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The interpretation of depositional environments and evaluation of potential source rocks in deepwater frontier basins are challenging because of the limited data availability. The Deepwater Taranaki Basin, the northwest extensional area of the Taranaki Basin in New Zealand, hosts the Late Cretaceous Rakopi Formation, which is one of the most important source rocks and potential reservoirs in the Taranaki Basin. This study utilized seismic data and well ties from the Romney-1 well to interpret three seismic units in the study area, representing different depositional environments and evolutions. These units were correlated with the regional Megasequences B2–B4 in the Deepwater Taranaki Basin. Sediment transport and progradation mainly occurred from the northeast to the southwest direction. Fluctuations in relative sea levels influenced the shifting of the shelf and marginal environments, potentially creating coal-bearing strata in the study area. The key source rock strata were identified within units 2 and 3 characterized by kerogen type III, coaly source rocks in a marginal environment. A minor source rock interval was found in unit 2, characterized by kerogen type II, marine organic matter in a bathyal environment in the depocenter of the study area. Coal seams were identified using seismic and well log data. However, thin coal seams were challenging to distinguish clearly, sometimes showing a similar response to sandstone beds, because of the limited seismic resolution. Thus, within limited data areas, source rock predictions can be made in the context of depositional interpretation. • Depositional environments and potential source rock can be interpreted by available seismic and well data. • Depositional environments can be correlated with the regional Megasequences B2 to B4. • The key source rock strata were identified within units 2 and 3 characterized kerogen type III. • Due to limited geochemical data, source rock predictions can be made in the context of the depositional interpretation. [ABSTRACT FROM AUTHOR]

Sediment transport and resuspension are essential processes in soft-sediment environments that mediate shellfish population dynamics, water column turbidity, and estuary geomorphology at multiple scales. Adult cockles, Austrovenus stutchburyi (in New Zealand), are key organisms on intertidal sand flats that influence sediment properties, and their removal could impact the stability of the seabed and affect crucial feedback processes in this system. We conducted a field experiment to explore our hypothesis that the loss of adult cockles will increase sediment transport and resuspension non-linearly. Changes in sediment transport regimes will then influence the properties of sediment such as grain size, organic content, and chlorophyll a content. We also expected that the direction and magnitude of this effect would depend on the varying environmental characteristics across the sites, such as hydrodynamic activity and sediment grain size. We excluded adult cockles from 3 × 3 m intertidal plots at 15 sites across a natural adult cockle density gradient (300–3500 ind/m2). After seven months, sediment traps were deployed in exclusion and control plots to measure the sediment transported over two tidal cycles associated with the bedload and water column with differing densities of adult cockles. Adult cockle density was a significant predictor in all models to explain sediment transport and accounted for the largest proportion of variability explained. Relationships between cockle density and sediment transport changed between sites and over time. In these situations, simple linear relationships were not always apparent due to the interacting effects of cockle density, hydrodynamic process, and sediment characteristics. The influence of adult cockles on sediment transport was also affected by the standing stock of microphytobenthos and interacted with the mud content in their surrounding environment. Our study demonstrates the existence of an important feedback between adult cockle density, sediment stability and sediment transport that is mediated by hydrodynamic processes and sediment characteristics. • We used traps to measure sediment transport across a cockle density gradient. • Changes in adult cockle densities alters sediment stability non-linearly. • Adult cockles interact with their environment to drive sediment transport processes. • Sediment transport is highly context-dependent, influenced by physical processes. [ABSTRACT FROM AUTHOR]

Shore platforms are generally supply-limited environments and few studies have attempted to measure sediment transport within this rock coast setting. This paper summarises a field-based pilot study that successfully collected fine-grain sediment moving across a sub-horizontal platform at Mudstone Bay, Kaikōura, New Zealand. Two large-aperture and two small-aperture Time-Integrated Mass-sediment Samplers (TIMS) were deployed for 9-days, encompassing 2 days of storm conditions (offshore significant wave heights between 2.0 and 3.6 m, with sediment trapped in both landward and seaward facing directions. The net flux of sediment captured in large aperture samplers was greatest in a seaward-direction (15.2 g), whereas the narrow-mouth samplers, that principally collected suspended sediment had a net onshore flux (5.4 g). The sediment traps yielded sufficient sample to undertake geochemical and textural analysis. Interpretation of these data suggests that the origin of transported material was autochthonous to the platform, being >80 % silt-sized and compositionally consistent with material derived from the shore platform and/or cliff colluvium. This pilot experiment demonstrates that mass-sediment samplers can be used in supply-limited intertidal shore platform settings. Further research involving greater sampling frequency and duration and concomitant detailed hydrodynamic measurements are likely to reveal important insights into the erosion environment. • TIMS can be used on an intertidal shore platform to collect saltating and suspended sediment in bi-directional flow. • Sediment caught in sufficient amounts to conduct provenance and geochemical analysis • Storm conditions were most favourable to collect both saltating and suspended sediment at Kaikōura. [ABSTRACT FROM AUTHOR]

Submarine canyons, channels and gullies are conduits that transport sediments across shelf-slope margins to deep water. In South Taranaki Basin, an increase in sediment supply through the Miocene resulted in progradation and significant steepening of the slope system. Previous studies have identified numerous sediment conduits developed within this system, however their morphology and morphometric relationships with the depositional slope have not been considered. Here we apply seismic geomorphology to establish the statistical relationships between the metrics of sediment conduits at three stratigraphic intervals between which the slope gradient progressively increased. In the early-Middle Miocene, sinuous upper Moki Formation channel complexes with an average width of 1.1 km developed on a slope with an average gradient of 0.2o, routing sediment from south to north. By the late-Middle Miocene, the slope began to prograde rapidly, concurrent with a regional reorientation of the slope to the northwest, on which the lower Mount Messenger Formation canyon networks developed with a slope gradient of 0.4–1.0o. At shallow slopes of less than 0.5o, canyon morphometrics (mean width 6.6 km) are 1.8–4.7 times larger than on related upper slopes with gradients steeper than 0.5o (mean canyon width of 2.7 km). This significant shift in morphometrics occurs abruptly across the clinoform toe line. Rapid Late Miocene slope progradation resulted in the development of steep clinoform slope surfaces up to 9o, into which linear upper Mount Messenger Formation gully complexes incised. The mean gully width throughout the Middle to Late Miocene interval decreased from 1.3 km to 1.0 km as the slope gradient became steeper. This study documents how the morphology and morphometrics of sediment conduits on the South Taranaki Basin slope system changed through time in relation to changes in depositional slope gradients. • Seismic geomorphology used to quantify the Miocene sediment conduit morphometrics. • Sinuous channel complexes in the upper Moki interval. • Large canyon networks dominate lower the Mount Messenger interval. • Numerous linear gully complexes represent the upper Mount Messenger interval. • Increase sediment supply resulted in basinward progradation slope system. [ABSTRACT FROM AUTHOR]

