The construction of a partial exclusion amenity barrage across the lower estuary of the River Tawe, South Wales, was completed in 1992. The structure includes a pool and weir fish pass consisting of 16 pools interlinked by deep notches in alternately downstream and cross facing traverses. Modifications to the fish pass weirs were carried out at the end of June 2000 in order to address the problem of excessive turbulence within the pools. The primary aim of this thesis was to examine the effectiveness of the modified fish pas under a range of environmental conditions. Underwater video was selected as the most suitable method for monitoring fish use of the pass and a system was designed and installed below the fish pass exit notch. The effects of time of day, tidal state, river flow volume and water quality on fish use of the modified pass were examined. Diel and tidal rhythms appeared to have the greatest impact on fish movements. The majority of fish exited the pass during daylight, supporting the hypothesis that fish utilise visual cues to negotiate obstacles. The timing of movement during tides which completely inundated the fish pass suggested that fish were using the rising tide to aid ascent, however a greater number of fish used the pass during non-inundating tides when this was main route past the barrage. Fish use of the pass appeared to be stimulated between river flows of 3.00 – 6.99 m<sup>3</sup> s<sup>-1</sup> and 10 – 10.99 m<sup>3</sup> s<sup>-1</sup>, and there was evidence that salmonids use of the fish pass increased in response to changes in flow. Dissolved oxygen concentrations remained above levels which would affect the swimming ability of fish, although oxygen supersaturation may potentially cause periodic problems.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:639353 |
| Date | January 2005 |
| Creators | Washburn, E. J. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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