RAPID: The effects of extreme drought on sediment transport and deposition in water-supply reservoirs

美国西南部正在经历一场极端干旱，导致河流系统的流量减少，供水水库的水位创历史新低。例如，新墨西哥州格兰德河上的象丘水库截至10月的蓄水量仅为5.6%，暴露出一个大楔形的沉积物，该沉积物在2021年夏季向水库内额外延伸了1公里。在干旱期间，山洪暴发是水进入水库的主要方式。山洪暴发带来的泥沙流可能在水库中积聚，进一步降低水库的容量。该项目将收集具有时效性的数据，以评估极端干旱对水资源收支、河流沉积物运输和水库沉积的影响。 该项目将培训一名研究生在现场，实验室方法和数值模拟的整合。该研究可应用于沿海地区发生的类似过程，并将有助于在西部河流走廊的湿地放水和管理方面做出复杂的决策。格兰德河流域的严重干旱导致在进入象丘水库的入口处出现了一个三角洲。在2021年的干旱年份，春季融雪受到抑制，风暴事件引发的山洪成为泥沙进入水库的主要机制。这些暴洪衍生的沉积物在进入水库后积聚，形成湖泊三角洲，与海洋三角洲不同，湖泊三角洲通常经历超密度流动。在2021年7月季风驱动的山洪期间的初步研究表明，增加的沉积物和有机碳运输影响了事件期间的地貌和生态。这个快速项目将确定干旱河流三角洲系统中驱动山洪沉积物运输和形态动力学的机制，并确定极端干旱如何放大这些过程。该研究还将对象丘水库三角洲系统进行数值模拟，以评估由高沉积物山洪驱动的水下三角洲的地貌变化，这也将为这种快速扩张的三角洲的碳固存潜力提供信息。拟议的研究涉及2022年冬季和春季的两次实地活动，以收集水和河床物质样本，通道几何形状，速度和水位测量，三角洲前缘的图像以及电导率，温度和深度传感器的铸件。这些数据将被纳入流体动力学和沉积物输运模型Delft3D，以高分辨率模拟山洪期间的沉积物输运和沉积过程，这在水库环境中从未实现过。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

The southwestern U.S. is experiencing an extreme drought that is reducing flow in river systems and producing record low levels in water-supply reservoirs. For example, the Elephant Butte Reservoir on the Rio Grande River in New Mexico was only 5.6% full as of October, exposing a large wedge of sediment that has extended an additional 1 km into the reservoir during the summer of 2021. During the drought, flash floods are the principal means by which water enters the reservoir. Flash floods bring sediment-laden flows that can accumulate in the reservoir and reduce the capacity further. This project will collect time-sensitive data to assess impacts of the extreme drought on water budgets, river sediment transport, and reservoir sedimentation. The project will train one graduate student in the integration of field, laboratory methods, and numerical modeling. The research has applications to similar processes occurring in coastal regions and will help in making complex decisions on water release and management of wetlands in western river corridors. The severe drought in the Rio Grande River basin has caused a delta to emerge at the entrance into the Elephant Butte Reservoir. During the drought year of 2021, spring snowmelt was subdued, and flash floods from storm events became the predominant mechanism for sediment transport into the reservoir. These flash flood-derived sediments accumulate upon entering reservoirs to form a lacustrine delta, which unlike marine deltas, typically experience hyperpycnal flows. Initial research during a monsoon-driven flash flood in July 2021 indicate that heightened sediment and organic carbon transport affected the geomorphology and ecology during the event. This RAPID project will identify the mechanisms driving flash flood sediment transport and morphodynamics in arid fluvio-deltaic systems and determine how extreme drought amplifies these processes. The research will also numerically model the Elephant Butte Reservoir deltaic system to evaluate geomorphic changes in the subaqueous delta driven by highly sediment-laden flash floods, which will also inform the carbon sequestration potential of such rapidly prograding deltas. The proposed research involves two field campaigns in the winter and spring of 2022 to collect water and bed material samples, channel geometry, velocity, and water level measurements, images of the delta front, and casts of a conductivity, temperature, and depth sensor. The data will be incorporated into the hydrodynamics and sediment transport model Delft3D to simulate sediment transport and deposition processes during a flash flood at high resolution, which has never been done in a reservoir setting.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.