Author(s): Breac Macleod; And Alan Ervine
Linked Author(s):
Keywords: Compound channel; Expansion; Contraction; Head loss; Flood plain
Abstract: To date the majority of the commercially popular 1D river models which are used in the UK (such as HEC-RAS and ISIS) have only incorporated divided channel friction methods to determine the basic discharge capacity in compound channels at adjacent cross-sections. The authors suggest that future generations of 1D models should include provisions to explicitly determine the influence of layer interaction head losses (such as expansion and contraction) on discharge capacity in order to reduce the need to arbitrarily adjust basic friction factors when calibrating river models as is current best practice. This new generation of 1D models will be more reliable when developing flood defence proposals. University of Glasgow as part of the EPSRC Flood Channels programme in order to determine the relationship between 3 morphological parameters (pertaining to compound channels) and the magnitude of the head losses generated when upper channel flow expands and contracts as it passes over a trench. The authors postulate that the basic flow interaction mechanisms observed will be similar to those generated in meandering compound channels when flood plain flow (with a high relative depth) passes over a main channel in a flooded river basin and that consequently the magnitude of the head losses generated will also be similar. The authors present two equations that have been developed to relate the magnitude of both head loss sources to the 3 parameters. These equations can be adapted for inclusion in future generation 1D models in order to explicitly account for a proportion of the overall interaction head losses. because at these depths the main channel flow effectively forces a passage through the near stagnant flood plain flow so expansion and contraction does not occur. At these depths the main source of interaction head loss results from the transfer of momentum between the main channel and flood plain flows via vertical shear layers.
Year: 1999