Protecting headwater streams is essential to minimise downstream sediment loads to rivers, estuaries, and oceans. This study analyses the gully and sheet erosion risk from a 33,000 ha agricultural development proposal in the Normanby catchment draining to the Great Barrier Reef (GBR) Lagoon, Australia. The slope-area threshold for channel initiation was assessed for existing gully channel head locations using satellite images and a hydrologically enforced digital elevation model (SRTM). Thresholds were used to predict whether other stream lines (1:25k scale) were prone to gully incision under development. Results indicated that 430 km out of 1,200 km of streams were at risk of gullying, which could increase erosion by 2-times, delivering 7,500 t yr(-1) locally and 1,700 t yr(-1) (worth A$1.8 million) to the GBR. Sheet erosion under agriculture is estimated (RUSLE) to increase by 13-times from 0.12 to 1.5 t ha(-1) yr(-1), with 2,200 t yr(-1) to streams and 900 t yr(-1) (worth A$1 million) to the GBR. Buffering (+/- 50 m) 560 km of headwater streams would cover 5,600 ha or 17% of the area. Precision agriculture using higher resolution topographic data (LiDAR) and improved slope-area thresholds for gully erosion should be a minimum prerequisite for development, which would reduce but not eliminate increased sediment loads to the GBR. Forest clearance for agriculture is ongoing in Australia, but this first-world country does not have effective policies or regulations to protect headwater streams or cumulative impacts to the World Heritage Great Barrier Reef, despite millions of dollars spent annually to reduce past land degradation.

Many tropical river systems have altered water quality due to human land use, impacting the biodiversity of freshwater and coastal ecosystems. Long-term, catchment-scale monitoring is needed to understand pollutant sources, controls, and trends. This 12-year study monitored baseflow and flood event nutrient and sediment concentrations, and estimated sediment loads across the Normanby Basin in northern Australia. Suspended sediment concentrations and yields were highest in upper catchment areas where cattle grazing occurred on erosion-prone sodic soils. Mid- and lower catchment rivers and floodplains were a sink for sediments and nutrients, trapping around 75% of suspended sediments during events. Clays (<4 μm) were preferentially transported to the estuary, with an estimated 46% sediment delivery ratio. In the estuary, suspended sediment concentrations were influenced by tidal resuspension processes and there were significant sources of DIN. These findings can help prioritise land management investments for the protection of Great Barrier Reef and freshwater ecosystems.

Badlands occur in dissected landscapes on all continents and are of interest to tourists for their landscape and aesthetic value. People choose these eroded landforms as tourist destinations to pursue active tourism, movie tourism and geotourism. The geotouristic value of badlands varies across the world: some of them are listed as UNESCO World Heritage Sites and attract hundreds of thousands of tourists per year; others, located in less accessible areas without tourist infrastructure are only known to scientists and adventure tourists. Global geotourism is now developing primarily within geoparks, some of which contain a small number of badlands. Establishing new geoparks containing badland areas will increase the attraction and conservation of these unique geomorphic features on Earth.

Along low gradient rivers in northern Australia, there is widespread gully erosion into unconfined alluvial deposits of active and inactive floodplains. On the Mitchell River fluvial megafan in northern Queensland, river incision and fan-head trenching into Pleistocene and Holocene megafan units with sodic soils created the potential energy for a secondary cycle of erosion. In this study, rates of alluvial gully erosion into incipiently-unstable channel banks and/or pre-existing floodplain features were quantified to assess the influence of land use change following European settlement. Alluvial gully scarp retreat rates were quantified at 18 sites across the megafan using recent GPS surveys and historic air photos, demonstrating rapid increases in gully area of 1.2 to 10 times their 1949 values. Extrapolation of gully area growth trends backward in time suggested that the current widespread phase of gullying initiated between 1880 and 1950, which is post-European settlement. This is supported by young optically stimulated luminescence (OSL) dates of gully inset-floodplain deposits, LiDAR terrain analysis, historic explorer accounts of earlier gully types, and archival records of cattle numbers and land management. It is deduced that intense cattle grazing and associated disturbance concentrated in the riparian zones during the dry season promoted gully erosion in the wet season along steep banks, adjacent floodplain hollows and precursor gullies. This is a result of reduced native grass cover, increased physical disturbance of soils, and the concentration of water runoff along cattle tracks, in addition to fire regime modifications, episodic drought, and the establishment of exotic weed and grass species. Geomorphic processes operating over geologic time across the fluvial megafan predisposed the landscape to being pushed by land used change across an intrinsically close geomorphic threshold towards instability. The evolution of these alluvial gullies is discussed in terms of their initiation, development, future growth, and stabilisation, and the numerous natural and anthropogenic factors influencing their erosion.

