Turbulence and sediment transport in complex open channels

城市河流的水文情势变化和直接操纵的渠道深刻地改变。 经常尝试恢复河流，以减轻由此造成的物理和环境退化。 然而，科学家和管理机构仍然对沉积物迁移问题感到困惑，特别是在不稳定的河流中，以及通过由沙洲、水池、浅滩和其他特征形成的复杂几何形状的自然河流。 除了最理想的情况外，这种无法预测泥沙输运的能力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）以及纠正不利趋势的能力。 拟议的研究将遵循两个主要途径：a）河流恢复措施建设前后城市河流泥沙输运的实地研究; B）复杂非均匀河道剪切应力和泥沙输运性质的实验室试验和数值模拟。 目标是测试城市化和恢复对河流中泥沙流动性和行程距离的影响;澄清复杂的渠道如何干扰流量和湍流的正态分布;使用考虑力脉冲来改善复杂流动环境中泥沙运动的预测;并更新一个简单的泥沙输运模型，以了解复杂的渠道如何从小尺度过程中出现。 这是一项及时的研究，将解决实际目标，同时从根本上推进河流工程科学。 预计拟议的研究将提高我们对湍流如何通过天然渠道移动沉积物的理解，量化城市化对渠道的干扰，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实现了目标。

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.