The identification of four stages during micro-rill development

Separation of rill and inter-rill erosion is required in many of the soil erosion models currently being developed. The feasibility of basing the separation on the hydraulic properties of the flow and resultant sediment production is examined in a laboratory simulation of rill initiation and development. Four stages are identified in the process of rill formation; these are sheetflow, flowline development, micro-rills, and micro-rills with headcuts. There are significant differences in terms of flow characteristics between the stages, especially between sheetflow and flowlines, indicating the promise of this method for making a more precise distinction between rill and inter-rill erosion.     

Reach-scale channel geometry of mountain streams

The basic patterns and processes of steep channels remain poorly known relative to lower-gradient channels. In this analysis, characteristics of step-pool, plane-bed, and pool-riffle channels are examined using a data set of 335 channel reaches from the western United States, Nepal, New Zealand, and Panama. We analyzed differences among the three channel types with respect to hydraulics, channel geometry, boundary roughness, and bedforms. Step-pool channels have significantly steeper gradients, coarser substrate, higher values of shear stress and stream power for a given discharge, and larger ratios of bedform amplitude/wavelength (H/L). Pool-riffle channels have greater width/depth ratios and relative grain submergence (R/D₈₄) than the other channel types. Plane-bed channels tend to have intermediate values for most variables examined. Relative form submergence (R/H) is statistically similar for step-pool and pool-riffle channels. Despite the lesser relative grain submergence and greater bedform amplitude of step-pool channels, mean values of Darcy–Weisbach friction factor do not change in response to changes in relative grain submergence. These patterns suggest that adjustments along mountain streams effectively maximize resistance to flow and minimize downstream variability in resistance among the different channel types.     

The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog

The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.