Replication Data for Oblique aggradation: a novel explanation for sinuosity of low-energy streams in peat-filled valley systems

Low-energy streams in peatlands often have a high sinuosity. However, it is unknown how this sinuous planform formed, since lateral migration of the channel is hindered by relatively erosion-resistant banks. We present a conceptual model of Holocene morphodynamic evolution of a stream in a peat-filled valley, based on a palaeohydrological reconstruction. Coring, ground-penetrating radar (GPR) data, and 14C and OSL dating were used for the reconstruction. We found that the stream planform is partly inherited from the Late-Glacial topography, reflecting stream morphology prior to peat growth in the valley. Most importantly, we show that aggrading streams in a peat-filled valley combine vertical aggradation with lateral displacement caused by attraction to the sandy valley sides, which are more erodible than the co-evally aggrading valley-fill. Owing to this oblique aggradation in combination with floodplain widening, the stream becomes stretched out as channel reaches may alternately aggrade along opposed valley sides, resulting in increased sinuosity over time. Hence, highly sinuous planforms can form in peat-filled valleys without the traditional morphodynamics of alluvial bed lateral migration. Improved understanding of the evolution of streams provides inspiration for stream restoration. (2017-02-24)

泥炭地中的低能水流通常具有较高的蜿蜒度。然而，由于河岸抗侵蚀能力较强，阻碍了河道的侧向迁移，目前尚不明确这种蜿蜒平面形态的形成机制。本研究基于古水文重建结果，提出了泥炭充填河谷中河流全新世地貌动力演化的概念模型。研究采用取芯、探地雷达（ground-penetrating radar, GPR）数据、碳十四（14C）与光释光（OSL）测年手段开展重建工作。研究发现，河流的平面形态部分继承自晚冰期地形，反映了河谷内泥炭发育前的河流形貌。最为关键的是，本研究表明，泥炭充填河谷中的加积型河流兼具垂直加积与侧向迁移过程：侧向迁移由河流向砂质河谷岸坡的趋附作用引发，而此类岸坡的可侵蚀性强于同期加积的河谷充填物。由于这种斜向加积作用与河漫滩拓宽共同作用，河道会被拉伸——河道段可沿相对的河谷岸坡交替加积，随时间推移导致蜿蜒度不断提升。因此，泥炭充填河谷中可形成高度蜿蜒的平面形态，而无需依赖冲积河床侧向迁移这一传统地貌动力机制。对河流演化过程的深入理解，可为河流修复工作提供理论借鉴。（2017-02-24）