【作者】 毕乃双；

【导师】 杨作升；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2009， 博士

【摘要】 以973项目2002CB4124第四课题为依托,根据2003年夏季黄河低流量期间、2007年夏季调水调沙期间以及2006年冬初风暴后的多船同步多断面及夏、冬有关大面站水文泥沙观测资料,本文研究了不同条件下黄河三角洲毗邻海域悬浮泥沙的扩散特征,定量比较了黄河三角洲海域悬浮泥沙扩散的季节性特征,分析了泥沙扩散的过程、控制因素和沉积动力机制,并与1976-2003黄河三角洲沿岸36个观测断面的水深资料对比,探讨了现行黄河水下三角洲蚀积变化对悬浮泥沙扩散的响应。同时分析了渤海海峡南部海域水沙输送的季节性变化,重新估算了渤海通过渤海海峡南部海域向黄海输送的年均泥沙通量,获得以下主要结果。1.除黄河河口地区存在潮流切变锋外,在三角洲南北部近岸分别发现了潮流切变锋,它们对泥沙的阻隔效应与河口切变锋相反,其形成机制与河口切变锋有所不同。2.黄河低流量期间,由于黄河口切变锋的阻隔、河口垂向环流的捕获作用以及黄河入海径流较弱,导致黄河入海泥沙在河口附近5 m等深线以内的浅水区大量沉积,向外海的传输较少。部分黄河入海泥沙在被涨、落潮流携带向南、北传输的过程中,由于近岸切变锋的阻隔作用,三角洲南北部靠近海岸的浅水区反而得不到泥沙供应,形成侵蚀区,悬浮泥沙主要通过较深水区向南北传输。3.夏季黄河调水调沙期间黄河入海泥沙扩散主要局限在离岸约20km以内,向南达到至莱州湾西南部海域,向北最远至北纬38°附近,扩散范围远小于冲淡水扩散范围。由于河口切变锋的阻隔和辐聚作用以及河口垂向环流的捕获,使得黄河入海泥沙绝大部分都沉积在河口13m水深以内区域,不能直接扩散至深水区。夏季存在明显的水体密度跃层,悬浮泥沙主要在跃层以下的下层水体中传输。在现行河口和废弃钓口流路废弃河口存在两个高浓度泥沙中心,分别由黄河入海泥沙扩散和废弃钓口流路地区海底泥沙的再悬浮形成,两个高浓度泥沙中心很少有泥沙交换。4.冬季调查区含沙量整体较高,底层泥沙远高于表层,表明波浪导致海底泥沙再悬浮是悬浮泥沙的主要来源。受北风和南向波浪的作用,黄河三角洲海域产生较强的南向沿岸流,携带再悬浮泥沙向南传输。在莱州湾海域,悬浮泥沙主要通过其中部输向渤海海峡,沿莱州湾顶部沿岸向渤海海峡的传输不明显。5.泥沙通量分析表明,黄河三角洲海域悬浮泥沙输送具有鲜明的季节性。夏季泥沙通量主要指向东偏北,冬季主要指向偏南。冬季悬浮泥沙含量约为夏季低流量期间的约10-25倍,而悬浮泥沙通量可达约4-128倍。即使在黄河调水调沙期间,除河口区悬浮泥沙含量及悬浮泥沙通量较冬季高外,其他区域冬季悬浮泥沙含量及即悬浮泥沙通量可分别达夏季调水调沙期间的约2-27倍和2-123倍。冬季是黄河口海域泥沙输送的主要季节,泥沙向南部输送也主要发生在冬季,这与中国东部陆架海沉积物“夏储冬输”的格局一致,主要原因是冬季海洋动力远高于夏季。6.黄河三角洲海域悬浮泥沙输送的季节性变化导致了渤海海峡南部西侧海域水悬浮泥沙输送具有明显的季节性差异,冬季平均泥沙含量约是夏季的4.2倍,净泥沙单宽通量方向向东指向黄海,冬季通量约是夏季的5倍,说明冬季是渤海泥沙向黄海输送的主要季节。同时,冬、夏季该区净单宽水通量方向与悬浮泥沙通量方向相同,冬季净单宽水通量约是夏季的1.2倍。根据前人方法,初步估算了渤海通过渤海海峡南部海域向黄海输送泥沙的通量约为30.8 Mt/yr,是前人仅根据夏季8月通量计算结果的3倍左右。可以初步认为,夏季渤海基本上是黄河入海泥沙的汇,冬季是黄河泥沙向黄海输送的源。海洋动力的季节性差异是渤海黄河泥沙源-汇关系转换的主要因素。7. 1976-2003黄河三角洲沿岸36个水深观测断面的冲淤变化结果表明,黄河水下三角洲冲淤形态呈现为水滴状的淤积体,在南北近岸形成两个蚀积转换带,淤积中心主要在南部,与本文有关泥沙扩散的时空过程和机制的结论比较一致。前人对黄河三角洲泥沙扩散的定量和机制研究主要集中在洪季和河口区,本文较全面地展示了黄河三角洲沿岸及毗邻海域悬浮泥沙的扩散特征、过程和不同的季节性变化,得出了定量性的结果,揭示了有关机制,其结果与黄河水下三角洲多年的冲淤形态比较一致。同时初步计算了不同季节通过渤海海峡由渤海向黄海输送的水沙通量。更多还原

