Fish lifts, screws, locks, and others

Introduction

Figure 1: Nature-like fishway in the River Günz, Germany (photo: Atle Harby).

Locks for fish have, in principle, the same function as locks for ships, whereas lifts for fish resemble regular lifts in houses. Both methods require technically bulky constructions. They are both costly and operationally demanding but use relatively little water. The lift solution has been used especially at high altitude differences and little available construction area. In the locks, migrant fish is led into a chamber, then the entrance closes and the water level increases until it is on the same level as the above barrier. Then an outlet opens up and the fish can swim out. In lifts, fish are led and caught in pools that are then raised and emptied into the water above the barrier. Fish pumps have also been used to transport fish. The solutions are often selective since one and the same capture device rarely works for all occurring species and age classes. In addition, the plant itself has a deterrent effect on some fish. In England, Germany and France, the functionalities of such plants have been considered as low, as only a small proportion of the fish found their way into the pump (Armstrong et al 2010). We know there is only one such example in Norway; a sluice called "fishing lift" in the Vegård river. Salmon has migrated through this system, but the effectiveness is considered uncertain and smaller than expected.

Archimedes screws turbines (AST) and propeller pumps are additional solutions for upstream transportations fish. Studies from Belgium show that mortality rates are high for all fish species studied. Archimedes screws are less harmful to fish populations than propeller pumps, however in contrast with what is often thought, they do cause significant fish mortality (Buysse et al. 2015). Other studies suggest that ASTs can be less harmful and effective at low head dams (< 5 m)

Methods, tools, and devices

During planning

Planning of fish lifts, screws and locks are strongly dependent on the product and technical solution and screws is a turbine itself, making it a part of the powerplant. The specific site also plays an important role since, for instance, locks might be part of an existing navigation system. Specific attention must be paid on fish behaviour and how to guide fish into lift, screw or lock. Pre-studies with radio or acoustic telemetry might be required and planning will need to cover mapping of the hydropower plant and surrounding river reaches and banks.

During implementation

The implementation of a fish lift, screw or lock solution must be conducted in close collaboration with manufacturer and by use of fish migration experts on both biology and engineering.

During operation

The maintenance and monitoring of a fish lift, screw or lock solution must be conducted in close collaboration with manufacturer and by use of fish migration experts on both biology and engineering.

Classification table

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Classification	Selection (multiple)
Fish species measure designed for	All (in principle)
Does the measure require loss of power production?	Structural (requires no additional flow release)
Recurrence of maintenance	Irregular at events
Which life-stage of fish is measure aimed at?	Upstream movement and migration
Which physical parameter mitigated?	All
Hydropower type the measure is suitable for	All
Dam height [m] the measure is suitable for	Screws and pumps: 0-10 meters Lifts: All heights.
Section in the regulated system measure is designed for	Bypass section
River type implemented	All
Level of certainty in effect	Very uncertain
Technology readiness level	TRL 7	system prototype demonstration in operational environment