Low-gradient Slopes Research Articles

Physico-Chemical Properties of Soil in Jita and Taksar Area of Lamjung District, Nepal

Physicochemical property of top layer of soil is very important for plant growth having life supporting agriculture production, forestry and environmental sustainability. Soil texture and its chemical properties are determined by various factors inversely soil property determines productivity for them. This study was conducted in Jita and Taksar area of Lamjung district of Nepal. Soil samples were collected from the field. Coarse fragments, soil texture and pH were measured from soil samples. Properties of soil were analyzed by mechanical and chemical methods such as sieve, hydrometer and digital pH meter. Dominant soil textural class is loam followed by silt loam. Higher proportion of sand is found in higher elevation and steeper slope. Inverse relationship is found of silt. Dominant soil is found to be slightly to moderately acidic. Soil pH level decreases with increasing altitude and slope gradient. Cultivated land is less acidic than other land cover category. It is found that lower elevation and lower slope gradient have more proportion of coarse fragments. Chi-square test proves the significant difference of pH, soil texture class, soil particle size and coarse fragment at different elevation, slope gradient and land use. However, variation of sand at different slope gradient and land use is not explained well.The Geographical Journal of NepalVol. 11: 45-62, 2018

Sedimentary architecture and depositional controls of a Pliocene river-dominated delta in the semi-isolated Dacian Basin, Black Sea

Sedimentological facies models for (semi-)isolated basins are less well developed than those for marine environments, but are critical for our understanding of both present-day and ancient deltaic sediment records in restricted depositional environments. This study considers an 835 m thick sedimentary succession of mid-Pliocene age, which accumulated in the Dacian Basin, a former embayment of the Black Sea. Detailed sedimentological and palaeontological analyses reveal a regression from distal prodelta deposits with brackish water faunas to delta-top deposits with freshwater faunas. Sediments contain frequent hyperpycnal plumes and an enrichment in terrestrial organic material, ichnofossils and in situ brackish and freshwater faunas. Deltaic progradation created thin, sharply-based sand bodies formed by multiple terminal distributary channels, covering a wide depositional area. The system experienced frequent delta-lobe switching, resulting in numerous thin parasequences. Parasequences are overlain by erosive reddish oxidized sand beds, enriched in broken, abraded brackish and freshwater shells. These beds were formed after sediment starvation, on top of abandoned delta lobes during each flooding event. A robust magnetostratigraphic time frame allowed for comparison between the observed sedimentary cyclicity and the amplitude and frequency of astronomical forcing cycles. Our results indicate that parasequence frequencies are significantly higher than the number of time equivalent astronomical cycles. This suggests that delta-lobe switching was due to autogenic processes. We consider the observed facies architecture typical for a delta prograding on a low-gradient slope into a shallow, brackish, protected, semi-isolated basin. Furthermore, in the absence of significant wave and tidal influence, sediment progradation in such a protected depositional setting shaped a delta, strongly river-dominated.

Bryophyte-dominated biological soil crusts mitigate soil erosion in an early successional Chinese subtropical forest

Abstract. This study investigated the development of biological soil crusts (biocrusts) in an early successional subtropical forest plantation and their impact on soil erosion. Within a biodiversity and ecosystem functioning experiment in southeast China (biodiversity and ecosystem functioning (BEF) China), the effect of these biocrusts on sediment delivery and runoff was assessed within micro-scale runoff plots under natural rainfall, and biocrust cover was surveyed over a 5-year period. Results showed that biocrusts occurred widely in the experimental forest ecosystem and developed from initial light cyanobacteria- and algae-dominated crusts to later-stage bryophyte-dominated crusts within only 3 years. Biocrust cover was still increasing after 6 years of tree growth. Within later-stage crusts, 25 bryophyte species were determined. Surrounding vegetation cover and terrain attributes significantly influenced the development of biocrusts. Besides high crown cover and leaf area index, the development of biocrusts was favoured by low slope gradients, slope orientations towards the incident sunlight and the altitude of the research plots. Measurements showed that bryophyte-dominated biocrusts strongly decreased soil erosion, being more effective than abiotic soil surface cover. Hence, their significant role in mitigating sediment delivery and runoff generation in mesic forest environments and their ability to quickly colonise soil surfaces after disturbance are of particular interest for soil erosion control in early-stage forest plantations.

