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首页> 外文期刊>Geological Society of America Bulletin >The rate and pattern of bed incision and bank adjustment on the Colorado River in Glen Canyon downstream from Glen Canyon Dam,1956-2000
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The rate and pattern of bed incision and bank adjustment on the Colorado River in Glen Canyon downstream from Glen Canyon Dam,1956-2000

机译：1956-2000年格伦峡谷大坝下游格伦峡谷的科罗拉多河上河床切缝和河床调整的速度和方式

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Closure of Glen Canyon Dam in 1963 transformed the Colorado River by reducing the magnitude and duration of spring floods,increasing the magnitude of base flows,and trapping fine sediment delivered from the upper watershed.These changes caused the channel downstream in Glen Canyon to incise,armor,and narrow.This study synthesizes over 45 yr of channel-change measurements and demonstrates that the rate and style of channel adjustment are directly related to both natural processes associated with sediment deficit and human decisions about dam operations.Although bed lowering in lower Glen Canyon began when the first cofferdam was installed in 1959,most incision occurred in 1965 in conjunction with 14 pulsed high flows that scoured an average of 2.6 m of sediment from the center of the channel.The average grain size of bed material has increased from 0.25 mm in 1956 to over 20 mm in 1999.The magnitude of incision at riffles decreases with distance downstream from the dam,while the magnitude of sediment evacuation from pools is spatially variable and extends farther downstream.Analysis of bed-material mobility indicates that the increase in bed-material grain size and reduction in reach-average gradient are consistent with the transformation of an adjustable-bed alluvial river to a channel with a stable bed that is rarely mobilized.Decreased magnitude of peak discharges in the post-dam regime coupled with channel incision and the associated downward shifts of stage-discharge relations have caused sandbar and terrace erosion and the transformation of previously active sandbars and gravel bars to abandoned deposits that are no longer inundated.Erosion has been concentrated in a few pre-dam terraces that eroded rapidly for brief periods and have since stabilized.The abundance of abandoned deposits decreases downstream in conjunction with decreasing magnitude of shift in the stage-discharge relations.In the downstream part of the study area where riffles controlling channel elevation have not incised,channel narrowing has resulted from decreased magnitude of peak discharges and minor post-dam deposition.These physical changes to the aquatic and riparian systems have supported the establishment and success of an artifact ecosystem dominated by non-native species.Models for the channel response downstream from large dams typically consider factors such as the degree of sediment deficit,the pre-dam surface and subsurface grain size,and the magnitude of post-dam average flows.These results suggest that it is also necessary to consider (1) the possibility of variable responses among different channel elements and (2) the potential importance of exceptional flows resulting from management decisions.
机译：1963年格伦峡谷大坝的关闭减少了春季洪水的数量和持续时间，增加了基流的数量，并截留了从上游流域输送来的细沙，改变了科罗拉多河。这些变化导致格伦峡谷的下游河道切开，这项研究综合了超过45年的河道变化测量结果，证明了河道调整的速率和方式与与泥沙淤积和人类对大坝运行的决策有关的自然过程都直接相关。峡谷始于1959年安装第一座围堰时，大多数切口于1965年发生，并伴有14条脉冲高流量，从河道中心冲刷出平均2.6 m的沉积物。床层材料的平均粒度从0.25增加到从1956年的1毫米减少到1999年的20毫米以上。沉积物从池中的排泄量在空间上是可变的，并且向下游延伸得更远。床层物质迁移率分析表明，床层物质粒度的增加和河床平均梯度的减小与可调节床冲积河向河床的转化是一致的。大坝后政权的高峰流量下降，加上河道切口以及相关的水位流量关系的下移，导致了沙坝和梯田侵蚀以及先前活动的沙坝和河道的转变。废弃的沉积物不再被淹没的碎石棒。侵蚀集中在几个大坝前阶地，这些阶地在短时间内迅速侵蚀并稳定下来。下游的废弃沉积物减少，并且阶段位移减小排放关系。在研究区的下游，浅滩控制通道高海拔尚未切开，峰流量减少和坝后沉积减少导致了河道变窄。这些对水生和河岸系统的物理变化支持了以非本地物种为主的人工生态系统的建立和成功。大型大坝下游的河道响应通常考虑诸如泥沙淤积程度，大坝前表面和地下颗粒大小以及大坝后平均流量的大小等因素。这些结果表明，也有必要考虑（1 ）不同渠道要素之间可能做出不同反应的可能性;（2）由管理决策产生的异常流动的潜在重要性。

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