Geomorphic coupling and sediment connectivity in an alpine catchment - exploring sediment cascades using graph theory
Geomorphic coupling and sediment connectivity in an alpine catchment - exploring sediment cascades using graph theory
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DOI：
10.1016/j.geomorph.2012.10.033
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发表时间：
2013-01
期刊：
影响因子：
3.9
通讯作者：
T. Heckmann;W. Schwanghart
中科院分区：
文献类型：
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作者：
T. Heckmann;W. Schwanghart
地貌耦合和（沉积物）连通性与沉积物收支和地貌系统的敏感性相关，是地貌学的重要课题。自乔利和肯尼迪（1971）将系统观点引入自然地理学以来，流域被视为由地貌要素（如地貌、子流域）组成，这些要素通过沉积物输运与地貌过程相耦合。在这项研究中，我们提出了一个新的应用数学图论探索粗泥沙路径在中央高山流域的网络结构。利用崩塌、泥石流、坡面和河道演变的数值模拟模型，建立了泥沙源、径、汇的空间显式图形模型。数字高程模型的栅格单元构成该图的节点，模拟的沉积物轨迹表示相应的边缘。模型结果通过与实地情况和航空照片的目视比较进行了验证。沉积路径的相互作用，即一个地貌过程的沉积物形成另一个过程的沉积源，形成沉积级联，在图形模型中用路径（一系列边）表示。我们展示了如何使用此图来探索上坡（贡献区）和下坡（源汇）功能的连接，通过分析它的节点，边缘和路径。对沉积物瀑布的空间分布、组成和频率的分析提供了有关地貌过程及其相互作用的相对重要性的信息（但无论其输送能力如何）。在研究区域，分析强调了质量运动及其相互作用的重要性，例如，大型落石源区与可能进入通道网络的泥石流之间的联系。此外，它表明，只有一小部分的研究区域耦合到通道网络本身是纵向断开的自然和人为的障碍。除了案例研究，我们讨论的方法框架和替代方案的节点和边缘表示的图形模型在地貌。我们的结论是，图论提供了一个很好的方法框架，地貌系统的分析，特别是对沉积物连通性的定量方法的探索。
Through their relevance for sediment budgets and the sensitivity of geomorphic systems, geomorphic coupling and (sediment) connectivity represent important topics in geomorphology. Since the introduction of the systems perspective to physical geography by Chorley and Kennedy (1971), a catchment has been perceived as consisting of landscape elements (e.g. landforms, subcatchments) that are coupled by geomorphic processes through sediment transport. In this study, we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment. Numerical simulation models for rockfall, debris flows, and (hillslope and channel) fluvial processes are used to establish a spatially explicit graph model of sediment sources, pathways and sinks. The raster cells of a digital elevation model form the nodes of this graph, and simulated sediment trajectories represent the corresponding edges. Model results are validated by visual comparison with the field situation and aerial photos. The interaction of sediment pathways, i.e. where the deposits of a geomorphic process form the sources of another process, forms sediment cascades, represented by paths (a succession of edges) in the graph model. We show how this graph can be used to explore upslope (contributing area) and downslope (source to sink) functional connectivity by analysing its nodes, edges and paths. The analysis of the spatial distribution, composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction (however regardless of their transport capacity). In the study area, the analysis stresses the importance of mass movements and their interaction, e.g. the linkage of large rockfall source areas to debris flows that potentially enter the channel network. Moreover, it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers. Besides the case study, we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology. We conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems, especially for the exploration of quantitative approaches towards sediment connectivity.