• Executive Summary
• Summary of Existing Knowledge and Gaps
• Implementation Plan
• Phase I - Immediate Needs
• Phase II - Mid-term Needs
• Phase III - Long-term Needs
• Appendix
• Uplands Conceptual Model
• Printable version of this report

Executive Summary

Most humans live on and utilize the continental margin, the surface of which changes continually in response to environmental perturbations such as weather, climate change, tectonism, earthquakes, volcanism, sea level, and human settlement and land use. Part of the margin is above sea level, the rest is submarine, but these land- and seascape components are contiguous, and material transport from source to sink occurs as a continuous but varying cascade. The margin responds to environmental perturbations by changing the nature and magnitude of a variety of important functions, including: soil formation and erosion; biogeochemical functioning (especially the storage and release of water, limiting nutrients and contaminants); and the form and behavior of geomorphic components from hill slopes and floodplains through the coastal zone to the continental rise. Whereas some areas of the margin are eroding (e.g., hill slopes), others accumulate sediment (e.g., terraces, tectonic basins, continental slope and rise), which records the history of surface changes.

A major goal of the Earth Science community is to provide quantitative explanations and predictions of the effects of perturbations on surface environments and on the geologic record preserved in sedimentary strata of continental margins. In past decades, margins have been investigated piecemeal, by researchers who have tended to focus on a particular segment (from a disciplinary perspective), and eschewed the broader perspective of the margin as an interconnected whole. Recognizing this shortcoming, the National Science Foundation (NSF) has initiated the MARGINS Source-to-Sink (S2S) program that, for the first time, will attempt to understand the functioning of entire margin systems through dedicated observational and community modeling studies. Following input from the Earth science community, the Waipaoa Sedimentary System (WSS) of the North Island, New Zealand, was chosen as one of the focus sites for possible study (see MARGINS Source to Sink science plan for selection criteria and rationale: http://www.ldeo.columbia.edu/margins/S2S/S2Ssciplan02.html).

A workshop held in Gisborne, Palmerston North and Wellington, New Zealand, May 4-9 2003, visited the Waipaoa area and discussed the existing knowledge base and outstanding questions in order to develop a comprehensive research plan. Forty scientists participated, roughly half each from the US and NZ, including: geomorphologists, geologists, oceanographers, geochemists and hydrologists. The workshop presentations and working group reports, which outline MARGINS S2S research opportunities in the WSS, is on a living workshop website (http://www.vims.edu/margins/workshop.html). For practical purposes, working groups addressed Uplands, Flood Plain/Coast, Shelf and Slope environments, and their various interconnections. Some of the highlights follow.

The Uplands group concluded that the overarching research goal should be to understand and predict the mechanisms and rates of surface geometry change in response to environmental perturbations. A difficulty in previous attempts in other areas has been the sparseness of land-surface age indicators that could be used to calibrate and test predictions of rates of change. The WSS has one of the highest densities of age indicators to be found worldwide. These exist as dated bedrock terraces, widespread tephra, and radiocarbon-dated sediments in landslide-dammed lakes, bogs, and oxbow lakes. Given the rich existing database, we can attempt to construct a quantitative model of sediment generation, storage and transfer that will: 1) summarise effects of the dominant perturbations on the history of sediment delivery to the flood plain and coast since the Last Glacial Maximum (LGM) and, 2) make quantitative predictions of sediment delivery for various scenarios envisioned for the future WSS, or for other similar systems.

The Flood Plain/Coastal group focused on understanding the mechanisms controlling sediment transfer across the land/sea interface. This interface links source and sink, and is perhaps the most dynamic and sensitive component of the entire dispersal system. It records responses to climatic, eustatic, tectonic and anthropogenic forcings at a range of spatial and temporal scales. The WSS is an ideal site to investigate these key mechanisms because it: 1) has loud, well-documented terrestrial signals from the uplands that are forced by clearly defined natural and anthropogenic drivers; 2) for the past 7 kyr has a littoral system confined in a subsiding basin, which has experienced incremental increases in accommodation space; 3) has a well-constrained (both spatially and temporally) progradational record; and 4) provides the opportunity to investigate a variety of dispersal mechanisms (such as the change from a braided to meandering channel that subsequently has been modified by flood control works, and the importance of surface plumes and hyperpycnal flows) over time.