The formation of the geologic record offshore of small mountainous rivers is event-driven and, more so than many other environments, can result in relatively complete sequences. One such river, the Waipaoa in New Zealand, has been studied from its terrestrial source to its oceanic sink over timescales spanning storms, seasons, and the Holocene. This study focused on the formation of riverine deposits on the Waipaoa Shelf during episodic flood and wave events, contrasting deposition during short-lived events to accumulation patterns created over thirteen months. Sediment fluxes and fate were estimated using the numerical hydrodynamic and sediment transport model ROMS, the Regional Ocean Modeling System, using CSTMS, the Community Sediment Transport Modeling System. During the study period (January 2010–February 2011), the model indicated that initial flood deposition generally occurred near the river mouth and along the coast in water shallower than 40 m, and that deposition during any one event was sensitive to variations in shelf currents and wave energy. Also, the sedimentation due to plume settling and suspended transport during these relatively short flood and wave events were not aligned with longer time-scale accumulation patterns (months or greater) previously reported for the Waipaoa shelf. In the days to months following a flood pulse, waves episodically reworked this initial deposit, resuspending centimeter-scale layers of sediment during energetic periods. Frequent and intense resuspension occurred in shallow areas where bed stresses were high. This encouraged redistribution of material toward deeper areas having lower near-bed wave stresses, including continental shelf depocenters and offshore areas. While fast settling material was preferentially retained near the river mouth, currents dispersed slower settling sediment farther before deposition. Overall, accumulation depended on characteristics of oceanographic transport (wave energy, current velocities), not just source characteristics (flood size, sediment size distribution). [ABSTRACT FROM AUTHOR]

A one-year study examining water-column and near-bed time-series observations from benthic-boundary-layer tripods was undertaken in the Waipaoa Sedimentary System (WSS) on the Poverty Bay continental shelf, offshore of the Raukumara Ranges, New Zealand. Here, the nature of the adjacent post-glacial shelf deposits, fed by the Waipaoa River, and century-scale sediment accumulation is well established, but event-scale sediment dispersal and hydrodynamics had not been measured. Data from two tripods outfitted with acoustic and optical instrumentation, and x-radiograph images of seabed cores collected at 4-month intervals, were analyzed to quantify progressive sedimentological changes, and to document processes responsible for seabed strata formation, destruction, and preservation. At the Northern Tripod (NT) mid-shelf location 15 km southeast of the river mouth, we observed increases in near-bed suspended sediment concentration when shear velocities exceeded 0.03 m s −1 on 33 occasions over an 11.5-month period. Of these events, 9 were depositional, 10 were erosional, and 14 had no bed-elevation change at the 1-cm resolution of our instrumentation. Relatively high (2–5 m) and short-period (<11–12 s) waves, combined with current velocities <0.15 m s −1 , led to deposition on the seabed. Smaller-height (2–3 m) and longer-period (11–13 s) waves with stronger current velocities (>0.15 m s −1 ) typically induced erosion. Despite the short reach of this mountainous riverine dispersal system, we observed a consistent delay between river discharge and apparent deposition on the mid-shelf at the NT location. Following the three largest floods, ~120 h of strong, wave-driven bed shear stress preceded measurable deposition on the mid-shelf, suggesting that event duration and intensity are key for transporting material offshore from Poverty Bay. The largest flux event recorded over the study year was a 130-hour-long storm and associated river flood that resulted in near contemporaneous deposition at the NT site. Suspended-sediment concentration data suggest transport by a wave-supported fluid mud. X-radiographs from the NT location corroborate the instrumental record of 5 cm deposition, but only the two largest depositional events were preserved in the strata. On the southern shelf we observed no evidence of deposition in either the instrumental data or in the x-radiographs of cores. This study suggests that event duration, and spatial and inter-annual variability are critical considerations when evaluating along- and across-shelf sediment transport and seabed stratigraphic evolution associated with discharge from small mountainous rivers. [ABSTRACT FROM AUTHOR]

The Waipaoa River Sedimentary System in New Zealand, a focus site of the MARGINS Source-to-Sink program, contains both a terrestrial and marine component. Poverty Bay serves as the interface between the fluvial and oceanic portions of this dispersal system. This study used a three-dimensional hydrodynamic and sediment-transport numerical model, the Regional Ocean Modeling System (ROMS), coupled to the Simulated WAves Nearshore (SWAN) wave model to investigate sediment-transport dynamics within Poverty Bay and the mechanisms by which sediment travels from the Waipaoa River to the continental shelf. Two sets of model calculations were analyzed; the first represented a winter storm season, January–September, 2006; and the second an approximately 40 year recurrence interval storm that occurred on 21–23 October 2005. Model results indicated that hydrodynamics and sediment-transport pathways within Poverty Bay differed during wet storms that included river runoff and locally generated waves, compared to dry storms driven by oceanic swell. During wet storms the model estimated significant deposition within Poverty Bay, although much of the discharged sediment was exported from the Bay during the discharge pulse. Later resuspension events generated by Southern Ocean swell reworked and modified the initial deposit, providing subsequent pulses of sediment from the Bay to the continental shelf. In this manner, transit through Poverty Bay modified the input fluvial signal, so that the sediment characteristics and timing of export to the continental shelf differed from the Waipaoa River discharge. Sensitivity studies showed that feedback mechanisms between sediment-transport, currents, and waves were important within the model calculations. [ABSTRACT FROM AUTHOR]

Abstract: A distinctive deposit of unaltered reworked volcaniclastic sediment, here designated the Kiwikiwi Formation, is described from the upper Whangaehu Valley at Mount Ruapehu, New Zealand. The grain-size distribution and sedimentary features of the unit suggest deposition from a sheetflow-dominated alluvial system, but simple sediment entrainment calculations show that the unit''s granulometry is inconsistent with normal streamflow deposition at the observed steep depositional slope. Streams have produced deposits at Mount St. Helens and Mount Pinatubo under similarly anomalous conditions following debris avalanche and/or volcanic eruptions, when highly charged with sediment and subject to common lahars (debris flows and hyperconcentrated flows). Reported sediment transport rates from Mount St. Helens'' Toutle River, and Pinatubo''s Pasig–Potrero River, show that a virtually unlimited supply of relatively fine-grained (sand-range) tephra renders some established sediment transport formulae inapplicable because the volume of available material effectively exceeds the transport capacity of the system. We use simple equilibrium flow calculations to demonstrate that this sedimentary unit, which has open porosity, framework grain support and bedding characteristics compatible with alluvial sheet flows, would not have been deposited under normal streamflow conditions. This approach provides a means to confirm the role of capacity limitations on stream behaviour during the post-eruptive sedimentary response phase in catchments overwhelmed by pyroclastic material, and is particularly useful given the lack of clear depositional fingerprints for hyperconcentrated flow. We further infer that because the material in the Kiwikiwi Formation is uniform, unaltered and minimally abraded, differs from older sediment in the valley, overlies a 4.6ka debris-avalanche deposit, and was emplaced from an over-capacity stream by hyperconcentrated flows or extremely thinned ones, and without evidence of interruption, it represents the previously unidentified proximal products of an unstudied Holocene eruption of Ruapehu. [Copyright &y& Elsevier]

