Abstract
The present case study deals with a controlled drawdown beyond the operational level of the Gepatsch reservoir (Austria). Based on the awareness of potential ecological consequences, an advanced set of measures was conducted and an integrative monitoring design was implemented. This pre- and post-event monitoring included measurements regarding the cross sectional variability and habitat-related turbidity, freeze-core sampling to obtain knowledge on fine sediment infiltration and an evaluation of the macroinvertebrate communities as well as fish egg development (salmonid incubation). The results of the sedimentological as well as biological investigations show a negligible impact on the downstream located aquatic system due to the controlled drawdown of the Gepatsch reservoir. In addition, recommendations based on the findings from this study regarding possible methods for local scale monitoring can be given.
Highlights
The construction of hydropower plants and their operation affects the aquatic ecology on various scales [1]
The continuous recording of the suspended sediment concentration (SSC) was based on single point measurements in the selected cross sections and close to the river bank
Local-scale abiotic and biotic elements were evaluated concerning their quality for environmental assessment related to the drawdown of the Gepatsch reservoir
Summary
The construction of hydropower plants and their operation affects the aquatic ecology on various scales [1]. Sediment management actions in terms of preserving storage volume of reservoirs (e.g., mainly for energy production) were studied, which may result in additional negative impacts on aquatic organisms, like reduced macroinvertebrate communities [7], hypoxia of fish [8] and mechanical damage of fish. Water 2020, 12, 1055; doi:10.3390/w12041055 www.mdpi.com/journal/water (like gills) [9]. All these mentioned impacts happen during a limited period. In contrast to reach scale assessment (compare to [10]), local scale studies in terms of sediment management for controlled drawdowns or reservoir flushings were more frequently applied [7]. The increased fine sediment loads, which may follow controlled reservoir drawdowns or reservoir flushing, were investigated on a local scale; e.g., [9]
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