The runoff and sediment balance of the Upper Isar – the last large wild river landscape in Bavaria – has been considerably disturbed since 1924, especially by the transfer of Isar water at the Krüner weir to Walchensee. The associated impairment of river and floodplain dynamic processes endangers above all the occurrence and conservation status of the FFH river habitat types 3220 "Alpine rivers with herbaceous riparian vegetation", 3230 "Alpine rivers with riparian shrubs of Myricaria germanica", 3240 "Alpine rivers with riparian shrubs of Salix eleagnos". Measures to revitalise the economy carried out so far have only affected individual smaller areas with a local and temporary effect. In addition, complex sediment management measures are regularly required in the Wallgau/Krün area to ensure flood and drinking water protection, which are currently being implemented by the Weilheim Water Management Office. In 2030, the Walchensee transition system will be reassigned. On this occasion and against the background of the above-mentioned situation, the river morphological boundary conditions or nature conservation requirements for the future operation must be developed. Especially at the Krüner weir, where the Isar water is diverted to the Walchensee, new possibilities for action arise in the course of the new decision.

With a numerical sediment transport model, possibilities for improving the sediment balance are now to be investigated. This is intended to contribute to answering the question of how the Isar can be managed sustainably in the long term while at the same time forming and maintaining the above-mentioned, typical river habitat types or a branched channel.

A description has already been given under II.1.4