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Spatiotemporal variability of channel and bar morphodynamics in the Gorai-Madhumati River,Bangladesh using remote sensing and GIS techniques

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Frontiers of Earth Science 2020年第4期14卷 828-841页

作者： Md.Yousuf Gazi Farhad Hossain Sumiya Sadeak Md.Mahin Uddin Department of Geology University of DhakaDhaka1000Bangladesh Department of Geography and Environment University of DhakaDhaka1000Bangladesh

Bangladesh is a riparian country that is criss-crossed by the many tributaries and distributaries of the mighty Ganges,Brahmaputra,and Meghna river systems.Gorai-Madhumati,a distributary of the Ganges River is an example where morphological development of the river is associated with frequent channel shifting within the catchment area.The main objective of this research is to quantify the extent of channel migration,erosion-accretion,river width,sinuosity,and charland morpho-dynamics from 1972 to 2018 using geospatial techniques combined with satellite images and hydrological data.The study also addressed the impacts of Farakka Barrage construction in India on the shifting,flow behavior,and siltation of Gorai-Madhumati River.The study shows that bar surface areas have abnormally increased in both segments after 1975 due to the construction of Farakka Barrage.Water flow in the Gorai-Madhumati has dropped remarkably in the downstream and instigated huge sedimentation in this region.Analysis of the time series satellite images revealed that the morphology of the river channel experienced huge changes simultaneously with the changes in the seasonal flow and sedimentation all over the study period.Migration trend has frequently shifted and taken place in the NW and NE direction in the observed sections of the river.Throughout the study period,total amount of accretion was greater than the net percentage of erosion on both banks of the river.River discharge,bar accretion,and erosion history show that the Gorai-Madhumati River will no longer exist with the present flowing condition without attention and proper river management.

关键词： channel migration erosion-accretion morphodynamics geospatial techniques Gorai-Madhumati Bangladesh

Processes,feedbacks,and morphodynamic evolution of tidal flat-marsh systems:Progress and challenges

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Water Science and Engineering 2022年第2期15卷 89-102页

作者： Zeng Zhou Meng-jiao Liang Lei Chen Meng-piao Xu Xue Chen Liang Geng Huan Li Daniel Serrano He-yue Zhang Zheng Gong Chang-kuan Zhang State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai UniversityNanjing 210098China Jiangsu Key Laboratory of Coast Ocean Resources Development and Environment Security Hohai UniversityNanjing 210098China Department of Civil Environmental and Architectural EngineeringUniversity of PaduaPadua 35122Italy

Tidal flats and saltmarshes have been a long-standing research focus because of their high socio-economic and ecological values.The evolution of tidal flat-marsh systems is highly complex due to the intertwined processes operating over a variety of spatial and temporal scales.As a traditional research highlight,the role of regular hydrodynamic processes such as tides,waves,and river flows have been explored comprehensively with fruitful outcomes.Over past decades,the changing environment(e.g.,sea level rise,increasing anthropogenic activities,and extreme weather conditions)has attracted more attention with many reported insightful results.More recent advances indicate that biological activities play a critical role in tidal flat-marsh morphodynamics but are still poorly understood.The field of research that connects the bio-logical and physical processes is commonly described as"biogeomorphology"and requires the joint efforts by scientists from multiple dis-ciplines ranging from hydraulics,ecology,and geography to sociology.This review aims to provide a synthesis of the current research status of tidal flat-marsh morphodynamics,with a particular emphasis on the understanding of various processes and feedbacks underlying the devel-opment of morphodynamic models.Some future research needs and challenges are identified to facilitate a more sustainable management strategy for tidal flats and saltmarshes under climate change.

