Geomorphic Units Research Articles

INTEGRATION OF GIS AND RS FOR LAND RESOURCES SURVEY AND ASSESSMENT OF El-SADAT AREA, EGYPT

The current work aims to study the geomorphological and pedological characteristics for soils in the area located at south west of EL-Sadat city. The integration of Remote Sensing (RS) and Geographic Information System (GIS) techniques was used to perform this work. Soil classification quantitative land capability evaluation, and suitability of these soils for growing certain main crops were achieved using ALES-Arid program. This work could be presented important information about the potentiality of land resources for proper sustainable agriculture of these soils. The geomorphic map produced using RS and GIS technology indicated that, there are three identified and interpreted geomorphic units in this area. These units are Plain, High land, and Elevated area. Fourteen soil profiles were selected representing these three geomorphic units.The land and site features are observed and registered. Soil profiles were dug deep down to 120 cm. Profiles were morphologically described, and then samples were collected representing the subsequent layers in each profile for integrated physical and chemical analyses. The important morphological properties were used for evaluating pedological development of these profiles. The soils have almost flat topography to gently undulating landforms. The elevation of the studied profiles varies between 14 and 52 m. above sea level. Land surface and most of studied soils are slightly gravelly to gravelly. The soils are deep and mostly have well to excessive drainage system. These soils have light texture mostly loamy sand with rapid hydraulic conductivity. The soils vary between weak to moderate subangular to granular structure and some layers have single grains. The morphological rating scale of relative distinctness of horizons (RHD) and relative profile distinctness (RPD) values for the most of studied soilsindicated a slight distinctness between horizons and weak profile development. The analytical data of the studied soils revealed that, the soil reaction is slightly alkaline. All the studied soils are non-saline and not sodic. The soils differ from slightly to strongly calcareous according their CaCO3 content. Organic matter (OM), cation exchange capacity (CEC) and gypsum were low. The studied soils were classified up to sub great group level according to Soil Survey Staff (2014) under Entisols order as Typic Torripsaments. Land capability evaluation for these soils indicated that these soils could be categorized into grades between III to IV.

INTEGRATION OF RS AND GIS FOR STUDYING THE GEOMORPHOLOGICAL AND PEDOLOGICAL FEATURES OF SOME SOILS SOUTH WEST OF EL-SADAT CITY, EGYPT

The current work aims to study the geomorphological and pedological characteristics as well as classification for soils in the area located at south west of El-Sadat City. The integration of Remote Sensing (RS) and Geographic Information System (GIS) techniques was used to perform this work. This work could be presented important information about the potentiality of these soils for proper plans of reclamation, improvement and management. The geomorphic map produced using RS and GIS technology indicated that, there are three identified and interpreted geomorphic units in this area. These units are Low Terraces, Moderate Terraces and High Terraces. Fourteen soil profiles were selected representing these geomorphic units.The land and site features are observed and registered. Profiles were morphologically described, and then samples were collected representing the subsequent layers in each profile for integrated physical and chemical analyses. The elevation of the studied profiles varied between 14 and 52 m. that increased from the Low Terraces to the High ones. The soils have almost flat to gently undulating topography with gentle sloping. All studied soils are deep and characterized as freely well drained. These soils have almost slightly to gravelly loamy sand texture with rapid hydraulic conductivity. The soils have mainly weak granular to subangular structure and some layers have single grains. The most of studied soils are virgin without or with scanty vegetation. The morphological rating scale (relative distinctness of horizons RHD and relative profile development RPD) indicates a slight distinctness between horizons which mainly attributed to the depositional pattern and /or regimes of soil materials more than development. The analytical data of the studied soils revealed that, the soil reaction is slightly alkaline. All the studied soils are non-saline and not sodic. The soils differ from slightly to strongly calcareous according their CaCO3 content. Organic matter (OM)and gypsum were low. The cation exchange capacity (CEC) was also low due to the low content of fine fractions and OM in these soils. The studied soils haven't any diagnostic horizons, therefore they were classified up to sub great group level under Entisols order mainly as Typic Torripsaments.

