长江三角洲潮滩季节性冲淤循环的多因子分析

MULTI-FACTOR ANALYSIS OF THE ANNUALLY CYCLIC EROSION DEPOSITION OF THE CHANGJIANG RIVER DElTAIC

根据７个断面的月平均资料建立滩地高程同动力泥沙因子之间的回归方程。结果证明：除奚家港断面外，其它６个断面的月均滩高同月均海面和月均潮差之间有较明显的负相关，同水体含沙量之间有较明显的正相关。说明海面上升、潮差增大和含沙量的减少导致滩面刷低。季节性风况变化与滩地高程之间的相关性只有在具沙质海岸特点（岸坡＞１０‰，Φ５０＜４）的奚家港和石化厂断面才有清楚的反映；在正常的淤泥质海岸，风（浪）的作用被其它因素掩盖而居其次。由于海洋因素的影响，长江口门附近和口外（包括杭州湾）的含沙量表现出同上游来沙相反的特点，从而造成滩地高程同上游来沙量之间的负相关假象。

Based on the surveyed data of seven coastal sections (4 in the Changjiang River Estuary and 3 in the Hangzhou Bay) and the collected data of wind, sea level, tide, offshore suspended sediment concentration and river supplied sediment flux from adjacent stations, the paper deals with the regressive correlations between the monthly average flat elevations and monthly average figures of the influential factors. All sections except Xijagang which is located within the river mouth show negative correlations between flat elevation and sea level height and between flat height and tide range, with the correlative coefficients being -0 53￣-0 91 (averagely -0 77) under the former condition and -0 56￣-0 97 (averagely -0 80) under the latter condition. All of the five sections with available suspended sediment concentration data show positive correlations between flat elevation and sediment concentration, with the correlative coeffitionts being 0 35￣0 97 (averagely 0 66). Only two sections (one in the Changjiang River Estuary and the other in the Hangzhou Bay), which have the features of sand in sediment composition (Φ 50 <4 0) and slope gradient (> 0%), show negative correlation between flat elevation and shoreward wind frequncy and average wind velocity, with the correlative coefficients being -0 57 and -0 69 (averagely -0 63) and -0 61 and -0 75 (averagely -0 68) respectively as in sand beaches. Other sections do not show uniform relationship between flat elevation and wind conditions. Due to the local marine factors the offshore water sediment concentration has obvious negative correlation with the Changjiang River sediment flux, which results in unrational negative correlation between flat elevation and river sediment flux. The paper also gives sediment dynamic and morphodynamic explanations of the above correlations. Sea level rise results in the spread of wave breaker zone from subtidal area to intertidal area and then increases the intertidal water energy. The larger the tide range, the stronger the tide current and the erosion effects. The larger the flood water sediment concentration, the easier for the sediment to deposit on the flat. In the condition of precipitous slope (as in sand beach) wind driven wave holds more energy when it reaches intertidal flat than in the condition of gentle slops, so wind playe a more important role in the former condition than in the latter condition.