NSF-BSF: Monitoring bedload transport: Advancing seismic and acoustic surrogate methods in ephemeral channels

河流中的水流，特别是在洪水期间，输送沙子、砾石、岩石，甚至巨石。泥沙的这种运动(输沙)塑造了河道本身，影响了河床和堤岸的侵蚀，并有助于塑造更广阔的地貌。然而，测量推移质输运是困难的，因为它在空间和时间上都变化很快，在大多数物质移动的高能洪水期间收集数据可能非常危险。该项目将试验新的测量技术，这些技术可以在河道外安全地进行。调查人员将比较放置在河岸附近的地震传感器收集的振动和声能，与放置在河床中的物理采样器收集的推移质输运的直接测量结果。采样将在新墨西哥州、美国和以色列的半干旱地区的两条短暂溪流进行，这两条溪流通常是干燥的，但在山洪暴发期间流动时会输送大量物质。该项目产生的数据将用于测试和扩展推移质运动如何产生地震能量的模型，这将使希望以非侵入性方法监测河流和推移质过程的科学家的广泛受众受益。此外，由于了解推移质如何移动对河流管理至关重要，研究结果将有助于美国填海局和美国陆军工程公司等水管理机构。该项目还培训了不同的美国和国际学生在水文学、地震学和地貌学方面，项目团队包括来自美国、以色列、法国和德国的专家。泥沙通量是河流动态和景观演变的基础，但由于其时空变异性以及在高能环境(例如沙漠山洪)中采样而不改变运输的挑战，这一关键参数的代表性测量的收集受到了限制。替代方法是一种很有前途的方法，但校准仍然是一个挑战，检测的颗粒尺寸下限是不确定的。该项目将利用已建的基础设施直接测量推移质运移，使用这些数据来校准声学替代物，然后使用这两种数据来校准和测试推移质运移的地震监测。这种方法将通过检验推移质地震能量产生的理论模型，为旱地河流地震学和泥沙输运模拟的发展提供重要的现场数据。研究地点是新墨西哥州、美国和以色列半干旱地区的短暂河道，在那里河床槽采样器将监测海峡中多个地点的推移质流量。这些数据将被用于校准配置的管道麦克风，这些麦克风在整个洪水过程中收集数据。一组约70-80个短周期的三分量地震检波器将采集航道附近的地震数据，然后将其与直接和声波推移质数据进行比较。在接下来的几年里，还将沿着河道系统部署地震仪，以研究整个流域的泥沙运动。数据收集和分析将完善对地球半干旱和干旱地区富沙砾石运输的总体理论框架。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The flow of water in rivers, especially during floods, transports sand, gravel, rocks, and even boulders. This movement of particles (bedload transport) shapes the river channel itself, influences the erosion of bed and banks, and helps give shape to the broader landscape. Measuring bedload transport is difficult, though, because it changes rapidly in both space and time and can be quite dangerous to collect data during the high-energy flood events when most material moves. This project will experiment with new measurement techniques that can be done safely outside of the river channel. The investigators will compare the vibration and sound energy collected by seismic sensors placed near the river bank with direct measurements of bedload transport collected by physical samplers set into the riverbed. Sampling will take place on two ephemeral streams in semi-arid regions of New Mexico, USA and Israel, streams which are usually dry, but which transport a great deal of material when they do flow during flash floods. The data generated by this project will be used to test and expand models of how bedload movement generates seismic energy, which will benefit a wide audience of scientists who want non-invasive methods to monitor river and bedload processes. In addition, because understanding how bedload moves is critical for river management, the results will assist water management agencies such as the US Bureau of Reclamation and the US Army Corp of Engineers. This project also trains diverse US and international students in hydrology, seismology, and geomorphology, with a project team that includes experts from the US, Israel, France, and Germany. Bedload flux is fundamental to river dynamics and landscape evolution, yet the collection of representative measurements of this key parameter is inhibited by its spatial and temporal variability as well as the challenge of sampling in high-energy environments (for example, desert flash floods) without altering transport. Surrogate methods are a promising approach, yet calibration remains a challenge, and the lower grain size limit of detection is uncertain. This project will take advantage of already-built infrastructure to directly measure bedload transport, use these data to calibrate acoustic surrogates, and then use both of these to calibrate and test seismic monitoring of bedload transport. This approach will provide vital field data to enable the advance of fluvial seismology and sediment transport modeling in drylands by testing theoretical models of bedload seismic energy generation. The study sites are ephemeral channels in semi-arid regions of New Mexico, USA, and Israel, at which riverbed slot samplers will monitor bedload flux at multiple locations across the channel. These data will be used to calibrate collocated pipe microphones that collect data throughout the flood. An array of ~ 70-80 short period, 3-component geophone seismometers will collect seismic data near the channel, which will then be compared with the direct and acoustic bedload data. In subsequent years, seismometers will also be deployed along the channel system to study the movement of bedload throughout an entire catchment. The data collection and analysis will refine the overarching theoretical framework of understanding for the transport of sand-rich gravel in semiarid and arid regions of our planet.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.