Ryan Robert J, Boufadel Michel C
Department of Civil and Environmental Engineering, Temple University, 1947 N 12th Street, Philadelphia, PA, 19122, USA.
J Environ Manage. 2006 Oct;81(1):50-7. doi: 10.1016/j.jenvman.2005.09.016. Epub 2006 Apr 17.
Conservative solute tracer experiments were conducted in Indian Creek, a small urban stream located in Philadelphia, Pennsylvania, USA. Estimated flow rates were between 46 Ls(-1) and 81 Ls(-1), average stream width was 5.5m and average stream depth was 0.2m. Given these dimensions, most researchers would think it reasonable to assume that the stream is completely mixed vertically and horizontally. However, we found that the stream was not vertically completely mixed in a 1.0m deep, 30 m long pool. The limited mixing was demonstrated by the vertical stratification of a tracer cloud which was completely mixed both laterally and vertically across the stream prior to entering the pool. We suggest that the cause of limited mixing is due to a balance between groundwater inflow and transverse dispersion at the cross-section. We show that the unsupported assumption of complete mixing may result in a wide range, and thus increased uncertainty, of the values of stream flow and longitudinal dispersion coefficient estimated from these data. We conclude that the assumption of complete mixing and one-dimensional modeling must be checked against actual field conditions, even in small streams.
在美国宾夕法尼亚州费城的一条小型城市溪流——印第安溪中进行了保守溶质示踪剂实验。估计流速在46升/秒至81升/秒之间，溪流平均宽度为5.5米，平均深度为0.2米。考虑到这些尺寸，大多数研究人员会认为假设该溪流在垂直和水平方向上完全混合是合理的。然而，我们发现，在一个深1.0米、长30米的水潭中，溪流并非在垂直方向上完全混合。示踪剂云团的垂直分层证明了混合有限，该云团在进入水潭之前在溪流横向上和垂直方向上都是完全混合的。我们认为，混合有限的原因是由于地下水流入与横截面上的横向扩散之间的平衡。我们表明，完全混合这一未经证实的假设可能会导致根据这些数据估算的溪流流量和纵向扩散系数的值有很大范围，从而增加不确定性。我们得出结论，即使在小型溪流中，也必须对照实际现场条件检验完全混合和一维建模的假设。
