Influence of sediment supply, lithology, and wood debris on the distribution of bedrock and alluvial channels
Influence of sediment supply, lithology, and wood debris on the distribution of bedrock and alluvial channels
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沉积物供应、岩性和木屑对基岩和冲积河道分布的影响
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
D. Montgomery
中科院分区：
文献类型：
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作者：
Tamara M. Massong;D. Montgomery
华盛顿州威拉帕河流域的实地调查表明，描述基岩和冲积河道分布的流域-河道坡度阈值受到底层岩性的影响，沉积物供应的局部变化可能压倒整个流域的趋势。 90 次短河段调查的现场数据表明，由于堵塞或当地沉积物源或汇的影响，大约八分之一的调查河段不符合自由形成的冲积层和基岩河段数据定义的阈值。 18 个河道宽度大于 100 个河道长度的扩展勘察中的河道类型分布图显示，约 75% 的河道网络是冲积河道，但强制冲积河道的比例从 0% 到 84% 不等。使用由短距离调查的基岩和冲积数据定义的流域面积坡度阈值，在较长勘察中绘制的河道总长度中只有 40% 能够从 10 m 网格数字高程模型中正确分类。在错误分类的河段中，80% 预测为基岩的冲积河道具有强制冲积形态，而几乎一半预测为冲积的基岩河道是由于沉积物供应量低而被迫形成的，通常是因为它们位于大型河道堵塞的下游。数字地形中河段尺度坡度的较差表示和/或沉积波传播的随机影响可能是造成剩余错误分类河道的原因，这些河道总共占了调查河道总长度的 7%。尽管沉积物供应的变化可以局部压倒阈值模型预测的河道类型，但堵塞的影响掩盖了传播沉积物波对威拉帕河流域基岩和冲积河道分布的任何影响。
Field surveys in the Willapa River basin, Washington State, indicate that the drainage area‐channel slope threshold describing the distribution of bedrock and alluvial channels is influenced by the underlying lithology and that local variations in sediment supply can overwhelm basinwide trends. Field data from 90 short-reach surveys indicate that about one-eighth of the surveyed reaches do not conform to a threshold defined by data from free-formed alluvial and bedrock reaches due to the effects of logjams or local sediment sources or sinks. Mapping of channel type distributions in 18 extended reconnaissance surveys of >100 channel widths in channel length show that ~75% of the channel network was alluvial, but that the proportion of forced alluvial channels varies from 0% to 84%. Using the drainage area‐slope thresholds defined by bedrock and alluvial data from the short-reach surveys, only 40% of the total channel length mapped in the longer reconnaissance surveys was correctly classified from a 10 m grid digital elevation model. Of the misclassified reaches, 80% of the alluvial channels predicted to be bedrock had forced alluvial morphologies, while almost half of the bedrock channels predicted to be alluvial were forced by low sediment supply, typically due to their location immediately downstream of large channel-spanning logjams. Poor representation of reach-scale slope in the digital topography and/or a stochastic influence of sediment wave propagation likely account for the remaining misclassified channels, which together compose 7% of the total surveyed channel length. Although variations in sediment supply can locally overwhelm the channel type predicted by the threshold model, the effect of logjams masks any influence of propagating sediment waves on the distribution of bedrock and alluvial channels in the Willapa River basin.