Dip Slope Research Articles

Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests

This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark’s theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark’s theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark’s theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.

Topography shapes the structure, composition and function of tropical forest landscapes.

Topography is a key driver of tropical forest structure and composition, as it constrains local nutrient and hydraulic conditions within which trees grow. Yet, we do not fully understand how changes in forest physiognomy driven by topography impact other emergent properties of forests, such as their aboveground carbon density (ACD). Working in Borneo – at a site where 70‐m‐tall forests in alluvial valleys rapidly transition to stunted heath forests on nutrient‐depleted dip slopes – we combined field data with airborne laser scanning and hyperspectral imaging to characterise how topography shapes the vertical structure, wood density, diversity and ACD of nearly 15 km2 of old‐growth forest. We found that subtle differences in elevation – which control soil chemistry and hydrology – profoundly influenced the structure, composition and diversity of the canopy. Capturing these processes was critical to explaining landscape‐scale heterogeneity in ACD, highlighting how emerging remote sensing technologies can provide new insights into long‐standing ecological questions.

Assessment of Aeolis Palus stratigraphic relationships based on bench-forming strata in the Kylie and the Kimberley regions of Gale crater, Mars

The stratigraphic context of rock layers is a critical piece of information needed for accurate reconstruction of their geologic history. Although sedimentary rocks are widespread in Gale crater, efforts to deduce stratigraphic relationships of rocks were challenging early in the Mars Science Laboratory mission because vertical bedrock exposures were relatively rare along the first ∼3 km the rover traversed across Aeolis Palus. Potential insights into the three-dimensional configuration of rock layers were made once the rover passed Dingo Gap, especially in the informally-named Kylie and Kimberley regions. Here, the terrain exhibits low relief ( < 10 m) cliffs, some of which are continuous over lengths > 75 m. Curiosity Mastcam and Navcam images show that the cliffs are capped by resistant, bench-forming rock layers corresponding to two facies: a poorly sorted, weakly stratified pebble conglomerate, and a massive, dark-toned, vuggy sandstone. In places, the inclination of the topographic surface (northward ∼2° to 3°) is similar to the apparent dip of the underlying strata, suggesting the presence of dip slopes in an area inferred to be generally flat-lying, conformable rock units. Further, we assessed potential strata correlations via plane-fitting exercises and a regional comparison to other capping strata. We speculate that bench-forming strata in the study region could be part of a widespread package of draping strata (the Siccar Point group) that post-dates deposition and exhumation of the lower strata of Mount Sharp.

Study of the effects of container boundary and slope on soil liquefaction by centrifuge modeling

Two centrifuge model tests were conducted as part of the Liquefaction Experiments and Analysis Project (LEAP), and three extra tests were used to compare with the LEAP tests. The two models selected from LEAP-GWU-2015 were prepared in rigid box with a slope angle of 5 degrees. One of the extra models was prepared in a laminar box with a slope angle of 5 degrees and has the same model properties as the models from LEAP-GWU-2015. The other two extra models were prepared as flat ground in rigid box and laminar box respectively and have the same model properties. The effects of the container boundary and the dip direction of the slope models on soil liquefaction were investigated by assessing the acceleration, excess pore water pressure, and ground surface deformation. From the test results for the model in the laminar box, it is concluded that the soil contained in a laminar box have different dynamic characteristics compared with a rigid box soil. For the models in a rigid box, the soil on the high side of the slope has larger excess pore water pressure value and the excess pore water pressure changes are greater than the soil on the low side of the slope during shaking. The interaction between the slope dip and the direction of input motion affects dynamic performance during a seismic event.

Comparison between scarp and dip-slope rivers of the Cotswold Hills, UK

The Cotswold Hills, southwest UK, are properly described as a cuesta, with a steep, west-facing scarp slope and a plateau-like dip slope. Drainage reflects this surface morphology, with most rivers flowing southeast along topographic and stratigraphic dip. Here, we compare two superficially highly similar rivers – the Frome and Churn – whose sources are nearly coincident, but whose behaviour dramatically diverges thereafter. We examine longitudinal profiles, channel steepness, predicted discharge, and valley shapes, using digital topographic data. River discharge and water hardness/temperature values were obtained at seven sites on the Churn and nine on the Frome over a two-year sampling campaign, delineated into summer and winter phases. Nearly 100 borehole records were interrogated from the two catchments in order to assess groundwater level variations. The Frome, flowing west against regional dips, develops a steep course and has carved a deep and wide valley that exposes the full sequence of Cotswold Jurassic stratigraphy. On the other hand, discharge and channel gradients are lower for the dip-slope Churn, whose valley exposes less stratigraphy and fewer springs. Our measurements of river water hardness and temperature suggest that a greater proportion of groundwater flows into the Frome, regulating discharge and maintaining baseflow over summer. We suggest that flank uplift of the Cotswolds is at least part of the reason for the higher incision rates of the River Frome, leading to its intersecting a greater number of highly transmissive fractures that contribute to its discharge. In turn, the increased discharge could positively impact local incision rates.

