Geomorphic Units Research Articles

Alluvial floodplain gully erosion in dryland rivers – An overlooked source of sediment with implications for river condition and management

Dryland alluvial rivers are naturally complex systems with a range of in-stream and floodplain geomorphic units that provide habitat for aquatic and terrestrial biota. These systems are increasingly threatened by accelerated rates of sedimentation leading to declines in geomorphic complexity, habitat quality, and ponding depth. The implications of sedimentation on waterholes, or deep pools, is of particular concern, as they provide critical refugia in arid environments. However, sources of sediment entering and infilling waterholes, and the flow-on effects for habitat and water quality, are not well understood. This study addresses the potential for sediment derived from alluvial floodplain gullies to influence geomorphic change in dryland rivers. Alluvial floodplain gullies are often overlooked in comparison to more widely documented hillslope, or colluvial, gullies. Alluvial gullying is a prevalent feature of the Barwon-Darling River, one of Australia's longest and most important waterways in the northern Murray-Darling Basin (MDB). The estimated volume of sediment derived from floodplain gullies is 168 million m3, which far exceeds estimates used in past sediment budgets. Gully size and complexity varied from small, linear features to large, complex, branching gullies and the total number of gullies increased by ~40 % from the 1960s to 2000s. However, the more recent episodes of gullying (i.e., post 1960s) are limited to smaller gullies, which are likely to yield less sediment than the side walls of the older, larger, more complex gullies. Based on the average decline in maximum waterhole depth, ~19 million m3 of sediment has accumulated in Barwon-Darling waterholes over the past 120 years (equivalent to ~158,000 m3 a−1). A predictive relationship between gully volume and change in waterhole depth was expected, but not observed. Nevertheless, the role of alluvial floodplain gullies as a significant source of sediment should not be overlooked when assessing dryland river forms and processes. River management should consider the implications of changing sediment sources and in-stream loads, with associated changes in water quality and aquatic habitats, which influence river condition.

Morphometry of the Mt Manengouba volcano: Insights into tephrostratigraphy of Eboga maars (South West Cameroon)

The GIS-based geomorphological and morphometric approaches were combined with field- and tephrostratigraphic analyses to reconstruct the history of the Mt Manengouba volcano including the Eboga maars in the southwestern part of the Cameroon Volcanic Line (CVL). The elevation, slope, relative relief, topographic position and terrain ruggedness indexes from the Digital Elevation Model (DEM, 12.5 m) were determined to constrain two main geomorphic units corresponding to the Elengoum and Eboga nested stratovolcanoes which were affected by differential erosional processes. The studied grain size, shape, vesicularity, structure, degree of lithification, sorting, thickness, grading patterns, sedimentary features, spatial distribution revealed three tephrostratigraphic units: U1 (U1-1, lithic and juvenile; U1-2 dominantly juvenile), U2 (U2-1 ash- and juvenile rich-deposits; U2-2, juvenile-scoria with few lithic) and U3 (scoria cone deposits). The total volume of ∼0.199 km3 of tephra deposits ranges the Eboga maars volcanoes within the small-volume monogenetic types. These results revealed dry/wet phreatomagmatism and strombolian activity as a contribution to the seven phases-eruptive history of the Mt Manengouba volcano: the pre-Manengouba; emplacement of Elengoum stratovolcano; collapse of Elengoum summit and formation of Elengoum caldera; emplacement of Eboga stratovolcano; the collapse of Eboga summit and formation of Eboga caldera; a phreatomagmatic phase and emplacement of Female and Male maars ending with an explosive stage associated with the formation of scoria and parasitic cones.

Inferring on fluvial resilience from multi-temporal high-resolution topography and geomorphic unit diversity