关键词： Tidal flats Coastal wetlands morphodynamics Saltmarshes Tidal channels Morphodynamic modeling

Temporal variations of sediment and morphological characteristics at a large confluence accounting for the effects of floodplain submergence

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International Journal of Sediment Research 2022年第5期37卷 619-638页

作者： Kun Li Hongwu Tang Saiyu Yuan Lei Xu Yang Xiao Carlo Gualtieri State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai University Yangtze Institute for Conservation and Development Department of Structures for Engineering and Architecture University of Napoli Federico Ⅱ

The large confluence between the Yangtze River and the outflow channel of Poyang Lake is receiving attention due to its importance in flood control and ecological protection in the Yangtze River basin.There is a large floodplain along the outflow channel of Poyang Lake, which is submerged during high flow and dry during low flow. The effects of the submergence of this floodplain on sediment and morphological characteristics at this large confluence have not been known. Hence, a field investigation was done in March 2019(relatively high flow, Survey 3) to complement the previous field studies done in August(high flow, Survey 1) and December 2018(low flow, Survey 2) to identify the temporal variations of sediment and morphological characteristics considering the submergence of this large floodplain. The predominant sediment transport modes were wash load for Poyang Lake and confluence particles and mixed bedload/suspended load for the Yangtze River particles. The sediment transport processes were largely affected by both the secondary flows and the water density contrast between the tributaries with a lock-exchange sediment rich, denser flow moving across the inclined mixing interface in Surveys 1 and 2. The sediment flux across the mixing interface was weakened in Survey 3 when the density contrast was very small. The stagnation zone near the confluence apex had a low sediment concentration and played a role in preventing the sediment flux exchange between the two flows, and its size, and, thus, its importance as a barrier to sediment mixing were related to the submergence of the floodplain. The bed morphology with the local scour holes at the confluence was largely affected by the large-size helical cells, and this kind of effect was weakened as the secondary flows got restricted in Survey 3. The current results expand the database and knowledge on the sediment transport and morphological features of large river confluences.

关键词： River confluence Yangtze river Poyang lake Compound channel Sediment transport morphodynamics

The morphodynamics of Wulan Delta and Its Impacts on the Coastal Community in Wedung Subdistrict, Demak Regency, Indonesia

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Journal of Environmental Protection 2016年第1期7卷 60-71页

作者： Muh Aris Marfai Desy Wahyuning Tyas Idham Nugraha Ayu Fitriatul’Ulya Widiana Riasasi Faculty of Geography Universitas Gadjah Mada Yogyakarta Indonesia

Wulan Delta in Central Java has been experiencd coastal morphodynamics due to interface between Wulan River’s sedimentation and Java sea’s oceanographic process. This paper aims to analyze Wulan Delta’s morphodynamics as well as its impacts on the socio-economic condition of the community. The morphodynamics is interpreted visually and digitally using a maximum livelihood analysis of multiscale and multi-temporal images. The socio-economic impact is defined by field observations and in-depth interviews to the community and stakeholders. Analysis during the period of 1931-2010 showed that Wulan Delta had been changed morphologically from straight with small arc-like (arcuate) to bird-foot (digitate) with a plausible change into rounded (lobate) in the future, which represented dominant sedimentation by oceanographic rather than fluvial processes. Land expansion in Wulan Delta led to landuse change in Wedung, i.e. expansion of settlement area to 167 ha and fish pond area to 1014 ha in 2000-2010. Most settlements in the area, which are built linearly to river levees, own a high vulnerability to both river flood and tidal inundation. Therefore, dissemination about knowledge of the disaster and coastal zone management, as a means of increasing awareness, becomes necessary in integrating the coastal management in Wulan Delta together with improvement in infrastructure and proper regional development. The proper development strategy for the coastal village is aggressive maintenance strategy, including public infrastructure revitalization, quality improvement for human resources, and silvofishery system. Law enforcement on coastal zoning regulations is necessary to achieve an integrated and sustainable coastal zone management.

