Flow field around single and multiple hollow hemispherical artificial reefs used for fish habitat

Armono, Haryo Dwito,1968- (1999) Flow field around single and multiple hollow hemispherical artificial reefs used for fish habitat. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (17MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The term artificial reefs is being used by many researchers to refer to a variety of submerged structures. These structures are widely used to reduce the wave energy as well as to provide a safe and productive environment for fish. Hydraulic properties of artificial reefs made with hollow hemispherical shaped balls are presented in this study. The hydraulic parameters such as wave heights, particle velocities, fluid flows, wave breaking and dissipation of wave energy in the vicinity of reefs are investigated using Finite Volume methods. The study considers two-dimensional and three-dimensional fluid motion over an artificial reef constructed with one or more reef units. -- As water moves through the reefs, the incoming wave energy is dissipated by turbulence; furthermore, pressure waves, which can be detected by fish, are produced as water exits through the holes on the top and sides of the hemispherical balls. Turbulent water, which exits/enters through the holes on the top and sides, moves upward/downward and modifies the incoming/outgoing wave field. This movement of water is found to be effective in attracting fish swimming near the sea surface. It was also confirmed that the water velocities decrease considerably within the reef facilitating the attachment of marine organisms and their subsequent growth. -- In the two-dimensional model, use of reefs with less than six units does not seem to reduce the wave height, significantly. However, use of a 12 unit reef seems to reduce the wave climate inside the basin, considerably. Provision of proper reefs placement provides a conducive environment and suitable locations wherein the fish can congregate and spawn; in addition it also provides areas wherein the benthic diatoms and seaweed spores can develop and grow. -- It was observed in three dimensional model that the energy dissipation was not due to the breaking of waves as observed in the two dimensional model, but due to the flow separation occuring at the crest and around the reefs. Therefore, the wider the crest of the reef within one or two wave lengths will result in more wave energy dissipated. Numerical studies by Tsujimoto, et. al (1999) as well as field observations by Ohnaka and Yoshizawa (1994) have confirmed the results of three-dimensional model presented here.

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