Assessment of Fish Interactions with the Energyminer Energyfish Hydrokinetic Turbine Prepared for Prepared by

Full text

Assessment of Fish Interactions with the Energyminer
Energyfish Hydrokinetic Turbine
Prepared for
Prepared by
Stephen Amaral and Jacob LaFontaine
Alden Research Laboratory, LLC
a Verdantas company
February 2024

Energyfish Fischverträglichkeitsprüfung
Februar 2024
i
EXECUTIVE SUMMARY (Deutsche Übersetzung)
Alden Research Laboratory, Inc. (Alden) hat im Rahmen der vorliegenden Studie die möglichen
Auswirkungen der hydrokinetischen Turbine Energyfish auf Flussfische für die Energyminer GmbH
bewertet. Die Ingenieure und Wissenschaftler von Alden sind führend in der Erforschung der
Auswirkungen von konventionellen sowie hydrokinetischen Turbinen auf Fische. Alden setzt sein
Fachwissen ein, um die Überlebensrate von Fischen sowie die relativen Auswirkungen von Mechanismen,
die mit verschiedenen Arten von Wasserkraft- und hydrokinetischen Turbinen verbunden sind, zu
bestimmen. Dazu werden Labortests zu Verletzungen und Mortalität bei Fischen durch
Turbinenschaufelschläge durchgeführt und Modelle für die Wahrscheinlichkeit von Schaufelschlägen
sowie deren Auswirkungen im Zusammenhang mit der Passage von Fischen durch hydrokinetische
Turbinen entwickelt (EPRI 2011a). Auch Daten aus Studien über die Verletzungsmechanismen
herkömmlicher Wasserturbinen (z. B. schädliche Scherwerte und Druckänderungen) wurden von den
Wissenschaftlern von Alden ausgewertet, um die Risiken für Fische zu bewerten, die die hydrokinetischen
Anlagen passieren oder sich in deren Nähe bewegen (EPRI 2011a). Darüber hinaus haben die
Wissenschaftler von Alden im Rahmen von Studien Verletzungen, Sterblichkeit und
Vermeidungsverhalten von Fischen im Zusammenhang mit hydrokinetischen Turbinen untersucht. Diese
Untersuchungen wurden in großen Strömungskanälen mit Pilotanlagen und realen Turbinen an lebenden
Fischen verschiedener Arten durchgeführt und dienen als Basis der vorliegenden
Fischverträglichkeitsprüfung des Energyfish (EPRI 2011b; EPRI 2014; Amaral et al. 2015).
Energyminer hat die hydrokinetische Turbine namens Energyfish entwickelt, die speziell für die
Installation in Schwärmen in Flüssen und Kanälen konzipiert ist. Es handelt sich um eine schwimmende
Turbine mit horizontaler Achse, die in Deutschland und Mitteleuropa eingesetzt wird. Die vorliegende
Studie stellt eine Fischverträglichkeitsprüfung dar und wurde durchgeführt, um die potenziellen
Auswirkungen der Energyfish-Turbinen auf Fische zu beurteilen.
Die Fischverträglichkeitsprüfung umfasst folgende Themengebiete:
- Eine Bewertung der Konstruktion und des Betriebs des Energyfishs
- Eine qualitative Bewertung der Begegnungswahrscheinlichkeit der Fische mit den Rotoren in der
Turbine und des Vermeidungsverhaltens der Fische, in diese Rotoren zu gelangen
- Eine Schätzung der Begegnungswahrscheinlichkeit und des Vermeidungsverhaltens auf der
Grundlage der Turbinenkonstruktion und der vorhandenen Fischreaktionsdaten
- Eine Schätzung der Überlebenswahrscheinlichkeit bei Turbinenpassage unter Verwendung eines
theoretischen Modells für die Schaufelschlagswahrscheinlichkeit
- Eine Schätzung der Gesamtüberlebenswahrscheinlichkeit aller Fische, die die Energyfish-Turbinen
stromabwärts passieren.
Die Fischverträglichkeitsprüfung der hydrokinetischen Turbine Energyfish durch Alden zeigt, dass für alle
Fische, die eine Gruppe von Energyfischen passieren, die Überlebenswahrscheinlichkeit in einem
typischen Einsatzszenario bei über 99,95% liegt. Hochgerechnet auf den gesamten Energyfish-Schwarm,
bestehend aus 100 Anlagen, liegt die Überlebenswahrscheinlichkeit immer noch bei über 99%. Dies liegt
vor allem an sehr niedrigen Begegnungswahrscheinlichkeiten, hohen Vermeidungs- und Überlebensraten
bei der Passage des Turbinenbereichs sowie an der physischen Ausgrenzung größerer Fische durch den
Treibgut- bzw. Fischrechen.

Energyfish Fischverträglichkeitsprüfung
Februar 2024
ii
Tabelle ES-1. Gesamtüberlebensraten für Fische, die flussabwärts eine Gruppe eines Energyfish-Schwarms passieren, in Abhängigkeit des
prozentualen Anteils der Installation zur Flussquerschnittsfläche (4,15% entspricht einem typischen Einsatzszenario, 10% und 25% zeigen
weitere konservative Szenarien zum Vergleich).
Gebräuchlicher Name
der Spezies
Durchschn.
Länge
(mm)
4.15%
10%
25%
1,0 m/s
1,5 m/s
2,4 m/s
1,0 m/s
1,5 m/s
2,4 m/s
1,0 m/s
1,5 m/s
2,4 m/s
Steinschmerle
120
100,00
99,97
99,98
100,00
99,93
99,96
100,00
99,82
99,89
Hasel
150
100,00
99,96
99,98
100,00
99,91
99,94
100,00
99,78
99,86
Quappe
150
100,00
99,96
99,98
100,00
99,91
99,94
100,00
99,78
99,86
Schleie
200
100,00
99,95
99,97
100,00
99,89
99,93
100,00
99,73
99,82
Nase
250
100,00
99,95
99,97
100,00
99,89
99,92
100,00
99,72
99,79
Flussbarsch
250
100,00
99,95
99,97
100,00
99,89
99,92
100,00
99,72
99,79
Döbel
300
100,00
100,00
99,99
100,00
100,00
99,98
100,00
99,99
99,96
Äsche
300
100,00
100,00
99,99
100,00
100,00
99,98
100,00
99,99
99,96
Karpfen
310
100,00
99,95
99,95
100,00
99,88
99,89
100,00
99,70
99,73
Hecht
400
100,00
100,00
99,99
100,00
99,99
99,97
100,00
99,98
99,93
Regenbogenforelle
600
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00
Europäischer Aal
350-1.000
100,00
100,00
99,97
100,00
100,00
99,93
100,00
99,99
99,81
Huchen
700
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00
Meerforelle
720
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00
100,00

