landslides and sediment delivery to a drainage system some observations from hong kong abstract the delivery of sediment from hillslopes to a drainage system has been examined for hong kong landslides may influence sediment production in small upland drainage basins by the direct delivery of material to the channel subsequent fluvial action on materials exposed in debris trails and erosion as the failure moves downslope sometimes to become channelised evidence of the direct delivery of sediment by landslides is presented from a small drainage basin on undeveloped terrain in hong kong in general less than half of the landslides deliver debris to the channel system examples of landslide debris volume exceeding that of source area failure in hong kong are presented and this relates to channelisation of debris flows revegetation of landslide debris trails may be quite rapid and this restricts the time for fluvial action on the exposed materials the temporal aspect of sediment delivery has been documented rainfall events that are guaranteed to generate large numbers of landslides are relatively rare

sediment budgeting a case study in the katiorin drainage basin kenya the primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in kenya results indicated that transfer of sediments inputs from primary source areas was minor in comparison to changes in storage the major sediment source area within the katiorin drainage basin was the colluvial hillslope zone the net change in storage within this zone was approximately 2100 mg yr 1 surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments sediment storage within the in channel reservoir increased by 60 mg yr 1 which was minor when compared to the total store of sediment in this reservoir during 1986 the channel network stored only a small fraction 3 per cent of the sediment delivered from the hillslope subsystem therefore the in channel reservoir had limited influence on sediment conveyance to the basin outlet these data indicate that a static equilibrium condition cannot be assumed within the katiorin drainage basin such an assumption would result in erosion estimates of approximately 5 5 mm yr 1 for the entire basin based on a sediment output of 7430 mg km 2 yr 1 and a measured bulk density of 1 35 mg m 3 however this masked the actual rates of 1 2 to 7 1 mm yr 1 in subbasin primary source areas and rates of 0 6 to 17 mm yr 1 for colluvial material in the various subbasins the extreme accelerated erosion rates resulted from minimal ground vegetation steep slopes soil crust formation an erodible substrate and a well integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet

holocene alluvial sediment storage in a small river catchment in the loess area of central belgium abstract soil erosion and sediment deposition widely affect landscape development particularly in erosion prone areas with loess derived soils nevertheless until now few attempts were made to quantify soil losses and sediment storage over long centennial or millennial timescales in this study the holocene alluvial sediment storage in a small river catchment 52 km2 of the belgian loess belt is estimated and a preliminary sediment budget for the catchment is presented in the valley of the nethen river c 13 km long a detailed survey of the alluvial sediment archive was conducted hand augerings and percussion drillings were made along cross valley transects at 12 locations in the catchment ams 14c dating of peat samples provided a temporal framework for the interpretation of the cores results show that the thickness of holocene sediment deposits in the nethen valley is 4 to 6 m which corresponds to a total clastic sediment mass of 14 106 t stored in the valley bottom three alluvial units could be distinguished and associated with deposition phases from 9600 to 2900 b c 2900 b c to a d 1000 and a d 1000 to present in contrast to the older sediments units 1 and 2 deposits from the last 1000 year unit 3 contain little organic matter they are seldom intercalated with peat layers and devoid of tufa unit 3 reaches a thickness of c 2 m thereby representing 50 of the holocene sediment mass stored in the alluvial plain the mean sedimentation rate in the alluvial plain for this last phase is 26 t ha 1 a 1 which is about tenfold larger than the sedimentation rates calculated for the older holocene sediment units sediment supply towards the alluvial plain has therefore increased tremendously since medieval times these results are in contrast to dating results obtained for colluvial sediments in a nearby dry valley within the catchment of the nethen where soil erosion and sediment deposition started in the early iron age and was already substantial during the roman age this means that there is a time lag of about one millennium between the onset of high sedimentation rates in the upstream area and high deposition rates in the alluvial plain this is probably caused by a change in coupling sediment connectivity between the plateau slopes and rivers as soil erosion proceeds first the dry zero order valleys in the catchment act as sediment traps and only after these are filled sediment reaches the floodplains the preliminary sediment budget for the nethen catchment illustrates that 50 of the sediment that was eroded during the holocene was stored in colluvial deposits which are mainly located on footslopes and in dry valley bottoms another 29 of the sediment mass is stored in the alluvial plain

magnitude and frequency of landsliding in a large new zealand catchment knowledge of long term average rates of erosion is necessary if factors affecting sediment yields from catchments are to be understood without such information it is not possible to assess the potential influence of extreme storms and therefore to evaluate the relative importance of various components of a sediment budget a study of the sediment budget for the waipaoa catchment north island new zealand included evaluation of long term rates of landsliding for six landslide prone land systems in the catchment the number of landslides per unit area generated by each of several storms was counted on sequential aerial photographs and correlated with the magnitude of the corresponding storm the resulting relationships were combined with magnitude frequency relationships derived for storms from 70 to 100 year rainfall records in the area to estimate a long term magnitude frequency relationship for landsliding for each land system the long term average values of the areal landslide frequency number of slides per unit area per unit time were then calculated from these relationships the volumes of a sample of landslide scars were measured in the field and the proportion of slides that deliver sediment to channels was determined from aerial photographs these measurements then allowed calculation of the long term average rate of sediment production to streams from landslides for different land systems and types of vegetation results suggest that shallow landslides currently contribute about 15 5 of the suspended sediment load in the waipaoa river above the kanakanaia gauging station and that 75 of the sediment production from the landslides occurs during storms with recurrence intervals of less than 27 years reforestation of 6 3 93 km2 of the slide prone lands in the catchment between 1990 and 1995 resulted in a calculated decrease in slide derived sediment of 10 calculations suggest that reforestation of an additional 3 66 km2 of the catchment in areas with the most sensitive combinations of land system and storm regime could decrease the total sediment inputs from landsliding by about 20

changing hillslope and fluvial holocene sediment dynamics in a belgian loess catchment floodplain deposition is an essential part of the holocene sediment dynamics of many catchments and a thorough dating control of these floodplain deposits is therefore essential to understand the driving forces of these sediment dynamics in this paper we date floodplain and colluvial deposition in the belgian dijle catchment using accelerator mass spectrometric radiocarbon and optical stimulated luminescence dating relative mass accumulation curves for the holocene were constructed for three colluvial sites and 12 alluvial sites a database was constructed of all available radiocarbon ages of the catchment and this database was analysed using relative sediment mass accumulation rates and cumulative probability functions of ages and site specific sedimen tation curves cumulative probability functions of ages were split into different depositional environments representing stable phases and phases of accelerated clastic deposition the results indicate that there is an important variation between the different dated sites after an initial stable early and middle holocene phase with mainly peat growth in the floodplains clastic sedimentation rates increased from 4000 bc on this first phase was more pronounced and started somewhat earlier for colluvial deposits then for alluvial deposits the main part of the holocene deposits both in colluvial and alluvial valleys was deposited during the last 1 ka the sedimentation pattern of the individual dated sites and the catchment wide pattern indicate that land use changes are responsible for the main variations in the holocene sediment dynamics of this catchment while the field data do not provide indications for a climatological influence on the sediment dynamics copyright 2011 john wiley sons ltd

