The meander-type fish pass: An alternative to the conventional vertical slot pass - IUB Engineering AG
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Received: 11 September 2020 Revised: 17 May 2021 Accepted: 19 May 2021
DOI: 10.1002/rra.3827
RESEARCH ARTICLE
The meander-type fish pass: An alternative to the conventional
vertical slot pass
Ulf Helbig1 | Matthias Mende2 | Werner Dönni3 | Klaas Rathke4
1
Institute of Hydraulic Engineering and
Technical Hydromechanics, Technische Abstract
Universität Dresden, Dresden, Germany The meander-type fish pass is a slotted fishway characterised by the exclusive use of
2
IUB Engineering AG, Bern, Switzerland
rounded and smooth components. Due to the specific geometry and arrangement of
3
Fischwerk, Luzern, Switzerland
4
the basins, which differ considerably from the conventional vertical slot pass, there
Fachgebiet Hydraulik/Quantitative
Wasserwirtschaft, Technische Hochschule are significantly different hydraulic conditions. The water flow is guided along the
Ostwestfalen-Lippe, Umweltingenieurwesen
basin walls by means of a dominant main current while the water body is much
und Angewandte Informatik, Höxter, Germany
calmer towards the centre of the basin, where very low flow velocities are found. A
Correspondence
detailed assessment of the functionality is currently impossible due to the small num-
Ulf Helbig, Institute of Hydraulic Engineering
and Technical Hydromechanics, Technische ber of surveys of fish passage hitherto carried out. However, considerable potential
Universität Dresden, D-01062 Dresden,
is indicated by the high passage rates at some sites and the lack of selectivity with
Germany.
Email: ulf.helbig@tu-dresden.de regard to species and small fish, together with the design advantages and the adapta-
tion possibilities after construction work is completed. In this study, we offer some
recommendations for dimensioning to enable this potential to be exploited. These
are oriented around recommendations for conventional vertical slot passes regarding
basin size, flow depth and slot width. Due to the great potential of the meander-type
fish pass, it is desirable to construct still more individual pilot passes to implement
comprehensive surveys of fish passage on a sound methodological basis.
KEYWORDS
fish ladder, fishway, meander-type fish pass, vertical slot pass
1 | I N T RO DU CT I O N et al., 2015). In addition to these hydropower-related obstacles to fish
migration (which are to be remedied by 2030), the revitalisation plan
The Swiss Water Protection Act and the Federal Act on Fisheries aims to make non-hydropower-related obstacles passable to fish by
demand a reduction in the negative impact of hydropower plants on around 2090. In Switzerland, a total of over 100,000 artificial barriers
watercourses. The associated ordinances call for improvements in fish with a drop height of over 50 cm impair the free migration of fish
migration, in hydropeaking and bedload balance by 2030, at a total (Zeh Weissmann, Könitzer, & Bertiller, 2009). In view of the major
cost of Swiss Francs (Swiss currency) 4–5 billion according to current tasks ahead, the question arises as to how fish migration can be
estimates (SRF, 2018). A large part of this money will be spent on restored as effectively and cost-efficiently as possible.
restoring fish migration. Approximately 1,000 hydropower plants are To restore upstream passage, fish passes are constructed where
affected by the law's implementation, with upstream and downstream obstacles to migration cannot be removed. In confined spaces, such as
passage at about 700 plants requiring upgrading (Bammatter those often found in the vicinity of hydropower plants, space-saving
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any
medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2021 The Authors. River Research and Applications published by John Wiley & Sons Ltd.
River Res Applic. 2021;1–13. wileyonlinelibrary.com/journal/rra 1
2 HELBIG ET AL.
passes are required. The standard construction method today is the method are discussed with regard to design, flexibility of implementa-
conventional vertical slot pass, of which a great many have been tion and the possibilities of adaptation after construction is completed.
constructed around the world. A more recent construction Further, we suggest some dimensioning principles.
method is the meander-type fish pass (MFP; manufacturer's name:
Mäanderfischpass®). On the market since the mid-1990s, it has been
further developed by the manufacturer Peters Ökofisch GmbH and 2 | CON S T R U CT I O N A N D D ES I GN
Co. KG to reflect gathered experience. To date, 66 such passes have
been constructed (Helbig, Aigner, & Stamm, 2016). In Switzerland, 2.1 | The three basic types
two MFPs have been built in brown trout rivers.
Like the conventional vertical slot pass, the meander-type fish The meander-type fish pass takes the form of a basin ladder, that is, an
pass presents a continuous series of vertical slots. However, the alignment of interlinked rounded basins, mounted in a rectangular chan-
hydraulic properties (dominant peripheral current, flow-calmed centre) nel. The basins are generally constructed from pipe segments made of
are rather different owing to the particular geometry and arrangement glass fibre-reinforced plastic. There are three basic designs, C, J and H,
of the rounded basins, which differ significantly from the conventional also referred to in the following as construction types. Mixed designs are
vertical slot pass (rectangular basins, variable flow pattern). Further- also possible. The main differences between the construction types are
more, there are differences in the application and design of this con- the shape and length of the basins, the slope of the rectangular channel
struction method. In particular, the lateral contouring and slope of the (ramp gradient) and the flow gradient (see Table 1 and Figure 1):
passes are highly adaptable. In this way, the MFP can be easily
customised to meet local conditions, resulting in significantly lower • Type C, comprising circular basins, is designed for ramp gradients
construction costs than conventional vertical slot passes. However, it of 17%–30%. It is intended to enable the construction of fish pas-
must be noted that currently the MFP is only rarely constructed. This ses in confined spaces.
is due, on the one hand, to a lack of basic dimensioning guidelines • Type J is designed for ramp gradients of 8%–17%. The main difference
and, on the other hand, to the fact that current regulations overlook to the C type is the elongation of the C-shaped basin into a J shape.
this form of fish pass (owing to a lack of scientific studies). In addition, • Type H is designed for ramp gradients of 4%–8% and can be called
the relatively small dimensions of existing passes have often been a “half-meander fish pass.” Compared to the C and J types, the H
criticised as not complying with the geometric threshold values of type has an even more elongated basin to produce the longest
current regulations (e.g., DWA, 2014). length of pass.
