ABSTRACT
This study aims at investigating possible colmation effects of the river bed of a residual flow reach of the river Brixentaler Ache in Austria. Therefore, three sites within the residual flow reach are investigated and compared to three sites that are located up- and downstream of the residual flow reach. In order to investigate the current state of the river bed with respect to colmation, three methods are applied and combined in this study, namely: substrate mapping, sediment sampling and dissolved oxygen measurements in the hyporheic zone. The results from the substrate mapping show almost no colmation within the main stream, neither in the residual flow stretch nor in the reference stretches. Only close to the river banks outer colmation areas are mapped along the river stretches. In addition, the sediment analyses confirm the visual observations. Although, a high degree of fine sediments within the river bed could be measured in both residual and reference reaches almost no cohesive material is found. Hence, the obtained data show no evidence of negative effects on the river substrate quality due to the water diversion has negative effects at the the Brixentaler Ache. This is also proved by the measurements of the dissolved oxygen in the hyporheic zone.