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

self organized criticality in layered lacustrine sediments formed by landsliding landsliding is the dominant mass wasting process in humid temperate uplands and an important regulator of sediment yield from steep land drainage basins information about the magnitude and frequency distribution of landslides has been derived from aerial photography but it has proved difficult to set limits on the long term scaling behavior of landsliding because the requirements of spatial and temporal coherence and the large number of observations necessary to undertake magnitude versus frequency analyses are not easy to fulfill we use a 2250 yr long record of hillslope erosion associated with extreme hydrologic events preserved in sediments from lake tutira new zealand to investigate scaling in landslide deposits both the magnitude versus frequency distribution of sediment layers attributed to landsliding and the distribution of time intervals between landsliding events take the form of power laws the former with an exponent b 2 06 and the latter with an exponent b 1 4 these results suggest that the erosional events originate from a self organized critical process and are in agreement with observations of scaling in turbidite deposits and grain flows in controlled laboratory experiments the implications are that the aggregate behavior of landsliding at the catchment scale is orderly and that the stratigraphic record preserves a unique long term perspective on a fundamental geomorphic process and the extreme hydrologic events that trigger it

estimation of temporally averaged sediment delivery ratio using aggradational terraces in headwater catchments of the waipaoa river north island new zealand the sediment delivery ratio was estimated for two periods 28 years and eight years following reforestation of seven tributary catchments 0 33 to 0 49 km2 in the headwaters of the waipaoa river basin north island new zealand in these catchments gully erosion which largely resulted from clearance of the natural forest between 1880 and 1920 is the main source of sediment to streams reforestation commenced in the early 1960s in an attempt to stabilize hillslopes and reduce sediment supply efforts have been partially successful and channels are now degrading though gully erosion continues to supply sediment at accelerated rates in parts of the catchment data from the area indicate that the sediment delivery ratio sdr can be estimated as a function of two variables the product of catchment area and channel slope and ag the temporally averaged gully area for the period sediment input from gullies was determined from a well defined relationship between sediment yield and gully area sediment scoured from channels was estimated from dated terrace remnants and the current channel bed terrace remnants represent aggradation during major floods this technique provides estimates of sdr averaged over periods between large magnitude terrace forming events and with the present channel bed the technique averages out short term variability in sediment flux comparison of gully area and sediment transport between two periods 1960 1988 and 1988 1996 indicates that the annual rate of sediment yield from gullies for the later period has decreased by 77 per cent sediment scouring in channels has increased by 124 per cent and sediment delivered from catchments has decreased by 78 per cent however average sdr for the tributaries was found to be not significantly different between these periods this may reflect the small number of catchments examined it is also due to the fact that the volume of sediment scoured from channels was very small relative to that produced by gullies according to the equation for sdr determined for the waipaoa headwaters sdr increases with increasing catchment area in the case where ag and channel slope are fixed this is because the amount of sediment produced from a channel by scouring increases with increasing catchment area however this relationship does not hold for the main stem of the study catchments because sediment delivered from its tributaries still continues to accumulate in the channel higher order channels are in effect at a different stage in the aggradation degradation cycle and it will take some time until a main channel reflects the effects of reforestation and its bed adjusts to net degradation results demonstrate significant differences among even low order catchments and such differences will need to be taken into consideration when using sdr to estimate sediment yields copyright 2001 john wiley sons ltd

landslide occurrence as a response to land use change a review of evidence from new zealand abstract vegetation cover is an important factor influencing the occurrence and movement of rainfall triggered landslides and changes to vegetation cover often result in modified landslide behaviour however it is difficult to relate the occurrence of landslides directly to variations in land use especially in some european countries in contrast new zealand provides a good opportunity to investigate geomorphic responses to anthropogenic land cover changes before european settlers first arrived in the 1840s hilly regions were only marginally influenced by human activity the maoris new zealand s first settlers lived largely on coastal plains or near lakes and rivers they influenced general vegetation cover only through localized burning practices in contrast european settlers moved into the back country and converted extensive hill areas from native forest and bush to pasture this reduced the strength of the regolith and rendered the slopes more susceptible to landslides pulses of natural sedimentation in the pre european period have been related to volcanic activity climatic variability including changes in frequency of cyclonic storms and wind erosion and fluvial erosion following forest fires initiated either by volcanic eruptions or lightning strikes since european deforestation began sediment production has largely been determined by landslide events on unstable slopes thousands of landslides were triggered by high magnitude low frequency climatic events during storms with estimated return periods in excess of 50 years in contrast low magnitude high frequency rainfall events have caused gully and channel erosion examples from different parts of new zealand indicate changes in sediment generating processes following land use modifications after deforestation landslides have contributed significantly to sediment sequences in depositional basins such as lakes swamps estuaries coastal wetlands and the nearshore and offshore zones of continental platforms

a source to sink perspective of the waipaoa river margin abstract a fundamental goal of the earth science community is to understand how perturbations on earth s surface are preserved in the stratigraphic record recent source to sink s2s studies of the waipaoa sedimentary system wss new zealand are synthesized herein to provide a holistic perspective of the processes that generate transport and preserve sedimentary strata and organic carbon on the waipaoa margin in the late quaternary rapid uplift associated with subduction processes and weak sedimentary units have conspired to generate rapid rates of incision and erosion in the waipaoa catchment since the last glacial maximum lgm we show that although much of the sediment exported offshore during this time interval originated from valley excavation a substantial portion emanated from hillslopes mostly through deep seated landslide and earthflow processes that were vigorous during periods of rapid fluvial incision just prior to the pleistocene holocene transition lacustrine sediments deposited in naturally dammed 7 ky old lake tutira provide a record of holocene environmental controls on upper catchment sedimentation in the wss with 1400 storms identified storm frequency is modulated by the waxing and waning of atmospheric teleconnections between the tropics and antarctica furthermore clear long term changes in sediment yield are evident from the lake tutira record following human settlement as conversion to pasture is accompanied by a 3 fold increase in the long term lake sediment accumulation rate whereas there is ample evidence that waipaoa river flood deposits are routinely deposited offshore in the sheltered confines of poverty bay over the longer term waves and currents subsequently resuspend and transport these deposits both landward sandy fraction and seaward finer fraction thus the timing of sediment supply to areas of net sediment accumulation is more often driven by wave events that are not associated with river flooding therefore we conclude that asynchronicity of river sediment delivery and of wave resuspension in most instances precludes the direct preservation of flood events in the stratigraphic record of the waipaoa shelf over the longer term the sediment package preserved on the shelf and slope since the lgm can be explained in large measure by sequence stratigraphic models forced by varying sea level and ongoing tectonic deformation of the margin as sea level rose sediment supply to the slope was reduced by about a factor of 5 due to shelf trapping despite this reduction turbidites are found at similar frequency throughout the lgm present as the dominant trigger appears to be subduction earthquakes with large ones having a return interval of about 200 100 years sediment budget exercises that consider both modern river discharge versus centennial accumulation rates and post lgm terrestrial production versus offshore isopachs mass balances indicate that about half of the total sediment production from the waipaoa escapes the study area moreover a coupled sediment transport hydrodynamic model and observations of textural trends on the shelf indicate that a large fraction of the sediment is carried outside the study area along the shelf to the northeast by the river plume or by combined current wave activity therefore we conclude that the wss is an open system with sediment escape from the present day through the lgm the organic matter associated with sediment as it moves from upland source to marine sink is a product of particle history and provides a record of materials that have cycled over timescales of days to millions of years the ubiquity of fossil organic carbon oc in both the terrestrial and marine realms of the waipaoa attests both to the chronic nature of its source crumbling mudstones further destabilized by land use and its biogeochemical recalcitrance modern oc persists by virtue of its continual production along the s2s transit and is buried and preserved within the adjacent marine depocenters the waipaoa contrasts with dispersal systems on wide energetic shelves e g the amazon and fly rivers where sediment is extensively refluxed in oxygenated overlying water resulting in the biogeochemical incineration of particulate oc the waipaoa like other small mountainous rivers on active margins exhibits a high riverine oc preservation efficiency 50 in its marine depocenters because of the relatively rapid event driven accumulation of sediment

