| 摘要: |
| 1997年枯季和1998年特大洪水后期，在长江口南支-南港用直读式海流计和Endeco／YSI Inc．174SSM 流速仪定点测量近底和表层流速大小和方向，并采集床面泥沙样品经室内分析得到底沙粒径，用声学测深仪和Ultra Electronics旁侧声纳仪走航测量床面形态。结果表明：1)枯、洪季时落潮流近底和表层流速比涨潮流流速大，落潮流周期比涨潮流周期长，且洪季落潮流表层流速大于枯季时，洪季落潮流周期比枯季时长；2)床面泥沙枯季时为粗粉砂至极细砂，而洪季时为极细砂至细砂；3)枯、洪季床面上的沙波形态受落潮流控制，波高与波长之比值以及背流面坡度较小，洪季时沙波波高比枯季时高，波长比枯季时长。显然，长江口南支一南港落、涨潮流和床面泥沙粒径及沙波形态的特征均与季节性变化的径流有关。此外，在Van den Berg and Van Gelder(1993)底形稳定相图中，作者提出了一个新的沙纹与沙波间的转化边界。 |
| 关键词: 长江口，沙波，稳定域 |
| DOI： |
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| 基金项目:国家杰出青年科学基金资助项目，40225014号；国家基础研究发展规划项目，2002CB4124007号、上海市教委曙光计划资助项目，99SG13号。 |
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| STABILITY FIELD FOR SAND BEDFORMS AT THE SOUTH BRANCH AND THE SOUTH CHANNEL IN THE CHANGJIANG (YANGTZE)ESTUARY |
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CHENG He-Qin1,2, SHI Zhong3, Kostaschuk Ray4, DONG Li-Xian2
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1.State Key Laboratory of Estuarine&Coastal Research，East China Normal University;2.Key Laboratory of Ocean Dynamic Processes&Satellite Oceanography，Second Institute of Oceanography，State Oceanic Administration;3.Department of Harbour&Coastal Engineering，Shanghai Jiao Tong University;4.Department of Geography，University of Guelph
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| Abstract: |
| A set of measurements were made at the South Branch and the South Channel during the dry season in 1997 and the flood season in 1998，respectively，in the Changjiang Estuary，China．Dune bed profiles and planform morphology were measured with Thermal Depth Recorder of Inner Space(449M)and Sonar Sidescan (3050L)being deployed along the survey lines at the South Channe1．Tidal current velocities were measured from two mooring sites．Near surface current velocity was measured with Current Meter of Endeco／YS1 Inc(174SSM)being deployed 1m below the surface over 14h period during both the dry season in 1997 and the flood season in 1998．During the dry season，near bottom tidal current velocity was also measured with a mechanical current meter for 10h deployed 1m above the bed．Six bottom grab samples were taken during the 1997 survey and three samples during the 1998 survey．The particle size distributions of bed samples were determined using standard sieving techniques and the laser Coulter LQ100A．Ratio of height to length of lee side slope and stoss side slope are calculated to be the lee side slope angle and stoss side slope，respectively．Results show that：(1)near surface ebb tidal velocities exceed 2 m／s during the 1998 flood survey but were less than 1.5m／s during the dry season in 1997 and the ebb tides had longer durations than the flood tides； (2)the bed sediments were composed of coarse silts and very fine sands with an average median particle size of0．088mm(D50)enriched 20％-3O％ of fine sands during the dry season but of fine sands with a mean median particle size of 0.13mm (D50)during the flood season；(3)mean height／length ratios are similar in 1997(0.036)and 1998(0.040)，and dune lee-sides face downstream in both 1997 and 1998 indicating a dominance by ebb tidal currents and (4) stoss and lee side slope angles are also steeper for flood dunes，probably because of coarser bed sediments in 1998 and dune modification by upstream flood tidal currents in 1997．Therefore，the ebb and flood tidal currents，bed sediment particle size and dune morphology at the South Branch and South Channel in the Changjiang Estuary were controlled by the seasonal runoff variations．And then，a new boundary is proposed for the transition between ripples and dunes based on the Van den Berg and Van Gelder(1993)diagram in deep flows with very fine sand． |
| Key words: Stability,Bedforms,Changjiang Estuary |
