Rugged Plateaus and Extensive Floodplains — Modelling Landform Evolution in a Northern Australian Catchment

Medium to large natural catchments are often more spatially heterogeneous than small catchments or single landforms. Attempting to model landform evolution of large areas is consequently more complex. This paper demonstrates that modelling landform evolution in medium to large catchments can be improved by calibrating the model to smaller, more geomorphologically homogenous sub‐catchments. The paper investigates landform evolution in the Ngarradj catchment in the Northern Territory of Australia (a medium scale catchment of approximately 67 km²). The catchment is complex and contains two distinct landform regions; an upland plateau region with highly dissected sandstone and shallow, sandy soils, and a lowlands region with gentle, wooded slopes and floodplains with deep, sandy soils. The SIBERIA landform evolution model is calibrated and applied to the Ngarradj catchment. The complexity of the Ngarradj catchment is incorporated into the modelling by dividing the catchment into three sub‐catchments (Swift Creek (SC), Upper Main (UM) and East Tributary (ET)) which are relatively homogeneous and for which hydrology and sediment transport data are available. A discharge‐area relationship and long‐term, sediment loss rates for the catchment are derived based on an annual series flood frequency analysis of a 20 year runoff record predicted in a previous study. Sediment transport modelling incorporates both suspended and bedload sediment loss. The denudation rates derived using these data are 37, 63 and 77 mm kyr^?1 for the SC, UM and ET sub‐catchments, respectively. Model predictions indicate that the UM sub‐catchment will have the greatest mean erosion. This is balanced by the large amount of deposition that will occur in the upper Ngarradj valley of the UM sub‐catchment. Further deposition occurs on the floodplain of Ngarradj, with the area between the SC and ET/UM (up‐stream) sub‐catchments experiencing a small net accretion of sediment (15 mm kyr^?1).     

‘Torrents of Terror’: the August 1998 Storm and the Magnitude,Frequency and Impact of Major Floods in the Illawarra Region of New South Wales

The Illawarra Region some 80 kilometres south of Sydney is characterised by a prominent coastal escarpment that rises to 700 m within 12 km of the coast and forms a locus for frequent, high intensity rainfall events. One of the most recent recorded events occurred on 17 August 1998 with rainfall intensities at several pluviometers exceeding 120 mm hr^‐1 over a duration of one hour, with up to 249 mm falling in 3.5 hours during the main storm burst. Detailed pluviometer data indicate that the storm was non‐stationary and moved down catchment producing a widespread zone of 120 mm hr^‐1 intensity rainfall over a 30 minute duration across mid‐lower catchment areas after similar intensity but longer duration rainfall in catchment headwaters. Slope‐area reconstructions of peak discharge indicate that small catchments on the escarpment within the zone of maximum intensity experienced close to 100% rainfall‐runoff relationships, with peak discharges correlated to short duration (<1 hr) peak rainfall intensities. Widespread erosion occurred particularly where urban development had encroached on natural water courses. Debris/hyperconcentrated flows originating from both anthropogenic and natural sediment sources caused damage to urban areas. This paper provides an overview of the spatial and temporal characteristics of the 17 August 1998 storm, the hydrologic and geomorphic response of the streams, and the nature of damage to urban areas. It reassesses the frequency of recent high‐magnitude rainfall/flood events in the region, discussing the relationships between rainfall intensities, estimates of flood magnitudes and stormwater channel capacities.     

HOLOCENE ACCUMULATION OF COLLUVIAL AND ALLUVIAL SEDIMENTS IN THE WEIßE ELSTER RIVER VALLEY IN SAXONY,GERMANY*

Geoarchaeological investigations at two archaeological excavation sites lead to new results with respect to the Holocene landscape development of an archaeologically important loess landscape of Central Europe. Colluvial and alluvial sediments were sampled during archaeological excavations on the valley edge of the Weiße Elster and dated by means of ¹⁴C, TL and dendrochronology, and on the basis of archaeological finds. Thus, for the first time, the development of a valley edge of a river in the Leipzig area, which has been continuously settled for 7300 years, can be reconstructed. The first soil erosion on the valley edge is established towards the end of the Atlantic period. During the High Middle Ages, a colluvial sediment developed. Its deposition time can be limited to between ad 1000 and 1100. The flood loam near Großstorkwitz, which can be stratified by means of the soil and colluvial deposits, originated in the late Sub‐Boreal and early Sub‐Atlantic, as well as after ad 1100. During the first millennium ad, a soil developed in the older flood loam, which indicates a phase of reduced flood loam sedimentation.     

