Quantifying the Delivery & Dispersal of Landslide-Derived Sediment to the Dart River, New Zealand

Lead Research Organisation: Queen Mary, University of London
Department Name: Geography

Abstract

Following heavy rainfall on the 4/1/14, a major debris flow at Slip Stream (44.59 S 168.34 E) introduced >10^6 m^3 of sediment to the Dart River valley floor in NZ Southern Alps (S. Cox, pers. comm). Runout over the existing fan dammed the Dart River causing a sudden drop in discharge downstream. This broad dam was breached quickly, however the loss of conveyance has since impounded a 4 x 1 km lake with depths that exceed 20 m.

This event presents a rare and unprecedented opportunity to study the impacts of a discrete, high magnitude 'sediment pulse', remarkable in its capacity to dam a large river in flood (peak discharge during the event was recorded at ~790 m^3/s). Quantifying the impact of this disturbance on the form and stability of the receiving body, the Dart River, will advance our understanding of how such low frequency geophysical events shape the evolution of large alpine rivers and will create a vital baseline for future research that seeks to test theories of how such large bed wave propagates and disperse sediment downstream.

The impact of this pulse also elevates the risks posed by natural hazards in the region. Enhanced sediment transport has the potential to raise riverbed levels, destabilise floodplain assets, reduce standards of flood protection, increase the risk of channel avulsion and impact on freshwater and riparian ecology with a legacy that long outlasts the initial disturbance. Locally, this event may result in rapid advance of the Dart-Rees delta into Lake Wakatipu threatening the lakeshore communities of Glenorchy and Kinloch. The assessment of how large fluvial sediment pulses migrate, disperse and condition such hazards will offer key insights that may be transferable to other dynamic alpine settings. However, in order to constrain this event effectively, an initial topographic and sedimentological survey must be undertaken urgently, in the immediate aftermath of the event, to enable robust quantification of the sediment pulse and the existing channel morphology.

This research aims to advance this goal by seeking to: develop a unique baseline dataset that will be used to quantify the delivery and dispersal of sediment inputs from the Slip Stream landslide, from its source at Te Koroka to its sedimentary sink in Lake Wakatipu. Using a combination of aerial, terrestrial and bathymetric surveying, we will acquire two synoptic, system-wide snapshots of this highly charged sediment cascade that record the 3d morphology and sedimentology of the interlinked components of the sediment transfer system. Surveys will be undertaken in April 2014 and then one year later in March 2015, following the annual summer floods that dominate fluvial sediment transport in the region. The first survey will establish the initial state of the system and so create the opportunity to quantify the downstream pattern of sediment storage and transport through comparison with the second and any subsequent re-surveys direct differencing of Digital Elevation Models. The simultaneous bathymetric surveys of the upstream impounded lake and the delta morphology will provide constraints on sediment flux across the boundaries of the study area, enabling closure of the coarse sediment budget.

The combined results of these two survey campaigns will create an unparalleled dataset to help frame and test hypotheses that seek to explain the dispersal of major sediment pulses within rivers.

Planned Impact

The natural environment and geophysical processes of the Dart River catchment sustain a wide range of ecosystem services that impact significantly on the regional economy, cultural heritage and social welfare of the residents of the Wakatipu basin and beyond. In addition, this specific geophysical event also elevates the potential risks associated critical natural hazards - both on-site (at the landslide) and off-site (through impacts upstream in the backwater lake and the downstream events triggered by the sediment pulse).

The complex chain of processes now set in action presents a series of major challenges for the local inhabitants of the region and its wider social, economic and cultural stakeholders. These concerns have both immediate consequences and future impacts which are yet to be realized and include:

1) The recent activity at Slip Stream threatens a sacred source of the precious nephrite jade, known as 'pounamu' and treasured by the Maori communities of New Zealand. The local caretakers of the site, or Kaitiaki, our project partners Te Runanga o Ngai Tahu, are anxious to understand the processes that are undermining Te Koroka, which due to its history of limited human occupation and unspoilt archaeology is unique within New Zealand.

2) The new lake formed upstream of Slip Stream has submerged approximately 3 km of an internationally renowned hiking trail, the Dart-Rees Track. While the track has temporarily re-routed, continuing instability poses serious questions over the continuing access to this popular trail which is a major source of tourist revenue for the nearby communities of Glenorchy, Kinloch and Queenstown.