In this paper, the hydraulic characteristics of the MFP are investi-
gated, and an attempt is made to assess these in relation to fish migra- The predominant flow patterns depend on the respective construc-
tion. In addition, the advantages and disadvantages of this construction tion types. However, in all types of MFP the flow direction alternates
TABLE 1 Characteristic parameter of the three basic MFP types (source: manufacturer)
Type
Parameter C J H
View
Ramp gradient I (%) 17–30 8–17 4–8
Basin outside diameter DB (m) 1.00–2.40 — —
Basin length LB (m) — 1.50–3.50 1.50–3.60
Basin width BB (m) — 1.00–2.00 1.00–2.50
Basin height HB (m) 0.85–3.00 0.75–3.00 0.75–3.00
Discharge Q (l/s) 80–610 110–610 120–1,040
Overflow head between basin/ 0.15–0.24 0.15–0.24 0.08–0.24
difference in water level Δh (m)
Number of built passes 42 15 5
HELBIG ET AL. 3
F I G U R E 1 Ramp slope and flow
path depending on the type (middle
row: blue dashed line = flow path
slope [effective]; dark green = ramp
slope, is equal to the given
percentage range)
(source: manufacturer, modified)
[Color figure can be viewed at
wileyonlinelibrary.com]
(or “meanders”), with a dominant main current running along the outer
sides of the basin (defined as the basin boundary) (Figure 1). In this way
a continuous flow path is established. In addition to the passes shown
in Table 1, four special passes have also been constructed as mixed or
tower systems (Helbig et al., 2016). In all watercourses, including moun-
tain streams, abrasion of the bed load removes any sharp edges, which
could injure migrating fish. For this reason, an essential characteristic of
the design is that the basins only have rounded and smooth compo-
nents. The manufacturer deliberately avoids sharp-edged slots, right
angles and crushed base material, assuming that migrating fish will
avoid sharp edges and rough surfaces due to the likelihood of injury
(e.g., to mucous membranes or scales) and thus maintain a greater dis-
tance to these than to rounded, smooth surfaces.
F I G U R E 2 Left: Arrangement and design of basins of a type C
(under construction), right: design of the slots (Rat'sches Wehr/Echaz,
2.2 | Design of the base and slots Reutlingen/Germany, pictures: J. Stork) [Color figure can be viewed at
wileyonlinelibrary.com]
2.2.1 | Design of the base
The base consists of a layer of rounded gravel (usually of grain size water celery), offering additional hiding places for fish alongside the
16/32 mm, approx. 80 mm thick), onto which a PE twisted-mesh mat of pipe sections as well as habitats for invertebrates (Figure 3). The sedi-
approx. 3 cm thickness is applied to stabilise the gravel layer. The mat and mentation has little influence on the hydraulic functionality of the
the rounded gravel are fixed into place using sections of plastic piping pass as it primarily appears in the flow-calmed inner basin. No signifi-
(D = 14 cm, L = 25 cm, cut lengthwise into three parts), which are cant sedimentation occurs in the area of the main current along the
anchored to the concrete base by means of threaded rods passing through walls. Despite an often steep gradient (Table 1), the design of the base
the mat and gravel layer. In newer MFPs, the base is additionally strength- ensures a stable bottom-layer of loose material. A further advantage
ened by means of a galvanised steel mat (Figure 2). The plastic pipe sections over a standard bottom made of crushed substrates is that height of
serve not only to secure the base elements but also to create flow-calmed the base can be precisely defined and constructed, thereby ensuring
areas near the bottom as well as to provide useful structures for species that the desired hydraulic conditions in the pass.
tend to hug the riverbed. The arrangement of sections near the slot enables
fish swimming close to the bottom to move from flow shadow to flow
shadow without having to enter the main current. 2.2.2 | Design of the slots
Due to the low flow velocities towards the centre of the
basin, areas of sedimentation eventually cover large parts of the base. Like the conventional vertical slot pass, the MFP possesses a continu-
These are often overgrown with aquatic plants (e.g., water mosses, ous series of vertical slots. However, in the MFP these are rounded
4 HELBIG ET AL.
and tapered in a V-shape towards the bottom (Figure 2, right). basin length or diameter as well as the drop height from basin to basin
The width of the slots can be modified by means of adjustable plastic correspond to those of a conventional vertical slot pass.
piping (diameter 15 cm, slit lengthwise and inserted onto the ends of For fish passes with rectangular basins such as found in conven-
the basin walls, Figure 2, right). The slots can be adjusted by up to tional slotted designs, larger basins are required to enable a change in
±7 cm even during operation. Apart from subsequent adjustments of direction of the linear contour of the pass. For example, basins facili-
the flow, this also enables a precise regulation of the drop height tating a 90 directional shift are about 25% larger than normal while
between the basins in the rare case that this is non-uniform. those facilitating a turn of 180 are twice the standard size.
The type-C MFP offers the most compact arrangement. Adjacent
basins are interlinked in such a way as to enable a gradient twice that
2.3 | Space requirements and lateral contouring of type J (Table 1). In a slightly modified form, the C-type pass can
also be constructed as a kind of spiral staircase to create a “helical
The MFPs realised thus far have generally been built with smaller tower fish pass” (Figure 4).
basins than usual for conventional slot passes. By modifying the rec- With conventional vertical slot passes, it is seldom possible to
ommendations for geometrical threshold values (e.g., DWA, 2014) in create an arrangement of basins with such steep gradients as type
this way, the MFPs take up less space than conventional vertical slot C. The most comparable are conventional slot passes with staggered
passes. In the following discussion, however, it is assumed that the basins (Figure 5). Since the flow in the basins is perpendicular to the
slope, the basin width (perpendicular to the base gradient) is taken to
be the basin length LB (distance from the slot to the opposite wall).
