Geomorphic Approach Research Articles

Integrated uplift, subsidence, erosion and deposition in a tightly coupled source‐to‐sink system, Pagliara basin, northeastern Sicily, Italy

AbstractHow tectonic forcing, expressed as base level change, is encoded in the stratigraphic and geomorphic records of coupled source‐to‐sink systems remains uncertain. Using sedimentological, geochronological and geomorphic approaches, we describe the relationship between transient topographic change and sediment deposition for a low‐storage system forced by rapid rock uplift. We present five new luminescence ages and two terrestrial cosmogenic nuclide paleo‐erosion rates for the late Pleistocene Pagliara fan‐delta complex and we model corresponding base level fall history and erosion of the source catchment located on the Ionian flank of the Peloritani Mountains (NE‐Sicily, Italy). The Pagliara delta complex is part of the broader Messina Gravel‐and‐Sands lithostratigraphic unit that outcrops along the Peloritani coastal belt as extensional basins have been recently inverted by both normal faults and regional uplift at the Messina Straits. The deltas exposed at the mouth of the Pagliara River have constructional tops at ca. 300 m a.s.l. and onlap steeply east‐dipping bedrock at the coast to thickness between ca. 100 and 200 m. Five infrared‐stimulated luminescence (IRSL) ages collected from the delta range in age from ca. 327 to 208 ka and indicate a vertical long‐term sediment accumulation rate as rapid as ca. 2.2 cm/yr during MIS 7. Two cosmogenic 10Be concentrations measured in samples of delta sediment indicate paleo‐erosion rates during MIS 8–7 near or slightly higher than the modern rates of ca. 1 mm/yr. Linear inversion of Pagliara fluvial topography indicates an unsteady base level fall history in phase with eustasy that is superimposed on a longer, tectonically driven trend that doubled in rate from ca. 0.95 to 1.8 mm/yr in the past 150 ky. The combination of footwall uplift rate and eustasy determines the accommodation space history to trap the fan‐deltas at the Peloritani coast in hanging wall basins, which are now inverted, uplifted and exposed hundreds of metres above the sea level.

Geomorphic floodplain mapping in small Mediterranean catchments using LiDAR data

Recent advances in remote sensing technologies along with the increased availability of topographic data have lately encouraged the development of automatic DEM (Digital Elevation Model)-based procedures for floodplain delineation. Geomorphic methods, establishing relationships between flood descriptors and morphologic catchment characteristics, appear particularly suitable to be implemented within a GIS algorithm. In the present work, four simplified geomorphic approaches based on “flow-depth scaling laws” (FD) or “flow-cross-sectional area scaling laws” (FA) with contributing area and two methods employing two different flood descriptors (Hydro-Geomorphic Method, HGM and Geomorphic Flood Index method, GFIM) have been applied for the preliminary evaluation of floodplain extent using high resolution DEMs (i.e. LiDAR at 1 and 2 m resolution) as the main input. Taking as a case study six of the largest basins located in southern Italy, the performances of these methods were evaluated and critically compared using government agency derived flood hazard maps as benchmarks. Results show that the adoption of FD especially when combined with morphology to formulate the GFIM, allows to efficiently predict the flood-prone areas with low computational costs. At the same time, performances of the flood mapping procedures based on “flow-area scaling laws”, although in principle more appealing, seem to be slightly lower. Overall, the proposed approaches can be applied for rough mapping of floodplains in ungauged basins or in data-scarce regions where standard flood hazard maps are unavailable.

