波浪作用下沙质海滩沉积物运动特征

The Wave-Induced Sedimentology and Sorting Character of Sandy Beach

基于二维波浪水槽实验,采用沙质斜坡概化海滩,分别选用规则波和椭圆余弦波进行实验,测量波浪作用前后的海滩剖面形态及断面沉积物粒径组成,探讨波浪作用下沙质海滩沉积物运动特征,包括剖面形态演化特征及其床沙分选规律.结果表明:沙质海滩剖面形态时空演化特征受波浪类型、波高、周期等因素影响,呈现出沙坝形态和滩肩形态,发现波浪Irribarren参数可以作为沙质海滩剖面演化形态的判别参数.在本实验条件下,Irribarren参数大,海滩剖面呈现滩肩形态;Irribarren参数小,海滩剖面则呈现沙坝形态.海滩床面沉积物在波浪作用下产生了明显的分选现象,波浪破碎产生的强烈紊动造成床面沉积物的起动、并为小颗粒的运动提供动力.水体紊动导致水流挟沙力降低,大颗粒泥沙在紊动较强区域产生沉积,部分被水流挟带发生向岸推移;小颗粒泥沙则随水流运动,在紊动较弱的区域分散沉积.

To explore the sandy beach morphology characteristic induced by wave action and crossshore sorting of sediment,a set of 2D wave flume experiments on a sandy beach were performed. Non-uniform sand slope was used to generalize the sandy beach,which were exposed to the regular waves and cnoidal waves respectively. The evolution of cross-shore beach profile and the grain size of sediment in different location were measured and recorded. Experimental results show that sandy beach profile under regular waves and random waves could appear sandbar and beach berm profiles,which affected by some certain factors,such as wave type,wave height,wave period,etc. It has been found that irribarren parameter can be used as a discriminant parameter in the profile of sandy beach geomorphic evolution. The landforms of sandy beach present berm profile when irribarren parameter is large and sandbar profile when Irribarren parameter is small. The surface sediment of sandy beach under wave action produced obvious sorting phenomenon. The intense turbulence generated by waves breaking leads to the sediment transporting,and provides power for the movement of small size particles. Large size sediment deposited in the area of strong turbulence because the sediment-carrying capacity is not enough due to turbulence effect. Small size sediment,carryed by the flow after threshold induced by breaking wave,deposited in the area of weak turbulence scatteredly.