入海泥沙减少背景下黄河清水沟亚三角洲海岸线的发育与演化

The development and evolution of the coastline of the Qingshuigou sub-delta in the Huanghe River under the background of reduced sediment discharge into the sea

三角洲岸线的变迁是研究地貌冲淤最直接的要素。黄河三角洲是世界上发育最快的三角洲,研究其海岸线变化规律和演化趋势对地区生态环境保护、海洋资源开发、基础设施建设等至关重要。本文在前人研究的基础上,采用修正归一化水体指数(Modified Normalized Difference WaterIndex,MND-WI)与多年水频率指数(Multi-year Water Frequency Index,MWFI)相结合的方法对1976–2021年期间典型年份的207幅遥感影像进行岸线提取,使获取到的海岸线更具科学性和代表性,并在此基础上通过定量计算分析了海岸线的时空演变及其稳定性特征,以此探讨黄河清水沟亚三角洲海岸线自1976年以来的演化机制。研究结果表明:(1)总体上,清水沟亚三角洲海岸线演化呈现先快速向海淤积后波动稳定的趋势,以1996年和2002年为节点划分为“快速发育”“缓慢发育”“动态平衡”3个阶段;(2)45年来,研究区海岸线稳定性持续增强,其中孤东海堤段岸线与黄河清水沟亚三角洲南部岸线保持相对稳定,而清8汊河口段岸线与清水沟废弃河口段岸线较为活跃,其岸线稳定性指数基本低于0.5;(3)陆上三角洲淤积、侵蚀中心的迁移同河口位置变动相对应,尤其是淤积中心的迁移与河口位置变动之间在经度向存在明显的正向关系,R^(2)=0.6904;(4)黄河入海泥沙减少、河口位置迁移以及人类活动对三角洲海岸线的发育演化影响显著。从长远来看,在黄河入海泥沙持续减少的背景下,三角洲的未来仍面临侵蚀的威胁。

The shoreline change is the most direct factor in studying landform erosion and deposition.The Huanghe River Delta is the world’s fastest-growing delta,and understanding its coastline changes and evolution trends is crucial to regional ecological environment protection,marine resource development,and infrastructure construction.In this study,we combined modified normalized difference water index(MNDWI)and multi-year water frequency index(MWFI)to analyze water quality in typical years from 1976 to 2021,based on previous research.We visually interpreted 207 remote sensing images to obtain an annual coastline that makes the obtained coastline more scientific and representative.We then analyzed the temporal and spatial evolution and stability characteristics of the coastline through quantitative calculations to explore the Qingshuigou sub-delta coastline of the Yellow River’s evolution mechanism since 1976.Our main findings are as follows:(1)In general,the evolution of Qingshuigou subdelta coastline shows a trend of rapid sedimentation towards the sea,followed by fluctuations and stability.We can divide it into“rapid development”and“slow development,”with the“dynamic equilibrium”in between,taking 1996 and 2002 as nodes.(2)Over the past 45 years,the stability of the coastline in the study area has continued to increase.The coastline of the section of the coastline and the abandoned estuary section of Qingshuigou is relatively active,and its coastline stability index is generally lower than 0.5.(3)The migration of the sedimentation and erosion center of the land delta corresponds to the estuary location’s change,especially the migration of the sedimentation center,which has a positive relationship in the longitude direction between the change of the estuary position and the position of the estuary,R^(2)=0.6904.(4)The Huanghe River’s sediment reduction into the sea,the relocation of the estuary position,and human activities have a significant impact on the delta coastline’s development and evolution.In the long run,the Huanghe River’s silt into the sea is still continuously reducing,and the future of the delta is still facing the threat of erosion.