Energyfish Fischverträglichkeitsprüfung
Februar 2024
iii
Für die Bewertung der Auswirkungen des Energyfish-Schwarms auf Fische wurde eine Beispielinstallation
herangezogen, um in erster Linie die Gesamtüberlebensrate von Fischen zu ermitteln, die am Standort
eines typischen Energyfish-Schwarms flussabwärts wandern. Der gewählte Standort befindet sich am
Lech in Augsburg, Deutschland. Der für diesen Standort vorgesehene Energyfish-Schwarm umfasst 20
Gruppen zu je fünf Energyfish-Anlagen (zwei Rotoren pro Anlage), die von flussaufwärts nach
flussabwärts aufgereiht sind. Die durchschnittliche Querschnittsfläche des Flussabschnitts, in dem der
Energyfish-Schwarm installiert wird, beträgt etwa 140 m2. An diesem Standort hat der Energyfish-
Schwarm eine Grundfläche, die nur etwa 4,15 % des gesamten Flussquerschnitts ausmacht. Im Rahmen
der Analyse wurde auch ein theoretisches Worst-Case-Szenario analysiert, in dem der Energyfish-
Schwarm 25 % des gesamten Flussquerschnitts ausmachen würde.
Die Begegnungswahrscheinlichkeit bezeichnet die Wahrscheinlichkeit, dass Fische in den Rotorbereich
des Energyfishs gelangen. Sie wird durch die Verteilung der Fische im gesamten Flussquerschnitt am
Standort der Turbine sowie durch die Position der Turbine innerhalb dieses Querschnitts beeinflusst,
sowohl vertikal (unterer, mittlerer oder oberer Teil der Wassersäule) als auch horizontal (näher am Ufer
oder in der Flussmitte). Das Verhältnis der vom Energyfish-Schwarm abgedeckten Fläche zur
Gesamtfläche des Flussquerschnitts führt zu niedrigen Begegnungsraten für die meisten Fischarten.
Besonders wenn die Anlagen in schnell fließenden Abschnitten weit vom Ufer entfernt und nahe der
Wasseroberfläche installiert sind, ist es möglich, dass einige Fischarten nie mit einer Anlage in Kontakt
kommen, da sie tiefere Gewässer, niedrigere Strömungsgeschwindigkeiten oder küstennahe Bereiche
bevorzugen. Die für diese Studie herangezogene konservative Schätzung der
Begegnungswahrscheinlichkeit beruht auf der Annahme, dass sich alle Fische gleichmäßig über den
Flussquerschnitt am Standort einer Anlage verteilen. Das bedeutet, dass die Wahrscheinlichkeit, dass ein
Fisch auf eine Turbine trifft, gleich dem Anteil der Turbinen am gesamten Flussquerschnitt ist, der bei der
Beispielanlage am Lech 4,15 % beträgt.
Die Wahrscheinlichkeit, dass Fische, die sich in einem Fluss stromabwärts bewegen, auf eine Energyfish-
Turbine treffen, ist mit weniger als 5 % (4,15% am Lech) im Allgemeinen sehr gering und ist abhängig
vom Standort der Turbinen sowie der Größe ihrer Grundfläche im Verhältnis zur Querschnittsfläche des
Flusses.
Zudem ist die Wahrscheinlichkeit, dass die Fische, die einer Anlage zwar begegnen, dann aber den
Rotorbereich meiden, bei vielen Arten mäßig (50 bis 75 %) oder hoch (> 75 %). Beobachtungen aus
Strömungsstudien zeigen, dass die höchsten Vermeidungsraten (> 90 %) bei größeren Fischen und bei
Arten mit starken Schwimmfähigkeiten, wie z.B. Salmoniden, festzustellen sind. Kombiniert man die
Wahrscheinlichkeiten des Zusammentreffens und des Ausweichens, so liegt die Wahrscheinlichkeit, mit
der stromabwärts passierende Fische mit dem Turbinenbereich in Kontakt kommen bei nur etwa 2,5 %
anhand der Beispielanlage am Lech.
Um das Verletzungs- und Mortalitätsrisiko zu verringern, begrenzt Energyminer die
Rotationsgeschwindigkeiten auf ein Niveau, das die Überlebensrate für alle Fischgrößen über den Bereich
der Fließgeschwindigkeiten, bei denen die Turbinen betrieben werden, maximiert (d. h. 1,0 bis 2,4 m/s).
Die Untersuchungen ergaben, dass alle Fischarten, unabhängig von ihrer Größe, eine Überlebensrate von
100 % aufweisen, wenn die Turbinen bei einer Fließgeschwindigkeit von 1 m/s oder weniger betrieben
werden. Bei höheren Fließgeschwindigkeiten liegt die Überlebensrate bei der Rotorpassage des
Energyfish zwischen 95 und 100 %.

Energyfish Fischverträglichkeitsprüfung
Februar 2024
iv
Die Gesamtüberlebensrate von Fischen, die sich einem Flussabschnitt nähern, in dem sich ein Energyfish-
Schwarm befindet, ist eine Schätzung des Anteils aller Fische, die flussabwärts wandern und diesen
Flussabschnitt lebend passieren.
In die Schätzung der Gesamtüberlebensrate fließen auch die Begegnungs- sowie die
Vermeidungswahrscheinlichkeit, sowie die Überlebensrate der wenigen Fische ein, die durch den
Rotorbereich schwimmen.
Die geschätzte Gesamtüberlebensrate für eine Gruppe eines Energyfish-Schwarms liegt für alle Arten und
Fischlängen (Tabelle ES-1) im gesamten Bereich der untersuchten Fließgeschwindigkeiten und
Begegnungswahrscheinlichkeiten bei über 99,95 % für die Beispielinstallation. Daraus ergibt sich, dass
die Gesamtüberlebensrate für Fische, die theoretisch einen aus 20 Gruppen bestehenden Energyfish-
Schwarm stromabwärts passieren, ebenfalls mit über 99% sehr hoch ist.
Hierbei muss jedoch berücksichtigt werden, dass ein großer Teil der Fische, die auf die ersten oder
nachfolgenden Gruppen Energyfische treffen, ausweichen und außerhalb des von der
Turbinenanordnung eingenommenen Bereichs weiter stromabwärts wandern. Dies führt zusätzlich zu
niedrigeren Begegnungswahrscheinlichkeiten und einer höheren Gesamtüberlebensrate für den
Energyfish-Schwarm als in dieser Studie berechnet.
Immer mehr Ergebnisse aus Labor- und Feldstudien deuten darauf hin, dass die Wahrscheinlichkeit eines
Zusammentreffens gering ist, die Vermeidungsraten hoch sind und die Überlebensrate bei der Passage
des Turbinenbereichs für die meisten Fischarten, die Standorte mit hydrokinetischen Turbinen
stromabwärts passieren, hoch ist.

Energyfish Fish Impact Assessment
February 2024
v
EXECUTIVE SUMMARY
In this study Alden Research Laboratory, Inc. (Alden) evaluated the potential impacts of a hydrokinetic
turbine, referred to as the Energyfish developed by Energyminer GmbH on riverine fishes. Alden
engineers and fisheries scientists have been leaders in the assessment of fish injury and mortality
associated with passage of fish through conventional and hydrokinetic turbines and have used this
knowledge and experience to determine entrainment and survival rates and relative impacts of injury
mechanisms associated with many hydroelectric and hydrokinetic turbines. Alden’s staff have
conducted laboratory testing of turbine blade strike injury and mortality and have developed theoretical
models for blade strike probability and the probability of mortality from strike associated with passage
of fish through hydrokinetic turbines (EPRI 2011a). Alden scientists have also evaluated data developed
from studies of conventional hydro turbine injury mechanisms (e.g., damaging shear levels and pressure
changes) to assess the risks to fish passing through or near hydrokinetic devices (EPRI 2011a). In
addition, Alden’s fisheries scientists have evaluated fish injury, mortality, and avoidance associated with
hydrokinetic turbines during studies conducted in a large flume using pilot and full-scale turbines and
live fish of several species (EPRI 2011b; EPRI 2014; Amaral et al. 2015).
Energyminer has developed the Energyfish hydrokinetic turbine for installation in schools in rivers and
canals. It is a floating horizontal-axis turbine and is designed for deployment in arrays of multiple units
throughout Germany and central Europe. This report describes an evaluation that was conducted to
assess potential effects, or lack thereof, of Energyfish turbines on fish using an established theoretical
model for turbine survival and data and information from laboratory research on fish interactions with
hydrokinetic turbines. This includes:
• An assessment of the Energyfish design and operation.
• A general qualitative assessment of encounter and avoidance probabilities for selected fish
species of interest.
• An estimation of encounter and avoidance probabilities based on turbine design and existing
fish response data.
• An estimation of turbine passage survival using a theoretical blade strike probability and
mortality model.
• An estimation of total project survival for all fish moving downstream past a deployment of
Energyfish turbines.
The fish compatibility test of the Energyfish hydrokinetic turbine undertaken by Alden, shows
overall survival probabilities of over 99.95% for all fish passing an Energyfish school. When this
value is extrapolated for the school of Energyfish, based on 100 turbines, the overall survival rate is
still above 99%. This is primarily due to the very low encounter probabilities and high avoidance and
survival rates when passing the Energyfish turbine area. As well as the physical exclusion of larger
fish associated with the debris and fish guide bars provide.

Energyfish Fish Impact Assessment
February 2024
vi
Table ES-1. Total passage survival rates for fish passing downstream of a group of Energyfish turbines dependent on the proportion of the
river cross-sectional area that would be occupied by a group of Energyfish units (4.15% represents this proportion at a typical deployment
site; 10 and 25% provide more conservative estimates of encounter probabilities for comparison).
Common Name
for species of
Interest
Common
Length
(mm)
4.15%
10%
25%
1.0 m/s
1.5 m/s
2.4 m/s
1.0 m/s
1.5 m/s
2.4 m/s
1.0 m/s
1.5 m/s
2.4 m/s
Stone Loach
120
100.00
99.97
99.98
100.00
99.93
99.96
100.00
99.82
99.89
Common Dace
150
100.00
99.96
99.98
100.00
99.91
99.94
100.00
99.78
99.86
Burbot
150
100.00
99.96
99.98
100.00
99.91
99.94
100.00
99.78
99.86
Tench
200
100.00
99.95
99.97
100.00
99.89
99.93
100.00
99.73
99.82
Common Nace
250
100.00
99.95
99.97
100.00
99.89
99.92
100.00
99.72
99.79
European Perch
250
100.00
99.95
99.97
100.00
99.89
99.92
100.00
99.72
99.79
European Chub
300
100.00
100.00
99.99
100.00
100.00
99.98
100.00
99.99
99.96
Grayling
300
100.00
100.00
99.99
100.00
100.00
99.98
100.00
99.99
99.96
Common Carp
310
100.00
99.95
99.95
100.00
99.88
99.89
100.00
99.70
99.73
Northern Pike
400
100.00
100.00
99.99
100.00
99.99
99.97
100.00
99.98
99.93
Rainbow Trout
600
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
European Eel
350-1,000
100.00
100.00
99.97
100.00
100.00
99.93
100.00
99.99
99.81
Huchen
700
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
Sea Trout
720
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00
100.00

