Nomograms for calculating the funcionality of technical fish passes on small sills

Sa？etak The construction of biological passes (usually fish passes in engineering practice) reduces, to a certain degree, negative ecological impacts of economic development and enables the achievement of longitudinal watercourse connectivity that is vital for meeting migratory needs of water organisms. Technical fish passes are one of the most used types of fish passes for upstream fish migration. The goal of the paper was to derive nomograms for implementing direct calculations of functionality in the technical fish pass design procedure. Considering fish species in the area of the Republic of Croatia, the paper analysed two types: basin fish passes and fish passes with vertical openings. The most important parameters for technical fish pass functionality are water depth, critical flow velocity, ensuring minimum flow and volumetric energy dissipation within defined limits. For investigation purposes, a physical model in the lab and a numerical model in OpenFOAM were developed. Based on the conducted investigation, basic recommendations for designing fish pass geometry in hydraulic conditions determined by fish species in the area of the Republic of Croatia were defined