Mobility of a remobilised parabolic dune in Kennemerland, The Netherlands

A parabolic dune in the Netherlands was remobilised in December 1998 by removing vegetation and soil. The main aim of the experiment was ecological: to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes. If processes can be reactivated at coarse scale, periodic rejuvenation of the landscape over the long term is possible, without the need for managers to interfere further. The experiment provides the opportunity to address another important question: can large parabolic dunes in the Netherlands be mobile in the present climate? Mobility of the dune is investigated by means of erosion pins, aerial photography and measurement of cross sections. Activity indices are derived from erosion pin recordings and correlated to weather conditions. From 1999 to 2001, displacement of the dune ranged from 0 to 12 m in east–northeasterly direction. Activity of the dune is related to wind conditions, but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods. Periods with extreme wind speeds resulted in much less geomorphic change than expected.     

LANDSLIDE POTENTIALITY OF THE TSENGWEN RESERVOIR WATERSHED, TAIWAN

To recognize the geographical characteristics of the landslide areas will be helpful for the watershedmanagement in the reservoir watershed. According to the quantitative analysis, we'll take differentscores and weighting for the potential parameters of the landslide areas in the Tsengwen reservoirwatershed, and in the meanwhile, we'll extract the different factors, including the slope, aspect,altitude, soil and geological textures etc., and the results shown as maximum one--day rainfall, ratio offorests and average relief is the most affecting parameters on the potential risk map of landslide areas.     

Debris flow erosion and deposition in Jiangjia Gully, Yunnan, China

The erosion and deposition of debris flows at Jiangjia Gully in Dongchuan section of Yunnan province, southwestern China, was surveyed at 12 cross sections from 1999 to 2003. Deposition occurred in most sections because of the low debris-flow magnitude. The result was an increase in their elevations except for two sections at D17 and D19, where the channel was diverted in September 1999. As the annual sediment discharge of debris flow increased, the deposited volume decreased in the upper channel and increased in the lower channel. In each debris flow event, the erosion or deposition at the upper and the lower channel were different, but the eroded/deposited volume and the trend of erosion or deposition were similar between the neighboring sections. The average elevation change of all cross sections between consecutive surveys can reasonably represent the debris flow influence on the channel. Its relationship with the total sediment discharge between two surveys follows a three-stage pattern: when debris flow magnitude is small, deposition in the channel increases with the magnitude. When the magnitude reaches a certain level, the deposition begins to decrease and eventually erosion takes place. In three typical cross sections which had similar channel width, the debris flow showed a clear trend that the deposited volume decreased, while the eroded volume increased as the discharge of debris flow sediments increased.     

Investigating the spatial distribution of summit flats in the Uinta Mountains of northeastern Utah, USA

Isolated, laterally extensive, gently sloping surfaces known as summit flats are present at high elevations in many Laramide ranges, and are particularly well developed in the Uinta Mountains of northeastern Utah. To investigate the spatial distribution of these surfaces, and to consider possible controls on this pattern, a map of summit flats in the Uintas was developed from digital elevation data. Summit flats were identified as unglaciated areas of the landscape above an elevation of 3400 m, having a slope of less than 0.3 m m^− 1, and an area greater than 5 × 10^− 2 km². As defined, summit flats comprise 43% of the unglaciated land area above 3400 m in the Uintas, with the largest individual flat covering nearly 34 km². To quantitatively evaluate the distribution of summit flats in the Uintas, the area of summit flats was normalized to the total unglaciated area above 3400 m in 10-km-wide swaths oriented normal to the range axis. Values of percent summit flats obtained by this method decrease dramatically westward, from a high of more than 60% at the eastern end of the Uintas, to 0% at the western end. Given that individual summit flats can be diminished through lateral erosion by surrounding valley glaciers, and that the summit flats themselves were apparently never glaciated, this result suggests that glacial erosion has been more effective in the western Uintas over the course of the Quaternary. Focused glacial erosion at the upwind end of the range is consistent with the hypothesis that the proximity of Lake Bonneville enhanced precipitation over the western Uintas during the Last Glacial Maximum [Munroe, J.S., and, Mickelson, D.M., 2002. Last Glacial Maximum equilibrium-line altitudes and paleoclimate, northern Uinta Mountains, Utah, U.S.A. Journal of Glaciology, 48, 257–266].     