Abstract: The Darfield earthquake caused widespread damage in the Canterbury region of New Zealand, with the majority of damage resulting from liquefaction and lateral spreading. One of the worst hit locations was the small town of Kaiapoi north of Christchurch, an area that has experienced liquefaction during past events and has been identified as highly susceptible to liquefaction. The low lying town sits on the banks of the Kaiapoi River, once a branch of the Waimakariri, a large braided river transporting gravelly sediment. The Waimakariri has been extensively modified both by natural and human processes, consequently many areas in and around the town were once former river channels. Using historical accounts and maps of the region, areas of land reclamation and old channels that had been cut off from the river since the beginning of European settlement in the 1850s were identified. These areas correlated well with many of the areas having significant liquefaction damage following the Darfield event. Substantial lateral spreads and sand boils developed in areas of reclamation along the current river path, causing significant damage to stopbanks and structures along the river, with fissures up to 2m deep and 1m wide. Much of the residential housing was damaged by lateral spreading, with cumulative displacement offsets up to 3m parallel to old channel beds that had aggraded over time due to river shifts. In former channel areas that were free of lateral spreading, large volumes of ejecta were present over wide areas, with depths of up to 400mm in places. Houses in these regions were damaged as a result of settlement and tilting. In all these areas underground services and roadways were severely impacted as a result of ground deformation. The severity of this damage indicates the importance of knowing the location of old channels when defining liquefaction prone regions. [Copyright &y& Elsevier]

Abstract: Few large-scale field measurements of longshore sediment transport have been undertaken on beaches composed of coarse sediments, in part owing to difficulties associated with measurement in energetic swash zones in which large clasts are moving. Here we present results from a field experiment in which Passive Integrated Transponder tags were used to investigate patterns of cobble transport over 8months on a mixed sand and gravel beach on the east coast of New Zealand. The study objectives were to document rates of alongshore transport, and measure rates of cobble abrasion under field conditions. Cobble recovery rates were highly variable over the study period with 30–60% recovery at site 1 compared to much lower (0–20%) recovery rates at sites 2 and 3. Consistent uni-directional patterns of net alongshore sediment transport were observed. The median cobble transport rate was approximately 500m over 207days, indicating long-term net northward transport rates on the order of 2–2.5m/day. Results highlight a number of factors, in addition to longshore energy flux, that are important for understanding the observed patterns. In particular, across-shore sediment transport during storms may have been smaller at site 1 than the other sites owing to lesser wave exposure. This is partly responsible for higher cobble recovery rates at this site and also an increased amount of time during which cobbles were able to be transported alongshore on the lower beachface. Unique to this study, results demonstrate the use of PIT tags to provide direct measurement of cobble abrasion under natural processes. Repeat weight measurement on individually tracked cobbles show that after 207days the median loss was 11.3g, or 1.8% of total weight. There was a general trend of abrasion increasing with net transport distance, but longshore cobble movement was highly variable ranging from 130 to 2500m. [Copyright &y& Elsevier]

Abstract: Connectivity between an actively eroding gully complex and upper Waipaoa catchment via a steep, 1-km-long alluvial fan is assessed using digital elevation models (DEMs) of the Tarndale fan derived from 10 high resolution GPS surveys between 2004 and 2008. Repeat DEM analysis provides a means of assessing transfer of sediment supplied from the Tarndale gully through the fan to the Te Weraroa Stream and thus inferring connectivity between these landscape components from which a conceptual coupling model is derived. Analysis indicates the operation of two critical junction switches at the (i) gully–fan and (ii) fan–stream nexus, which contribute to considerable complexity in patterns of erosion and deposition on the fan as it responds to sediment supply or starvation from the Tarndale gully and evacuation to the Te Weraroa Stream (described in Fuller and Marden, 2010). The fan does not respond as a coherent unit. Each of six fan feeder tributaries behaves independently according to sediment supplied from six discrete source areas within the gully complex. This reflects sediment production within specific activity zones of Tarndale Gully. Mass movements, triggered by single rainstorm events and/or wet periods contingent upon sediment availability and intrinsic slope mechanics, frequently deliver sediment to the upper fan tributaries. This enhanced gully–fan coupling during storms or wetter periods promotes rapid fan aggradation, with each feeder tributary responding to its discrete source zone. Infilling may propagate down fan in response to upper fan incision once the gully–fan switch deactivates, transferring sediment as far as the Te Weraroa Stream, coupling the fan with the stream system. Floods generated in the Te Weraroa Stream may also activate the junction switch at the fan–stream nexus by trimming the lower fan, prompting up-fan incision via head-cutting in response to changed local base level. Slope–channel coupling in this environment is a function of a range of slope and channel processes responding to discrete storms and intrinsic gully dynamics. The high rates of geomorphic activity in this environment mean the Tarndale system provides a natural laboratory in which to assess key slope–channel coupling processes beyond the plot or discrete event scale. [Copyright &y& Elsevier]

Abstract: Nearshore regions act as an interface between the terrestrial environment and deeper waters. As such, they play important roles in the dispersal of fluvial sediment and the transport of sand to and from the shoreline. This study focused on the nearshore of Poverty Bay, New Zealand, and the processes controlling the dispersal of sediment from the main source, the Waipaoa River. Hydrodynamics and sediment-transport in water shallower than 15m were observed from April through mid-September 2006. This deployment afforded observations during 3–4 periods of elevated river discharge and 5 dry storms. Similar wind, river discharge, wave, current, and turbidity patterns were characterized during three of the wet storms. At the beginning of each event, winds blew shoreward, increasing wave heights to 2–3m within Poverty Bay. As the cyclonic storms moved through the system the winds reversed direction and became seaward, reducing the local wave height and orbital velocity while river discharge remained elevated. At these times, high river discharge and relatively small waves enabled fluvially derived suspended sediment to deposit in shallow water. Altimetry measurements indicated that at least 7cm was deposited at a 15m deep site during a single discharge event. Turbidity and seabed observations showed this deposition to be removed, however, as large swell waves from the Southern Ocean triggered resuspension of the material within three weeks of deposition. Consequently, two periods of dispersal were associated with each discharge pulse, one coinciding with fluvial delivery, and a second driven by wave resuspension a few weeks later. These observations of nearfield sediment deposition contradict current hypotheses of very limited sediment deposition in shallow water offshore of small mountainous rivers when floods and high-energy, large wave and fast current, oceanic conditions coincide. Consistently shoreward near-bed currents, observed along the 10m isobath of Poverty Bay, were attributed to a combination of estuarine circulation, Stokes drift, and wind driven upwelling. Velocities measured at the 15m isobath, however, were directed more alongshore and diverged from those at the 10m isobath. The divergence in the currents observed at the 10 and 15m locations seemed to facilitate segregation of coarse and fine sediment, with sand transported near-bed toward the beach, while suspended silts and clays were exported to deeper water. [Copyright &y& Elsevier]