The Shelf group examined the question of what determines dispersal and deposition on a high-discharge, basin-filling shelf? A fundamental building block of the margin stratigraphic record is the clinoform, which tends to be scale invariant. Preliminary observations from the Waipaoa shelf suggest that such building blocks are absent. Thus a key question is how are the processes affecting strata on the Waipaoa shelf distinct from those producing clinoforms? The answer is fundamental in deconvolving the relative roles of climatic, tectonic, eustatic and even anthropogenic forces from the preserved stratigraphy. Furthermore, conceptual and numerical models developed from this new understanding will allow us to predict sedimentary facies relationships (e.g., porosities, permeability networks) for reservoir characterization and resource assessment. A second question concerns how the signal of storm-generated sediment input is modified during transport and preserved in the shelf sediment record? The high discharge and storm-frequented Waipaoa shelf provides an opportunity to resolve the impact of storms, and relate those to natural and anthropogenic perturbations affecting the terrestrial part of the Waipaoa system. Observation of modern events passing through the terrestrial catchment and onto the shelf basin will provide an insight into event transformation through a range of settings. We will utilize a high resolution, 6500 year-old record of storm events from nearby Lake Tutira, and longer records (to ~30ka) from other upland lake sediments. This will allow direct comparison between terrestrial storm signals and those preserved on the continental shelf. Thus, we can evaluate those events preserved offshore and the reasons for their preservation as derived from process-based and paleoenvironmental data. Such information, coupled with the model outputs, become immediately relevant with respect to predicting the response of the shelf, and indeed the entire WSS, to intense ENSO cycles and increased storminess as projected for the Southern Hemisphere by the Intergovernmental Panel on Climate Change.

Globally, small mountainous drainage basins comprise a major component of active margin systems. Continental shelves and slopes may be the major depocenters for terrestrially derived material at most stages of sea level. In these settings, sources and sinks are tightly coupled, adjusting quickly to environmental changes. The Slope Group posed the question do large sediment inputs associated with high-standing, easily erodible drainage basins quickly overwhelm the storage capacity of the adjacent shelf, leading rapidly to off-shelf sediment transfer? Furthermore, the slope group addressed the question are sediment-gravity flows a significant mechanism of off-shelf transport in flood-dominated, anthropogenically altered dispersal systems? Deforestation, agricultural activity, and river management have significantly augmented the already large flood loads, in some cases increasing sediment discharge to the shelf by as much as 4-5 fold. Highly turbid river floods can generate sediment gravity flows on continental margins that are capable of rapidly moving sediment and associated materials seaward beyond shelf depocenters.

Finally, the Slope group asked if intraslope sources dominate slope sediment flux on an actively deforming margin? Despite the potentially large river sediment supply from the shelf, the slope today shows an abandoned canyon system and slope basins overprinted by numerous gullies, slumps, and avalanches. This margin features regular earthquakes, deformation from tectonic erosion, products from volcanism and elevated pore pressures. Slope processes may be dominated by sediment-tectonic interactions that buffer the terrestrial signal, and now bypass the canyon.

Workshop participants concluded that a major increase in our understanding of the linkages between the various components of margin system most likely will be accomplished through coordinated observational and modeling activities. The ability to model changes in the WSS since the LGM is key to the success of this component of the MARGINS S2S program. The WSS offers the modeling community a first-time opportunity to approach closure on a sediment budget through time (Late Quaternary) and space (an entire S2S basin). It also presents an early opportunity to develop the first suite of linked Community Sediment Models (CSM). The advantage of the Waipaoa is that it represents a relatively simple setting to model the modulation of forcing signals (climate, eustatic, tectonic and human) across a near-complete spectrum of sedimentary environments. This is enhanced by a large database for model calibration or verification for future CSM initiatives. Finally, from a geologic perspective, the study offers a tantalizing opportunity to solve the inverse problem of stratigraphic interpretation - in other words getting the billiard balls back onto the pool table.