Quantifying sediment transport across an undisturbed prairie landscape using cesium-137 and high resolution topography

Soil erosion is a global environmental problem, and anthropogenic fallout radionuclides offer a promising tool for describing and quantifying soil redistribution on decadal time scales. To date, applications of radioactive fallout to trace upland sediment transport have been developed primarily on lands disturbed by agriculture, grazing, and logging. Here we use ¹³⁷Cs to characterize and quantify soil erosion at the Konza Prairie Long-Term Ecological Research (LTER) site, an undisturbed grassland in northeastern Kansas. We report on the small scale (< 10 m) and landscape scale (10 to 1000 m) distribution of fallout ¹³⁷Cs, and show significant variability in the concentrations and amounts of ¹³⁷Cs in soils at our site. ¹³⁷Cs soil concentrations and amounts typically vary by 10% to 30% on small scales, which most likely represents the spatial heterogeneity of the depositional processes. Landscape scale variability of soil ¹³⁷Cs was significantly higher than small scale variability. Most notably, soils collected on convex (divergent) landforms had ¹³⁷Cs inventories of 2500 to 3000 Bq m^− 2, which is consistent with the expected atmospheric inputs to the study area during the 1950s and 1960s. Concave landforms, however, had statistically lower inventories of 1800 to 2300 Bq m^− 2. The distribution of ¹³⁷Cs on this undisturbed landscape contrasts significantly with distributions observed across disturbed sites, which generally have accumulations of radioactive fallout in valley bottoms. Because the upslope contributing area at each sampling point had a significant negative correlation with the soil inventory of ¹³⁷Cs, we suggest that overland flow in convergent areas dominates soil erosion at Konza on time scales of decades. Very few points on our landscape had ¹³⁷Cs inventories significantly above that which would be predicted from direct deposition of ¹³⁷Cs on the soil surface; we conclude therefore that there is little net sediment storage on this undisturbed landscape.     

Regional soil erosion risk mapping in Lebanon

Soil erosion by water is one of the major causes of land degradation in Lebanon. The problem has not yet been treated in detail although it affects vast areas. This study elaborates a model for mapping soil erosion risk in a representative area of Lebanon at a scale of 1:100,000 using a spatial database and GIS. First, three basic maps were derived: (1) runoff potential obtained from mean annual precipitation, soil-water retention capacity and soil/rock infiltration capacity; (2) landscape sensitivity based on vegetal cover, drainage density and slope; and (3) erodibility of rock and soil. Then two thematic maps were derived: potential sensitivity to erosion obtained from the runoff potential and landscape sensitivity maps, and erosion risk based on the potential erosion and erodibility maps. The risk map corresponds well to field observations on the occurrence of rills and gullies. The model used seems to be applicable to other areas of Lebanon, constituting a tool for soil conservation planning and sustainable management.     

Soil erosion prediction at the basin scale using the revised universal soil loss equation (RUSLE) in a catchment of Sicily (southern Italy)

Soil erosion by water is a serious problem in southern Italy, particularly in Sicily which is one of the Italian administrative regions prone to desertification. Soil erosion not only affects soil quality, in terms of agricultural productivity, but also reduces the availability of water in reservoirs. This study was conducted in the Comunelli catchment in south-central Sicily, to predict potential annual soil loss using the revised universal soil loss equation (RUSLE) and to test the reliability of this methodology to predict reservoirs siltation. The RUSLE factors were calculated for the catchment using survey data and rain gauge measurement data. The R-factor was calculated from daily, monthly and annual precipitation data. The K-factor was calculated from soil samples collected in May and November 2004. The LS topographic factor was calculated from a 20 m digital elevation model. The C- and P-factors, in absence of detailed data, were set to 1. The results were compared with those obtained from another soil loss estimation method based on ¹³⁷Cs and with the soil loss estimated from the sediment volume stored in the Comunelli reservoir between 1968 and 2004.     