Land cover change and eco-environmental quality response of different geomorphic units on the Chinese Loess Plateau

Land cover in the Chinese Loess Plateau has undergone dramatic changes since the late 1980s. Revealing the trend in land cover change and eco-environmental quality response of different geomorphic units in this stage is a realistic requirement for promoting sustainable development of the Chinese Loess Plateau. Based on the data of geomorphic units and land cover in 1990, 2000, 2010 and 2018 of the Chinese Loess Plateau, we studied the trend of land cover change and eco-environmental quality response of different geomorphic units by using a significance index of land cover change, a proportion index of land cover change and an eco-environmental response model. The results indicated that from 1990 to 2018, the areas of forestland and construction land substantially increased, whereas those of cropland, grassland, wetland and unused land considerably decreased. Land cover change exhibited large geomorphic differences, and the main conversion of land cover was from cropland into other land types. Unstable trend of land cover change in the loess tablelands and sandy loess hills declined, whereas the unstable trends in the other geomorphic units enhanced. Eco-environmental quality varied among different geomorphic units. The expansion of construction land and degradation of forestland, grassland and wetland resulted in the deterioration of eco-environmental quality. The conversion of cropland and unused land into forestland and grassland, and the conversion of grassland into forestland were the main factors that drove the improvement of eco-environmental quality. The findings of this study may provide theoretical reference and support decision making for the optimization of land use structure and the improvement of eco-environmental quality on the Chinese Loess Plateau.

Beaver dam influences on streamflow hydraulic properties and thermal regimes

Beaver dams alter channel hydraulics which in turn change the geomorphic templates of streams. Variability in geomorphic units, the building blocks of stream systems, and water temperature, critical to stream ecological function, define habitat heterogeneity and availability. While prior research has shown the impact of beaver dams on stream hydraulics, geomorphic template, or temperature, the connections or feedbacks between these habitat measures are not well understood. This has left questions regarding relationships between temperature variability at different spatial scales to hydraulic properties such as flow depth and velocity that are dependent on the geomorphology. We combine detailed predicted hydraulic properties, field-based maps with an additional classification scheme of geomorphic units, and detailed water temperature observations throughout a study reach to demonstrate the relationship between these factors at different spatial scales (reach, beaver dam complexes, and geomorphic units). Over a three-week, low flow period we found temperature to vary 2 °C between the upstream and downstream extents of the reach with a net warming of 1 °C during the day and a net cooling of 0.5 °C at night. At the beaver dam complex scale, net warming of 1.15 °C occurred during the day with variable cooling at night. Regardless of limited temperature changes at these larger scales, the temperature variability within a beaver dam complex reached up to 10.5 °C due to the diversity of geomorphic units. At the geomorphic unit scale, the highly altered flow velocity and depth distributions within primary geomorphic units provide an explanation of the temperature variability within the dam complex and insight regarding increases in habitat heterogeneity.

A Lentic Breeder in Lotic Waters: Sierra Nevada Yellow-Legged Frog (Rana sierrae) Habitat Suitability in Northern Sierra Nevada Streams

