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，携带着沙子、砾石、岩石甚至巨石。这种颗粒运动（河床搬运）塑造了河道本身，影响了河床和河岸的侵蚀，并有助于塑造更广阔的景观。然而，测量河床搬运是困难的，因为它在空间和时间上都迅速变化，而且在大多数物质移动的高能洪水事件期间收集数据是相当危险的。这个项目将试验新的测量技术，这些技术可以在河道外安全地完成。研究人员将把放置在河岸附近的地震传感器收集到的振动和声能，与放置在河床上的物理采样器收集到的直接测量的河床负载移动量进行比较。采样将在美国新墨西哥州和以色列半干旱地区的两条短暂的河流上进行，这些河流通常是干燥的，但在山洪暴发期间流动时，它们会携带大量物质。该项目产生的数据将用于测试和扩展河床运动如何产生地震能量的模型，这将使希望采用非侵入性方法监测河流和河床过程的广大科学家受益。此外，由于了解河床如何移动对河流管理至关重要，因此研究结果将有助于美国垦务局和美国陆军工程兵团等水管理机构。该项目还培养了水文学、地震学和地貌学方面的美国和国际学生，项目团队包括来自美国、以色列、法国和德国的专家。河床通量是河流动态和景观演变的基础，但这一关键参数的代表性测量值的收集受到其时空变异性以及在不改变运输的高能环境（例如沙漠山洪暴发）中采样的挑战的抑制。替代方法是一种很有前途的方法，但校准仍然是一个挑战，并且检测的最低粒度限制是不确定的。该项目将利用已建成的基础设施直接测量床质输运，利用这些数据校准声波代替物，然后使用这两种方法校准和测试床质输运的地震监测。这种方法将提供重要的现场数据，通过测试河床地震能量产生的理论模型，使河流地震学和干旱地区的沉积物运输模型取得进展。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跨河道多个地点的河床通量。这些数据将用于校准在整个洪水过程中收集数据的管道麦克风。一个由70-80个短周期3分量检波器组成的地震仪阵列将在水道附近收集地震数据，然后将这些数据与直接和声波层载数据进行比较。在其后数年，地震仪亦会沿水道系统布设，以研究整个集水区河床的移动情况。数据收集和分析将完善总体理论框架的理解，在我们的星球的半干旱和干旱地区的富砂砾石运输。该奖项反映了美国国家科学基金会的法定使命，并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，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.