Natural flood management: small-scale progress and larger-scale challenges

ABSTRACT

Management of fluvial flood risk in the UK is undergoing a paradigm shift, with a change in emphasis from solely working with structural defences to considering catchment-based measures which attenuate flood runoff. Natural Flood Management (NFM) is promoted as a method that can reduce flood risk through the alteration, restoration or use of landscape features. Here we highlight the potential to manage runoff locally in the rural landscape using NFM by targeting flow pathways and utilising floodplains and riparian zones. Using two case study examples from the UK, we show that by accumulating dispersed small-scale storage in small catchment areas (<10 km²) can assist in attenuating flood runoff. However, there is currently a lack of evidence of measure effectiveness at larger catchment scales and for managing extreme flood events. Nevertheless, there is a strong evidence base to suggest many of these measures deliver a range of different ecosystem services if installed in the correct location in the landscape.     

Lake Nuga Nuga: a Levee‐dammed Lake in Central Queensland,Australia

Lake Nuga Nuga is a levee‐dammed lake in the dry sub‐humid tropics of the Fitzroy Basin in Central Queensland, Australia, that has expanded significantly since it was first mapped in 1866. ²¹⁰Pb dating of a sediment core from the lake indicates that the rate of sedimentation has been constant for the past 67 years at 3 mm yr^?1 despite widespread clearing and land use intensification in the catchment during that time. Pollen analysis confirms this and shows that there was little change in vegetation during the early settlement period (1863–1962), but the intensification of land use that started in the early 1960s brought about a dramatic change in the vegetation communities. This study demonstrates that while sediment production may be significantly impacted by land‐use activities, sediment delivery is primarily controlled by topography.     

An Examination of Vertical Accretion of Floodplain Sediments in the Labasa River Sugarcane Belt of Northern Fiji: Rates,Influences and Contributing Processes

The ¹³⁷Cs (caesium‐137) method was used to investigate medium‐term rates of sediment deposition on the floodplain of the Labasa River, on Vanua Levu island in northern Fiji. The Labasa basin is commercially important for sugarcane farming, which provides much revenue and sustains the economy in the greater Labasa area. Alluvium was sampled at three riverbank sites in vertical increments of 30 mm. Measured net vertical accretion rates, based on analysis of depth‐profiles of ¹³⁷Cs activity, ranged from 10 mm yr^?1 at a low‐lying site near a tributary confluence with the main river, to 60 mm yr^?1 on a levée that was elevated slightly above the adjacent floodplain. These rates of accretion are high, but in general agreement with rates recorded using similar methods in other tropical Pacific island river systems. Soil erosion under sugarcane on hilly parts of the lower Labasa basin is an important factor in rapid floodplain development. Observations made during Cyclone Ami, which traversed Vanua Levu island in early 2003, illustrate the major contribution of severe storm events to floodplain sediment supply, by triggering numerous landslides on catchment slopes and in‐channel debris floods, and by generating large‐magnitude overbank floods.     

The deserts of the Kashmir‐Tibetan frontier

Abstract

Semi-arid landscapes are vulnerable to cultivation, overgrazing and climate variability, although it is difficult to identify the relative significance of these three factors. In the South African Karoo, the ‘desertification debate' seeks to explain a change to more shrubby vegetation in heavily grazed areas. We examine these issues in catchments where farm reservoirs provide sediment stores with 137Cs, 210Pb, geochemical and mineral magnetic signatures. Rainfall data and stocking numbers are reported and current erosion rates are estimated. Sediment accumulation in the reservoirs increases between 1935 and 1940, probably due to rises in the frequency of rainfall events of >25mm day. Significant increases in sedimentation rates (×8) occur during rain-fed wheat cultivation. In an uncultivated catchment, sediment yields remain relatively high and reflect increases in erosion from hillslopes, colluvial storage, and cultivated land sources. Gully systems have acted as transport routes rather than sediment sources over the last ～70 years. Badland erosion rates average ca. 50t ha^?1 yr^?1. At Ganora, their development in the 1920s strongly influences peak sedimentation between 1970 and 1980. Any delay between badland initiation and increased sediment yield appears to be a function of landscape connectivity. Recovery following disturbance is occurring slowly and is likely to take >100 years. De-stocking and better management systems are reducing erosion rates but may be offset by increases in rainfall intensity.     

