The influence of network structure upon sediment routing in two disturbed catchments, East Cape, New Zealand

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Landscape evolution is governed by the interplay of uplift, climate, erosion, and the discontinuous pattern of sediment transfer from the proximal source of erosion to distal sedimentary sinks. The transfer of sediment through the catchment system is often referred to as a cascade, the pattern of which is modulated by the interaction of key network characteristics such as the distribution of transport capacity and resultant zones of sediment storage. An understanding of how sediment production is modulated through river networks with different topological structures at the associated timescales has remained elusive but presents significant implications for the knowledge of river response to disturbance events, and floodplain asset management. A multivariate method of identifying representative topological structures from a range of river networks is presented. Stream networks from 59 catchments in the South Island of New Zealand were extracted from a digital elevation model and their key topological parameters quantified. A principal component analysis was implemented to reduce these to two‐dimensional axes that represent the magnitude of network branching and the topographic structure of each catchment, respectively. An agglomerative hierarchical clustering analysis revealed five network ‘types’, which are examined in terms of their internal structural characteristics and relationships to potential regional‐scale controls. Implications for sediment transfer in these network ‘types’, and their use as representative networks for further analysis, are discussed. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

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confidence: 71%

Section: Topological Structures Of River Networkmentioning

confidence: 99%

Section: Internal Network Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Topological structures of river networks and their regional‐scale controls: A multivariate classification approach

Walley

Henshaw

Brasington

2020

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Quantifying sediment connectivity: Moving toward a holistic assessment through a mixed methods approach

Turley

Hassan

Slaymaker

2021

The sediment connectivity concept is particularly suitable for tackling complex, multidisciplinary questions through systems thinking. However, it is unclear how to directly measure connectivity, and so proxy variables are often applied by indices to provide estimates. In this study, we critically evaluate a broad range of connectivity indices encompassing structural and functional connectivity as well as hillslope channel coupling. We then discuss their role in providing a more holistic estimation of connectivity within the Tahoma Creek Watershed, WA. Of the 14 km of channel below the glacier front, the upper 6 km (0–6 km) are coupled to the adjacent hillslopes. Coupled reaches correspond to regions with a high proportion of area contributing sediment and relatively high connectivity values, where all measures decrease in the downstream direction. A significant transition occurs near river kilometer 6. Here the valley bottom abruptly widens, deposition occurs, and the hillslopes become decoupled from the active channel. This transitional reach is also identified as a geomorphic hotspot based on the network structure. The lower 8 km of channel downstream of this reach are largely depositional and percent contributing area and connectivity values remain low, eventually reaching a minimum. Despite their limitations, we found each method to provide unique and useful information regarding connectivity. The effect of scale and event magnitude on connectivity is illustrated. We also found vegetation, topographic characteristics, and network structure to be important in high‐gradient glacio‐volcanic landscapes. The choice of an index will depend on the research objectives, data availability, and the proxy variables that best describe the variability within the defined area.

Topological controls on catchment‐scale sediment dynamics

Walley

Henshaw

2022

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The episodic transfer of sediment from source to sink is a fundamental process in fluvial systems that influences river morphology, aquatic and riparian ecosystems, and risk from a variety of associated natural hazards.The hierarchical structure of river networks has been identified as a key control on spatiotemporal patterns of sediment routing at the catchmentscale, but very few studies have systematically explored this relationship.In this paper, we investigate the role that drainage network topology plays in modulating sediment flux and morphodynamic activity. We simulate the geomorphological responses of four topologically distinct catchments from New Zealand's South Island to sequences of flood events using a landscape evolution model. Spatiotemporal variation in different types of geomorphological activity is assessed via a link-based framework, and potential interrelationships between within-network changes and discharge and sediment yield at the catchment outlets are explored to provide insights into relative levels of network connectivity. We also investigate the occurrence of geomorphic 'hotspots' in relation to network topology, and their impact on the downstream transfer of sediment in different network 'types'. Dissected networks were found to exhibit much greater spatiotemporal variability in geomorphological activity compared to narrow, elongated networks where change was concentrated in mainstem reaches. The frequency and significance of geomorphological hotspots are shown to vary between network types, with strong contrasts evident between dissected networks with steep topography and elongated networks with more gentle gradients. Dissected networks exhibited mostly non-linear relationships between within-network geomorphological activity and outlet discharge and sediment yield. However, moderate-strong linear relationships between these variables were observed in mainstemdominated networks, indicating much greater levels of connectivity across a range of flow conditions. We discuss the implications of these findings on the transformation of environmental signals through fluvial systems with different topological structures, and the differential responses of catchments to disturbance events.