Active tectonic assessment of the SW Cameroon Atlantic Coast using morphometric and geomorphic approaches

Active tectonic assessment of the SW Cameroon Atlantic Coast using morphometric and geomorphic approaches

3D Inundation Mapping: A Comparison Between Deep Learning Image Classification and Geomorphic Flood Index Approaches

Inundation mapping is a critical task for damage assessment, emergency management, and prioritizing relief efforts during a flooding event. Remote sensing has been an effective tool for interpreting and analyzing water bodies and detecting floods over the past decades. In recent years, deep learning algorithms such as convolutional neural networks (CNNs) have demonstrated promising performance for remote sensing image classification for many applications, including inundation mapping. Unlike conventional algorithms, deep learning can learn features automatically from large datasets. This research aims to compare and investigate the performance of two state-of-the-art methods for 3D inundation mapping: a deep learning-based image analysis and a Geomorphic Flood Index (GFI). The first method, deep learning image analysis involves three steps: 1) image classification to delineate flood boundaries, 2) integrate the flood boundaries and topography data to create a three-dimensional (3D) water surface, and 3) compare the 3D water surface with pre-flood topography to estimate floodwater depth. The second method, i.e., GFI, involves three phases: 1) calculate a river basin morphological information, such as river height (hr) and elevation difference (H), 2) calibrate and measure GFI to delineate flood boundaries, and 3) calculate the coefficient parameter (α), and correct the value of hr to estimate inundation depth. The methods were implemented to generate 3D inundation maps over Princeville, North Carolina, United States during hurricane Matthew in 2016. The deep learning method demonstrated better performance with a root mean square error (RMSE) of 0.26 m for water depth. It also achieved about 98% in delineating the flood boundaries using UAV imagery. This approach is efficient in extracting and creating a 3D flood extent map at a different scale to support emergency response and recovery activities during a flood event.

Tectonic and Climatic Control on Quaternary Exhumation in the Eastern Pamir Domes, Western China: Insights From Geomorphic Approaches

The Kongur Shan and Muztaghata massifs, bounded by the Kongur Shan extensional system (KES), represent tectonic and topographic anomalies in the eastern Pamir region. They are ideal examples to study how normal faulting and surface erosion influence Quaternary exhumation of the dome system. We apply multiple geomorphic parameters, including hypsometric integral, stream length-gradient index, drainage basin shape, drainage basin asymmetry and ratio of valley floor width to valley height, for the catchments on both sides of the range. We first evaluated the validity of various indices and chose three active tectonic-sensitive indices to establish a newly-integrated parameter (Iat) that is used to measure relative intensities of tectonic activity in active orogens. Results suggest stronger tectonic activity west of the domes along the Kongur Shan normal fault (KSF) and Muji dextral strike-slip fault, compared to the eastern side, along the Ghez and Kalagile faults. This first-order observation reflects tectonic control on the topographic development of the domal structure, consistent with eastward crustal tilting, attested by older thermochronology ages to the east. On the western flank of the range, stronger tectonic activity occurs mostly on the Muji fault, Kingata Tagh - Kongur Shan fault segment, as well as along the western and southern Muztaghata segments of the Kongur Shan fault. This is consistent with field investigations of Quaternary offsets of landforms, which suggest continuous activity of the Muji fault and KSF since the late Miocene. Average basin-wide erosion rates derived from stream power models are highest near the Kongur Shan dome, and gradually decrease southwards and northwards, in agreement with the spatial pattern of long-term exhumation rates in the footwall of the KSF obtained by low-temperature thermochronology data. Positive correlation between exhumation/erosion rates and extensional rates along the active faults located west of the domes indicates that extensional deformation likely plays a dominant role in controlling focused dome exhumation/erosion. However, considering peaked exhumation/erosion rates, stronger rock resistivity and steeper glacial landforms, attest to the important role of glacial buzz-saw in reshaping the recent dome’s landscape.

Tectonic instability of the petroliferous upper Assam valley (NE India): A geomorphic approach

Tectonic instability of the petroliferous upper Assam valley (NE India): A geomorphic approach

Age attribution to a karst system using river long profile analysis (Hyblean Plateau, Sicily, Italy)

