the ladder entrance
horizontally along the water surface. This fact, it was concluded, was the
chief reason why most of the fish selected the Denil-type over the pool-
type ladder.
In arldition to providing what appears to be a better attraction
to fish, the Denil-type proved to be superior with regard to facilitation
of fish passage. Salmon and fish of several other species, including
squawfis'h, suckers and certain less active fish, appeared to arrive at
the upper end of the ladder with little effort. The ease with which
fish appeared to negotiate the ladder is attributed to the dissipation of
energy by the baffles. Part of this dissipation of energy produces up-
ward currents which /jere demonstrated by Furuskog in a model, as shown in
Figure 2.
It was not always possible to see fish entering the two ladders,
hence the length of time it took fish to negotiate the two types was
not measured. However, there were a few occasions when the water was
13
clear so that individual fish could be seen entering the ladders and
later crossing the counting board. The short time required for a
salmon to pass upstream through the Denil-type never failed to startle
the observers, and was especially in contrast to the slow progress
through the pool-type ladder.
During short periods of observation, fish passed through the
Denil-type at an average of 2U second intervals. (On August 18^ 1951,
in 100 minutes of observation, 2^7 fish passed through) „ On numerous
occasions several bluebacks passed through the ladder simultaneously,
or in rapid succession. However, it would be desirable tu make an
additional study at a location where there is a greater concentration of
fish and other species of salmon present. The apparently more attractive
entrance flow of the Denil-type could be a deciding factor in preventing
delay or acc^;lmulation of salmon such as now occurs below pool-type ladders.
From the standpoint of flow and number of fish concerned,, the Denil-
tj'pe ladder conveyed more fish per second-foot of flow than the pool-type
ladder. That is, 89 percent of the fish used the Denil-type ladder, al-
though it carried only 1|0 percent more flow,
A saving in space can be an important factor where there is limited
room for construction. Fishery engineers in Sweden are convinced that
the Denil-type ladder, with a width of approximately that of the Dryden
Dam installation ( h feet 3-l/U inches), will replace the pool-type
ladder with a width of 10 feet, commonly used in Sweden. In addition,
the steep gradient of the Denil-type ladder would result in a somewhat
shorter over-all length than for a pool-type ladder with pools of normal
length, thereby conserving space.
Some difficulty was experienced in keeping the Dool-type ladder con-
tinually adjusted to produce optimum flow conditions for upstream passage
of fish. The removal or addition of stop-logs or for that matter, even
minor changes in water level, will alter the hydraulic conditions within
the pool to influence to some de gree the response of fish to the fishway.
A distinct advantage in the Denil-type structure is the automatic adjust-
ment for changes in water level obtained from use of the vertical baffles.
Although the optimum conditions for salmon have never been adequately
determined, the accepted operational procedure for pool=type ladders was
followed to even a greater degree than would be done in normal operational
practice.
Although it might at first appear that there would be considerable
savings affected — due to the smaller size of the Denil-type ladder, size
alone does not necessarily control cost. The Denil-type ladder requires
higher walls, and numerous specially constructed baffles which increase the
cost. Therefore, it is the opinion of the authors that the Denil-type
ladder would not represent any savings in construction cost over the
pool-type ladder,
lU
SUMMARY AND CONCLUSIONS
Interest in the Denil-type fish ladder constructed at the Herting
power dam in Sweden led to the construction at Dryden Dam of one patterned
after the Swedish installation. Comparison of the Denil-type and pool-
type ladders was facilitated because it was possible to construct a Denil-
type ladder in one-half of the existing pool-type ladder at Dryden Dam.
During the actual time that counting observations were conducted in
19li9 and 1951, the Denil-type was preferred by fish utilising the ladders.
In 110 hours ii5 minutes, 1,828 fish used the Denil-type ladder, and in 96
hours 55 minutes a total of 226 fish were counted through the pool-type
ladder.
The Denil-type ladder at Dryden Dam occupies essentially the same
amount of space as the pool-type ladder. There is, therefore, some advan-
tage in the Denil construction in conservation of space, both from the
standpoint of its narrowness, and shorter length made possible by a steeper
slope.
It was concluded, because of the baffles and higher flume wall con-
struction of the Denil-type ladder, that there is no substantial saving
in cost of construction over the standard pool-type ladder.
'^th regard to flow requirements, Ihe data collected revealed that
the Denil-type ladder passed a greater number of fish per second-foot
of floxiT and required less attention. With only i^O percent more flow than
in the pool-type ladder, the Denil-tj'pe was utilized by 89 percent of the
fish counted through the ladders.
Probably the most desirable feature of the Denil-tj'pe was the attrac-
tion flow it presented to fish.
The study undertaken at Dryden Dam was somewhat limited in scope, and
it is hoped that the encouraging results may stimiilate further research
into the possibilities of the Denil-type ladder. One possibility for
adoption of the Denil-type which should be investigated is its installa-
tion at the downstream end of a pool-type ladder, since, on the basis of
observations at Drj'-den Dam, the Denil-type fish ladder is apparently
more effective in attracting fish than the small pool-type ladder common
to the Pacific Northwest. Additional studies also should be undertaken
to determine the height of dam that different species of fish can nego-
tiate by a continuo\is baffled channel without resting pools, and
investigations should be carried out to determine the practicability of
the Denil-type ladder at higher dams.
15
ACKNOWLEDGEMENTS
The authors wish to acknowledge the assistance of J. T. Barnaby,
under whose direction this experiment was planned and initiated, and
C. J. Burner and H. B, Holmes for their suggestions and help in the
preparation of the manuscript o We are grateful also to Milo C. Bell,
Technical Coordinator, and D. R« Johnson, Chief Biologist, Washington
State Department of Fisheries, for their review and comments.
LITERATURE CITED
COMMITTEE ON FISH PASSES, BRITISH INSTITUTION OF CIVIL ) ENGINEERS
I9U2 Report of the Committee on Fish Passes, $9 PP»
DENIL, G.
1909 Les echelles a poissons et leur application aux barrages
de Meuse et d'Ourthe (Fish passes and their application at the
Meuse and Orthe dams), Bull, Acad, Sci. Belgique 1908(1909) s
1221-1221;,
DENIL, G.
1936-38 La mechanique du poisson de riviere. Qualities
nautiques du poissonj ses methodes locomotricesj ses capacities;
ses limites; resistances du fluide; effet de la vitesse, de la
pente; resistance du seuil (The mechanics of river fishes.
Swxmming properties of fishes; their methods of locomotion;
their abilities and their limitations; the resistance of fluids;
the influence of velocity and slope; threshold resistance),
Annales des Travaux Publics de belgique, Vol. 37 No. It pp.
507-583, Vol. 37, Noo 5 pp. 707-720, Vol. 38 No. 1 pp. 69-8U,
Vol. 38 No. 2 pp. 255-28U, Vol. 38 No. 3 pp. U11-U33, Vol, 38
No. 1; pp. 609-638, Vol, 38 No. 5 Dp. 733-763, Vol, 38 No. 6
pp. 957-9(80, Vol. 39 No. 1 pp. 131-171, Vol. 39 No. 2 pp. 399-111,
Vol. 39 No. 3 pp. 537-578, Vol. 39 No. h pp. 783-803.
FURUSKOG, VALTER
19U5 En ny laxtrappa (A new salmon pass), Sartryck ur Svensk
Fiskeri Tidskrift, No, 11, pp. 236-239.
16
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