Energyfish Fish Impact Assessment
February 2024
vii
An example installation was used for the assessment of fish impacts, primarily to evaluate total survival
of fish passing downstream at the location of a typical deployment of Energyfish turbines. The site that
was used is located on the Lech River in Augsburg, Germany. The deployment being considered for this
location includes 20 groups of five Energyfish units (two rotors per unit) in line from upstream to
downstream. The average cross-sectional area of the river where the turbines would be deployed is
about 140 m2. At this location, the first group of turbines would have a footprint that is about 4.15% of
the total river cross section. The analysis also included a theoretical worst case scenario of the most
extreme blockage of 25% which may occur in canal systems.
Encounter probability is the likelihood that fish will directly approach an operating Energyfish in the flow
entrained through the turbine blade swept area. Encounter probabilities will be influenced by fish
distributions throughout the cross-section of a river at the location of turbine, as well as where the
turbine is located within that cross-section both vertically (bottom, mid, or upper part of water column)
and horizontally (closer to shore or near the middle of the river). The area covered by a typical group of
Energyfish relative to the area of a river’s cross section will lead to low encounter rates for most fish
species. In particular, if Energyfish units are located away from shore and near the surface in fast flowing
reaches, some species may never encounter a unit due to preferences for deeper water, lower
velocities, or nearshore areas. A conservative approach to estimating encounter probabilities is to
assume that all fish are distributed uniformly throughout a river’s cross-section at the location of a
turbine. This means the probability that a fish will encounter a turbine is equal to the proportion of the
total river cross-section occupied by the turbines, which is 4.15% for the example installation on the
Lech River.
The probability that fish moving downstream in a river will encounter an Energyfish turbine will
generally be low (< 5%, e.g. 4.15% at the example location) and will depend on the location of the
turbines and the size of their footprint relative to the cross-sectional area of the river. For the few fish
that may encounter an Energyfish turbine the avoidance of entrainment through turbines rotors is likely
to be moderate (50 to 75%) or high (>75%) for many species. Based on observations from flume studies,
the highest avoidance rates (> 90%) will occur for larger fish and species with strong swimming
capabilities (e.g., salmonids). When encounter and avoidance probabilities are combined, the estimated
entrainment rate through turbine rotors for a group of five units is only about 2.5% or less of fish
passing downstream at the example location.
To reduce the potential for injury and mortality, Energyminer will limit rotational speeds to a level
maximize survival for all fish sizes over the range of flow velocities at which the turbines will operate
(i.e., 1.0 to 2.4 m/s). Turbine survival was estimated to be 100% for all fish, regardless of length, when
the units are operating at a flow velocity of 1 m/s or less and ranged from 95 to 100% at the higher flow
velocities.
Total passage survival or fish approaching a section of a river with an installed Energyfish school is an
estimation of the proportion of all fish moving downstream that pass the installation and survive.
Estimates of total passage survival include encounter and avoidance probabilities and turbine passage
survival rates for the few fish that are entrained through the rotor. Total passage survival estimates for a
single group of Energyfish units at the demonstration site will exceed 99.95% for all species and fish
lengths (Table ES-1) across the range of flow velocities and encounter probabilities evaluated. As a
result, the total passage survival rate for fish passage in an Energyfish school, consisting of 20 groups, is
very high, at over 99%.

Energyfish Fish Impact Assessment
February 2024
viii
It should be considered that the total passage survival is also expected to be high for fish passing
downstream through a deployment array of Energyfish units. This is because a large proportion of fish
encountering the lead group or subsequent groups will continue downstream outside of the area
occupied by the turbine array, which will result in lower encounter probabilities for each successive
turbine group and thus a higher overall survival rate.
There is growing evidence from lab and field studies that suggest encounter probabilities will be low,
avoidance rates will be high, and turbine survival will be high for most fish species and life stages that
pass downstream at sites where hydrokinetic turbines are installed.

Energyfish Fish Impact Assessment
February 2024
ix
TABLE OF CONTENTS
EXECUTIVE SUMMARY (Deutsche Übersetzung) .................................................................................. i
EXECUTIVE SUMMARY ....................................................................................................................... v
1.0 Introduction ...........................................................................................................................1
1.1 Summary of Alden’s Capabilities Relative to Hydrokinetic Technologies and Environmental
Impacts 1
2.0 Energyfish Design and Operation and Example Installation ......................................................3
2.1 Energyfish Design and Operation ................................................................................................ 3
2.2 Example Installation .................................................................................................................... 4
3.0 Fish Species of Interest ............................................................................................................7
4.0 Fish Interactions and Potential Impacts ...................................................................................9
4.1 Encounter and Avoidance Probabilities ...................................................................................... 9
4.1.1 Encounter Probabilities..................................................................................................... 10
4.1.2 Avoidance Probabilities .................................................................................................... 11
4.1.3 Estimation of Encounter and Avoidance Probabilities for Energyfish .............................. 11
4.2 Turbine Passage Survival ........................................................................................................... 13
4.2.1 Theoretical Blade Strike Probability and Mortality Model ............................................... 13
4.2.2 Laboratory and Field Evaluations of Fish Interactions with Hydrokinetic Turbines ......... 15
4.3 Total Passage Survival................................................................................................................ 19
5.0 Summary and Conclusions ..................................................................................................... 24
6.0 Literature Cited ..................................................................................................................... 26

Energyfish Fish Impact Assessment
February 2024
x
List of Tables
Table 1. Energyfish turbine design parameters used for estimating fish survival with a theoretical blade
strike probability and mortality model. ........................................................................................................ 4
Table 2. Summary of fish length, general habitat use, and estimated level of turbine encounter and
entrainment risk. Encounter risk is based on habitat preferences relative to where Energyfish turbines
are likely to be located within the water column (near surface) and across the width of a river (closer to
shore). Entrainment risk is for fish that encounter a turbine and is based on the expected ability of a
species to determine the turbine presence as they move downstream and their ability to avoid it (i.e.,
swim speed capabilities) in the range of current velocities at which Energyfish units will operate. ........... 8
Table 3. Avoidance rates estimated for three species of fish approaching an axial-flow hydrokinetic
turbine in a laboratory flume. Species codes are: RBT, rainbow trout (Oncorhyncus mykiss); WST, white
sturgeon (Acipenser transmontanus); and HSB, hybrid striped bass (Morone saxatilis x Morone chrysops)
[SOURCE: EPRI 2014] ................................................................................................................................... 12
Table 4. Estimated turbine avoidance rates for species of interest at Energyfish deployments based on
data from EPRI (2014). ................................................................................................................................ 13
Table 5. Survival, injury, and descaling estimates for fish evaluated with the Welka UPG and Free Flow
Power ducted axial-flow turbines (EPRI 2011b, 2014). Survival rates greater than 100% indicate control
fish mortality was greater than it was for treatment (turbine-passed) fish. .............................................. 16
Table 6. Estimated strike probability, strike mortality (probability of mortality if a fish is struck), and
turbine passage survival rates for fish passing through an Energyfish turbine at four approach velocities.
Turbine survival is calculated by multiplying strike probability by strike mortality and subtracting the
product from one; results are multiplied by 100 to provide results as percentages. These survival rates
only apply to fish that pass through the guidance rods and the turbine blades, which is a very low
proportion of all fish moving downstream in a river. Rotational speeds of the turbine are 124, 130, 125,
and 120 for flow approach velocities of 1.0, 1.5, 2.0, and 2.4, respectively. ............................................. 18
Table 7. Estimated total passage survival rates for the species of interest passing a single group of five
Energyfish units with an encounter probability of 4.15%. Fish with lengths of 600 mm or greater (with
the exception of European Eel) are expected to be physically excluded from turbine passage by the
angled guidance rods. ................................................................................................................................. 20
Table 8. Estimated total passage survival rates for the species of interest passing a single group of five
Energyfish units with an encounter probability of 10%. Fish with lengths of 600 mm or greater (with the
exception of European Eel) are expected to be physically excluded from turbine passage by the angled
guidance rods. ............................................................................................................................................. 21
Table 9. Estimated total passage survival rates for the species of interest passing a single group of five
Energyfish units with an encounter probability of 25%. Fish with lengths of 600 mm or greater (with the
exception of European Eel) are expected to be physically excluded from turbine passage by the angled
guidance rods. ............................................................................................................................................. 22