In steady-state tectonic-climate systems, the fluvio-karst processes attain a stable base level, whether it be local or global. In contrast, in an uplifting region, relative base-level changes force river incision processes and a concurrent lowering of the karst water-table. Even at local scales (e.g., single fault-controlled valley), combined tectonically- and climatically-driven base-level drops induce geomorphic and hydrogeological disequilibrium. Thus, the karst system develops vertically and the water-table lowers trying to attain the new local base level. Conversely, the paleo-karst network dries, and becomes abandoned as a hanging relic with aligned karst morphologies. They are exhumed by the entrenchment of the fluvial network, as base-level fall related knickpoints migrate upstream. We propose a geomorphic approach to build fluvio-karst age models, based upon the analysis of river long-profiles. This approach is complementary to altimetric correlation between karst horizons and coastal paleo-sea level markers. Our approach is useful for an inland study area that is far from the marine terraced coast or where active faulting cuts off the coastal area from the inland landscape. We tested the approach in the eastern sector of the Hyblean Plateau (Sicily, Italy), where a carbonate sequence experienced Middle-Late Pleistocene tectonic uplift combined with active faulting. Specifically, we investigated the Cassibile River basin, at the footwall of the active Cassibile-Noto Fault. By reconstructing river paleo-long profiles we fixed time-space reference lines, connecting the abandoned and hanging fluvio-karst levels to the correlative marine strandlines carved along the fault-controlled coastal landscape.

Assessing geomorphic floodplain models for large scale coarse resolution 2D flood modelling in data scarce regions

River valleys are dynamic living ecosystems of utmost importance for flood attenuation that are shaped by inundation dynamics. Topographic and bathymetric surveys represent pivotal information for accurate and up-to-date floodplain studies. Both floodplain morphology as well as fluvial river cross section and thalweg profiles are required for inundation modelling and mapping. However, economic and technical limitations hinder their availability in some regions, resulting in challenges to build two dimensional (2D) flood wave routing simulations at proper accuracy and resolution. In this study, we assess the effectiveness of characterizing the fluvial morphology by means of geomorphic methods (GMs). Different GMs, used as surrogates of fluvial bathymetry, are tested and compared to a dataset of surveyed natural cross sections available for the Tiber River basin (Italy). Quantitative flood modelling performances are developed using a validated 150 m flood model, providing inundation extent and floodplain flow depths for the 200 years return period event. The ability (or inefficiency) of surrogating the lack of surveyed fluvial bathymetric data with GMs for supporting large scale hydraulic inundation modelling studies is assessed by testing the following 5 floodplain modelling configurations: (1) rectangular shaped cross section; (2) floodplain-based; (3) global river database; (4) linear regression bathymetric relationship; and (5) and a very coarse 700 grid resolution. In addition, two Global Flood Hazard Mapping (GFHM) products (hydrological, and hydrogeomorphic) were used as part of the large scale floodplain modelling evaluation framework. Results demonstrate that, once the fluvial channel flow area is preserved, all tested GM models produce consistent simulation of inundation depths and extents (Fit index ≥ 0.90). This work provides a quantitative assessment of the validity of the hypothesis stressing that the floodplain conveyance capacity is the driving principle of flood inundation dynamics under extreme flooding scenarios. Understanding the role of geomorphology during extreme magnitude floods may support the idea that under specific conditions, high resolution models and detailed topography/bathymetry are surplus to requirements. This work supports the application of geomorphic approaches over large riparian domains as a parsimonious solution for flood hazard mapping in data scarce regions for applications beyond flood mitigation and forecasting.

Drainage network evolution and reconstruction in an open pit kaolin mine at the edge of the Alto Tajo natural Park

Landform instability of the abandoned Nuria kaolin mine, surrounding the Alto Tajo Natural Park in Spain, has caused frequent and severe environmental impacts due to deficient mining practices, environmental mismanagement and closure planning. Geomorphic instability has caused widespread soil erosion and elevated sediment yields with off-site effects. We quantified such land instability, the evolution of the resulting drainage networks and catchments, and ensuing gully processes. High Resolution Topography sources were compared with historic maps and photos. The current mine rehabilitation practices are depicted based on a geomorphic approach that introduces a sustainable drainage system designed to avoid detected risks. Our aim is reconstructing fluvial channels and related hillslopes that mimic their natural counterparts adapted to a rehabilitation of pre-existing gradient terraces. We demonstrate that: i) mining activity produced a 31–58% decrease in the original site drainage network ii) a post-mining active advancing gully is an indicator of drainage network redevelopment advancing toward an upstream pond with flash-flooding risk; iii) a geomorphic designed and constructed fluvial network and proper drainage density adapted to pre-existing gradient-terraces seeks reestablishing stability; and iv) in absence of sufficient funding for rehabilitation, public/private collaboration agreements play an important role to reinstate landscape stability of abandoned or erroneously restored mines.