The basins thus need to be at least a third wider than a standard basin
in order to maintain the recommended minimum length according to
DWA (2014). In this way, the total width of two neighbouring basins
is at least twice the recommended basin length. In contrast, the total
width of a type-C ladder is only 1.5 basin diameter due to the over-
lapping design, making this fish pass 25% narrower. A further reduc-
tion in the total width of the MFP is achieved by utilising slender
fibreglass pipe segments for the basins. These offer much thinner wall
thicknesses (15–34 mm) than those of conventional vertical slot
passes, which are usually made of concrete. Due to the compact
arrangement and the steep ramp gradient, type-C passes can be
implemented in confined spaces where it would be impossible to con-
struct a standard vertical slot pass. With a similar width-to-length
ratio as the conventional vertical slot pass, type J offers no further
F I G U R E 3 Drained type C with water celery in the basin's centre
(picture: U. Helbig) [Color figure can be viewed at advantage in terms of reduced space requirements apart from the
wileyonlinelibrary.com] thinner partition walls and the lower total height due to the narrower
F I G U R E 4 Helix tower system on the river Schwentine/Schleswig-Holstein/Germany (pictures: E. Kuberski) [Color figure can be viewed at
wileyonlinelibrary.com]
HELBIG ET AL. 5
F I G U R E 5 Conventional vertical slot pass with alternating basin
arrangement (picture: www.ib-handrick.de) [Color figure can be
viewed at wileyonlinelibrary.com]
base structure (cf. Section 2.2; design-related thickness of the filling
material in the base substrate of a conventional vertical slot pass
dF ≥ 30 cm [DWA, 2014]). Type H, on the other hand, has a smaller
width-to-length ratio than type J, and can, therefore, be used in nar-
row corridors (Figure 6). By combining the three construction types, F I G U R E 6 Mixed MFP (types C and H) at the Drakenburg
meander-type fish passes can often make the best possible use of the impoundment weir (river Weser/Germany) immediately before
available space (Figure 6). They also permit a variable design of the lat- commissioning (picture: manufacturer, modified) [Color figure can be
eral gradient. This means that, for example, large pipes for sewage dis- viewed at wileyonlinelibrary.com]
posal or bundled cables as well as any other obstacles can often be
bypassed and cost-intensive adjustments avoided.
the current consistently follows the concave basin wall, creating a
curved and uninterrupted flow corridor (Figure 7, left, and Figure 8).
3 | H Y DR A U LI C CH A R A C T E R I S T I C S Such a curved peripheral flow remains much more compact and
(TYPE C) stable than, for example, a linear inflow travelling alongside a basin wall.
The authors consider this to be a considerable improvement on an
As the majority of MFPs constructed to date have been type C unguided current or a linear flow guided on one side only, as these are
(Table 1), the characteristic hydraulic conditions of this type of pass associated with a continuous widening of the current as it moves
will be considered in greater detail below. The more elongated types J through each basin (Rajaratnam, 1976). Unguided inflows into basins as
and H are less compact than type C and resemble conventional verti- found in conventional vertical slot passes (Figure 7, right) tend to pro-
cal slot passes in terms of their basin shape. However, the typical flow duce an instable current due to the shear zone between the inflow and
characteristics of an MFP (alternating flow path, dominant main cur- the main water body. Even slight changes in the boundary conditions
rent on the basin walls and continuous flow path) are also evident in can lead to premature and uncontrolled disruption of the current, for
these types (Section 2.1). example, an unplanned change in the flow pattern from “flow-stable”
to “flow-dissipating” (according to DWA, 2014) or vice versa. In con-
trast to the strong main current along the basin wall, a large, slowly
3.1 | Water flow in the basins rotating vortex forms around a vertical axis in the centre of the MFP
basin. This is driven in the shear zone by the inertial force of the periph-
In contrast to the conventional vertical slot pass, where the outflow eral current running from slot to slot, creating a “rigid vortex.” A charac-
from a slot is directed straight towards the centre of the basin teristic feature of the basin hydraulic is the pronounced drop in velocity
(Figure 7, right), the current in type C follows the walls of the from the walls to the centre of the vortex, where the current velocity
basin from the upper to a lower slot. This results in a dominant stable can fall to almost v = 0 m/s (Figure 7, left, and Figure 8).
current in the form of a relatively sharply defined jet. Due to the per- As in any type of basin ladder, the majority of the kinetic energy
manent redirection of the water in combination with its inertial force, released as the water passes through the MFP slots must be
6 HELBIG ET AL.
F I G U R E 7 Left: Flow pattern in a type C (example: Birs/Courrendlin JU/Switzerland; picture: J. Stork), right: flow pattern (“flow-dissipating”
– left side and “flow-maintaining” – right side, according to DWA, 2014) in a conventional vertical slot pass (example: river Mosel/Coblenz,
Rhineland-Palatinate/Germany; picture: M. Mende) [Color figure can be viewed at wileyonlinelibrary.com]
dissipating effect than the shear zone in the fluid. Compared to the
conventional vertical slot pass, we can, therefore, expect a slightly
higher average flow velocity near the slot for the same overflow head
(Δh) and the same flow path into the basin. If necessary, this could be
reduced by increasing the basin diameter and/or lowering the
overflow head.
Due to the typical flow pattern (dominant peripheral current,
flow-calmed centre), we can draw the following conclusions:
• The peripheral current along the basin wall is characterised by a
clearly defined and compact high-velocity directed flow. Our own
measurements show that maximum velocities are found just
behind each slot (IWD, 2016, see also Section 3.2). The flow condi-
tions in the individual basins are relatively uniform throughout
the pass; in particular, the peripheral flow is continuous and
permanent.
