Quantifying Lateral Flow of Water in Alpine Snowpacks Using High Resolution Geophysical Techniques

利用高分辨率地球物理技术量化高山积雪中的水的横向流动项目摘要除了降雪的固有变异性外，风的重新分配和辐射平衡的变化都会导致融雪输入地面的时间和位置的巨大空间变异性。然而，即使考虑到这些主要驱动力，基于物理的水文模拟也是具有挑战性的，这表明可能还有其他过程控制着积雪融化进入地下的时间和地点。大多数融雪模型将积雪视为均匀的，并假设所有融化的水垂直移动到地面。许多实验表明，积雪融化在积雪中遵循一条复杂的路径，既沿地层边界横向移动，又在集中的圆柱形水道中垂直移动。虽然已经开发了理论方法来解释地层和垂直优先流动路径等非均质性，但由于缺乏基于现场的定量测量，这些方法并未在实践中应用。我们认为，融化和雨雪事件期间液态水的横向运动可能是陡峭、以雪为主的集水区水分再分配的重要机制。积雪中的水流是一种复杂且鲜为人知的现象。渗透率边界导致长距离的斜面平行横向流动，再加上圆柱形的垂直熔体路径，导致在斜率尺度上有很大的空间变异性。更好地了解雪中水的横向流动将对一系列问题产生影响，包括：1)雨落雪事件，有可能导致洪水和山体滑坡。积雪提供了大量融化的水，并可能为雨水进入溪流提供一条更快的途径。2)定量地了解积雪在季节性积雪中融化的时间和位置是必要的，以便评估在融雪为主的盆地中横向流动在季节性过程线上的重要性；3)量化雪中的横向流动对于估计融水从极地冰盖和冰川进入海洋的旅行时间是重要的，而这反过来又是预测海平面上升时间尺度的基础。了解雨雪期间横向流动的重要性对于预测洪水、湿雪雪崩和山体滑坡非常重要，因为在气候变暖的情况下，仲冬雨可能会变得更加常见。这个项目将利用我们机构内部已经存在的最先进的地球物理工具来量化高山积雪中的横向水流。这些措施包括：1)对控制水力传导性的微结构敏感的测量；2)快速、无损地测量积雪地层、深度、雪水当量以及雪和下伏土壤的液态水含量；以及3)直接原位测量液态水含量。这些测量，结合示踪剂实验，将被用来描述导致侧向流动的微尺度积雪条件。详细的雪和土壤特性将被用来估计初始模型条件下的水文特性。现场数据将被用来建立实验山坡的水文模型(使用HYDRUS2D)，以评估融雪为主的集水区雪和土壤中横向径流的相对重要性。

Quantifying lateral flow of water in alpine snowpacksusing high resolution geophysical techniquesPROJECT ABSTRACTIn addition to inherent variability in falling snow, both wind redistribution and variations in radiation balance cause large spatial variability in the timing and location of input of snowmelt to the ground. However, even when these major drivers are accounted for, physically based hydrologic modeling is challenging, suggesting that there may be other processes controlling when and where snowmelt enters the subsurface. Most snowmelt models treat the snowpack as homogeneous, and assume that all meltwater moves vertically to the ground. Numerous experiments have shown that snowmelt follows a complicated path through the snowpack, moving both laterally along stratigraphic boundaries and vertically in concentrated cylindrical channels. While theoretical approaches have been developed to account for heterogeneities such as stratigraphy and vertical preferential flow paths, they are not applied in practice due to a lack of quantitative field-based measurements.We suggest that lateral movement of liquid water during melt and rain-on-snow events can be an important mechanism of water redistribution in steep, snow-dominated catchments. Flow of water within snowpacks is a complicated and poorly understood phenomenon. Permeability boundaries cause slope-parallel lateral flow over large distances, and coupled with cylindrical, vertical melt pathways, there is a resulting large spatial variability at the slope scale. An improved understanding of the lateral flow of water in snow will have impacts for a broad range of problems including: 1) rain-on-snow events which have the potential to cause flooding and landslides. The snowpack provides a large mass of water to melt, and may provide a faster route for the rainwater to enter streams. 2) A quantitative understanding of the timing and location of snowmelt within the seasonal snowpack is necessary in order to evaluate the importance of lateral flow on the seasonal hydrograph in snowmelt-dominated basins, and 3) quantifying lateral flow in snow is important for estimating the travel-time of meltwater traveling from polar ice caps and glaciers to the ocean which in turn is a basis for predicting time scales of sea level rise. Understanding the importance of lateral flow during rain-on-snow is important for forecasting floods, wet snow avalanches, and landslides, as mid-winter rain may become more common in a warming climate.This project will leverage state-of-the-art geophysical tools that already exist in-house at our institution to quantify lateral flow of water in alpine snowpacks. These include 1) measurements sensitive to microstructure which controls hydraulic conductivity, 2) rapid, non-destructive methods for measuring snow stratigraphy, depth, snow water equivalent, and liquid water content of both snow and the underlying soil, and 3) direct in-situ measurements of liquid water content. These measurements, combined with tracer experiments, will be used to characterize the snowpack conditions at the microscale that lead to lateral flow. The detailed snow and soil characterization will be used to estimate hydrologic properties for initial model conditions. Field data will be used to develop hydrologic models (using HYDRUS2D) of the experimental hillslopes to evaluate the relative importance of lateral flow in snow and soil in snowmelt-dominated catchments.