Turbulence and sediment transport in complex open channels

城市河流受到水文状况变化和河道直接操纵的深刻影响。溪流恢复经常被尝试作为一种手段来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的运输问题感到困惑，特别是在不稳定的河流中，以及通过由沙洲、池塘、河汊和其他特征形成的复杂几何形状的天然河流。除了最理想的情况外，我们无法预测所有情况下的沉积物迁移，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。

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.