The Formation And Evolution Study Of Lacustrine Shallow-water Delta Based On The Natural Model Method

Deltas develop because of the reduced dynamic and sediment deposit in estuary regions.In a stable structural environment and under arid climate conditions,fluvialdominated shallow-water deltas form with developed natural levees.The study can not only improve the evolution theories,but also provide effective guidance for river way planning,preventing disasters and predicting oil and gas resources.This paper studies the evolution of the shallow-water delta based on the natural model method.The influence of the upstream sediment concentration and downstream water level on the evolution is discussed.It is found that the delta shoreline first moves forward like a tongue,and then changes with the growth of the front lobes.Delta surface channels evolve among straight,divided and no-trough patterns.Moreover,the phenomenon of upstream deposition causes the cyclical horizontal movement of the main channel.The shape of the surface flow field is consistent with the river patterns,and the flow velocity at the branch decreased rapidly.The surface flow rate is different according to the stages of channel evolution.Both the vertical and the horizontal extension of the delta show rapid growth at the beginning and then enter a stable stage with "step-shaped" growth.When the sediment concentration increases,the length-width ratio of the delta become smaller,the swing rate and the swing angle of the main stream become larger and the position of the swing points move upstream.In addition,it accelerates the rate of horizontal and vertical advance.More sedimentation deposit upstream while the cross-section slope downstream and the longitudinal gradient of the whole delta increase.The whole channel shape changes from bird-foot to radial shape.When the downstream water level becomes higher,the overall delta area is smaller,the growth of the longitudinal shoreline advances.The overall sediment thickness increases while the slope profile,cross-section shape,longitudinal siltation distribution and the slope are not changed significantly;In addition,the higher the water level is,the less of number of the channels appear,but it does not affect the river patterns fundamentally.