DENIL II - Adaptation Denilpass

The Denil fish pass is a technical fish migration aid with a long tradition. Its original form was built as early as the beginning of the 20th century and has already achieved demonstrable results with regard to the migration of commercial fish species. In the course of time, the fish pass has been modified several times, especially with regard to the lamella geometry and the resulting flow hydraulics, so that a number of building types from the original form have been manifested, which enjoy a wide distribution in the most diverse countries of the world. The main focus of this construction variant remained commercial fish species (salmonids and herring), where good ascent rates were demonstrated at numerous power plant locations. However, this construction type is viewed critically for the passability of small fish species and young fish stages. The reason for the restriction regarding these fish species or stages is usually attributed to the high turbulence and the lack of bottom substrate. Many species have a pronounced bed reference in their ascent behaviour and are therefore more or less strongly bound to the arrangement of a natural river bed.   Since 2016, Graz has been working on a modification of the system. The new open-soil Denilpass is intended to improve the passability of small bottom-oriented fish species in particular. The adapted Denilpass was hydraulically tested in a model test at the Technical University of Graz and, based on this, the first natural systems were built. For example, a pilot plant was set up in the trout region and subjected to biological and abiotic monitoring. Based on the positive results of these functional checks, the fish ladder is now to be further developed and optimised.