关键词： Coastal morphodynamics Wulan Delta Demak Regency

Regional-Scale Study on Sediment Processes of Khuran Strait at Persian Gulf with Implications for Engineering Design

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China Ocean Engineering 2019年第3期33卷 356-364页

作者： A. Shanehsazzadeh H. Ardalan Faculty of Civil Engineering and Transportation University of Isfahan Isfahan Iran Water Research Institute (WRI) Tehran Iran

In this article, the sediment transport processes in the Khuran Strait between the mainland Iran and Qeshm Island at North Central Persian Gulf are studied in regional scale in a comprehensive manner. The objectives of this study include defining the type and origin of the sediment, the influencing factors, and the dominant mode of sediment transport. Four possible scenarios of sediment processes in terms of sediment sources and influential environmental forces are examined. The results of the conceptual and 2D numerical model of MIKE21 applied for this purposes indicate that the sediment sources in the transport processes are mainly provided by the sediments suspended from the central and eastern zones of the strait bed. Other sources including input from rivers do not have direct influence on the processes. The results are applied to the study of morphological changes for engineering applications including the pattern and amount of deposit in the Rajaee port approach channel and harbor basin. The pattern and amount of annual sediment deposits in the approach channel predicted by the model is satisfactory, compatible with annual dredging records.

关键词： sediment transport morphodynamics 2D numerical model Persian Gulf Khuran Strait Rajaee Port

Routing the asteroid surface vehicle with detailed mechanics

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Acta Mechanica Sinica 2014年第3期30卷 301-309页

作者： Yang Yu He-Xi Baoyin School of Aerospace N931 Mengminwei Research BuildingTsinghua University

The motion of a surface vehicle on/above an irregular object is inv.estigated for a potential interest in the insitu explorations to asteroids of the solar system. A global valid numeric method, including detailed gravity and geo- morphology, is developed to mimic the behaviors of the test particles governed by the orbital equations and surface cou- pling effects. A general discussion on the surface mechanical environment of a specified asteroid, 1620 Geographos, is presented to make a global evaluation of the surface vehicle＇s working conditions. We show the connections between the natural trajectories near the ground and differential features of the asteroid surface, which describes both the good and bad of typical terrains from the viewpoint of vehicles＇ dynamic performances. Monte Carlo simulations are performed to take a further look at the trajectories of particles initializing near the surface. The simulations reveal consistent conclusions with the analysis, i.e., the open- field flat ground and slightly concave basins/valleys are the best choices for the vehicles＇ dynamical security. The dependence of decending trajectories on the releasing height is studied as an application; the results show that the pole direction （where the centrifugal force is zero） is the most stable direction in which the shift of a natural trajectory will be well limited after landing. We present this work as an example for pre-analysis that provides guidance to engineering design of the exploration site and routing the surface vehicles.

关键词： Asteroid exploration Numeric model morphodynamics 1620 Geographos Path planning

Control of wind-wave power on morphological shape of salt marsh margins

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Water Science and Engineering 2020年第1期13卷 45-56页

作者： Alvise Finotello Marco Marani Luca Carniello Mattia Pivato Marcella Roner Laura Tommasini Andrea D'alpaos Department of Geosciences University of PadovaPadova 35131Italy Department of Environmental Sciences Informatics and StatisticsUniversity of Venice Ca'FoscariVenice 30172Italy Center for Lagoon Hydrodynamics and morphodynamics University of PadovaPadova 35131Italy Department of Civil Environmental and Architectural EngineeringUniversity of PadovaPadova 35131Italy

Salt marshes are among the most common morphological features found in tidal landscapes and provide ecosystem services of primary ecological and economic importance.However,the continued rise in relative sea level and increasing anthropogenic pressures threaten the sustainability of these environments.The alarmingly high rates of salt marsh loss observed worldwide,mainly dictated by the lateral erosion of their margins,call for new insights into the mutual feedbacks among physical,biological,and morphological processes that take place at the critical interface between salt marshes and the adjoining tidal flats.We combined field measurements,remote sensing data,and numerical modeling to investigate the interplays between wind waves and the morphology,ecology,and planform evolution of salt marsh margins in the Venice Lagoon of Italy.Our results confirm the existence of a positive linear relationship between incoming wave power density and rates of salt marsh lateral retreat.In addition,we show that lateral erosion significantly decreases when halophytic vegetation colonizes the marsh margins,and that different erosion rates in vegetated margins are associated with different halophytes.High marsh cliffs and smooth shorelines are expected along rapidly eroding margins,whereas erosion rates are reduced in gently sloped,irregular edges facing shallow tidal flats that are typically exposed to low wind-energy conditions.By highlighting the relationships between the dynamics and functional forms of salt marsh margins,our results represent a critical step to address issues related to conservation and restoration of salt marsh ecosystems,especially in the face of changing environmental forcings.