Abstract: Large marine algae such as kelp can, when dislodged, remove part of the substrate to which they are attached and subsequently transport it. Quantification of this process and the causes behind it have rarely been investigated. This study examines sediment transport by the kelps Durvillaea antarctica and Durvillaea willana in southeast New Zealand. Five beaches near Dunedin were surveyed weekly for 30weeks and all beach-cast kelp was counted and identified; the weight and nature of any attached sediment was also recorded. Additionally, 60 sections of the southeast New Zealand coastline (totaling 130km) were surveyed once and all beach-cast kelp examined. Rocks were found to be attached to 27% of examined holdfasts, usually occurring as a thin veneer. The weight per holdfast ranged from 0.1g to 83kg (with an unusual outlier of 365kg) with a mean weight of 77.1g (SE=15.3, n =1560). Most holdfasts transported less than 100g. Carbonate material occurred on 84% of holdfasts with weights per holdfast ranging from 0.02 to 116.56g with a mean of 7.8g (SE=0.3, n =1695). The character of local rock strongly influences the kelp-mediated flux: South Coast beaches with schist rocks nearby received a significantly greater mean flux (7.49g m2 year−1) than basalt-surrounded Peninsula beaches (mean flux 0.50g m2 year−1). Kelp-transported material provides a small but significant source of sediment to beaches in southeast New Zealand and therefore should be considered when constructing sediment budgets in coastal areas. This study has shown that it is often necessary for geologists to consider biological processes. [Copyright &y& Elsevier]

Abstract: The Waiapu River sedimentary system, New Zealand, provides a prototype for investigating the relative importance of wave- versus current-supported gravity flows on continental shelf deposition. A two-dimensional model was used to represent gravity-driven sediment transport and deposition on the Waiapu shelf over an annual cycle of storm events and associated Waiapu River floods. Model inputs of waves and wind-driven currents were derived from WAVEWATCH III hindcasts and constrained by benthic tripod data. The 12-month model run included a low-energy period (September 2003 to May 2004) with weak waves and currents and low river discharge, and a high-energy period (May to August 2004) with stronger waves and wind-driven currents and more frequent river floods. Model results suggested that during the low-energy period, riverine sediment was trapped between the 20- and 80-m isobaths. During the high-energy period, sediment was deposited obliquely across the shelf between the 60- and 120-m isobaths. The predicted deposit locations for the low- and high-energy periods, respectively, were consistent with short- and long-term observed accumulation patterns based on 7Be and 210Pb activity [Kniskern, T.A., Kuehl, S.A., Harris, C.K., Carter, L., 2010. Sediment accumulation patterns and fine-scale strata formation on the Waiapu River shelf, New Zealand. Marine Geology 270, 188–201]. Gravity flows were mainly wave-supported landward of the 60-m isobath, but became increasingly current-supported as wave orbital velocity attenuated in deeper water. Both analytical theory and numerical results indicated that wave-supported gravity currents were sensitive to local water depth and favored deposition parallel to isobaths as depth increased. In contrast, current-supported gravity currents were more sensitive to spatial variations in seabed slope, with seaward decreases in slope and along-shelf embayment of bathymetry favoring transport convergence and deposition. We conclude that the longer term (∼100yr) shelf-oblique mud deposit on the Waiapu shelf mainly reflects current-supported gravity flows responding to local variations in seabed slope and curvature of isobaths. [Copyright &y& Elsevier]

Summary: Lahars, and other sudden onset floods, are highly dynamic with temporally and spatially evolving sediment loads. Numerical models of sudden onset flood behaviour, particularly those applied to real world events, have tended to neglect sediment transport processes. This is a serious though perhaps understandable shortcoming given a lack of field measurements on flow-bed interactions, the extra computational complexity required, and the problem of iteratively updating ‘plastic’ channel boundaries. This paper applies a fluid dynamics model with suspended sediment and bedload transport to calculate flow conditions and rapid landscape change due to an initially dilute lahar from Mt. Ruapehu, New Zealand. We take advantage of an unprecedented dataset of net topographic changes determined from pre- and post-lahar airborne LiDAR surveys and time-series of hydrological measurements to run and validate the model. A sensitivity analysis of key controls on water surface elevation and final sediment thickness illustrates how the flow was supply-limited in the upper reaches. It was capable of transporting a greater volume and calibre of material than that available. Modelled patterns of net erosion and deposition can replicate those observed (r 2 =0.79) and are dominantly controlled by channel gradient and topographic confinement. Peak bed shear stress exceeded 9000Nm−2 in the Whangaehu Gorge, whilst rates of change of bed shear stress >600Nm−2 min−1 were modelled in the flow front. Of the total modelled in-channel erosion 3.36×106 m3, or 75%, was achieved between 10 and 40min of the event initiation. Most erosion occurred during the rising limb and peak of the lahar hydrograph, with 45% of total deposition occurring on the waning limb. Overall, the model offers new insights towards a mechanistic understanding of longitudinal, lateral and temporal evolution of hydrodynamics and volumetric changes within a lahar and therefore has considerable advantages for physically linking processes and products and for hazard management. [Copyright &y& Elsevier]

Abstract: Over the late Holocene highstand, the shoreline at Poverty Bay, NZ migrated 12km seaward, fed by sediment from the Waipaoa river. Paleo-shorelines indicate steadily decelerating progradation, possibly signaling changes in forcing on the Waipaoa Sedimentary System. To isolate the cause of this progradation slowdown we reconstruct late Holocene tectonics and stratigraphy over the Waipaoa coastal plain and nearshore from 7ka–present. We find that decreasing rates of sediment storage by coastal progradation were driven by increasing tectonic storage in the steadily subsiding but rapidly growing coastal plain, such that net terrestrial storage remained constant at ∼0.8Mt/yr. Hence changes in shoreline migration were due to autogenic increases in accommodation rather than allogenic changes in forcing. Furthermore, while the Waipaoa sediment load is primarily mud, reconstructions suggest that progradation was largely controlled by the supply of coarse-grained sediment. Our results suggest that in coastal systems such as the Waipaoa, where progradation is confined and wave energy is high, net accumulation of muds occurs only behind the prograding sandy shoreface, which shelters them from wave attack. Accounting for mud storage in the Waipaoa coastal plain and Poverty Bay suggests that export of muddy sediment to the Waipaoa shelf remained roughly constant at ∼2.0Mt/yr from 7ka until the onset of anthropogenic deforestation in the 19th century. [Copyright &y& Elsevier]