Genesis and evolution of the mass transport deposits in the middle segment of the Pearl River canyon, South China Sea: Insights from 3D seismic data

Abstracts Utilizing newly acquired 3D seismic data, piston core, bathymetry and wells, this study investigated the geomorphological characters, genesis and evolution of two main phases of Quaternary mass transport deposits (MTDs) in the Pearl River canyon's middle segment. The older MTDs_1 almost covers the whole trough zone of Pearl River canyon's middle segment with an area of 1570 km2, which is sourced from north, west and south. Whereas the younger MTDs_2 has a much smaller coverage area of 840 km2 and is mainly from the northern slope. These MTDs could be divided into western and northern slope-attached MTDs and southern slope-detached MTDs based on their source areas. Within the MTDs-dominated study area, coarse sediments are presented at the area connecting to the slope channels and canyons. These two phases of MTDs probably occurred at ∼0.79 Ma and ∼0.54 Ma according to a published dating result. The homogeneous, organic-rich fine-grained sediments have high compressibility, preconditioning the generation of weak layers for submarine failures on the low gradient slope in the Pearl River canyon's middle segment. Our results showed that slope canyon types, variations of sediment supply and the regional tectonic evolution exerted important controls on the generation and evolution of these MTDs. The eastern slope canyons with little slope fans have a steeper slope at the canyon mouths, resulting the northeastern MTDs to be prone to retrograde landwards. The change of shelf-channel system from un-incised type to incised type increased the sediment delivery efficiency, resulting in larger scale MTDs_1 in the Pearl River canyon. While the subsequent decrease in the number of incised shelf channels cut down the sediment delivery into the deep-water and reduced the younger MTDs' scale as well. The variation of sediment supply had a greater impact on the development of slope-attached MTDs. The rapid subsidence of Baiyun Sag and tectonic activities of Dongsha Rise during the Quaternary favored the occurrence of the submarine landslides on low gradient slopes in the study area. However, the weakening of the tectonic activities resulted the Quaternary MTDs’ scale to be decreased upwards, especially for the southern slope-detached MTDs. The complex topography formed by the slope-attached MTDs has a greater potential to capture the subsequent turbidity currents from the shelf-edge deltas, bringing the generation of potential good turbidite reservoirs in the deep-water region.

Drag coefficient estimation using flume experiments in shallow non-uniform water flow within emergent vegetation during rainfall

Vegetation persistence on low-gradient slopes in dryland regions is presumed to be supported by lateral flow of water originating from bare sites with low permeability soil. The hydrodynamics of these flows, which occur during and immediately following intense rainfall events, are challenging to describe with classical approximations to the Saint-Venant equations (SVE). Flume experiments with varying rod density and applied water along the vegetated section are conducted to explore common approximations used to close the SVE when predicting water depth. Guided by these experiments, expressions are then derived that describe the simultaneous effects of spatially uniform vegetation density and rainfall intensity on the drag coefficient (Cd) linking the friction slope to the local kinetic energy head for steady non-uniform flow on a flat surfaces. Spatial variations in Cd through the vegetated patch either exhibit monotonic declines during rain or a non-monotonic ‘hump’ shape without rain with increasing longitudinal distance into the vegetated section. These spatial variations arise due to the indirect effect of rainfall on the dynamic component of the mean pressure gradient driving flow.