Mechanism of the catastrophic June 2017 landslide at Xinmo Village, Songping River, Sichuan Province, China

On June 24, 2017, a catastrophic landslide (Xinmo landslide) occurred on the left bank of Songping river in Diexi town, Sichuan Province, China. Based on field investigations, this paper tries to reveal the cause and mechanism of the initiation and development of the Xinmo landslide. Xinmo landslide is located in the so called “Minshan block.” This tectonic block is very active and generates many earthquakes. Among them, the 1933 Diexi Ms 7.5 earthquake which had an indispensable effect on the occurrence of the Xinmo landslide, whose distance to the recent Xinmo landslide is only 8.7 km. The 1933 earthquake triggered the collapse of the Qianxin gully, which damaged the rock mass forming the source of the Xinmo landslide and creating a free prominent ridge. The later 1976 Songpan Ms 7.2 earthquake and the 2008 Wenchuan Ms 8.0 earthquake further damaged the integrity of the rock mass in the source area of the 2017 Xinmo landslide. The Xinmo landslide developed on a typical bedding dip slope with metasandstone intercalated with a few thin bedded slate layers. The slate intercalation gives the slope a very low shear strength in the dip direction and the long term rainfall may have softened the slip zone and the locked section. These two aspects have promoted the occurrence of Xinmo landslide.

Influence of Failure Probability Due to Parameter and Anchor Variance of a Freeway Dip Slope Slide—A Case Study in Taiwan †

The traditional slope stability analysis used the Factor of Safety (FS) from the Limit Equilibrium Theory as the determinant. If the FS was greater than 1, it was considered as “safe” and variables or parameters of uncertainty in the analysis model were not considered. The objective of research was to analyze the stability of natural slope, in consideration of characteristics of rock layers and the variability of pre-stressing force. By sensitivity and uncertainty analysis, the result showed the sensitivity for pre-stressing force of rock anchor was significantly smaller than the cohesive (c) of rock layer and the varying influence of the friction angle (ϕ) in rock layers. In addition, the immersion by water at the natural slope would weaken the rock layers, in which the cohesion c was reduced to 6 kPa and the friction angle ϕ was decreased below 14°, and it started to show instability and failure in the balance as FS became smaller than 1. The failure rate to the slope could be as high as 50%. By stabilizing with a rock anchor, the failure rate could be reduced below 3%, greatly improving the stability and the reliability of the slope.

Risk-based models for potential large-scale landslide monitoring and management in Taiwan

ABSTRACTSeveral related pre-event environment indices coupled with a 200-year event of Typhoon Morakot were used in this study to analyse landslide risk/scale for mapping and verifying the danger grade of watershed landslides. Risk analysis was modelled using maximum daily rainfall of the tested event as the hazard factor, and a complex indicator derived from indices of return period, road development and green deterioration as the vulnerability factor. The vulnerability factor was then modified using the slope to adjust the weight for excluding the flat areas and increasing impact of steep areas. A comprehensive indicator integrated from indices of river concave, headward erosion and dip slope was provided as the hotspot of potential large-scale landslides which were modified by vegetation index to correct sediment yield due to antecedent effects. Finally, sites with high potential large-scale landslide could be interpreted by the danger grade calculated from collapse risk/scale analysis. The results show that the higher the danger grade, the greater the collapse ratio; and the coefficient of determination for the relationship is greater than 0.9. The model developed in this study for accurately estimating the risk/scale of rainfall-induced landslide can be fulfilled.