A Geomorphic Approach for Identifying Flash Flood Potential Areas in the East Rapti River Basin of Nepal

Basin geomorphology is a complete system of landforms and topographic features that play a crucial role in the basin-scale flood risk evaluation. Nepal is a country characterized by several rivers and under the influence of frequent floods. Therefore, identifying flood risk areas is of paramount importance. The East Rapti River, a tributary of the Ganga River, is one of the flood-affected basins, where two major cities are located, making it crucial to assess and mitigate flood risk in this river basin. A morphometric calculation was made based on the Shuttle Radar Topographic Mission (SRTM) 30-m Digital Elevation Model (DEM) in the Geographic Information System (GIS) environment. The watershed, covering 3037.29 km2 of the area has 14 sub-basins (named as basin A up to N), where twenty morphometric parameters were used to identify flash flood potential sub-basins. The resulting flash flood potential maps were categorized into five classes ranging from very low to very high-risk. The result shows that the drainage density, topographic relief, and rainfall intensity have mainly contributed to flash floods in the study area. Hence, flood risk was analyzed pixel-wise based on slope, drainage density, and precipitation. Existing landcover types extracted from the potential risk area indicated that flash flood is more frequent along the major Tribhuvan Rajpath highway. The landcover data shows that human activities are highly concentrated along the west (Eastern part of Bharatpur) and the east (Hetauda) sections. The study concludes that the high human concentrated sub-basin “B” has been categorized as a high flood risk sub-basin; hence, a flood-resilient city planning should be prioritized in the basin.

Estimating floodwater depth using SAR-derived flood inundation maps and geomorphic model in kosi river basin (India)

Flooding is the most widespread and frequent natural disaster in developing countries. Until recent years, determining flood extent and inundation depth were undertaken using hydrodynamic models but have pertinence constraints in data-scarce regions. This has given the new potential to characterize floods (e.g., inundation, depth, duration) at a large-scale using a geomorphic approach. The SAR data was employed to derive flood extent and the 12.5 m resolution DEM-based geomorphic method was applied to determine inundation depth in flooded domains of Kosi River Basin (KRB) in North Bihar (India) to characterize 2017 floods. The total inundated area in flooded domains over KRB was estimated at 4,108.2 km2 (20.88%). Most of the area (2,750 km2, 14%) of flooded domains over land had a water depth of 0.1 to 1 m. The geomorphic approach is appropriate for characterizing floods over large-scale and data-sparse basins like KRB and afforded a new horizon for flood risk assessment on flood vulnerable areas.

Combining geodetic and geomorphic methods to monitor restored side channels: Feedback from the Upper Rhine

Producing accurate and rapid geomorphic surveys is a key issue for the growing scientific and operational area of physical river restoration. A geodetic survey using 3-D modelling (lasergrammetry, photogrammetry, tacheometry) was combined with a geomorphic survey (RFID bedload tracking, survey of grain size, geomorphic units evolution and geometrical changes) in order to monitor morphodynamic adjustments in a restored anastomosing channel of the Upper Rhine. On this basis, functioning indicators were developed to survey morphological changes at different spatio-temporal scales. Because Structure from Motion (SfM)-photogrammetry is a fast and low-cost method able to produce high-resolution point clouds, the method is particularly well-suited for monitoring complex fluvial environments that have been subject to rapid and intense changes. A hybrid method was developed to complement bank point-clouds with bathymetric data obtained by Total Station leveling. By using the Multiscale Model to Model Cloud Comparison method (M3C2), volumes of erosion-deposition were determined for all surveys. Combining geodetic and geomorphic approaches resulted in a detailed assessment of channel adjustments. This was achieved by creating a set of indicators (e.g., related to vertical and longitudinal evolutions, sediment budget, etc.) that allowed us to both characterize geomorphic adjustments and identify morphodynamic limiting factors. These indicators may be used in the future in a wide range of restoration surveys.

