Water provides an important living environment for many creatures. Every intrusion poses a threat to what are often very fragile ecological systems.
As every usage of open waters automatically interferes with existing aquatic life-forms, many projects cannot be approved, or, in the case of existing plants, authorizations may not be extended. Regulatory problems can only be avoided if applicants can prove that the best available techniques are being used to minimize the effects on the fish population, as well as meeting other environmental requirements.
As a provider of machines and equipment in the area of water intake, UBOW has been dealing with the development of effective fish protection solutions for many years. As might be expected, there is no perfect fish protection solution.
Each usage case has to be carefully considered, as effective fish protection is only possible using an intelligent combination of individual measures, tailor-made to meet local requirements.
Mechanical barriers reliably prevent fish from swimming into structures (using passive mechanical barriers such as static screens) or collect fish as they are swimming in and gently return them back to the water of origin (using active mechanical barriers such as moving screens). As long as these barriers are set up correctly, loss of fish can be almost completely avoided no matter what type and size of fish involved. However, mechanical barriers are usually more complex than behavioural barriers and often also require construction measures at existing water intake plants.
Mechanical barriers such as mesh screens are installed in the transition area between natural waters and the water use area to reduce ingress of aquatic life and water impurities. There are several kinds of screens, including passive screens with no moving parts cleaned with jets of air or water, or active screens with rotating filter elements arranged in a water wheel-type configuration that are cleaned by a fixed spray-wash system.
Screens are often arranged in two or three stages to perform two contrary functions. On one hand filters prevent ingress of the smallest aquatic life; for example, a hole diameter of less than 5mm is required for adult lampreys, and a hole diameter of around 2mm is required to protect young fish. On the other hand, multiple stages allow a way for fish that penetrate an outer barrier to return safely to the water source. The arrangement and design of the first cleaning step, which is for removal of coarse matter, must allow enough space for larvae and small fish that have passed the fish repelling zone. A special control system with defined stop positions and a slow ascent of the cleaner carriage allow fish to pass the coarse screen.
Special machines enable efficient return systems for fish, fish spawn and other important organisms which are already located in the intake duct. Fish return systems in screening plants are based on the use of bucket systems to remove fish and other organisms from the screens. The different systems mainly vary in the different ways that the fish buckets are emptied. These screen systems can be retrofitted into existing screening plants as a secondary (fine) screen.