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The general nature of bulk flow within bedrock single-channel reaches has been considered by several studies recently. However, the flow structure of a bedrock-constrained, large river with a multiple channel network has not been investigated previously. The multiple channel network of the Siphandone wetlands in Laos, a section of the Mekong River, was modelled using a steady one-dimensional hydraulic model. The river network is characterized by a spatially-varying channel-form leading to significant changes in the bulk flow properties between and along the channels. The challenge to model the bulk flow in such a remote region was the lack of ideal boundary conditions. The flow models considered both low flow, high inbank and overbank flows and were calibrated using SPOT satellite sensor imagery and limited field data concerning water levels.

The application of the model highlighted flow characteristics of a large multi-channel network and also further indicated the field data that would be required to properly characterize the flow field empirically. Important results included the observation that adjacent channels within the network had different water surface slopes for the same moments in time; thus calibration data for modelling similar systems needs to account for these significant local differences. Further, the in-channel hydraulic roughness coefficient strongly varied from one cross-section to the next (Manning’s ’n’ range: 0.01 to 0.10). These differences were amplified during low flow but persisted in muted form during high discharges. Copyright (C) 2012 John Wiley & Sons, Ltd.