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List of Figures
Figure 1. Ducted axial-flow Energyfish turbine (paired unit with debris and fish guidance bars). .............. 3
Figure 2. Energyfish turbines deployed in 20 groups of 5 at the installation site on the Lech River in
Augsburg, Germany. ..................................................................................................................................... 5
Figure 3. Section (top) and plan (bottom) views of Energyfish units deployed in groups of five (depths
and river widths will vary with deployment location). ................................................................................. 6
Figure 4. Computational fluid dynamics (CFD) model results showing flow velocities associated with an
Energyfish turbine (plan view). ................................................................................................................... 10
Figure 5. Schematic of absolute inflow, axial velocity (or radial for Francis turbines), and relative velocity
of flow (and fish) to a blade leading edge. The parameter Δs is the incremental blade motion in the time
fish move through the leading edge circumference. .................................................................................. 14

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1.0 Introduction
Energyminer GmbH has developed a hydrokinetic turbine for installation in rivers and canals. It is a
floating horizontal-axis turbine, referred to as the Energyfish, and is designed for deployment in arrays
of multiple units in rivers and canals throughout Germany and central Europe. As with any power
generation device placed in a flowing water environment, there could be concerns regarding potential
impacts to fish that encounter Energyfish turbines.
The development of hydrokinetic turbine technologies as a renewable energy source has garnered
considerable interest in recent years and, not surprisingly, interest in the assessment of potential
impacts to aquatic resources has also grown. Blade strike is often cited as a primary area of concern for
fish that encounter hydrokinetic turbines and are entrained through the sweep area of rotating blades.
However, laboratory and field studies have demonstrated relatively high rates of turbine avoidance and,
for fish that are entrained, high turbine passage survival rates.
The goal of the fish impact assessment described in this report was to evaluate potential effects that
Energyfish turbines may have on fish and habitat. To achieve this goal, the following tasks were
completed:
• Assessment of Energyfish design and operational features with respect to potential impacts to
fish.
• General assessment of encounter and avoidance probabilities for the species of interest based
on habitat preferences and swimming capabilities.
• Estimation of encounter and avoidance probabilities for each species of interest based on
turbine size and existing information data.
• Estimation of turbine passage survival for each species of interest using a theoretical model for
strike probability and mortality.
• Estimation of total passage survival for all fish moving downstream past an array of Energyfish
units using estimates of encounter, avoidance, and survival rates.
Using the information and data generated from the completion of these tasks, conclusions on the likely
impacts to fish associated with Energyfish installations were developed.
1.1 Summary of Alden’s Capabilities Relative to Hydrokinetic Technologies and
Environmental Impacts
Alden engineers and fisheries scientists have been leaders in the assessment of fish injury and mortality
associated with passage of fish through conventional and hydrokinetic turbines and have used this
knowledge and experience to determine entrainment and survival rates and relative impacts of injury
mechanisms associated with many hydroelectric and hydrokinetic turbines. Alden’s staff have
conducted laboratory testing of turbine blade strike injury and mortality and have developed theoretical
models for blade strike probability and the probability of mortality from strike associated with passage
of fish through hydrokinetic turbines (EPRI 2011a). In addition to blade strike, Alden scientists have

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evaluated data developed from studies of conventional hydro turbine injury mechanisms (e.g.,
damaging shear levels and pressure changes) to assess the risks to fish passing through or near
hydrokinetic devices (EPRI 2011a). Alden’s fisheries scientists have also evaluated fish injury, mortality,
and avoidance associated with hydrokinetic turbines during studies conducted in a large flume using
pilot and full-scale turbines and live fish of several species (EPRI 2011b; EPRI 2014; Amaral et al. 2015).
Mr. Stephen Amaral, the lead investigator for the fish impacts assessment of the Energyfish turbine, has
more than 30 years of experience in the design, evaluation, and application of fish passage and
protection technologies at hydropower dams and various types of water intakes and power generating
facilities. This includes numerous projects involving development and application of upstream and
downstream fish passage facilities at hydropower projects, as well as management of laboratory and
field evaluates of screening technologies, behavioral guidance systems, and innovative systems for
transferring fish upstream. Mr. Amaral has also led investigations of injury mechanisms experienced by
fish passing through conventional and hydrokinetic turbines (EPRI 2011a, 2011b, 2011c, 2014; Amaral et
al. 2015, 2018, 2020) and assisted with development of theoretical models for predicting turbine
passage survival. Mr. Amaral’s fish passage and protection experience includes studies with endangered
or threatened species, including American and European Eel, Shortnose and Lake Sturgeon, Atlantic
Salmon and several Pacific salmonids. Mr. Amaral has worked on fish passage and protection issues
internationally, including for existing or proposed projects in England, France, Germany, Romania,
Serbia, Estonia, Brazil, New Zealand, and Cambodia.

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2.0 Energyfish Design and Operation and Example Installation
2.1 Energyfish Design and Operation
The Energyfish (Figure 1) is a duo rotor hydrokinetic turbine design optimized for slow propeller rotation
rates according to the EIA guidelines on fish mortality avoidance. The device is equipped with 10-mm
diameter rods angled horizontally from the nose of the housing frame downstream to the outside of the
rotor ducts (Figure 1). The angled rods are expected to reduce entrainment of fish through the rotors by
eliciting behavioral avoidance of fish small enough to pass through spacing of the rods and physically
excluding larger fish. Energyfish turbine arrays are expected to be deployed in lower velocity sections or
river channels (1.0 to 1.8 m/s), which will lead to greater fish avoidance of entrainment and improved
survival of fish that pass through the rotors due to lower rotational speeds. The floating Energyfish is
designed to stay at the surface of a river/canal section and only dives below the surface during high flow
events. It is secured to the riverbed with a single anchor cable at a 20 to 30 degree angle. All moving
parts are surrounded by a PE housing, preventing riverbed sediment movement and habitat disruption.
Turbine design and operational parameters that affect the potential for blade strike and mortality from
strike include the number of blades (with respect to blade spacing), runner diameter (blade tip to blade
tip), rotational speed, inflow angle relative to blade leading edge, flow velocity relative to blade speed
(i.e., this is the strike velocity assuming fish travel at the same speed as the flow), and blade leading
edge thickness. The parameter inputs for blade strike probability and mortality model used to estimate
turbine survival of fish passing through an Energyfish are provided in Table 1.
Although the Energyfish can operate at rotational speeds up to 280 rpm at a maximum flow velocity of
2.4 m/s, Energyminer has indicated the units will not be operated at rotational speeds greater than 130
rpm to reduce the potential for injury and mortality of fish that may pass through the rotors. Therefore,
the assessment of fish impacts was based on this operational limit.
Figure 1. Ducted axial-flow Energyfish turbine (paired unit with debris and fish guidance bars).

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Table 1. Energyfish turbine design parameters used for estimating fish survival with a theoretical
blade strike probability and mortality model.
Parameter (units)
Turbines
Number of blades
3
Blade tip diameter (m)
0.86
Hub diameter (m)
0.15
Flow velocity operational range (m/s)
1.0-2.4
Rotational speeds (rpm)
130 max
Leading edge blade thickness at mid blade (mm)
9.7
Blade speeds at mid-blade (m/s)
4.6-11.1
Axial flow velocities (m/s)
1.0-2.4
Relative velocities of flow/fish to blade (m/s)
4.7-11.3
2.2 Example Installation
An example installation was used for the assessment of fish impacts, primarily to evaluate total survival
of fish passing downstream at the location of a typical deployment of Energyfish turbines. The site that
was used is located on the Lech River in Augsburg, Germany. The deployment being considered for this
location includes 20 groups of five Energyfish units (two rotors per unit) in line from upstream to
downstream (Figure 2 and Figure 3). Each group of five turbines has an upstream row of three units and
a downstream row of two units, with the downstream units being in line with the two openings between
the upstream units. The distance between two consecutive five-unit groupings is 17.5 m and the total
length of all 20 groups is about 400 m. Each Energyfish housing with the two rotors is 2.3 m wide and 1
m high and the units in each row are spaced about 6 m on center (Figure 3). The average cross-sectional
area of the river where the turbines would be deployed is about 140 m2. Water depths at the location of
the turbine array ranges from about 1.5 to 2.0 m. It is expected that Energyfish installations will not
have footprints that exceed 50% of the width or 25% of the cross section of a river channel.

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Figure 2. Energyfish turbines deployed in 20 groups of 5 at the installation site on the Lech River in
Augsburg, Germany.

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Figure 3. Section (top) and plan (bottom) views of Energyfish units deployed in groups of five (depths
and river widths will vary with deployment location).

