Quantitative metrics that describe river deltas and their channel networks
Quantitative metrics that describe river deltas and their channel networks
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DOI：
10.1029/2010jf001955
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发表时间：
2011-11-16
影响因子：
3.9
通讯作者：
Sheets, Ben A.
中科院分区：
文献类型：
--
作者：
Edmonds, Douglas A.;Paola, Chris;Sheets, Ben A.
人口稠密的河流三角洲正在以惊人的速度失去土地，为了成功地恢复这些环境，我们必须了解它们的形态细节。为此，我们提出了一套五个指标，描述三角洲形态：（1）分形维数，（2）岛屿大小的分布，（3）最近的边缘距离，（4）在海岸线的沉积物通量的综合分布，（5）营养区。最近边缘距离是从三角洲上给定位置到渠化或非渠化水的最短距离，类似于支流网络中排水密度的倒数。营养区是由来自给定河道横截面的沉积物供应的下游三角洲区域，类似于支流网络中的集水区。作为第一步，我们将这些指标应用到四个相对简单的，河流为主的三角洲网络。对于所有这些三角洲，平均最近边距离是非常恒定的，这表明网络组织自己以保持到最近通道的一致距离。营养区的分布可以从河口坝三角洲生长模型预测，也与通道的宽度和最长通道的长度成比例，类似于哈克定律的流域。四个三角洲通道网络是分形的，但幂律和尺度不变性似乎比支流网络更不普遍。因此，三角洲可能占据完全相似和完全不相似之间的有利中间地带，其中形态差异指示不同的行为。
Densely populated river deltas are losing land at an alarming rate and to successfully restore these environments we must understand the details of their morphology. Toward this end we present a set of five metrics that describe delta morphology: (1) the fractal dimension, (2) the distribution of island sizes, (3) the nearest-edge distance, (4) a synthetic distribution of sediment fluxes at the shoreline, and (5) the nourishment area. The nearest-edge distance is the shortest distance to channelized or unchannelized water from a given location on the delta and is analogous to the inverse of drainage density in tributary networks. The nourishment area is the downstream delta area supplied by the sediment coming through a given channel cross section and is analogous to catchment area in tributary networks. As a first step, we apply these metrics to four relatively simple, fluvially dominated delta networks. For all these deltas, the average nearest-edge distances are remarkably constant moving down delta suggesting that the network organizes itself to maintain a consistent distance to the nearest channel. Nourishment area distributions can be predicted from a river mouth bar model of delta growth, and also scale with the width of the channel and with the length of the longest channel, analogous to Hack's law for drainage basins. The four delta channel networks are fractal, but power laws and scale invariance appear to be less pervasive than in tributary networks. Thus, deltas may occupy an advantageous middle ground between complete similarity and complete dissimilarity, where morphologic differences indicate different behavior.