Ecology of the Sierra Nevada Yellow-Legged Frog (Rana sierrae) is well understood in high elevation lakes, but data on habitat preferences in stream-dwelling populations are lacking. We sought to expand understanding of stream habitat use by R. sierrae by investigating habitat suitability at the microhabitat and reach scales. We collected habitat availability and use data during 2016–2017 at five stream sites representative of geomorphic diversity in the northern Sierra Nevada mountains of California. At each frog use and availability location, we collected data on geomorphic unit type (e.g., riffles, pools), water depth, water velocity, substrate (e.g., gravel, cobble), and percent cover, including herbaceous, canopy, and total cover. Bootstrapped logistic regression models for all study sites combined indicated water depth and velocity were the strongest predictors of post-metamorphic (adult and subadult) use by R. sierrae, while substrate and total cover provided moderate improvement in microhabitat use predictions. Specifically, adults had the highest probability of use in microhabitats with <0.3 m depth and <0.1 m s–1 velocity. For tadpoles, we found velocity was the strongest microhabitat predictor for all study sites combined, with the highest probability of use in habitats with <0.01 m s–1. Site-level models highlighted the relative importance of non-hydraulic habitat variables, such as cover, when suitable depth and velocity conditions occurred. At the reach scale, we found hydraulic conditions varied widely in geomorphic units over time, but suitable microhabitat conditions emerged in differing geomorphic units as flows changed over the season. These data indicate that R. sierrae, like other ranid species, may be limited by hydraulically suitable habitat availability, but habitat preferences can be met in a variety of stream reaches when variations in flow conditions over time and space are considered.

Distribution, diversity, and geomorphic evolution of floodplain wetlands and wetland complexes in the Ganga plains of north Bihar, India

Floodplain wetlands are important features in alluvial settings across the world because of their ecological and hydrological significance. Understanding the geomorphic evolution of such wetlands is therefore not only interesting from an academic viewpoint but also necessary for their conservation and protection. Using a hierarchical system of geomorphological ‘elements’ and ‘units’, detailed geomorphic investigations have been carried out in the Kosi-Ganga interfluve, Eastern Ganga Plain (EGP) in the Himalayan foreland to understand the distribution and diversity of the floodplain wetlands in this region. The major geomorphic elements in this region consisting of lentic (wetlands, lakes) and lotic (streams) water bodies were mapped using multispectral satellite images. The distribution of the wetlands analysed through chord diagrams suggests that these are highly localised and associated with the regional geomorphic setting and the fluvial dynamicity. The morphometric characterisation of these wetlands using their count, % area, average area, and total area shows significant variability among the geomorphic units. The equal-area circle (EAC) such as the shoreline development index (DL) was found to be inadequate to assess the geomorphic maturity of the lentic water bodies and hence a new maturity index MCH, has been designed in this work using the convexity and area of the water bodies. Further, the space-for-time substitution approach has been used to develop the evolutionary pathway for the wetlands and the wetland-complexes in this interfluve over time scale of 10–102 years. We suggest that the evolution of the wetlands in a dynamic fluvial system such as the interfluve region of the EGP is governed by two different processes. Firstly, fluvial scouring and channel abandonment provide negative relief at a regional scale, and secondly, erosional processes (cut and fill) acting on the local scale transform the narrow and deep fluvial scours into large and shallow wetland systems.

Some issues of geomorphology to serve coastal environmental management of Quang Nam province

This paper presents the results of studies on the coastal geomorphological processes, which have been happening, to serve the coastal environmental management of Quang Nam province. Research results show that the geomorphological process is mainly destruction or coastal erosion, which has been occurring in most of the shores formed by loose material. In particular, coastal erosion has occurred strongly on the beaches of Cua Dai ward (Hoi An), in the south of Cua Dai (Duy Xuyen) and the south of Cua Lo (Nui Thanh). On the other hand, using geomorphological research methods, in the study area, we have determined five different geomorphic units belonging to the nearshore seabed. Thus, the zonation is carried out for risk warning according to different levels of risk of geomorphological hazards. This can help managers get a general picture for planning as well as have a specific planning policy for each coastal region in the coastal strip of Quang Nam province.