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3.0 Fish Species of Interest
The primary species of interest include those that are commonly found in Germany and rivers of other
European countries. A general summary of fish length, habitat, and potential hydrokinetic turbine
encounter and entrainment risk is provided in Table 2. Hydrokinetic turbine encounter risk is based
primarily on general habitat use, including depth and water velocity preferences. Entrainment risk is
based on fish size and expected swimming capabilities.
All of the species of interest have a low or moderate risk of encountering a hydrokinetic turbine and of
being entrained if a turbine is encountered. Consequently, overall entrainment risk should be
considered low for each species because they are either unlikely to encounter a hydrokinetic turbine
installed in a riverine environment or, if they do approach a turbine, the risk to entrainment is low or
moderate depending on assumed swimming capabilities (e.g., salmonids are expected to have high
avoidance rates due to strong swimming capabilities, whereas common carp or European perch would
likely demonstrate moderate avoidance due to weaker swimming abilities, particularly when in higher
velocity flows). The catadromous European eel is the only species that might have a moderate risk for
encountering a turbine and of being entrained. The risk of encountering a turbine may be low for
yellow-phase eels (i.e., freshwater life stage), which are benthic and prefer slower flowing water.
However, silver-phase adults (spawning migrants) typically move downstream in the main channel of
rivers and are often found throughout the water column. Consequently, silver eels would have a higher
probability of encountering a hydrokinetic turbine; entrainment risk of silver eels is considered
moderate because they often are not aware of obstructions in the flow path until they are very close to
them.

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Table 2. Summary of fish length, general habitat use, and estimated level of turbine encounter and entrainment risk. Encounter risk is based
on habitat preferences relative to where Energyfish turbines are likely to be located within the water column (near surface) and across the
width of a river (closer to shore). Entrainment risk is for fish that encounter a turbine and is based on the expected ability of a species to
determine the turbine presence as they move downstream and their ability to avoid it (i.e., swim speed capabilities) in the range of current
velocities at which Energyfish units will operate.
Family
Common Name
Common
Length
(mm)
Habitat Location
in Rivers
Current
Preference
Depth Preference
in Rivers
HK Turbine
Encounter
Risk
HK Turbine
Entrainment
Risk
Anguillidae
European eel
350 - 1,000
variable
variable
benthic
moderate
moderate
Cyprinidae
European chub
300
nearshore
slow
variable
low
Moderate
common dace
150
variable
slow
variable
moderate
Moderate
common nase
250
variable
moderate-fast
variable
moderate
Moderate
common carp
310
variable
slow
bottom to mid
low
Moderate
tench
200
variable
slow
variable
low
Moderate
Esocidae
northern pike
400
nearshore
slow-moderate
variable
low
Low
Gadidae
Burbot
150
nearshore
slow
benthic
low
Moderate
Nemacheilidae
stone loach
120
variable
moderate-fast
benthic
low
moderate
Percidae
European perch
250
variable
slow
variable
low
Moderate
Salmonidae
Grayling
300
nearshore
fast
shallow
low
low
rainbow trout
600
variable
moderate-fast
bottom to mid
moderate
low
sea trout
720
variable
moderate-fast
bottom to mid
moderate
low
Huchen
700
deeper regions
moderate-fast
deep
moderate
low

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4.0 Fish Interactions and Potential Impacts
4.1 Encounter and Avoidance Probabilities
The likelihood of a physical interaction between a fish and a hydrokinetic turbine is determined by the
probability that a fish will encounter a turbine (i.e., approach rotating blades) and, if encountered, the
probability a fish can avoid entrainment by actively or passively following the flow passing around a
turbine. Because hydrokinetic turbines are an obstruction, a back pressure is created immediately
upstream of a turbine unit and flow accelerates around the tips of the blades or duct, if present (Figure
4). Fish moving downstream and approaching a turbine are able to detect these changes in flow, which
can be referred to as hydraulic cues, and alter their path as they would in response to any obstruction in
the flow. It is also possible that fish approaching a turbine near the outer edge of the blade swept area
may follow these streamlines with little effort and passively or semi-passively avoid entrainment.
Avoidance probabilities for fish that encounter a turbine can be developed from published data or site-
specific studies, and would include behavioral responses to hydraulic cues and, in the case of the
Energyfish, exclusion (physical and behavioral) from entrainment produced by the guidance rods.
Encounter probabilities can be estimated using the cross-sectional area of a turbine and by assuming
fish are distributed uniformly across the width and depth of a river at the location of the turbine. For
example, if a turbine’s cross-sectional area is 10% of the river cross-section, then it would be assumed
10% of fish moving downstream would encounter the turbine. Encounter probabilities can be adjusted
by species based on habitat preferences relative to the location and depth of a turbine. Encounter and
avoidance probabilities can be combined to provide an overall estimate of entrainment for all fish
passing downstream of single turbine or multiple units. As an example, if the encounter probability is
0.10 and the estimated avoidance probability is 0.90, then the probability of entrainment through the
turbine for all fish moving downstream in a river past the location of a turbine would be 0.01 (i.e., 1%).
A unique aspect of the Energyfish design that may also influence avoidance rates is the use of angled
rods to protect the turbine rotors from debris and to provide a guidance mechanism for diverting fish
away from the rotors. Behavioral avoidance will occur for some fish that are small enough to pass
through the rod spacing. Impingement of fish too large to pass through rod spacing is unlikely because
of the rod angle and fish of this size will have swimming speeds that are sufficient to avoid impingement,
even at the higher flow velocities of the Energyfish operating range.

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Figure 4. Computational fluid dynamics (CFD) model results showing flow velocities associated with
an Energyfish turbine (plan view).
4.1.1 Encounter Probabilities
Encounter probability refers to the likelihood that fish will directly approach an operating turbine in the
flow entrained through the blade swept area. Encounter probabilities will be influenced by fish
distributions throughout the cross-section of a river at the location of turbine, as well as where the
turbine is located within that cross-section both vertically (bottom, mid, or upper part of water column)
and horizontally (closer to shore or near the middle of the river). If a turbine is installed near the middle
of a river at a relatively deep location, species or life stages that typically occur closer to shorelines or
higher in the water column may never encounter the turbine. Some species and life stages may be
found across the width or a river or throughout the water column depending on the time of year and/or
river flow rate. Without field data to accurately determine where various species and life stages
typically occur, a conservative approach to estimating encounter probabilities is to assume that all fish
are distributed uniformly throughout a river’s cross-section at the location of a turbine. This means the
probability that a fish will encounter a turbine is equal to the proportion of the total river cross-section
occupied by the blade swept area.
The cross-sectional area of the blade sweep of a single Energyfish rotor is 0.58 m2 based on a diameter
of 0.86 m. Therefore, an Energyfish unit with two rotors has a total cross-sectional area of 1.16 m2. The
river cross-sectional area at the location of the example installation on the Lech River averages about
140 m2. Consequently, one Energyfish unit comprises 0.83% of the river cross section and the proposed
grouping of five units will cover about 4.15%. If fish are distributed uniformly across the river width and
depth, about 4.15% of fish moving downstream would be expected to encounter one of the Energyfish
rotors in the leading group of five units. Encounter probabilities are likely to decrease for the 19
groupings of units placed in succession downstream of the lead group.

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4.1.2 Avoidance Probabilities
The ability of fish to avoid entrainment through hydrokinetic turbines has been evaluated during flume
studies (EPRI 2011b, 2014; Amaral et al. 2015). The most pertinent data to Energyfish installations were
collected from tests with a 1.5-m diameter axial-flow turbine (EPRI 2014). These tests were conducted
with two size groups of rainbow trout and one size group of white sturgeon and hybrid striped bass at
approach velocities up to 2 m/s (Table 3). Turbine avoidance was high (> 85%) for both size groups of
trout, but was higher for the larger fish, particularly at the two highest velocities evaluated (1.5 and 2.0
m/s; Table 3). Trout avoidance also decreased slightly with increasing velocity (Table 3). Juvenile white
sturgeon also had high turbine avoidance rates (about 87 to 100%) at the three velocities evaluated
(Table 3). Juvenile hybrid bass experienced lower avoidance rates (about 32 to 65%) than trout or
sturgeon, and neither bass or sturgeon showed a clear trend in avoidance with respect to velocity (Table
3). Tests conducted with the lowest velocity (1.1 m/s) under day and nighttime light conditions did not
demonstrate any clear differences in avoidance for any of the three species (Table 3). This indicates that
detection and avoidance of the turbine by each species was likely more dependent on hydraulic cues
and/or noise. Hydrokinetic turbines are a physical obstruction in the flow path and create a back
pressure and acceleration of flow around them, both of which can be sensed by fish as they approach a
turbine. These hydraulic cues are probably the primary sensory stimuli detected by fish and which lead
to high avoidance rates.
4.1.3 Estimation of Encounter and Avoidance Probabilities for Energyfish
Based on the information provided above, encounter and avoidance probabilities were estimated for
the species of interest selected for the assessment of fish impacts associated with Energyfish
installations in Europe. A range of encounter probabilities were evaluated for each species, including
the proportion of the total river cross-section of the example installation (i.e., 4.15% for five Energyfish
units in the lead grouping) and two more conservative estimates (10 and 25% encounter probabilities).
Avoidance probabilities were assigned to each species using the data from EPRI (2014) (Table 4).
Rainbow trout data were used for stronger swimming species and hybrid striped bass data were used
for weaker swimmers. However, neither the trout or hybrid bass data are considered appropriate for
European Eel due to more extensive differences in size, morphology, and swimming mode.
Consequently, estimates of avoidance for eel were based on professional judgment, particularly the
knowledge that their size would result in higher avoidance rates due physical and behavioral exclusion
associated with the guidance rods and stronger swimming capabilities. The avoidance rates from EPRI
(2014) that were applied to each species of interest were adjusted by fish size and velocity (i.e.,
increased avoidance was assigned to larger fish and decreased avoidance was assigned to higher
velocities).

