Evolution of Bars in Braided Rivers Controlled by Discharge Variability
The discharge variability controls the formation and evolution of braid bars and influences the internal structure and superimposition of braid bars.However,the control of discharge variability on the developments and evolution of braid bars are unclear.Google Earth software was used to selected 13 river reaches with braided river deposits worldwide,and the discharge data of the selected river reaches are collected from the Global Runoff Data Center(GRDC).Then,the coefficient of annual peak discharge variation(CVQp)was used to study the process and evolution of the braid bars.The results are as follow.(1)In terms of the degree of discharge variability,the braid bar evolution of braided river with lower discharge variability(CVQp＜0.4)mainly develops bar tail deposition and downstream migration.In braided rivers with higher discharge variability(CVQp＞0.4),the braid bar evolves relatively fast.Before and after flood event,the original braid bar is easy to be destroyed and transformed into a new braid bar,and the braid bar burst is common.(2)In a single river,the braid bar distribution of length to width ratio of the braided river with lower discharge variability is relatively concentrated,and the morphology is relatively stable,which is easy to form a relatively-stable braided river.While braided river with higher discharge variability is easy to form classical braided river because of the scattered braid bar distribution of length to width ratio,different morphology and great changes in development position.(3)Downstream accumulation is more common in the evolution of braid bar with lower discharge variability,so it is easy to form compound bars after long time evolution.The flood events of braided rivers with higher discharge variability have a strong influence on the evolution process of the bars,and the braid bar evolution is relatively complex and has poor regularity in the time scale.Clarifying the evolution of braid bars under different discharge conditions can provide guidance for the prediction of sandstone distribution of braided river reservoirs and may provide a basis for the paleo-environment reconstruction and paleo-discharge restoration.
braided riverdischarge variabilitypeak dischargebraid bar evolutiondepositional modelpetroleum geology
万方数据
维普