reconstructing high magnitude low frequency landslide events based on soil redistribution modelling and a late holocene sediment record from new zealand a sediment record is used in combination with shallow landslide soil redistribution and sediment yield modelling to reconstruct the incidence of high magnitude low frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part eleven sediment cores were obtained from a dune impounded wetland at te henga west auckland northern new zealand sediment stratigraphy and chronology were interpreted by radiocarbon dating foraminiferal analysis and provisional tephrochronology gradual impoundment of the wetland began c 6000 cal yr bp coinciding with the start of a gentle sea level fall but complete damming and initial sedimentation did not begin until c 1000 cal yr bp after damming four well defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores for interpreting the sediment pulses a physically based landslide model was used to determine spatially distributed relative landslide hazard applicable at the catchment scale an empirical landslide soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material sediment delivery ratio and the impact on total catchment sediment yield sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back analysis of modelled sediment yield output in general at least four major high magnitude landslide events both natural and intensified by forest clearance activities occurred in the catchment upstream of te henga wetland during the last c 1000 years the spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard the magnitude of the sediment pulses represented in the wetland can be back calculated to critical rainfall thresholds representing a shallow landslide model scenario

validation of a region wide model of landslide susceptibility in the manawatu wanganui region of new zealand since european settlement 160 years ago much of the indigenous forest in new zealand hill country has been cleared for pastoral agriculture resulting in increased erosion and sedimentation to prioritise soil conservation work in the manawatu wanganui region we developed a model of landslide susceptibility it assigns high susceptibility to steep land not protected by woody vegetation and low susceptibility everywhere else following the commonly used approach for identifying inappropriate land use a major storm on 15 16 february 2004 that produced many landslides was used to validate the model the model predicted hills at risk to landsliding with moderate accuracy 58 of erosion scars in the february storm occurred on hillsides considered to be susceptible the model concept of slope thresholds above which the probability of landsliding is high and below which the probability is low is not adequate because below 308 the probability of landsliding is approximately linearly related to slope thus reforestation of steep slopes will need to be combined with improved vegetation management for soil conservation on moderate slopes to significantly reduce future landsliding d 2005 elsevier b v all rights reserved

a temporarily changing holocene sediment budget for a loess covered catchment central belgium abstract this study presents a holocene sediment budget for the nethen catchment a typical river catchment 55 km 2 in the belgian loess belt soil erosion and hillslope sediment storage are quantified by extrapolating detailed data obtained from soil profile truncation studies in three representative zero order sub catchments floodplain sediment storage is estimated by augerings along several transects across the main river and some of its tributaries the sediment budget shows that ca 38 of the soil eroded during the holocene is redeposited as colluvium on hillslopes and in dry valley bottoms another 23 of the eroded sediment is now stored as alluvium in the floodplain the remaining 39 or 21 10 6 mg is exported from the catchment dating of both colluvial and alluvial sediment deposits reveals that sediment dynamics between the hillslopes the dry valley bottoms and the floodplain behave highly non linearly before 500 bc sediment delivery from the hillslopes to the river channels was near maximum however since the onset of significant agriculture in the late bronze age early iron age increased rates of soil erosion are only reflected in the colluvium but not in the floodplain resulting in very low hillslope sediment delivery ratios from the medieval period onwards soil erosion increased even further mainly as a result of a further increase in agricultural land use but now also accelerated floodplain sedimentation took place due to an improved slope channel coupling and the management of floodplains

a preliminary assessment of the impact of landslide earthflow and gully erosion on soil carbon stocks in new zealand abstract in geomorphically active landscapes such as new zealand quantitative data on the relationship between erosion and soil carbon c are needed to establish the effect of erosion on past soil c stocks and future stock changes the soil c model currently used in new zealand for soil c stock reporting does not account for erosion this study developed an approach to characterise the effect of erosion suitable for soil c stock reporting and provides an initial assessment of the magnitude of the effect of erosion a series of case studies were used to establish the local effect of landslide earthflow and gully erosion on soil c stocks and to compare field measurements of soil c stocks with model estimates multitemporal erosion mapping from orthophotographs was used to characterise erosion history identify soil sampling plot locations and allow soil c stocks to be calculated accounting for erosion all eroded plots had lower soil c stocks than uneroded by mass movement and gully erosion plots sampled at the same sites landsliding reduces soil c stocks at plot and landscape scale largely as a result of individual large storms after about 70 years soil c stocks were still well below the value measured for uneroded plots by 40 for scars and 20 30 for debris tails indicating that the effect of erosion is very persistent earthflows have a small effect on estimates of baseline 1990 soil c stocks and reduce soil c stocks at landscape scale gullies have local influence on soil c stocks but because they cover a small proportion of the landscape have little influence at landscape scale at many of the sites the soil c model overestimates landscape scale soil c stocks

erosive effects of the storm helena 1963 on basse terre island guadeloupe lesser antilles arc erosive effects of the tropical storm helena that hit the volcanic island of basse terre guadeloupe lesser antilles arc on 24 october 1963 has been measured using 80 aerial images acquired by the french geographic institute ign institut geographique national at the approximate scale of 1 8000 less than three months after the storm helena on these images 253 landslides triggered during the storm were identified and mapped these landslides were located in the central region of the island where catchments exhibit the highest relief even though the average thickness of the landslides was only 1 m i e less than the thickness of the weathered layer the total volume of displaced sediments corresponded to an average denudation of 2800 t km 2 i e 1 4 mm on the watersheds affected by landsliding to assess the erosional significance of this single climatic event we compare the volume of sediment mobilized by the storm helena to the long term denudation rate the latter estimated from a calculation of the total volume of material eroded since the emplacement of lavas using a digital elevation model is found to be 0 14 mm y assuming that helena is representative of the storms that hit basse terre island during the quaternary we find that a return period of about 10 to 15 years is enough to account for the long term denudation rate recorded for this island such a period is comparable with the actual return period of the tropical cyclones of the order of 4 to 5 years suggesting that the erosion of basse terre island is entirely controlled by tropical hurricanes

post deforestation soil loss from steepland hillslopes in taranaki new zealand soil erosion on steepland hillslopes in taranaki new zealand where landsliding is the dominant erosion form was investigated by comparing mean regolith depths between first order basins that have had their forest cover removed for different periods of time regolith depth and slope angle data were collected along 19 profile lines and 30 profile lines from steepland basins that had been deforested for 10 and 85 years respectively these profile lines were subdivided into a total of 236 profile segments of relatively linear slope angle and uniform regolith depth that averaged 17 5 m in length the depth of pre existing regolith on post deforestation landslide sites is estimated from a regression of regolith depth on slope angle for undisturbed non landslide profile segments regolith depletion on landslide sites is in turn estimated by subtracting the depth of regolith on landslide sites from the estimate of pre existing regolith depth regolith depletion by post deforestation landslides averaged over the entire length of profile lines gives an estimate of average surface lowering for the area deforested for 85 years average surface lowering by post deforestation landslides is 0 15 0 04 m and is the same as the difference in mean depth of 0 15 0 11 m between this area and the area deforested for 10 years erosion of regolith from hillslopes by processes other than landsliding appears to be minimal the 0 15 m average surface lowering represents a regolith depletion rate of 1 8 0 5 mm yr 1 for hillslopes steeper than 28 where all post deforestation landslides occur average surface lowering is 0 20 0 05 m and the regolith depletion rate is 2 4 0 6 mm yr 1 average surface lowering is greatest at 0 23 0 07 m on hillslopes steeper than 32 where most post deforestation landslides occur here the regolith depletion rate is 2 7 0 8 mm yr 1 a large magnitude low frequency storm in march 1990 produced an average surface lowering of 0 041 m there were proportionately more landslides in the area deforested for 10 years illustrating the importance of previous erosion history of hillslopes on the spatial distribution of landslides there were also comparatively few landslides on steeper hillslopes because previous lower magnitude storms had already removed much of the deeper regolith

