Turbulence and sediment transport in complex open channels

城市河流由于水文状况的改变和对航道的直接操纵而发生了深刻的变化。人们经常尝试将溪流恢复作为减轻由此造成的物理和环境退化的一种手段。然而，科学家和监管机构仍然对泥沙输送问题感到困惑，特别是在不稳定的溪流中，以及通过具有由沙洲、水池、冲沟和其他特征形成的复杂几何形状的天然溪流。除了最理想的情况外，在所有情况下都无法预测泥沙输送，这限制了我们预测城市化和其他人类活动对河流的累积影响(包括恢复)和纠正不利趋势的能力。 拟议的研究将遵循两个主要途径：a)对河流修复措施建造前后城市河流中的泥沙输送进行实地研究；b)关于剪切力和复杂非均匀河道中泥沙输送性质的实验室实验和数值模拟。目的是测试城市化和恢复对河流中泥沙流动和移动距离的影响；阐明复杂的河道如何干扰水流和湍流的正常分布；使用力脉冲的考虑来改进对复杂水流环境中泥沙运动的预测；以及更新泥沙输送的简单模型，以了解复杂的河道是如何从小尺度过程中出现的。 这是一项及时的研究，将解决实际目标，同时从根本上促进河流工程科学的发展。预计拟议的研究将加深我们对湍流如何将泥沙通过天然河道的了解，量化城市化对河道的干扰，并评估为恢复小溪的物理和生态完整性而采取的措施是否达到目标。

Urban rivers are profoundly altered by hydrological regime change and direct manipulation of the channel. Stream restoration is frequently attempted as a means of mitigating the physical and environmental degradation that results. However, scientists and regulatory bodies remain confounded by the problem of sediment transport, particularly in unstable streams and through natural streams with complex geometry created by bars, pools, riffles and other features. This inability to predict sediment transport in all but the most ideal cases limits our ability to anticipate the cumulative effect of urbanisation and other human activities on rivers, including restoration, and to correct adverse trends. The proposed research will follow two main avenues: a) field research on sediment transport in urban streams before and after the construction of stream restoration measures; b) laboratory experiments and numerical modelling on the nature of shear stress and sediment transport in complex non-uniform channels. Objectives are to test the effects of urbanisation and restoration on sediment mobility and distance of travel in rivers; clarify how complex channels disturb normal distributions of flow and turbulence; use a consideration of force impulse to improve predictions of sediment movement in complex flow environments; and update a simple model of sediment transport to understand how complex channels emerge from small scale processes. This is timely research that will address practical goals while fundamentally advancing the science of river engineering. It is anticipated that the proposed research will improve our understanding of how turbulent flow moves sediment through natural channels, quantify the disturbance to channels as a result of urbanisation, and assess whether the measures being taken to restore the physical and ecological integrity of creeks are achieving their goals or not.