Westward advance of the deformation front and evolution of submarine canyons offshore of southwestern Taiwan

This study analyzes both 2D and 3D seismic images around the Palm Ridge area offshore of southwestern Taiwan to understand how the deformation front shifted westward and how tectonic activities interact with submarine canyon paths in the transition area between the active and passive margins. Palm Ridge is a submarine ridge that developed on the passive China continental margin by down-dip erosion of several tributaries of Penghu Canyon; it extends eastward across the deformation front into the submarine Taiwan accretionary wedge. The presence of proto-thrusts that are located west of the frontal thrust implies that the compressional stress field has advanced westward due to the convergence of the Philippine Sea Plate and Eurasian Plate. Since the deformation front is defined as the location of the most frontal contractional structure, no significant contractional structure should appear west of it. We thus suggest moving the location of the previously mapped deformation front farther west to where the westernmost proto-thrust lies. High-resolution seismic and bathymetric data reveal that the directions of the paleo-submarine canyons run transverse to the present slope dip, while the present submarine canyons head down slope in the study area. We propose that this might be the result of the westward migration of the deformation front that changed the paleo-bathymetry and thus the canyon path directions. The interactions of down-slope processes and active tectonics control the canyon paths in our study area.

Dip-slope mapping of sedimentary terrain using polygon auto-tracing and airborne LiDAR topographic data

Dip-slope mapping is a fundamental task for landslide investigation and mitigation. However, most dip-slope mapping methods involve visual interpretations and manual processes that are inevitably subjective and time consuming. The advent of high-resolution digital elevation models (DEM) and increases in computing power have provided opportunities to improve the dip-slope mapping process. This study proposes a polygon auto-tracing method for generating dip-slope maps based on airborne Light Detection and Ranging (LiDAR) data and a customized spatial analysis toolset developed in Python. This method requires the input of strata boundaries produced for sedimentary terrain based on 2m resolution LiDAR DEMs. The method begins by deriving the raster layer of the dip direction of the bedding, and it then executes a series of raster calculations among the three raster layers slope, aspect, and dip direction to extract the dip-slope raster cells. Using the clustering pattern of the dip-slope raster cells, we implement the Point-Density analysis tool to determine the dip-slope areas. The ArcGIS ModelBuilder platform is used to lay out an automated workflow for the proposed polygon auto-tracing method using the customized toolset. For demonstration purposes, we successfully mapped 298 dip slopes in the study area, which frequently experiences dip-slope landslides and is located in the sedimentary terrain of northern Taiwan. The dip-slope mapping results were compared and validated against two government-funded visually interpreted dip-slope maps. Our dip-slope mapping results were also used in a daylight analysis along major freeways to identify potential locations of daylighted dip slopes.

Recent Landslide Movement in Tsaoling, Taiwan Tracked by TerraSAR-X/TanDEM-X DEM Time Series

The Tsaoling Landslide in Taiwan has captured attentions of researchers worldwide due to its frequent catastrophic failure and distinctive features. Thanks to the launch of TerraSAR-X/TanDEM-X (TSX/TDX) constellation, retrieval of global DEM with high spatial resolution and accuracy becomes possible, which is extremely useful for the study of natural hazards (e.g., landslides) globally. We attempt here for the first time to track recent landslide movements in Tsaoling Taiwan by analyzing DEM time series reconstructed from TSX/TDX image pairs. Quality improvement of InSAR derived DEM through an iterated differential operation is addressed during the data processing. Five cliffs and the Chingshui River are selected to determine the spatial pattern of morphologic changes of the landslide. The results show that: (a) A large amount of collapses occurred on dip slopes in the period from 2011 to 2014 and on surrounding debris deposits during the rainy seasons; (b) The average recession rate of the Chunqui Cliff decreased from 24.4 m/yr to 19.6 m/yr compared with the result between 1999 and 2009; (c) The Tsaoling Landslide has lost 6.90 ×106 m³ of soil from November of 2011 to April of 2014, which shows a positive correlation of 0.853 with rainfall; (d) The Chingshui River is undergoing a gradual bed erosion with a volumes of 1.84 ×106 m³.

Massive rock slope failure in Central Switzerland: history, geologic–geomorphological predisposition, types and triggers, and resulting risks