Soil moisture variation on the outlet area of devices dewatering forest roads in Beskid Sądecki

Abstract Water run-off - a natural part of water circulation in the natural environment - is a harmful and undesired phenomenon for humans. The most spectacular and most serious one is its erosive activity. In adverse conditions, such a runoff has high energy, it causes serious reshaping of a terrain and it destroys the natural environment and infrastructure. In the forest environment, a run-off process occurs basically on roads, skidding trails and in log storage sites, which are areas with soil cover properties changed by humans. The devices used for dehydrating a transport system direct water collected in the form of concentrated streams to a slope, which frequently causes serious linear damage or landslides. The objective of the tests carried out was to determine the spatial distribution of soil moisture on the area behind the outlet of devices dehydrating forest roads within the context of changes in selected soil properties affecting a risk of landslide formation. The tests included four water drains dehydrating a forest slope road with a soil surface. In the area located behind the outlet, according to the model accepted, soil samples were collected for testing a current moisture value, determining grain composition and a hydraulic conductivity coefficient, calculated based on the simplified Hazen formula. There were significant differences in the soil moisture means in the three-measurement series conducted; nevertheless, the highest moisture means were obtained after the lowest precipitation, and the lowest moisture means were obtained after the highest precipitation. It applies to all water drains observed, separately and collectively. Average moisture measures in all dehydrating facilities differed among one another, although in different sessions, this dependence was observed in various facility pairs. The statistical analysis did not demonstrate any significant differences in moisture in terms of the distance of moisture testing location from the road edge, or in locations with different distances from the water run-off line behind the outlet of dehydrating devices. Significant differences could be observed in the analysis of average moisture values in the soil layers. Such an analysis result could be explained by a relatively low soil permeability and low slope gradient on the area examined. Usually, a few percent fluctuation in soil moisture, despite precipitation diversity, in combination with a high amount of granular soil structure, does not create conditions facilitating the formation of landslides.

A multi-method approach for the characterization of landslides in an intramontane basin in the Andes (Loja, Ecuador)

In the last several decades, population growth in the cities of the Andes has caused urban areas to expand into landslide-prone areas. Fatal landslides affecting urban settlements are especially frequent in cities located in the Neogene intramontane basins of the Andes. These basins have similar situations and include geographical and geological features that frequently generate ground instabilities. We studied the characteristics of the mass movements observed in these basins by carrying out a detailed analysis of four landslides that have occurred in the Loja Basin (Ecuador). This multi-method study integrated geophysical, geotechnical methods, mineralogical studies and analyses of precipitation time series. Our study characterizes the slope movements as active, slow-moving, complex earthslide earthflows. According to Differential GPS measurements, these landslides move at velocities of up to several metres per year. Electrical resistivity tomography profiles show that most of the landslides are mainly surficial. Time-series analyses of precipitation reveal that rainfall events that are not exceptionally intensive can reactivate these landslides. This characteristic and the development of these landslides on low-gradient slopes are explained using the results obtained from the geotechnical and mineralogical analyses. We find that the smectite clay minerals detected in the mobilized geological formations, combined with the tropical climate of the northern Andean region, induce the observed weak slope stability conditions. The conceptual model for the studied landslides may aid in assessing landslide-prone areas in Loja and other Neogene intramontane basins of the Andes and can help to mitigate the associated risks.

Analytical method for determining rill detachment rate of purple soil as compared with that of loess soil

