长江口横沙附近河势变化与可利用港航资源分析

STUDY ON EVOLUTION TREND OF THE HENGSHA EAST SHOAL IN THE CHANGJIANG ESTUARY AND ITS IMPLICATION FOR THE WATERWAY RESOURCE

以1998／1999年长江流域洪水后奠定的河日河势为参照，利用四期大比例尺海图，数字化分析了1998／1999-2011年长江口北港河势与横沙东滩演变，讨论了北港和横沙东滩受河口重大工程影响产生的新变化。结果表明：青草沙水库工程稳定了北港河势；依托深水航道导堤工程和圈围工程，横沙东滩快速淤长，至2011年，-2m、～5m以上面积分别达到304km2、522km2，扣除深水航道坝田区面积，还有237km2、450km2；围绕横沙岛和横沙东滩，北岸可利用-10m岸线达到16km，在未来的7～23a，可为上海的发展提供大量的新增岸线资源和土地资源。横沙北靠北港，南依长江口深水航道，东临东海；吹填成陆的横沙东滩土地资源丰富，经济地理位置优越，使得在横沙建设上海新港区成为可能。

The Hengsha East Shoal is one of the main estuarine shoals in the Changjiang Estuary. The shoal is open to the East China Sea. It never becomes a land due to strong wind waves in winter seasons. There is a plan to reclaim the Hengsha East Shoal to meet increasing land need or to build a new harbor in Shanghai. Before the plan is implemented, we should understand the basic situation about the shoal and sedimentary dynamics in the adjacent water areas. We collected 21 marine charts and classified them into four periods to analyze the evolution of the North Channel and the Hengsha East Shoal using geographic information system. At the north of the Hengsha East Shoal, the results showed that the Qingcaosha Reservoir Project （located at the upstream part of the North Channel） stabilized the water and sediment diversion of the South and North Channel, and kept the main flow stable in the North Channel in recent years. Since 1998--1999, the 10 m isobaths in the upper part of the North Channel have moved a little to north while the other part moved to south. The shallowest water was less than 5 m near the mouth bar in the North Channel, which is located at 122~15＇E. The mouth sand bar in this channel was moving towards downstream. Along the north coast of the Hengsha Island and the Hengsha East Shoal, the coastline deeper than 10 m reaches 16 km in recent years. The waterway showed that it had the capacity to become navigation channel at the upper streams of the North Channel. At the south of the Hengsha East shoal, the jetty construction of the deep-water navigation channel in the North Passage also stabilized the tidal flat of the Hengsha East shoal and reduced the water and sediment exchange between the mud flat and the waterway. The new reclamation engineering on the Hengsha East shoal also increased the accretion rate of the Hengsha East shoal remarkably. By the year 2011, areas of up to -- 2 m and up to -- 5 m have reached 304 km2 and 522 km2, respectively. Deducting the area within the deep--water navigation channel dams, there are also 237 km2 and 450 km~, respectively. There are abundant dredged soils in the Changjiang Estuary every year, especially in the deep- water navigation channel. Now the dredged soils are abandoned as waste in the estuary. If it could be used as hydraulic fill material upon to the new reclaimed Hengsha East shoal areas, the mud flat will become the land in 13 to 41 years as the filled soil number reach 60 million m3 per year, 7 to 23 years as the soil reach 100 million m3 per year. In conclusion, in foreseeable future, the Hengsha East shoal could provide a number of land resource and navigation coastal lines to meet the local development needs.