Bedrock channel geometry along an orographic rainfall gradient in the upper Marsyandi River valley in central Nepal
Bedrock channel geometry along an orographic rainfall gradient in the upper Marsyandi River valley in central Nepal
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DOI：
10.1029/2006jf000589
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发表时间：
2007-07-25
影响因子：
3.9
通讯作者：
Gabet, Emmanuel J.
中科院分区：
文献类型：
--
作者：
Craddock, William H.;Burbank, Douglas W.;Gabet, Emmanuel J.
明显的降雨梯度结合第四纪时间尺度上岩石的均匀剥露和均匀的岩石强度，使尼泊尔中部的Marsyandi河上游河谷成为一个有用的天然实验室，用于探索基岩通道宽度的变化。我们关注的是小流域（0.6-12.4 km（2）），沿着季风降雨的十倍以上的梯度。降雨数据收集从一个密集的天气网络和校准的卫星观测，第四纪折返的模式推断磷灰石裂变径迹冷却年龄，并在现场测量岩石抗压强度。在高冲刷指标下测量的基岩河道宽度，其比例为流量的幂律函数（w α Q（w）（0.38）（+/-）（0.09）），通过结合降雨数据和90 m数字地形进行估算。结果表明，幂律宽度缩放模型适用于（1）具有明显降雨梯度的地区，（2）分布在气候多样性地区的支流集水区，（3）大型，快速剥蚀的造山带。对降雨数据的分析表明，在驱动侵蚀性排放事件的风暴期间，降雨的区域梯度大约是同一地区季节性降雨梯度的一半。最后，数值模型中，最大降雨量是从上游下游位移显着预测一个midcatchment区的相对快速下降的渠道梯度和增加渠道的排水量，是由当地增强放电。由于差异性的岩石抬升可以产生类似的梯度变化，因此在进行构造推断之前，应评估降雨梯度的影响。
Pronounced rainfall gradients combined with spatially uniform exhumation of rocks at Quaternary timescales and uniform rock strength make the upper Marsyandi River valley in central Nepal a useful natural laboratory in which to explore variations in bedrock channel width. We focus on small catchments (0.6-12.4 km(2)) along a more than tenfold gradient in monsoon rainfall. Rainfall data are gathered from a dense weather network and calibrated satellite observations, the pattern of Quaternary exhumation is inferred from apatite fission track cooling ages, and rock compressive strength is measured in the field. Bedrock channel widths, surveyed at high scour indicators, scale as a power law function of discharge (w alpha Q(w)(0.38) (+/-) (0.09)) that is estimated by combining rainfall data with 90-m digital topography. The results suggest that power law width scaling models apply ( 1) to regions with pronounced rainfall gradients, ( 2) to tributary catchments distributed across a climatically diverse region, and ( 3) to large, rapidly denuding orogens. An analysis of rainfall data indicates that the regional gradient of rainfall during storms that drive erosive discharge events is about half as large as the gradient of seasonal rainfall across the same area. Finally, numerical models in which the maximum rainfall is displaced significantly downstream from the headwaters predict a midcatchment zone of relatively rapid decreases in channel gradient and increases in channel concavity that are driven by locally enhanced discharge. Because differential rock uplift can produce analogous changes in gradients, the influence of rainfall gradients should be assessed before tectonic inferences are drawn.