Antarctic history: A reply to professor W. H. Hobbs

On July 25th 1983 a severe thunderstorm brought torrential rain and flooding to a small valley near Newcastleton in Roxburghshire. At one site within the valley, around 65 mm of rainfall was recorded in 75 minutes, though this was probably 2 km from the centre of the storm. The resulting peak flow was estimated at almost 170 m³s^‐1 from a drainage area of 36.9 km². Lightning killed some livestock whilst many more were drowned. The storm triggered peat slides on several hillsides and caused extensive erosion of river banks and damage to buildings and bridges. The associated high sediment load killed fish stocks in the receiving waters. The flood was a significant event in terms of its human disruption and its impact on the natural environment.     

Groundwater discharges in the Baltic Sea: survey and quantification using a schlieren technique application

Groundwater seeps are known to occur in Eckernförde Bay, Baltic Sea. Their discharge rate and dispersion were investigated with a new schlieren technique application, which is able to visualize heterogeneous water parcels with density anomalies down to Δσ_t = 0.049 on the scale of millimeters. With the use of an inverted funnel, discharged fluids can be captured and the outflow velocity can be determined. Overall, 46 stations could be categorized by three different cases: active vent sites, seep‐influenced sites, and non‐seep sites. New seep locations were discovered, even at shallow near‐shore sites, lacking prominent sediment depression, which indicate submarine springs. The detection of numerous seeps was possible and the groundwater‐influenced area was defined to be approximately 6.3 km². Flow rates of between 0.05 and 0.71 l m^?2 min^?1 were measured. A single focused fluid plume, which was not disturbed by the funnel was recorded and revealed a flux of 59.6 ± 20 ml cm^?2 min^?1 and it was calculated that this single focused plume would be strong enough to produce a flow rate through the funnel of 1.32 ± 0.44 l m^?2 min^?1. The effect of different seep‐meter funnel sizes is discussed.     

Hillslope Runoff and Soil Erosion Following Reforestation in the Copper Basin,Tennessee, USA

The landscape of the 130 km² Copper Basin, in the southeastern USA, became extremely degraded during more than a century of logging, mining, acidification, grazing, and fire. In the twentieth century, the Copper Basin became the focus of a series of reforestation programs and is now largely tree‐covered again. To investigate the effects of over 50 years of reforestation efforts, we developed a space‐for‐time substitution and conducted rainfall simulation experiments in ‘forest’ patches of various ages, at sites remaining unvegetated, and at forested reference sites outside the basin. At 59 sites, we monitored surface runoff and sediment detachment rates during 30‐minute rainfall simulation experiments; and at 54 of those sites, we determined soil organic matter content. Then, we measured litter and observed soils at 25 of the sites, and measured soil respiration at a site in each age zone. The results demonstrate that soil erosion by sediment detachment decreases within a decade following reforestation. Recently reforested sites have soils with significantly less organic matter and have higher runoff rates than forests more than 50 years old. The long‐term persistence of low infiltration rates suggests that, at sites where the A and B soil horizons and the biological health of the soil have been lost, restoration of the hydrologic function of a landscape by reforestation may require centuries.     

Temporal Patterns and Effects of Surface‐Water Diversions on Daily Flows and Aquatic Habitats: Bega‐Bemboka River,New South Wales,Australia

An understanding of the nature and magnitude of hydrological, physical habitat and physico‐chemical effects resulting from surface‐water diversions in river systems is essential for effective management of water resources. For most coastal‐draining rivers in New South Wales, however, there are few data available on irrigation diversions, their hydrological impacts and environmental effects. This paper therefore presents an analysis of mean daily surface‐water diversions for pasture irrigation from approximately three years of metered data and the resultant effects on daily flows and aquatic habitats in the Bega‐Bemboka River. The period of analysis of the hydrological effects of irrigation diversions is extended to the full length of record (approximately five years) for gauging stations most affected by irrigation diversions, using Maintenance of Variance Extension Type 1 (MOVE.1) modelling techniques. The annual mean, median and peak daily rates of water diversion by metered surface‐water licences used to irrigate 925 ha of dairy pasture are 10.5 Ml d^?1, 7.3 Ml d^?1 and 41.5 Ml d^?1, respectively. Diversion effects on flow duration statistics are such that the measured 90th and 95th daily flow duration percentiles at the gauging station most affected by upstream irrigation diversions are equivalent to the 97th and 99th flow duration percentiles, respectively, under MOVE.1 modelled natural flow conditions. While diversions for irrigation over the three‐year data period account for only 6.6% of total flow volumes, diversions as a proportion of daily surface‐water inflows increase exponentially under decreasing flow rates. Median and maximum daily diversion rates attain 91% and 118%, respectively, of total surface‐water inflows to the diversion‐affected reach when upstream inflows range from 15 to 20 Ml d^?1. This exponentially‐increasing relationship between daily diversion rates and declining surface‐water inflows suggests that ‘rule of thumb’ guidelines on sustainable diversion limits based on mean or median annual percentage diversion volumes need to be applied cautiously to river systems with no or limited capacity to manipulate flows to meet downstream consumptive demands.     