Abstract: One of the major environmental controls on sedimentary systems is tectonics, and thus in order to make quantitative explanations and predictions of the behaviour of sedimentary systems, it is important to quantify tectonic rates and mechanisms. In this study we show how a combined Holocene fluvial and marine terrace dataset can be used to place constraints on coastal uplift mechanisms at Pakarae River mouth, to the east of the Waipaoa sedimentary system. Mapping and surveying of fluvial terraces shows that the terraces can be divided into three sets, (i) PgT, a fill terrace formed during post-glacial sea level rise (~10000–7000cal. yr BP), (ii) a sequence of post-7000cal. yr BP degradation terraces, and (iii) historical (post ~AD 1880) flood terraces. A conceptual model of terrace evolution proposes that coseismic uplift has resulted in the observed back-tilting, downstream divergence, and successive abandonment of tectonic terraces. Coastal uplift mechanisms are then examined by comparing the fluvial and marine terrace uplift distribution and the uplift-per-event from the marine terraces with those predicted by forward elastic dislocation models. The models agree with the interpretation that the terrace uplift can be explained by coseismic slip on a steeply west-dipping reverse fault located close to the shore, possibly in combination with rupture of the Hikurangi Margin subduction interface 10–24km below. This study also provides insights into the tectonic drivers and impacts on the adjacent Waipaoa sedimentary system including: the possible role of subduction earthquakes, growth of structures on the shelf and upper slope, and the role that the interplay between sea level and tectonic controls has on sediment dispersal. [Copyright &y& Elsevier]

Abstract: Diatom microfossils preserved in 38 core top samples from offshore of eastern New Zealand are examined to develop the first offshore modern analogue dataset for diatoms in New Zealand waters. The sample set consists of seven, approximately E–W trending depth transects with samples from the continental shelf, slope and abyssal plain between latitudes 33° and 54°S. The identification of terrestrial and coastal species in open marine core top samples indicates that offshore transport of diatom microfossils occurs to an extent that could be useful for sediment provenance studies or at least to enable improved identification of transported versus in-situ deposition on the continental shelf. Cluster analysis and ordination indicate that the Chatham Rise and/or the overlying Subtropical Front are the most significant bathymetric/oceanographic features in the dataset as this location shows up as a major barrier or transition zone in terms of diatom distribution. The strongest environmental control on diatom distribution is the north–south sea surface temperature gradient. A statistically strong relationship (r 2 =0.81; RMSEP=1.57) exists between diatom abundance and sea surface temperature making diatoms ideal for quantitative reconstruction of past sea surface temperatures in future paleoclimate studies. [Copyright &y& Elsevier]

Abstract: In the headwaters of the Waipaoa catchment, fluvio-mass movement gully complexes are currently significant contributors of sediment, delivery of which is buffered by fans which have developed in the small tributaries that lead from the gully complexes. Biannual channel cross-section surveys made since 1983 show seasonal aggradation / incision cycles; channels generally incise in summer and infill during the winter months. This seasonal pattern of cutting and filling is driven by variations in sediment supply from the gully complexes. In this paper, to better understand patterns and processes of sediment delivery at the top of the sediment cascade, we examine cut and fill cycles on the ~11ha Tarndale Fan over a two and a half year period. Analysis of sequential DEMs compiled from survey data obtained between December 2004 and August 2007 indicates cutting and filling may involve up to 47,000tonnes of sediment over as little as three months. During discrete severe rainstorm and/or wet weather periods, mass movements in the gully complex are enhanced and contribute large quantities of sediment to the fan, via debris flows and landslides, which infill channels. During drier periods, mass movement activity is inhibited and runoff incises the feeder channels. [Copyright &y& Elsevier]

Abstract: The Poverty margin was sampled in 2005 and 2006 as part of an international initiative to examine the terrestrial and marine sedimentary response to natural and human impacts on dispersal systems at mud-dominated coasts: the NSF MARGINS Source-to-Sink Initiative. 210Pb accumulation rates generally decrease from ~1g/cm2 y in the mid-shelf depocenter on the outer shelf to ~0.1g/cm2 y on the mid-slope plateau (range 0.04–2.53g/cm2 y). Higher accumulation rates are observed all along the outer Poverty shelf, extending over the shelf break onto the upper Poverty slope in canyons and gullies. Rates are fast in gullies that incise into the shelf edge (0.75–1g/cm2 y), particularly in the area between Waipaoa Canyon and Poverty Canyon, and in the axis of Poverty Canyon (1.29–1.89g/cm2 y). Below ~1200m water depth, rates in the axis of Poverty Canyon are no more rapid than those found at open slope cores in similar water depths (0.12–0.15g/cm2 y). Excess 210Pb profiles generally exhibit steady state characteristics, except in the axis of Poverty Canyon, where non-steady-state 210Pb profiles are observed. 137Cs was not found above minimum detection limits or above statistical background levels in any cores from the Poverty margin. 7Be was found distributed widely along and across the margin during both summer and winter periods, observed to depths of up to 4cm. Widespread presence of 7Be on the margin in both winter and summer suggests that terrestrially derived sediment is reaching the outer shelf and upper slope throughout the year. A sediment budget based on 210Pb accumulation rate data shows that approximately 13–18% of the Waipaoa annual discharge is accumulating on the outer Poverty margin as a whole, and approximately 11–15% of the annual discharge is accumulating on the continental slope alone. Notably, approximately 28% of the sediment annually accumulating in the outer margin is being sequestered in slope gullies and canyons, although they represent only 6% of the area of the outer margin. [Copyright &y& Elsevier]