floodplain evolution in a small tectonically active basin of northern california sediment cores were collected along oodplains in the navarro river basin of coastal northern california to examine the controls on oodplain evolution in a tectonically active setting sedimentary strata were subsampled for organic content bulk density and grain size measurements organic samples were analysed for 14c age which yielded net averaged sedimentation rates for all cores overbank deposition rates decreased at all study sites through time and declined in the downstream direction the ability of intermediary order streams to store sediment in oodplains decreased the ability of highest order streams to record sediment pulse events the effects of anthropogenic disturbance primarily logging on long term overbank deposition rates were minimal climatic variability by affecting sediment loading in the channel network is the principal control on oodplain evolution through the holocene a hypothetical model is proposed to explain overbank deposition rates in the navarro basin which may be extrapolated to the northern coastal california region during the late pleistocene and holocene the complexities observed in sediment storage and routing in this study imply that caution should be made when extrapolating sediment yield measurements obtained at river mouths or coastal shelves to geomorphic events within small tectonically active basins

reaction and relaxation in a coarse grained fluvial system following catchment wide disturbance abstract the waiapu river catchment drainage area of 1734 km2 is one of the most prolific conveyors of sediment in the world annually delivering roughly 35 mt of fine material to the ocean from eroding gullies hillslopes and reworked sediment on valley floors tectonic and geologic influences in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes predisposes this region to high rates of erosion the bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse grained poorly sorted sediment mixture rapid abrasion and breakdown leads to high rates of suspended sediment yield a wave of bedload material manifesting as elevated bed levels and significant widening of active alluvial fills has been triggered by large inputs of hillslope material from a few key tributary catchments following cyclone bola in 1988 we review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years appraising some of the legacy effects that may endure as associated with reworking of the considerable alluvial stores within the waiapu system we use structure from motion sfm techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades a record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment 1958 2017 indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley bottom deposits the channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network the largest impacts occur in the upper steepland rivers closest to the landslide derived sediment supply transport rates here as inferred from cross section change are at a maximum during an aggradational phase following cyclone bola then taper off despite the large sediment accumulations remaining in the system as of 2017 the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre bola conditions the compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment

establishing a holocene sediment budget for the river dijle abstract a holocene sediment budget was constructed for the 758 km 2 dijle catchment in the belgian loess belt in order to understand long term sediment dynamics hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings which was extrapolated to the entire catchment using morphometric classes as large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times a correction was applied for the presence of forests total holocene erosion amounts 817 66 mt for the catchment of which 327 34 mt was deposited as colluvium this corresponds with a net holocene soil erosion rate of 10 8 0 8 10 3 mg ha 1 for the entire dijle catchment alluvial deposits were studied through 187 augerings spread over 17 cross valley transects the total alluvial sediment deposition equals 352 11 mt or 42 of total eroded sediment mass results indicate that at the scale of a medium sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected as a result the estimation of erosion through alluvial storage and sediment export would yield large errors dating of sediment units show an important increase in alluvial deposition from medieval times onwards indicating the important influence of agricultural activities that developed from that period mean sediment export rates from the catchment for the last 1000 1200 years range between 0 8 and 1 3 mg ha 1 a 1 and are consistent with present suspended sediment measurements in the dijle erosion for agricultural land for this period is 9 2 2 2 mg ha 1 a 1 sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment

twentieth century channel change on the dunajec river southern poland patterns causes and controls abstract spatial and temporal patterns of the twentieth century channel changes of the dunajec the second largest river of the polish carpathians are analysed using data from six historical maps hand auger drillings in paleochannels and hydrometric data from 10 gauging stations in its lower course the river was considerably narrowed shortened and embanked between the 1880s and the 1920s here bed degradation commenced in the late 19th century and has so far resulted in 3 1 m of channel incision in the middle river course little change occurred in mountain reaches where the dunajec is confined by valley sides and where bedrock exposures prevent channel incision in the reaches within intramontane basins channelization works carried out in the 1950s 1970s considerably narrowed the river and transformed its multi thread channel into a single thread straight channel rapid bed degradation induced by the works resulted in up to 2 m of channel incision over the second half of the century upstream progression of bed degradation into the adjacent mountain reach was hindered by bedrock exposures at its downstream end in the upper river course reaches with the deeply incised channels up to 3 5 m prevail over a few past decades in response to gravel exploitation river channelization and a reduction in catchment sediment supply more scarce are vertically stable reaches which owe their stability to low unit stream power in wide unmanaged reaches and to fixing of the channel bed by drop structures in channelized reaches this study shows that despite the overall tendency to incision over the 20th century considerable differences in the timing and course of channel changes occurred between particular river reaches due to variable human impact and local geological and geomorphological conditions the main phase of channel incision took place progressively later in the upstream direction however upstream progression of bed degradation from the already incised downstream reaches was precluded by the roznow dam and bedrock controlled reaches where bed material flushed out from an incising upstream reach had been introduced into an artificially narrowed channel of high transport capacity it was easily transferred downstream and could not restore the downstream reach to its pre channelization vertical position

late caledonian northeastward ophiolite thrusting in the shetland islands u k abstract kinematic analysis of the deformation in the shetland ophiolitic nappe unst and fetlar islands and in the underthrust caledonian basement indicates a northeastward sense of nappe emplacement this deformation is interpreted as silurian in age it occurred in greenschist facies metamorphic conditions and it post dated the initial thrusting of the ophiolite in the oceanic domain the similarities found between the emplacement histories of the shetland and scandinavian ophiolites can be accounted for by a three plate model for the caledonian orogen the northeasterly direction of nappe emplacement in shetland parallel to the axis of the caledonian belt is attributed to the proximity of a zone of large sinistral transcurrent motion

linkage of sediment supply and transport processes in miyagawa dam catchment japan 1 linkages between sediment supply by episodic geomorphic processes obtained from aerial photographs and field surveys and sediment transport estimated from changes in sediment deposition behind a large dam were investigated in the miyagawa dam catchment central japan a total of 6667 landslides were confirmed in the period from 1965 to 2000 on the basis of seven temporal pairs of aerial photographs both the occurrence of landslides and discharge into the dam lake affect sediment yield indicating that fluvial systems in miyagawa dam catchment are supply limited with respect to sediment sediment yields are affected by not only the initial failed volume of landslides but also the mobility of landslides and debris flows in miyagawa dam catchment percentages of landslides reaching channels varied from 56 in 1997 2000 to 75 in 1976 1981 and were correlated with maximum hourly rainfall in addition the mobility of debris flows was higher during periods with high maximum instantaneous discharge compared to lower discharge suggesting that the water content both in initially failed materials and transported sediment controlled their mobility topography also affected the mobility of landslides debris flows for catchments 0 1 km2 the percentage of channel network length impacted by debris flows decreased with increasing catchment area due to reduced channel gradient thus both the magnitude of rainfall runoff events and the catchment topography affect how landslide sediment contributes to sediment yield at the large catchment scale