Ecohydrology and Environmental Change to Lake Albacutya and Wyperfeld Park in North‐Western Victoria,Australia

Lake Albacutya is a well‐known intermittent lake in north‐western Victoria. The lake is near the termination of the Wimmera River. From time‐to‐time the lake fills and flow passes down Outlet Creek into Wyperfeld National Park. The wetlands associated with the lake have a high biodiversity value and are named in international treaties. This paper examines the hydrologic factors associated with lake filling and flow into Wyperfeld. The lake has filled approximately six times since 1880 and has partially filled on other occasions. Examination of rainfall data from 1875 at Horsham gave no indication of long term rainfall decline, and showed that rainfall at Horsham can be viewed as representative of rainfall in the Wimmera River catchment. However a double‐mass analysis showed that the relationship between the Wimmera River flow and rainfall has varied from 1890 to the present. Examination of data associated with six fillings of Lake Albacutya suggested that filling is a two‐year event requiring at least 550 GL of flow passing Horsham over the two years immediately associated with the flood. A simple model based on rainfall and this threshold reproduced observed characteristics of the data reasonably well. This suggested that the flooding frequency of Lake Albacutya has dropped from about one in 25 years in the natural state to a substantially lower frequency under current river conditions. The results also suggested that because of changes in the Wimmera River the last filling and flood into Wyperfeld in 1976 was far smaller than it would otherwise have been. This is consistent with field mapping of the flood in relation to River Red Gum (Eucalyptus camaldulensis Dehnh.) stands. Analysis of the health of these stands showed major dieback with the severity of this being roughly proportional to the distance from the 1976 flood boundaries. An examination of values associated with the lake and adjoining Wyperfeld National Park suggested that biodiversity and economic values are and will be compromised by the reduction in flooding. In particular, an internationally‐known provenance of Red Gum is at risk, and bird‐breeding opportunities have diminished.     

Estimation of Soil Erosion Using Field and Modelling Approaches in an Undisturbed Arnhem Land Catchment,Northern Territory,Australia

An assessment of slope erosion at Tin Camp Creek catchment, Arnhem Land, Northern Territory, Australia, was carried out using the fallout environmental radioisotope caesium‐137 (¹³⁷Cs) as an indicator of soil erosion status, two numerical models (SIBERIA and the Revised Universal Soil Loss Equation (RUSLE)) and erosion pins. This undisturbed drainage basin is situated in the seasonally wet‐dry tropics, with high energy storms and a mean annual rainfall of 1389 mm. Tin Camp Creek catchment is unaffected by European agriculture or pastoral activities, but often experiences fire during the dry season. Two transects were sampled for ¹³⁷Cs in 2002 and 2004, and two models were used to convert ¹³⁷Cs measurements into soil loss estimates. Two methods using the theoretical Profile Distribution Model (PDM) gave net soil redistribution rates between +2.72 and –22.19 t ha^?1 yr^?1 and +2.95 and –24.06 t ha^?1 yr^?1, respectively, while an Australian empirical model (AEM) for uncultivated soils produced estimates between +1.84 and –7.00 t ha^?1 yr^?1 (negative values indicate soil erosion, positive, deposition). The RUSLE gave estimated soil losses for the two transects of approximately 10 t ha^?1 yr^?1, while the SIBERIA model produced values between 0.5 and 2 t ha^?1 yr^?1 for the transects and between 3.5 and 11 t ha^?1 yr^?1 for the total catchment. Average net soil losses of 14 and 15 t ha^?1 yr^?1 for the total catchment and slopes, respectively, were measured by erosion pins. The soil losses in the catchment are similar to those for some other transects in the Northern Territory and the Kimberley region of Western Australia (measured by the ¹³⁷Cs AEM), even though these areas are affected by pastoral activities. This may be at least partly explained by erosion in Tin Camp Creek catchment during high intensity rainstorms at the commencement of the wet season, especially if the slopes have been affected by fire during the previous dry season.     

