人类活动与黄河断流及海岸环境影响

HUMAN ACTIVITIES, BREAKOFF WATER DISCHARGE OF THE YELLOW RIVER AND THE IMPACTS ON COASTAL ENVIRONMENT

黄河特性：水少沙多，水沙异源且时空分布不均匀，下游河道迁徙频繁．黄河水资源７４４×１０８ｍ３，平均径流量５８０×１０８ｍ３，枯水年与丰水年径流量之比可达１：１０．３．黄河平均含沙量高达３７．６ｋｇ／ｍ３，三门峡站年最大输沙量３９．１×１０８ｔ，最小仅４．８８×１０８ｔ．６０年代以来，黄河下游出现断流，最近７年连续断流．本文分析了断流的自然与人为两大原因，主因是流域沿途引水量过大，入不敷出．提出当汛期降水量为２１０ｍｍ、径流量为２８０×１０８ｍ３、流域引水量１７５×１０８ｍ３、年径流量净余值高于１００×１０８ｍ３，黄河仍有一定数量径流人海．由此，２００×１０８ｍ３人工引水量或１００×１０８ｍ３净余径流量可能是黄河断流的临界值．黄河断流直接影响的三角洲平原面积达５．４×１０４ｋｍ２，累计直接经济损失２６８亿元．断流减少河流行水维护河道的自然能力，召致河道萎缩恶化；减少入海径流量，改变河口生态环境；减少泥沙入海，促使海岸侵蚀后退．断流犹如历史上黄河改道，引起渤海湾与苏北黄海两地河口海岸环境发生剧烈变化．对策是提高全民节水意识；全流域规划计划用水，将引水量控制在２００×１０８ｍ３以内，保证下游有２００×１０８ｍ３径?

Three characteristics of the Yellow River are lower water discharge with highest volume of sediment; runoff and sediment originating from different areas, running and distributing in the different seasons and sections; and migrating often in its lower reaches. The total volume of water resources in the Yellow River drainage basin is 744×108m3, the annual average water discharge is 580×108m3. The lowest and highest recorded annual water discharge is in the ratio of 1:10.3. The average sediment concentration reaches 37.6kg/m3. The maximum annual sediment discharge recorded at the Shanmenxia gorge station is 39.1×108t, while the minimum is only 4.88×108t.Breakoff water discharge in the lower Yellow River channel was first recorded in the 1960's; it is 7 years without water discharge in the lower reaches of the Yellow River since 1991. After the analysis of the natural factors of climate changes and the artificial factors of diverting water discharge for urban and farmland water supply, it is determined that the main reason for breakoff runoff is over diverting water discharge along the Yellow River drainage basin, which makes the "outcome" of water discharge larger than "income". In conclusion, the paper indicates that even the precipitation in flood season is as low as 210 mm, volume of runoff is only 280×108m3, while the artificial diverting of water is 175×108m3, annual net runoff still keeps larger than 100×108m3, thus, the Yellow River runs smoothly to the Bohai Sea. The 200×108m3 volume of artificial diverting or 100×108m3 of net runoff may be the critical features to retain the water running in the lower river channel.The affected area being out of river water in the Yellow River delta is about 54000 km2, and cumulative economic loss reaches 268×108 Yuan. The impacts of breakoff water discharge in the Yellow River are great, as it has decreased natural agent to retain river channel, which changes the ecological environment in river mouth, decreases soil fretility and then turns it into sandy soil. Because of cutting off sediment discharge, coastline erosion is caused and it retreats landward. Historical records indicate the great environmental changes in the Yellow River estuary and its adjacent coastal area as a result of the Yellow River migrating from the Bohai Bay to the Yellow Sea visàvis. The way to avoid the damaged situation is to raise the public awareness, take good care of fresh water using, have a systematic plan and management of the whole river water discharge, limit the volume of diverting water below 200×108m3 and maintain 200×108m3 of runoff discharging to the sea at the same time.