Screw pumps are utilised to draining low laying areas, such as the polders of Northwest Europe. A screw pump consists of a long worm wheel that is placed in a diagonal pipe or through, and creates upward displacement of water when driven. These pumps, also called Archimedian screws, have been in use for many centuries as applications are found in irrigation and draining purposes.
In conventional screw pump the first winding scoops water from the polder that is lifted to the downstream waters by the subsequent windings. Migrating fishes have the possibility to pass through the displaced water to find their way out of the polder, but approximately 15% of all fish that utilise this transport route suffer some kind of damage while passing the screw pump. The premium cause for damage is that a number of fish is hit by the first winding when it hits the water. A secondary cause is that fishes get stuck between the screw and the wall of the pipe in which the screw is placed.
Adjustments to the design of conventional screw pumps have resulted in a design that does not inflict any damage on passing fish. In the FishFlow screw pump the blades do not stretch across the full width up to the tip of the screw, instead the width of the blades gradually decreases from the middle outwards during the last few windings. The second adaptation concerns the housing of the screw. In the FishFlow screw pump, the screw is provided with tight plating that rotates together with the screw within the pipe or through.
The adaptations make damage to passing fish through hits of the first winding and damage following entrapment impossible and make the screw pump into a fish friendly facility for downstream migration.
Characteristics of the fish friendly screw pump are:
- fish friendly
- higher yield than conventional screw pumps
- existent screw pumps can be altered to fish-friendly screw pumps