Field experiment on alternate bar dynamics

JPC Eekhout and AJF Hoitink

September 5-8, 2012

RiverFlow, San Jose, Costa Rica

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Within the Dutch research project ’Valley wide meander restoration’ six restored streams will be monitored over a 2-year period. The monitoring program aims at understanding initial morphological processes and the associated ecological developments. The present study focuses on the morphodynamic developments that took place after the completion of one of the restoration projects. The morphology and hydraulics of the field sites are evaluated using sequential GPS-surveys, discharge records and information from sediment samples. The present contribution concerns the Hooge Raam, where a new channel is constructed parallel to the stream that was to be restored. The channel was designed to investigate the autogenous formation of a meandering channel from an initially straight reach, designed based on hydraulic geometry relations. Eight months after construction of the stream, alternating bars emerged in the downstream part of the stream. Analysis of ten successive bed level surveys about two months apart shows channel bar migration and an increase of both the bar height and their wavelengths. Bar wavelength is increasing in time until it reaches an equilibrium value. The dynamics of both migration speed and bar height respond to the dynamics in the varying discharge.