analysis of hillslope erosion rates using dated colluvial deposits hollows are sites of long term deposition of colluvium and contain a valuable record of the timing and rates of hillslope erosion a model is presented that uses measured depositional rates of colluvium in hollows to calculate transport rates of colluvium and bedrock lowering rates on the surrounding slopes this model has been applied to eight dated colluvial deposits in the clearwater river basin of western washington the calculated average transport rate is about 34 cm 3 cm yr and the calculated average bedrock lowering rate is about 0 04 mm yr equivalent to an average sediment yield of 90 t km 2 yr for the holocene there is significant variability in erosion rates between sites which may be due to local lithologic variations although the average values are similar to an independent estimate of modern erosion rates for this area multiple stratigraphic levels have been dated in five deposits and document that the deposits are cumulative and that deposition has been active through the

regolith stripping and the control of shallow translational hillslope failure application of a two dimensional coupled soil hydrology slope stability model hawke s bay new zealand rainfall triggered regolith landslides constitute a dominant erosional process in new zealand hill country conversion of forest to pasture about 150 years ago decreased the size of event required to trigger slope failure resulting in greater landslide activity recent research indicates that shallow landslides then cause progressive regolith stripping with redeposition at the slope base the exposed bedrock is less permeable than the pre existing regolith cover and the redeposited soil has a higher unit weight hence alterations in both hydrological and geotechnical conditions result changing the triggering thresholds for further failure in this paper three phases of regolith stripping are investigated using a process based model to define variations in both the triggering storms as well as the failure mechanisms under these altered hydrological and geotechnical conditions over time as the regolith is stripped progressively upslope the threshold for slope failure also changes such that the landscape becomes more stable however there is a varying sensitivity to storm type for each of the three phases which adds complexity to the relationship between regolith stripping and slope failure model results suggest different hydrological conditions for slope instability depending on the degree of stripping and redeposition adding further complexity future advances in process based modelling are required for detailed investigation of temporal changes in landscape susceptibility to slope failure and uncertainty in both model parameterisation as well as process representation should be emphasised when applying such models to the long term

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

hillslope response to climate modulated river incision in the waipaoa catchment east coast north island new zealand quantifying how hillslopes respond to river incision and climate change is fundamental to understanding the evolution of uplifting landscapes during glacial interglacial cycles we investigated the interplay among uplift river incision and hillslope response in the nonglacial waipaoa river catchment located in the exhumed inner forearc of an active subduction margin on the east coast of the north island of new zealand new high resolution topographic data sets light detection and ranging lidar and photogrammetry combined with field mapping and tephrochronology indicate that hillslopes adjusted to rapid latest pleistocene and holocene river incision through the initiation and reactivation of deep seated landslides in the erodible marine sedimentary rocks of the waipaoa sedimentary system postincision deep seated landslides can occupy over 30 of the surface area the ages of tephra cover beds identified by electron microprobe analysis on 80 tephra samples from 173 soil test pits and 64 soil auger sites show that 4000 5000 yr after the initiation of river incision widespread hillslope adjustment started between the deposition of the ca 14 000 cal yr b p waiohau tephra and the ca 9420 cal yr b p rotoma tephra tephrochronology and geomorphic mapping analysis indicate that river incision and deep seated landslide slope adjustment were synchronous between main stem rivers and headwater tributaries hillslope response in the catchment can include the entire slope measured from river to ridgeline and in some cases the interfluves between incising subcatchments have been dramatically modified through ridgeline retreat and or lowering using the results of our landform tephrochronology and geomorphic mapping we derive a conceptual time series of hillslope response to uplift and climate change induced river incision over the last glacial interglacial cycle

recent sedimentation patterns and facies distribution on the poverty shelf new zealand abstract modern sediment dispersal and accumulation on the poverty shelf off the waipaoa river new zealand is investigated using x radiographic radio isotopic and physical property analyses of nearly 200 box and kasten cores collected in january 2005 aboard the r v kilo moana the high yield small mountainous waipaoa river empties onto a tectonically active narrow margin and represents an important analog for shelf sedimentation in similar environments worldwide x radiographs and bulk density measurements from a multi sensor core logger show three distinct facies on the shelf where physical and or biological factors dominate strata formation spatial distribution of these facies delineates a radial pattern with distance from the river mouth from areas dominated by stratified layers on the inner shelf to mottled muds on the outer shelf demonstrating a continuum of controls from wave reworking to episodic and extreme wet event sedimentation despite a tectonic framework that supports rapid accumulation in two recently identified shelf depocenters analysis of short lived 7 be t 1 2 53 days reveals a broad spatial distribution across and along shelf in surface sediments suggesting rapid transport from the waipaoa source however beryllium 7 inventories are consistent with centennial scale trends observed by other researchers using longer lived 210 pb analyses with highest inventories in the shelf depocenters box core bulk density analyses show lower than average bulk densities within these depocenters and higher than average bulk densities on the inner shelf and between the depocenters these observations confirm rapid deposition of low density muds in the depocenters with higher bulk density possibly physically reworked sediments remaining off the mouth of poverty bay and between the depocenters based on this single observational period there appears to be no fundamental difference between seasonal and longer term accumulation patterns on the poverty shelf

earthquake dammed lakes in new zealand eleven small lakes were formed by landslides caused by the 1929 buller earthquake four others were formed by other historic earthquakes in new zealand at least nine other new zealand lakes are also dammed by landslides and were probably formed by prehistoric earthquakes when recognized by morphology synchronous age and areal distribution earthquake dammed lakes could provide an estimate of paleoseismicity for the past few hundred or thousand years

sediment budget to assess the geomorphic effect of a cyclonic storm new zealand abstract a short term sediment budget was constructed to assess the erosion response of a soft rock hill country watershed to an intense rainstorm event the watershed is located in a landslide prone area on the east coast of the north island new zealand during march 1988 753 mm of rain was recorded over a four day period with 320 mm and 329 mm on successive days known as cyclone bola this was the largest rainstorm event in the tutira watershed in the 93 year rainfall record the budget quantifies the total sediment generated during the storm the relative contribution of erosion processes involved the amount of sediment held in storage and the amount discharged into two lakes within the watershed a landform map of the watershed was constructed and the contribution of each landform type to the total budget was calculated a total of 1 35 0 13 million m3 of sediment was generated during the storm at an average of 420 m3 ha this is equivalent to a denudation value of 42 mm for the total watershed 3208 ha and 83 mm for the landforms severely affected by landsliding 1427 ha of the sediment generated 21 remained on hillslopes 22 was deposited on valley floors 51 was deposited on the lakebeds and the remaining 6 was discharged from the watershed via the lake outlet most of the sediment generated during the storm was from primary source areas on hill slopes with sediment in secondary storage providing only a small contribution landslide erosion was the main process accounting for 89 of the sediment generated channel tunnel gully and sheet erosion were only minor contributors to the budget six hillslope landforms which occupy only 44 of the watershed generated 90 of the sediment the results of this sediment budget when put in context with the storm magnitude frequency history being analysed from lake cores contribute to the identification of sustainable land use and management of soft rock hill country

