The Inn river, with a length of 217 km in Bavaria, is the river with the highest discharge in Bavaria and at the same time the largest northern alpine tributary of the Danube. It is characterized by a high discharge in summer, low water temperatures as well as high bed load and suspended sediment transport. The Inn river can be classified as typical Alpine river due to its high flow velocities.
In 1924, the VERBUND-Innkraftwerke GmbH built the Jettenbach weir and the Innwerk channel together with the Töging power plant for the generation of hydroelectricity. As a result of the construction work, the residual flow stretch shows considerable water management and ecological deficits due to a lack of bedload supply and a reduced discharge in middle and low flow periods.
The VERBUND-Innkraftwerke GmbH plans to expand the Jettenbach/Töging power plant in the upcoming years, with the aim of increasing the efficiency of the power plant. For this purpose, the amount of extracted water for hydropower utilization will be increased from 340 m³/s to 410 m³/s. Even if a seasonally staggered residual water discharge (35 - 50 m³/s) is released into the residual flow stretch, the higher water withdrawal will have an effect on the characteristics of the discharge hydrograph.
Within the study " Development of a holistic and sustainable sediment management concept to improve the hydromorphological situation of the residual water stretch Jettenbach – Töging at the River Inn", the Department of Hydraulic Engineering and Water Resources Management will determine to what extent the formation of small structures and an ecologically oriented bedload and flushing concept can improve the substrate quality and thus the habitat suitability for gravel spawning fish species in a sustainable manner. These measures shall finally result in a good ecological status in accordance with the EU WFD. In a first step, the current situation and status of the residual water stretch will be evaluated. The focus will be set on a detailed investigation of sediment properties of existing gravel banks. It will further be examined to what extent the combination of ecological flushing and active sediment management represents a suitable management strategy to improve the residual water stretch with regard to its morphological condition.
The work packages include a comprehensive field study as well as hydromorphodynamic modelling to analyze and evaluate the current status and the planned measures. In cooperation with the Karlsruhe University of Applied Sciences in-depth investigations and habitat suitability modelling will in addition be carried out. This will be followed by the planning, modelling and implementation of an in-situ ecological flushing experiment in combination with active bedload management in accordance to the local flood protection. Within the framework of the study, a holistic package of measures and monitoring strategies will be developed to achieve sustainable good ecological conditions.
Karlsruhe University of Applied Sciences