The resilience of a river corridor represents its ability to withstand and recover from disturbances. Quantifying fluvial resilience in the face of various stressors is essential for integrating ecology and geomorphology in a context of river management. Geomorphic unit diversity analysis emerges as a valuable tool for characterizing and quantifying fluvial resilience to disturbances due to its inherent connection with fluvial dynamics. This paper aims to analyse and quantify the fluvial resilience of a wandering gravel-bed river affected by natural (e.g., floods) and human-induced (e.g., instream gravel mining) stressors. To achieve this goal, we use multi-temporal high-resolution topographic surveys of the Upper River Cinca (South-Central Pyrenees) spanning from 2014 to 2020. By employing the Geomorphic Unit Tool (GUT) on these surveys, we can map geomorphic units over time, quantify their diversity, and study geomorphic adjustments through morphodynamic signatures, altogether allowing inferring fluvial resilience.Our findings reveal that topographic changes (i.e., erosion and sedimentation) correlate with the type of stressor: maintenance works and gravel mining lead to degradation, while floods induce aggradation. Geomorphic Unit Diversity decreases following channel disturbances caused by gravel mining but rebounds after periods primarily stressed by floods, returning to pre-impact levels within six years. Geomorphic adjustments, such as channel incision and mid bar development, reflect erosion and sedimentation processes respectively, with channel maintenance works and floods being the main drivers. Despite the recovery of the geomorphic unit diversity within the reach, the deficit resulting from gravel extraction remains unresolved, perpetuating a degrading trend that poses risks in reducing lateral connectivity and could potentially catalyse future vegetation encroachment in bars and floodplains, causing changes on flood conveyance and hydraulics. Monitoring the river's geomorphic diversity provides crucial insights for effective conservation and management decisions regarding land use, development, and conservation along riverbanks, thereby sustaining or enhancing fluvial system resilience.

Detailed detection and extraction of estuarine tidal channels with multispectral and full‐polarised SAR remote sensing

AbstractEstuarine tidal channels are active geomorphic units in tidal flats. However, accurate information on the spatiotemporal changes in tidal channel systems remains scarce. The width of the tidal channels may vary from several kilometres to tens of centimetres. Monitoring tidal channel evolution is complicated because of periodic tidal scouring, anthropogenic activities and sea level rise. In this study, we propose a synergetic classification method to detect and extract morphological information of estuarine tidal channels with a spatial resolution of up to 3 m by fusing PlanetScope multispectral data with C‐band GaoFen‐3 fully polarised Synthetic Aperture Radar (SAR) data and machine learning algorithms. Considering the Yellow River Estuary as an example, the spectral features, vegetation and water index, polarisation and texture features derived from the multispectral and SAR images were selected as input data for classifiers according to feature importance ranking. Comparison to the maximum likelihood, and support vector machine classifiers, the synergetic classification with random forest showed the best performance, with an overall accuracy of 99.6%. Based on these results, the total number of tidal channels in the Yellow River Estuary reached 872, with a total length of 348.8 km. The spatiotemporal changes in the central axis over the last 4 years (2019–2022) suggest that the evolution of tidal channels was mainly controlled by ocean dynamics and anthropogenic activities. This method provides a cost‐effective alternative to accurately map tidal channel systems in global estuarine and coastal zones and helps to quantitatively describe their morphological evolution, stability and drivers.

Evolution of riparian vegetation in response to anthropogenic effects: The Taleqan River, Iran

AbstractDuring the last decades, human interventions, such as dam construction and land‐use change, have caused changes in geomorphic patterns and riparian zones in many rivers in Iran. This study aimed to assess the spatio‐temporal evolution of riparian vegetation and the spatial area of biogeomorphic feedback windows (BFWs) located in the riparian Salicaceae vegetation patches and their traits responding to human interventions in the Taleqan River during 1990–2022. The river was divided into five reaches using the geomorphic unit system (GUS) method, and the river sensitivity index (SI), location of BFWs, vegetation typology and main cover typology were investigated in the reaches using aerial photographs and satellite images from 1990 to 2022. For this purpose, the main cover typology was classified into grassland, woody vegetation, bank‐attached bars, islands, vegetated islands, river channels and urban areas. The stem diameter and density, degradation level and longitudinal/latitudinal alluvial bars in each of the BFWs were investigated using the field survey. Based on the findings, the lowest values of the SI (braiding index [BI], channel activity [CA] and channel width [CW]) and the highest expansion of BFWs were observed in the upstream reaches of the Taleqan River. Human disturbances in these reaches were less than in the reaches downstream, allowing the expansion of vegetation habitats. The vegetation patches were unstable and scattered in the midstream and downstream, and the width decrease of the river channel was created by land‐use change and channelization. A significant direct relationship was observed between BFW establishment, stem diameter and density, and vegetation height. The BFWs create an opportunity for engineer vegetation to prevent erosion and expand new habitats by creating biogeomorphic accumulation landforms and trapping alluvial bars on the lee side of engineer woody vegetation. This study highlights the interactions between riparian areas and hydrogeomorphic processes within riparian corridors exposed to human disturbances to help better define a comprehensive plan for river management.