ABSTRACTAlluvial gullies are often formed in dispersible sodic soils along steep banks of incised river channels. Field data collected by Shellberg et al. (Earth Surface Processes and Landforms 38: 1765–1778, 2013) from a gully outlet in northern Australia showed little hysteresis between water discharge and fine (<63 µm) and coarse (>63 µm) suspended sediment, indicating transport‐limited rather than source‐limited conditions. The major source of the fine (silt/clay) component was the sodic soils of upstream gully scarps, and the coarser (sand) component was sourced locally from channel bed material. In this companion paper at the same study site, a new method was developed for combining the settling velocity characteristics of these two sediment source components to estimate the average settling velocity of the total suspended sediment. This was compared to the analysis of limited sediment samples collected during flood conditions. These settling velocity data were used in the steady‐state transport limit theory of Hairsine and Rose (Water Resources Research 28: 237–243, 245–250, 1992) that successfully predicted field data of concentrations and loads at a cross‐section, regardless of the complexity of transport‐limited upstream sources (sheet erosion, scalds, rills, gullies, mass failure, bank and bed erosion, other disturbed areas). The analysis required calibration of a key model parameter, the fraction of total stream power (F ≈ 0.025) that is effective in re‐entraining sediment. Practical recommendations are provided for the prediction of sediment loads from other alluvial gullies in the region with similar hydrogeomorphic conditions, using average stream power efficiency factors for suspended silt/clay (Fw ≈ 0.016) and sand (Fs ≈ 0.038) respectively, but with no requirement for field data on sediment concentrations. Only basic field data on settling velocity characteristics from soil samples, channel geometry measurements, estimates of water velocity and discharge, and associated error margins are needed for transport limit theory predictions of concentration and load. This theory is simpler than that required in source‐limited situations. Copyright © 2015 John Wiley & Sons, Ltd.

ABSTRACTSediment production, transport and yield were quantified over various timescales in response to rainfall and runoff within an alluvial gully (7 · 8 ha), which erodes into dispersible sodic soils of a small floodplain catchment (33 ha) along the Mitchell River, northern Australia. Historical air photographs and recent global positioning system (GPS) surveys and LiDAR data documented linear increases in gully area and volume, indicating that sediment supply has been relatively consistent over the historic period. Daily time lapse photography of scarp retreat rates and internal erosion processes also demonstrated that erosion from rainfall and runoff consistently supplied fine washload (< 63 µm) sediment in addition to coarse lags of sand bed material. Empirical measurements of suspended sediment concentrations (10 000 to >100 000 mg/L) and sediment yields (89 to 363 t/ha/yr) were high for both Australian and world data. Total sediment yield estimated from empirical washload and theoretical bed material load was dominated by fine washload (< 63 µm). A lack of hysteresis in suspended sediment rating curves, scarp retreat and sediment yield correlated to rainfall input, and an equilibrium channel outlet slope supported the hypothesis that partially or fully transport‐limited conditions predominated along the alluvial gully outlet channel. This is in contrast to sediment supply‐limited conditions on uneroded floodplains above gully head scarps. While empirical data presented here can support future modelling efforts to predict suspended sediment concentration and yield under the transport limiting situations, additional field data will also be needed to better quantify sediment erosion and transport rates and processes in alluvial gullies at a variety of spatial and temporal scales. Copyright © 2013 John Wiley & Sons, Ltd.

Sediment budget models such as SedNet/ANNEX and Source Catchments have become widely used in Australia as a basis for highlighting end of catchment sediment loads and erosion hotspots and hence prioritising catchment and stream management activities. The hillslope erosion component of these models is based on the widely used Revised Universal Soil Loss Equation (RUSLE) which has now been applied over large areas of Australia as a basis for catchment and river management. In this paper we present data from erosion plots in the Normanby catchment, Cape York, Australia, for which extremely high rates of suspended hillslope sediment production have been predicted in models used to predict sediment runoff to the Great Barrier Reef. Using a novel, low budget sediment trap, total sediment yield is measured across the annual wet season (November to April) in 11 plots ranging in size from 0.1 to 1.9ha. Total hillslope erosion rates (i.e. suspended and bed material load) measured within the four main geologies in the Normanby catchment, range between 0.03 – 256 kg/ha/yr across two distinctly different wet seasons. These data are compared with the RUSLE modelled sediment yields determined for the same sites, using five different model formulations; two existing catchment scale models (DNRM, 2012; Brodie et al., 2003) and three plot scale formulations based on measured plot scale parameters in which the RUSLE was applied at the individual plot scale using a 1m DEM, with L and S factors determined for each plot and the erosivity (R factor) determined from local rain gauge data across the study period, C values derived from: 1) timelapse photography for the mean late November (end of dry season) condition and, 2) the season average C factor using the same approach as 1) from fortnightly snap shots; and 3), the DNRM 2012 data. The K factor is the value used in the latest Source Catchments modelling of the Reef Catchments (DNRM, 2012). Modelled sediment yields using the first method range from 7309680 kg/ha/yr; the second method, 4290 to 57040 kg/ha/yr, and the plot scale methods, from 1410 – 204700 kg/ha/yr. Depending on which spatial scale is used for the modelled data, this represents an average ratio of over prediction by the RUSLE model of between 12 to 11700 times. We suggest that the over-prediction is due to four key factors: 1) because RUSLE is being applied well outside the bounds for which it was originally designed (i.e. agricultural soils); 2) K factors are wildly inaccurate and because of