Geomorphic Approaches to Estimate Short-Term Erosion Rates: An Example from Valmarecchia River System (Northern Apennines, Italy)

Studying fluvial dynamics and environments, GIS-based analyses are of fundamental importance to evaluate the network geometry and possible anomalies, and can be particularly useful to estimate modifications in processes and erosion rates. The aim of this paper is to estimate short-term erosion rates attributable to fluvial processes in two sample catchment sub-basins of the Marecchia river valley, by conducting quantitative morphometric analyses in order to calculate various descriptive parameters of the hierarchisation of the river networks and the mean turbid transport of streams (Tu). Sediment yield transported by streams can in fact partially express the amount of erosional processes acting within the drainage basin. The study area includes two sub-basins of the Marecchia valley (Senatello river, 49 km2 and Mazzocco river, 47 km2), chosen because of their similar extent and of the different location in the major catchment basin. Starting from geomorphological maps of the two river basins, the Tu parameter has been calculated and converted in short-term rate (average value 0.21 mm/year). Moreover, the comparison of these short-term mean data with the uplift rates calculated on a regional scale (0.41 ± 0.26 mm/year) in the Marecchia valley confirms that the northern Apennines may represent a non-steady state system.

Use of Remote Sensing Tools to Measure a Fluvial Geomorphic Design-Input Parameter for Land Reclamation

Fluvial geomorphic approaches for reclamation landform design have been applied since 2000, mostly in mined lands, as an alternative to conventional landform design methods. Those approaches aim to reconstruct mature landforms and drainage networks that would develop within a natural catchment, after thousands of years of work performed by geomorphic processes. Some fluvial geomorphic design methods take specific measurements from natural and stable reference areas for initial input values for reclamation design. Valid reference areas can be difficult to find, can be in highly anthropized environments, or may be difficult to access. This paper evaluates the use of remote sensing tools to measure morphometric parameters in upper sections of agricultural land catchments considered for use as reference areas. The ridge to head of channel distance (Xrh) was the parameter of interest. We used land surface profiles developed from LiDAR (Laser Imaging Detection and Ranging) data and planimetric measurements from orthoimages to estimate Xrh. The results obtained by the two methods were encouraging but showed a significant difference. Ground truthing showed that ploughing obliterated between 19.5 and 22.4 m (on average) of the headwater section of first-order channels, reducing the channel length by 15.1 to 32.4%. Using a greater Xrh value than appropriate for near steady-state conditions as a design input for a geomorphic reclamation project would be expected to result in active erosion processes in the constructed reclamation to regain their missing channel length. We recognize the advantages and limitations of remote sensing methods for measuring the morphometric parameters of the landform relief design inputs. We show how these tools may be used to help select and prioritize reference areas, and warn about the use of disturbed landscapes as reference areas to assure the geomorphic stability of the constructed reclamation designs.

Quantitative Geomorphic Approach for Identifying Active Deformation in the Foreland Region of Central Indo-Nepal Himalaya