The basis of this article about landslides from massive rock slope failures (MRSFs) in the northern part of the Lake Lucerne area in Central Switzerland is a newly collected inventory of 25 mass-transport deposits (MTDs) within an area of 251 km2. Clearly dependent on the geologic–geomorphic predisposition, the pertaining processes are to be classified either as rock irregular slides originating from steep rock cliffs or as rock planar slides moving along dip slopes. All the investigated large-scale MTDs with spatial extents from 0.1 up to 14.6 km2 demonstrate excessive runout distances, especially the deposits associated with rock planar slides. Many of the MRSF are composite, by rock fragmentation into rock avalanches. Some of the mass transport processes involve cascades of events, including debris slides and debris flows. One MRSF was triggered by an earthquake and is thus considered a spontaneous event, whereas another two might be related to a cluster of strong seismic activity. The remaining MTDs cannot be assigned to identifiable triggers, except the Goldau rock slide in the aftermath of a period of heavy rainfall. The MTD inventory of the investigation area is assumed to be incomplete and suggests a low probability of large to very large events; it indicates high hazard ratings, should an event occur. A biasing towards larger and younger events is demonstrated. The M–F plot derived from the inventory, with magnitudes expressed as affected areas, shows two separate populations, distinguished by the occurrence (or absence) of rock avalanches. Using a statistical approach, the hazard associated with MRSF within the study area was rated as high. The societal risks emerging from the examined MRSF would nowadays be classified as unacceptable, especially if the massive spatial impact of rock avalanches is considered.

Applicability Research on the Dip Slope with Interbeddings of Weak and Strong Rocks Using Strength Reduction Method

Based on the combination of FLAC3D software and strength reduction method, the applicability of three kinds of instability criterion of the stability of dip slopes with interbeddings of weak and hard rocks is studied. Then the failure process, failure mode and stability of the slopes are analyzed. The results show that: (1) the maximum unbalance rate affects the final calculated results; there is no certain relation between the convergence of calculation and the slope stability. The convergence of the displacement curves of key points and the ultimate displacement values should also be concerned to determine the slope stability. The maximum unbalance rate and the amplitude of the reduction affect the determination of the characteristic point in the displacement curve. It is difficult to quantitatively evaluate the shear strain rate when judging the slope stability, the judgment is not convenient and the error is large. Combining with calculation convergence criterion and feature point displacement mutation criterion is helpful to improve the accuracy of judgment on the limit state of the slope. (2) Slope deformation and failure process can be roughly divided into four stages qualitatively; the rock mass has buckling failure can be divided into three stages according to the deformation characteristics. The potential shear export of slope with buckling failure locates above the slope toe. Different combinations of weak and strong rock thickness does not affect the failure mode of slope, which all bellows to buckling failure mode, but it will affect the slope stability coefficient; with the increase of the thickness of strong rock and weak rock, the stability coefficient increases. If the thickness of the strong rock increases, the stability coefficient increases as well when the thickness ratio is constant.

Failure mechanism analysis of rainfall-induced landslide at Pingguang stream in Taiwan: mapping, investigation, and numerical simulation

On September 15, 2012, torrential rains carried by the peripheral circulation of Typhoon Sanba and the northeast monsoon induced a translational landslide near Pingguang Road in Xindian District of New Taipei City, Taiwan. The total volume of the landslide was ~162,000 m3. The sliding mass destroyed two houses across the stream and formed a landslide dam at the toe of the slope, constricting the stream. For the purpose of reducing sediment-relative hazard around mountainous area, the paper attempts to explore the dynamics and phenomenon of the landslide on dip slope. This study interpreted remote sensing images and terrestrial LiDAR scanning, conducted onsite surveys to obtain material parameters, and performed simulations using the discrete element method to reconstruction the post-event, in order to elucidate the mechanisms involved in the landslide process. Survey results revealed complex geological conditions with tension cracks spreading in all directions at source area. This facilitated the infiltration of surface runoff into weak surfaces and raised groundwater levels. Slope failure may occur along the stratum boundary once the intrinsic shear strength of regolith drops below a critical value. The results of numerical simulation reveal that at 80 s after the Pingguang stream landslide began, a maximum deposition depth of 20 m had been reached. The sliding mass cut off the stream and pushed the stream flow roughly 35 m to the southeast. Because the slope materials surrounding the study area and the landslide-inducing mechanisms are similar, the top of the slopes to the northwest of the study area requires close monitoring. Finally, a detailed potential landslide mapping and interpretation from the high-resolution digital elevation model also present to prevent further landslides. The investigation indicates that the occurrence of landslide is highly related to seepage effect of accumulated rainfall, toe erosion by surface runoff, and local unstable geological structure.