Abstract: The rivers that drain active, collisional margins of the southwest Pacific deliver up to 35% of particulate organic carbon (POC) to the world ocean, and are a key component of the global organic carbon flux. However, knowledge of the fate of terrestrial POC in the ocean is both limited and necessary for quantifying terrestrial and coastal ocean carbon budgets. Here, the fate of terrestrial POC is determined off the high discharge, Waipaoa River (sediment yield 15Mty−1) based on a transect of seven cores from the river floodplain to the adjacent continental shelf and slope. Total organic carbon (%TOC), δ 13C, 14C, C/N ratios and lipid biomarker compounds were used to determine biogeochemical characteristics of surface sediments from terrestrial source to marine sink, and how these characteristics vary with river discharge. Complementary to surface sediments, down-core characteristics of three multi-cores covering the shelf and slope regions were used to identify perturbations in sediment supply via major floods. The presence of flood deposits allows us to compare their OC characteristics with non-flood sediment, thereby helping address the question of how flood events in the river catchment affect the transfer and fate of terrestrial OC through the marine environment. Results from this study show that as surface sediments are physically and biologically processed across the continental margin, they gain a marine signature. Biomarker analyses of surface samples show decreases in terrigenous vascular plant sources with increasing distance offshore. Biomarkers also demonstrate that terrestrial OC is being transferred across the continental margin, with plant sterols, long-chain alcohols and long-chain fatty acids (biomarkers indicative of vascular plants) persisting as far offshore as the mid-continental slope. In contrast to ambient conditions represented by surface sediments, rapid delivery by floods allows for more complete transfer of terrestrial carbon to the marine environment. A 1–10 cm thick flood layer preserved from Cyclone Bola (March 1988) contains a significant amount of terrestrially-sourced OC which subsequently was rapidly buried by sediments delivered during less extreme conditions. [Copyright &y& Elsevier]

Abstract: Multiple sediment transport and reworking processes influence fine, cm-scale strata formation and long-term accumulation on the Waiapu River shelf, New Zealand. Gravity cores collected during two cruises, in August 2003 and May 2004, were analyzed using 7Be and 210Pb geochronologies, bulk carbon, δ 13C, X-radiographs, and grain-size to investigate sediment mixing and accumulation patterns. The presence of 7Be on the inner- and mid-shelf regions (<~80m) indicated recent (within the last 4–5 months) deposition of fluvial muds, whereas the distribution of excess 210Pb accumulation rates revealed that the middle to outer shelf (50–130 m) acted as fine sediment repositories on longer time scales. Excess 210Pb accumulation rates were high, with an area weighted average of 1.1±0.1 cm/yr and ranging between 0.2 and 3.5 cm/yr, yet were localized such that only an estimated ~23% (ranging between 17 and 38%) of the fluvial load was retained on the shelf between 40 and 200 m depths over the last 80 to 100 yr. Sediments not retained on the shelf were either transported to deeper waters or along the shelf beyond the sampling area. Several cores collected from the high sediment accumulation zone on the middle to outer shelf exhibited non-steady state excess 210Pb profiles, suggesting that multiple transport processes influenced fine-scale strata formation. Layers of low excess 210Pb activity and predominantly terrestrial δ 13C and C/N values were likely formed during floods, when sediments were rapidly deposited and buried on the shelf. These event layers were sufficiently thick (up to ~20 cm), such that all or a portion of the initial flood layer immediately transited through the surface mixing layer, ensuring preservation in the sediment record. Sediments inter-bedded with these event layers reflected a relatively marine source indicating either that they were not deposited rapidly or were significantly bioturbated. A gradient of physical and biological mixing signatures, extending radially from the Waiapu River mouth, suggested that high background accumulation rates and flood deposits negatively impacted the preservation of biological structures and enhanced preservation of event-produced beds. [Copyright &y& Elsevier]

Abstract: A one-dimensional sediment transport model (TUGS) and a climate-driven hydrological model (HydroTrend) are used to predict changes to the sediment transport regime of the Waipaoa River that may occur in response to forecast 21st Century variations in climate. Climate change may reduce the mean flow in the Waipaoa River at Matawhero by an average of 13% in the 2030s and 18% in the 2080s. In the 2030s, the maximum simulated change in the mean annual suspended sediment discharge of ±1 Mt y− 1 may be difficult to discern because of the large variation in the contemporary suspended sediment load (13.4±7.3 Mt y− 1). Depending on the climate change scenario, in the 2080s the suspended sediment discharge may either decline by 1 Mt y− 1 or increase by 1.9±1.1 Mt y− 1. Adverse impacts have the potential to be offset or ameliorated by a modest (35%, ~12000 ha) increase in forest cover across the basin headwaters. Size-selective transport and deposition throughout the lower reaches of the Waipaoa River currently limit the amount of bed load exported at the coast to 10.2±24.3 Kt y− 1. In the 2030s this may decline to 6.3±16.1 Kt y− 1, but in the 2080s it may rise to 9.4±20.1 Kt y− 1 as aggradation reduces the amount of accommodation space and modifies the long profile of the simulated river. The bed in the lower 27 km of the river could aggrade by an average of 0.31 m in the 2030s, and 0.85 m in the 2080s. This is likely to be the most costly consequence 21st Century climate change, because rising bed levels have the potential to cause a loss of capacity throughout 75% of the Waipaoa River flood control scheme. [Copyright &y& Elsevier]

Abstract: We report rates of Australian dust deposition in New Zealand over the last ~8000 years using records extracted from an ombrotrophic peat bog. The trace element chemistry of deposited dust is used to identify the Australian source areas, and to calculate Australian dust deposition rates in New Zealand. This is used to infer patterns of aridity and climate variability in eastern Australia during the Holocene. Prior to 4800 cal. BP, dust deposition patterns imply that the Australian climate was relatively wet due to an active/persistent monsoon. Southern Australian source regions supplied the majority of dust transported to New Zealand at this time. After 4800 cal. BP the Australian climate became significantly more arid and variable, attributed to the onset of ENSO-type conditions. The Lake Eyre Basin switched on as a dust source, while overall Australian dust deposition in New Zealand increased >4 times. Rates of Australian dust deposition were found to match patterns of increased ENSO variability, which is attributed to the combined effect of enhanced sediment supply to Australian dust source areas (during wet La Niña events) and preferable conditions for dust transport (during El Niño induced drought). Results also show that Australian dust deposition is a significant sedimentary process in New Zealand and is likely to influence both geochemical cycles and soil development suggesting that it may contribute up to 90% of material in the bog. [Copyright &y& Elsevier]

Abstract: We observed the onshore migration (3.5 m/day) of a nearshore sandbar at Tairua Beach, New Zealand during 4 days of low-energy wave conditions. The morphological observations, together with concurrent measurements of waves and suspended sediment concentrations, were used to test a coupled, wave-averaged, cross-shore model. Because of the coarse bed material and the relatively low-energy conditions, the contribution of the suspended transport to the total transport was predicted and observed to be negligible. The model predicted the bar to move onshore because of the feedback between near-bed wave skewness, bedload, and the sandbar under weakly to non-breaking conditions at high tide. The predicted bathymetric evolution contrasts, however, with the observations that the bar migrated onshore predominantly at low tide. Also, the model flattened the bar, while in the observations the sandbar retained its steep landward-facing flank. A comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water (<0.25 m) may have been responsible for most of the observed bar behaviour. These processes are missing from the applied model and, given that the observed conditions can be considered typical of very shallow sandbars, highlight a priority for further field study and model development. The possibility that the excess water transported by the bores across the bar was channelled alongshore to near-by rip-channels further implies that traditional cross-shore measures to judge the applicability of a cross-shore morphodynamic model may be misleading. [Copyright &y& Elsevier]