landslide geomorphology an argument for recognition with examples from new zealand the role and significance that have been ascribed to landsliding within geomorphology were examined with respect to some of the influential historical concepts of landform evolution landsliding was almost completely ignored as a geomorphic process in the earliest models of landform evolution while there has been a growing acknowledgement of landsliding as a hillslope process capable of performing significant erosion and transportation it has received only sparse recognition as a formative process in its own right notable exceptions are the rarely referenced model of relief development of skempton a w 1953 soil mechanics in relation to geology proceedings of the yorkshire geological society 29 3 33 62 pt 1 and the reply of selby m j 1974 dominant geomorphic events in landform evolution bulletin international association of engineering geology 9 85 89 to the frequency magnitude findings of wolman m g miller j p 1960 magnitude and frequency of forces in geomorphic processes journal of geology 68 1 54 74 together these two contributions provide a sound basis of geomechanical theory and ample empirical evidence to indicate that landslides have the potential to control landform evolution it is proposed that landslide geomorphology systems exist within which landslides dominate form and process by governing the mechanisms rhythm and pace of geomorphic change in time and space a review of new zealand terrain suggests that these criteria are met in six distinctive landslide geomorphology systems each of these can be characterised not only by the landslide regime but also by the fundamental pre conditions of tectonic setting and geology it is argued that the existence of such systems and the complex interrelations involved require the recognition of a landslide geomorphology in its own right

terrestrial sources and export of particulate organic carbon in the waipaoa sedimentary system problems progress and processes abstract the composition of particulate organic carbon in sedimentary systems can provide information concerning sources of materials and their history the nsf margins source to sink study of the waipaoa sedimentary system in new zealand provides a platform to calibrate the particulate organic carbon sedimentary record by linking chemical characteristics to terrestrial and marine sedimentary processes this report is a preliminary evaluation of the available organic carbon concentration elemental c n ratio and c isotopic composition data for the terrestrial portion of the system samples analyzed were rocks soils floodplain sediments and riverine suspended sediments measurements confirm previous conclusions that a portion of the riverine particulate organic carbon is derived from sedimentary rocks the rock c kerogen concentration is relatively invariant 0 25 from rock source to riverine and floodplain sediments the non rock c is derived from c3 vegetation in most of the watershed the exception being the floodplain in which local c4 plant inputs are detected the non rock organic carbon has a mean 14c age of approximately 1000 years which reflects a mixture of modern and aged components the presence of aged non rock c which is chronic in its supply to the river indicates storage of particulates within the watershed remobilized colluvial and alluvial deposits are among the possible sources systematic differences are found between 13c databases generated by various groups while there may be natural explanations for these differences methodological artifacts have to be considered standardization of methods that cross source to sink boundaries is recommended

palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand abstract a ca 2250 year storm history has been identified from a high resolution lake sediment record from the east coast of the north island new zealand this event based chronology identifies 340 storms in the pre european record the record is largely one of natural variability without human impacts layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores these storm sediment pulses derived mainly from landslides record the frequency and magnitude of storms clusters of pulses identify six periods of high sedimentation and associated erosion before european settlement a d 1878 at least five of these are interpreted as periods of higher rainfall and probably warmer temperatures since historic records show that most large storms are derived from the subtropics tropics most of the storm periods correspond to warm climate intervals previously identified from new zealand and from southern hemisphere palaeoclimatic evidence the mapara 2 period ca 2090 1855 cal yr b p was the stormiest other periods were of shorter duration the mapara 2 period occurred at times of sustained warmth in the tasmanian and chilean tree ring records which might suggest hemispheric warming at this time one storm period burrell which occurred during the historical enso record was at a time of moderately high enso activity three earlier periods also appear to show responses to enso two storm periods correspond to previously proposed new zealand wide periods of increased erosion and sedimentation estimates of palaeo storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca 12 mm thick represent palaeo storms of ca 450 mm rainfall

slope control on the frequency distribution of shallow landslides and associated soil properties north island new zealand the extrapolation of results from field trials to larger areas of land for purposes of regional impact assessment is an important issue in geomorphology particularly for landform properties that show high stochastic variability in space and time such as shallow landslide erosion it is shown in this study that by identifying the main driver for spatial variability in shallow landslide erosion at field scales namely slope angle it is possible to develop a set of generic functions for assessing the impact of landslides on selected soil properties at larger spatial scales and over longer time periods research was conducted within an area of pastoral soft rock tertiary hill country in the north island of new zealand that is subject to infrequent high intensity rainfall events producing numerous landslides most of which are smaller than several hundred square metres in size and remove soil to shallow depths all landslides were mapped within a 0 6 km2 area and registered to a high resolution 2 m slope map to show that few landslides occur on slopes 24 the areal density of landslides from all historical events showed an approximately linear increase with slope above 24 integrating landslide densities with soil recovery data demonstrates that the average value of a soil property fluctuates in a saw tooth fashion through time with the overall shape of the curve controlled by the frequency of landslide inducing storm events and recovery rate of the soil property between events despite such fluctuations there are gradual declines of 7 5 in average total carbon content of topsoil and 9 5 in average soil depth to bedrock since the time of forest clearance results have application to large scale sediment budget and water quality models and to the new zealand soil carbon monitoring system cms copyright 2012 john wiley sons ltd

late caledonian northeastward ophiolite thrusting in the shetland islands u k refutation abstract cannat 1989 uses misplaced and absent boundaries on her geological sketch map of unst and fetlar to support her proposal of a numerous set of northeast trending sinistral faults and the presence of only one ophiolite nappe in the area her proposal of northeastward directed thrusting arises from her assertion based on her interpretation of several deformed pebbles that the rocks in the imbricate thrust zone below the nappe were deformed by simple shear as a result of northeastward thrusting previous published work has shown that both fabrics and structures in these rocks indicate a major episode of orthorhombic deformation resulting in a shortening of the intermediate deformation axis pure shear with no signs of any monoclinic structures indicative of such thrusting

rainfall conditions typhoon frequency and contemporary landslide erosion in japan dealing with predicted increases in extreme weather conditions due to climate change requires robust knowledge about controls on rainfall triggered landslides we explore relationships between rainfall and landslide size throughout the japanese archipelago we test whether the total volume of landslides can be predicted directly from rainfall totals intensity and duration using a nationwide inventory of 4744 rainfall triggered landslides recorded from a d 2001 to 2011 we find that larger landslides were more abundant at the expense of smaller ones when total maximum and mean rainfall intensity exceeded 250 mm 35 mm h and 4 mm h respectively frequency distributions of these rainfall parameters are peaked and heavily skewed yet neither the most frequent nor the most extreme values of these rainfall metrics coincide consistently with the maximum landslide volumes a striking decrease of landslide volumes at both mean and maximum rainfall intensity as well as duration points to an exhaustion in hillslope geomorphic response regardless of sample size landslide type mobilized volume dominant lithology or reporting bias our results underscore substantial offsets between the peaks of rainfall metrics and maximum associated landslide volumes thus complicating straightforward estimates of geomorphic work from metrics of rainstorm magnitude or frequency only the rainfall total appears to be a suitable monotonic predictor of landslide volumes mobilized during typhoons and frontal storms