• Low velocity flows and turbulence is present in most of the basin
F I G U R E 8 Section of an MFP type C (3d-CFD-Simulation
interior, offering sufficient space for fish to rest before they ascend
OpenFOAM®, LES-method, DS = downstream water, US = upstream
water; source: TU Dresden/IWD) [Color figure can be viewed at to the next basin.
wileyonlinelibrary.com] • The slowly rotating central vortex as well as the clear transition to
the peripheral directed jet flow provides migrating fish with clear
converted. Depending on the water level, a fairly standard overflow directional information to indicate the location of the next slot.
head between the basins of the MFP will ensure uniform energy con-
version and thus a regular water flow throughout the pass. The energy
dissipation of the characteristic peripheral current is primarily the 3.2 | Discharge calculations and maximum flow
result of friction along the sides of the basin as well as due to turbu- velocity
lence in the shear zone between the rigid central vortex and the
periphery. Both the boundary layer along the basin wall as well as The size of the opening at the base of the slot represents a reference
the free boundary layer of the peripheral flow towards the centre of cross section that determines the discharge and thus is hydraulically
the basin are more compressed than in the case of a straight fall relevant. The advantage of the MFP is that the base can be precisely
(Guitton, 1964; Rodney, 1972). In contrast to an inflow into a free designed and the slot width varied and adapted to the respective
water body, the total absolute energy dissipation is lower in the local conditions (Section 2.2). The water flow through the slot is a
C-type basin, since the friction of the external wall has a lower combination of backed-up outflow (Torricelli's law, Qu) and overflow
HELBIG ET AL. 7
F I G U R E 9 Left: Flow of a slot as
a combination of over- and outflow,
right: definitions at a slot (with corner
shaping) [Color figure can be viewed
at wileyonlinelibrary.com]
(Poleni's law, Qo, Figure 9, left). The authors do not recommend esti- In Equation (1) μ () represents the discharge coefficient,
mating the flow in the slot as laid out in the current guideline DWA-M s (m) the slot width at base level (Figure 9, right) and ho and hu (m) the
509 (DWA, 2014, p. 244), because the approach on which it is based water depth directly above and below the slot, respectively, in relation
was only developed for vertical slot passes. Discharge measurements to the mean water level. The coefficient Δh (m) is the overflow head
of the TU Dresden showed deviations of up to 30%. According to between the mean water levels of two adjacent basins, m () is the
these investigations, the flow can be precisely calculated using the mean value of the inclination of the slot edges (Figure 9, right). For
approach described in Aigner (2016). While the inflow velocity (va) m = 0, Equation (1) describes a rectangular cross-section.
required by this method is difficult to determine under practical condi- As with all slotted passes, the maximum average flow velocity in
tions, the measurements show that this value cannot be neglected in the system occurs just below each slot and can be closely estimated
view of the lower effective energy dissipation within the MFP basins using the extended Torricelli equation:
(as previously discussed in Section 3.1).
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Adopting a simplified approach, therefore, we only consider the v max ¼ 2gΔh þ v2a : ð2Þ
overflow head (Δh) as well as a modified discharge coefficient (μmod)
to represent the kinetic energy of va. In this way, the following equa-
tion can be applied to a trapezoidal slot (cf. Figure 9, left): Here, too, the inflow velocity va cannot be ignored due to the
lower energy dissipation in the MFP. Using the relation.
1:5
Trapezoidal cross section : v2a
μ1 ¼ 1 þ 2gΔh > 1:0 (Aigner & Bollrich, 2015, p. 337), the
" ! !#
pffiffiffiffiffiffiffiffiffiffiffiffiffiffi h2 2 Δh2 maximum average flow velocity vmax can then be calculated as
Q ¼ μmod s 2gΔh hu þ m u þ Δh þ 0:406m with ,
s 3 s
μmod ¼ μ0 μ1 qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2=
ð1Þ v max ¼ 2gΔhμ1 3 , ð3Þ
or in the case of a narrow channel with no shift from subcritical to giving a figure approx. 20% higher than when the inflow velocity is
supercritical flow neglected (i.e., va in Equation [2] = 0; this applies, for example, to con-
ventional slot passes with “flow-dissipating” flow patterns).
pffiffiffi 3
Q ¼ μeq gsho=2 with It should also be noted that while the flow velocity near the
sffiffiffiffiffiffi " ! !#
Δh fho Δhg2 1 Δh2 , slot is not linearly dependent on the overflow head (Δh)
μeq ¼ 1:35 ho þ m Δh 0:406m
h3o s 3 s (cf. Equation [2]), the power density (pD), which is a substitute
parameter for turbulence, shows this dependency. For example, an
increase in the overflow head from Δh = 0.15 m to Δh = 0.20 m
where μ0 is the base coefficient of the cross-section according to the increases the flow velocity by only approx. 15% if we neglect va,
Euler equation (μ0 = 0.537–0.577 for trapezoidal cross-sections with whereas the power density as a substitute parameter for turbulence
rounded edges, Aigner & Bollrich, 2015) and μ1 describes the influ- increases by 33%. This suggests that the degree of turbulence,
ence of the inflow velocity. The value for μ1 could be determined whose distribution within the basins of the meander fish pass can be
within the scope of various investigations (on-site/laboratory mea- viewed positively (Section 3.1), is more significant for passability
surements and simulations) for the C-type pass as μ1 ≈ 1.715. than the flow velocity.
