Browsing by Author "McCord J"

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Managing at source and at scale: The use of geomorphic river stories to support rehabilitation of Anthropocene riverscapes in the East Coast Region of Aotearoa New Zealand
(Frontiers Media S A for American Physical Society, 2023-04-13) Fuller IC; Brierley GJ; Tunnicliffe J; Marden M; McCord J; Rosser B; Hikuroa D; Harvey K; Stevens E; Thomas M; Thoms M
Recently uplifted, highly erodible rocks, and recurrent high intensity storms, generate exceedingly high erosion and sedimentation rates in the East Coast Region (Tairāwhiti) of Aotearoa New Zealand. Despite the recent nature of the Anthropocene record in global terms (∼650 years since Māori arrival, 250 years of colonial impacts), human disturbance has profoundly altered evolutionary trajectories of river systems across the region. Here we document catchment-by-catchment variability in anthropogenic signature as geomorphic river stories for five catchments (Waiapu, Hikuwai, Waimatā, Waipaoa, Mōtū). We show how targeted, fit-for-purpose process-based rehabilitation programmes that manage at source and at scale are required to facilitate river recovery in each of these catchments. The largest rivers in the region, Waiapu and Waipaoa, comprise steep, highly dissected terrains that are subject to recurrent hillslope failures, including systemic shallow landslides, occasional deep-seated rotational slumps and earthflows. Localised sediment input from large (>10 ha) gully mass movement complexes overwhelms valley floors. Targeted revegetation programmes are required to reduce extreme sediment inputs from these sources. Although there are fewer gully complexes in the Hikuwai, multiple landslips supply vast volumes of fine-grained sediment that aggrade and are recurrently reworked along channel margins in lowland reaches. Waimatā has no gully complexes and a smaller number of landslips, but large areas are subject to sediment input from earthflows. The terrace-constrained flume-like nature of this system efficiently flushes materials ‘from the mountains to the sea’, recurrently reworking materials along channel banks in a similar manner to the lower Hikuwai. Systematic reforestation in the middle-upper catchment and revegetation of riparian corridors is required to reduce sedimentation rates in these catchments. In contrast, terraces buffer sediment delivery from hillslopes in the upper Mōtū catchment, where a bedrock gorge separates large sediment stores along upper reaches from the lower catchment. As reworking of valley floor sediments in response to bed incision and reworking (expansion) of channel margins is the primary contemporary sediment source in this system, bed control structures and revegetation of riparian corridors are required as part of targeted sediment management plans. We contend that geomorphic river stories provide a coherent platform for Anthropocene rehabilitation strategies that work with the character, behaviour and evolutionary trajectories of river systems. Although this generic lens can be applied anywhere in the world, we highlight particular meanings and implications in Aotearoa New Zealand where such thinking aligns directly with Māori values that respect the mana (authority), mauri (lifeforce) and ora (wellbeing) of each and every river
Tectonic and climatic controls on the regionally anomalous geomorphic character and behaviour of the Upper Mōtū River, Aotearoa New Zealand
(Elsevier B V, 2025-12-01) McCord J; Brierley G; Tunnicliffe J; Fuller I; Marden M; Mazengarb C
Interpreting patterns of landforms is key to geomorphic understandings of landscapes. This study applies Stage One of the River Styles Framework to describe and explain contemporary river character, behaviour and patterns of river types in the Upper Mōtū Catchment on the East Coast of Aotearoa New Zealand. The Mōtū Catchment is regionally anomalous as it stores large volumes of sediment within a perched drainage basin at high elevations in the landscape. Landscape memory exerts a primary control upon contemporary process interactions in the Upper Mōtū Catchment. Geologic and climatic controls upon landscape configuration determine contemporary sediment sources and connectivity relationships, in turn influencing landscape responses to human disturbance and resulting patterns and rates of sediment flux. Tectonic uplift has shaped the relief and valley configuration while the lithological fabric created structural weakness that the river has exploited to form the current drainage pattern. Significant accommodation space has been created on valley floors in the upper catchment. Quaternary climate change instigated phases of valley floor aggradation and reworking that created a complex sequence of river terraces upstream of a knickpoint (Mōtū Falls) in the upper catchment. Terraces now act as confining margins for the laterally adjusting river. Contemporary headcut incision and channel expansion are the dominant contemporary sediment sources in this river system. In contrast to other river systems in the region where targeted revegetation of hillslopes is the key to process-based restoration programmes, bed control structures and a continuous riparian vegetation corridor are required to address sediment issues in the Upper Mōtū Catchment.