Reconstructing large‐scale karst paleogeomorphology at the top of the Ordovician in the Ordos Basin, China: Control on natural gas accumulation and paleogeographic implications

AbstractKarstification in carbonate successions has an important influence on hydrocarbon accumulation. Taking the Ordos Basin, currently the largest petroliferous basin in China, as an example, this study examines the large‐scale, long‐term (~120 Myr) paleokarst at the top of the Ordovician. The objectives of the study are to characterize the karst paleogeomorphology of this area, to explain the inconsistency between existing understandings of karst paleogeomorphology and exploration in the eastern Ordos Basin, and to reveal the control of paleokarst on natural gas accumulation and its paleogeographic significance. A total of 860 exploration wells were used for detailed stratigraphic correlation and analysis, along with core observations, well‐logging analyses, physical property characterization, and isotope analyses. Results of residual thickness and moldic thickness reconstruction reveal variation in karst paleogeomorphology between north and south in the eastern Ordos Basin, differing from the traditionally recognized E‐W variation. Two geomorphic units are classified as follows: the karst highland and the karst slope from north to south, with the karst slope being subdivided into northern and southern slope areas. The karst highland area has negligible reservoir capacity and hydrocarbon accumulation owing to the enhanced denudation that occurred there. In contrast, the northern karst slope shows favorable reservoir properties and has abundant gas wells according to well‐logging interpretations, whereas the southern karst slope is of poor reservoir quality and hosts mainly water wells. Differences in dissolution‐filling effects controlled by the surface paleodrainage system are suggested to be the main contributor to differential reservoir space preservation, which, together with the variable width and depth of source rocks in the grooves (thereby variably exposing source rock), further promoted differential gas accumulation. The Ordos Basin and its periphery in the southwestern North China Craton (NCC) show inheritance of sedimentary‐tectonic patterns from the Middle Ordovician to the Late Carboniferous. These results should provide a reference for hydrocarbon exploration in the Ordovician of other basins in the NCC in which karst occurs and karst basins worldwide, and deepens understanding of the paleogeographic framework in the context of regional uplift of the North China Platform.

Relationships between landform properties and vegetation patterns in the Cerro Zonda Mt., Central Precordillera of San Juan. Argentina

Arid environments are dynamic systems due, in part, to the action of hydrological processes. However, studies on the relationship between the abiotic factors and the properties of arid vegetation communities of Argentina are scarce. In this paper, the connection between these two parameters is researched using DEM analysis and exhaustive field work in order to model vegetation changes and landform evolution. The aim of this paper is to determine whether geomorphological properties influence vegetation patterns along the Cerro Zonda Mt. This mountain range is located in an arid central sector of Monte Desert, a phytogeographic region of Argentina. The classification of geomorphological units was made by combining interpretation of images provided by Google Earth and the analysis of Alos Palsar DEM using SAGA GIS. The geomorphic units were sorted into categories based on slope, elevation, hillslope aspect, terrain roughness and topographic wetness. In addition, surface characteristics of units were evaluated considering the properties of coverage of rock fragments, fine sediment and mulch. Afterwards, community patterns were explored using PCA analysis and linear correlations. Our results showed five geomorphological units: a) Pediment of mountain upland; b) Active landforms; c) Inactive landforms; d) Inactive landforms raised by neotectonics and e) Lacustrine landforms. The vascular flora is represented by 35 species distributed in 15 families. The landforms' surface property of rock fragments is correlated both directly with species richness and inversely with vegetation coverage. Furthermore, roughness explains the higher vegetation diversity while slope promotes an increase in the vegetation cover, but this does not suggest more species richness. In addition, our results indicate that topographic wetness, as well as hillslope aspect and elevation, are not determining variables of vegetation patterns across the landforms. The vegetation patterns of Cerro Zonda Mt. are associated with topographic properties as slope and roughness. In turn, rock fragment surface coverage also affects these vegetation patterns. The landforms' properties not only expose spatial changes in the development of the plant communities but also show the direct implications of geomorphological changes over such communities. In particular, there is a need to integrate a geomorphological view for the analysis of vegetation in arid zones.

