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Rill Development (rill + development)
Selected AbstractsFlow energy and channel adjustments in rills developed in loamy sand and sandy loam soilsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2009Jovan R. Stefanovic Abstract The storms usually associated with rill development in nature are seldom prolonged, so development is often interrupted by interstorm disturbances, e.g. weathering or tillage. In laboratory simulated rainfall experiments, active rill development can be prolonged, and under these conditions typically passes through a period of intense incision, channel extension and bifurcation before reaching quasi-stable conditions in which little form change occurs. This paper presents laboratory experiments with coarse textured soils under simulated rainfall which show how channel adjustment processes contribute to the evolution of quasi-stability. Newly incised rills were stabilized for detailed study of links between rill configuration and flow energy. On a loamy sand, adjustment towards equilibrium occurred due to channel widening and meandering, whereas on a sandy loam, mobile knickpoints and chutes, pulsations in flow width and flow depth and changes in stream power and sediment discharge occurred as the channel adjusted towards equilibrium. The tendency of rill systems towards quasi-stability is shown by changes in stream power values which show short-lived minima. Differences in energy dissipation in stabilized rills indicate that minimization of energy dissipation was reached locally between knickpoints and at the downstream ends of rills. In the absence of energy gradients in knickpoints and chutes, stabilized rill sections tended toward equilibrium by establishing uniform energy expenditure. The study confirmed that energy dissipation increased with flow aspect ratio. In stabilized rills, flow acceleration reduced energy dissipation on the loamy sand but not on the sandy loam. On both soils flow deceleration tended to increase energy dissipation. Understanding how rill systems evolve towards stability is essential in order to predict how interruptions between storms may affect long-term rill dynamics. This is essential if event-based physical models are to become effective in predicting sediment transport on rilled hillslopes under changing weather and climatic conditions. Copyright © 2008 John Wiley and Sons, Ltd. [source] The measurement and modelling of rill erosion at angle of repose slopes in mine spoilEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2008G. R. Hancock Abstract The process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands. Rills also often develop very quickly (from a single rainfall event to a season) and can develop into gullies if sufficient runoff is available to continue their development. This study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope. It also examines the ability of the SIBERIA erosion model to simulate the rill's spatial and temporal behaviour. While there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields, little work has been done to examine rill development at angle of repose sites. Results show that while the overall hillslope morphology was captured by the laser scanner, with the morphology of the rills being broadly captured, the characteristics of the rills were not well defined. The digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks, therefore delineating a series of ill defined longitudinal downslope depressions. These results demonstrate that an even greater density of points is needed to capture sufficient rill morphology. Nevertheless, SIBERIA simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used. This result provides confidence in the SIBERIA model and its parameterization. The results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process. Copyright © 2007 John Wiley & Sons, Ltd. [source] Assessment and demarcation of trail degradation in a nature reserve, using GIS: case of Bukit Timah Nature ReserveLAND DEGRADATION AND DEVELOPMENT, Issue 5 2007K. Chatterjea Abstract With a significant rise in popularity of nature areas, particularly in urban settings like Singapore, Nature Reserves are being increasingly opened for public recreational use. In the Bukit Timah Nature Reserve (BTNR), the only remnant primary rain forest reserve in Singapore, trail networks are being expanded to meet this growing public demand. The physical condition of the present trail networks was assessed by monitoring the changes in surface compaction, soil moisture, infiltration rates, soil organic matter content, root density, litter cover and rill development. These parameters were compared with similar data obtained from undisturbed forested slopes to analyse the degree of changes brought about by trail usage. Significant changes occurred in all measured parameters, indicating observable degradation of the trails, particularly on vulnerable slopes. These changes are due to the heavy and increased use of the forest by visitors. Penetration resistance and shear strength of the top surface layers of the trails are important indicators of trail degradation status and these have been plotted, using GIS, to demarcate trails under different levels of stress. This field monitoring provides a relevant local assessment of trail conditions. It has potential for use in decision-making in future planning and forest management under similar site conditions. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||