last glacial aggradation and postglacial sediment production from the non glacial waipaoa and waimata catchments hikurangi margin north island new zealand abstract the sediment flux generated by postglacial channel incision has been calculated for the 2150 km 2 non glacial waipaoa catchment located on the tectonically active hikurangi margin eastern north island new zealand sediment production both at a sub catchment scale and for the waipaoa catchment as a whole was calculated by first using the tensioned spline method within arc map to create an approximation of the aggradational waipaoa 1 surface contemporaneous with the last glacial maximum and second using grid calculator functions in the gis to subtract the modern day surface from the waipaoa 1 surface the waipaoa 1 surface was mapped using stereo aerial photography and global positioning technology fixed the position of individual terrace remnants in the landscape the recent discovery of kawakawa tephra within waipaoa 1 aggradation gravels in this catchment demonstrates that aggradation was coincidental with or began before the deposition of this 22 600 14 c year old tephra and using the stratigraphic relationship of rerewhakaaitu tephra the end of aggradation is dated at ca 15 000 14 c years ca 18 000 cal years bp the construction of the waipaoa 1 terrace is considered to be synchronous and broadly correlated with aggradation elsewhere in the north island and northern south island indicating that aggradation ended at the same time over a wide area subsequent downcutting a manifestation of base level lowering following a switch to postglacial incision at the end of glacial age aggradation points to a significant southern hemisphere climatic warming occurring soon after ca 15 000 14 c years ca 18 000 cal years bp during the older dryas interval elevation differences between the waipaoa 1 c 15 ka terrace and the level of maximum channel incision i e before aggradation since the turn of the 20th century suggest about 50 of the topographic relief within headwater reaches of the waipaoa catchment has been formed in postglacial times the postglacial sediment flux generated by channel incision from waipaoa catchment is of the order of 9 5 km 3 of which 6 6 km 3 is stored within the confines of the poverty bay floodplain thus although the postglacial period represented a time of high terrigenous sediment generation and delivery only 30 of the sediment generated by channel incision from waipaoa catchment probably reached the marine shelf and slope of the hikurangi margin during this time the smaller adjacent waimata catchment probably contributed an additional 2 6 km 3 to the same depocentre to give a total postglacial sediment contribution to the shelf and beyond of 5 5 km 3 sediment generated by postglacial channel incision represents only 25 of the total sediment yield from this landscape with 75 of the estimated volume of the postglacial storage offshore probably derived from hillslope erosion processes following base level fall at times when sediment yield from these catchments exceeded storage

spatial and temporal patterns of off slope sediment delivery for small catchments subject to shallow landslides within the waipaoa catchment new zealand abstract the waipaoa catchment in new zealand has one of the highest measured specific suspended sediment yields measured in new zealand compared to basins of comparable size a significant source of this sediment is from shallow landslides which are often triggered on a regional scale during large magnitude storm events defined as 200 mm rainfall within 72 h the first step of this sediment cascade is removal of landslide material from the slope and into the fluvial system when the debris tail is in physical contact and hence considered connected the difference between the volume of sediment liberated in the event and the volume remaining on the slope immediately following the event is termed the off slope sediment delivery ratio this value ranged from 0 12 to 0 28 for small sub catchments within the waipaoa catchment depending on catchment morphology landslide and triggering event characteristics in the waipaoa catchment a decrease in the catchment sediment delivery ratio is observed as the sub catchment size increased a human induced process which may affect off slope sediment delivery is regolith exhaustion as scars move further upslope in response to removal of preferred weathered material during previous events on the lower sections of slope however it appears that temporal scar migration away from the channels is not prevalent therefore the hypothesis that hillslope relaxation since deforestation is prevalent in this setting is considered null rather the temporal pattern to sediment delivery ratios supports the context of evolving catchment in response to deforestation in the terrain event resistance model

geomorphic change implied by regolith slope relationships on steepland hillslopes taranaki new zealand abstract slope angle and regolith depth were measured along profile lines covering a range of hillslopes in several small neighbouring drainage basins in taranaki hill country new zealand slope measurements show a cyclic variation along the length of broadly rectilinear profiles variation in slope on the lower portion of profiles adjacent to stream channels indicates that hillslopes have undergone phases of accelerated downcutting and hillslope rejuvenation a recent phase of increased erosion and hillslope rejuvenation is suggested for hillslopes steeper than 31 by the steep lowerslope and incised stream channel hillslope evolution occurs primarily by parallel retreat of steeper swale sites and slope decline during pauses in the rate of downcutting all slope profiles show a large range in regolith depth mean regolith depth of swale sites is highly correlated with mean profile slope angle mean regolith depth decreases and the frequency of landslides increase with increasing mean profile slope angle microtopographic variation in regolith depth is attributed mainly to vegetation effects recurrent landsliding and in part to bedrock curvature hillslope position and slope angle shallowing of regolith is caused by recurrent landsliding on steep swale sites fluvial erosion at the base of steep profiles and surface erosion on extremely convex spur sites the very shallow soil on the steep lowerslope portion of profiles suggests a phase of soil removal consistent with hillslope rejuvenation average depth of regolith is least at 97 cm and variability greatest on hillslopes with a profile mean exceeding 31 erosion rates are greater on these sites where soil is derived predominantly from underlying tertiary sandstone this is attributed to a greater frequency of landsliding compared to hillslopes with a profile slope less than 31 where a more regular and deeper average regolith of 153 cm infers a longer period of hillslope stability consistent with the high volcanic ash content of soils airfall andesitic volcanic ash deposited throughout the holocene has largely been removed from steeper sites the work demonstrates the need to interpret the frequency and distribution of landslides in context with natural geomorphic changes in order to assess the effect that landuse changes has on erosion rates

a budget of marine and terrigenous sediments hanalei bay kauai hawaiian islands abstract the sediment budget of hanalei bay on the north shore of kauai was calculated using sedimentological and geophysical methods the calculations of the budget subsequently allowed an interpretation of the holocene history of the bay the bay sediments are easily separated into marine carbonate and terrigenous siliciclastic grains surficial sediments are dominated by carbonate grains 70 of coralline algae coral and mollusc fragments as well as foraminifera halimeda bryozoa and echinoderm tests however siliciclastic grains e g olivine plagioclase volcanic lithics from the hanalei river watershed draining shield volcanic highlands are the most common individual grain type 27 and form a zone of high concentration from the mouth of the hanalei river into the center of the bay flooding in the bay by the post glacial sea level rise began soon after 11 7 kyears the resulting marine environment caused the net deposition of 45 5 1 5 10 6 m 3 of sediment in the bay and approximately 33 7 11 2 10 6 m 3 of sediment on the hanalei coastal plain the total volume of carbonate sediment stored in the bay and coastal plain is greater than the volume likely to have been produced exclusively within the bay during the same time calculations indicate that approximately 2490 m 3 year 1 have been imported into the bay or coastal plain and deposited since 11 700 years ago the majority of this sediment influx is likely delivered from the east by the strong tradewind driven littoral currents that characterize kauai s north shore net carbonate sediment deposition in hanalei bay peaked at a rate of 15 500 m 3 year 1 between 5000 and 3000 years ago when sea level may have been 2 m above present diminishing to 3890 m 3 year 1 from 1000 years ago to the present this influx is likely to have played a significant role in the mid to late holocene progradation of the hanalei shoreline