8
TABLE 2 Realised biological evaluation of meander-type fish passes
Water Meander-type fish pass
River Fish Width at Number
(location) region location Type of basins Commissioning Details Detectability
Havel (Bahnitz) Bream- region 60 m H 5 2005 Slope 4.0%; length of basins 3.60 m, width of basins 2.50 m, width of slots Insufficient: Optimal positioning of
41–60 cm; rough bed entrance, but attraction flow too
small
Mildenitz (Borkow) Bream- region 10 m J 17 2006 Total height difference 2.4 m, slope 8.3%. Length 46 m (part with basins No information
29.68 m), width of basins 1.45–1.5 m; rough bed
Mildenitz (Rothen) Bream- region 10 m C 9 2005 Total height difference 1.2 m. width of slots 10–15 cm No information
Weser (Drakenburg) Barbel- region 150 m C and H combined 34 (thereof 7 as type H) 2000 Width of slots downwards 12.5 cm, upwards 25 cm; water level difference No information
15 cm, max. Velocity 2.2 m/s; rough bed
Weser (Hameln) Barbel- region 50 m C 18 2002 Total height difference 2.0 m, length 19 m, width of basins 2.0 m, width of No information
slots downwards 12.5 cm, upwards 25 cm, water level differences 19.3–
20.0 cm; max. Velocity 2.0 m/s; discharge 300 L/s; rough bed
Oker (Braunschweig) Barbel- region 20 m H 20 2003 Total height difference 2.1 m, slope 4.4%, length 67 m, length of basins Unclear; with increased flow,
2.26 m, width of basins 1.4 m, width of slots downwards 12–14 cm, additional flow of about 100 L/s
upwards 19–24 cm, water level differences 10–15 cm; max. Velocity gets induced to improve attraction
1.3 m/s; discharge 156 L/s flow
Alster (Hamburg- Bream- region 50 m C No information 2013 Total height difference 4 m; length of basins 2 m, width of slots upwards 0.31, Good; outlet of bypass and turbine
Ohlsdorf) downwards 0.29 m; water level differences 20 cm; water depths 0.79– flow on right side of entry of the
0.98 m; velocities at basin border 1.7–2.1 m/s, in slots 0.9–2.5 m/s; fish pass.
discharge 500 L/s
Survey methodology Results
Remarks Literature
Method to Days with
catch fish Mesh size Funnel Period catches Frequency Species-selectivity Length-selectivity Tailwater
Combination 8–9 mm Net funnel May 30 18,433 individuals 13 species, thereof 7 Not in small 18 species, Several improvements Wolter &
rectangular species with more fishes; in big thereof 11 of catching device Menzel, 2011
wired fish than 10 individuals, fishes (up to species with during the first
trap/ missing species 60 cm) unclear, more than 10 10 days; afterward
counting during electric due to small individuals. operational, but not
basin fishing only found catching at full catching
as stray finds numbers. capacity,
(exception construction works
bitterling).
Cylindrical fish 6–8 mm Net funnel Beginning of 23 (all 2 weeks 1,125 individuals 12 species, thereof 7 Up to 65 cm 12 species, Performance index Waterstraat,
trap April–middle of during 72 hrs.) species with more thereof 5 according to Ebel, Renner, &
June, end of than 10 individuals, species with Fredrich, Gluch, Blohm, 2007
October – no selectivity more than 10 Lecour, and
Beginning of found. individuals Wagner (2006):
November well (class B)
Cylindrical 6–8 mm Net funnel 2005: Middle of 16 (all 2 weeks 54 individuals 8 species, thereof 2 Up to 25 cm 12 species, Problems with fish Waterstraat, 2005
twined fish April–end of during 48 or species with more thereof 4 trap (vandalism)
trap may, end of 72 hrs.) than 10 individuals species with
October– more than 10
beginning of individuals
November
HELBIG ET AL.
TABLE 2 (Continued)
Survey methodology Results
Remarks Literature
Method to Days with
HELBIG ET AL.
catch fish Mesh size Funnel Period catches Frequency Species-selectivity Length-selectivity Tailwater
Cylindrical 6–8 mm Net funnel 2007: Middle of 10 (all 2 weeks 51 individuals 6 species, thereof 2 Up to 22 cm Unknown Waterstraat et
twined fish April–end of during 72 hrs.) species with more al., 2007
trap may, end of than 10 individuals
October–
beginning of
November
Rectangular 14–16 mm Wire mesh, 2002: End of 337 83,897 individuals 24 species, thereof 24 No information Unknown Problems with fish Wieland &
wired fish loophole 30 May–end of species with more trap (occasional Nöthlich, 2003
trap x 30 cm, October; 2003: than 10 individuals theft of fish)
length End of march–
1.25 m end of October
Counting basin 10 mm Overlapping April–November 546 100,559 25 species, thereof 19 More than 70 cm 29 species, Construction works, Rathcke, 2004
(perforated 20 mm (2 years) individuals species with more (with relatively thereof 16 increased flow over
sheet metal) plastic than 10 individuals frequent big species with weir
fingers fish) more than 10
individuals
Counting basin 10 mm Perforated Middle of April – 23 883 individuals 17 species, thereof 7 Up to 51 cm; no 4 species, thereof Problems with fish NLWK, 2004
(perforated sheet beginning of species with more apparent 1 species with trap (clogging)
sheet metal) metal July than 10 individuals; selectivity more than 10
no apparent individuals
selectivity
Cylindrical 11 m Net funnel 2018: Middle of 30 330 individuals 9 species, thereof 2 Up to 37 cm; it is 15 species, Count presumably Lübker &
twined fish April – species with more expected that thereof 8 after beginning of Schubert, 2019
trap Beginning of than 10 individuals; basins are too species with migration
June due to high small for big more than 10
velocities in slots fish; proof for individuals
critical for weak big fish missing
swimmers;
evaluation good
since only spring
spawners were
evaluated
9
10 HELBIG ET AL.
4 | A SS ES SI N G T H E B I OL OG I CA L 4.1 | Effectiveness
PERFORMANCE
The site with the most fish caught per day was Bahnitz on the river
The functionality of a fish ladder can be assessed in terms of its effec- Havel (type H). On average, slightly more than 600 fish were caught
tiveness, efficiency and selectivity with respect to migrating fish (for per survey day during May. On the river Weser at Drakenburg (a mix
details see Zaugg, Dönni, Boller, & Guthruf, 2017). The effectiveness of type C and H) and Hamelin (type C), an average of approx. 250 and
is determined by the absolute numbers of migrating fish. Typically, 180 fish, respectively, were caught per day during each of two sum-
counting methods are used for this purpose (fish traps, counting mer half-years. The number of caught fish was significantly lower at
chambers/tanks and video). The level of efficiency is determined by the other sites.
