挖槽回淤物粒度变化对航道回淤的影响

Effect of waterway siltation by bed-material grain-size variation processes

根据吕四海域地形、水文、泥沙和浅层柱状样观测资料的分析,研究航道浚深后回淤物的粒度变化过程及其对航道回淤的影响。研究表明,航道浚深后,航槽内底质呈明显粗化现象,底质中值粒径由浚前的0.045-0.071 mm增加至浚后的0.128-0.135 mm,0.005-0.062 mm的细颗粒组分由36.0%减小至8.9%,0.075-0.250 mm粗颗粒组分由37.9%增加至78.2%,疏浚船舶的水力分选是泥沙组分变化的主要因素。吕四海域航道泥沙回淤形式为悬沙沉降和底沙推移共同作用的结果,夏季7—8月试挖槽内回淤强度较大,回淤泥沙颗粒较细,冬季10—12月回淤强度较小,回淤泥沙颗粒较粗。根据粒度谱计算结果,正常天条件下悬沙沉降对航道回淤的贡献率约为15%,夏季贡献率高于冬季,大风天可增至30%-40%。回淤贡献率的计算方法可为类似工程的回淤研究提供借鉴和参考。

Based on topography,hydrology,tidal current,bed sediment and core data collected at the Lvsi sea area,an analysis of the bed-material grain-size variation processes and its effect of the waterway siltation is carried out. The results show that the bed-material armoring is shown at the Lvsi trial dredged channel after the waterway dredging. The median diameter of the bed-material is 0. 045 - 0. 071 mm before dredging,which increases to0. 128 - 0. 135 mm after dredging. The sediment component between 0. 005 mm and 0. 062 mm decreases from36. 0% to 8. 9%,and that between 0. 075 and 0. 250 mm increases from 37. 9% to 78. 2% by comparison with before and after dredging. The main course of the sediment composition change is the hydraulic sorting by the dredging. The silting forms combining with the suspended sediment deposition and bed load transport is a mechanism of the Lvsi waterway siltation. The siltation intensity of the trial dredged channel is great during the period from July to August in summer,and it is small during the period from November to December in winter.Furthermore,the medium diameter of the bed-material has become finer in summer and coarser in winter. The results of grain size spectral calculation show that the contribution rate of the suspended sediment deposition on the waterway siltation is about 15% in the normal condition,and the contribution rate in summer is higher than that in winter. However,this rate can be increased to 30% - 40% in the windy condition. The calculation method of the contribution rate provides a reference for the siltation studies of the similar works in the future.