development of a new zealand sednet model for assessment of catchment wide soil conservation works abstract much hill country in new zealand has been converted from indigenous forest to pastoral agriculture resulting in increased soil erosion following a severe storm that hit the manawatu wanaganui region in 2004 and caused 62 000 landslides the horizons regional council have implemented the sustainable land use initiative slui a programme of widespread soil conservation we have developed a new zealand version sednetnz of the australian sednet model to evaluate the impact of the slui programme in the 5850 km2 manawatu catchment sednetnz spatially distributes budgets of fine sediment in the landscape it incorporates landslide gully earthflow erosion surficial erosion bank erosion and flood plain deposition the important forms of soil erosion in new zealand modelled suspended sediment loads compared well with measured suspended sediment loads with an r2 value of 0 85 after log transformation a sensitivity analysis gave the uncertainty of estimated suspended sediment loads to be approximately plus or minus 50 at the 95 confidence level it is expected that by 2040 suspended sediment loads in targeted water management zones will decrease by about 40 the expected decrease for the whole catchment is 34 the expected reduction is due to maturity of tree planting on land at risk to soil erosion the 34 reduction represents an annual rate of return of 20 on 20 million nz of investment on soil conservation works through avoided damage to property and infrastructure and avoided clean up costs

resistance to shallow landslide failure through root derived cohesion in east coast hill country soils north island new zealand measured shear strength cohesion and friction of airfall derived east coast hill country regolith is insufficient for the maintenance of existing regolith depth slope angle relationships in the catchment of lake waikopiro in northern hawke s bay new zealand if these regoliths are attributed with an additional increment of cohesion derived mechanically from a turf mat membrane existing depth slope angle distributions are explicable sites where failure has occurred have been measured and back analysis used to derive a range of values for additional mechanical cohesion values are in the range 0 2 7 6 kpa consistent with earlier findings this range is narrowed further to 0 7 6 9 kpa with assumptions regarding soil moisture status at failure copyright 1999 john wiley sons ltd

a proposed cell model for multiple occurrence regional landslide events implications for landslide susceptibility mapping abstract multiple occurrence regional landslide events morles consist of hundreds to thousands of shallow landslides occurring more or less simultaneously within defined areas ranging from tens to thousands of square kilometres while morles can be triggered by rainstorms and earthquakes this paper is confined to those landslide events triggered by rainstorms globally morles occur in a range of geological settings in areas of moderate to steep slopes subject to intense rainstorms individual landslides in rainstorm triggered events are dominantly small shallow debris and earth flows and debris and earth slides involving regolith or weathered bedrock the model used to characterise these events assumes that energy distribution within the event area is represented on the land surface by a cell structure with maximum energy expenditure within an identifiable core and rapid dissipation concentrically away from the centre the version of the model presented here has been developed for rainfall triggered landslide events it proposes that rainfall intensity can be used to determine different critical landslide response zones within the cell referred to as core middle and periphery zones these zones are most readily distinguished by two conditions the proportion of the slope that fails and the particular type of the slope stability factor that assumes dominance in determining specific sites of landslide occurrence the latter condition means that the power of any slope stability factor to distinguish between stable and unstable sites varies throughout the affected area in accordance with the landslide response zones within the cell certain factors critical for determining the location of landslide sites in one part of the event area have little influence in other parts of the event area the implication is that landslide susceptibility maps and subsequently derived mitigation measures based on conventional slope stability factors may have only limited validity for many events the overall ability to predict the impact of these events and consequently the development of effective mitigation measures is limited by the ability to predict the travel path storm centre and intensity range within the cell structure of extreme weather systems

paired geochemical tracing and load monitoring analysis for identifying sediment sources in a large catchment draining into the great barrier reef lagoon while sediment tracing has been typically applied to identify sediment sources that are difficult to measure by gauging monitoring it can also be useful in estimating relative sediment yields from gauged river catchments the major and trace element composition of river sediments from eleven locations in the 130000 km2 burdekin river catchment northeastern australia was analysed to examine relative contributions from upstream source areas in the 2011 12water year sediment tracing results are compared against estimates derived fromsediment load monitoring at three locations comparisons show that there is good agreement between tracing results and monitoring data at one of the tributary confluences at the second site notable contrastswere found between the load estimates from the monitoring and tracing data at this site a large impoundment occurs between the upstream sampling gauging sites for source sediments and the downstream sampling gauging sites for target sediments the contrast is likely caused by temporal variations in particle size distributions of suspended sediment fromeach river and differential trapping efficiencies in the impoundment for sediment derived fromthe different tributaries in the absence of the detailed particle size data and trapping efficiency estimates sediment tracing provides the unique opportunity to elucidate source contributions of the finer fractions of suspended sediment at a third site where there were recognised measurement gaps in the monitoring data during large discharge events the relative load estimates fromthe tracing data provided a means of constraining the recognized uncertainty of monitored load estimates we conclude that sediment tracing can be used as a valuable adjunct to monitoring data particularly in remote large and data sparse catchments both tracing results and monitoring data showthat the upper burdekin river and bowen bogie riverswere the dominant source of the b10 m sediments being delivered to the gbr lagoon from the burdekin river catchment in the 2011 12 water year more substantial contribution from the belyando suttor rivers indicated by the tracing results than the monitoring data is attributed to preferential delivery of the 1 10 m sediments through the impoundment and has uncovered a knowledge gap in sediment budgets in the catchment

centennial to millennial changes in maar lake deposition during the last 45 000 years in tropical southern africa lake masoko tanzania abstract the masoko maar southern tanzania provides one of the most continuous late quaternary lacustrine sedimentary records from africa a detailed chronostratigraphic framework coupled with sedimentological and magnetic measurements allows us to construct a 30 year resolution continuous sedimentary sequence covering the last 45 000 years and to address local depositional environment and climate variability in the tropical southern africa based on present day observations and measurements our results indicate that the low field magnetic susceptibility of the sediment is highly controlled by climate driven processes wind stress and or lake level amplitude changes acting on the titanomagnetite rich shoreline reservoir the tephra and turbidite free magnetic susceptibility record is strongly modulated by a persistent multi decadal to centennial variability 80 to 200 years probably linked to the gleissberg and suess cycles of solar activity at lower frequency the variability of deposition is controlled by the precessional cycle and its harmonics suggesting a dominant multi millennial forcing of low latitude insolation on climatic changes in tropical southern africa inferred wetter conditions during the last glacial maximum and the younger dryas at masoko 9 s indicate southward shifts of the intertropical convergence zone associated with the north atlantic glacial dynamics and or contrasted hydrological changes in the rungwe highlands compared to the neighbouring areas finally former regional transfer function between diatom assemblages and water chemistry suggested drier conditions during the last glacial maximum at lake masoko barker p williamson d gasse f gibert e 2003 climatic and volcanic forcing revealed in a 50 000 year diatom record from lake massoko tanzania quaternary research 60 368 376 in this context further climate proxy data such as pollen and hydrobiological studies in small deep lakes are needed to support our alternative interpretation of the masoko record

some methodological developments in the analysis of sediment transport processes using age distribution of floodplain deposits abstract floodplain areas are primary storage sites for river sediment in the saru river ages of floodplain surfaces were examined by tree ring analysis and vertical and horizontal configurations of floodplain deposits were measured by field and aerial photo surveying a flood in 1992 provided a good opportunity to examine depositional and erosional processes of floodplain sediment before and after the flood predominant disturbances were observed in the unconstrained wide reaches where floodplains develop this event indicated that eroded areas of floodplain deposits in each age class linearly increased with sediment volume and that the proportion of the total area eroded decreased exponentially with increase in the age of sediment we constructed basic equations expressing continuity of age distribution in order to analyze river sedimentation in a time series according to the results of the 1992 flood the floodplain disturbance rates determined by this analysis showed similar temporal changes with sediment transport rates monitored at the iwachishi reservoir a sharp increase in sediment discharge was seen after 1962 associated with the historical maximum rainfall in the temporal analysis of floodplain sediment the time series approach presented here is useful for evaluating the speed of sediment waves and the cumulative impact of sedimentation in a river basin