ABSTRACT

The emplacement of offshore, artificial sea-grass beds directly influences near-shore sand transport, Artificial sea-grass will decrease wave energy due to bending of the fronds, increased bottom drag, internal deformation and refraction. The latter three effects change as a result of the increased bottom slope caused by the sea-grass beds. In turn, the mean longshore current and longshore component of wave power are reduced. Total wave power and incident angle to the beach specifies the longshore component of wave power (P_L) which is equated to the quantity of sand moved per unit distance (dq/dx).

The average bending moment per individual frond was calculated to be approximately 2.0 lb.-in. A dense bed of sea-grass has the potential to reduce wave energy by twenty percent, based solely on energy lost to bending. The reduction of wave height, corresponding to the energy loss, results in decreased wave power per unit distance expended at the breaker zone.

Ginsburg and Lowenstam (1957), reported that Thallassia testudinum offers a suitable substrate for many benthic communities. Algae, Foraminifera, bryozoans, etc., attach to the fronds, while mollusks, echinoderms and crustaceans use the network of baffles for protection and food gathering. These organisms add substantially to the binding ability of the grass and sediment will be readily accumulated within the bed. Variations in the type of community present will depend on wave energy (turbulence), temperature of the water, tidal range and salinity. In areas of low wave energy, embankments may grow, forming a series of offshore bars which will further influence approaching orthogonals.