3) The downstream reworking of the sediment pulse has the potential to raise riverbed levels on the Dart with a series of co-related impacts. These include: a reduced standard of protection associated with existing flood defences at Kinloch and Glenorchy; elevated risk of major avulsion that could threaten critical infrastructure (roads and bridges) and farmland; the potential for rapid progradation of the Dart River delta, that could impact seriously on the tourist-based township of Glenorchy, posing a major flood hazard and drowning the local wharf facilities.

4) Aggradation of the braided channel also has consequences for the activities of a major commercial jet boat business operating from both Queenstown and Glenorchy (Dart River Safaris - an internationally renowned tourist enterprise and major component of the regional economy) and other public users of the river.

5) Riverbed aggradation and increases in the flux of fine sediment may also have a profound impact on the quality and sustainable of the regional fisheries, directly in the Dart River, but also for the wider Lake Wakatipu. Fishing for the trout and salmon are a major draw to the region both nationally and internationally.

6) Finally, there is mounting concern (see the letter of support from PP GNS Science) that the increased availability of fine sediment on the exposed fan and bars of the Dart River, might contribute to major dust-storms the could cause respiratory problems for vulnerable inhabitants.

The importance of these impacts on the environment is exacerbated by the regional importance of tourism to the local economy of region, prized for its pristine mountain scenery. However, while these consequences are largely regional in scale, an improved understanding of the processes that link catastrophic sediment pulses to the dynamics of the receiving rivers, has broader implications for the management of alpine rivers worldwide, many of which occupy valley floors with considerable densities of population (e.g., European Alps). Advancing the science base to help understand and predict the consequences of such landslides into rivers is therefore urgently required to support strategic and emergency planning.
 
Description This project aims to quantify the impact of a large landslide into the Dart River, NZ, that occurred in January 2014. Hyper-resolution remote sensing, employing on a combination of helicopter-based Structure-from-Motion photogrammetry and terrestrial laser scanning, will be used to derive high quality terrain models of the landslide and the Dart River along a 30 km reach downstream. These terrain models will provide a first order estimate of the sediment budget of the coupled landslide-river system, as the material is reworked over the summer flood season, and also provide topographic data to parameterize numerical models of this sediment pulse. The first field campaign was undertaken in May/June 2014, and provided the first measurements of a new lake impounded by the landslide and generated unprecedented quality terrain models of the system. A second field campaign in 2015 will provide a snapshot to quantify how the landscape has evolved over 12 months.
Exploitation Route Direct use of the research to inform an understanding of the role of landslides in alpine sediment budgets. Methodological advances in remote sensing.
Sectors Environment

URL http://www.geog.qmul.ac.uk/staff/brasingtonj.html
 
Description This research has been conducted with the local Maori Iwi or tribe (Te Runanga o Ngai Tahu) who are principally interested to learn to landslide and sediment transport processes affect the fate of their scared nephrite jade or Pounamu as it is transport from source to sink through the alpine sediment system.
First Year Of Impact 2014
Sector Education,Environment,Culture, Heritage, Museums and Collections
Impact Types Cultural,Societal,Economic

 
Description Research methods being used to inform the working practice of regulatory bodies (Canterbury, Otago and Hawkes Bay Regional Councils) in NZ and the UK (Scottish Environment Protection Agency)
Geographic Reach Multiple continents/international 
Policy Influence Type Influenced training of practitioners or researchers
Impact The development of high resolution topographic survey methods and change detection is being used by regulatory bodies to improve the design morphology and gravel extraction consents from active gravel bed rivers. This has direct implications for flood management and sustainable aggregate extraction. New software is being co-designed with regulatory authorities to meet their precise needs and being illustrated through a set of international case studies.
 
Description Innovation Projects
Amount £123,000 (GBP)
Funding ID NE/P016804/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 04/2017 
End 05/2018
 
Description International Academic Fellowship
Amount £27,629 (GBP)
Funding ID IAF-2014-038 
Organisation The Leverhulme Trust 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 12/2015
 
Title Watershed-scale Structure-from-Motion Photogrammetry 
Description In this project we have pioneered the application of novel image processing methods, specifically dense terrain model generation by structure-from-motion photogrammetry, at watershed-scales (80 km2) using multiangle photography from helicopters. This approach has delivered 3D catchment scale datasets comparable to airborne lidar for a fraction of the cost. 
Type Of Material Physiological assessment or outcome measure 
Year Produced 2014 
Provided To Others? Yes  
Impact Update by GNS Science (NZ) geospatial group for monitoring geological hazards 
 