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Table 3. Avoidance rates estimated for three species of fish approaching an axial-flow hydrokinetic
turbine in a laboratory flume. Species codes are: RBT, rainbow trout (Oncorhyncus mykiss); WST,
white sturgeon (Acipenser transmontanus); and HSB, hybrid striped bass (Morone saxatilis x Morone
chrysops) [SOURCE: EPRI 2014]
Species
Fish
Length
(mm)
Approach
Velocity
(m/s)
Light
Condition
% of Fish
Recovered
Downstream
of Turbine
Estimate
of Number
Entrained
Turbine Avoidance
(%)
and 95%
Confidence
interval
RBT
170
1.1
Day
77.3
3
97.4 (97.3 - 97.5)
Night
96.0
3
98.2 (96.4 - 99.4)
1.5
Day
94.7
12
92.1 (74.4 - 99.8)
2.0
Day
99.3
21
86.1 (74.7 - 94.5)
RBT
250
1.1
Day
49.0
4
98.5 (85.8 - 100.0)
Night
95.0
5
98.1 (96.9 - 99.0)
1.5
Day
69.0
8
96.5 (86.9 - 100.0)
2.0
Day
99.7
14
95.4 (90.6 - 98.5)
WST
125
1.1
Day
98.6
6
92.1 (68.4 - 99.9)
Night
100.0
9
87.4 (80.0 - 93.3)
1.5
Day
100.0
9
87.9 (62.7 - 99.7)
2.0
Day
98.6
0
100.0 (--)
HSB
125
1.1
Day
97.3
59
59.3 (46.9 - 71.1)
Night
97.3
52
65.4 (57.1 - 73.2)
1.5
Day
97.3
95
32.6 (0.0 - 89.1)
2.0
Day
100.0
61
59.2 (23.6 - 90.1)

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Table 4. Estimated turbine avoidance rates for species of interest at Energyfish deployments based on
data from EPRI (2014).
Common Name
for Species of
Interest
Common
Length
(mm)
Surrogate Species
from EPRI (2014)
Estimated Avoidance Probability (%) by
Approach Velocity (m/s)
1.0
1.5
2.0
2.4
Stone Loach
120
hybrid bass
62
60
59
57
Common Dace
150
hybrid bass
65
63
61
59
Burbot
150
hybrid bass
65
63
61
59
Tench
200
hybrid bass
70
68
66
64
Common Nace
250
hybrid bass
75
73
71
69
European Perch
250
hybrid bass
75
73
71
69
European Chub
300
hybrid bass
100
99
97
95
Grayling
300
Rainbow Trout
100
99
97
95
Common Carp
310
hybrid bass
75
73
71
69
Northern Pike
400
Rainbow Trout
100
98
96
94
Rainbow Trout
600
Rainbow Trout
100
100
100
100
European Eel
350-1,000
--
100
95
90
85
Huchen
700
Rainbow Trout
100
100
100
100
Sea Trout
720
Rainbow Trout
100
100
100
100
4.2 Turbine Passage Survival
Survival of fish passing through an Energyfish turbine was estimated using a theoretical blade strike
probability model that includes a coefficient for strike mortality based on fish length, blade thickness,
and strike velocity (relative speed of fish to the leading edge of a blade). This model, described below,
was applied to all species except European eel. Lab and field studies conducted for conventional hydro
turbines have demonstrated that the blade strike probability and mortality model significantly
underestimates eel turbine survival estimates. Consequently, professional judgment was used to
develop turbine survival rates of eel based on knowledge from survival studies conducted with
conventional hydro turbines. Blade strike survival data developed from studies conducted with rainbow
trout (EPRI 2008, 2011c) were applied to the other species of concern. Field studies conducted at
conventional hydro projects (Franke et al. 1997) and a pilot-scale biological evaluation of the Alden
turbine (Cook et al. 2003) have demonstrated that turbine passage survival rates do not vary
considerably among teleost fishes.
4.2.1 Theoretical Blade Strike Probability and Mortality Model
The probability that a fish will be struck by a turbine blade is a function of the distance that blade
leading edges move, compared to the total distance between two consecutive leading edges, in the time
it takes a fish to be carried or swim past the arc of leading edge motion (Figure 5). Consequently, the
probability of strike is given by the following equation (Ploskey and Carlson 2004, Hecker and Allen
2005):

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ax
V
nNL
P60
cos

=
(1)
Where:
P = probability of strike (non-dimensional)
n = runner rpm
N = number of leading edges (blades)
L = fish length

= angle between absolute and axial (or radial) velocity vectors (degrees)
Vax = axial velocity
Note that cosθ = sinα, where α is the angle between the absolute inflow velocity and a tangent line to
the runner circumference (Figure 5). The parameter Lcosθ (or Lsinα) is the projected fish length in the
axial direction. The flow angle for axial-flow turbines is defined as the angle between the absolute
velocity and tangential velocity, α. The strike probability model presented above assumes that fish
orient along the absolute inflow direction.
For application of the strike probability model to hydrokinetic turbines, fish are assumed to orient with
their body length parallel to the ambient current, which is considered typical behavior when fish are
moving in fast currents. Rheotactic behavior (i.e., whether fish are oriented head or tail first relative to
flow direction) may vary, but observations at dams indicate fish will exhibit positive rheotaxis (head
facing upstream) when approaching objects or zones of rapidly increasing water velocities. Side to side
movement may occur in front of a turbine and fish may turn (to head facing downstream) as they pass
into a region of rapid flow acceleration. The assumption that fish are oriented parallel with the flow as
they pass through a HK turbine is a conservative one, because it takes more time for the total fish length
to pass between the moving blades and injury potential would likely be less if fish were angled less than
90 degrees to a turbine blade (EPRI 2011c).
Figure 5. Schematic of absolute inflow, axial velocity (or radial for Francis turbines), and relative
velocity of flow (and fish) to a blade leading edge. The parameter Δs is the incremental blade motion
in the time fish move through the leading edge circumference.

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The absolute velocity immediately upstream of the blade leading edges, Va, is equal to the ambient
water velocity. Vector addition of the absolute velocity and the (negative) blade leading edge speed
(which depends on the distance from the center of rotation) provides the relative velocity (speed and
direction) of the flow to the blade. The relative velocity is the speed at which the fish strike the leading
edge of the blade.
The blade speed at the radius of interest can be calculated from:
u = 2πrn/60 (2)
where:
u = blade speed (ft/s)
r = radius from center of rotation a point on the leading edge (ft)
n = rpm
The relative water-to-blade velocity (i.e., strike velocity, assuming fish travel at the same speed as the
approaching flow) is used with fish length-to-blade thickness ratios (L/t) to determine the strike
mortality coefficient, K, based on data from blade strike tests conducted with rainbow trout (EPRI 2008,
2011c). Since K represents the probability that fish struck by a turbine blade will be killed, Equation 1
(blade strike probability) is multiplied by K to estimate turbine passage survival (ST):
))((1 PKST−=
(3)
Other sources of mortality associated with the passage of fish through conventional turbines (e.g.,
damaging pressure changes, shear, and turbulence) are not expected to affect fish passing through
hydrokinetic turbines (EPRI 2011c).
4.2.2 Laboratory and Field Evaluations of Fish Interactions with Hydrokinetic Turbines
Survival of fish passing through three HK turbine designs was evaluated during a series of studies
conducted in a laboratory flume (EPRI 2011b, 2014; Amaral et al. 2014). Two of the turbines evaluated
were ducted axial-flow propeller turbines and one was a spherical-cross flow design. Test species
included rainbow trout, smallmouth bass, hybrid striped bass, and white sturgeon. Results from tests
conducted with the two axial-flow turbines and the three teleost species are relevant to the assessment
of survival of fish passing through the Energyfish turbine.
The two axial-flow turbines evaluated during the laboratory studies included a 4-bladed unit (Welka
UPG) and a 7-bladed design (Free Flow Power turbine). Both of these turbines were about 1.5 m in
diameter and had rotational speeds of about 65 and 85 rpm at test velocities of 1.5 and 2.1 m/s,
respectively. Two size groups of rainbow trout were tested with each turbine, as well as one size group
of hybrid striped bass tested with the Free Flow Power turbine and two size groups of smallmouth bass
with the Welka UPG. With the exception of the larger trout and hybrid bass tested at the lower velocity
with the Free Flow turbine, total turbine survival rates were greater than 99% (Table 5). The lower
survival observed for hybrid bass tested at an approach velocity of 1.5 m/s was considered an
experimental artifact and not related to turbine passage, particularly since survival of this species was
100% at the higher velocity.