A hierarchical method and workflow for the semi‐automated mapping of valley bottom geomorphic units using publicly available remote sensing datasets

AbstractGeomorphic units (GUs) are the landforms that make up the valley bottom and are produced by fluvial processes that determine river structure and function. Mapping of GUs can be used to interpret river type and behaviour and to analyse river condition and recovery processes. The advancement of remote sensing technologies and big‐data acquisition are enabling the development and operationalisation of tools to semi‐automate the mapping of assemblages of GUs across large spatial areas. In this study, we develop a hierarchical method that combines a landscape classification approach (Geomorphons) with supervised classification using light detection and ranging data (LiDAR) and satellite images to semi‐automate the mapping of GUs across valley bottoms. We have also produced a new method for identifying and mapping pools in the absence of bathymetry data. We applied our method on 78 river sections in coastal catchments of NSW, Australia. We were able to identify 20 refined GU types and four further sub‐types of bank‐attached bars. Our method produced GU maps that are consistent with desktop manual delineation from aerial images and digital elevation models. Our hierarchical method offers GU maps with varying accuracy and resolution, accommodating a user's decisions regarding amount of effort invested relative to map quality and accuracy required. Initial runs produce maps with 12 preliminary GUs with 61%–75% consistency when compared to desktop manual mapping. With additional effort and manual corrections, a higher level of GU identification is possible (i.e. refined GU mapping increases the consistency to 70%–81%). The delineation of more intricate sub‐types of GU or sub‐units on compound GUs, which is essential for interpretation of river behaviour, condition, and recovery, still requires on‐site field verification to achieve the best results.

SOIL ORGANIC CARBON CONTENT ACROSS VARIOUS GEOMORPHIC UNITS IN MANGROVE FOREST: A CASE OF DUBLAR CHAR, SUNDARBANS

Lying at the tidally active region of the Bengal Delta, the Sundarbans act as a terrestrial carbon sink and play a crucial role in climate change mitigation. However, this forest is underrepresented in term of soil organic carbon research. The purpose of this study was to investigate the Soil Organic Carbon dynamics across various geomorphic units within a small area of mangrove forest ecosystem of Dublar char of Sundarbans. Salinity and pH trends were also examined across geomorphic units to understand their interplay with soil organic carbon dynamics. Soil samples from 25 locations across various geomorphic units were collected and analyzed to determine soil organic carbon, salinity and pH levels. The Walkley-Black wet oxidation method was employed to determine the organic carbon content. Results indicate varying degree of organic carbon concentration across geomorphic units with Highland areas having high level of soil organic carbon concentrations with average concentration level of 2.05%, followed by Creeks with 1.55%. Salinity levels also varied across different geomorphic units with values ranging from 4.8 ppt to 12.7 ppt, with creek area having high level of salinity due to its close proximity to seawater. Fringe forest areas had the highest pH levels with average value of 7.4 and the lowest average pH value (6.86) was observed in Beach areas of the study area. The study holds immense significance in understanding the organic carbon dynamics of mangrove ecosystem in the Sundarbans, providing essential insights for long term climate resilient land management and biodiversity conservation efforts.

Geochemical characteristics of saline soils formed during the recent retreat of the Caspian Sea