Abstract: Results are presented from a new cellular model of braided river dynamics that simulates flow, sediment transport, morphological change and the effects of braidplain vegetation. This model is used to investigate the effect of changes in upstream sediment supply on braided river systems over simulation periods of 200 years. Modelled changes in channel morphology, associated with both aggradation and degradation, were seen to be consistent with those reported in the literature. In addition, simulation results allowed the identification of diagnostic characteristics of aggrading and degrading reaches, in the form of relationships between the age, extent and relative elevation of fluvial surfaces. Interpretation of spatial patterns of valley floor surface characteristics in the Avoca River, New Zealand, on the basis of these relationships, allowed the identification of channel reaches that appear to be experiencing either aggradation or degradation. These inferences are shown to be consistent with independent evidence of spatial patterns of sediment supply to the main valley floor, derived from aerial photographs and an existing sediment source inventory. These results illustrate the potential for using cellular models to develop an improved understanding of natural river behaviour. [Copyright &y& Elsevier]

Abstract: The last decade has witnessed the development of a series of cellular models that simulate the processes operating within river channels and drive their geomorphic evolution. Their proliferation can be partly attributed to the relative simplicity of cellular models and their ability to address some of the shortcomings of other numerical models. By using relaxed interpretations of the equations determining fluid flow, cellular models allow rapid solutions of water depths and velocities. These can then be used to drive (usually) conventional sediment transport relations to determine erosion and deposition and alter the channel form. The key advance of using these physically based yet simplified approaches is that they allow us to apply models to a range of spatial scales (1–100 km2) and time periods (1–100 years) that are especially relevant to contemporary management and fluvial studies. However, these approaches are not without their limitations and technical problems. This paper reviews the findings of nearly 10 years of research into modelling fluvial systems with cellular techniques, principally focusing on improvements in routing water and how fluvial erosion and deposition (including lateral erosion) are represented. These ideas are illustrated using sample simulations of the River Teifi, Wales. A detailed case study is then presented, demonstrating how cellular models can explore the interactions between vegetation and the morphological dynamics of the braided Waitaki River, New Zealand. Finally, difficulties associated with model validation and the problems, prospects and future issues important to the further development and application of these cellular fluvial models are outlined. [Copyright &y& Elsevier]

Abstract: If knickpoints transmit signals of base level fall in river networks, then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation. Many studies of knickpoint retreat focus on the response of trunk streams to base level fall. Here we examine the response of an entire fluvial network, as recorded by 236 active knickpoints distributed within the Waipaoa River on the North Island of New Zealand. Base level fall within the Waipaoa catchment initiated 18,000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision. Using observations from field work, aerial photo analysis and a digital elevation model (DEM), we study the knickpoint positions within the network. We find that ∼70% of the knickpoints are located at drainage areas between 1×105 m2 and 1×106 m2 and more than half are <1 km upstream of a large change in drainage area. For the knickpoints <1 km upstream of large tributary junctions, we find that the retreat distances were well correlated with the tributaries'' drainage areas. In order to determine how a pulse of incision distributes itself throughout a fluvial network, we develop two simple, end-member models and compare their behavior to the observed knickpoint distribution in the Waipaoa. In the first model, we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area. In the second model, we propose that knickpoints form near a threshold drainage area, below which channels cannot incise with the same efficiency as possible in downstream reaches. Though neither model addresses the along-stream variability in substrate or knickpoint form, the misfit between the modeled and the observed knickpoints'' along-stream positions are surprisingly low (<1 km; ∼1.25% of the total stream length) for knickpoints with drainage areas <1×106 m2. Large misfits (up to 3.5 km) are observed for knickpoints with present-day drainage areas greater than 1×106 m2. The large, single step in channel elevation that characterizes knickpoints presently observed in tributaries of the Waipaoa River may not characterize the base level fall signal that propagated through the trunk streams. Evidence for progressive (rather than instantaneous) incision in the trunk streams, the knickpoints’ vicinities to tributary junctions and the equivalent success of the two-end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas. [Copyright &y& Elsevier]

Abstract: In 1996 the vegetation on Aorangi Island within the Poor Knights Island Nature Reserve, New Zealand, was found to be severely damaged. The damaged zone consisted of a distinct trail of stripped soil and broken vegetation starting at sea level and travelling in an arc across the northeastern flank of the island. Cobbles encrusted with marine life, sea urchins and seaweeds, were deposited at elevations up to 45 m above sea level along and beside the damaged zone. Boulders up to 2 m in size were transported horizontally at elevations of 5–15 m above sea level, and larger boulders were destabilised at 25 m above sea level causing them to slide and roll downslope. Application of threshold entrainment relationships for tsunamis, storm waves and waterspouts indicates that a waterspout is the most probable mechanism for the observed damage and transport of large clasts. The addition of 2.5–5% of atomised water to the waterspout vortex significantly increases the flow competence. Hence, intensity T3–T5 (TORRO Tornado Intensity Scale) or F2 (Fujita Tornado Intensity Scale) waterspouts commonly observed around the New Zealand coast are capable of moving boulders up to 2 m in size. [Copyright &y& Elsevier]

Abstract: Detailed measurements of cross-shore wave energy transformation, swash sediment transport and beach profile change under low energy conditions are reported from a mixed sand and gravel beach at Torere Bay, Bay of Plenty, New Zealand. Measurements were undertaken during a 10-day period following a storm event and document post-storm recovery of the beach. Nearshore wave spectra identify periods in which incident wave energy is dominated by swell and wind wave energy. Results show that wind wave energy observed in the nearshore is effectively removed from beachface spectra at the break-point step under lower tidal stages. Swash is driven by longer period swell energy although dissipation of short period wave energy is critical in entraining sediments on the lower beach. At higher tidal stages wind wave energy is able to propagate across the break-point step, shoal and break on the lower beachface. Tidal modulation of wave processes across the lower beachface under low incident wave conditions is found to stimulate active sediment reworking, migration of the break-point step and shoreward sediment flux to promote beach accretion. [Copyright &y& Elsevier]

