Description: ABSTRACT Flow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models, such as soil erosion and rill development models, as well as for modelling sediment and solute transport by runoff. This study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities. Laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer (heated dye) into shallow flowing surface water. The leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared. The results show that thermal tracers can be used to estimate both overland and rill flow velocities, since measurements are similar to those resulting from using dye tracers. The main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Taking the width-to-depth ratio of a river channel as an independent variable, a variational analysis of basic flow relationships shows that alluvial-channel flow adjusts channel geometry to achieve stationary equilibrium when the condition of maximum flow efficiency (MFE) is satisfied. As a test of the veracity of MFE and to examine if this theory of self-adjusting channel morphodynamics can be practically applied to large river systems, this study examines the degree of correspondence between theoretically determined equilibrium channel geometries and actual measurements along the middle and lower Yangtze River. Using four different forms of the Meyer-Peter and Müller bedload relation and relations of flow continuity and resistance we show that the Meyer-Peter and Müller bedload relation modified on the basis of MFE theory predicts channel dimensions most accurately when applied to the middle and lower Yangtze River. This provides convincing evidence supporting MFE equilibrium theory. This article is protected by copyright. All rights reserved.

Description: Depth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One-size 6 mm diameter spherical glass beads were transported at equilibrium in a two-dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high-speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation coexisted, and above this, a logarithmic-like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The links between structural glaciology, glacial debris entrainment and transport have been established in a number of different glacier settings. He we document the structural evolution of a temperate Alpine valley glacier (Vadrec del Forno, Switzerland) and demonstrate that individual flow units within the glacier have very different structural and debris characteristics. The glacier consists of a broad accumulation area with multiple basins feeding a relatively narrow tongue and is formed from six distinct flow units. Each flow unit has its own characteristic structural assemblage. Flow units that narrow rapidly down-glacier are dominated by primary stratification that has evolved into longitudinal foliation. In contrast, wider flow units preferentially develop an axial planar foliation. Glacier structure plays a limited role in the entrainment of debris, which is more strongly influenced by ice-marginal rockfall and avalanche inputs onto the glacier surface. However, once entrained, glacier structure controls the reorientation and redistribution of debris within the ice mass. By taking a whole-glacier approach to describing glacier structure and debris transport, we conclude that individual flow units are unique with regard to structure and debris transfer. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Both the rate and the vertical distribution of soil disturbance modify soil properties such as porosity, particle size, chemical composition and age structure; all of which play an important role in a soil's biogeochemical functioning. Whereas rates of mixing have been previously quantified, the nature of bioturbation's depth dependence remains poorly constrained. Here we constrain, for the first time, the relationship between mixing rate and depth in a bioturbated soil in northeast Queensland, Australia using a novel method combining OSL (Optically Stimulated Luminescence) ages and meteoric 10 Be inventories. We find that the best fit mixing rate decreases non-linearly with increasing soil depth in this soil and the characteristic length scale of 0.28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients. In addition we show that estimates of surface mixing rates from OSL data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified. We calculate surface diffusion-like mixing coefficients of 1.8 × 10 -4 and 2.1 × 10 -4  m 2  yr -1 for the studied soil for two different estimates of soil erosion. This article is protected by copyright. All rights reserved.

Description: ABSTRACT This article reports on the Special Issue of Earth Surface Processes and Landforms dedicated to planetary dune analogues and the advances that have been made through the integration of remote sensing and terrestrial field data to better model and understand aeolian systems. The eleven articles presented demonstrate a spectrum of analytical techniques that are employed to investigate ripples, dunes, draa and ergs across a variety of spatial and temporal scales. Nine of the papers involve innovative research about aeolian bedforms and processes, while the final two papers are examples of how vast quantities of data may be organized and scrutinized using a GIScience approach. Based on these eleven papers and the many abstracts archived in a series of three planetary dunes workshops at the Lunar Planetary Institute ( http://www.lpi.usra.edu/publications/abstracts.shtml; LPI Contributions 1403, 1552, and 1673) it is evident that there exists diverse and complementary approaches to the comparative study of landforms and processes for terrestrial and extra- terrestrial aeolian landscapes that is driven by a vibrant international community of scientists and educators that engage in the cross-fertilization of ideas. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In many Alpine catchments the monitoring and hazard mitigation of debris-flow events require enormous economic and social resources. To confront these problems, a subjective estimation of the most hazardous zones of the basin could be useful in the best, sustainable planning of protective measures. In this paper, a new methodology is proposed that develops a Management Priority Index (MPI) to rank sediment source areas by their quantitative capability to deliver debris-flow volumes to a point of interest within the catchment. The MPI sets the intervention priority based on a combination of three sub-indicators: a susceptibility indicator evaluating the overall catchment predisposition to generate debris flow, a triggering indicator and a volume budget indicator assessing the rate of deliverable volume to a selected outlet. MPI was applied to the basin of the Rio Gadria catchment (Venosta Valley, Bolzano, Italy), an alpine basin with an unlimited sediment supply that is characterised by multiple, very active, shallow landslides and bare soil zones. The proposed ranking method was successfully verified using post-event surveys and through evidence from consolidation check dams built over many years in the basin. This article is protected by copyright. All rights reserved.

