Unravelling the conundrum of river response to rising sea‐level from laboratory to field. Part II. The Fly–Strickland River system, Papua New Guinea
Unravelling the conundrum of river response to rising sea‐level from laboratory to field. Part II. The Fly–Strickland River system, Papua New Guinea
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DOI：
10.1111/j.1365-3091.2008.00962.x
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发表时间：
2008-12
期刊：
影响因子：
3.5
通讯作者：
G. Parker;T. Muto;Y. Akamatsu;W. Dietrich;J. Wesley Lauer
中科院分区：
文献类型：
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作者：
G. Parker;T. Muto;Y. Akamatsu;W. Dietrich;J. Wesley Lauer
最近的一次冰川消融导致全球海平面在12000年内上升了约120米。开发了一个移动边界数值模式来预测河流对这次上涨的响应。该模型受小规模实验的启发，已确定描述河口海侵的两种模式：(I)在不放弃河流三角洲的情况下自动后退(在顶层-前缘断裂处没有沉积物饥饿)；(Ii)在放弃三角洲的情况下缺乏沉积物的自动后退。在后一种情况下，海侵要快得多，其影响可以感受到河口上游更远的地方。一个在实验三角洲中捕捉到这些特征的移动边界数值模式适用于描述巴布亚新几内亚Fly-Strickland河系统的响应。在没有更好的信息的情况下，该模型适用于新几内亚海平面上升而没有局部气候变化的情况。模型表明：(I)自上一次冰期盛期以来，海平面上升迫使河口侵入700多公里；(Ii)缺乏泥沙的自退迫使河床淤积，堵塞了一条含沙量较低的支流，形成了今天的墨累湖；(Iii)由此造成的淤积足以将斯特里克兰河的砾沙过渡推向上游；(Iv)今天的苍蝇河口可能部分是被海平面上升淹没并部分被潮汐作用填满的残存河谷；以及(V)苍蝇河目前正在改造其河岸几何形状，并向苍蝇河口进发。模型的参数研究表明，洪水期间的含沙量在决定海侵是否以及在多大程度上以缺乏泥沙的自退来表达方面起着关键作用。足够高的沉积物浓度可以防止在整个海平面循环中沉积物匮乏的自退。这一观察可以解释为什么今天的一些河口是以伸入大海的三角洲来表示的，而另一些则完全被限制在海湾或河口内，在这些海湾或河口中，水已经向陆地入侵。
The most recent deglaciation resulted in a global sea‐level rise of some 120 m over ca 12 000 years. A moving boundary numerical model is developed to predict the response of rivers to this rise. The model was motivated by experiments at small scale, which have identified two modes describing the transgression of a river mouth: (i) autoretreat without abandonment of the river delta (no sediment starvation at the topset–foreset break); and (ii) sediment‐starved autoretreat with abandonment of the delta. In the latter case, transgression is far more rapid, and its effects are felt much further upstream of the river mouth. A moving boundary numerical model that captures these features in experimental deltas is adapted to describe the response of the Fly–Strickland River system, Papua New Guinea. In the absence of better information, the model is applied to the case of sea‐level rise without local climate change in New Guinea. The model suggests that: (i) sea‐level rise has forced the river mouth to transgress over 700 km since the last glacial maximum; (ii) sediment‐starved autoretreat has forced enough bed aggradation to block a tributary with a low sediment load and create the present‐day Lake Murray; (iii) the resulting aggradation was sufficient to move the gravel–sand transition on the Strickland River upstream; (iv) the present‐day Fly Estuary may be, in part, a relict river valley drowned by sea‐level rise and partially filled by tidal effects; and (v) the Fly River is presently reforming its bankfull geometry and prograding into the Fly Estuary. A parametric study with the model indicates that sediment concentration during floods plays a key role in determining whether or not, and to what extent, transgression is expressed in terms of sediment‐starved autoretreat. A sufficiently high sediment concentration can prevent sediment‐starved autoretreat during the entire sea‐level cycle. This observation may explain why some present‐day river mouths are expressed in terms of deltas protruding into the sea, and others are wholly contained within embayments or estuaries in which water has invaded landward.