Characteristics of ground motion and threshold values for colluvium slope displacement induced by heavy rainfall: a case study in northern Taiwan

Abstract. The Huafan University campus is located in the Ta-lun Shan area in northern Taiwan, which is characterized by a dip slope covered by colluvium soil of various depths. For slope disaster prevention, a monitoring system was constructed that consisted of inclinometers, tiltmeters, crack gages, groundwater level observation wells, settlement and displacement observation marks, rebar strain gages, concrete strain gages, and rain gages. The monitoring data derived from hundreds of settlement and displacement observation marks were analyzed and compared with the displacement recorded by inclinometers. The analysis results revealed that the maximum settlement and displacement were concentrated on the areas around the Hui-Tsui, Zhi-An, and Wu-Ming buildings and coincided with periods of heavy rainfall. The computer program STABL was applied for slope stability analysis and modeling of slope failure. For prevention of slope instability, a drainage system and tieback anchors with additional stability measures were proposed to discharge excess groundwater following rainfall. Finally, threshold value curves of rainfall based on slope displacement were proposed. The curves can be applied for predicting slope stability when typhoons are expected to bring heavy rainfall and should be significant in slope disaster prevention.

Tectonic foliations and the distribution of landslides in the southern Central Range, Taiwan

Geometry of planner geological structures can interact with topographic slope and cause different types of slope failure (e.g. wedge failure, dip slope failure, and toppling etc.). This study focus on how the tectonic foliation influences the landslide pattern in the southern Central Range of Taiwan. The tectonic foliations in this area range from pencil cleavage to schistosity depending on the increasing of metamorphic grade, and different foliations have different influences on the landslide behaviors. To describe the relation between foliation and topographic slope, we create the θD value as the angle between the foliation dip direction azimuth and the topographic downslope direction azimuth at a given location. The location of landslides in the area with pencil cleavage has no preferential θD value, and it suggests the landslide distribution has no correlation with foliation. The location of landslides in the area with well-developed slaty cleavage is mostly in the lower θD value, which suggests the landslides are more likely located in the area where the foliation dip direction is parallel to the topographic downslope direction. The location of landslide in the area with schistosity is mostly in the high θD value area, which suggests the landslides are more likely located in the area where the foliation dip direction is opposite to the topographic downslope direction.

Geomorphic evolution of Dehra Dun, NW Himalaya: Tectonics and climatic coupling

The Dehra Dun is a good example of a piggyback basin formed from the growth of the Siwalik hills. Two large rivers, the Ganga and the Yamuna, and their tributaries deposit a significant part of their sediment load in the Dun before they enter the Gangetic plains. This work documents the geomorphic complexities and landform evolution of the Dehra Dun through geomorphic mapping and chronostratigraphic investigation of the incised fan sections. Lesser Himalayan hills, inner and outer dissected hills, isolated hills, proximal fan, distal fan, dip slope unit, floodplains, and terraces are the major geomorphic units identified in the area. Isolated hills of fan material (IHF), proximal fan (PF), and distal fan (DF) are identified as fan surfaces from north to south of the valley. The OSL based chronology of the fan sediments suggests that the IHF is the oldest fan consisting of debris flow deposits with a maximum age of ~43ka coinciding with the precipitation minima. The proximal fan consisting of sheet flow deposits represents the second phase of aggradation between 34 and 21ka caused by shifting of deposition locus downstream triggered by high sediment supply that exceeded the transport capacity. The distal fan was formed by braided river deposits during 20–11ka coinciding with the deglacial period. The IHF, PF and DF surfaces were abandoned by distinct incision phases during ~40–35, ~20–17, and ~11–4ka respectively. A minor phase of terrace deposition in Dehra Dun was documented during 3–2ka. Our results thus show that the evolutionary history of the alluvial fans in Dehra Dun was primarily controlled by climatic forcing with tectonics playing a minimum role in terms of providing accommodation space and sediment production.

The hermitage of Cerbaiolo (Tuscany, Italy): stability conditions and geomorphological characterization

The Italian cultural heritage is one of the most noticeable in the world; an important part of it is subjected to natural hazard and risk conditions. Religious buildings, due to their location on impervious sites are particularly exposed to landslides. In this paper we study the hermitage of Cerbaiolo (Tuscany, central Italy). The hermitage, founded in the 8th century as a Benedictine monastery is now a Franciscan Women Institute seat. The buildings are on the edges of a limestone plate overlapped to a clayey formation. Falls, toppling and slides are present along the limits of the plate due to the geomechanics properties of the rock and to the contrast between the two lithological complexes. In order to identify the main joint sets affecting the rock mass a structural-geological survey was carried out and four sets are identified. The rock plate was classified according to Bieniawski, Barton and Geological Strength Index approaches. The outcomes confirm the predisposing factors to mass movements, corresponding to the intensity and characteristics of fracturing of the rock mass. With regard to the slope stability analysis, a failure mechanism involving sliding along a single plane (plane failure) was assumed on the first approximation. The analyses take into account the presence of tension cracks as an indicator factor for the instability phenomenon. The results of stability analyses, performed in static and seismic conditions, indicate a widespread instability condition. The dip slope direction, the properties and type of discontinuities and the local variation of composition influence the hazard assessment.

