Sedimentary elements,evolutions and controlling factors of the Miocene channel system:a case study of the deep-water Taranaki Basin in New Zealand

Deep-water channel systems are important petroleum reservoirs,and many have been discovered worldwide.Understanding deep-water channel sedimentary elements and evolution is helpful for deep-sea petroleum exploration and development.Based on high-resolution 3D seismic data,the Miocene channel system in the deep-water Taranaki Basin,New Zealand,was analyzed by using seismic interpretation techniques such as interlayer attribute extraction and strata slicing.The channel system was divided into five composite channels(CC-I to CC-V)according to four secondary level channel boundaries,and sedimentary elements such as channels,slump deposits,inner levees,mass transport deposits,and hemipelagic drape deposits were identified in the channel system.The morphological characteristics of several composite channels exhibited stark variances,and the overall morphology of the composite channels changed from relatively straight to highly sinuous to relatively straight.The evolution of the composite channels involved a gradual and repeated process of erosion and filling,and the composite channels could be divided into three evolutionary stages:initial erosion-filling,later erosion-filling(multistage),and channel abandonment.The middle Miocene channel system may have formed as a consequence of combined regional tectonic activity and global climatic change,and its intricate morphological alterations may have been influenced by the channel's ability to self-regulate and gravity flow properties.When studying the sedimentary evolution of a large-scale deep-water channel system in the Taranaki Basin during the Oligocene-Miocene,which transitioned from a passive margin to plate convergence,it can be understood how tectonic activity affected the channel and can also provide a theoretical reference for the evolution of the deepwater channels in areas with similar tectonic conversion environments around the world.

Geomorphology Processes of Channel Planform Migration on Meandering Rivers

1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the

Flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam

Since the Three Gorges Dam(TGD)was put into operation,the flood water level at an identical discharge rate has not displayed a decreasing trend along the middle reaches of the Yangtze River(MYR).The flow resistance variations of the channel and bars in response to the operation of the TGD remain poorly understood,despite the importance of understanding these for water disaster mitigation and water environment regulation.Herein,the impacts of the TGD on the downstream flow resistance of the channel and bars in the MYR were analyzed using systematic surveys of hydrological datasets,cross-sectional profiles,sediment datasets,and remote sensing images,during different periods.Under the actual natural conditions in the MYR,a modified semi-empirical formula,which considered the grain,dune resistance,as well as the topographic features of the riverbed,was proposed to predict the channel resistance.Furthermore,the effect of various dam-control flow and sediment elements on the variation in different flow resistance components,and the corresponding relationships among them were investigated.Results showed a decline in the comprehensive,channel,and bar resistances as the discharge increased,whereas there was a slight increase when reaching the bank-full discharges.Notably,the bar resistance occupied 65%,while the channel resistance,in which dune resistance was much larger than grain resistance,contributed 35%to the comprehensive resistance.In addition,while flow resistance rose over time,there was a decline as the distance from the TGD increased.In conclusion,the increased dune and bar resistances,interpreted by the fluctuated channel longitudinal profile and growing vegetated area on bars,were the dominant factors preventing the flood water level from dropping.

Evolution characteristics and drivers of the water level at an identical discharge in the Jingjiang reaches of the Yangtze River

The operation of large-scale reservoirs have modified water and sediment transport processes,resulting in adjustments to the river topography and water levels.The polynomial fitting method was applied to analyze the variation characteristics of water levels under different water discharge values in the Jingjiang reach of the Yangtze River from 1991–2016.The segregation variable method was used to estimate the contributions of the varied riverbed evaluation,the downstream-controlled water level,and the comprehensive roughness on the altered water level at an identical flow.We find that low water levels in the Jingjiang reach of the Yangtze River from 1991–2016 are characterized by a significant downward trend,which has intensified since 2009.Riverbed scouring has been the dominate factor causing the reduced low water level while increased roughness alleviated this reduction.From 1991–2016,there was first a decrease followed by an increase in the high water level.The variation characteristic in terms of the'high flood discharge at a high water level'before 2003 transformed into a'middle flood discharge at a high water level'since 2009.The increased comprehensive roughness was the main reason for the increased high water level,where river scouring alleviated this rise.For navigation conditions and flood control,intensified riverbed scouring of the sandy reaches downstream from dams enhanced the effects that the downstream water level has on the upstream water level.This has led to an insufficient water depth in the reaches below the dams,which should receive immediate attention.The alteredvariation characteristics of the high water level have also increased the flood pressure in the middle reaches of the Yangtze River.