Rill detachment is an important process in rill erosion. The rill detachment rate is the fundamental basis for determination of the parameters of a rill erosion model. In this paper, an analytical method was proposed to estimate the rill detachment rate. The method is based on the exact analytical solution of rill erosion to the differential equation of rill detachment. The rill sediment concentration distribution as a function of rill length was identified through laboratory experiments under different slope gradients and flow rates. The sediment concentration processes from experiments on loess and purple rills were considered to estimate the rill detachment rates of both soils analytically. They were respectively used as a function of rill length and sediment concentration. The analytical detachment rates were compared with the numerically determined values to verify the analytical methods. The rill detachment rates of the two soils under different flow rates and slope gradients estimated by the analytical method were further compared on the basis of detachment-sediment function and detachment-rill length function. Results indicated that the analytically estimated values were very close to the numerically estimated values. Numerical and analytical methods were equally useful for rill detachment rate estimation. Therefore, the analytical method was verified to be rational and applicable for the rapid determination of the rill detachment rates based on either sediment concentration or rill length. The analytical detachment values of purple and loess soils suggested that the detachment rates of loess soil were significantly and considerably higher than those of purple soil. The erosion potentials of loess soil were also significant higher than those of purple soil. The differences in the erosion of the two soils decreased as the slope gradient and flow rate increased. These observations implied that the degree of loess soil erosion was greater than that of purple soil erosion at low slope gradients and flow rates. The factors causing these differences may be determined in terms of the properties of the two soils. Therefore, the proposed analytical method, in addition to the concepts and direct relationship to erosion process, could be applied to obtain the rill detachment rate for the determination of rill erosion model parameters.

Using ignimbrites to quantify structural relief growth and understand deformation processes: Implications for the development of the Western Andean Slope, northernmost Chile

Large-volume ignimbrites are excellent spatial and temporal markers for local deformation and structural relief growth because they completely inundate and bury the underlying paleotopography and leave planar surfaces with relatively uniform, low-gradient slopes dipping less than 2°. Using one of these planar surfaces as a reference frame, we employed a line-balanced technique to reconstruct the original morphology of an ignimbrite that has undergone postemplacement deformation. This method allowed us to constrain both the amount of posteruptive deformation and the topography of the pre-eruptive paleolandscape. Our test case was the unwelded surface of the 21.9 Ma Cardones ignimbrite, located on the western slope of the Central Andes in northernmost Chile (18°20′S). By reconstructing the original surface slope of this ignimbrite, we demonstrate that the pre–21.9 Ma topography of the Western Andean Slope was characterized by structural relief growth and erosion in the east, and the creation of accommodation space and sedimentation in the west. The paleoslope at that time was dissected by river valleys of up to 450 ± 150 m deep that accumulated great thicknesses (>1000 m) of the Cardones ignimbrite, and likely controlled the location of the present-day Lluta Quebrada as a result of differential welding compaction of the ignimbrite. Our reconstruction suggests that growth of the Western Andean Slope had already started by ca. 23 Ma, consistent with slow and steady models for uplift of the Central Andes. Subsequent deformation in the Miocene generated up to 1725 ± 165 m of structural relief, of which more than 90% can be attributed to fault-related folding of the ∼40-km-wide Huaylillas anticline. Uplift related to regional forearc tilting is less than 10% and could have been zero. The main phase of folding likely occurred in the mid- to late Miocene and had ceased by ca. 6 Ma.

Absolute and relative height-pixel accuracy of SRTM-GL1 over the South American Andean Plateau