【Abstract】 Hydrographic and suspended sediment data were collected in 3 synchronic multi-station hydrographic time-series surveys along 4 sections and 24 grid stations off the recent Huanghe (Yellow River) delta and its adjacent Bohai Sea conducted during 3 cruises in low river discharge period in 2003, water-sediment regulation scheme period in 2007 and after storm period in winter of 2006. Based on these data suspended sediment dispersal characteristics, process and its seasonal variation, off the recent Huanghe delta and its adjacent Bohai Sea were studied quantitatively. Its controlling factors and mechanism were analyzed. Based on the bathymetric data of 36 survey transects along the delta in 1976-2003, the effect of the sediment dispersal on the subaqueous Huanghe delta erosion-accumulation were estimated. Additionally, the seasonal variation of the water and sediment fluxes from the Bohai Sea to the Yellow Sea through the southern Bohai Strait were reestimated based on the in-situ time-serious hydrographic data collected in summer of 2007 and in winter of 2006. The major results and conclusions are presented as follows.1. The tidal shear fronts with different mechanisms were found not only in the river mouth area but also in southern and northern area off the Huanghe delta. The tidal shear fronts combined with the tidal currents in the northern and southern delta bared the suspended sediment dispersing to the nearshore area, which was opposite with the function of the tidal shear fronts off the river mouth, resulting in formation of two erosion area off the northern and southern delta .2. Most of the sediment from the river mouth as hypopycnal flow deposited within 5 m isobath due to the jointed effects of tidal shear front and vertical circulation off the river mouth during river low discharge period. Part of suspended sediment was transported northward or southward by the ebb and flood currents through deeper water area but not via shallower area.3. Suspended sediment discharged from the Huanghe to the Bohai Sea was mainly delivered along the coast within the area of about 20 km from the coast during water-sediment regulation scheme period in summer. It was transported southward by the flood current and reach the southwestern sea area of the Laizhou Bay, and was delivered northward by the ebb current but can not extend over 38°N. Most of the river-delivered suspended sediment deposited within 13 m isobath due to the barrier and convergence effects of the tidal shear fronts as well as the trapping effect of the vertical circulation. Moreover, the well-developed pycnocline in the upper water layer in the study area in summer season limited the suspended sediment transport mainly below the pycnocline. Two centers with high suspended sediment concentration were formed in abandoned Diaokou river mouth area and current river mouth area, resulting from resuspension of seabed sediment and river discharged sediment respectively,. There was little sediment exchange between the two centers.4. The suspended sediment concentration, primarily resulted from the resuspension of seabed sediment induced by the waves, was increased substantially in winter in the study area. It was mainly transported southward by strong longshore current induced by wind and waves. The high turbid water mass, originated from the northern delta and river mouth area, was delivered towards to the Bohai Strait through the middle of the Laizhou Bay and the sediment transport along its coast was not significant.5. The suspended sediment dispersal in the study area showed strong seasonal variation. The suspended sediment concentrations and fluxes, mainly directing southward, in winter were 10-25 times and 4-128 times higher than those during river low discharge period in summer, and 2-27 times and 2-123 times those during water-sediment regulation scheme period in summer, except for river mouth area. Therefore, major sediment-transport season off the Huanghe delta was winter, when the marine dynamics was much stronger than that in summer, which was in good agreement with the sediment-transport pattern in East China 6. The suspended sediment transport from the Bohai Sea to the Yellow Sea had a significant seasonal variation resulted from the seasonal variation of the sediment dispersal off the Huanghe delta. The suspended sediment concentrations and fluxes in winter were 4.2 times and 5.0 times higher than those in summer, respectively, which indicated that most of the sediment was transported from the Bohai Sea to the Yellow Sea through the southern Bohai Strait in winter season. Moreover, the water discharge from the Bohai Sea to the Yellow Sea in winter was about 1.2 times that in summer. Based on the method of previous study and in-situ data of this paper, the annual sediment flux was reestimated, which was 30.8 Mt/yr and about 3 times higher than that based on the data collected in August in previous studies. Therefore, it can be concluded that the Bohai Sea basically is the sink of the Huanghe delivered sediment in summer season, and it was transformed to the source of the Huanghe sediment in winter due to the significant difference of the marine dynamics in two seasons.7. The accumulation-erosion pattern of the Huanghe subaqueous delta from 1976 to 2003 showed that there was a water-drop-like accumulation area in the southern delta and two nearshore erosion-accumulation zones in southern and northern delta which was approximately in accordance with our results of fluxes, temporal-spatial process and mechanism of suspended sediment dispersal off the Huanghe delta.更多还原