Diatom and dinoflagellate assemblages of the Hawkesbury River,N.S.W., over the last two centuries: evidence for changes in hydrology

Diatom and dinoflagellate cyst analysis of a 77 cm long sediment core from Cowan Creek, Hawkesbury River estuary, N.S.W., revealed changes in the catchment hydrology over the last 266 years. High abundances of the freshwater/brackish diatom genus Cyclotella at the base of the core imply sustained periods of reduced salinity that now no longer occur. Reduction of freshwater flow after approximately circa 1800 (60 cm) has allowed the development of marine planktonic diatoms Thalassiosira spp.,Ditylum brightwellii, Rhizosolenia setigera, Pseudo-nitzschia pungens and Chaetoceros spp. Benthic diatom diversity has remained relatively unchanged. The toxic dinoflagellate Gymnodinium catenatum, although identified in a cyst survey in April 1995, was not found in the sediment cores. Changes in dinoflagellate assemblage are consistent with the effects of increasing urbanisation and eutrophication.     

The use of Caesium–137 to Assess Surface Soil Erosion Status in a Water–Supply Catchment in the Hunter Valley,New South Wales,Australia

In the absence of direct erosion measurements, the soil activity of the fallout radionuclide caesium–137 (¹³⁷Cs) offers an attractive tool for the estimation of long–term (approximately 45 years) net surface and minor rill soil erosion rates for hillslopes. A transect–based soil sampling technique was applied to one woodland and five grazed pasture hillslopes in the Williams River water–supply catchment in the Hunter Valley, New South Wales. An Australian regression model (SOILOSS) relating net soil loss from runoff–erosion plots to ¹³⁷Cs deficit in soils was used to calculate a weighted net surface and minor rill erosion rate for the six hillslopes. The net median surface erosion rates ranged between 0.00 and 0.64 t ha^–1yr^–1with the average median soil erosion rate of 0.19 t ha^–1 yr^–1(std. dev. = 0.23), indicating that these hillslopes were unlikely to be major sources of sediment to the catchment's waterways. Net soil loss rates were also shown to be low in comparison to Australia–wide data and comparable to hillslope data obtained elsewhere in the same region. Minimum and maximum error bounds were provided with each erosion rate to account for radionuclide detector count error. For one hillslope the estimated error due to detection was 1.34 t ha^–1yr^–1, while the remaining five hillslopes exhibited error of up to 0.41 t ha^–1yr^–1. Correlation analyses between the net soil loss rates and physical hillslope characteristics were non–significant.     

Spatial Variability of Controls on Downstream Patterns of Sediment Storage: a Case Study in the Lane Cove Catchment,New South Wales,Australia

This study uses GIS techniques to examine the spatial distribution of stream power along major streamlines in the Lane Cove catchment in northern Sydney, Australia. Channel gradient estimates derived from a 5 m resolution digital elevation model (DEM) are combined with streamflow data to estimate stream power along river courses. Stream power and its constituent components are then related to a detailed field‐based assessment of sediment storage along the trunk stream and primary tributaries. At the catchment scale, sediment storage per unit length decreases as channel gradient and gross stream power increase. However, local controls such as variability in valley width and occurrence of confluence zones exert a greater influence upon sediment storage, disrupting systematic catchment‐wide relationships. The total volume of storage along each streamline has a strong linear relationship to the area of the subcatchment, but the distribution of sediment along streamlines varies between subcatchments. The GIS framework employed in this project allows generation of continuous, empirical data, thereby providing catchment‐specific predictive capacity that can accompany theoretical approaches to stream power modelling.     

Erosion and Nutrient Loss on Sloping Land under Intense Cultivation in Southern Vietnam

To help improve the well‐being of the local people, a joint Vietnamese‐UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment‐wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuóc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha^?1 y^?1 under cassava saplings with cashew nuts, 43.3 t ha^?1 y^?1 on uncultivated land and 41.7 t ha^?1 y^?1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side‐slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing.     