Previously available only over the Continental United States (CONUS), the 1 arc-second mesh size (spatial resolution) SRTM-GL1 (Shuttle Radar Topographic Mission – Global 1) product has been freely available worldwide since November 2014. With a relatively small mesh size, this digital elevation model (DEM) provides valuable topographic information over remote regions. SRTM-GL1 is assessed for the first time over the South American Andean Plateau in terms of both the absolute and relative vertical point-to-point accuracies at the regional scale and for different slope classes. For comparison, SRTM-v4 and GDEM-v2 Global DEM version 2 (GDEM-v2) generated by ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) are also considered. A total of approximately 160,000 ICESat/GLAS (Ice, Cloud and Land Elevation Satellite/Geoscience Laser Altimeter System) data are used as ground reference measurements. Relative error is often neglected in DEM assessments due to the lack of reference data. A new methodology is proposed to assess the relative accuracies of SRTM-GL1, SRTM-v4 and GDEM-v2 based on a comparison with ICESat/GLAS measurements. Slope values derived from DEMs and ICESat/GLAS measurements from approximately 265,000 ICESat/GLAS point pairs are compared using quantitative and categorical statistical analysis introducing a new index: the False Slope Ratio (FSR). Additionally, a reference hydrological network is derived from Google Earth and compared with river networks derived from the DEMs to assess each DEM’s potential for hydrological applications over the region. In terms of the absolute vertical accuracy on a global scale, GDEM-v2 is the most accurate DEM, while SRTM-GL1 is more accurate than SRTM-v4. However, a simple bias correction makes SRTM-GL1 the most accurate DEM over the region in terms of vertical accuracy. The relative accuracy results generally did not corroborate the absolute vertical accuracy. GDEM-v2 presents the lowest statistical results based on the relative accuracy, while SRTM-GL1 is the most accurate. Vertical accuracy and relative accuracy are two independent components that must be jointly considered when assessing a DEM’s potential. DEM accuracies increased with slope. In terms of hydrological potential, SRTM products are more accurate than GDEM-v2. However, the DEMs exhibit river extraction limitations over the region due to the low regional slope gradient.

Assessing the vulnerability of pumping stations to trash blockage in coastal mega-cities of developing nations

Pumping stations are important flood mitigation infrastructure used in coastal cities to remove accumulating floodwater from low-lying areas, where drainage is naturally poor due to very low slope gradient. In coastal mega-cities situated in developing nations, these pumping stations are often vulnerable to trash blockage as a result of frequent dumping of solid waste in water bodies. Given that blocked pumps are common causes of drainage infrastructure failure, the inability to identify the most vulnerable pumping stations can lead to inefficient allocation of limited resources for preventative maintenance of the drainage system. This study proposes an approach for measuring and ranking the vulnerability of pumping stations to trash blockage. In this approach, a trash blockage vulnerability index (TBVI) is developed based on the concepts of exposure, sensitivity and resilience. Using a graph-based network analysis technique, the proposed TBVI is applied to assess and rank the vulnerability of pumping stations in one of the most representative coastal mega-cities − Jakarta, Indonesia. The results show that TBVI can point to the pumping stations that are most vulnerable to trash blockage. Such information are vital to decision makers when planning and prioritising infrastructure to be serviced or upgraded as part of flood preparedness in coastal cities.

Impacts of topographic attributes on Soil Taxonomic Classes and weathering indices in a hilly landscape in Northern Iran

Geochemical weathering indices are widely used in evaluating the stage of soil development. However, their compatibility with Soil Taxonomic Classes has not been studied yet. This study was conducted in a hilly region to illustrate the relations between soil development indices and topographic attributes and Soil Taxonomic Classes. A grid sampling method was carried out with 100m intervals. Physico-chemical analyses and total elemental analyses were performed on 184 and 56 soil samples respectively. In addition, eight topographic attributes and 12 common soil development indices were determined. Results showed that among the topographic attributes, slope gradient and topographic wetness index (TWI) had the highest correlation with Soil Taxonomic Classes and development indices. Morphological index (r=0.60) and Feo/Fed ratio (r=0.52) increased with progress in soil development from Entisols to Alfisols and Mollisols. Despite the significant correlations between most of the geochemical weathering indices and Soil Taxonomic Classes (Vogt index had the highest correlation coefficient (r=−0.74)), these indices represented lower weathering intensity in more developed soils. These relationships were due to the predominance of more developed soils in low gradient slopes, where the weathering products of upper slopes accumulate and their parent materials are carbonatic.

When does colonisation of a semi-arid hillslope generate vegetation patterns?

