ABSTRACT: Sediment transport and flow dynamics in a fish-habitat restoration project: Field and numerical experiments.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Few studies have examined sediment transport patterns around instream structures used to enhance fish habitat despite the importance of this variable in the successful design of stream restoration schemes. This paper presents results from a field experiment on particle movement around flow deflectors during a series of floods in a restored reach of the Nicolet River (Quebec). Bedload transport is investigated using passive integrated transponder (PIT) tags with particles ranging from 0.05 m to 0.16 m. These were followed from positions upstream of a pair of current deflectors which were designed to maintain a deep downstream pool. Three-dimensional numerical simulations of the flow field at various flow stages (when deflectors are either emerged or submerged) are also used to relate near-bed velocity and bed shear stress to transport patterns. A key question is whether particles are capable of leaving the restored pool afterwards, since it determines whether the pool will be maintained in the long term. Results indicate that from 2005 to 2008, of the 117 pit-tagged particles that fell in the pool only 27 are known to have exited. None of the 30 largest rocks entering the pool escaped. To explain bedload transport, the three-dimensionality of the flow field when structures are submerged must be taken into account. The interaction between submerged deflectors and the dug pool gives rise to large streamwise, lateral and vertical velocity gradients, resulting in several interconnected mixing layers which likely affect sediment transport. To further understand the interactions between the morphology of the dug pool and flow dynamics, various pool geometries are tested in numerical experiments.

Bibliography of Canadian Geomorphology