The objectives of this study are: 1- Determining geochemical characteristics and soil formation processes that lead to soil salinity. 2- To investigate the variability of soil properties across different geomorphic units. The coastal landforms of the Caspian Sea have experienced several seawater retreat and progress in recent decades, which has caused changes in terms of pedology and geomorphology. Routine soil properties, including soil cations and anions (Ca2+, Mg2+, Na+, K+, Cl-, SO42-, CO32–, and HCO3–), and total and available forms of some micro-elements (Fe, Mn, Zn, and Cu) of 136 samples collected from 0-20 cm of soils were analyzed according to standard methods. Mapping of the obtained results was done using inverse distance weighting (IDW) in ArcGIS 10.8. The results showed that although the main source of cations and anions in the soil solution is seawater, their concentration and changes in the soil solution are different depending on the processes carried out in soil. Mg2+, Na+, and Cl- were highly enriched in saturated soil extracts compared to seawater (261 %, 153 %, and 149 % respectively). While, K+ and Ca2+, increased by 81 % and 47 % accordingly, and HCO3– and SO42-, decreased by −56 % and −25 % due to precipitation of carbonate and gypsum in the soil. Total and available forms of micro-nutrients were high across the study area. The distribution pattern of the total micro-nutrients follows the type of landforms (affecting drainage condition) and their clay contents (mineralogical composition and abundance), however, the available form of micro-nutrients depends on soil moisture conditions and proximity or distance to the coastline. The results showed that the chemistry of seawater is the main factor controlling the chemical and physical properties of soils and their distribution patterns. The geochemical processes of soil formation cause special interactions between the components of soil solution, which leads to the removal of carbonate, bicarbonate, and sulfate from the soil solution and precipitation with calcium as calcium carbonate and calcium sulfate.

Middle-Late Holocene climate change in an East Asian sandy land: Perspectives from the phytolith record of different geomorphic units

The accuracy of the regional palaeoclimate reconstruction is vital for ecological restoration and future climate predictions. Clarifying the regional climate signal on different geomorphological units within the same region plays a key role in regional climate researches. Here, we select the Horqin Sandy Land as the research area, and collect sedimentary from two typical geomorphological units (interdune lowlands: ML profile, DBS profile; dunes: CS profile, FX profile) as the research objects. The regional averaging method is employed to isolate distinct climate signals originating from interdune lowlands (IC-Score (Peat)) and dunes (IC-Score (Dune)), alongside an amalgamated climate signal (IC-Score (Peat&Dune)) synthesized from these two geomorphological units. This methodological approach facilitates the identification of variations in climate signals that collectively encapsulate the broader regional context. Meanwhile, local microclimate signals from dunes (IC-D-Value (Dune)) and interdune lowlands (IC-D-Value (Peat)) were separately analyzed to examine microclimate changes on different geomorphological units. The results indicate that different sedimentary carriers on various geomorphological units capture the local climate characteristics of their own units while recording regional climate changes. IC-D-Value (Peat) reflects ‘warm-humid’ climate, and IC-D-Value (Dune) represents ‘cold-dry’ climate. Climate signals derived from diverse geomorphological units exhibit the capacity to portray overarching regional climate patterns, yet they manifest variations concerning both semi-quantitative and quantitative climate parameters, notably temperature and precipitation. A regional average method is used to synthesize climate signals from different geomorphological units, which is more advantageous in documenting regional climate change. Regional climate signal reveals a change from warm-humid (9300 ∼ 4000 cal yr BP) to cold-dry (4000 ∼ 2000 cal yr BP) and then to slightly warm-humid (2000 ∼ 560 cal yr BP). Furthermore, regional climate signal shows the significant ∼ 2000-yr，∼1000-yr, ∼500-yr periodicities since 7300 cal yr BP, and solar activities are identified as one of the important driving factors.

Hydromorphological analysis of the middle Sebou river system (Eastern Saïss basin, Morocco): Functioning, morphogenesis, and antecedent controls

The hydromorphological characteristics of the Middle Sebou Valley were examined across various scales within a nested fluvial system, including catchment, landscape unit, valley segment, reach, and geomorphic unit. This study aims to explore hydromorphological functioning, morphogenesis of sedimentary forms, and antecedent controls on contemporary hydromorphological processes. The valley spans two distinct landscapes: the tabular plateaus of the Middle Atlas and the hills of the Saïss foreland basin. The valley is divided into three homogeneous reaches based on the landscape unit traversed and the valley setting, including the degree of confinement, the absence or presence of the floodplain, and the channel planform. In the Plateaus landscape unit, the upstream reach R1 is confined to deep gorges and displays a sinuous pattern. In contrast, the middle reach R2 in the rounded hills landscape unit is partially confined, showing a sinuous to slightly sinuous pattern with entrenched meanders and a tendency to braid. Finally, the downstream reach R3 is laterally unconfined and generally meandering, with free meanders. Along these reaches, floodplain pockets are respectively absent, discontinuous, and continuous. Each type of reach is characterized by an assemblage of instream and floodplain units genetically linked by a process-form association and by a different natural capacity for adjustment. The geomorphic river diversity and its behavior along the Middle Sebou catchment are shaped by the imprint of geological, climatic, and anthropic memory, which continues to influence contemporary processes.