Measurements of waves, currents and sediment suspension from a 35-day deployment of three instrumented tripods on the wave-dominated shoreface off Tairua Beach, New Zealand, are presented. Two tripods were deployed at 22-m depth, one within a coarse-sand rippled scour depression (RSD), and the other nearby on the surrounding, relatively featureless fine-sand plain. A third tripod was deployed at 15-m depth, also on fine sand. To distinguish between suspended fine and coarse sand at each site, a method of simultaneously inverting two-frequency acoustic backscatter data was applied.Background, long-period swell was interrupted by two 6-day periods of high waves. At the 15-m/fine-sand site, only fine sand appeared in suspension. However, at the 22-m/fine-sand site, coarse sand appeared in suspension together with fine sand when the waves were highest. This suggests that coarse sand resuspended from the RSD can be dispersed on the adjacent fine-sand plain, at least along the same isobath. At the RSD, there was no coarse sand in suspension under background swell, but there was a fine-sand “washload”, presumably advected from the surrounding fine-sand plain, even though the coarse bed sediment in the RSD itself was not in motion. Under high waves, both fine and coarse sands were in suspension over the RSD. The fine sand appeared again as a washload, but the coarse sand was confined relatively close to the bed in accordance with a sediment diffusivity that decreased linearly with elevation above the bed.Measurements of fine-sand reference concentration over both fine-sand beds (15 and 22-m depth) plot against wave-induced skin friction in one cluster under the background swell and in another cluster under the high waves, which suggests a change in bedforms, possibly to a hummocky bed, that is related to wave conditions and that alters the suspension dynamics. The coarse-sand reference concentrations over the RSD fall into the “hummocky cluster”, which supports this interpretation.The fine-sand washload is indicative of an unfavourable settling environment over the RSD, which could constitute a positive feedback that causes RSDs to self-organize from initial perturbations. Under high waves, the suspended-sediment load impinging from the surrounding plain will be high, but turbulence will also be more energetic on the RSD, thus more effectively inhibiting deposition. Under low waves, deposition may be less inhibited on the RSD, but the suspended-sediment load arriving from the surrounding fine-sand plain will also be lower. Thus, the fine-sand deposition rate on the RSD will be small, even though conditions are more favourable for settling. Modelling could be expanded to consider the balance between inhibition of settling and tendency for burial by the sediment load that impinges from the area surrounding an RSD, and the way wave climate and water depth might mediate the basic self-organization process. Escape of coarse sand from RSDs under high waves may seed the growth of new RSDs. [Copyright &y& Elsevier]

Foveaux Strait has been commercially fished for oysters for over 100 years, focusing principally upon bryozoan biogenic reefs that once covered large areas of the strait. Bryozoan biogenic reefs consisted of linear swards of bryozoan patch reefs, paralleling the peak tidal current, and were formed by the frame-building bryozoan Cinctipora elegans and associated epifauna. Two side-scan surveys one in the late 1970s and the other in the late 1990s and estimates of distribution of oyster density and distribution of fishing effort, show how fishing has effected the distribution of habitat, oysters and sediments over the last 30 years. Fishers dredged the biogenic reefs for their oysters, damaging the framework structure, removing epifauna and exposing associated sediments, which were then reworked and transported down-current in the strong tidal flow. Large volumes of biogenic sediments released in this process formed thick sheets and dune bedforms. When dredging ceased locally (after removal of biogenic reef habitat and oysters), sediment supply downstream dwindled and ceased, bedforms diminished and the seafloor ultimately reverted to relict pebble gravel. Sediment derived from the dredging of biogenic reefs in northern Foveaux Strait was mostly transported and deposited in deeper water to the east, however, sediment derived from biogenic reefs in southern Foveaux Strait was transported in the opposite direction, giving rise to a group of large dunes in the southwest that in 1999 contained ∼58×106 m3 of coarse biogenic sediment. By 1998 none of the original bryozoan biogenic reefs remained.We interpret sediment distribution in Foveaux Strait in the light of these processes, and compare with earlier data to provide snapshots of human-induced modification of the benthic environment. We also explore evidence for regeneration of simple biogenic reefs in areas no longer fished, and discuss the conditions in which this has occurred. Communities dominated by byssally attached Modiolus appear to provide the early framework and shelter for development of new patch reefs. However the recent discovery of regenerating colonies of the reef-building bryozoan Cinctipora in eastern Foveaux Strait suggests that bryozoan patch reefs may also be capable of re-establishing where conditions are suitable. We favour helical circulation cells in the strongly linear tidal flow of Foveaux Strait as a mechanism for controlling, not only the linear aspect of the reef frameworks, but also for concentrating nutrients, propagules and the settlement of larvae. Our observations of regenerating epifaunal habitat on the fishery-modified seafloor suggest that careful management could reverse much of the deleterious effect of fishing. (4 0 6) [Copyright &y& Elsevier]

To identify the drivers of sediment deposition within a mangrove-lined river delta, we developed a three-dimensional numerical model in an idealized domain. Our model system is based on the Firth of Thames, a modern flat-fronted, bay-head deltaic system, in the Hauraki Gulf, in the North Island of New Zealand. The interactions of the buoyant river plume with mangroves are examined, including sediment deposition and erosion patterns. The morphological study presented here is restricted to cohesive sediments, whose patterns are observed after 4 months of morphological evolution. For the non-vegetated case, represented by a spatially uniform roughness, sediment deposited throughout the central model domain with a formation of a cuspate delta at the river mouth. However, in the vegetated case (with vegetated areas represented by an enhanced and spatially varying roughness coefficient), sediment deposition occurred in the regions of forests and flats, whereas the fringe areas experienced erosion. The sediment deposition patterns along cross-sections were qualitatively consistent with field observations from the Firth of Thames. Analysis of the across-transect and along-transect momentum balances demonstrates that the predominant balance between the bottom shear stress and baroclinic pressure gradient largely controls the sediment deposition in the riverine sections of the domain. However, close to the center of the plume, vertical advection promotes suspension of the sediments in the fringe region during the flood tide. • The presence of mangroves altered sediment deposition patterns. • Sediment deposition occurred in the forests and over the mudflats. • The fringe area between vegetation and bare mudflat experienced erosion. • Sedimentation patterns are explained by across- and along-shore momentum balances. [ABSTRACT FROM AUTHOR]

This study provides a detailed sedimentological, stratigraphic and depositional model for the lower Whakataki Formation. The fine-grained nature of the turbidite successions and common T bcde successions suggests deposition associated with medial to distal submarine fan deposits. However, the textural and compositional immaturity, combined with a high carbonaceous and carbonate content of the clastic sediments indicates a proximal detrital input. In the examined section of the lower Whakataki Formation the sedimentology and facies associations identified that the turbidite successions were deposited as dilute low-density turbidity currents that transported sediment down-slope, overflowing or bypassing upper- and mid-trench-slope basins into a structurally confined lower trench-slope basin. Flows entering the structurally confined basin were deflected to the north-northeast, producing palaeo-flow along the axis of the basin and represent deposition in the early stages of trench-slope basin development. Here, we provide a depositional model for a lower (immature) trench-slope basin and highlight that the application of the 'classical' submarine-fan model to all fine-grained turbidite deposits is not always appropriate. [ABSTRACT FROM AUTHOR]