de Haas Tjalling, van der Valk Lambertus, Cohen Kim M, Pierik Harm Jan, Weisscher Steven A H, Hijma Marc P, van der Spek Ad J F, Kleinhans Maarten G
Department of Physical Geography Utrecht University Utrecht The Netherlands.
Department of Geography Durham University Durham UK.
Depos Rec. 2019 Feb;5(1):84-108. doi: 10.1002/dep2.56. Epub 2019 Jan 2.
The long-term morphodynamic evolution of estuaries depends on a combination of antecedent topography and boundary conditions, including fluvial input, sea-level change and regional-landscape interactions. Identifying effects of such boundary conditions on estuary evolution is important to anticipate future changes in specific boundary conditions and for hindcasting with numerical and physical models. A comprehensive synthesis of the evolution of the former Old Rhine estuary is presented here, together with its boundary conditions over its full lifespan from 6,500 to 1,000 cal. yr bp. This system formed during a period of sea-level high stand, during which the estuary served as the main River Rhine outlet. The estuary went through three stages of evolution: a maturation phase in a wide infilling back-barrier basin, a stable mature phase and an abandoning phase, both in a laterally confined setting. The Old Rhine River formed by a river avulsion around 6,500 cal. yr bp that connected to a tidal channel within a large back-barrier basin. Decelerating sea-level rise caused the back-barrier basin to silt up around 5,700 cal. yr bp, resulting in shoreline progradation by beach-barrier formation until 2,000 cal. yr bp. Beach-barrier formation along the coast and natural levee formation along the river triggered peat formation in the coastal plain, laterally constraining the estuary and limiting overbank deposition, which caused most sediment to accumulate offshore. The abandoning phase started around 2,200 cal. yr bp when a series of upstream avulsions led to a substantial reduction in fluvial input. This induced a period of enhanced estuarine overbank clay deposition that continued into near-complete silting up and estuary closure around 1200 ad. These findings exemplify how tidal systems, formed in wide coastal plains during sea-level high stand, depend on antecedent conditions, and how they respond to connection and disconnection of a large river over long, millennial timescales.
河口的长期形态动力学演变取决于前期地形和边界条件的综合作用，包括河流输入、海平面变化和区域景观相互作用。识别这些边界条件对河口演变的影响，对于预测特定边界条件的未来变化以及利用数值模型和物理模型进行后向推算至关重要。本文介绍了前莱茵河河口的演变及其在公元前6500年至1000年整个生命周期内的边界条件。这个系统形成于海平面高位期，在此期间河口是莱茵河的主要出水口。河口经历了三个演变阶段：在宽阔的充填型后滨盆地中的成熟阶段、稳定的成熟阶段以及在横向受限环境中的废弃阶段。大约在公元前6500年，莱茵河因河流改道形成，连接到一个大型后滨盆地内的潮汐通道。海平面上升减速导致后滨盆地在公元前5700年左右淤塞，导致海岸线通过滩脊屏障的形成向前推进，直到公元前2000年。沿海滩脊屏障的形成和沿河流天然堤的形成引发了沿海平原的泥炭形成，从横向限制了河口并限制了漫滩沉积，这导致大部分沉积物在近海堆积。废弃阶段始于公元前2200年左右，当时一系列上游改道导致河流输入大幅减少。这引发了一段河口漫滩粘土沉积增强的时期，一直持续到公元1200年左右几乎完全淤塞和河口封闭。这些发现例证了在海平面高位期宽阔沿海平原上形成的潮汐系统如何依赖前期条件，以及它们如何在长达数千年的时间尺度上对一条大河的连接和断开做出响应。
