Author(s): Michael Hengl; Mariela Langle
Linked Author(s): Michael Hengl
Keywords: No Keywords
Abstract: For the design of bed stabilization measures physical models are still an indispensable tool. A straight flume model with vertical walls (mostly a tilting flume) is usually used for almost straight river reaches to keep the costs low. As part of one specific project it was established, that a simplified model in a straight flume resulted in higher bed stability then the real one in a full scale model. For the river Bregenzerach a so called rip rap was tested in a straight flume. This rip rap consisted of coarse stones which were extracted from an artificial bed incision of a flood protection work. The aim of the rip rap is to prevent bed degradation along the 1. 3% steep passage from the unchanged bed upstream to the incised bed downstream. The same bed stabilization measure was also tested in a full scale model, but it has been less stable. The essential differences between the two models were the transition from the rip rap to the river bed upstream and downstream, short groins for ecological and morphological river design and slightly changing bed widths. All inhomogenities of the river led to higher local stresses. This situation has resulted in an earlier movement of the rip rap. Thereby local channels were formed, which finally led to complete destruction of the bed stabilization. In conclusion at least the final implementation proposal for a bed stabilization measure should be tested in a full scale model. For an engineer it is important to be careful in using design equations developed in a straight flume if the real situation is different.