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Rill Erosion (rill + erosion)
Selected AbstractsInitial hydrologic and geomorphic response following a wildfire in the Colorado Front RangeEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2001John A. Moody Abstract A wildfire in May 1996 burned 4690 hectares in two watersheds forested by ponderosa pine and Douglas fir in a steep, mountainous landscape with a summer, convective thunderstorm precipitation regime. The wildfire lowered the erosion threshold in the watersheds, and consequently amplified the subsequent erosional response to shorter time interval episodic rainfall and created both erosional and depositional features in a complex pattern throughout the watersheds. The initial response during the first four years was an increase in runoff and erosion rates followed by decreases toward pre-fire rates. The maximum unit-area peak discharge was 24 m3 s,1 km,2 for a rainstorm in 1996 with a rain intensity of 90 mm h,1. Recovery to pre-fire conditions seems to have occurred by 2000 because for a maximum 30-min rainfall intensity of 50 mm h,1, the unit-area peak discharge in 1997 was 6.6 m3 s,1 km,2, while in 2000 a similar intensity produced only 0.11 m3 s,1 km,2. Rill erosion accounted for 6 per cent, interrill erosion for 14 per cent, and drainage erosion for 80 per cent of the initial erosion in 1996. This represents about a 200-fold increase in erosion rates on hillslopes which had a recovery or relaxation time of about three years. About 67 per cent of the initially eroded sediment is still stored in the watersheds after four years with an estimated residence time greater than 300 years. This residence time is much greater than the fire recurrence interval so erosional and depositional features may become legacies from the wildfire and may affect landscape evolution by acting as a new set of initial conditions for subsequent wildfire and flood sequences. Published in 2001 by John Wiley & Sons, Ltd. [source] Evaluation of a dynamic multi-class sediment transport model in a catchment under soil-conservation agricultureEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008Peter Fiener Abstract Soil erosion models are essential tools for the successful implementation of effective and adapted soil conservation measures on agricultural land. Therefore, models are needed that predict sediment delivery and quality, give a good spatial representation of erosion and deposition and allow us to account for various soil conservation measures. Here, we evaluate how well a modified version of the spatially distributed multi-class sediment transport model (MCST) simulates the effectiveness of control measures for different event sizes. We use 8 year runoff and sediment delivery data from two small agricultural watersheds (0·7 and 3·7 ha) under optimized soil conservation. The modified MCST model successfully simulates surface runoff and sediment delivery from both watersheds; one of which was dominated by sheet and the other was partly affected by rill erosion. Moreover, first results of modelling enrichment of clay in sediment delivery are promising, showing the potential of MCST to model sediment enrichment and nutrient transport. In general, our results and those of an earlier modelling exercise in the Belgian Loess Belt indicate the potential of the MCST model to evaluate soil erosion and deposition under different agricultural land uses. As the model explicitly takes into account the dominant effects of soil-conservation agriculture, it should be successfully applicable for soil-conservation planning/evaluation in other environments. Copyright © 2008 John Wiley & 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] Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands , towards a sediment budgetEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2008Jan Nyssen Abstract This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100,2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area-weighted average rate of soil erosion by water in the catchment, measured over four years (1998,2001), is 14·8 t ha,1 y,1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha,1 y,1. Calculated sediment yield (5·6 t ha,1 y,1) is similar to sediment yield measured in nearby catchments. Seventy-four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present-day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. [source] A simulation model for unified interrill erosion and rill erosion on hillslopesHYDROLOGICAL PROCESSES, Issue 3 2006Q. Q. Liu Abstract A mathematical model was developed for simulating runoff generation and soil erosion on hillslopes. The model is comprised of three modules: one for overland flow, one for soil infiltration, and one for soil erosion including rill erosion and interrill erosion. Rainfall and slope characteristics affecting soil erosion on hillslopes were analysed. The model results show that the slope length and gradient, time distribution rainfall, and distribution of rills have varying influence on soil erosion. Erosion rate increases nonlinearly with increase in the slope length; a long slope length leads to more serious erosion. The effect of the slope gradient on soil erosion can be both positive and negative. Thus, there exists a critical slope gradient for soil erosion, which is about 45° for the rate of erosion at the end of the slope and about 25° for the accumulated erosion. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modelling plumes of overland flow from logging tracksHYDROLOGICAL PROCESSES, Issue 12 2002P. B. Hairsine Abstract Most land-based forestry systems use extensive networks of unsealed tracks to access the timber resource. These tracks are normally drained by constructing cross-banks, or water bars, across the tracks immediately following logging. Cross-banks serve three functions in controlling sediment movement within forestry compartments: 1.they define the specific catchment area of the snig track (also known as skid trails) so that the overland flow does not develop sufficient energy to cause gullies, and sheet and rill erosion is reduced; 2.they induce some sediment deposition as flow velocity reduces at the cross-bank; 3.they redirect overland flow into the adjacent general harvesting area (GHA) so that further sediment deposition may take place. This paper describes a simple model that predicts the third of these functions in which the rate of runoff from the track is combined with spatial attributes of the track and stream network. Predictions of the extent of the overland flow plumes and the volume of water delivered to streams is probabilistically presented for a range of rainfall-event scenarios with rainfall intensity, time since logging and compartment layout as model inputs. Generic equations guiding the trade-off between intercross-bank length and flow path distance from cross-bank outlet to the stream network needed for infiltration of track runoff are derived. Copyright © 2002 John Wiley & Sons, Ltd. Copyright © 2002 John Wiley & Sons, Ltd. [source] Farmers' perceptions of soil erosion and its consequences in India's semiarid tropicsLAND DEGRADATION AND DEVELOPMENT, Issue 3 2005J. Kerr Abstract This paper investigates farmers' perceptions of soil erosion and how it affects crop yields, land values, and private conservation investments in India's semiarid tropics. It is based on three types of data: (1) a survey of farmers in three study villages; (2) a plot survey by a professional soil surveyor in the same villages; and (3) experimental and simulated data from nearby research stations with similar conditions. Farmers' perceptions of erosion are compared to the surveyor's using kappa, a statistical measure of interrater agreement. Perceived erosion,yield relationships are estimated econometrically and compared to experimental and simulated data. Effects on land values and conservation investments are estimated econometrically. Findings suggest that farmers are keenly aware of rill erosion but less aware of sheet erosion; kappa values ranging from 0 to 0·28 suggest low agreement with the soil surveyor. They anticipate annual yield losses of 5·8,11,per,cent due to rill erosion; these figures are reasonably consistent with those from nearby research stations. They anticipate yield increases of 3·8,14·5,per,cent due to installation of soil conservation bunds, largely because they can harvest soil from up the slope and capture organic matter. Perceived erosion has some effect on land values and soil conservation investments, but other factors such as irrigation and soil type have a much greater effect. These findings suggest that promoting soil conservation requires capitalizing on farmers' interest in short-term gains, such as from water and nutrient management. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||