Complexity in a cellular model of river avulsion
Complexity in a cellular model of river avulsion
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DOI：
10.1016/j.geomorph.2007.04.022
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发表时间：
2007-11-01
期刊：
影响因子：
3.9
通讯作者：
Paola, Chris
中科院分区：
文献类型：
--
作者：
Jerolmack, Douglas J.;Paola, Chris
我们提出了一种新的河流撕裂模型，该模型强调简单、自组织和非编程行为，而不是详细的模拟。该模型在固定单元格线上运行，并追踪每个单元中的两个高程，高高程表示渠道(堤坝)顶部，低高程表示渠道底部。在达到撕裂的超高阈值之前，通道一直在原地移动。在撕裂被触发后，根据低的高程值通过最陡峭的下降来选择新的流动路径。水流路径敏感地取决于泛滥平原的地形，特别是以前废弃的河道的存在。从这个简单的模型中可以看出几个一致的行为特征：(1)活动水流在很长一段时间内在少数几条河道路径之间切换的趋势，我们称之为活动河道集，导致沉积中多层砂体的聚集和形成；(2)被撕裂的河道返回到以前的路径，从而往往在相对较短的区段中产生新的河道长度；(3)与撕裂有关的沉积物储存和释放，即使在持续输入的情况下，也会导致脉冲沉积物输出。这些行为中的每一种都与从沉积河流系统中观察到的一致。单值阈值会产生各种各样的撕裂大小和样式。更大的“节点”撕裂更罕见，因为先前存在的泛滥平原地形将水流引导回活跃的河道。河道堆积方式对滩地沉积非常敏感。这项工作突出表明，需要在大的时间和空间尺度上开发滩地演变模型，以补充改进的河道演变模型。(C)2007 Elsevier B.V.保留所有权利。
We propose a new model of river avulsion that emphasizes simplicity, self-organization, and unprogrammed behavior rather than detailed simulation. The model runs on a fixed cellular grid and tracks two elevations in each cell, a high elevation representing the channel (levee) top and a low one representing the channel bottom. The channel aggrades in place until a superelevation threshold for avulsion is met. After an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation. Flow path depends sensitively on floodplain topography, particularly the presence of former abandoned channels. Several behavioral characteristics emerge consistently from this simple model: (1) a tendency of the active flow to switch among a small number of channel paths, which we term the active channel set, over extended periods, leading to clustering and formation of multistory sand bodies in the resulting deposits; (2) a tendency for avulsed channels to return to their previous paths, so that new channel length tends to be generated in relatively short segments; and (3) avulsion-related sediment storage and release, leading to pulsed sediment output even for constant input. Each of these behaviors is consistent with observations from depositional river systems. A single-valued threshold produces a wide variety of avulsion sizes and styles. Larger "nodal" avulsions are rarer because pre-existing floodplain topography acts to steer flow back to the active channel. Channel stacking pattern is very sensitive to floodplain deposition. This work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution. (C) 2007 Elsevier B.V. All rights reserved.