Summary of Existing Knowledge and Gaps

Uplands - A key goal of uplands research is to develop predictive models for sediment output to Poverty Bay Flats with respect to the dominant environmental perturbations since the LGM. Although a good understanding now exists for some of the extant sub-environments (e.g., gullies), others need further observational study and incorporation into transport models. Of particular high priority is an improved understanding of hillslope and terrace evolution, storage and transport in shallow colluvial deposits, and the throughput and temporary storage along the transport pathways. In order to provide realistic boundary conditions for model runs, the initial landsurface geometry needs to be determined. Modeling the Upland area should initially proceed as a series of empirical efforts as data gathering and assimilation proceed. This will depend heavily on age control estimates from landscape indicators. The modeling should eventually evolve towards more theory-based efforts and the generation of digital elevation models through time.

Poverty Bay / Flats - The lower floodplain is a particularly sensitive indicator of environmental change in the mid-late Holocene. The shoreline has prograded ~20km across Poverty Bay Flats during the past ~7ka, and hence the Flats potentially contain a high-resolution record of varying sediment inputs. Basic surface and subsurface characteristics of the flats have been established (see Appendix), and the major effort here would be to provide high-resolution subsurface data on the geometry and ages of the flats over time. This would also serve to provide changing shoreline boundary conditions for modeling efforts.

Poverty Bay/Flats represent the gateway for sediments delivered from the uplands to the open shelf. While there is a basic knowledge of Bay sedimentation, major events such as floods and subsequent sediment segregation and transport in the Bay have not been characterized. Therefore, observational studies are needed to understand how sediment initially delivered to the bay is transported both seaward (effecting offshore delivery), and landward (effecting shoreline progradation).

Shelf - The Waipaoa shelf represents the most significant repository of sediment during the past ~10ka. Rapid tectonic subsidence in the mid-shelf area has created significant accommodation space, yielding a relatively thick (~45m max.) and hence high-resolution Holocene record. Scattered core and some geophysical (subbottom) data have been collected and analyzed to provide a basic understanding of the shelf deposit. An important goal here will be to generate detailed bathymetry (swath) data for shelf sediment transport and modeling studies. Moreover, the evolution of the shelf mud deposit over the mid-late Holocene to present, especially its response to varying scales of terrigenous input, will need to be determined through systematic coring (shipboard as well as IODP shallow-water drilling) and geophysical studies. In order to provide input to model development of shelf sediment transport, additional physical oceanographic observations ultimately will be needed.

Slope - Recent work on the continental slope off the Waipaoa River suggests that it could represent a major sediment sink throughout the sealevel cycle. Extensive existing swath and MCS data and a suite of piston cores provide a solid framework in which to address questions of potential escape of modern sediment to the slope. An important goal here will be to evaluate recent sedimentation patterns on the slope, and to discriminate inputs from shelf bypassing versus intra-slope supply. This should be accomplished through coring and chirp surveys, and the development of models that can incorporate the various sediment sources as they change in response to river input, sea level, paleocirculation and sediment-tectonic interactions.

Implementation Plan

MARGINS research in the Waipaoa focus area will need to integrate modeling and observational studies in order to answer outstanding questions regarding how the system operates and ultimately to be able to predict how sediment is transported from source to sink. Modeling studies should commence relatively early, using the existing data to begin testing hypotheses throughout the source-to-sink system. At the same time, significant knowledge gaps have been identified that can only be addressed through observational studies that should also begin early in the study. As the program matures, new observational knowledge will have to be incorporated into developing models, and models will have to be refined to be consistent with these observations. At the same time, model predictions can also be tested through dedicated observational experiments, and hence the latter phase of the project will require ever closer coordination of modeling and observational studies. Priorities for Waipaoa studies are listed below, and are divided into immediate, mid- and long-term needs.