relative frequencies, namely the proportion of fish that discover the Fish traps with funnels made of wire mesh, plastic grating or per-
pass, swim into it and successfully ascend the pass. Here the time forated sheet metal were employed at three of the seven locations.
required for finding and negotiating the pass is also recorded by However, it is likely that many fish swimming into these traps swam
means of fish marking. Finally, selectivity describes whether all fish out again before being counted. The traps at the other four sites were
species and length classes are able to migrate. This parameter can be equipped with funnels made of netting. This ensured better retention
assessed by counting and marking methods. of the fish, although only partial details were available of the trap
Migration can only be meaningfully assessed if the relevant func- design in terms of length, diameter of the funnel and mesh size. But
tional parameters are recorded using the appropriate methodology these did not comply with the recommendations of Wilmsmeier,
over the relevant seasons and for a sufficiently long period of time. In Schölzel, and Peter (2018), which suggest a funnel with a perforated
addition, information on the species and abundance of fish in the tail- metal base and an extension made of netting. In addition, funnels may
water, variations in water flow and temperature, operating data on deter fish from entering, which means that not all ascending fish
turbines and weirs and, if necessary, other data are all required to cor- swam into the trap.
rectly carry out a survey. Finally, it is essential to conduct careful data No data were available on the extent to which fish were able to
evaluation and an objective assessment based on clearly defined locate the MFP (or this factor was classified as unclear or insufficient).
criteria. A total of eight surveys of migrating fish were conducted at Consequently, it is unknown whether the ascent count reflects, at
seven MFPs in Germany from 2002 to 2018 (Table 2). These were least in part, poor detectability of the MFP. Some other limitations to
conducted independently of the manufacturer. The surveys were of the survey arose in connection with construction work in the water,
three C-type and two H-type passes, one J-type and one mixed MFP vandalism or technical problems. The ascent numbers recorded at all
of types C and H (Figure 7). As was customary at the time, all surveys passes should thus be regarded as minimum values for the number of
were carried out using counting methods (i.e., traps or counting fish that actually migrated upstream via the MFP. This data cannot be
basins). considered suitable for assessing the effectiveness of the passes,
preventing a comparative evaluation of the different types of MFP at
T A B L E 3 Fish species caught in the meander-type fish pass on this point.
the Oker River and in its tailwater (NLWK, 2004)
Species detected In MFP In tailwater
Abramis bjoerkna X
4.2 | Efficiency
Abramis brama X
No findings on the level of efficiency can be derived from the
Anguilla anguilla X X
employed counting methods. Specifically, it is not known how many
Carassius carassius X
of the fish that found their way to the MFP also entered it, how
Carassius gibelio X
many of them arrived at the top and how much time they needed for
Cyprinus carpio X the passage.
Esox lucius X
Gobio gobio X X
Leuciscus idus X 4.3 | Selectivity
Leuciscus leuciscus X
Perca fluviatilis X X The surveys provide clearer results regarding species selectivity. Com-
Rutilus rutilus X X paring the species caught in the tailwater with those detected in the
Salmo salar X counting devices, the majority of the passes showed no obvious spe-
cies selectivity – at least when species are included for which only
Salmo trutta X
individual specimens were counted. In one facility, the number of spe-
Scardinius erythrophthalmus X
cies detected in the MFP was higher than in the tailwater (see
Squalius cephalus X
Table 3). In Bahnitz the proportion of species detected was just over
Thymallus thymallus X
60% of those known to be present. At this location, however,HELBIG ET AL. 11
counting was only carried out for one month. In Rothen, where only distribution, the basin dimensions have only a comparatively small
very few fish ascended the pass, the proportion was 50% in 2005 and influence on the passability for large fish, two to three MFPs of type
20% in 2007. C should be constructed as test passes at locations where large spe-
Based on the survey results, we can rule out (with a high degree cies are also present, and intensively monitored to assess their biologi-
of probability) the negative selection of small fish. With regard to large cal effectiveness. If selective effects are detected to the detriment of
fish, however, it is not possible at present to make any definitive larger fish, then Type C should only be used for the migration of tar-
statement due to the low catch figures. get fish species where Lfish ≤ 80 cm.
5 | C U R RE N T R E C O M M E N D A T I O N S F O R 5.3 | Flow depth hu
THE USE OF THE MFP
For the flow depth hu below the slots, it is recommended that the
Definitive recommendations for the dimensions of MFPs can only be dimensions published for conventional slot passes in DWA-M
made after basic questions have been answered regarding fish 509 (DWA, 2014, tab. 43) be observed. This results in a minimum
passability in relation to the design of the slot and basin as well as the water depth H of, for example, hu = 0.5 m for brown trout and 0.8 m
associated hydraulic conditions. As long as this is not the case, dimen- for salmon.
sioning should err on the side of caution.
5.4 | Overflow head between basin (difference in
5.1 | Slot width s water level) Δh
In DWA-M 509 (DWA, 2014), geometric threshold values are gener- In the RBPs (of type C) realised thus far, the ratio of overflow head
ally derived from the masses and proportions of fish. Thus the width Δh to basin diameter DB has generally been Δh/DB = 1:10, giving a
of a slot should be at least three times the maximum fish width ramp slope of 20%. An exception is a small meander pass with
(s = 3 Dfish). In the case of previously constructed meander-type fish DB = 1.0 m and Δh = 15 cm (ramp slope 30%), which are primarily
passes, the average slot width has often been smaller than 3 Dfish. used to facilitate trout migration. Due to their small slot widths, they
This has the desired “side effect” of reducing the water flow through are only recommended at sites where frequent maintenance is
the pass. The choice of the smaller slot width is based on the assump- guaranteed. The ratio Δh/DB = 1:10 also applies to the comparatively
tion that fish will swim closer to the edges of the MFP's rounded slots well-investigated MFP at the Pfortmühle site in Hameln on the river
than in the case of rectangular slots (Section 2.1). As long as this Weser (Germany), which is a barbel region (DB = 2.0 m, Δh = 20 cm).
