Recent Morphological Changes Research Articles

How Does Human Activity Shape the Largest Estuarine Bay of the Pearl River Estuary, South China (1964–2019)

The morphological changes in an estuarine bay are affected by fluvial and oceanic dynamics, as well as human activities. Human activity has increased considerably in recent years, especially in Lingding Bay of the Pearl River Estuary. Based on mass measured bathymetric data and remote sensing images, morphological changes in Lingding Bay were examined and its long-term morphological evolution from 1964 to 2019 was studied using GIS method and EOF methods. The water area of Lingding Bay gradually decreased through this period due to shore reclamation and the evolutionary characteristics of the underwater topography were different before and after 2007 due to changes in the intensity of human activities. From 1964 to 2007, the water depth and volume of Lingding Bay decreased slightly and the bay experienced a slow silting process with the geomorphic pattern of “three shoals and two troughs” under low-intensity human activity. From 2007 to present, high-intensity sand-dredging activities in the bay have led to considerable deepening and a significant increase in water volume in the East Trough and Middle Shoal areas. The amount of sediment loss caused by the sand-dredging activities after 2007 far exceeded the amount of sediment deposition over the past four decades prior to 2007. Therefore, even if the sand-dredging activities had been banned, the eroded parts of Lingding Bay (i.e., East Trough and Middle Shoal) may not recover in a short time due to the small sediment load from the Pearl River. These recent morphological changes in Lingding Bay may bring about challenges for estuary regulation, disaster control, environmental protection, and the operational safety of the nearby ports and channels. Consequently, the subsequent evolution of the bay requires further research. This will enrich the scientific work for estuarine and coastal research and be conducive to revealing the interaction mechanisms between humans and nature, guiding sustainable development, estuarine disaster control, and promoting interdisciplinary innovation in estuarine research.

Historical morphological changes (1956-2017) and future trends at the mouth of the Ebro River delta (NE Spain)

The present work focuses on the recent morphological changes recorded in the Ebro River delta, by using aerial photographs in the last six decades and by analyzing changes in the main constitutive features through geomorphological maps. Geomorphological maps of the years 1956 and 2017 are here presented. The results obtained give very valuable clues about the recent trends of the river delta mouth, which can be used to predict future coastal changes to be expected in the following decades. In this sense, by analysing changes in the surface by means of the geomorphological maps together with a shoreline analysis, a differential behavior has been described at both sides of the river mouth: the left side, El Garxal wetland, shows an accretionary trend with rates reaching +40 m/year, while the right side, San Antonio Island, shows erosive trends of more than -20 m/year. This last side also presents a surface reduction of more than 50 ha in the last 60 years. These results suggest that, approximately by the year 2050, the emerged San Antonio Island may disappear if shoreline retreat trends are maintained, making El Garxal exposed to easterly storms, the main erosive dynamic processes in this zone and, therefore changing the entire configuration of the Ebro River delta mouth in the upcoming years. Despite possible solutions have been described in recent works, they may not contribute to a total recovery of the most natural part of the Ebro Delta. Urgent management plans are required to attempting to slow or reverse these trends, otherwise one of the most valuable ecosystems of the delta could disappear.

Caracterização e evolução da história natural da zona costeira de Tibau, Grossos e Areia Branca/RN

Geodiversity encompasses several aspects; pedological, hydrological, geological among others, of which we will deal with the geomorphological component, which acts as a record of different evolutionary processes throughout the Earth's natural history. Within this context, the present work aims to define the elements that occurred on the coast of Tibau, Grossos and Areia Branca/RN, serving as basis for undertanding the morphology of the area, serving as a basis for the further study or geodiversity. Recovering natural history, from the formation of the Potiguar Basin, with the separation of the Gondwana Super Continent, to the most recent morphological changes, bringing the constitution and age of constitution of the geological formations, the Tibau Formation, Jandaíra and Barreiras. As for the features, it was identified as barcanoid dunes(active and inactive dunes and sand sheets), marine deposits (Beach rocks), as well as alluvial deposits associated with the Apodi-Mossoró estuary , coastal plains, cliffs and association with coastal plateaus and presence of a reef line (Beach rocks).

