FIELD STUDY ON THE FLOOD FLOW AT THE CONJUNCTION OF COMPOUND CHANNELS —THE CASE OF THE CONJUNCTION OF THE TONE RIVER AND THE WATARASE RIVER—

Abstract

 The design of the confluence is one of the most difficult aspects of the implementation of a compound channel because the streamlines during high water may deviate from the banks of the low-water channel depending on the inflow conditions. This paper reports a field study on flood flow at the confluence of the Tone River and Watarase River. Stereo image analysis of the aerial photographs taken at a flood peak in 1981 revealed the flow divergence and convergence across the low-water channel banks as well as flow stagnation around the tree communities in the high-water channel. A quasi-3D shallow water model with unstructured triangular mesh system was used to simulate the flow field. The drag force of the tree communities was also taken into consideration based on the results of a field survey. The simulation fairly well reproduced the surface flow field obtained by the image analysis. The calculated difference between the streamlines at the surface and the bottom of the water suggested that large dispersive stress in the flow near the low-water channel banks, especially around the tree communities.