Variability of hydrological connectivity and fish dynamics in a wide subtropical–temperate floodplain

AbstractFish are subject to diverse stimulus in floodplain rivers resulting from interactions between environmental factors. In such complex and interconnected ecosystems, fish assemblages are thus highly dynamic across space and time. Here, we analysed fish assemblage structures in lotic/lentic habitats of a geomorphic unit of the Middle Paraná River during summer, autumn, and winter of seven consecutive years. We observed that three main factors trigger significant structural changes: seasonality, habitat characteristics, and floodplain connectivity. The last one appears to have a determinant role on fish structures. Processes of connection/isolation of floodplain environments produced significant variations in fish abundance and species richness. Main results showed that some ecological processes can be largely explained by connectivity variations, such as fish dispersal in the floodplain, fish concentration in remnant floodplain lakes, and migrations back to permanent floodplain water bodies. This study provided a quantitative measurement of connectivity to understand fish dynamics in a giant floodplain and highlights the importance of similar investigations to preserve the fish fauna in these rather unique ecosystems.

Profile Distribution and Source Identification of Potentially Toxic Elements in North Nile Delta, Egypt

ABSTRACTVertical distribution and source appointment of potentially toxic elements (PTEs) provide a deeper vision for soil contamination. Contamination factor (CF), contamination degree (CD), enrichment factor (EF), principal component analysis (PCA), and cluster analysis (CA) were used for soil contamination assessment in north Nile Delta, Egypt. Twenty-one soil profiles representing main geomorphic units were dug, and 63 soil samples were collected at three depth intervals (0–30, 30–60 and 60–90 cm). Mean values of the three layers showed that Al, Fe, Mn, Cr, Cu, Pb, Mo, and V did not exceed average natural content of the Earth’s crust, while As, Cd, Co, Ni, and Zn exceeded that limit, except in the sand sheets unit. The studied elements showed irregular vertical distribution trend, except Cr, Ni, and Mo. Both Cr and Ni showed a downward migration, while Mo accumulated in the topsoil. Based on mean values, the CF indicated low contamination with Cr, Cu, Pb, Mn, Mo and V, moderate contamination with Cd and Zn, considerable contamination with As, Co, and Ni, while the CD was low to considerable. Furthermore, the EF indicated safe degree for Cr, Cu, Pb, Mo and V, deficiency to a minimal degree for Cd and Zn, while moderate degree for As, Co, and Ni. The PCA and CA indicated that soil parent materials controlled Al, Fe, Mn, Cu, Cr, Co, Pb, Ni, Mo, and V, while agricultural activities controlled As, Cd and Zn. Similar investigations should be considered in various regions in Egypt to verify potential sources of PTEs and to manage pollution of agricultural fields.

Spatially Consistent High-Resolution Land Surface Temperature Mosaics for Thermophysical Mapping of the Mojave Desert.

Daytime and nighttime thermal infrared observations acquired by the ASTER and MODIS instruments onboard the NASA Terra spacecraft have produced a dataset that can be used to map thermophysical properties across large regions, which have implications on surface processes, thermal environments and habitat suitability for desert species. ASTER scenes acquired between 2004 and 2012 are combined using new mosaicking and data-fusion techniques to produce a map of daytime and nighttime land surface temperature with coverage exclusive of the effects of clouds and weather. These data are combined with Landsat 7 visible imagery to generate a consistent map of apparent thermal inertia (ATI), which is related to the presence of exposed bedrock, rocks, fine-grained sediments and water on the surface. The resulting datasets are compared to known geomorphic units and surface types to generate an interpreted mechanical composition map of the entire Mojave Desert at 100 m per pixel that is most sensitive to large clast size distinctions in grain size distribution.

Characterization and Classification of soils on different Geomorphic Units of North-Eastern Haryana, India

Twelve pedons occurring on different landforms of North-Eastern Haryana were characterized for morphological, physical and chemical characteristics and classified. The soil colour of pedons varied from yellowish brown to reddish/ dark brown in the hues of 10YR, 5YR and 2.5YR. The soils of Shiwalik hills, upper piedmont plains and flood plains, lower piedmont plains and old alluvial plains were medium to moderately heavy in texture, relatively lighter and light to moderately heavy in texture, respectively. The soils have weak to medium subangular blocky structure. The sub surface horizons in old alluvial plains showed the translocation and accumulation of clay. The soils of the area were moderately alkaline to strongly alkaline (pH 7.5-9.4). The organic carbon was less than 1 per cent except surface horizons of forest areas. The water retention characteristics of soils were strongly associated to texture with the finer soil showing higher retention and vice-versa. The particle density, bulk density and total porosity varied from 2.20 to 2.84, 1.16 to 1.45 Mg m−3 and 40.43 to 56.78 per cent, respectively and did not show regular pattern down the profile. The cation exchange capacity varied from 5.21 to 17.00 cmol (p+) kg−1.

