Experimental and numerical analyses on the capacity and the control management of a large flood retention basin situated at the Inn River in Tyrol

Abstract

The consideration of recent extreme events in flood statistics implies an increase of design flood peaks and discharge loads. With the focus on the 75 km long Tyrolean Inn River reach downstream the regional capital city Innsbruck, the harmonization of the 100-year flood peak and comprehensive 2d-hydrodynamic modelling simulations indicate the need for an extension of the existing flood protection measures. Lateral protection and object protection measures represent the only feasible option due to the confined areal conditions. However, an increase of the channel capacities would worsen the situation for downstream areas demonstrably. In order to counter this impact, it is planned to build several large controlled flood retention basins situated along the Inn River at the valley floor between Innsbruck and the border to Germany. The retention basin “Voldöpp” as one of these flood polders features a maximum capacity of 1.7 million m³ and a maximum design water depth of 3.6 m. According to current planning the inlet structure consists of four uniform weir fields with two gates each. Aims of the presented experimental and numerical analyses are the investigation of the flow characteristics in close range of the inlet structure, the weir capacity and a possible weir control management. Hydraulic model tests are accomplished at the scale 1:35 according Froude similarity and numerical modelling is done with the software FLOW-3D. Preliminary modelling results confirmed the functionality of the inlet structure and pointed out the need of further tests concerning the potential impacts of intense sediment transport and woody debris.