Description Collaboration with GNS Science NZ 
Organisation GNS Science
Country New Zealand 
Sector Public 
PI Contribution Co-creation of datasets documenting the impact of a major landslide on the hydrology, geomorphology and sedimentology of the Dart River, NZ. Collaboration involved technology transfer of photogrammetric methods to key researchers/practitioners at GNS Science.
Collaborator Contribution Provided foundation datasets, expertize in the local site and regional geology. Major logistic support involved equipment loans, technical and field support.
Impact Co-presentation of seminars
Start Year 2014
 
Description Collaboration with the National Institute for Water and Atmospheric Research, New Zealand 
Organisation National Institute of Water and Atmospheric Research (NIWA, New Zealand)
Country New Zealand 
Sector Public 
PI Contribution This collaboration has involved the transfer of datasets and new methods for quantifying river dynamics using terrestrial remote sensing.
Collaborator Contribution Our partners provided field and logistical support and have transferred new numerical models they have developed and applied to our datasets.
Impact The collaboration has resulting in seven co-authored peer reviewed articles with partners, and multiple conference papers.
Start Year 2009
 
Description GeoTERM Project Partnerships 
Organisation Environment Canterbury
PI Contribution NERC GeoTERM has established partnerships with three regional councils in New Zealand (Environment Canterbury, Hawkes Bay Regional Council, Otago Regional Council) and the Scottish Environment Protection Agency. These partnerships are being used actively to design a software tool to that leverages emerging high resolution survey and modelling tools to better inform estimates of river flood capacity and gravel storage.
Collaborator Contribution The project partners met with the research team as part of three day workshop held in Christchurch NZ in June 2017. During this workshop the scope and critical steps involved in the engineering the software toolkit were mapped out and aligned with the expectations of the various stakeholders. Subsequently, the research team converted the outcome of this meeting into a software design brief that has been discussed with the partners and is currently being implemented and validated.
Impact 1) Unpublished project workshop minutes; 2) software design brief.
Start Year 2017
 
Description GeoTERM Project Partnerships 
Organisation Hawke's Bay Regional Council
PI Contribution NERC GeoTERM has established partnerships with three regional councils in New Zealand (Environment Canterbury, Hawkes Bay Regional Council, Otago Regional Council) and the Scottish Environment Protection Agency. These partnerships are being used actively to design a software tool to that leverages emerging high resolution survey and modelling tools to better inform estimates of river flood capacity and gravel storage.
Collaborator Contribution The project partners met with the research team as part of three day workshop held in Christchurch NZ in June 2017. During this workshop the scope and critical steps involved in the engineering the software toolkit were mapped out and aligned with the expectations of the various stakeholders. Subsequently, the research team converted the outcome of this meeting into a software design brief that has been discussed with the partners and is currently being implemented and validated.
Impact 1) Unpublished project workshop minutes; 2) software design brief.
Start Year 2017
 
Description GeoTERM Project Partnerships 
Organisation Otago Regional Council
PI Contribution NERC GeoTERM has established partnerships with three regional councils in New Zealand (Environment Canterbury, Hawkes Bay Regional Council, Otago Regional Council) and the Scottish Environment Protection Agency. These partnerships are being used actively to design a software tool to that leverages emerging high resolution survey and modelling tools to better inform estimates of river flood capacity and gravel storage.
Collaborator Contribution The project partners met with the research team as part of three day workshop held in Christchurch NZ in June 2017. During this workshop the scope and critical steps involved in the engineering the software toolkit were mapped out and aligned with the expectations of the various stakeholders. Subsequently, the research team converted the outcome of this meeting into a software design brief that has been discussed with the partners and is currently being implemented and validated.
Impact 1) Unpublished project workshop minutes; 2) software design brief.
Start Year 2017
 
Description GeoTERM Project Partnerships 
Organisation Scottish Environment Protection Agency
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution NERC GeoTERM has established partnerships with three regional councils in New Zealand (Environment Canterbury, Hawkes Bay Regional Council, Otago Regional Council) and the Scottish Environment Protection Agency. These partnerships are being used actively to design a software tool to that leverages emerging high resolution survey and modelling tools to better inform estimates of river flood capacity and gravel storage.
Collaborator Contribution The project partners met with the research team as part of three day workshop held in Christchurch NZ in June 2017. During this workshop the scope and critical steps involved in the engineering the software toolkit were mapped out and aligned with the expectations of the various stakeholders. Subsequently, the research team converted the outcome of this meeting into a software design brief that has been discussed with the partners and is currently being implemented and validated.
Impact 1) Unpublished project workshop minutes; 2) software design brief.
Start Year 2017