The term, Working Knowledge, is introduced to describe the content of a local cross-cultural knowledge recovery and integration project focussed on the indigenous-owned Oriners pastoral lease near Kowanyama on the Cape York Peninsula, Queensland. Social and biophysical scientific researchers collaborated with indigenous people, non-indigenous pastoralists, and an indigenous natural resource management (NRM) agency to record key ecological, hydrological and geomorphological features of this intermittently occupied and environmentally valuable ‘flooded forest’ country. Working Knowledge was developed in preference to ‘local’ and/or ‘indigenous’ knowledge because it collectively describes the contexts in which the knowledge was obtained (through pastoral, indigenous, NRM, and scientific labour), the diverse backgrounds of the project participants, the provisional and utilitarian quality of the collated knowledge, and the focus on aiding adaptive management. Key examples and epistemological themes emerging from the knowledge recovery research, as well as preliminary integrative models of important hydro-ecological processes, are presented. Changing land tenure and economic regimes on surrounding cattle stations make this study regionally significant but the Working Knowledge concept is also useful in analysing the knowledge base used by the wider contemporary indigenous land management sector. Employees in this expanding, largely externally funded, and increasingly formalised sector draw on a range of knowledge in making operational decisions – indigenous, scientific, NRM, bureaucratic and knowledge learned in pastoral and other enterprises. Although this shared base is often a source of strength, important aspects or precepts of particular component knowledges must necessarily be deprioritised, compromised, or even elided in everyday NRM operations constrained by particular management logics, priorities and funding sources. Working Knowledge accurately characterised a local case study, but also invites further analysis of the contemporary indigenous NRM knowledge base and its relationship to the individual precepts and requirements of the indigenous, scientific, local and other knowledges which respectively inform it.

Sediment budget modeling has become a widely used management tool for natural resource management prioritization in Australia and globally. Two of the most widely used models in Australia, SedNet, and its more recent successor Source Catchments, rely on the Revised Universal Soil Loss Equation (RUSLE) to predict sediment production from hillslope erosion. However, very few empirical data exist in Australia with which to test hillslope sediment yields predicted by the RUSLE, particularly in the more remote unimproved savannah woodlands of northern Australia that are utilized by the cattle grazing industry. These savannah woodland landscapes comprise the vast majority of the catchment area draining into key ecological assets such as the Great Barrier Reef. An increasing number of sediment tracing studies suggest that hillslope erosion is not the dominant sediment source in most tropical savannah environments, which calls into question the validity of the modeling studies that have predicted a dominance of hillslope erosion. In this paper we present a design and evaluation of a simple, low cost Hillslope Sediment Trap (HST) that requires little to no maintenance across an entire wet season in low sediment yield environments dominated by sheet flow transport of sand, silt and clay. It can consequently be deployed in remote, inaccessible areas of Australia to collect data on hillslope sediment production as a means of testing predictions of

Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.

This report presents a sediment and nutrient budget for the Mitchell River catchment, located on the western flanks of Cape York and draining to the Gulf of Carpentaria. A catchment sediment (or nutrient) budget accounts for the major sources, transport pathways and sinks of sediments and nutrients within a catchment. It is difficult to measure all of the relevant components of a catchment sediment budget across space and time. Consequently a modelling framework is useful to bring together the individual components of the budget in a coherent manner, whether derived from local empirical data or theoretical models. The SedNet and ANNEX models have been used in this study; these models have been widely applied in tropical Queensland settings and elsewhere in Australia. Each sediment budget term comprises its own sub-model and here, a combination of national-scale models (terrain, hillslope erosion, colluvial gully density and surface soil nutrient concentrations), state-wide data sets (foliage projected cover) and locally-derived models (alluvial gully erosion, floodplain extent) have been used for input data. For some aspects of the model, such as the dissolved nutrient concentrations in overland flow, no local data were available and values have been derived from reference to the literature. Some budget components (particularly floodplain deposition, and also partially hillslope erosion) have been derived as “residual value” terms; that is model parameters and/or terms have been adjusted to match other data with limited independent constraint on the exact magnitude of that budget term. These residual terms contain not only the data attributed to them, but also unmeasured components of the sediment budget and the associated error from the known or directly measured components, such as total load at gauges and alluvial gully erosion.