Limited effect of the confluence angle and tributary gradient on Alpine confluence morphodynamics under intense sediment loads

Abstract. Confluences are dynamic morphological nodes that are found in all river networks. In mountain regions, they are influenced by hydraulic and sedimentary processes that occur in steep channels during extreme events in small watersheds. Sediment transport in the tributary channel and aggradation in the confluence can be massive, potentially causing overbank flooding and sedimentation into adjacent settlement areas. Previous works dealing with confluences have mainly focused on lowland regions, and those that have focused on mountain areas have used sediment concentrations and channel gradients that are largely under-representative of mountain river conditions. The presented work contributes to filling this research gap with 45 experiments that use a large-scale physical model. Geometric model parameters, the applied grain size distribution, and the considered discharges represent the conditions at 135 confluences in South Tyrol (Italy) and Tyrol (Austria). The experimental program allowed for a comprehensive analysis of the effects of (i) the confluence angle, (ii) the tributary gradient, (iii) the channel discharges, and (iv) the tributary sediment concentration. In contrast to most research dealing with confluences, results indicate that, in the presence of an intense tributary sediment supply and a small tributary-to-main-channel discharge ratio (0.1), the confluence angle does not have a decisive effect on confluence morphology. Adjustments to the tributary channel gradient yielded the same results. A reoccurring range of depositional geomorphic units was observed in which a deposition cone transitioned to a bank-attached bar. The confluence morphology and tributary channel gradient rapidly adjusted, tending towards an equilibrium state to accommodate both water discharges and the sediment load from the tributary. Statistical analyses demonstrated that the confluence morphology was controlled by the combined channel discharge and the depositional or erosional extent was controlled by the sediment concentration. Applying conclusions drawn from lowland confluence dynamics could misrepresent depositional and erosional patterns and the related flood hazard at mountain river confluences.

Evaluation of water ecological health of Yanhe River based on benthic fauna integrity index.

Yanhe River Basin is located in the hilly gully area of the Loess Plateau with serious soil erosion. Strong human activities in the middle and lower reaches lead to fragile ecological environment. Soil erosion status varies among different geomorphic units within the watershed (loess liang hilly and gully region, loess mao hilly and gully region, and broken platform region). In this study, we surveyed the benthic community from the Yanhe River Basin in April (spring) and October (autumn) of 2021. To evaluate the water ecological health status of the watershed and investigate the effects of different geomorphic units on the benthic integrity of the benthos, we constructed the benthic-index of biotical integrity (B-IBI) based on the biological data. We identified a total of 113 species of 73 genera in 4 phyla of benthic fauna, with aquatic insects as the dominant taxa in both seasons. Through screening 26 candidate indicators, we found that the spring B-IBI consisted of three indicators: relative abundance of individuals of dominant taxonomic units, family biotic index (FBI), and relative abundance of predator individuals, and that autumn B-IBI was composed of the number of taxonomic units of Ephemeroptera, FBI value, and the relative abundance of predator individuals. Results of the B-IBI evaluation showed that 83.3% of the sampling sites in the upper mainstem and tributaries were at a healthy condition, while only 28.6% sampling sites in the middle and lower mainstem and tributaries were at a healthy condition. In addition, the health status of the watershed was better in spring than in autumn. The Kruskal-Wallis nonparametric tests showed that benthic density, species number, and B-IBI percentile scores in the fragmented loess area were significantly higher in spring than in autumn, and significantly lower in autumn than in the loess liang hilly and gully region and loess mao hilly and gully region, being mainly caused by the increasing erosion due to the concentrated rainfall in wet season. Results of the redundancy analysis showed that key environmental factors affecting benthic community structure in spring were boulder substrate, chlorophyll-a, oxidation reduction potential, turbidity, conductivity, and dissolved oxygen, and were nitrate-nitrogen, oxidation reduction potential, and pH in autumn.

