Upstream channel degradation triggered by a meander cutoff: Potential replacement for channel dredging

Meander cutoffs represent a natural cause of a river course shortcut. This typically results in a local increase in channel slope, which triggers modification in a large-scale longitudinal river profile. In this study, an anticipated meander cutoff in the Huallaga River, a meandering river in Peruvian Amazon, is investigated. Approximately 80 km of the study reach includes six sites where channel dredging is planned for the purpose of improving navigability. All these six sites are located upstream of the anticipated meander cutoff point. However, the negative environmental impact is of major concern for local communities. Therefore, the natural channel degradation due to the meander cutoff is expected to replace the artificial river modification. In this study we examine progradation of the upstream bed degradation and the downstream bed aggradation triggered by the cutoff, as well as the channel adjustment timescale with the use of a simple numerical model. Ahead of model development, field measurements are conducted in order to obtain model input parameters such as channel geometry, water discharge, suspended load, bed load, bed material size and hydraulic resistance. The model results are analyzed in terms of the timescale and degree of the channel degradation, and potential replacement of the channel dredging with the natural channel modification triggered by the downstream meander cuff is discussed.