Waiapu River, New Zealand

 

Funding Agency: NSF

Objectives: This study seeks to understand the mechanisms and depositional products of hyperpycnal sediment flows on continental shelves, using a mud supercharged river-mouth/shelf system to test and evolve emerging paradigms for gravity-driven sediment transport.  The proposed field site is located seaward of the mouth of the Waiapu River on New Zealand’s northeast coast (Fig. 1).  The sediment yield of this river is among the highest in the world, and hyperpycnal plumes issue from the mouth during annual floods.  By examining the down slope movement of these dense flows across the shelf and their relation to shelf bathymetry and fine-scale stratigraphy, we will extend our knowledge of key processes that operate on high-yield margins.  By capitalizing on the Waiapu’s large sediment load and using state-of-the-art observational techniques, this study promises to relate observed sediment fluxes to depositional products during a single flood season and to resultant geomorphology that develops over longer time scales.  These observations will be used to refine numerical models of negatively buoyant flows that will enable predictions of stratal development in these important environments.

aerial

 

Collaborators:

VIMS: Carl Friedrichs, Courtney Harris, Jesse McNinch, Don Wright

NIWA: Malcolm Green, Alan Orpin, Terry Hume

Victoria: Lionel Carter

NCSU: Neal Blair and Lonnie Leithold

 

Field Methods, Equipment, and Vessels: The proposed study combines field observations (see table) and models to elucidate sediment dynamics and resulting stratigraphy.  Bottom-boundary layer measurements of resuspension and transport due to waves and currents will be made under a range of forcing conditions on the inner and middle shelf using near-bottom tripods.  An instrument array moored along-shelf on the ~30 m isobath will complement the bottom boundary measurements.  Seabed sampling and measurements will document deposition from the initial flood pulse as well as the subsequent redistribution of material by waves and currents, and examine both the fine-scale stratigraphy developed over a flood season and longer-term accumulation and stratigraphic signatures.  We expect to find evidence in the seabed of the massive increase in sediment discharge resulting from European deforestation.  All of these observations will be used to calibrate analytical and numerical models of sediment transport and deposition that will be refined to test emerging hypothesis of transport processes, and to extend the observations to longer spatial and temporal scales.

Field equipment included the EM1002 Swath Bathymetric System, Chirp 512i, 3.5 kHz pinger, kasten, box, and multi-corers, and x-ray device. 

Research Vessels used were the RV Tangaroa (08/2003) and the RV Kilo Moana (05/2004). 

 

RV Tangaroa
RV Kilo Moana