Modeling for the prediction of beach changes considering sea level rise : a laboratory approach

通过波浪水槽试验，研究了海平面上升方式和速率对沙滩地貌的影响。建立了初始底坡度为1/10的模型滩，选择了细砂(直径0.22 mm)和粗砂(0.69 mm)两种分选好的沙子作为滩料。水深从20 cm增加到30 cm，根据水位上升的两种模式：一种是阶跃函数逼近的不连续模式，另一种是线性函数的连续模式。前者有五种不同的上升率，后者有两种。实验波浪分为侵蚀波和吸积波两种，前者波周期T=0.8s，深水波高Ho=6.5 cm，后者T=2.2s，Ho=2.8 cm。在不连续水位上升试验中，当侵蚀波作用于粗沙海滩时，岸线形态的变化不受水位上升速率的影响，而当侵蚀波作用于细沙海滩时，随着侵蚀波上升速率的降低，岸线侵蚀更为严重。在连续水位上升试验中，当侵蚀波作用在粗沙海滩上时，无论上升速率如何，最终的岸线地貌都没有明显的差别；当侵蚀波作用在细沙海滩上时，在高上升速率下发生淤积，而在低上升速率下发生侵蚀。在增积波作用下，粗沙滩地在上升率较低时出现淤积形态，在上升率较高时不发生淤积；在细沙滩地上，无论上升率如何，均未出现典型的淤积形态。

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.