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

美国有8万多座水坝，用于水力发电和防洪的大型水坝的激增导致了河流系统的重大水文、地貌和生态调整。最近的地貌学研究记录了水流调节导致的深刻而持续的变化，包括河道性质的变化、泥沙运输和河道复杂性的降低，导致河道内和更广泛的河岸带的生态栖息地受损。关于水流调节和下游支流的水沙输入的相互作用所造成的横向和纵向影响的大小和方向，出现了几个重要的研究问题。该研究项目将重点关注康涅狄格河流域的地下水流域，这是一个受历史流量调节和洪水控制和水力发电大坝蓄水影响显著的地区。研究人员将量化(1)横向跨越洪泛平原和水坝下游的蓄水影响的长度尺度；(2)与支流输入有关的地貌调整；(3)蓄水和下游流量对河岸群落结构的影响。该项目特别侧重于这些水坝通过其相关的流量减少所施加的影响的长度尺度，它们通过水库捕获而导致的沉积物排放制度的变化，以及水坝对沉积物运输和储存以及流量的综合互动影响，特别是作为支流逐步向下游输入水和沉积物的一部分。通过使用放射性沉降核素，特别是在洪泛区进行的210-Pb清查、阶段排放流量建模和河岸植被采样，该项目将量化与支流流量增加相关的水坝下游连通性增加。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)作为沉积物指纹的7-Be的活性和(2)沿着纵剖面的床高程变化。然后，通过使用7-Be，将梯度和累积调整与沉积物停留时间联系起来。该研究项目将阐明水流和淹没模式、泥沙输入和生态响应的水文变化之间的联系。本研究的结果可以作为衡量蓄水的横向和纵向影响的模板，从而有助于提供生态改善的方法。此外，从地貌学的角度来看，项目结果将有助于确定流域的形态结构以及支流输入在管制和不管制条件下影响主要特征的基本方式。

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.