Widespread recent changes in morphology of Old World birds, global warming the immediate suspect

AbstractAimA decline in body size has been proposed as a universal response to global warming, but this is often questioned. We describe and characterize recent morphological changes in the avifauna of Israel as a whole and test several hypotheses regarding their cause.LocationIsrael.Time period1950–2020.Major taxa studiedAves.Methods We analysed the morphology of 7,981 museum specimens. For each of the 106 species, we calculated the rate of change in mass, head and body length, wing length and approximate relative surface area, both over time and as a function of temperature anomaly (the difference between temperatures in a given year and the interannual average). We used phylogenetic generalized linear mixed models (PGLMMs) to determine trends and their relationship to the ecology of species.ResultsOver the last 70 years there have been consistent changes through time in mass, length and surface area‐to‐volume ratio. Mass decreased by 18.3%, length increased by 5.1%, and surface area‐to‐volume ratio increased by 28.9%. The increase in the ratio of surface area to volume through time corresponds to a 12.2% increase per degree Celsius of warming. In contrast, changes in wing length were few and inconsistent. Most species changed in either mass or length, but seldom in both. The effect of rising temperature on morphology was roughly an order of magnitude stronger than the effect of a comparable geographical difference in habitat temperature. Changes were modulated by migratory habits but not explained by human commensalism or diet.Main conclusionsA decrease in mass and increase in length are widespread, both leading to higher relative surface area. Results conform with predicted responses to global warming, but not with any of our other tested hypotheses. If warming is the driver of these changes, the diverging responses observed between different species might represent different solutions to solve a common problem.

Recent morphological changes of the Changjiang (Yangtze River) mega-delta in the Anthropocene, China: Impact from natural and anthropogenic changes

Many of the world’s largest deltas are increasingly threatened by impact of climate change and human activities. The Changjiang (Yangtze River) is among the largest river, and its change of delta has received extensive attention. However, many studies covered smaller delta areas, which cannot reflect the changes of the entire delta region. Here, we present an assessment of the Changjiang (Yangtze River) mega-delta (CMD) using 60 years of bathymetric data covering the entire study area in order to gain clear insight into the comprehensive morphological changes in the Anthropocene. The net deposition rate decreased from 3.47 cm/year over the period 1954–1986 to 0.074 cm/year for the period 2005–2013 in the subaqueous-delta because of a dramatic decline in the sediment load. In particular, as the sediment load further decline due to the implementation of soil and water conservation engineering since 1980s, slight erosion occurred at a rate of −0.0019 cm/year during 1986–2002. However, the subaqueous-delta converted to a balanced state from one of slight erosion, and the depocenter moved southward between 2002 and 2013. Consequently, the morphological change of the CMD went through the following periods: fast accumulation from 1954 to 1986, and balanced accumulation/erosion during 1986–2013 (conservative state in1986–2002 and steady state in 2002–2013). Moreover, the subaerial delta of the Changjiang experienced continued progradation; the area of the subaerial delta increased from 14,857.74 km2 in 1974 to 16,039.03 km2 in 2013 (7.9% increase), with a net progradation rate of 29.53 km2/year; and the most pronounced progradation occurred at Chongming Island and the eastern parts of Nanhui. An important reason for these changes was land reclamation, deep-water channel projects, and shore protection, despite a marked decrease in the river sediment supply. In the future, whether the accumulation/erosion balance continues to be maintained will be an urgent research in the CMD.

Pedological properties related to formation and functions of ancient ridge and furrow cultivation in Central and Northern Germany

Ridge and furrow cultivation is an example for a historic agriculture technique that has been very common in Germany, especially during medieval times. It seemed to be well-known how the ridge and furrows (RIFUs) were used and formed but previous studies came to contradictory conclusions which raised additional questions concerning their formation. Furthermore, the RIFUs’ morphological and physicochemical soil properties and their influence on current soils that developed after the RIFUs had been abandoned are not fully understood. In order to answer these questions, morphological and physicochemical analyses (pH, EC, TOC, TN, δ15N, C:N ratios, “Olsen P”, soil texture) were conducted on 11 preserved RIFUs in forested areas of Northern and Central Germany. The results showed that the studied RIFUs occur on sites with different properties (e.g. soil texture, inclination, vegetation) and presented various morphological shapes. They are also characterised by differences in the formation of soil horizons and general low TN (<1.5 g kg−1) and TOC (<10 g kg−1) contents. However, higher contents at some sites comparing to their references, indicated that the RIFU cultivation promoted a slight long-lasting soil improvement if not induced by secondary soil processes after RIFU use. Moreover, for some sites, high P and δ15N values may suggest the application of manure. Recent morphological changes also had a significant influence on some study sites. In summary, neither the formation and agricultural strategies of RIFU cultivation nor their function and any influences on the current soil and woodland characteristics can be regarded as identical for all RIFU sites.