Description: ABSTRACT The Boteti palaeo-estuary in northern Botswana is located where the endoreic Boteti river, an overflow from the regional Okavango river system, enters the Makgadikgadi pans. The present work considers diagenetic silica and calcium carbonate dominated transformations. The aims are to help identify precursor conditions for the origin of microcrystalline silcrete-calcrete intergrade deposits while developing insight into pene-contemporaneous silica and calcite matrix formation. General precursor conditions require the presence of cyclical endoreic freshwater inflow into a saline pan. The pan should be deep enough to sustain a permanent watertable under climatic conditions sufficient to cause carbonate fractionation within the groundwater. Freshwater inflow into a saline pan drives the geochemistry of the system (from freshwater to saline, from neutral to high pH). The geochemistry is controlled by the periodicity of inflow relative to salinity levels of phreatic groundwater in the receptor saline pan. The source of most silica and localized CaCO 3 is derived from the dissolution and precipitation of microfossils, while more general CaCO 3 enrichment stems from saline pan based carbonate fractionation. Diagenetic change leads to colloidal then more consolidated bSiO 2 /CaO aggregate formation (amorphous silica) followed by transformations into opaline silica over time. Irregular zones of siliceous sediment forming in otherwise calcareous deposits may relate to the irregular occurrence of biogenic silica in the source sediments, inferring a source for local silica mobilization in intergrade deposits. The distribution of calcareous micro-fossils may have a similar converse effect. Diagenetic evidence from an intergrade deposit with a low SiO 2 /CaO ratio suggests that transformation occurred more into the pan, while an intergrade deposit with a high SiO 2 /CaO ratio more likely formed closer to a land margin and was frequently inundated by freshwater. Pene-contemporaneous silcrete-calcrete intergrade formation under the above conditions may take place where dissolved silica crystallizes out in the vicinity of calcite crystals due to local decreases in pH. The continuing consolidation of bSiO 2 /CaO aggregates may be facilitated by the presence of increasing amounts of calcite. It appears that CaCO 3 may act as a catalyst leading to pene-contemporaneous bSiO 2 /CaO aggregate formation. However the processes involved require further work. This article is protected by copyright. All rights reserved.

Description: ABSTRACT Riverine ecosystems are recurrently rejuvenated during destructive flood events and vegetation succession starts again. Poplars (i.e. species from Populus genera) respond to hydrogeomorphological constraints, but, in turn, also influence these processes. Thus, poplar development on bare mineral substrates is not exclusively a one-way vegetative process. Reciprocal interactions and adjustments between poplar species and sediment dynamics during their life cycle lead to the emergence of biogeomorphological entities within the fluvial corridor, such as vegetated islands, benches and floodplains. Based on a review of geomorphological, biological and ecological literature, we have identified and described the co-constructing processes between riparian poplars and their fluvial environment. We have explored the possibility that the modification of the hydrogeomorphological environment exerted, in particular, by the European black poplar ( Populus nigra L.), increases its fitness and thus results in positive niche construction. We focus on the fundamental phases of dispersal, recruitment and establishment until sexual maturity of P . nigra by describing the hierarchy of interactions and the pattern of feedbacks between biotic and abiotic components. We explicitly relate the biological life cycle of P . nigra to the fluvial biogeomorphic succession model by referring to the ‘biogeomorphological life cycle’ of P . nigra . Finally, we propose new research perspectives based on this theoretical framework. This article is protected by copyright. All rights reserved.

Description: ABSTRACT In the European Alps many high mountain grasslands which where traditionally used for summer pasturing and haying have been abandoned during the last decades. Abandonment of mown or grazed grasslands causes a shift in vegetation composition and thus a change in landscape ecology and geomorphology. Alpine areas are very fragile ecosystems and are highly sensitive to changing environmental conditions, which can affect the geomorphic regime of these high energy environments. The effect of land use intensification on erosion rates is well documented, whereas the effect of land abandonment on erosion rates is still discussed controversially, particularly in relation to its short-term and long-term consequences. Generally, an established perennial vegetation cover improves the mechanical anchoring of the soil and the regulation of the soil water budget, including runoff generation and erosion. However, changing vegetation composition affects many other above- and below-ground properties like root density, -diversity and -geometry, soil structure, pore volume and acidity. Each combination of these properties can lead to a distinct scenario of dominating surface processes. The study of soil properties along a chronosequence of green alder ( alnus viridis ) encroachment on the Unteralptal in central Switzerland revealed that shrub encroachment changes soil and vegetation properties towards an increase of resistance to run-off related erosion processes, but a decrease of slope stability against shallow landslides. This article is protected by copyright. All rights reserved.