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Title: Low-cost modifications of the Crump weir to improve fish passage
Author: D.G. Rhodes
Author: S.A. Servais
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1591, Representation ID: 3, Object ID: 1328
This three-year research project was carried out in response to the need for a lowcost strategy for improving fish passage over Crump or triangular profile weirs, as an alternative to expensive traditional fish pass solutions. The aim was to develop a range of low-cost modifications to the Crump and other similar sloping weirs, and to investigate their effect upon flow gauging. A multiplicity of quick-fit baffle arrangements, assembled from LEGO bricks, were trialled before the preferred geometry was accurately fabricated and tested. At this later stage, water depth profiles on the fish pathway were carefully measured with a wave probe and detailed velocity distributions were obtained in the plane of each baffle slot, using a Pitot and static tube combination. The velocities were compared with fish swimming speeds in the Environment Agency’s Swimit database. The self-cleansing properties of the modifications, and the hydraulic effect on the modifications of a slight increase in the downstream slope of the weir, were also investigated. It is expected that air entrainment will be greater at field scale than in the laboratory model and might deter some fish passage. The effects on the weir discharge coefficient and drowned flow reduction factor of several different baffle arrangements, each parallel to the crest, were investigated for modular and non-modular flows respectively. Most effort was directed towards the effect of the single baffle acting in modular flow, but the single baffle in non-modular flow was also investigated, as were twin baffles and the complete baffle arrangement in both flow regimes. In order to test the effectiveness of the proposed modifications and to make minor adjustments for optimizing fish passage, it is recommended that fish-movement studies should be carried out in the field on a non-gauging weir, modified as recommended in this study. The baffle arrangement should be fabricated as a light-weight, quick-fit assembly that can be easily adjusted or replaced. When the effectiveness of the modifications for fish passage has been confirmed, they will be immediately deployable on non-gauging weirs and, subject to further hydrometric physical modelling, later deployable on gauging weirs.
Publisher: Environment Agency
Subject Keywords: RiversWeirsDesignMigrationFisheries
Extent: 86
Total file downloads: 326

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