Near-surface permeability in a supraglacial drainage basin on the Llewellyn Glacier, Juneau Icefield, British Columbia

Supraglacial channel networks link time varying melt production and meltwater routing on temperate glaciers. Such channel networks often include components of both surface transport in streams and subsurface porous flow through near-surface ice, firn or snowpack. Although subsurface transport if present will likely control network transport efficacy, it is the most poorly characterized component of the system. We present measurements of supraglacial channel spacing and network properties on the Juneau Icefield, subsurface water table height, and time variation of hydraulic characteristics including diurnal variability in water temperature. We combine these data with modeling of porous flow in weathered ice to infer near-surface permeability. Estimates are based on an observed phase lag between diurnal water temperature variations and discharge, and independently on measurement of water table surface elevation away from a stream. Both methods predict ice permeability on a 1–10 m scale in the range of 10−10–10−11 m2. These estimates are considerably smaller than common parameterizations of surface water flow on bare ice in the literature, as well as smaller than most estimates of snowpack permeability. For supraglacial environments in which porosity/permeability creation in the subsurface is balanced by porous flow of meltwater, our methods provide an estimate of microscale hydraulic properties from observations of supraglacial channel spacing.

Raw project data is available by contacting [e-mail]

冰面河道网络（supraglacial channel networks）将温带冰川上随时间动态变化的融水生成量与融水输运路径紧密关联。这类河道网络通常兼具两类组分：一是河道内的地表输运过程，二是近表层冰、粒雪（firn）或积雪中的地下多孔介质渗流。尽管地下输运若存在，大概率会调控整个网络的输运效率，但其却是该系统中特征刻画最为薄弱的组成部分。

本研究针对朱诺冰原（Juneau Icefield）开展观测，采集得到冰面河道间距、河道网络特征、地下水位高度，以及包括水温日变化在内的水力特性的时间演化特征。我们将这些观测数据与蚀变冰（weathered ice）中的多孔渗流模型相结合，以反推近表层渗透率。

渗透率估算基于两个独立的依据：一是观测到的水温日变化与流量（discharge）之间的相位滞后，二是远离河道处的地下水位高程测量结果。两种方法均得到，在1~10米尺度下的冰渗透率范围为10⁻¹⁰~10⁻¹¹ 平方米。该估算结果远小于文献中裸冰地表水流常用的参数化方案，同时也比多数积雪渗透率的估算值更低。

在地下孔隙度/渗透率的生成过程与融水多孔渗流达到动态平衡的冰面环境中，本研究方法可通过冰面河道间距的观测数据，反推得到微尺度水力特性参数。

本项目的原始数据可通过联系[e-mail]获取。