Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California)
Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River basin (Sierra Nevada, California)
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DOI：
10.5194/esurf-3-201-2015
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发表时间：
2015-01-01
影响因子：
3.4
通讯作者：
Naylor, M.
中科院分区：
文献类型：
--
作者：
Attal, M.;Mudd, S. M.;Naylor, M.
河流输送的沉积物的特性（例如沉积物通量、粒度分布GSD）决定了河流是侵蚀还是淤积其底质。它们还决定着盆地沉积序列的结构和性质。本研究主要探讨地形坡度与山坡及河流沉积物粒径的关系。研究区域位于北方加州的Feather河流域，研究的盆地完全由英云闪长岩岩性构成。研究区域的侵蚀速率在一个数量级上变化，从羽毛河峡谷峡谷的> 250 mm ka（-1）到邻近低起伏高原的< 15 mm ka（-1）。结果表明，坡面沉积物的粗度随坡度和侵蚀速率的增大而增大。我们假设，在我们的土壤样品中，当坡度从0.38 m m（-1）增加到0.83 m m（-1）时，测量到的D-50增加了10倍，大于1 mm的碎片数量增加了一倍，这是由于岩石碎片的停留时间减少，导致颗粒暴露在可以减小粒度的过程中的时间缩短。对于超过0.7 m m（-1）的斜坡，滑坡和碎石锥向河流提供更粗的沉积物，D-50和D-84比土壤中大一个数量级以上。在羽毛河的支流流域，一个显着的坡折发展，以响应羽毛河的快速切割。在坡折的下游，河流沉积物粒度增加，这是由于流动能力的增加（主要是由通道变陡驱动）以及沉积物来源和沉积物动力学的变化：在坡折上游的高原上，河流运输容易流动的细颗粒沉积物，这些沉积物完全来自土壤。在坡折带的下游，质量浪费过程提供了各种各样的颗粒大小，河流选择性地夹带，这取决于它们的流动能力。我们的研究结果还表明，在这个研究地点，山坡迅速响应基准面降低率的增加相比，河流。
The characteristics of the sediment transported by rivers (e.g. sediment flux, grain size distribution GSD) dictate whether rivers aggrade or erode their substrate. They also condition the architecture and properties of sedimentary successions in basins. In this study, we investigate the relationship between landscape steepness and the grain size of hillslope and fluvial sediments. The study area is located within the Feather River basin in northern California, and studied basins are underlain exclusively by tonalite lithology. Erosion rates in the study area vary over an order of magnitude, from > 250 mm ka(-1) in the Feather River canyon to < 15 mm ka(-1) on an adjacent low-relief plateau. We find that the coarseness of hillslope sediment increases with increasing hillslope steepness and erosion rates. We hypothesise that, in our soil samples, the measured 10-fold increase in D-50 and doubling of the amount of fragments larger than 1 mm when slope increases from 0.38 to 0.83 m m(-1) is due to a decrease in the residence time of rock fragments, causing particles to be exposed for shorter periods of time to processes that can reduce grain size. For slopes in excess of 0.7 m m(-1), landslides and scree cones supply much coarser sediment to rivers, with D-50 and D-84 more than one order of magnitude larger than in soils. In the tributary basins of the Feather River, a prominent break in slope developed in response to the rapid incision of the Feather River. Downstream of the break in slope, fluvial sediment grain size increases, due to an increase in flow competence (mostly driven by channel steepening) as well as a change in sediment source and in sediment dynamics: on the plateau upstream of the break in slope, rivers transport easily mobilised fine-grained sediment derived exclusively from soils. Downstream of the break in slope, mass wasting processes supply a wide range of grain sizes that rivers entrain selectively, depending on the competence of their flow. Our results also suggest that, in this study site, hillslopes respond rapidly to an increase in the rate of base-level lowering compared to rivers.