Morphologic Adjustment of a River Reach with Groynes to Channel Bypassing

AbstractThis article is focused on the investigation of the spatio-temporal variability of the Danube River reach’s vertical accretion thickness due to the response of the Danube River reach to bypassing. Five groyne-induced benches (GIBs) of the bypassed channel developed after water diversion in 1992 was studied by changes in topography for three-time spans (for the original gravel surface, for the surface before the 2013 flood and for the surface after the 2013 flood). The allostratigraphic approach was applied to 548 drilling probes at all GIBs and toptop, supra-platform, tail and backchannel geomorphic units have been identified at each GIB. The main to side-channel system connectivity increase sedimentation rates and the accretion was controlled by large flood events. The 100-year flood in 2013 contributed to the total volume by almost 26%. During study period 1992–2017, totally 1,146,589 m3 was accreted on five GIBs, of this 209,752 m3 during flood event in 2013 and 267,700 m3 in post flood period 2014–2017. The top geomorphic unit exhibits the highest median values of vertical accretion and for all GIBs accretion thickness are not related to the height above the mean channel water level. The thickness of accretion varied, likely because the variability of the vegetation cover caused variable hydraulic conditions and accretion rate span from 3.8 cm.year−1 to 5.3 cm.year−1. The investigation of the sediment thickness over long time spans 24 years and a large flood event) allowed us to conclude that the thickness is spatially variable for individual GIBs; however, its trend over time remains constants depending on the intake of sediments during large floodsd events. This article also provides a methodological template for the detailed investigation of river channel adjustment due to bypassing.

Geomorphic Imprints of Active Tectonics of the Bikaner-Nagaur Petroliferous Rift Basin and its Surroundings (Western Rajasthan, India)

Abstract Geology of sedimentary rift-basins require strong geomorphic input for a proper interpretation of active tectonics. Rift-related sedimentation took place in western Rajasthan of the Indian shield, which includes the Bikaner-Nagaur basin (BNB) and a few other adjacent basins. The sedimentation history of the BNB includes Proterozoic, Cambrian, Permo-Carboniferous and from Paleocene to the Recent. This study analyses river profiles with the best-fit curve (R2) model for the BNB and the surrounding regions. The research shows that the watershed 3 within the study area is most active tectonically, through which multiple faults and lineaments pass. Hypsometric Curves (HCs) of watersheds 1, 2 and 3 indicate that these watersheds are tectonically active. This inference is based on the concave profiles of HCs at the head, and convex profiles of HCs at the body and toe sections. Clustering of sixty segments (S) of the considered rivers based on linear-scale morphometric parameters, e.g., sinuosity index (SI), stream length gradient index (SL) and concavity (θ) enabled segment-wise comparison of river profiles with similar values. These segments were compared pair-wise, and Euclidean-based dissimilarity (dR) values were calculated between each such pair. The findings too imply that tectonic activeness exists in parts of watersheds 1, 2 and 3. The channel flow lines are controlled by faults/lineaments as per the micro-scale examination of the drainage network and faults/ lineaments analysis. Under structural control, nine major geomorphic units emerged with distinct erosional surfaces, denudational hillocks, dissected hills and inselbergs. Detailed geomorphic map with micro-scale studies revealed a slope retreat process that resulted in landforms viz., pediment, pediment slope and active flood plains.

Shift in the quantitative relationship between sedimentary records and catchment floods influenced by dam construction

Interpretation of sedimentary records is a crucial method for studying paleo-floods. However, the response intensity of sedimentary records to floods may be altered by reservoir storage. Therefore, depicting flood intensity in sedimentary records and alterations in the response relationship is the primary challenge in paleo-flood reconstruction. This study used the Yalu River catchment–estuary–coast as the research area and quantitatively reconstructed the response relationship between sediment grain size composition and flood intensity. This was conducted through a combination of forward simulation of the HYDROTREND hydrological model and reconstruction of sedimentary records, as well as evaluating the impact of reservoir regulation on the quantitative relationship. The findings showed that the lower Yalu River channel and tidal flat were both efficient at preserving flood records. However, there were significant differences in the response of different geomorphic units to floods. The river channel showed a significant increase in the coarse-sensitive component, whereas the tidal flat exhibited a substantial increase in the fine-sensitive component. Further study showed that there was a significant logarithmic relationship between the content of the fine-sensitive fraction and flood intensity. The sensitivity of the fine-sensitive fraction towards small floods was much higher than that toward extreme floods. In addition, reservoir construction caused a significant shift in the relationship between flood intensity and flood-related sensitive sediment fractions. Consequently, the reconstructed flood intensities of the pre-dam construction showed diverse levels of magnification based on the quantitative relationship between the sedimentary record and flood intensity of the post-dam. Meanwhile, this shift led to an increase in flood intensity corresponding to the critical value of the flood record that could be detected: from floods with a return period exceeding two years before dam construction to floods with a return period exceeding five years after dam construction. This study has quantitatively reconstructed the relationship between sediment grain size fractions and flood intensity and assessed the impact of reservoir construction on the quantitative relationship. It has also provided new ideas for more accurate reconstruction of paleo-flood intensity changes in the future.

