Modelling braided river morphodynamics using a particle travel length framework
Modelling braided river morphodynamics using a particle travel length framework
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DOI：
10.5194/esurf-7-247-2019
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发表时间：
2019-03
影响因子：
3.4
通讯作者：
A. Kasprak;A. Kasprak;J. Brasington;Konrad C. Hafen;Konrad C. Hafen;R. Williams;J. Wheaton
中科院分区：
文献类型：
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作者：
A. Kasprak;A. Kasprak;J. Brasington;Konrad C. Hafen;Konrad C. Hafen;R. Williams;J. Wheaton
抽象的。预测通道演变的数值模型是调查过程中发生的时间尺度，使现场观察棘手的一个重要工具。然而，当前这一代的形态动力学模型要么过度简化了相关的物理过程，要么在基于计算流体动力学（CFD）的物理上更完整的代码的情况下，具有严重限制其应用的时空范围的计算开销。在这里，我们提出了一种新的，开源的，混合的方法，旨在调和这些建模哲学。该框架将稳态二维CFD水力学与基于规则的泥沙输运算法相结合，以预测用于路由泥沙和演变河床地形的颗粒流动性和输送路径。两个对比的天然辫状河（里斯，新西兰和Feshie，英国）的数据用于模型验证，将达到规模的定量形态变化预算和体积评估不同的编织机制。该模型能够模拟8的10个经验观察到的编织机制，从参数化的床面侵蚀，泥沙输运和沉积。河岸侵蚀和沙洲边缘修整的表示需要包括横向河道偏移算法。基于稳定有效流量与离散成一系列模型运行的事件过程线的模拟之间的比较发现，只有轻微增加预测的体积变化，更大的沉积抵消侵蚀。十年尺度模拟表明，事件规模冲刷深度和后续沉积的准确预测提出了方法上的挑战，因为如果采用简单的路径长度分布，预测的沉积模式可能永远不会“赶上”侵蚀，从而导致河道过度冲刷。因此，可能有必要增加路径长度分布，以优先在某些地貌单元中存款材料。我们预计，这里提出的模型将被用作一个模块化的框架，以探索不同的过程表示的效果，并作为一个学习工具，旨在揭示在多个时间尺度的河流地貌输运过程的相对重要性。
Abstract. Numerical models that predict channel evolution are an essential tool for investigating processes that occur over timescales which render field observation intractable. The current generation of morphodynamic models, however, either oversimplify the relevant physical processes or, in the case of more physically complete codes based on computational fluid dynamics (CFD), have computational overheads that severely restrict the space–time scope of their application. Here we present a new, open-source, hybrid approach that seeks to reconcile these modelling philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a rule-based sediment transport algorithm to predict particle mobility and transport paths which are used to route sediment and evolve the bed topography. Data from two contrasting natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for model verification, incorporating reach-scale quantitative morphological change budgets and volumetric assessment of different braiding mechanisms. The model was able to simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming necessitated the inclusion of a lateral channel migration algorithm. Comparisons between simulations based on steady effective discharge versus event hydrographs discretized into a series of model runs were found to only marginally increase the predicted volumetric change, with greater deposition offsetting erosion. A decadal-scale simulation indicates that accurate prediction of event-scale scour depth and subsequent deposition present a methodological challenge because the predicted pattern of deposition may never “catch up” to erosion if a simple path-length distribution is employed, thus resulting in channel over-scouring. It may thus be necessary to augment path-length distributions to preferentially deposit material in certain geomorphic units. We anticipate that the model presented here will be used as a modular framework to explore the effect of different process representations, and as a learning tool designed to reveal the relative importance of geomorphic transport processes in rivers at multiple timescales.