Morphological response of Lingding Bay in the Pearl River Estuary to human intervention in recent decades

The evolution of the Pearl River Estuary (PRE) in China has been intensely disturbed by diverse human activities in recent decades. In this study, the morphological changes of Lingding Bay in the PRE, consisting of three shoals (West, Middle, and East Shoals) and two channels (West and East Channels), in response to human activities since the 1970s were examined. From 1974 to 1985, the subaqueous delta was dominated by siltation, with siltation in the West and Middle Shoals but erosion in the East Shoal and West Channel. From 1985 to 1999, the subaqueous delta was eroded with increasing water volume of 347.9 × 106 m3, resulting from the combined influences of land reclamation and channel dredging. In addition, water area in the Lingding Bay reduced by 8.0% in 1999 compared with that in 1985. From 1999 to 2011, the water area continued to decrease and water volume still increased, indicating the subaqueous delta was narrowed and deepened. And the Middle Shoal was dominated by siltation, but other geomorphic units were eroded. Furthermore, the subaqueous delta in inner and outer Lingding Bay switched from siltation to erosion and from erosion to siltation during this period compared with the previous period of 1985–1999, respectively. Such phenomenon revealed that the sediment sink had evolved towards outer Lingding Bay (i.e., southern subaqueous delta) during this period. Our study has important implications for understanding the individual and combined effects of human activities on the evolution mode of PRE and provides scientific guidelines for the sustainable managements in the PRE.

Demersal fish assemblages and their diversity on the Yucatan continental shelf: Gulf of Mexico

Spatial variation in demersal fish assemblages (86°- 92∘W) and depth (<100 m, 101–200 m) on the Yucatan Shelf were determined using data from eighteen sampling stations collected during two periods (November 2015; August 2016). Estimates of ecological parameters and dominant species were made, and any spatial and causal associations between fish species and environmental variables (temperature, salinity, depth, nutrients) were identified. Alpha and beta diversities were recorded for each spatial and depth gradient, and gamma diversity was estimated for the entire region. A total of 161 species were recorded (27 orders and 52 families), with Syacium papillosum being the dominant species due to its high biomass (10.3%), relative density (11.7%) and occurrence. Followed in dominance by Haemulon aurolineatum, Eucinostomus gula and Upeneus parvus. No inter-annual change in the fish assemblages was detected using multivariate analysis, however, differences were identified between geomorphic units by depth gradient. Canonical correspondence analysis showed that depth gradient was the principal factor affecting variation in fish community structure. Based on gamma diversity (202) and species richness (161 species) the study area appears in good health. The data generated constitute an invaluable baseline for quantifying future changes and impacts on this ecosystem’s biodiversity.

Morphometric Analysis of River Donga Watershed in Taraba State Using Remeote Sensing and Gis Techniques

As climate change infiltrate and influence every sphere of the globe, the continuous study of the drainage features and assessment of the drainage basin as a fundamental geomorphic unit in water resources development and management cannot be relegated. This work has considered the analytical description of the physical division of RDCA. The three domains of the morphometric parameters (linear, areal, and relief aspects of the basin) were considered for the analysis. Remote sensing and GIS techniques were adopted in the analysis of the data using hydrological and surface tool in ArcGIS 10.2. The acquired SRTM DEM was used to delineate the catchment area and major morphometric parameters were estimated. The results show that the basin is elongated with low leminiscate ratio. RDCA is a 7th order drainage basin, with an area of 11,355 km2, having a length of about 164 km2. Value of drainage density indicates moderate runoff potentials. Stream frequency, bifurcation ratio and constant channel maintenance indicate medium permeability and that the basin produces a flatter peak of direct runoff for a longer duration. Channel encroachment, land use and land cover change seems the cause of perennial flooding in the region than change in drainage features. This study provides scientific database for further comprehensive hydrological investigation of RDCA around which Kashimbilla dam is located.