关键词： Salt marshes Wind waves Lateral erosion morphodynamics Vegetation

Investigation and Discussion on the Beach Morphodynamic Response Under Storm Events Based on A Three-Dimensional Numerical Model

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China Ocean Engineering 2021年第1期35卷 12-25页

作者： XIE Ming-xiao LI Shan ZHANG Chi YANG Zhi-wen HOU Zhi-qiang ZHANG Huaqing Key Laboratory of Engineering Sediment Tianjin Research Institute for Water Transport EngineeringM.O.T.Tianjin 300456China CCCC First Harbor Engineering Co.Ltd. Tianjin 300461China State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Hohai UniversityNanjing 210098China

A well-established 3D phase-averaged beach morphodynamic model was applied to investigate the morphodynamics of a typical artificial beach,and a series of discussions were made on the surfzone hydro-sedimentological processes under calm and storm events.Model results revealed that the nearshore wave-induced current presents a significant 3D structure under stormy waves,where the undertow and longshore currents exist simultaneously,forming a spirallike circulation system in the surfzone.Continuous longshore sediment transport would shorten the sediment supply in the cross-shore direction,subsequently suppress the formation of sandbars,showing that a typical recovery profile under calm waves does not necessarily develop,but with a competing process of onshore drift,undertow and longshore currents.Sediment transport rate during storms reaches several hundreds of times as those under calm waves,and two storm events contribute approximately 60%to the beach erosion.Sediment transport pattern under calm waves is mainly bed load,but as the fine sands underneath begin to expose,the contribution of suspended load becomes significant.

关键词： beach evolution phase-averaged model wave-induced current storm surge morphodynamics

Reduction of bend scour with an air-bubble screen-morphology and flow patterns

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International Journal of Sediment Research 2013年第1期28卷 15-23页

作者： Violaine DUGU Koen BLANCKAERT Qiuwen CHEN Anton J.SCHLEISS Ecole Polytechnique Fédérale de Lausanne(EPFL) Laboratory of Hydraulic Constructions(LCH)Station 18CH-1015 LausanneSwitzerland State Key Laboratory of Urban and Regional EcologyResearch Center for Eco-Environmental SciencesChinese Academy of Sciences

The interplay between streamwise flow,curvature-induced secondary flow,sediment transport and bed morphology leads to the formation of a typical bar-pool bed morphology in open-channel bends.The associated scour at the outer bank and deposition at the inner bank may endanger the outer bank’s stability or reduce the navigable width of the channel.Previous preliminary laboratory experiments in a sharply curved flume with a fixed horizontal bed have shown that a bubble screen located near the outer bank can generate an additional secondary flow located between the outer bank and the curvature-induced secondary flow and with a sense of rotation opposite to the latter.This bubble-induced secondary flow redistributes velocities and bed shear stresses.The reported study investigates the implications of a bubble screen on the flow and the morphology in configurations with mobile bed.Velocity measurements show that the bubble-induced secondary flow shifts the curvature-induced secondary flow in inwards direction and reduces its strength.The bubble screen considerably reduces morphological gradients.Maximum bend scour is reduced by about 50%and occurs further away from the outer bank where it does not endanger the bank stability anymore.The location of maximum scour coincides with the junction of the curvature-induced and bubble-induced secondary flows.At this same location,the maximum streamwise velocities and maximum vertical velocities impinging on the bed also occur,which indicates their importance with respect to the formation of bend scour.The bubble screen also substantially reduced deposition at the inner bank.These preliminary experiments show the potential of a bubble screen to influence and modify the bed morphology.

关键词： Bubble screen Erosion Scour morphodynamics Open-channel bend