Modeled Postglacial Landscape Evolution at the Southern Margin of the Laurentide Ice Sheet: Hydrological Connection of Uplands Controls the Pace and Style of Fluvial Network Expansion
Modeled Postglacial Landscape Evolution at the Southern Margin of the Laurentide Ice Sheet: Hydrological Connection of Uplands Controls the Pace and Style of Fluvial Network Expansion
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DOI：
10.1029/2017jf004509
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发表时间：
2018-05
期刊：
影响因子：
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通讯作者：
Jingtao Lai;A. Anders
中科院分区：
文献类型：
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作者：
Jingtao Lai;A. Anders
美国中部低地的地貌多次受到劳伦泰德冰原的影响。冰川作用降低了地势起伏，扰乱了排水网络。由融水雕刻而成的深谷与周围的高地断开连接。与排水网络没有地表水连接的高地地区被称为非汇水区（NCA）。较古老地表上非汇水区比例的下降表明，非汇水区会随着时间推移而具备排水能力。我们提出，这种整合可能通过以下两种方式发生：（1）当河道向高地延伸时，非汇水区被纳入其中；（2）非汇水区通过地下或间歇性的地表连接与外部排水网络相连，从而增加流量以促进河道下切。由于这两种情况的关键区别在于高地与外部排水系统的水文连接，我们将这两种情况分别称为“断开连接”和“连接”。我们利用数值模拟研究了在断开连接和连接两种情况下，低地势地貌中河道网络在演化和形态上的差异。我们观察到，在连接情况下，河道网络的侵蚀和整合速度要快得多。与断开连接的情况相比，连接情况还会形成更长、更蜿蜒的河道。敏感性测试表明，坡面扩散率对演化和形态几乎没有影响。河流侵蚀系数对演化速度有显著影响，对形态的影响较小。我们的研究结果以及与美国中部低地冰川地貌的定性比较表明，非汇水区的连接是对冰后期地貌演化和形态的一种潜在控制因素。
Landscapes of the U.S. Central Lowland were repeatedly affected by the Laurentide Ice Sheet. Glacial processes diminished relief and disrupted drainage networks. Deep valleys carved by meltwater were disconnected from the surrounding uplands. The upland area lacking surface water connection to the drainage network is referred to as noncontributing area (NCA). Decreasing fractions of NCA on older surfaces suggest that NCA becomes drained over time. We propose that the integration could occur via (1) capture of NCA as channels propagate into the upland or (2) subsurface or intermittent surface connection of NCA to external drainage networks providing increased discharge to promote channel incision. We refer the two cases as “disconnected” and “connected” since the crucial difference between them is the hydrological connection of the upland to external drainage. We investigate the differences in evolution and morphology of channel networks in low‐relief landscapes under disconnected and connected regimes using numerical simulations. We observe substantially faster rates of erosion and integration of the channel network in the connected case. The connected case also creates longer, more sinuous channels than the disconnected case. Sensitivity tests indicate that hillslope diffusivity has little influence on the evolution and morphology. The fluvial erosion coefficient has significant impact on the rate of evolution, and it influences the morphology to a lesser extent. Our results and a qualitative comparison with landscapes of the glaciated U.S. Central Lowland suggest that connection of NCAs is a potential control on the evolution and morphology of postglacial landscapes.