Morphometric Analysis and Flash Floods Assessment for Drainage Basins of the Ras En Naqb Area, South Jordan Using GIS

Morphometric analysis and flash floods assessment were conducted for the watersheds of Ras En Naqb escarpment, south Jordan. The study area comprises of twelve small watersheds occupying the faulted-erosional slopes, and the dip slopes. The drainage network shows that dendritic and sub-dendritic patterns dominated the dip slopes, whereas trellis pattern characterized the faulted-erosional slopes. Stream orders range from fourth to sixth order. The mean bifurcation ratios vary between 4.2 and 5.38 for the dip slope basins, and between 3.5 and 5.0 for the faulted-erosional slope watersheds, indicating a noticeable influence of structural disturbances (i.e., faulting and uplifting), and rejuvenation of drainage networks. All watersheds have short basin lengths, ranging from 23.8 km to 42.2 km for the dip slope basins, and between 15.3 km and 45.4 km for the faulted-erosional slope catchments. This is indicative of high flooding susceptibility associated with heavy rainstorms of short duration. The circularity ratios range from 0.177 to 0.704 which denote that the catchments are moderately circular on the faulted-erosional slopes, and to some extent elongated on the dip slopes. The length of overland flow values ranges from 0.854 to 0.924 for the dip slope catchments, whereas LO values for the faulted-erosional slopes vary from 0.793 to 0.945 denoting steep slopes and shorter paths on both dip slope and faulted-erosional slope watersheds. Values of stream frequency range from 1.509 to 1.692 for the dip slope, and from 1.688 to 2.0 for the faulted-erosional slope catchments. FS values are also indicative of slope steepness, low infiltration rate, and high flooding potential. The watersheds of the dip slopes show lower values of form factor varying from 0.079 to 0.364, indicating elongated shape and suggesting a relatively flat hydrograph peak for longer duration. Similarly, values of Dd are high for catchments on the dip slope basins (1.709 - 1.85) and the faulted-erosional slope watersheds (1.587 - 2.0) indicating highly dissected topography, high surface runoff, low infiltration rate, and consequently high flooding potential. Furthermore, high relief values exist, ranging from 388 m to 714 m for the dip slope basins, and from 421 m to 846 m for the faulted-erosional slope catchments indicting high relief and steep slopes. Morphometric analysis, and flash flood assessment suggest that ten watersheds (83.3%) are categorized under high and intermediate flooding susceptibility, and the faulted-erosional slope catchments are more hazardous in terms of flooding. Thus the protection of Ma’an, El Jafr rural Bedouin settlements, and Amman-Aqaba highway from recurrent flooding is essential to ensure sustainable future development in Ras En Naqb-Ma’an area.

The Impacts and Implications of Anthropogenic Forces on the Unstable Geologic Platform in Parts of Anambra and Imo States Southeastern, Nigeria

Anthropogenic activities have exacerbated the incidences of floods, soil and gully erosion and landslides in parts of southeastern states of Anambra and Imo, Nigeria. Intense urbanization, deforestation, agricultural, commercial/industrial activities has extensively-denudated and elluviated the total environment. The variations in climatic condition also have associated implications. The rainy season registers an average annual rainfall of 2000 mm. The Geology comprises an unstable platform of a regional escarpment/cuesta subtended by sandy, highly-fractured and faulted Nanka sands/Ameki Formation. The underlying unstable geology facilitates the development of gullies with depth ranging from 2 m to over 80 m. The calculated rate of soil removal from the gully prone areas is about 9.20 to 10.16 ton/ha/yr. The significant cuesta of the area with steep scarp slope and gentle dip slope forms both surface and groundwater divide that also facilitates gully and landslide developments. The underlying geologic sandy structure is quite porous and permeable with huge aquiferous horizons of high pore-water pressures and effective stress. The problems of laissez faire attitude and poor understanding of the destructive implications of the unstable regional geologic platform result in the failure of measures to prevent myriads of environmental destructions and economic wastes.