| The coastal zone is located in the transition zone of land-sea interaction,which is affected by the dual action of land-sea material exchange.Affected by climate change and human activities,a new pattern has emerged in the coastal zone,especially the estuarine delta system,and the dynamic evolution of the constantly changing coastline is an important process.The coastal evolution of the Yellow River Delta and its dynamic monitoring are not only related to the prediction of future delta landform evolution trends,but also are of great importance to the stability and management of flow channels,coastal land use,watershed ecological protection and sustainable development.This paper studies the evolution process of the coastline in Qingshuigou load of the Yellow River Delta from 1976 to 2020,including the change of coastline,land area,siltation process and different influencing factors.Based on the Landsat series remote sensing satellite images of the Yellow River Delta from 1976 to 2020,by extracting the coastline data before and after the flood season year by year,and using the Digital Coastline Analysis System(DSAS)to analyze the coastline evolution process of the coastline in Qingshuigou load of the Yellow River Delta on the interannual and intra-annual scales over the past 45 years.In order to clarify the dynamic change characteristics of coastal land area erosion and growth in different regions of the Yellow River Delta,explore the potential connection between coastline evolution and related hydrological elements,and provide practical reference for stable governance,regional coastal land use,ecological protection and sustainable marine development.The main findings of the study are:1.On the interannual scale,the coastline of the study area was silted into the sea during the Qingshuigou channel period,and the rate was fast at first,then slowed down,and gradually decreased;during the Qing 8 channel period,the coastline experienced both sedimentation and erosion processes.The rate of change first increases and then decreases.During the Qingshuigou channel period,the average seaward change of the coastline was 11.13 km,the average velocity was 497.74 m/a,and the average annual land area increased by 21.89 km~2/a,the shape of the coastline changed from constant swing to gradually stabilized to the east and then to the southeast.In the early stage of the diversion of Qingshui ditch,the coastline silted forward obviously.The average change of the coastline from 1976 to 1980 was 5.03 km,and then the rate slowed down with the passage of time.The coastline grew slowly,and the average change of the coastline from 1991 to 1995 was only 0.81 km.During the period of the Qing 8 branch,the average seaward change of the coastline was 1.72 km,the average velocity was 62.21 m/a,and the average annual change of land area was-0.65 km2/a,the sand mouth of old estuary continues to decline,and the shape gradually becomes smooth.The current estuary develops and accumulates in the northeast direction.In the study area,the proportion of the siltation part of the coastline was lower than that in the previous period,and it was concentrated in the current estuary.The area change first increased,then decreased and then increased.The most obvious period of siltation was from 2002 to 2008,and the average change of the coastline was 1.49 km.The abandoned estuary of Qingshuigou continued to erode,and the change rate gradually decreased,with an annual average area change rate of-5.05 km2/a.2.On the intra-year scale,the change rate of the coastline in the study area gradually decreased during the Qingshuigou channel period,and the area changed from siltation to erosion.During the period of the Qing 8 branch,the siltation of the existing river port line was obvious before and after the flood season in the water and sediment adjustment years,and the deposition was slow before and after the flood season in the non-water and sediment adjustment years.The changes of the old estuary coastline were basically consistent with the interannual changes.During the Qingshuigou channel period,the average change of the coastline during the flood period during the year was 0.67 km to the sea,the average speed was 2387.84m/a,and the average annual increase of land area was 21.89 km~2/a.During the flood period,the overall change of the coastline gradually decreased with time,and the change of land area changed from siltation to erosion,from fast to slow.In 1976,the area increased by 141.87 km~2,and then the growth rate slowed down.By 1992,the area changed to-0.37 km2,and area erosion occurred during the flood period.During the period of the Qing 8 branch,the current estuary siltation rate fluctuated and changed,from erosion to siltation,and the siltation rate changed from fast to slow to fast.The periods of rapid area increase were in 2003,2005 and 2009.The area increment decreased after 2010,and the increase was very small in 2016 and 2017.After 2018,the deposition rate increased again.The old estuary eroded as a whole,with an average annual change of-4.91 km~2 and a decreasing rate,which was basically consistent with the interannual variation.3.The amount of sand entering the sea and ocean dynamics are the main factors affecting the evolution of coastlines.The amount of sand entering the sea has different influences on the evolution of the coastline in different flow paths.The influence of the Qingshuigou flow path has changed from strong to weak.During the period of the Qing 8 branch,the amount of sand entering the sea had a significant impact in the water-sediment regulation years,but was weaker in the non-water-sediment regulation years.The ocean dynamics gradually increased from weak to strong during the period of the Qingshuigou flow path,and the effect of the water-sediment regulation in the water and sediment regulation years was weaker than that in the non-water-sediment regulation years.On the interannual scale,the influence of the amount of sediment entering the sea on the land area changed from strong to weak during the Qingshuigou channel period.During the Qing 8 branch channel period,the amount of sand entering the sea had a significant impact on land area changes at the beginning of water and sediment regulation and after the restart(R~2=0.93,p<0.01),but before the start of water and sediment regulation(1996-2001).and after several years(2009-2015)the impact diminished.On the intra-year scale,the correlation between the amount of sediment entering the sea and the area change was within ten years of the diversion of Qingshuigou and the start of water-sediment regulation.It was extremely significant later,and the impact was limited in 1987-2001.During the Qingshuigou channel period,the influence of ocean dynamics on the evolution of the coastline was initially weak,and the effect on the evolution of the coastline gradually increased after 1987.In the early stage of the Qing 8 branch channel period,the marine dynamic was the dominant factor.After the water and sediment regulation began,the relative strength of the marine dynamic was related to whether the water and sediment regulation was implemented.The influence of ocean dynamics on coastline evolution in non-water-sand regulation years is stronger than that in water-sand regulation years.The climatic factors such as precipitation and surface temperature in the basin mainly affect the change process of the coastline indirectly by affecting the amount of sediment entering the sea.Precipitation decreases,temperatures rise,sediment intake decreases,coastlines grow slowly,and erosion increases,conversely,the precipitation increases,the temperature drops,the coastline grows faster,and the siltation increases.Human factors such as water and sediment regulation and artificial water diversion indirectly affect the evolution of the coastline,and at the same time enhance the temporal and spatial complexity of the delta coastline change. |
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