| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1994: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1993: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1992: ¥6,200,000 (Direct Cost: ¥6,200,000)
|
|---|
| Research Abstract |
A wave tank experiment was conducted to examine the effect of the mode and rate of sea level rise on sandy beach morphologies using a wave tank. A model beach was constructed with an initial bottom slope of 1/10. Two kinds of well-sorted sand were selected for beach material : one was fine sand (0.22mm in diameter) and the other was coarse sand (0.69mm). Water depth was increased from 20 to 30 cm, according to two modes of water level rise : one was a discontinuous mode approximated by a step function and the other was a continuous mode with a linear function. The former had five different rising rates and the latter had two. Two kinds of laboratory waves were selected : erosional and accretionary waves ; the former had a wave period, T,of 0.8s and a deepwater wave height, Ho, of 6.5cm, and the latter T=2.2s and Ho=2.8cm.
In the discontinuous water level rise tests, changes in beach morphology near shoreline suffered no influence of water level rising rates when erosional waves acted on the beach of coarse sand, while more serious shoreline erosion occurred as rising rates became lower when erosional waves acted on the fine-sand beach. Shoreline accreted irrespective of rising rates and sediment grain sizes in the case of action of accretionary waves.
In the continuous water level rise tests, there was no considerable difference in final shoreline landforms irrespective of rising rates when erosional waves acted on the coarse-sand beach ; accretion arose under the condition of high rising rates, while erosion occurred under low rising rates when erosional waves acted on the fine-sand beach. In the case of the action of accretionary waves berm morphology occurred on the coarse sand beach when the rising rate was low, while no accretion took place when it was high ; and no typical accretionary morphology appeared on the fine-sand beach in regardless of rising rates.
|