Patterned vegetation occurs in many semi-arid regions of the world. Most previous studies have assumed that patterns form from a starting point of uniform vegetation, for example as a response to a decrease in mean annual rainfall. However an alternative possibility is that patterns are generated when bare ground is colonised. This paper investigates the conditions under which colonisation leads to patterning on sloping ground. The slope gradient plays an important role because of the downhill flow of rainwater. One long-established consequence of this is that patterns are organised into stripes running parallel to the contours; such patterns are known as banded vegetation or tiger bush. This paper shows that the slope also has an important effect on colonisation, since the uphill and downhill edges of an isolated vegetation patch have different dynamics. For the much-used Klausmeier model for semi-arid vegetation, the author shows that without a term representing water diffusion, colonisation always generates uniform vegetation rather than a pattern. However the combination of a sufficiently large water diffusion term and a sufficiently low slope gradient does lead to colonisation-induced patterning. The author goes on to consider colonisation in the Rietkerk model, which is also in widespread use: the same conclusions apply for this model provided that a small threshold is imposed on vegetation biomass, below which plant growth is set to zero. Since the two models are quite different mathematically, this suggests that the predictions are a consequence of the basic underlying assumption of water redistribution as the pattern generation mechanism.

Effects of rain intensity, slope gradient and particle size distribution on the relative contributions of splash and wash loads to rain-induced erosion

Soil erosion during rainfall is a complex phenomenon resulting from detachment by raindrop impact and overland flow. The objective of this study is to investigate the transportation rate of splash load (SL) and that of wash load (WL) and their relative contributions to the rain-induced erosion rate affected by rain intensity, slope gradient and particle size distribution. A total of 60 simulation runs were carried out using a detachment tray under simulated rainfall with no inflow. The experiments were done on two soil samples (aggregate sizes finer than 2 and 4.75mm) from an agricultural land use at different rain intensities (57 and 80mmh−1) and varying slope gradients (0.5%, 2.5%, 5%, 10%, and 20%). Under unsteady state conditions, WL showed relatively high dependency on slope gradient, whereas approaching steady state conditions, nearly similar values of WL occurred at different slopes. SL and WL increased with increasing rain intensity and slope gradient, implying the importance of rain-induced erosion on bare agriculture lands especially at steeper slopes. The ratio of WL/SL decreased when slope gradient increased; however, WL increased more significantly than SL as soil aggregates became finer. The result indicates that at all the slope gradients, WL was much larger than SL, indicating that wash load significantly contributes to the rain-induced erosion in the agricultural soil. Furthermore, with increasing slope gradient, the contribution of wash load to rain-induced erosion decreased, while it was greater in the soil containing finer aggregates. Also, with increasing rain intensity at lower slope gradients (<10%), further increase in splashed materials than that in washed materials occurred, whereas the reverse order was found at steeper slopes (>10%). The finding of this study revealed that the rain-induced erosion was transport-limited at the gentler slopes, whereas at the steeper slopes, it shifted to detachment-limited conditions.

A groundwater recharge perspective on locating tree plantations within low-rainfall catchments to limit water resource losses

Abstract. Despite the many studies that consider the impacts of plantation forestry on groundwater recharge, and others that explore the spatial heterogeneity of recharge in low-rainfall regions, there is little marriage of the two subjects in forestry management guidelines and legislation. Here we carry out an in-depth analysis of the impact of reforestation on groundwater recharge in a low-rainfall (&lt; 700 mm annually), high-evapotranspiration paired catchment characterized by ephemeral streams. Water table fluctuation (WTF) estimates of modern recharge indicate that little groundwater recharge occurs along the topographic highs of the catchments (average 18 mm yr−1); instead the steeper slopes in these areas direct runoff downslope to the lowland areas, where most recharge occurs (average 78 mm yr−1). Recharge estimates using the chloride mass balance (CMB) method were corrected by replacing the rainfall input Cl− value with that for streamflow, because most recharge occurs from infiltration of runoff through the streambed and adjacent low gradient slopes. The calculated CMB recharge values (average 10 mm yr−1) are lower than the WTF recharge values (average 47 mm yr−1), because they are representative of groundwater that was mostly recharged prior to European land clearance (&gt; BP 200 years). The tree plantation has caused a progressive drawdown in groundwater levels due to tree water use; the decline is less in the upland areas. The results of this study show that spatial variations in recharge are important considerations for locating tree plantations. To conserve water resources for downstream users in low-rainfall, high-evapotranspiration regions, tree planting should be avoided in the dominant zone of recharge, i.e. the topographically low areas and along the drainage lines, and should be concentrated on the upper slopes, although this may negatively impact the economic viability of the plantation.

