Assessment of Hydropeaking Impact on Macrozoobenthos Using Habitat Modelling Approach

Abstract

The effects of daily discharge variation as a result of hydropeaking on the macrozoobenthos species of Litzauer Schleife, one of the last few free-flowing reaches of the River Lech in Germany, are assessed using habitat modelling approach. Integrated distributions of habitat quality within a river reach under two typical hydropeaking regimes with the range of the base to peak discharges of 10 m³/s to 155 m³/s and 25 m³/s to 135 m³/s respectively are  compared to the habitat quality distribution at the reference constant discharge of 30 m³/s. Habitat quality is assessed using the so called Fliesswasserstammtisch (FST) preference curves for the selected macrozoobenthos species Baetis alpinus, Baetis rhodani, Rhithrogena semicolorata, Allogamus auricollis, and Hydropsyche incognita. Hydropeaking causes a pronounced reduction in suitable habitats compared to the situation at a constant flow. While large areas of suitable habitats can still be found for the species B. rhodani, R. semicolorata, and H. incognita at the tested flow regimes, very less areas remain suitable for B. alpinus and A. auricollis. All target species react sensitive to flows below the reference discharge while only B. rhodani, R. semicolorata, and H. incognita show tolerance to high flows. Modelling results show that riffle areas offer more sustainable habitat during the whole range of hydropeaking discharges as pool areas for macrozoobenthos species. Among the target species, R. semicolarata is the most tolerant to changes in hydraulic conditions while A. auricollis is the least. From the analysis of habitat modeling results a hydropeaking regime with the base flow of 30 m³/s and a peak flow of 70 m³/s is suggested to be acceptable for the selected macrozoobenthos species of Litzauer Schleife.

Keywords: hydropeaking, FST hemisphere number, preference function, habitat modelling, macrozoobenthos