Author(s): H. M. Habersack
Linked Author(s):
Keywords: River morphology; Hydraulic engineering; Numerical modeling
Abstract: The aim of this paper is to analyse the possibilities and restricitions of 1-D and 2-D hydraulic models applied to natural river sections with highly variable morphological features, used as reference sites for restoration measures. During a field study at the Lafnitz, an Austrian lowland, meandering river, data concerning morphology were sampled (repeated cross section measurements at 10 m intervalls), water level measurements at two gauging stations, 2-D and 3-D flow velocity measurements at various discharges and sieving analysis for the determination of grain size distributions of surface and subsurface material were performed. The 1-D hydraulic model could not simulate the real data sufficiently. Especially in the morphologically very dynamic part of the meander this model type is restricted. Using a 2-D finite element hydraulic model the unsteady behavior of the water level development and the measured 2-D flow velocity distribution could be simulated with high accuracy. It turned out that the roughness values and especially the eddy viscosity parameter have to be optimized for the model calibration. Flow velocity vectors at several individual points in cross sections gave a set of verification data. For the depth averaged flow velocity a satisfying result was achieved, although near bottom vectors deviated due to structural influences. The comparison between simulated and measured flow veloctiy vectors gave satisfying results. The detailled analysis of the influence of local morphological structures like islands, vegetation, pools demonstrated the restrictions of 2-D models for such applications. It is shown that especially for environmentally oriented studies at least 2-D models are necessary in order to verify the nature sufficiently.
Year: 1999