黄河河口泥沙扩散规律分析——以钓口河流路为例

Analysis of Sediment Dispersal of the Huanghe(Yellow) River Mouth——A Case of Diaokouhe Lobe

分析黄河口钓口河亚三角洲不同时期泥沙沉积速率和水沙条件变化,发现来沙输沙率是影响黄河三角洲沉积速率的主要因素,随输沙率增加三角洲泥沙沉积速率增大。来水流量和来沙粒度组成变化对沉积速率的影响不明显。还发现来水含沙量与三角洲泥沙淤积占来沙的比例(沉积比)之间为双值关系,在某一含沙量时沉积比达最大值。对比显示,在河口河道畅通,沙嘴突出时期,三角洲泥沙沉积比反而比河口改道初期大,意味着集中水流入海可能降低海流带走泥沙的比例。另外,根据前三角洲的地形测量资料分析发现,进入远海的泥沙随距离增加呈指数递减。对黄河口这些独特的泥沙扩散规律发生机理进行了深入分析。

The Huanghe （Yellow） River delta is characterized by retaining a high percentage of riverine sediment input. It was about 3/4 for the case of the Diaokouhe lobe over the period of 1965 - 1974. The rate and sediment retention index （ the proportion of sediment accumulation behind the delta front） vary considerably over time. It is found that the main factor responsible for the variation in sediment accumulation rate is the change in sediment discharge of the river. The anticipated negative relationships are not statistically significant between the sediment accumulation rate in the delta and the water discharge and clay content of sediment carried by the river. It is also found that with the increase of sediment concentration of river water, the sediment retention index increases and then decreases after a certain sediment concentration. Contrary to the common sense, the sediment retention index is positively related with the mouth channel efficiency. The nonlinear relationship between the sediment retention index and sediment concentration of river water is associated with the different sediment dispersal patterns at varying sediment concentrations of river water. With the increase of sediment concentration of river water, plumes of the Huanghe River mouth change from hypopycnal plumes, through sediment-charged hyperpycnal plumes to hyper-concentrated underflows. The hypopycnal plumes and hyper-concentrated underflows tend to carry a higher portion of riverine sediment beyond the delta front. In contrast, the rapid extinction of hyperpycnal plumes leads to both fine and coarse particles they carried depositing on the delta front. The hyperpycnal plumes, which are likely to occur when the daily mean sediment concentration of river flows is in the range of 30 - 110 kg/m^3 or so, are dominant in the plumes of the Huanghe River mouth. Also, overbank flows leave the sediment carried by them on the delta plain. These two processes result in a high portion of riverine sediment being deposited on the Huanghe River delta. They are also the causes for the close relationship of the sediment accumulation rate on the delta with the sediment discharge but the poor ones with the river discharge and grain size composition of sediment carried by the river. Moreover, the dominance of hyperpycnal plumes can be used to explain the disconnection between an unblocked mouth channel and a higher proportion of sediment escaping from the delta front because more sediment will be deposited from the hyperpycnal plumes, which are enhanced when more highly sediment-loaded flows are carried into the delta front. Since fine particles account for a low proportion in the sediment escaping from the delta front as a result of deposition of both fine and coarse particles in hyperpycnal plumes on delta front and overbank flows on delta plain, the sediment tends to deposit in a short distance. According to the bathymatric measurements in 1968 and in 1974, the amount of sediment dispersed to the sea reduced exponentially with the distance from the delta front.