Early medieval origins of iron mining and settlement in central Sweden: multiproxy analysis of sediment and peat records from the Norberg mining district

The historical Norberg mining district in central Sweden with its shallow, easily accessible iron ores figures prominently in the earliest documents from the 14th century concerning mining or metallurgy. This 1000-km² district is considered to be one of the first areas in Sweden exploited for iron ores and, in fact, Europe’s oldest known blast furnace, Lapphyttan, is located in the Norberg district about 10 km from the mines in the village of Norberg (Norbergsby). Earlier archaeological excavations suggest the furnace was in operation as early as the 11th or 12th century (870 and 930 ¹⁴C yr BP), and a number of other sites in the district have been dated to the 13th–15th centuries. Here, we have analyzed two lake sediment records (Kalven and Noren) from the village of Norberg and a peat record from Lapphyttan. The Lapphyttan peat record was radiocarbon dated, whereas the sediment from Kalven is annually laminated, which provides a fairly precise chronology. Our pollen data indicate that land use in the area began gradually as forest grazing by at least c. AD 1050, with indications of more widespread forest disturbance and cultivation from c. 1180 at Lapphyttan and 1250 at Kalven. Based on ²⁰⁶Pb/²⁰⁷Pb isotope ratios in Kalven’s varved sediment record, there is an indication of mining or metallurgy in the area c. 960, but likely not in immediate connection to our sites. Evidence of mining and metallurgy increases gradually from c. 1180 when there is a decline in ²⁰⁶Pb/²⁰⁷Pb ratios and an increase in charcoal particles at Lapphyttan, followed by increasing inputs of lithogenic elements in Noren’s sediment record indicating soil disturbance, which we attribute to the onset of mining the iron ore bodies surrounding Noren. From AD 1295 onwards evidence of mining and metallurgy are ubiquitous, and activities accelerate especially during the late 15th century; the maximum influence of Bergslagen ore lead (i.e., the minimum in ²⁰⁶Pb/²⁰⁷Pb isotope ratios) in both Kalven and Noren occurs c. 1490–1500, when also varve properties change in Kalven and in Noren sharp increases occur in the concentrations of a range of other ore-related metals (e.g., arsenic, cadmium, copper, iron, lead, mercury and zinc). From the 15th century onwards mining and metallurgy are the dominant feature of the sediment records.     

The Geography of the Anthropocene in New Zealand: Differential River Catchment Response to Human Impact

New Zealand provides a useful environment to test the notion that the Anthropocene is a new geological epoch. There are two well‐dated anthropogenic impact ‘events’: Polynesian settlement c. AD 1280, and European colonisation c. AD 1800. Little attention, however, has been given to regional catchment response to these, although it has been assumed that both Polynesian and European farming and land use management practices significantly increased erosion rates across most of New Zealand. This paper addresses the nature and timing of human impacts on river systems using meta‐analysis of a recently compiled nationwide database of radiocarbon‐dated fluvial deposits. This shows highly variable human impacts on erosion and sedimentation in river systems, which are often difficult to separate from naturally driven river activity. Catchment‐scale data with high resolution dating control record clearer evidence of human disturbance. In Northland, anthropogenic alluviation is recorded from c. AD 1300 linked to early Polynesian settlement, enhanced further in the late 19th and 20th centuries by European land clearance, when sedimentation rates exceeded 25 mm year^?1. This study demonstrates significant geographical variability in the timing of human impact on river dynamics in New Zealand, despite two synchronous phases of human settlement, and highlights the difficulty of formally designating a simple and single ‘Anthropocene Epoch/Age’.     

A Role for Geomorphology in Integrated Catchment Management

Catchments (watersheds) are integrated through water movements. Water moves sediments; and the translocation of materials has geomorphic and pedological responses. Fertiliser and pesticide residues and other toxic substances are also transported by water, in solution and attached to sediment particles, affecting various ecological components of catchments. The insertion of pollutants is directly caused by land‐use practices. In turn, land uses are influenced by the pedo‐geomorphology of the catchments (uplands, valley sides, flood plains and terraces, spurs and hollows, convexities and concavities; position in the upper, middle or lower catchment; and by catenary relationships). Therefore catchment management must deal with interrelationships amongst human activities and various geomorphic elements. Several case study examples from southwestern Australia demonstrate the importance of geomorphology in catchment management. They include: rates of hillslope erosion and translocation of P in micro‐catchments within a drainage basin context; stream salinisation; accumulation of heavy metals in stream sediments; geomorphic elements influencing the spread of weeds and the erosion of access tracks; and some relationships between valley‐side land uses and stream morphology. The incorporation of these and other issues in a management strategy is then illustrated. Complex skills are involved in producing and implementing a management strategy, including but extending well beyond those of the geomorphologist.