A Geostratigraphic Map of the Rachmaninoff Basin Area: Integrating Morphostratigraphic and Spectral Units on Mercury

AbstractGeological maps of Earth typically incorporate field observations of rock lithology, structure, composition, and more. In contrast, conventional planetary geological maps are often made using primarily qualitative morphostratigraphic remote sensing observations of planetary surfaces. However, it is possible to define independent quantitative spectral units (SUs) of planetary surfaces, which potentially contain information about surface composition, grain size, and space weathering exposure. Here, we demonstrate a generic method to combine independently derived geomorphic and SUs, using the Rachmaninoff basin, Mercury, as an example to create a new geostratigraphic map. From this geostratigraphic map, we can infer some compositional differences within geomorphic units, which clarifies and elaborates on the geological evolution of the region.

Landslide Mapping and Causes of Landslides in the China–Nepal Transportation Corridor Based on Remote Sensing Technology

The China–Nepal Transportation Corridor is vital to the country’s efforts to build a land trade route in South Asia and promote the Ring-Himalayan Economic Cooperation Belt. Due to the complex geological structure and topographical environment of the Qinghai–Tibet Plateau, coupled with the impact of climate change, the frequent occurrence of geological disasters has increased the operational difficulty of the China–Nepal Highway and the construction difficulty of the China–Nepal Railway. However, to date, there has been no systematic study of the spatial distribution of landslides along the entire route within the area, the factors influencing landslides at different scales, or the causes of landslides under different topographic backgrounds. There is an even greater lack of research on areas threatened by potential landslides. This study comprehensively applies remote sensing, mathematical statistics, and machine learning methods to map landslides along the China–Nepal transportation corridor, explore the influencing factors and causes of different types of landslides, and investigate the distribution characteristics of potential landslides. A total of 609 historic landslides have been interpreted in the study area and were found to be distributed along faults and locally concentrated. The strata from which landslides develop are relatively weak and are mainly distributed within 2 km of a fault with a slope between 20° and 30°. The direction of slope for the majority of landslides is south to south-west, and their elevation is between 4000 and 5000 m. In addition, we discovered a power law relationship between landslide area and volume (VL = 2.722 × AL1.134) and determined that there were 47 super-large landslides, 213 large landslides, and 349 small and medium-sized landslides in the area, respectively. Slope is the most significant influencing factor for the development of landslides in the area. Apart from slope, faults and strata significantly influence the development of large and medium-small landslides, respectively. We have identified 223 potential landslides in the region, 15 of which directly threaten major transport routes, mainly in the Renbu Gorge section of the China–Nepal Highway and the proposed China–Nepal Railway section from Peikucuo to Gyirong County. In addition, we also discussed the causes of landslides within three geomorphic units in the region. First, the combined effects of faulting, elevation, and relatively weak strata contribute to the development of super-large and large landslides in the Gyirong basin and gorge. Second, the relatively weak strata and the cumulative damaging effects of earthquakes promote the development of small and medium-sized landslides in the Xainza-Dinggye rift basin. Third, under the combined effect of the hanging wall effect of thrust faults and the relatively weak material composition, landslides of various types have developed in the Nagarzê mountain. It is worth noting that potential landslides have developed in all three geomorphic units mentioned above. This study provides data and theory to assist in the accurate mitigation and control of landslide hazards in the corridor.

