Tunnicliffe, JBrierley, GWalley, Yasmin2015-07-2320152015http://hdl.handle.net/2292/26380Full text is available to authenticated members of The University of Auckland only.A model of catchment-scale function is presented in order to clarify how network structure governs sediment “connectivity” in a landslide-dominated sediment regime. The catchment is a fundamental spatial unit of geomorphology; however, the focus on reach-scale dynamics has tended to divert attention from the influences of network structure on sediment delivery. In this study, I examine the network topology and longitudinal patterns within two 4th order catchments in New Zealand’s East Cape region, to highlight contrasting trends of sediment transfer and deposition between headwaters and the catchment outlet. Downstream changes in channel slope, grain-size, sediment storage and valley confinement relate to network order (thus catchment scale) in complex ways, but these can be interpreted in terms of network organisation using an adapted stream ordering framework. Building on the idea that river connectivity is the result of effective sediment transfer, unhindered by factors such as sediment diversion by storage in bars, blockages by alluvial fan development or accumulation in broad valley flats, I map out the principal factors contributing to connectivity within the two catchments. Mapping of longitudinal trends in cumulative catchment area, channel slope, sediment storage and landslide occurrence reveals contrasting trends that may be related to network structure. Sediment “delivery matrices” show the variable nature of connections between lower- and higher-order network links. Dendritic network form (Mangarakei) show increased deposition in the headwaters, relative to lower reaches, while trellis forms (Waiau) show punctuated contributions along a very long main-stem, culminating in significant downstream storage. Historical imagery emphasizes some dramatic, though transient changes in network linkages at a decadal time scale. These changes occur primarily at the reach-scale and at key tributary junctions within the network, with the exception of the widespread impact from tropical Cyclone Bola in 1988. Sampling of substrate at the catchment outlets highlights controls that may also be linked to network structure, including the role of magnitude-frequency relationships on connectivity. Field observations from the main-stem show the role of transient waves of fine material that build up within some reaches, profoundly influencing channel morphology and transport capacity. This study thus emphasizes how catchment analyses and sediment routing must necessarily take network form and tributary junction geometry into account, in order to effectively assess channel connectivity, and therefore sensitivity to disturbance and cumulative effects.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher.Restricted Item. Available to authenticated members of The University of Auckland.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmhttp://creativecommons.org/licenses/by-nc-sa/3.0/nz/ThesisCopyright: The AuthorQ112911097