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Table 5. Survival, injury, and descaling estimates for fish evaluated with the Welka UPG and Free Flow
Power ducted axial-flow turbines (EPRI 2011b, 2014). Survival rates greater than 100% indicate
control fish mortality was greater than it was for treatment (turbine-passed) fish.
Fish Species
Size Group
(mm)
Approach
Velocity
(m/s)
Rotational
Speed
(rpm)
Total
Survival (%)
± 95% CI
Injury Rate
(%)
Descaled
(%)
Welka UPG – 4 blades
rainbow trout
125
1.5
15
100.9 ± 1.4
0.4
4.3
2.1
35
101.6 ± 1.3
1.5
0.0
250
1.5
15
100.0 ± 0.0
1.3
0.0
2.1
35
99.4 ± 0.7
0.9
0.0
smallmouth bass
125
1.5
15
99.8 ± 0.9
1.4
0.0
2.1
35
102.9 ± 2.9
0.0
0.0
250
1.5
15
100.0 ± 0.6
0.0
0.2
2.1
35
99.6 ± 0.6
0.2
0.0
Free Flow Power – 7 blades
rainbow trout
175
1.5
64
100.0 ± 0.0
4.8
0.0
2.1
84
99.0 ± 1.1
11.8
0.0
250
1.5
64
100.0 ± 0.0
15.6
9.3
2.1
84
97.5 ± 1.4
27.1
22.1
hybrid striped bass
125
1.5
64
91.7 ± 5.1
14.7
0.0
2.1
84
100.5 ± 4.9
0.0
0.0
Injury rates were greater for fish tested with the Free Flow turbine than they were for those evaluated
with the Welka UPG, and descaling of larger trout was considerably higher for fish tested with the Free
Flow turbine (Table 5). Injury and descaling rates of trout tested with the Free flow turbine also
increased with velocity and fish size. These results are indicative of greater strike probability for larger
fish and for turbines with more blades and higher rotational speeds.
A field study that examined survival of fish passing through a hydrokinetic turbine was conducted in the
tailrace of conventional hydropower station with a ducted axial-flow unit with three blades (NAI 2009).
This turbine was evaluated with several species and life stages of fish. Total (48-hr) survival estimates
were 99% for yellow perch (118-235 mm in length), bluegill (115-208 mm), channel catfish (451-627
mm), and smallmouth and bigmouth buffalo (388-710 mm). The high survival rates estimated for this
turbine are likely the result of turbine design and operational features that lead to low strike

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probabilities (i.e., low rotational speed and only three blades) and minimal strike-related injury and
mortality (i.e., low strike velocity). The tip speed of this turbine was about 4 m/s with a rotational speed
of 21 rpm. Strike velocity would be higher than the tip speed, but for this particular design it probably
was about the same or less than the velocity at which strike mortality begins to occur (4.5 m/s,
depending on the ratio of fish length to blade leading edge thickness).
The results of the lab and field studies that investigated survival of fish passing through ducted axial-
flow turbines demonstrate that survival rates can be very high, even for turbines with a large number of
blades (7 for the Free Flow turbine) and for relatively large fish (up to 700 mm). However, higher
rotational speeds and more blades can lead to greater mortality, particularly for larger fish (> 200 mm in
length) mainly due to greater strike probabilities and higher strike mortality. Based on the lab and field
study results, most fish passing through an Energyfish turbine at lower approach velocities would be
expected to have very high survival rates, and the limitation on rotational rates of the Energyfish limits
an increase in mortality at higher flow velocities. The effects of the smaller diameter of the Energyfish
on fish survival are demonstrated by the theoretical analysis of blade strike probability and mortality for
an Energyfish in the following section.
4.2.3 Turbine Passage Survival Estimates for Fish Entrained through an Energyfish Turbine
Using the methods described in Section 4.2.1, turbine passage survival was estimated for each species of
interest. The theoretical model for blade strike probability and mortality was used to calculate survival
estimates for fish with lengths between 100 and 750 mm at four current velocities (1.0, 1.5, 2.0, and 2.4
m/s) covering the expected range of operation for Energyfish turbines. At the request of Energyminer,
the rotational speed was limited to a value at each flow velocity examined that would produce minimum
turbine passage survival rates of approximately 95%. This produced maximum rotational speeds of 130,
125, and 120 rpm at the three highest flow velocities (in increasing order from 1.5 to 2.4 m/s). Estimated
strike probability, strike mortality, and turbine passage survival rates for these fish lengths and approach
velocities are presented in Table 6. Strike mortality is 0% (i.e., 100% turbine passage survival) for all fish
sizes at the lowest current velocity (1 m/s) because the strike velocity is less than 5 m/s, which is the
speed below which no strike mortality is expected to occur (EPRI 2008, 2011c). Turbine passage survival
estimates ranged from 94.9 to 99.0% for the three higher flow velocities.

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Table 6. Estimated strike probability, strike mortality (probability of mortality if a fish is struck), and turbine passage survival rates for fish
passing through an Energyfish turbine at four approach velocities. Turbine survival is calculated by multiplying strike probability by strike
mortality and subtracting the product from one; results are multiplied by 100 to provide results as percentages. These survival rates only
apply to fish that pass through the guidance rods and the turbine blades, which is a very low proportion of all fish moving downstream in a
river. Rotational speeds of the turbine are 124, 130, 125, and 120 for flow approach velocities of 1.0, 1.5, 2.0, and 2.4, respectively.
Fish
Length
(mm)
Strike Probability (%) by Approach
Velocity (m/s)
Strike Mortality (%) by
Approach Velocity (m/s)
Turbine Survival (%) by Approach
Velocity (m/s) and RPM
1.0
1.5
2.0
2.4
1.0
1.5
2.0
2.4
1.0
1.5
2.0
2.4
100
61.6
43.3
31.2
25.0
0.0
3.2
3.2
3.3
100.0
98.6
99.0
99.2
150
92.5
65.0
46.9
37.5
0.0
3.6
3.6
3.7
100.0
97.6
98.3
98.6
200
100.0
86.7
62.5
50.0
0.0
4.0
3.9
4.0
100.0
96.6
97.5
98.0
250
100.0
100.0
78.1
62.5
0.0
4.2
4.2
4.3
100.0
95.8
96.7
97.3
300
100.0
100.0
93.7
75.0
0.0
4.4
4.4
4.5
100.0
95.6
95.9
96.6
350
100.0
100.0
100.0
87.5
0.0
4.6
4.6
4.7
100.0
95.4
95.4
95.9
400
100.0
100.0
100.0
100.0
0.0
4.7
4.7
4.8
100.0
95.3
95.3
95.2
450
100.0
100.0
100.0
100.0
0.0
4.9
4.8
4.9
100.0
95.1
95.2
95.1
500
100.0
100.0
100.0
100.0
0.0
5.0
4.9
5.1
100.0
95.0
95.1
94.9
550
100.0
100.0
100.0
100.0
0.0
5.1
5.1
5.2
100.0
94.9
94.9
94.8

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4.3 Total Passage Survival
Total passage survival or fish approaching a section of a river with a hydrokinetic turbine is an estimation
of the proportion of all fish moving downstream that pass the turbine(s) alive. Estimates of total
passage survival include encounter and avoidance probabilities and turbine passage survival rates for
entrained fish. Encounter probabilities are estimates of the proportion of fish moving downstream that
approach a turbine and which either avoid passage through the blade sweep or are entrained through it.
Avoidance probabilities are estimates of a fish’s ability to avoid entrainment when they are in the flow
approaching the blade swept area. Turbine passage survival is the proportion of fish entrained that are
expected to survive passage through the blade swept area and, with the exception of eel, was calculated
using the methods described in Section 4.2.1 (the resulting survival estimates are presented in Table 6).
Turbine survival estimates for eel are based on professional judgment and survival rates reported for
conventional hydro turbines. Using these inputs, the following equation was used to estimate total
passage survival (TS):
)]1)(1([1 SAETS−−−=
(4)
Where E is encounter probability, A is avoidance probability, and S is turbine survival. Total survival for
a deployment array with 20 groupings of five turbines (see Figure 2), can be calculated as TS20. However,
this should be considered an overly conservative estimate of total survival for fish passing all 20 turbine
groups because a large proportion of fish that avoid passage through a turbine in the lead group will
move downstream outside of the area of the successive 19 turbine groups as they continue
downstream.
Estimates of total passage survival rates for the flow velocity range of an Energyfish turbine array of five
paired units are presented for three encounter probabilities in Table 7 through Table 9. The lowest
encounter probability assessed was 4.15%, which is the proportion of the river cross-section covered by
the blade swept area the five units deployed in the lead array of turbines on the Lech River. Encounter
probabilities of 10 and 25% were also evaluated as conservative values that represent situations where
some species may occur in higher densities at the location of the example array due to diel, seasonal, or
life-stage dependent habitat preferences (e.g., the turbine location may be at a depth and/or in a
velocity zone that is utilized by one or more species as a migratory pathway).
For all three encounter probabilities evaluated for the example location on the Lech River, total survival
of fish passing through the lead group of five units is 100% for all species and size groups at the lowest
current velocity (1 m/s) regardless of encounter probability. This is due to strike velocities (i.e., relative
velocity of fish to blade) at this flow velocity being less than the value at which mortality begins to occur
for fish struck by a blade (about 5 m/s). At flow velocities greater than 1 m/s, total survival is greater
than 99% for all three encounter probabilities, mainly due to minimum turbine survival rates of about
95% for the few fish that would pass through the rotors (Table 7 - Table 9). At all flow velocities, larger
fish (600 mm and greater), are expected to have 100% total survival because the guidance rods will
physically exclude them from passing through a turbine’s rotor.