Investigation of site fundamental frequency using H/V method guided by geomorphic features derived from old aerial photos

The fundamental frequency of soil (non-lithified cover on the bedrock) is one of the most important factors in seismic hazard evaluations. On the other hand, this frequency expresses several factors such as the clast size, sorting, and the degree of compaction and cementation of soil, which is in close relationship with both the geomorphic setting and processes responsible for the soil formation. We present a rapid and cost-effective multi-disciplinary approach to study site effect in developing urban areas using the spatial correlation between geomorphic setting of soil units and their fundamental frequencies. As a case study, the city of Zanjan was selected because like many other cities of developing countries has been expanded drastically during the last half-century. We use old aerial photos (produced in 1966) of Zanjan and its surroundings to reconstruct a unified orthophoto-mosaic of the study area. This orthophoto-mosaic exhibits pristine geomorphic landforms and features, which predate the current urban coverage of the city, and provides an excellent possibility for mapping Quaternary geological units with distinct geomorphic settings and soil characteristics. Besides, the site effect is measured through the H/V spectral ratio method at 91 points along the profiles pre-designed based on our geomorphic mapping. Subsequently, the spatial pattern described in the geomorphic map was compared with the site effect values. This comparison shows a general correlation between the geomorphic setting of alluvia and the corresponding fundamental frequencies of the soil such that the closer to the mountain front, the higher the fundamental frequency. The results indicate that the peak frequency is observed in the northern regions of the city where a relatively thin layer of unsorted coarse-grained alluvium overlies the bedrock. In the southern geomorphic depressions close to the Zanjanrood river and behind the East-dipping North Zanjan reverse fault (east of the city), where a pile of fine-grained deposits is found, the fundamental frequency reaches its lowest values, namely less than 1 Hz. A comparison of the soil frequency map with the map of shear-wave velocities provided by geotechnical borehole data also indicates a meaningful correlation. Our approach provides a twofold benefit by (1) reducing both the time consumption and expenses in site effect studies through an optimal design of H/V measurement points and borehole drillings based on a precise mapping of distinct geomorphic units, and (2) proposing a unique possibility to produce a reliable site effect map in the urban areas developed during the last half-century.

Thinking from Horqin Grassland to Horqin Sandy Land

We systematically elaborated and compared the spatial scope and landscape changes of Horqin Grassland and Horqin Sand Land from their definitions and ranges. Horqin Grassland is an area with geographical units named after Mongolian tribes, but the boundary is unclear. Horqin Sand Land is also an area that borrows tribal names, but has independent topographic and geomorphic units, and clear boundaries. Horqin Grassland and Horqin Sand Land belong to two spatial regions that are both cross and different. The area and range of Horqin Grassland are larger than that of Horqin Sand Land which has obvious regional characteristics, and is a typical and research object area to study the development and restoration of aeolian desertification. Based on those cognition, we summarized the technologies and example models of comprehensive land management and desertification controlling over the years, and finally sorted out what should be focused on in the future to serve the annihilation war against desertification for Horqin Sand Land.

Evaluation of the ecohydrological separation of different geomorphological units in a semi-arid area

The ecohydrological separation (ES) phenomenon which states that there are two incompletely mixing subsurface water pools, one of which is supplied to plants for transpiration while the other flows to groundwater and river water, has far-reaching implications for hydrological model simulation and water resources management. Specifically, it is unclear whether it occurs under different geomorphological units (hillside, foothill, and floodplain) within the same climate zone, as well as the reasons for such variations. We collected samples of precipitation, groundwater, river water, soil water, and plant stem water from April to October 2019 and analyzed their stable isotopic composition. Moreover, in order to further confirm whether the ES phenomenon exists in both hillside, foothill, and floodplain, we also calculated the line-conditioned excess and the isotope values of source water. The isotope values of plant stem water were similar to that of soil water rather than groundwater on the hillside. Groundwater on the foothill in April, June, July, and August had considerably different isotope values from plant stem water. The isotopic composition of plant stem water was comparable to that of groundwater in the floodplain, but there were differences in the isotope values of source water and line-conditioned excess. On the hillside, foothill, and floodplain, this study found evidence of the ES phenomenon. As a result of preferential flows through soils that cause soil-water heterogeneity, the ES phenomenon under various geomorphic units differs from one another. This research disproved theories about translational flow across the rooting zone and offered a new perspective on the ES phenomenon.