assumption is not confirmed, the slot design should comply with the Despite the relatively large overflow head, there is apparently no neg-
recommendation s = 3 Dfish. As the slot widths of an MFP are also ative selectivity of small fish (Section 4.3). Possible reasons for this
adjustable the survey of biological effectiveness can then determine are the low influence (compared to the power density) of the overflow
whether smaller slot widths cause selectivity or not (see Section 2.2). head on the flow velocity in the slot, the positive turbulence distribu-
tion within the basins (Section 3.1), the systematic arrangement of
plastic pipe sections on the base (Section 2.2) and the short distances
5.2 | Basin size LB or DB that fish have to travel against high flow velocities when swimming
through the slots to the next resting zone (Figure 10). Based on the
From the few surveys of biological effectiveness that have been con- current findings, we recommend maintaining a ratio of Δh/DB ≤ 1:10.
ducted, it is impossible to prove or exclude a selective effect on large If the overflow head or the resulting flow velocity deviates signifi-
fish for the MFPs implemented to date with their comparatively small cantly from the recommendations, for example, according to DWA-M
basins (basin diameter based, for example, on the size of the common 509 (2014), a careful survey of the biological effectiveness should be
barbel, DB = 2.0 m) (Section 4.3). Therefore, we recommend that the carried out in order to identify any negative effects and avoid these in
basin length should initially be three times the body length of the future projects.
largest potential fish species, that is, LB = 3 Lfish. For type C, LB is
identical to the basin diameter DB. Based on the fish sizes specified in
DWA-M 509 (DWA, 2014, tab 15), we can derive basin lengths or 5.5 | Mixed designs
diameters of, for example, 1.5 m for the target species brown trout
and grayling, 2.1 m for barbel and 3.0 m for salmon. Due to To make the best possible use of available space, the various types of
manufacture-related restrictions, the diameter of type-C basins is cur- MFP can be combined. Since all variants have a pronounced periph-
rently limited to a maximum of 2.4 m. This means that the recommen- eral current running along the side of the basins, a continuous flow
dations for salmon and similarly large species cannot be observed. path is maintained in each combination of the three types, as well as
Since it can be assumed that, with an appropriate turbulence the large flow-calmed areas toward the basin centre. In the mixed12 HELBIG ET AL.
geometric thresholds of current regulations (e.g., DWA, 2014). These
recommend comparatively large basins to provide sufficient space for
large fish to manoeuvre as well as to comply with the boundary values
for power density (substitute parameter for turbulence). Since the tur-
bulence in MFPs is concentrated towards the walls while the rest of
the basin shows very low turbulence and transverse flows, the design
might enable the use of smaller basins while still offering sufficient
room for large fish to manoeuvre.
In view of the handful of surveys of fish migration, the authors
cannot reliably assess the effectiveness and efficiency of the MFP.
While the partially high passage rates and lack of selectivity with
regard to species and small fish hint at the great potential of this
design, comprehensive and standardised surveys of the performance
are still required. It is, therefore, recommended that MFPs be con-
structed according to the described dimensioning principles, which
are oriented around the recommendations for conventional vertical
F I G U R E 1 0 Fish migration corridor (red arrows) through the slots slot passes according to the DWA (2014). In order to further ensure
of a type C (3d-CFD-Simulation OpenFOAM®, LES-method, the functionality of the suggested dimensions, a modular design
DS = downstream water, US = upstream water; source: TU Dresden/
should be adopted when constructing passes, and these should be
IWD) [Color figure can be viewed at wileyonlinelibrary.com]
intensively assessed regarding their biological effectiveness.
In addition, it is recommended that two to three type-C pilot pas-
passes realised thus far, the slot widths and flow depths have been ses be implemented in watercourses inhabited by large species
the same in all basins, so that a standard flow velocity is achieved at (e.g., lake trout, pike, wels catfish). Thus far it has been impossible to
all slots. The basins were dimensioned in such a way to ensure the comply with the geometric recommendations (DB = 3 x Lfish) for such
same length of peripheral flow in all basins (cf. Figure 1), ensuring an large fish due to manufacturing difficulties (Section 5). Such passes, in
approximately identical energy conversion due to wall friction and tur- combination with intensive biological monitoring, would allow us to
bulence. This explains the more elongated basin shape of type H com- conclusively answer open questions regarding the possible negative
pared to the compact basins of type J. Regardless of the design, the selection of large fish. If positive results are available soon, consider-
basin volumes were chosen to be approximately the same. This proce- able financial savings could be made by constructing MFPs within the
dure seems effective and should, therefore, be retained in future framework of the revised Swiss Water Protection Act, to be
projects. implemented by 2030.
ACKNOWLEDG MENT
6 | CONCLUSIONS AND OUTLOOK Open access funding enabled and organized by Projekt DEAL.
The linear contouring and longitudinal gradient of each pass are highly DATA AVAILABILITY STAT EMEN T
adaptable, in particular, due to the possibilities of combining the dif- All data, models, and code generated or used during the study appear
ferent types of MFP, and hence can be customised to meet local con- in the submitted article.
ditions. In addition, the compact design means that the space
requirements and construction costs are often lower than for conven- OR CID
tional slot passes. The passability of the MFP is ensured by its Ulf Helbig https://orcid.org/0000-0002-8659-9100
favourable flow conditions. However, a definitive assessment of func-
tionality is prevented by the low number of surveys of upstream RE FE RE NCE S
migration carried out to date. The great potential of the MFP is indi- Aigner, D. (2016). Der Schlitzpass – Ausfluss- oder Überfallströmung.
cated by the high number of successful migrations recorded by some Wasserbauliche Mitteilungen Heft 57, TU Dresden.