LiDAR and UAV System Data to Analyse Recent Morphological Changes of a Small Drainage Basin

In this paper, the preliminary results of an integrated geomorphological study carried out in a 1.6 ha catchment area located on the eastern side of the Crati River valley (northern Calabria, South Italy) have been presented. An orthophoto and shaded relief map of the study catchment, obtained by 288 unmanned aerial vehicle (UAV) images, integrated with field geomorphological surveys have been used to produce a detailed map of landslides and water erosion phenomena. The study area is characterized by active morphodynamic processes that result in the occurrence of water erosion phenomena and several landslides. In particular, 29 slides and 37 earth slides that evolve into earth flows have been recognized. Spatial and temporal development of geomorphic processes (erosion/depletion and sedimentation/accumulation) have affected the catchment area in the last seven years. Indeed, the comparison between light detection and ranging digital terrain models (LiDAR-DTM) of 2012 and UAV-DTM of 2019 showed depletion values between −0.01 and –5.76 m, with a mean value of −0.96 m; whereas for the accumulation the mean value is 0.94 m, with a maximum thickness of the deposited material of about 2.98 m. The results obtained highlight the usefulness of the methodology to provide detailed information on geomorphic processes and related short-term landscape development in a small drainage basin.

Recent morphological changes of the mouth bar in the Modaomen Estuary of the Pearl River Delta: Causes and environmental implications

The Pearl River Delta (PRD) is one of the most economically important and urbanized deltas in Asia. The Modaomen Estuary, being the most important passage of water and sediment through the PRD into the sea, was regulated by estuarine reclamation since the mid-1980s. After the completion of regulation projects in the 1990s, it was transformed from a shallow bay into a series of regulated channels. As a result, the evolution of the mouth bar of the Modaomen Estuary, a key morphological unit determining delta formation, has been altered. In this study, we examine morphological responses of the mouth bar of the Modaomen Estuary to human activities and natural factors (i.e., riverine flood) from 1994 to 2010. As an effect of the estuarine extension towards the sea caused by the regulation projects, the mouth bar has gradually moved towards the sea. From 1994 to 2010, for instance, the west and east branches extended more than 2.1 km further seawards. In addition, flood scouring played an important role in the bar extension and the formation of secondary branches at the mouth bar. Furthermore, the front of the mouth bar was eroded by wave dynamics because of reductions in the sediment load from the Pearl River. In general, the mouth bar deflected southwestward after 1994, indicating an evolution of the sediment sink at the Modaomen estuary in the same direction. Our studies contribute to better understanding of the evolution of large estuaries and provide scientific guidelines for the sustainable management of the PRD.

Sand Spit Elongation and Sediment Balance at Cua Lo Inlet in Central Vietnam

Duy, D.V.; Tanaka, H.; Mitobe, Y.; Anh, N.Q.D., and Viet, N.T., 2018. Sand spit elongation and sediment balance at Cua Lo Inlet in Central Vietnam. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 32–39. Coconut Creek (Florida), ISSN 0749-0208.Erosion is significant on the downdrift beach of Cua Lo Inlet, which is located in Central Vietnam. The elongation of Cua Lo Inlet's updrift sand spit together with severe erosion of the downdrift bank is raising numerous social problems such as flood safety and land loss. In this study, a series of Landsat and Google Earth images were used to analyze and investigate the inlet recent morphological changes and evolution. Since 1970 the inlet has constantly migrated towards the sediment transport pathway, and its traveling distance has reached 1700 m. In order to quantitatively investigate such characteristics, the tip coordinates and the area of the sand spit updrift of the inlet were calculated. In particular, the area of the sand spit has increased remarkably, and the increasing rate is almost constant. Using this value, the rate of sand volume transported along the updrift sand spit by the waves was estimated and it is in good agreement with the longshore sediment transport rate of the surrounding beach.

Rapid morphological change of a top predator with the invasion of a novel prey.

