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Gully erosion is a significant process for delivering sediment to streams, and can be the dominant erosion process in some regions. As with other forms of erosion, we need methods to predict the extent and patterns of gully erosion across large areas. Such methods also improve our understanding of the environmental controls on gully erosion. Here, patterns of gully density are predicted across the 1 x [10.sup.6] [km.sup.2] Murray--Darling Basin in Australia, using aerial photograph mapping of gullies across part of the Basin and a multivariate statistical model of a range of environmental factors. Across the Basin, at a 10-km grid resolution, gully density is predicted to vary from 0 to 1.2 km [km.sup.-2], with 22% of the Basin having a gully density >0.1 km [km.sup.-2] and 3% a density >0.5 km [km.sup.-2]. The model is reasonably successful at predicting the variations in mapped gully density compared with similar attempts to predict erosion processes at this scale. Hillslope gradient and mean annual rainfall are the most important single factors across the region. The predicted mean gully density across the Basin is 0.08 km [km.sup.-2] and gullies contribute up to 27 x [10.sup.6] t [year.sup.-1] of sediment to the fiver network. This is more than the amount that has been estimated from the combined contribution of hillslope (14 x [10.sup.6] t [year.sup.-1]) and riverbank (8.6 x [10.sup.6] t [year.sup.-1]) erosion by other studies within the Basin., Introduction Gully erosion is a significant land degradation process and a source of increased sediment load to rivers (Wasson et al. 1998). Sand and fine gravel eroded from gullies can [...]

Natural wetlands can play a key role in controlling non-point source pollution, but quantifying their capacity to reduce contaminant loads is often challenging due to diffuse and variable inflows. The nitrogen removal performance of a small natural headwater wetland in a pastoral agricultural catchment in Waikato, New Zealand was assessed over a two-year period (2011-2013). Flow and water quality samples were collected at the wetland upper and lower locations, and piezometers sampled inside and outside the wetland. A simple dynamic model operating on an hourly time step was used to assess wetland removal performance for key N species. Hourly measurements of inflow, outflow, rainfall and Penman-Monteith evapotranspiration estimates were used to calculate dynamic water balance for the wetland. A dynamic N mass balance was calculated for each N component by coupling influent concentrations to the dynamic water balance and applying a first order areal removal coefficient (k20) adjusted to the ambient temperature. Flow and water quality monitoring showed that wetland was mainly groundwater fed. The concentrations of oxidised nitrogen (NOx-N, Total Organic Nitrogen (TON) and Total-N (TN) were lower at the outlet of the wetland regardless of flow conditions or seasonality, even during winter storms. The model estimation showed that the wetland could reduce net NOx-N, NH4-N, ton and TN loads by 76%, 73%, 26% and 57%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Fallout 137Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of 137Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total 137Cs inventories calculated from the detailed profile data. Information on the rates of 137Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of 137Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for 137Cs being known and without having to assume that 137Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total 137Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, 137Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites. [Copyright &y& Elsevier]

The article reports on the study conducted by Kathryn J. Amos and colleagues on the anabranching of Fitzroy River catchment in northeastern, Australia. Researchers conducted a catchment-scale investigation of the 143,000 square kilometers river to determine whether mapped and remotely sensed data can provide useful information about the characteristics of anabranching. They used mapped channel network, digital elevation models, geology maps and rainfall data, and found that a number of anabranching were manifested on the river wherein it become single channel downstream of a rapid valley narrowing, thus adding to the previous descriptions of anabranching morphologies.

Wetlands play a key role in controlling flooding and non-point-source (diffuse) pollution. They are therefore an important tool for mitigating diffuse water pollution from farms. However, to use this tool, it is necessary to obtain detailed assessments and identification of potential wetland restoration or creation sites. This is complicated by the diversity of landscapes, environmental conditions, and land ownership. Site suitability for wetland restoration or creation depends on many factors: the underlying geology, soils, topography, hydrology, drainage, and land ownership. Local hydrology and soils are among the most important factors. However, the inventory and characterization of a site’s soils and hydrology often requires extensive, expensive, and time-consuming ground surveys, and it is therefore limited to small areas. Another possibility would be to consider topography, which strongly determines water movement patterns. Light detection and ranging (LiDAR) data provides detailed topographic information and can be acquired by remote sensing. Our study showed that terrain analysis using high-resolution topographical data can produce suitability maps for wetlands that can be easily used by decision makers and planners in watershed management. The rapid methodology reveals potential wetland creation or restoration sites at a reasonable cost; with the resulting spatially explicit suitability map, managers can plan for wetland creation or restoration without having to wait for field-data collection. [ABSTRACT FROM AUTHOR]

The headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality. These systems are characterized by harsh climates, ephemeral flows that do not reach bank top, and bare cohesivebanks of clay and weathered bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose-built groundprofiler and photo-electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 1 2 mm a-1. Erosion is controlled by subaerial processes that loosen bank material. Observations show that needle-ice growth is important in winter and desiccation of clays predominates in summer. Flows are unable to erode firm cohesive clays from the banks, and erosion is generally limited by the availability of loosened material. This produces strong hysteresis in turbidity during events. Peak turbidity is related to the number of days with low flow between events, and not peak stage. Rehabilitation with a moderatecover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. [ABSTRACT FROM AUTHOR]