内陆湖泊三角洲河口区水动力特征及地质意义

Hydrodynamic characteristics and geological significance of estuaries of inland lake delta

分析河口区水动力特征是直观理解沉积过程、有效揭示沉积机理和模式及合理刻画砂体形态的重要前提和途径。应用流体力学的射流理论和牛顿内摩擦定律,分析内陆湖泊三角洲前缘河口区水动力特征和水动力场的主导机制。结果表明:河流入湖后,河流水体所受湖泊水体的阻力主要来源于河流水体与湖泊水体相对运动时产生的黏滞力即内摩擦力,河流水体平均流速越大,湖泊水体越浅,则速度梯度越大,内摩擦力或切应力越大;天然河流水体向湖泊水体的推进长度非常有限,主要受出口断面处河流水体的初始流速和河流深度的控制,而不受河流宽度控制。三角洲前缘河口区主要发育呈舌状平行于湖岸线展布的河口坝砂体,而水下分流河道砂体则不发育。河口区复杂多样的砂体形态本质上是多期垂直于湖岸线展布的平原河道砂体与平行于湖岸线展布的河口坝砂体垂向叠加和侧向拼接或改造后垂向叠加和侧向拼接的产物。

Analysis of hydrodynamic characteristics of estuaries is important premise and means for understanding sedimentary process, effective revealing deposition mechanism and model, reasonable characterizing sand body morphology. Jet theory and Newton internal friction law of fluid mechanics were applied to analyze hydrodynamic characteristics and dominant mechanism of estuary and hydrodynamic field respectively.The results show that after rivers into lake, the resistance suffered from lake water body derived from viscous force or internal friction force which produced by relative motion of river water body and lake water body, the greater the average flow velocity of river water body is, the more shallow the lake water body is, the greater the velocity gradient is, and the greater the internal friction or shear stress. The propulsion length of natural river water into the lake water is limited, which depends on the initial velocity and depth rather than width of exit section of river water. Tongue shaped mouth bar sand body distributed parallel to coast developed in estuaries of lake delta front rather than underwater distributary channel sand body. The complex and varied sand body morphology in estuaries is essentially overlaying and joining together of multiphase plain channel sand body distributed vertical underwater mouth bar sand body distributed parallel to shorelines. resulted from the to shorelines and