Invasive exotic species are spreading rapidly throughout the planet. These species can have widespread impacts on biodiversity, yet the ability for native species, particularly long-lived vertebrates, to respond rapidly to invasions remains mostly unknown. Here we provide evidence of rapid morphological change in the endangered snail kite (Rostrhamus sociabilis) across its North American range with the invasion of a novel prey, the island apple snail (Pomacea maculata), a much larger congener of the kite's native prey. In less than one decade since invasion, snail kite bill size and body mass increased substantially. Larger bills should be better suited to extracting meat from the larger snail shells, and we detected strong selection on increased size through juvenile survival. Using pedigree data, we found evidence of both genetic and environmental influences on trait expression and discovered that additive genetic variation in bill size increased with invasion. However, trends in predicted breeding values emphasize that recent morphological changes have been driven primarily by phenotypic plasticity rather than micro-evolutionary change. Our findings suggest that evolutionary change may be imminent and underscore that even long-lived vertebrates can respond quickly to invasive species. Furthermore, these results highlight that phenotypic plasticity may provide a crucial role for predators experiencing rapid environmental change.

Recent morphological changes of the Yellow River (Huanghe) submerged delta: Causes and environmental implications

The Yellow River (Huanghe) submerged delta (YRSD) has been under the threat of erosion and retreat during the Anthropocene due to dramatic climatic and anthropogenic changes in the Yellow River basin. The analysis of field data shows that over the period of 1977–2005, the changes in climate (decrease in precipitation and increase in air temperature) and human interventions (increase in water diversion projects) throughout the watershed have resulted in the sharp reductions of river flow and sediment discharges into the Bohai Sea. Consequently, over the decadal timescale, morphological evolution of the YRSD has gone through three stages: i.e. rapid accumulation (5.77×108m3/year) in 1977–1985, moderate accumulation (3.80×108m3/year) in 1986–1995 and slow accumulation (0.91×108m3/year) in 1996–2005. Climatic change within the catchment characterized by the rapid increase of air temperature contributed significantly to the transitions from the rapid accumulation to the moderate accumulation, and to the subsequent slow accumulation. The decadal morphological changes of the YRSD also show peculiar deposition/erosion characteristics over the medium timescale under river input reduction. Within the three decades, the patterns of the main sedimentary body exhibit irregular ellipses with the long axis parallel to the −5 or −10m isobaths and short axis perpendicular to the isobaths. The depocentres of the YRSD are located between the −10 and −15m isobaths close to the respective river mouths, with a high vertical accretion rate of ~1.20m/year. The time series data of annual volumetric change of the YRSD and river sediment load from 1977 to 2005 further demonstrate significant linear positive relationships between deltaic geomorphic change and fluvial input over shorter timescales (annual and 3-year). The critical sediment discharges for maintaining the deposition/erosion equilibrium state of the YRSD over the annual and 3-year timescales are found to be 1.79×108t/year and 1.29×108t/year, respectively. The analysis from the latest hydrological data (2006–2015) suggests that over the decadal timescale, the evolution state of the YRSD currently has transitioned from constructive to destructive due to the weakened fluvial input. Moreover, there exists a close quantitative link between the progradation of the Yellow River subaerial delta (YRAD) and the YRSD over the five-year timescale, indicating that every 1×108m3/year increase of the YRSD's yearly volumetric change will result in a 3.28km2/year increase of the YRAD's yearly land-accretion area, and the YRAD will reach the extension/retreat balance state when yearly morphological change of the YRSD is at 0.73×108m3/year.

Recent morphological changes in the Mekong and Bassac river channels, Mekong delta: The marked impact of river-bed mining and implications for delta destabilisation

The Mekong delta, in Vietnam, is the world's third largest delta. Densely populated, the delta has been significantly armoured with engineering works and dykes to protect populations and infrastructure from storms, and shrimp farms from saltwater intrusion. Considerable development pressures in Vietnam and in the upstream countries have resulted in the construction of several dams in China and in important channel-bed aggregate extractions especially in Cambodia. The effects of these developments impact the delta dynamics in various ways. In this study, changes in the channel morphology of the Mekong proper and the Bassac, the two main distributaries in the 250km-long deltaic reach from the Cambodian border to the coast, were analysed using channel depth data for 1998 and 2008. The channels display important and irregular bed changes over the 10-year comparison period, including significant incision and expansion and deepening of numerous pools. The mean depth of both channels increased by more than 1.3m. Both channels also showed correlative significant bed material losses: respectively 90millionm3 in the Mekong and 110millionm3 in the Bassac over the 10-year period. These important losses over a relatively short period, and weak correlations between bed incision and hydraulic parameters suggest that the marked morphological changes are not in equilibrium with flow and sediment entrainment conditions, and are therefore not related to changes in river hydrology. We claim that aggregate extraction, currently practised on a very large scale in the Mekong delta channels and upstream of the delta, is the main cause of these recent morphological changes. These changes are deemed to contribute actively to rampant bank erosion in the delta as well as to erosion of the Mekong delta shoreline. Other contributory activities include the numerous dykes and embankments. The role of existing dams in bed losses remains unclear in the absence of reliable data on the Mekong sediment load. Future large-scale hydropower dam development on the Lower Mekong main stem will have cumulative effects with aggregate extraction, leading to increased morphological changes that will further impact the delta, especially in terms of sediment supply and coastal erosion.