Seismic characterization of a Bottom Simulating Reflection (BSR) and plumbing system of the Cameroon margin, offshore West Africa

Analysis of a high-resolution 3D seismic dataset covering part of the Cameroon continental margin reveals a previously undocumented gas hydrate related Bottom Simulating Reflection (BSR) in water depths ranging from 940 m–1750 m. The BSR is mapped over an area of 350 km2, and at sub-sea depth of 104 m–250 m, increasing with increasing water depth. It is observed to vary in character depending on the present-day seabed slope gradient. In areas of low slope gradient, the BSR is high amplitude, with high amplitude reflections below it, and is associated with gas chimneys and single pockmarks. The high amplitude reflections immediately beneath the BSR are interpreted to indicate the presence of free gas, trapped under the hydrate seal and within thin sands within the sub-BSR free gas zone. In areas of high gradient slope, the BSR is comparatively weak and is associated with pockmark trains and pockmark clusters. The weakness of the BSR is interpreted to be caused by a lack of trapped free gas and thus low velocity contrast.The observed seabed pockmarks have been classified into three types defined by their appearance and distribution: (1) single pockmarks, (2) pockmark trains, and (3) pockmark clusters. Each style of pockmarks is related to a particular type of fluid migration pathway. The results suggest a number of migration mechanisms that deliver gas to the shallow succession, largely sealed beneath the gas hydrate, but also reaching the sea floor locally as evidenced by the pockmarks. The origin of the gas cannot be ascertained with the present data, but the style of overburden leakage features documented here is commonly found in petroleum provinces.

Transitions in Structure of Clay Fills due to Suction Oscillations

In North-western Bohemia the excavated overburden from open-cast coal mines is end-dumped in fills. Clay-type soil prevails among the filled soils. As a consequence of the character and state of the soil, together with the mining and dumping technology, the clay fill comprises a typical lumpy structure. Large and open macrovoids between the single lumps are a characteristic feature of the clay fills. The filled overburden forms spoil heaps under high angles of repose (as high as 40°) which is governed by size and shape of the lumps. However these slopes cannot be considered for design of clay fill final slopes. The lumpy clay fill structure is metastable. Structure transitions influencing the mechanical behaviour and thus slope inclination of the heaps are presented in this contribution. Three main agents are responsible for the transitions of the lumpy structure: Plastic straining of relatively weak lumps as a consequence of overburden load; collapse on wetting of the open metastable structure mainly in theearly stages after landfilling; and oscillations of matric suction. Long-term monitoring of matric suction in years 2004 - 2008 atdepths up to 2 metres in the low-gradient slope of the reclaimed clay fill in the Bílina mine show clear seasonal suction oscillations.

Depositional environment of a fan delta in a Vistulian proglacial lake (Skaliska Basin, north-eastern Poland)

ABSTRACT The study reconstructed the environment of a fan delta filling the vast end depression of the Skaliska Basin, and its overlying aeolian deposits. The formation of the large fan delta is associated with the presence of an ice-dammed lake functioning during the retreat of the Vistulian Glaciation (MIS 2). The examined material was collected from five boreholes. Sediments were analysed for their granulometric composition and subjected to analyses of frosting and rounding of quartz grains. Grain size analysis showed that the fan delta deposits are built of sand sediments of very low lateral and vertical variability. The fan delta was supplied with fluvioglacial sediments. Accumulation of sediments occurred in shallow water with a very low-gradient slope. The exposed fan delta became a site conducive to aeolian processes after the lake waters fell and the Skaliska Basin depression dried. Dune deposits overlying the fan were affected by short-distance transport so they did not acquire features typical for aeolian deposits.