GEOMORPHOLOGICAL AND PEDOLOGICAL STUDIES ON SOUTHEAST QATTARA DEPRESSION, EGYPT USING RS AND GIS

Remote Sensing (RS) and GIS techniques are used in this study to identify the geomorphic units and produce the geomorphic map in addition to soil map of southeast Qattara Depression, Western Desert, Egypt. Soil classification and land evaluation for this area are also performed. According to the RS and GIS works, seven geomorphic units are recognized in the studied area. These units are gently undulated Low Terraces (29.0%), undulated Low Terraces (25.0%), gently undulated High Terraces (15.0 %), undulated High Terraces (17.0 %), Out Wash Plains (8.0 %), Alluvial Plains (3.0 %) and Residual Hills (4.0 %). The soils of the different geomorphic units were represented by 22 soil profiles. The soil morphological description was carried out and 65 disturbed soil samples were collected for physical and chemical analyses. The correlation between geomorphic units and their soils was carried out and then the soil map was created using the Arc- GIS 10.x software. Based on the land characteristics, the studied soils were classified up to the family level according to Soil Survey Staff (2014). These soils could be affiliated to Aridisols and Entisols orders. The soils are evaluated according to their capability for agriculture in the current and potential situations. The results revealed that, the studied soils could be categorized into four classes namely, moderately suitable (S2), marginally suitable (S3), current not suitable (N1), and permanent not suitable (N2). The limitations affected these soils are texture, salinity & alkalinity and CaCO3. The potential capability of these soils are predicted when their limitations well be remedied.Also, the suitability for cultivation four main crops namely wheat, barley, potato and olive in the studied area are assessed. The results indicated that, olive was the most suitable for growing in these soils.

Sequence architecture and depositional evolution of the late Palaeogene in southwestern slope of Lufeng Depression, Pearl River Mouth Basin: Responses to tectonic processes and base‐level changes

The southwestern slope of Lufeng Depression, which is located in the central part of Zhu I Depression is a significant geomorphic unit due to its petroliferous discoveries and tectonic evolutions since early Palaeogene. Based on the comprehensive analysis of cores, wireline logs, seismic volumes, and other related geological and geophysical information, the sequence architecture and depositional evolution was analysed, and their responses to regional tectonic processes and base‐level changes were revealed. The results indicated that two second‐order sequences and six third‐order sequences defined by different types of sequence boundaries are recognized. The second‐order and third‐order sequences were bounded by regional erosional unconformities on the depression margin or slope and unconformities in the central depression with the assist of stacking patterns of wireline logs and depositional characteristics of cores. The second‐order sequence generally consists of two regional transgressive–regressive cycles which can be further subdivided into several local sub‐cycles equivalent to corresponding third‐order sequences which can be identified from wireline logs and cores. The palaeogeomorphology resulted from compound and complex tectonic events in the early Palaeogene plays an important and main role in controlling sequence architecture. In contrast, the base‐level changes largely controls the sequence architecture in the late Palaeogene. The depositional systems within the sequence stratigraphic framework are mainly composed of braided delta deposits and shore deposits, which respectively includes braided channel, subaqueous distributary channel, lacustrine shale, beach bar, maximum flooding surface, shoreface, and foreshore. The base‐level changes, which apparently originated from tectonic uplift and subsidence and sediment supply, controlled the regional transgressions and regressions in sedimentary facies distributions. The development of subsequence (what we call it sand units or sections) from 2,980 to 2,880 in Enping Formation in the Early Palaeogene is obviously influenced by a decrease in tectonic subsidence (rifting stage) and an increase in accommodation space (base‐level rising), while the case is opposite in subsequence 2,850 of Enping Formation. However, the subsequence in Zhuhai Formation in the late Palaeogene from 2,760 to 2,600 was formed in stable tectonic settings (transition stage), and thereby, it was mainly dominated by base‐level changes which were caused by sediment supply and accommodation space changes.