Aigner, D., & Bollrich, G. (2015). Handbuch der Hydraulik, Beuth, 2015,
surveys, the lack of selectivity for species and small fish as well as the
S. 334 ff, Berlin.
inherent flexibility of the design, the comparatively low construction Bammatter, L., Baumgartner, M., Greuter, L., Haertel-Borer, S., Huber
costs and the adaptation possibilities after completion. At the same Gysi, M., Nitsche, M., & Thomas, G. (2015). Renaturierung der
time, there is a lack of empirical-based guidelines for pass dimension- Schweizer Gewässer: Die Sanierungspläne der Kantone ab 2015.
ing; also, due to the lack of relevant studies, this design is yet not suf- Bundesamt für Umwelt, BAFU, 13 S.
DWA. (2014). Merkblatt DWA-M 509. Fischaufstiegsanlagen und
ficiently recognised in current regulations.
fischpassierbare Bauwerke – Gestaltung, Bemessung, Qualitätssicherung.
The main criticism of previously constructed MFPs has been in Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V.:
regard to their relatively small sizes, which do not comply with the 334 S. Stand: korrigierte Fassung Februar 2016HELBIG ET AL. 13
Ebel, G., Fredrich, F., Gluch, A., Lecour, C., & Wagner, F. (2006). Meth- Waterstraat, A. (2005). Nachweis der Funktionsfähigkeit der
odenstandard für die Funktionskontrolle von Fischaufstiegsanlagen. Fischaufstiegshilfen Vorbeck/ Warnow, Rothen/Mildenitz und Dobb-
Bund der Ingenieure für Wasserwirtschaft, Abfallwirtschaft und ertin/Mildenitz für Fische und Zoobenthos. Staatlichen Amt für
Kulturbau (BWK) e.V., 115 S. Umwelt und Natur Schwerin, 33 S.
Guitton, D. E. (1964). Two-dimensional Turbulent Wall jets over curved Waterstraat, A., Renner, K., & Blohm, J. (2007). Effizienzkontrolle am
surfaces, Department of Mechanical Engineering, McGill University, Mäanderfischpass Borkow in der Mildenitz (einschliesslich
Montreal Zusatzuntersuchung am Mäanderfischpass Rothen). Staatliches Amt
Helbig, U., Aigner, D., Stamm, J. (2016). Hydraulik der Schlitzöffnungen bei für Umwelt und Natur Schwerin, 30 S.
beckenartigen Fischaufstiegsanlagen. Bautechnik 93 (2016), Heft Wieland, S., & Nöthlich, I. (2003). Funktionskontrolle Mäanderfischpass
5, Ernst & Sohn, Berlin Drakenburg/Weser. Bundesanstalt für Gewässerkunde (BfG),
IWD. (2016). Hydraulische Untersuchung der Rundbeckenpassanlage Auftraggeber: Wasser- und Schiffahrtsamt Verden, BfG-1400, 20 S.
Höxter/Godelheim, Forschungsbericht 2014/08 TU Dresden, Institut Wilmsmeier, L., Schölzel, N., & Peter, A. (2018). Fischwanderung: Kon-
für Wasserbau und Technische Hydromechanik (IWD), Dresden, 2016, trollinstrument Zählbecken. Die unterschätzte Bedeutung der
123 S. Reusenkehle. Bundesamt für Umwelt (BAFU), 48 S.
Lübker, I., & Schubert, H.-J. (2019). Funktionsüberprüfung des Fischpasses Wolter, C., & Menzel, R. (2011). Funktionsüberprüfung der
an der Fuhlsbütteler Schleuse (Hamburg). Freie und Hansestadt Ham- Fischaufstiegsanlagen an den Havel-Staustufen Brandenburg und
burg, 22 S. Bahnitz. Wasser- und Schifffahrtsamt Brandenburg, 22 S.
NLWK. (2004). Funktionskontrolle Mäanderfischpass an der Oker-Mühle Zaugg, C., Dönni, W., Boller, L., & Guthruf, J. (2017).
in Rothemühle (LK Gifhorn). Aller - Oker - Lachs - Gemeinschaft Massnahmenumsetzung Sanierung Fischgängigkeit. Handbuch
(AOLG), Niedersächsischer Landesbetrieb für Wasserwirtschaft und Wirkungskontrollen. Bundesamt für Umwelt (BAFU), 82 S.
Küstenschutz (NLWK) – Betriebsstelle Süd, Niedersächsisches Zeh Weissmann, H., Könitzer, C., & Bertiller, A. (2009). Strukturen der
Landesamt für Ökologie (NLÖ) – Dezernat Binnenfischerei, 16 S. Fliessgewässer in der Schweiz. Zustand von Sohle, Ufer und Umland
Rajaratnam, N. (1976). Turbulent Jets. Amsterdam, Oxford, New York: (Ökomorphologie); Ergebnisse der ökomorphologischen Kartierung.
Elsevier Science 1976. Stand: April 2009. BAFU, Umwelt-Zustand 0926, 100 S.
Rathcke, P.-C. (2004). Überprüfung der Funktionsfähigkeit des
Mäanderfischpasses im Wasserkraftwerk Pfortmühle (Hameln). Stadt
Hameln, 49 S.
Rodney, J. S. (1972). Flow patterns in lakes and reservoirs – A theoretical
and experi-mental study of several aspects of jet-forced reservoir cir- How to cite this article: Helbig, U., Mende, M., Dönni, W., &
culations. University of London, Faculty of Engineering, London Rathke, K. (2021). The meander-type fish pass: An alternative
SRF. (2018). Todesfallen für Fische - Sanierung der Kraftwerke kostet bis
to the conventional vertical slot pass. River Research and
zu 5 Milliarden. Schweizer Radio und Fernsehen. Retrieved June
21, 2019 from https://www.srf.ch/news/schweiz/todesfallen-fuer- Applications, 1–13. https://doi.org/10.1002/rra.3827
fische-sanierung-der-kraftwerke-kostet-bis-zu-5-milliarden-frankenYou can also read
