Lateral Flow in Snow as a Runoff Generation Mechanism

Abstract:

Lateral downslope flow in snow during snowmelt and rain-on-snow (ROS) events is a well-known phenomenon, yet its relevance as a runoff generation mechanism and the impacts on soil moisture distribution have received little attention. We used dye tracers, geophysical methods, isotopic studies, and hydrometric measurements to describe the snow properties that promote lateral flow, assess the relative velocities of lateral flow in snow and soil, and estimate volumes of downslope flow in snow. Results demonstrate that rain and melt water can travel tens of meters downslope along layers within the snowpack or at the snowpack base within tens of hours. Lateral flow within the snowpack becomes less likely as the snowpack becomes saturated and stratigraphic boundaries are destroyed. Flow along the base can be prevalent in all snowpack conditions. The net result of lateral flow in snow can be deposition of water on the soil surface in advanced downslope positions relative to its point of origin, or direct discharge to a stream. While both melt and ROS events can redistribute water to downslope positions, ROS events produced the most significant volumes of downslope flow. This can help explain rapid delivery of water to streams during ROS events, as well as anomalously high contributions of event water during snowmelt hydrographs.