FISH DAMAGE AND FISH PROTECTION AT HYDRO POWER PLANTS EXPERIMENTAL INVESTIGATION OF SMALL FISH UNDER LABORATORY CONDITIONS

摘要

With increasing ecological awareness and consequential legislation fish downstream migration and thus fish protection are becoming an essential but relatively unresolved aspect for the implementation and continuance of hydro power usage. The most common approach to prevent fish from passing through a turbine and being subjected to the joint mortality rates is a mechanical barrier, i.e. a screen. An adapted approach velocity and downstream passage bypass are required furthermore. The mechanical barrier does in principle only account for relatively large fish and there remains a lack of knowledge concerning small individuals. Fish downstream passage of fish smaller than the bar clearance was investigated at a TUM-Hydro Shaft Power Plant prototype facility under nature like but controlled laboratory conditions to elucidate fish protection and fish downstream passage for small fish and weak swimmers which can physically pass through the screen and may subsequently be damaged in the turbine. In a large scale open air laboratory channel of the Technical University of Munich a fully functional 35 kW hydro power plant was installed, featuring a horizontal screen with 20 mm bar clearance. The test setup was sealed against the surrounding river system with 4 mm aperture fish barriers. Fish ensembles with body length from 5 cm to 20 cm were introduced in the head water. The fish movement at the hydro power plant, the migration movements and possible injury to the fish were recorded during the 24 h test periods. Subsequently all fish were extracted and observed for 96 h to account for possible long term damage. About 2000 brown trout, grayling, barbel, bullhead and minnow were investigated for three different approach velocities at the screen respectively turbine discharges and two different downstream migration bypass configurations. The detailed records of the test series include fish species, fish length, passage path, observed injury, turbine discharge and bypass arrangement for each individual. The statistical analysis of the data revealed species and size dependent characteristics of fish downstream passage and mortality rates. The screen did effectively serve as behavioral barriers for partitions of the small fish and the extent of the partition was influenced by the facility design. The partition of fish which passed through the screen and the turbine was subjected to turbine specific injury and mortality rates. Opposing trends with regard to screen passage/turbine passage and mortality rates entail relatively homogeneous mortality rates for different fish sizes, species and service conditions. The study enables in principle the targeted design of hydro power facilities at specific river sites in order to meet the required ecological obligations at best economic efficiency.