Flow pattern at a river diffluence at the alluvial system of the Paraná River

This communication presents field and numerical data depicting the flow pattern formed at a diffluence of the Colastiné River, Argentina, where one branch accesses the local harbour. The harbour has been in decline since the 1970s due to costly maintenance dredging of the access channel. The objective of this work is thus twofold: to show the persistence of the flow pattern developed at the diffluence despite recent morphological changes seen at the site, and to test a possible solution to the access channel sedimentation problem. Knowledge gained during the execution of the study helped to validate a code developed to process field data captured with two acoustic Doppler current profilers (ADCPs). The results confirm that both branches are prone to developing secondary currents. Simulations show that an engineering intervention downstream of the bifurcation can establish a self-dredging flow reversal along the access channel, turning the actual diffluence into a stable confluence.

Sensitivity analysis of a morphodynamic modelling system applied to a coastal lagoon inlet

This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the 2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period of 3 years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.

The effects of dredging operations on the hydrodynamics of an ebb tidal delta: Oka Estuary, northern Spain

The hydrodynamics associated with the Mundaka Sandbar are described. The sandbar (ebb tidal delta) is responsible for the formation and the quality of a “world famous” surfing wave, at the mouth of the Oka Estuary in the Urdaibai Biosphere Reserve. The primary factor controlling the shape of the sandbar is the shoreline configuration. In turn the size of the sandbar is controlled by the volume of the tidal outflow and the wave energy. Periods of tidal dominance occur during summer (associated with sandbar accretion); with mixed energy conditions during winter and wave dominance under storms (sandbar erosion). The surfing wave lost its characteristics following, intensive dredging along the estuary, combined with beach nourishment, in May 2003. Between May 2005 and April 2006, the outer part of the estuary was monitored, to understand the processes controlling recent morphological changes over the area. Recent studies undertaken in the mouths of estuaries, together with the results of the monitoring are described; these are complemented by the numerical modelling of wave hydrodynamics under medium and extreme sea states. Analyses of the wave and current survey data, combined with the modelling outputs, have demonstrated that the changes were not irreversible. As such, the natural shape of the sandbar has recovered gradually, as has the quality of the Mundaka surfing wave.

Morphological evolution of the Dee Estuary, Eastern Irish Sea, UK: A tidal asymmetry approach

Asymmetry in the tide (unequal ebb and flood duration) is a dominant factor in causing residual sediment transport and morphological changes in estuaries. The evolution of estuarine morphology is a process of dynamic equilibrium in the short-term, while these features are ephemeral in the long-term. In this study we investigate the spatial distribution of tidal distortion and asymmetry in the Dee estuary, UK, by 3-dimensional numerical modelling methods. High resolution LIDAR surveys are used to underpin and explain our numerical modelling results in terms of basin hypsometry and areas of recent erosion and deposition. Harmonic analysis of the numerical modelling results showed that the shallower intertidal areas (sand and mud banks) were the most tidally asymmetric, showing flood dominance. The main navigation channels showed some ebb dominance but the tides here were relatively undistorted. This overall flood dominance is likely to induce net sediment import to the Dee, which explains known historical morphological changes (large scale accretion over the last two centuries) and also recent morphological changes as seen from the LIDAR surveys (which show predominantly net accretion between 2003 and 2006). Hypsometrical analysis suggests the Dee may be approaching equilibrium, and that the flood dominance and sedimentation rate may therefore decrease in the future. In an infilling estuary, an increase in the area and elevation of tidal flats can eventually shift an estuary towards ebb dominance, as shown by previous research and by ‘idealised estuary’ modelling results presented in this study. The large tidal amplitude to hydraulic depth ratio of the Dee, however, suggests that the tidal flats would have to be very extensive indeed for this to occur.