The objectives of this study are to quantify preand post-European settlement alluvial gully erosion rates using savannah tree ages dated using radium radionuclides. Following gully head scarp retreat and destruction of original woodland communities, savannah vegetation (Eucalyptus spp.) can recolonise eroded habitat. Radionuclides such as radium become incorporated into tree xylem tissue and tree rings. The activities of radionuclides with known half-lives in tree rings can be used to estimate the age of tree establishment. Measurement of the age of trees distributed across an eroded gully floor could define the chronology of gully erosion through time.

The objective is to confirm tree ages (<50 years) in erosional gullies using bomb-pulse radiocarbon 14C dating. Tree sections of Eucalyptus microtheca in a pilot gully on Cape York, northern Australia, were collected in 2008. Tree rings have been counted, but annual ring production analysis is ongoing. 2009 AINSE funding had the objective to age trees using radium (228Ra / 226Ra) activities across tree radii. These analyses returned poor results, with useful information for only one tree. 2010 AINSE funding had the objective to age trees using radiocarbon. Confirmation of tree ages using 14C would provide multiple lines of evidence for tree age, validate the radium results, and determine the best tree dating technique to determine gully erosion rates.

We investigated the vulnerability of fall-spawned bull char ( Salvelinus confluentus ) embryos to redd scour during winter rain and rain-on-snow flood discharges in western Washington, USA. It was hypothesized that the magnitude of bedload scour at bull char redds is reduced by the provision and selection of stable refugia habitat controlled by local-, reach-, or subcatchment-scale variables such as hydraulic habitat unit and channel type. Bedload scour and channel change were measured using 96 scour monitors and 34 elevational transects in three catchments over 2 to 4 years. Scour to cited egg burial depths of bull char did not commence until discharge typically exceeded the 2-year recurrence interval. At a local scale, scour varied significantly among side channel, protected main channel, and unprotected main channel redd sites. Unprotected gravel patches in simplified channel types with moderate gradients were most susceptible to deep scour, especially if coupled with the transient supply and storage of sand and gravel from mass wasting. Partially transport-limited reaches had reduced scour due to lower stream power and armored gravel beds. Complex spawning habitat (i.e., with abundant large woody debris and side channels) was important in providing refuge from deep scour and in buffering embryos against inhospitable hydrologic or sediment regimes.

Considerable attention has been focused on the role of gullies as a contributor to contemporary sediment loads of rivers in Australia. In southern Australia rapid acceleration of hillslope gully erosion has been widely documented in the post-European period (similar to last 200 years). In the northern Australian tropics, however, gully erosion processes operating along alluvial plains have not been well documented and can differ substantially from those gullies eroding into colluvium on hillslopes. Aerial reconnaissance Surveys in 2004 along 13 500 km of the main stem rivers that drain into the Gulf of Carpentaria (GoC), identified extensive areas of alluvial lands that have been impacted by a pervasive form of gully erosion. More detailed remote sensing based mapping within the 31 000 km(2) Mitchell River fluvial megafan has identified that active gullying into alluvium occupies similar to 0.4% (129 km(2)) of the lower Mitchell catchment. These alluvial gullies are concentrated along main drainage channels and their scarp heights are highly correlated to the local relief between the floodplain and river thalweg. While river incision into the megafan since the Pleistocene has developed the relief potential for erosion, other factors such as floodplain hydrology, soil dispersibility, and vegetation also influence the distribution of gullies. In this paper we present a conceptual model of alluvial gullies, and contend that they represent a distinct end member in the continuum of gully forms that have been described in the geomorphic literature. An understanding of the processes driving this form of alluvial gullying can only be gained when they are differentiated from widely described colluvial hillslope gully models and theories. We present evidence of type examples of alluvial gullying in the Mitchell, and through analysis of their distribution and morphology at different scales, highlight some of the key mechanisms that are potentially initiating these features and driving their expansion. Copyright (C) 2009 John Wiley & Sons, Ltd.