Globally the remote sensing and geomorphometric analysis are frequently used for the assessment of tectonic activity. We used satellite-driven DEM data to analyze regional scale fluvial landform development in the parts of the central section of the Indo-Nepal Himalayan mountain chain, which is attributed the active deformation along the strike of major thrust. This deformation is accompanied by coexisting river incision and base-level fall along the longitudinal river course. These anomalies are obtained through conventional geomorphic parameters namely, stream-gradient index (SL), and steepness index (Ks) along with a new method called river Gradient Length Anomaly (GLA) analysis. GLA is a lied to deduct surface uplift and subsidence at the intersection between drainage basin and active thrusts. The deviations (offset) occurred along the river course are attributed to long-term active tectonic movement along thrust/fault or because of erosion/sedimentation processes. We analyzed 16 south-flowing rivers (e.g. Sarda, Kauriala, Girwa, and Babai), across the major Himalayan thrusts such as Main Boundary Thrust (MBT), Ramgarh Thrust (RT) and Himalayan Frontal Fault (HFT). The computed values of SL along the longitudinal course of these rivers range between 0.9‒4153 and Ks ranges from 0.1 to 173. The anomalous rise of SL and Ks values close to the major thrust points toward ongoing tectonics in the basin. The estimated results of fault parameters show that the horizontal shortening is higher than the vertical uplift. The empirical relationship of slip rate along the fault segments is estimated as 1.21, 2.65 and 1.084 mm/y respectively. Based on fault parameter, and abnormal GLA, SL and Ks analysis, and slip rate, a new E‒W oriented active fault structure have been inferred, which passes through the Beldandi, Bilsan, Bachua, Nandgaon, Dhagadhi Surat Nagar, and Bhagwanpur locations. The combined results of the present investigation can be used for evaluation of seismic hazard in the central section of Indo‒Nepal Himalayan front.

Monitoring Geomorphic and Traditional Post-Mine Reclamation using Digital Imagery: Vegetative Heterogeneity and Sampling Efficiency

Geomorphic reclamation creates variable topography and surface architecture, including rolling hillslopes and drainages. In contrast, traditional methods of reclamation result in landscapes susceptible to erosion due to steep, linear gradients. Geomorphic approaches to surface mine reclamation are relatively new, and hypotheses suggest the use of geomorphic principles in reclamation will improve vegetation outcomes relative to traditional methods. Topographic variability created by geomorphic reclamation likely results in more environmental heterogeneity, which should correlate with greater plant diversity. We examined revegetation outcomes of traditional and geomorphic reclamation on two reclaimed surface mines in Wyoming using nadir image sampling. Functional group diversity and measures of cover were compared between reclamation methods and undisturbed rangeland. Geomorphic reclamation supported greater total richness and greater native functional group richness relative to traditional reclamation. Native species cover on geomorphic reclamation, particularly for native perennial grasses, was either similar to undisturbed rangeland or greater than undisturbed rangeland and traditional reclamation. Reclamation shrub cover differed significantly from undisturbed sites, but was greater in geomorphic treatments. Results of nadir image analysis are compared to line-point intercept data from the same locations and outcomes are discussed in light of different reclamation techniques and sampling methods. Significant differences in cover categories were observed between nadir image and line-point intercept methods, however both methods revealed similar patterns between study sites.

Flood Inundation Modeling Using Geomorphic Approaches, UAV, and GIS

Flood is one of the most frequently occurring natural disasters in Indonesia. At the end of 2017, Tropical Cyclones Cempaka and Dahlia formed over the Indian Ocean, inducing extreme rains and floods in some parts of Java Island. The Special Region of Yogyakarta was among the most affected areas, especially along the Oyo River section in Imogiri District. This research was designed to identify and map the flood-prone areas in the district as part of flood mitigation measures. For this purpose, The Unmanned Aerial Vehicle (UAV) technology was used to not only provide a detailed and up-to-date description but also produce aerial photographs (orthoimages) and Digital Elevation Model (DEM). These two products were inputted to the inundation modeling developed with a geomorphic approach and simulated in a Geographic Information System (GIS). In terms of accuracy, the resulting models were quite reliable for mapping on a detailed scale and only slightly deviated from the traced inundation in the field. Also, five areas (sub-village) were found with the highest vulnerability to floods, namely, Trukan, Butuh, Dogongan, Siluk Satu, and Kedung Miri.

