一、对传统三角洲动力模式的批判与修正

传统模式（Bates，1953）：将河口射流分为圆形射流（等密度）和平面射流（密度差异），并认为平面射流可在二维空间缓慢混合，扩散至湖盆远处。

本文修正：

河水入湖实际上是矩形（三维）射流，而非圆形或平面射流。

湍流特性决定了河湖水体在三维空间充分混合，流速沿程以负指数快速衰减，无法扩散至远处。

密度差异并不改变混合机制，只是影响射流轴线位置。

二、基于湍流理论的动力模式

河控三角洲的河口动力主要来自河水的惯性作用，属于动量射流。

流速衰减规律可用公式：

umax​/u0​=2.28(2b0​/x) ^0.5

其中，2b0​ 为河流水深，x 为距河口距离。

流速衰减主要受水深控制，而非河宽，Bates将河宽作为控制因素的理解是错误的。

三、三角洲前缘沉积特征

单期洪水形成的以床沙载荷为主的前缘砂体规模极为有限，因流速快速衰减，床沙载荷在湖岸线附近迅速沉积。

河口是流速衰减的终点，前缘是床沙载荷沉积的终点。

水槽实验和数值模拟均表明：湖岸线控制砂体展布；水位下降是砂体推进的前提；早期沉积的砂体若无更大洪水改造，无法继续推进。

四、三角洲平原沉积特征与生长机制

平原是河控三角洲沉积的主体，而非前缘。

平原砂体生长机制为：流速衰减 → 挟沙能力降低 → 泥沙沉积 → 河床抬高 → 堤岸决口 → 河流分叉 → 流速衰减 → 泥沙沉积。这一过程体现了动力、沉积、地貌三者相互作用，是三角洲演化的核心。分流河道砂体构成平原骨架，河流的横向迁移是砂体扩展的重要方式。

五、沉积模式总结

河控三角洲的沉积模式可概括为：

动力模式：流速沿程快速衰减；

沉积模式：泥沙在湖岸线附近快速沉积，河流因淤积而改道，反复摆动，形成大面积平原砂体；

发展方向：准平原化。

六、理论意义与应用价值

该研究为河控三角洲的成因机制提供了流体力学和泥沙动力学支撑，具有较强的物理基础；

对陆相盆地油气勘探中砂体预测、储层评价具有指导意义；

修正了长期主导沉积学界的Bates模式，推动了三角洲沉积理论的完善。

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Growth Model of Fluvial-Dominated Deltas Constrained by Fluid Mechanics and Fluvial Sediment Dynamics

Based on a comprehensive analysis of estuarine dynamic characteristics, turbulent jet theory, flume physical simulation, and numerical simulation of fluvial-dominated deltas, this paper proposes a growth model constrained by fluid mechanics and fluvial sediment dynamics. The main viewpoints of the paper are summarized as follows:

1. Criticism and Revision of Traditional Delta Dynamic Models

Traditional Model (Bates, 1953):

Classifies estuarine jets into round jets (isopycnic) and plane jets (density-stratified), assuming plane jets mix slowly in two dimensions and spread far into lake basins.

Revisions in This Paper:

- River water entering lakes forms a rectangular (3D) jet, not round or plane jets.

- Turbulence characteristics drive full 3D mixing of river-lake water; flow velocity decays rapidly along the path in a negative exponential manner, preventing long-distance spreading.

- Density differences do not alter mixing mechanisms, only affecting jet axis position.

2. Dynamic Model Based on Turbulence Theory

Estuarine dynamics of fluvial-dominated deltas are dominated by river inertia, belonging to momentum jets.

The velocity decay law is expressed as:

u_{\text{max}}/u_0 = 2.28(2b_0/x)^{0.5}

where 2b_0 = river water depth, x = distance from the estuary.

Velocity decay is controlled by water depth, not channel width; Bates’ emphasis on channel width as the controlling factor is incorrect.

3. Sedimentary Characteristics of Delta Front

- Frontal sand bodies dominated by bed-load sediment formed by single flood events are extremely limited in scale, as rapid velocity decay causes bed-load sediment to deposit quickly near the lake shoreline.

- The estuary marks the end of velocity decay; the delta front marks the end of bed-load deposition.

- Flume experiments and numerical simulations confirm: lake shorelines control sand body distribution; falling water levels are a prerequisite for sand body progradation; early deposited sand bodies cannot prograde further without reworking by larger floods.

4. Sedimentary Characteristics and Growth Mechanisms of Delta Plain

- The delta plain is the main sedimentary body of fluvial-dominated deltas, not the delta front.

- Plain sand body growth mechanism: velocity decay → sediment-carrying capacity reduction → sediment deposition → riverbed aggradation → levee breach → river bifurcation → velocity decay → sediment deposition. This process reflects interactions between hydrodynamics, sedimentation, and geomorphology, forming the core of delta evolution.

- Distributary channel sand bodies constitute the plain framework; lateral channel migration is a key mode of sand body expansion.

5. Summary of Sedimentary Model

- Dynamic model: Rapid velocity decay along the flow path.

- Sedimentary model: Rapid sediment deposition near the lake shoreline; repeated avulsion and lateral migration of rivers due to aggradation, forming extensive plain sand bodies.

- Evolutionary direction: Peneplanation.

6. Theoretical Significance and Application Value

- Provides fluid mechanics and sediment dynamics support for the genetic mechanism of fluvial-dominated deltas, with a solid physical foundation.

- Guides sand body prediction and reservoir evaluation in continental basin hydrocarbon exploration.

- Revises the long-dominant Bates model in sedimentology, promoting the improvement of delta sedimentary theory.