Geomorphic change and sediment transport during a small artificial flood in a transformed post-dam delta: The Colorado River delta, United States and Mexico
Geomorphic change and sediment transport during a small artificial flood in a transformed post-dam delta: The Colorado River delta, United States and Mexico
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DOI：
10.1016/j.ecoleng.2016.08.009
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发表时间：
2017-09
影响因子：
3.8
通讯作者：
E. Mueller;J. Schmidt;D. Topping;P. Shafroth;J. E. Rodríguez‐Burgueño;J. Ramírez-Hernández;P. Grams-P.-G
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文献类型：
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作者：
E. Mueller;J. Schmidt;D. Topping;P. Shafroth;J. E. Rodríguez‐Burgueño;J. Ramírez-Hernández;P. Grams-P.-G
科罗拉多河三角洲是一个戏剧性的转变景观。1936年胡佛大坝建成后，河流水文和形态动力学开始发生重大变化。今天，科罗拉多河在其以前的三角洲的大部分地区有一个间歇性和/或短暂的通道。在20世纪40年代初，在沉积物供应急剧减少的条件下，胡佛大坝的溢洪道泄流导致三角洲上游约150 km的河道出现初始切割。随后是一段相对平静的时期，直到20世纪80年代和90年代上游水库的蓄水促使流向三角洲的水流复苏。20世纪80年代极端上游流域融雪期间的流量释放，1993年吉拉河流域的洪水，以及20世纪90年代末和21世纪初一系列不断下降的峰值流量进一步切割了上游河道，并导致整个河流走廊的大量河道迁移。这些不同量级的坝后洪水塑造了现代河流地貌。2014年，一项旨在恢复河岸生态系统和了解水文动力学的实验性脉冲流释放在三角洲河流走廊的长度上流动了100多公里。这场小型的人工洪水造成了河床的局部米级冲刷和填充，但由于规模较小，没有造成进一步的切割或显著的河岸侵蚀。悬浮泥沙输运率最初相对较高，直接下游的莫雷洛斯大坝释放点，但减少排放的渗透损失与渠道拓宽下游造成的快速下游减少悬浮泥沙输运率。美国南部下游出现了一个增强的运输区-墨西哥边界，坡度增加，但实际上在莫雷洛斯大坝下游65 km以外的地方没有发生地貌变化。因此，虽然脉冲流与现代河口连接，三角洲沉积过程没有恢复，相对较少的新的开放面创建本地河岸植被的建立。由于科罗拉多河流域的水是完全分配的，因此在可预见的未来，来自吉拉河流域的异常洪水是三角洲地貌发生重大变化的最有可能的机制。
The Colorado River delta is a dramatically transformed landscape. Major changes to river hydrology and morpho-dynamics began following completion of Hoover Dam in 1936. Today, the Colorado River has an intermittent and/or ephemeral channel in much of its former delta. Initial incision of the river channel in the upstream ∼50 km of the delta occurred in the early 1940s in response to spillway releases from Hoover Dam under conditions of drastically reduced sediment supply. A period of relative quiescence followed, until the filling of upstream reservoirs precipitated a resurgence of flows to the delta in the 1980s and 1990s. Flow releases during extreme upper basin snowmelt in the 1980s, flood flows from the Gila River basin in 1993, and a series of ever-decreasing peak flows in the late 1990s and early 2000s further incised the upstream channel and caused considerable channel migration throughout the river corridor. These variable magnitude post-dam floods shaped the modern river geomorphology. In 2014, an experimental pulse-flow release aimed at rejuvenating the riparian ecosystem and understanding hydrologic dynamics flowed more than 100 km through the length of the delta’s river corridor. This small artificial flood caused localized meter-scale scour and fill of the streambed, but did not cause further incision or significant bank erosion because of its small magnitude. Suspended-sand-transport rates were initially relatively high immediately downstream from the Morelos Dam release point, but decreasing discharge from infiltration losses combined with channel widening downstream caused a rapid downstream reduction in suspended-sand-transport rates. A zone of enhanced transport occurred downstream from the southern U.S.-Mexico border where gradient increased, but effectively no geomorphic change occurred beyond a point 65 km downstream from Morelos Dam. Thus, while the pulse flow connected with the modern estuary, deltaic sedimentary processes were not restored, and relatively few new open surfaces were created for establishment of native riparian vegetation. Because water in the Colorado River basin is completely allocated, exceptional floods from the Gila River basin are the most likely mechanism for major changes to delta geomorphology for the foreseeable future.