• Commence modeling studies of sediment generation, delivery, and accumulation including the full dynamic range of forcing functions since the LGM using existing databases.
• Conduct uplands studies to document hillslope and terrace evolution, and sediment throughput to Poverty Bay Flats using coupled landscape modeling and field investigations. Sediment monitoring at Pikes Weir and Matawhero to document sediment texture and load reaching the ocean.
• Determine the stratigraphic evolution of Poverty Bay Flats through geophysical studies, land-based borings and age dating.
• Provide detailed bathymetric and seabed data (swath including backscatter) from both Poverty Bay and Shelf.
• Determine historical and Holocene patterns of shelf and slope sediment distribution and fine-scale stratigraphy through Chirp profiling, coupled with short coring and age dating.

Phase II - Mid-term Needs

• Conduct coupled modeling and observational process studies on sediment segregation and transport in Poverty Bay and open shelf.
• Integration of Phase I observational knowledge into modeling efforts.
• Perform focused field observations in all sectors as necessary to test model predictions.

Phase III - Long-term Needs

• Stratigraphic documentation of high-resolution Holocene shelf mud deposit through IODP shallow-water drilling efforts.
• Modeling efforts that integrate across the entire source-to-sink system.
• Generalization of models to similar sedimentary systems worldwide.
• Application of results to key environmental and societal issues, in particular the response of terrestrial and marine systems to climate change scenarios as projected by IPCC.

APPENDIX

Outline of Existing Data and Data Gaps

Uplands

Poverty Bay/Flats

Data Base

• Water Well Logs ~300 (~50 detailed logs) - GDC/GNS
• National Petroleum Data Base (limited seismic lines) - GNS
• Radiocarbon data (wood/shell) - GNS
• National Fossil Record - GNS/GSNZ
• DEM (0.5 m) - GNS
• Q-map 1:250,000 Geology (GIS layer) - GNS
• Holocene Terraces (GIS layer) - GNS
• Pollen and shell- Landcare
• Archaeology - DOC
• Bibliographies - GNS/Landcare/NIWA
• Soil Chronosequences - Landcare
• W4 core (last 6.5 kyr) and other floodplain cores - Landcare
• Water and Sediment Guaging Records (Kanakanaia/Matewhero/Goodwin Road/Pikes Weir, limited bedload) - GDC/NIWA
• Estimates of flood peaks (>60 yr) - GDC
• Channel Cross Sections (0.5 mile interval, 1948 to present) - GDC
• Hydraulic Model (Mike11) - GDC/U. Auckland
• Water quality (Kanakanaia, monthly present; Gisborne Water Supply Catchment) NIWA/GDC
• Land Capability Survey (1994/5, GIS layer) - Landcare
• Aerial Photographs (1939 - 1938, historical oblique photographs) GDC/Landcare
• Historical shoreline and beach profiles and historical maps - GDC/NIWA
• Rainfall records (~1880 - present) - GDC
• Climate data - NIWA/Landcare GDC
• Long term tide gauge record - GDC
• Tidal model of NZ - NIWA
• Poverty Bay bathymetry/circulation model/bottom sediment - NIWA/U. Waikato/GDC
• Wave climate (Wainui beach, 20 yr hindcast wave model for NZ) - NIWA
• Intermittent 3.5 kHz sidescan sonar survey - U. Waikato
• Miscellaneous surface cores

Gaps

• High-resolution subsurface data on Poverty Bay Flats and nearshore
• Structural setting of Poverty Bay Flats
• Continuous Suspended Sediment data at Matawhero
• Total river load at Matewhero
• Sediment budget of Poverty Bay (input, output and output source terms)
• Late Holocene disposition of flats, shoreline and mouth
• High-resolution bathymetric, backscatter and oceanographic data from Poverty Bay to inner shelf.