A deep-seated slow movement controlled by structural setting in marly formations of Central Italy

The site investigation of low-gradient slopes composed by marly rocks usually focuses on shallow slides in weathered mantling material as it is assumed that the underlying bedrock has higher strength, but deeper investigations may reveal larger, active, deep-seated movements. A typical example of this is found in Montemartano (Perugia, Central Italy). Here aerial photo interpretation and field observations indicate that active movements involve the shallower portion of the slope, formed by a very old and large landslide body extending over an area of about 0.5 km2. Borehole core logging and probe inclinometer monitoring reveal that the area corresponding to the deep-seated landslide is moving at a maximum rate of 70 mm/year down to a maximum depth of 40 m. A comparison of inclinometer and piezometer data indicates that the movement seasonally reactivates even when rainfall and piezometer levels are below average values and suggests that structural setting of the whole slope influences both groundwater flow and movement kinematics. This hypothesis is reinforced by seepage analyses and stability analyses yielding a mobilized shear strength close to residual strength of the clayey interbeds of the marly limestone formations. This implies that instability occurs along bedding over a large part of the slide. The importance of these phenomena in land management policy is discussed and the critical aspects of their investigation and monitoring are addressed. The reconstruction of landslide geometry/stratigraphy and geotechnical characterization of the materials is closely considered, particularly as these are complicated by the limited representativeness of field and laboratory investigations in this type of material.

경사도와 인공강우 강도가 토양유실에 미치는 영향

대관령 지역에 많이 분포하고 있는 두 토양, 석비레 (Saprolite) 토양과 차항통 (Chahang series) 토양을 사용하여 경사면이 균일한 나지 토양에서 경사도 0.5, 7, 15, 30%와 강우강도 20, 60, <TEX>$90mm\;hr^{-1}$</TEX>의 조합으로 12처리를 하여 토양 유실에 대한 인공강우실험을 하였다. 그 결과를 요약하면 다음과 같다. 석비레 (Saprolite) 토양에서는 경사도 7% 까지는 토양유실이 적게 나타나다가 7% 이상의 경사면에서는 급격하게 증가하였고 차항통 (Chahang series) 토양은 경사도, 강우강도 증가와 함께 유실이 점증하였고, 경사도와 강우강도가 적은조합에서도 유실이 다소 크게 나타났다. 경사도 15, 30%와 강우강도 60, 90mm/hr의 조합처리에서는 두 토양 모두 토양유실이 크게 일어나고, 두 토양 간에 큰 차이는 없었다. 차항통 (Chahang series) 토양은 경사도, 강우강도가 적은 조합에서도 유실이 일어날 위험성이 크므로 토양관리에 주의를 요한다. This research was carried out to investigate the interaction effect of slope gradient and rainfall intensity on soil loss with rainfall simulator. The soils used in this experiment were saprolite, Chahang series which distributed extensively in Daegwanryong. Slope gradient applied was 0.5, 7, 15 and 30%. Rainfall intensity applied was 20, 60 and <TEX>$90mm\;hr^{-1}$</TEX>. The result obtained can be summarised as follow; Overall, Chahang series suffered more losses than saprolite. Chahang series shows the immediately large increase of soil loss with the increasing soil gradient and rainfall intensity. However, saprolite shows a little increasing loss up to 7% gradient and abruptly increasing loss logarithmically over 7% gradient in soil slope. In combination of slope gradient 15, 30% and rainfall intensity 60, <TEX>$90mm\;hr^{-1}$</TEX> processing, both soil erosion happened significantly. And there was no significant difference between the two soils. Because Chahang series have the danger of soil loss with low slope gradient and rainfall intensity, we should give greater attention to soil management in Chahang series.