Modelling braided river morphodynamics using a particle travel length framework

Abstract. Numerical models that predict channel evolution are an essential tool for investigating processes that occur over timescales which render field observation intractable. The current generation of morphodynamic models, however, either oversimplify the relevant physical processes or, in the case of more physically complete codes based on computational fluid dynamics (CFD), have computational overheads that severely restrict the space–time scope of their application. Here we present a new, open-source, hybrid approach that seeks to reconcile these modelling philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a rule-based sediment transport algorithm to predict particle mobility and transport paths which are used to route sediment and evolve the bed topography. Data from two contrasting natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for model verification, incorporating reach-scale quantitative morphological change budgets and volumetric assessment of different braiding mechanisms. The model was able to simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming necessitated the inclusion of a lateral channel migration algorithm. Comparisons between simulations based on steady effective discharge versus event hydrographs discretized into a series of model runs were found to only marginally increase the predicted volumetric change, with greater deposition offsetting erosion. A decadal-scale simulation indicates that accurate prediction of event-scale scour depth and subsequent deposition present a methodological challenge because the predicted pattern of deposition may never “catch up” to erosion if a simple path-length distribution is employed, thus resulting in channel over-scouring. It may thus be necessary to augment path-length distributions to preferentially deposit material in certain geomorphic units. We anticipate that the model presented here will be used as a modular framework to explore the effect of different process representations, and as a learning tool designed to reveal the relative importance of geomorphic transport processes in rivers at multiple timescales.

Response of Erosion and Deposition of Channel Bed, Banks and Floodplains to Water and Sediment Changes in the Lower Yellow River, China

River channel change can be very sensitive to environmental change and human activities and it has been one of the main research topics in fluvial geomorphology. In this study, repeated channel geometric measurements were used to investigate the channel adjustment to water and sediment changes of the lower Yellow River in China in the past few decades. With a high sediment concentration and large variations of water discharge, the lower Yellow River has a much active channel in its form and location, which has hindered previous research efforts to study long-term differentiated erosion/deposition of different geomorphic units in the channel. In this study, we divided each of four typical channel across-sections at hydrological stations in the lower Yellow River into different units according to the geomorphological features, and give a detailed investigation of erosion/deposition processes of these geomorphic units and the interactions between them besides the influence of incoming water and sediment conditions. The results show that with a significant decreasing trend of both the annual runoff and sediment load of the river and abrupt changes in 1985–1996, the overall siltation trend in the river channel before 1990 had been replaced by a slight erosion trend after 2006. In the earlier period, the siltation in the upstream wandering and transitional reaches mainly occurred on floodplains and that in the downstream straight reaches principally on main channel bed. In the later period, erosion occurred mainly on high and low bank slopes in the wandering reaches and on main channel bed in the transitional reaches. The erosion became weak in the wandering reaches after 2010, continued in the transitional reaches, and was still relatively minor in the straight reaches, reflecting the downstream hysteresis channel response to changes in water and sediment discharges down dams. Our results suggest that the seasonal erosion/deposition of a geomorphic unit of the river channel can be attributed to the changes in water and sediment discharges as well as to the interaction between geomorphic units. Siltation on the main channel bed could be attributed to erosion on the bank slopes in both the sections in the wandering and transitional reaches, and erosion of the main channel bed in flood seasons was negatively related with the mean water discharge at the two sections in the straight reaches. This result implies that fixing the bank slopes in the wandering and transitional reaches and raising the water discharge in the straight reach in flood seasons are favorable options for controlling the development of the two-level perching channel of the lower Yellow River.