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Table 7. Estimated total passage survival rates for the species of interest passing a single group of five Energyfish units with an encounter
probability of 4.15%. Fish with lengths of 600 mm or greater (with the exception of European Eel) are expected to be physically excluded from
turbine passage by the angled guidance rods.

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Table 8. Estimated total passage survival rates for the species of interest passing a single group of five Energyfish units with an encounter
probability of 10%. Fish with lengths of 600 mm or greater (with the exception of European Eel) are expected to be physically excluded from
turbine passage by the angled guidance rods.

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Table 9. Estimated total passage survival rates for the species of interest passing a single group of five Energyfish units with an encounter
probability of 25%. Fish with lengths of 600 mm or greater (with the exception of European Eel) are expected to be physically excluded from
turbine passage by the angled guidance rods.

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At the three higher flow velocities, total passage survival decreases slightly when calculated for fish
passing downstream of all 20 turbine groups in a deployment array at the Lech River location depending
on fish species and size and flow velocity. However, these estimates are based on a worst-case scenario
for which encounter probabilities are assumed to be the same for each of the 20 groups of five
Energyfish units. It is likely that encounter probabilities will decrease for each successive turbine group
due to fish that have avoided passage through an upstream unit continuing downstream outside of the
area occupied by downstream units.

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5.0 Summary and Conclusions
The following are the primary conclusions from the assessment of potential impacts to fish associated
with Energyfish installations:
- The area covered by a five-unit turbine group relative to the area of a river’s cross section will
lead to low encounter rates for most fish species. In particular, if Energyfish units are located
away from shore and near the surface in fast flowing reaches, some species may never
encounter a unit due to preferences for deeper water, lower velocities, or nearshore areas.
- The probability that fish moving downstream in a river will encounter an Energyfish turbine will
generally be low (< 5%) and will depend on the location of the turbines and the size of their
footprint relative to the cross-sectional area of the river. For the few fish that may encounter an
Energyfish turbine deployed in a group of five units, avoidance of entrainment through turbine
rotors is likely to be moderate (50 to 75%) or high (>75%) for many species. Based on
observations from flume studies, the highest avoidance rates (> 90%) will occur for larger fish
and species with strong swimming capabilities (e.g., salmonids).
- When encounter and avoidance probabilities are combined, the estimated entrainment rate
through turbine rotors for a group of five units is only about 2.5% or less of fish passing
downstream.
- Turbine survival rates for the few fish that will pass through a turbine will vary with fish length
and approach velocity. Larger fish and higher velocities typically result in greater turbine
mortality rates. However, Energyminer has indicated the Energyfish units will be limited to
rotational speeds at each flow velocity that produce a minimum turbine passage survival rate of
approximately 95%. Turbine survival was estimated to be 100% for all fish, regardless of length,
when the units are operating at a flow velocity of 1 m/s or less and will be about 95% and
greater at higher velocities.
- Total passage survival estimates (which combine encounter, avoidance, and turbine survival
probabilities) for a single group of five paired Energyfish units will be very high for all species
and size groups (99.4 to 100%, depending on encounter probabilities and fish species and size).
- Total passage survival for fish passing downstream through a deployment array of 20 groups of
five Energyfish units, as designed for the Lech River, are above 99% for the flow velocities
evaluated. Additionally, it is likely that a large proportion of fish encountering the lead group or
subsequent groups will continue downstream outside of the area occupied by the turbine array,
which will result in even lower encounter probabilities for each successive turbine group.
There is growing evidence from lab and field studies that suggest encounter probabilities will be low,
avoidance rates will be high, and turbine survival will be high for most fish species and life stages that
pass downstream at sites where hydrokinetic turbines are installed. Very low encounter probabilities
and high avoidance rates, as well as behavioral and physical exclusion associated with the guidance rods,
will contribute to high total passage survival rates for fish passing downstream at the location of multi-
unit Energyfish deployments. Additionally, limiting rotational speeds to a value that produces minimum
turbine passage survival rates will ensure very high total passage at all flow velocities regardless of the

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number of arrays deployed at any given location. This was evident in the case study using the
demonstration site where total passage survival for the Energyfish school were over 99%.

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6.0 Literature Cited
Amaral, S. V., M. S. Bevelhimer, G. F. Cada, D. J. Giza, P. T. Jacobson, B. J. McMahon, and B. M. Pracheil.
2015. Evaluation of Behavior and Survival of Fish Exposed to an Axial-Flow Hydrokinetic Turbine. North
American Journal of Fisheries Management, 35:97-113.
Amaral, S. V., B. S. Coleman, J. L. Rackovan, K. Withers, and B. Mater. 2018. Survival of Fish Passing
Downstream at a Small Hydropower Facility. Marine and Freshwater Research 69:1870-1881.
Amaral, S. V., S. M. Watson, A. D. Schneider, J. Rackovan, and A. Baumgartner. 2020. Improving Fish
Survival: Injury and Mortality of Fish Struck by Blades with Slanted, Blunt Leading Edges. Journal of
Ecohydraulics 5(2):175-183.
Cook, T. C., G. E. Hecker, S. V. Amaral, P. S. Stacy, F. Lin, E. P. Taft. 2003. Final Report – Pilot Scale Tests,
Alden/Concepts NREC Turbine. Prepared for the U.S. Department of Energy, Advanced Hydropower
Turbine Systems Program.
EPRI (Electric Power Research Institute). 2008. Evaluation of the effects of turbine blade leading edge
design on fish survival. Prepared by Alden Research Laboratory, Inc., EPRI Report No. 1014937.
EPRI (Electric Power Research Institute). 2011a. Fish Passage through Turbines: Application of
Conventional Hydropower Data to Hydrokinetic Technologies. Prepared by Alden Research Laboratory,
Inc., EPRI Report No. 1024648.
EPRI (Electric Power Research Institute). 2011b. Evaluation of Fish Injury and Mortality Associated with
Hydrokinetic Turbines. Prepared by Alden Research Laboratory, Inc., EPRI Report No. 1024569.
EPRI (Electric Power Research Institute). 2011c. Additional Tests Examining Survival of Fish Struck by
Turbine Blades. Prepared by Alden Research Laboratory, Inc., EPRI Report No. 1024648.
EPRI (Electric Power Research Institute). 2014. Evaluation of Survival and Behavior of Fish Exposed to
an Axial-Flow Hydrokinetic Turbine. Prepared by Alden Research Laboratory, Inc., EPRI Report No.
3002003911.
Franke, G. F., D. R. Webb, R. K. Fisher, D. Mathur, P. N. Hopping, P. A. March, M. R. Headrick, I. T. Laczo,
Y. Ventikos, and F. Sotiropoulis. 1997. Development of Environmentally Advanced Hydropower Turbine
System Concepts. Prepared for the U.S. Department of Energy, Voith Hydro, Inc. Report No. 2677-0141.
Hecker, G. E., and G. S. Allen. 2005. An Approach to Predicting Fish Survival for Advanced Technology
Turbines. Hydro Review, November 2005, HCI Publications, Inc., St. Louis, Missouri.
Hogan, T. W., G. F. Cada, and S. V. Amaral. 2014. The Status of Environmentally Enhanced Hydropower
Turbines. Fisheries 39(4):164-172).
Ploskey, G. R., and T. J. Carlson. 2004. Comparison of Blade Strike Modeling Results with Empirical Data.
Pacific Northwest National Laboratory, Report No. PNNL-14603.
NAI (Normandeau Associates, Inc.). 2009. An Estimation of Survival and Injury of Fish Passed through
the Hydro Green Energy Hydrokinetic System, and a Characterization of Fish Entrainment Potential at

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the Mississippi Lock and Dam No. 2 Hydroelectric Project (P-4306), Hastings, Minnesota. Prepared for
Hydro Green Energy LLC, Houston, Texas.