Local thickening of the Cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle

Seismic reflection profiles from three different surveys of the Cascadia forearc are interpreted using P wave velocities and relocated hypocentres, which were both derived from the first arrival travel time inversion of wide-angle seismic data and local earthquakes. The subduction decollement, which is characterized beneath the continental shelf by a reflection of 0.5 s duration, can be traced landward into a large duplex structure in the lower forearc crust near southern Vancouver Island. Beneath Vancouver Island, the roof thrust of the duplex is revealed by a 5–12 km thick zone, identified previously as the E reflectors, and the floor thrust is defined by a short duration reflection from a < 2-km-thick interface at the top of the subducting plate. We show that another zone of reflectors exists east of Vancouver Island that is approximately 8 km thick, and identified as the D reflectors. These overlie the E reflectors; together the two zones define the landward part of the duplex. The combined zones reach depths as great as 50 km. The duplex structure extends for more than 120 km perpendicular to the margin, has an along-strike extent of 80 km, and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity, where velocities are less than 7000 m s^− 1. We suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion. The absence of seismicity from within the E reflectors implies that they are significantly weaker than the overlying crust, and the reflectors may be a zone of active ductile shear. In contrast, seismicity in parts of the D reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex. Merging of the D and E reflectors at 42–46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km. We suggest that pervasive reflectivity in the upper mantle elsewhere beneath Puget Sound and the Strait of Georgia arises from similar shear zones.     

Evaluation of proposed waste rock dump designs using the SIBERIA erosion model

Computer-based landscape evolution models offer the ability to evaluate landscape stability over the short (annual), medium (decades to hundreds of years) and long-term (thousands of years). Modeling has advantages in that design ideas can be tested, different surface material properties can be evaluated and risk analysis carried out. Landscape evolution models allow landscape surface change through time. These models also offer the advantage that the landscape can be evaluated visually as it develops through time, which is not possible with other types of models. Landscape evolution models can be used for not only soil loss assessment (i.e. tonnes/hectare/year), but also to evaluate the method of soil loss (i.e. rill or interrill erosion). This study examines a range of waste rock dump designs for the Minera Alumbrera Ltd. copper mine, Argentina. An erosion assessment using the SIBERIA erosion model over a 1000-year simulation period demonstrates waste rock dump designs using a conventional stepped design of backsloping benches and caps with angle of repose slopes provide the lowest average erosion rates and depths of incision than do other designs. Caution should be applied in interpreting these results as the SIBERIA erosion model is sensitive to parameter input and in this case was calibrated and run using a generic set of parameters that are not site specific. Nevertheless, the results provide a guide as to the strengths and weaknesses of different rehabilitation designs and demonstrate the insights that modeling studies can provide.     

Dam breach simulations with multiple breach locations under wind and wave actions

Multiple breaches of a dam resulting from wind-generated waves and wave overtopping are studied for a hypothetical long non-cohesive earthen dam with an uneven crest. Both wind speed and direction affect breach locations and outflow for a particular reservoir surface geometry. Locations on the dam with longer fetches along the wind direction are more subject to wave overtopping and breaching than other locations. Higher wind speeds lead to wave overtopping and dam breaches under larger freeboards than lower wind speeds. For a specified inflow hydrograph and spillway configuration, there exists a location at which the smallest estimated peak outflow occurs among all possible breach locations and the pool drops too quickly for additional breaches to develop. Using this location for a fuse plug or a pilot channel could minimize downstream impact, perhaps as an interim or emergency measure for a dam with inadequate spillway capacity.