Development of Eelgrass(Zostera marina) Bed Utilizing Sand Drift Control Mats

Abstract

Field observation for the development of eelgrass(Zostera marina) beds was conducted off Kushiki beach, Naruto, Tokushima Prefecture. Chemical fiber mats were used to control the sand drift. Square seeds bags with side 30 cm long were laid under the mats in November and December 1995 and also in January 1996. In May 1996, the amount of eelgrass germinated per unit area reached up to 100/m². The results of numerical analysis indicated that the velocity inside mat decreases when the velocity at the upper boundary becomes large. A small amount of circulating flow takes place with the occurrence of vertical flow, which seems to relate to the diffusion of suspended sediment. Sediment concentration near the bed, averaged over a wave period, is about 10 ~ 30% of that without mat. The seeding method presented in this study is demonstrated to be one effective means for the development of eelgrass beds.

Keywords:

• Eelgrass bed
• chemical fiber
• sand drift
• sediment concentration