Filling The Gaps

• High-resolution subsurface data on Poverty Bay Flats and nearshore GPR, high-resolution seismic and Chirp surveys, borehole ground truth
• Structural setting of Poverty Bay Flats Seismics and borehole ground truth
• Continuous Suspended Sediment data at Matawhero (& Pikes Weir) Optical turbidity sensors, auto-sampling, salinity, temperature
• River load at Matewhero
• Depth integrated and point suspended sediment sampling and bedload sampling
• Sediment budget of Poverty Bay (input, output and output source terms) Near- river mouth and bay instrumented tripods, high-resolution swath bathymetric surveys, inner shelf oceanographic data
• Late Holocene disposition of flats, shoreline and mouth Seismics and borehole ground truth (deep core near coast)
• High-resolution bathymetric and inner shelf oceanographic data --> Sediment budget, residence times

Shelf

Data Base

Geophysical

• Single beam, naval hydrographic quality bathymetry to upper slope (1980s) -NZ Navy/NIWA
• 3.5 kHz using DGPS early 1990s ~ 4-5 km across-shelf line spacing ~10 lines along shelf - NIWA
• Uniboom, but problems with gas masking - NIWA
• High quality structural information based on multi-channel seismics - NIWA/GNS/U. Canterbury

Water column

• 1.5 year record of wave height and period (1980s) -NIWA
• Limited current velocity measurements shipboard ADCP and currents- NIWA/U. Waikato
• CTD casts at anchor stations (turbidity)- NIWA
• Circulation in Poverty Bay - U. Waikato thesis

Models

• Tide model - NIWA
• Global wave model - NIWA & ECWMF
• Global run of NCOM model - NIWA
• Regional scale couple model (MOMA) that could be modified to include sediment transport -NIWA

• Radioisotopes on scattered multicores and piston cores
• 210Pb at 56-m, 70-m and 90-m - VIMS, NIWA
• Across shelf piston cores (palynology, tephra, physical properties) - NIWA, Landcare, GNS
• Surface sediment samples (samples are archived) - NIWA
• Giant Piston Core [MD2122] with suite of geochemical and textural parameters - Landcare, Indiana State, NIWA
• Organic carbon analyses - Landcare, NIWA

• TOPEX- all routinely collected by NIWA receiver station, Wellington
• Modis
• SeaWifs

• High resolution multibeam and seismics out to shelf break
• Physical oceanographic and satellite observations
• Sediment core samples: improved spatial coverage, targeted objectives
• Inter-glacial time scale chronology: long cores, C14 dating
• Observations and modeling active transport processes that exchange sediment between Poverty Bay, the shelf and beyond

Slope

Data Base

Geophysical

• EM300 + backscatter - NIWA,
• EM12D + backscatter -IFREMER, NIWA
• 1000 km of 3.5 kHz (of variable quality) - NIWA
• 200+ km of MCS (good quality, reprocessed) - NIWA

Seabed Samples

• ~1 dozen piston cores - NIWA
• 3 multicores with Pb-210 and ash stratigraphy - VIMS, NIWA
• 2+ dredges with nannofossils - NIWA

Oceanographic Data

• 4-5 CTDT casts upslope from Hikurangi Trough - NIWA
• 2-3 ADCP Anchor stations on shelf break; one a Poverty Gap w/ CTDTs -NIWA
• Satellite data - SST, visible, dynamic height, etc. -NIWA
• Oceanographic mooring nearby - NIWA

Filling the Gaps

• Identify zones of active deposition through coring w/ Be-7, Pb-210, Cs-137 and tephra chronology
• Chirp sonar coverage
• Evaluate modern sediment supply and escape through observations and modeling
• Determine importance of intra-slope transport with geophysical, coring and modeling efforts
• Evaluate tectonic-sediment interactions over short- and long- (pre-Holocene) timescales as above