The Effects of Dams on Watershed Fragmentation and Riparian Disconnectivity Across Multiple Scales

大坝对多尺度流域破碎化和河岸断层的影响

• 批准号: 0724348
• 负责人: Francis Magilligan
• 金额: $ 31.5万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0724348&HistoricalAwards=false
• 关键词: Effects; Dams; Watershed; Fragmentation; Riparian

More than 80,000 dams exist in the U.S., and the proliferation of large dams for hydropower and flood control has led to significant hydrologic, geomorphic, and ecological adjustments in river systems. Recent geomorphic research has documented profound and sustained changes resulting from flow regulation, including changes in channel properties, sediment transport, and reduced channel complexity leading to impaired ecological habitat both within the channel and across the broader riparian zone. Several important research questions have emerged concerning the magnitude and direction of impacts across lateral and longitudinal scales caused by the interactive effects of flow regulation and the progressive downstream tributary inputs of both water and sediment. This research project will focus on subwatersheds of the Connecticut River valley, an area significantly affected by historical flow regulation and impoundment by both flood control and hydroelectric dams. The investigators will quantify (1) the length scale of impact of impoundment laterally across floodplains and progressively downstream of dams; (2) the geomorphic adjustments associated with tributary inputs; and (3) the changes in riparian community structure resulting from impoundment and downstream flow contributions. The project specifically focuses on the length scale of impact imposed by these dams through their associated flow reductions, their resulting changes to the sediment discharge regime by reservoir trapping, and the combined interactive effects of dams on sediment transport and storage as well as flow, especially as part of the progressive downstream inputs of water and sediment by tributaries. Through the use of fallout radionuclides, especially 210-Pb inventories on floodplains, stage-discharge flow modeling, and riparian vegetation sampling, this project will quantify the increased connectivity downstream of dams associated with increased tributary flow. To capture the effect of tributary inputs on sediment discharge, a field design will be employed to measure (1) the activity of 7-Be as a fingerprinting of sediment and (2) changes in bed elevation along the longitudinal profile. The gradient and aggradational adjustments then will be linked to the sediment residence time through the use of 7-Be.This research project will elucidate the links between hydrologic changes in flow and inundation patterns, sediment inputs, and ecological responses. Results from this research can be used as a template to gage the lateral and longitudinal impacts of impoundment and can thus help provide the approaches for ecological amelioration. Moreover, from a geomorphic perspective, the project results will help ascertain the morphologic structure of watersheds and the fundamental ways that tributary inputs influence mainstem characteristics in both regulated and unregulated conditions.

美国现有8万多座水坝，用于水电和防洪的大型水坝的激增导致了河流系统在水文、地貌和生态方面的重大调整。最近的地貌研究记录了水流调节引起的深刻和持续的变化，包括河道性质、泥沙输送的变化，以及河道复杂性的降低，导致河道内和更广泛的河岸带的生态生境受损。一些重要的研究问题出现在横向和纵向尺度上的影响的大小和方向上，这些影响是由水流调节和下游支流输入水和泥沙的递进相互作用造成的。这项研究项目将集中在康涅狄格河流域的次流域，该地区受到历史上流量调节和防洪大坝和水电大坝蓄水的显著影响。研究人员将量化(1)蓄水横向跨越泛滥平原并逐渐向大坝下游的影响的长度规模；(2)与支流输入相关的地貌调整；以及(3)蓄水和下游径流贡献导致的河岸群落结构的变化。该项目特别侧重于这些大坝通过其相关的流量减少而造成的影响的长度和规模、由此产生的水库截流对排沙制度的改变，以及大坝对泥沙运输和储存以及水流的综合互动影响，特别是作为支流逐渐向下游输入水和泥沙的一部分。通过使用沉降物放射性核素，特别是洪泛平原上的210-铅库存，阶段排放水流模拟和河岸植被采样，该项目将量化与支流增加相关的大坝下游连通性增加的情况。为了捕捉支流输入对泥沙流量的影响，将采用现场设计来测量(1)作为泥沙指纹的7-Be的活性和(2)沿纵向剖面的河床高程变化。然后，通过使用7-BE，将坡度和沉积调整与泥沙停留时间联系起来。这项研究项目将阐明水流的水文变化与淹没模式、泥沙输入和生态响应之间的联系。这项研究的结果可以作为测量蓄水横向和纵向影响的模板，从而有助于为生态改善提供途径。此外，从地貌的角度来看，项目成果将有助于确定流域的形态结构，以及支流输入在调节和非调节条件下影响干流特征的基本方式。