悬移质挟沙能力水槽实验方法探讨

New approach to flume experiment for transport capacity of fine suspended sediment

水流挟沙能力是研究悬移质泥沙输移的核心问题之一。对不均匀泥沙,由于细颗粒调整的滞后性,传统循环水槽实验较难获取悬移质与河床泥沙相对应的输沙平衡条件,需要大量精度不高的浓度测量和无法避免细沙在系统中循环影响实验精度。本文通过改进水槽进口加沙和增加出口过滤系统,并采用不平衡淤积方式逼近平衡输沙进行实验和研究挟沙。实验得到从淤积趋近平衡的水沙条件,将实验结果与传统实验测量结果及挟沙能力公式计算结果进行比较,结果初步表明:(1)改进系统能更准确控制进口加沙和得到近似平衡的悬移质泥沙浓度、提高悬移质输沙实验的可靠性;(2)解决了传统水槽实验难以获得平衡泥沙浓度的问题,并避免了频繁而且不准确的浓度测量;(3)初步显示传统实验测量泥沙浓度可能较大地偏大于真实挟沙能力。

River sediment transport capacity is of a key issue in suspended sediment studies.Due to the strong time-lag of fine sediment adjustment,it is difficult to obtain an equilibrium condition by the traditional recirculating flume experiments,especially for fine graded sediment.In this study,a special sand feeder and an outlet filter were implemented to the traditional experimental flume system,and experiments were carried out to approach the equilibrium transport process through sedimentation.Results were compared with traditional experiment data and the existing transport formulas,indicating:i)the implemented system can load more accurate inlet sediment for given compositions with the proposed feeder and outlet filter;ii)the non-equilibrium experiment can rather better approach equilibrium transport in a flume reach over the self-established depositional delta,where a sediment concentration,that is slighly higher than the actual transport capacity,can easily obtained without measurements;iii)results of limited runs indicate an extensively lower transport capacity than that from traditional experiments.Preliminary results reveal a somehow overestimation by the traditional formulas that calibrated using previous experiment data.