Hummocky terrain of the Kalibabak debris avalanche deposit, Lombok Island, Indonesia

The debris avalanche deposit (DAD) coverage can drastically modify the surrounding landscape of volcanoes. DAD can be distinguished by hummocky irregular surface, jigsaw fissure, and mixing horse-shoe shape. Due to its particular shape of a hummock, the topography can be easily identified using DEM (Digital Elevation Model) and satellite imagery. The aim of this study is to characterize hummocky terrain in Lombok Island, which is located in the Kalibabak formation on the Geological map through the geomorphic approach. Hummocky terrain in this study are analyzed using DEM data from DEMNAS (DEM Nasional: 0.27-arcsecond resolution). Our study of this DAD encompasses seven variables, namely H/L ratio, numbers hummocks, distance to source, slope, area (size), relative height, topographic section, and hummock-spreading shape. A minimum of 756 hills derived from this DEM are considered as hummocks from this DAD, which extends ~18 km (NS) and ~25 km (WE) in the central part of Lombok Island. With an area of ~200 km2 and a volume estimated around 8.8 km3, the Kalibabak DAD is more than three times larger than the one of the Mount St-Helens in 1980. The morphology of hummocky terrain is bounded by a sudden change of slope, which is indicated by a river confluence. Average hummock size is 2.7 ha and average distance between each hummock is 150 m to 300 m. The hummocks are characterized by steep slopes (25 % to 45 %) at the boundary to colluvium plain (debris deposit), which makes them easy to identify using DEM. Hummocks spreading distribution forms a conical-like shape with a H/L ratio of 0.13. The spreading distribution shape, the H/L and V/L ratios are useful as an input for reconstructing the mechanism of debris avalanche emplacement.

Landslide Distribution and Processes in the Hills of Central Nepal: Geomorphic and Statistical Approach to Susceptibility Assessment

The study examined the landslide distribution, processes, and susceptibility of the Lalbakaiya watershed using GIS and remote sensing technology. Inventory of landslides was done using high-resolution satellite imagery available on Google Earth and was verified and further investigated during the field visit. Geomorphic as well as statistical approaches were applied to assess landslides susceptibility and the significance of their outputs was discussed. Map layers representing conditioning and triggering factors of landslide occurrence were produced from various spatial data sources. The study found that the landslide of the Lalbakaiya watershed is primarily controlled by geology representing young, weak, fragile, and weathered sedimentary rocks. Besides, the role of topography such as steep slope, high relative relief, and land use and land cover played an important role in determining the landslide susceptibility. These processes are triggered by monsoon precipitation, seismicity, and land use change in addition to other factors. The geomorphic approach produces a reliable landslide susceptible map as evidenced by past and present (active) failures on a landscape unit, but this map has low predictability of the landslides occurrence. In contrast, the landslide susceptibility map derived from the landslide index method fairly conforms with that derived from the geomorphic approach. Susceptibility calculated by landslide index map is represented by a pixel value that indicates a probability of landslides occurrence, and is amenable to group into various susceptible classes. The model can predict areas of landslides based on quantitative relation between landslides and geo-ecological factors. The limitation of this approach is that these susceptible areas do not represent clearly defined landscape units, and can also overlook highly erodible areas where landslides are not apparent despite severe erosion and numerous minor failures. The study confirms that both geomorphic and statistical approaches can be complementarily integrated to produce predictable, reliable, and applicable landslide susceptibility maps that can make a plausible planning tool for conservation, development, and disaster risk reduction in the populated slopes of the Himalayas and like.

A Geomorphic Framework for the Analysis of Microplastics in Riverine Sediments

The wide-spread use and persistence of plastics in the environment have placed them on the list of significant emerging pollutants. In contrast to marine environments, the analysis of plastic debris, including microplastics (particles <5 mm in maximum diameter), in freshwater systems is limited, and even fewer studies have examined microplastics in riverine sediments. Nonetheless, it has become clear that microplastics are now a ubiquitous component of riverine ecosystems and their distribution is dependent on anthropogenic inputs and the physical and chemical processes that control their transport, transformation, and deposition along the drainage network. In many ways, the transport and fate of microplastics will parallel that of other particulate matter that has been extensively studied for at least the last 50 years. Here, we briefly explore the application of a geomorphic approach to the assessment of sediment-contaminated rivers to the microplastic problem, and argue that future studies can significantly benefit by incorporating the principles of this approach into their analyses.