An investigation on the development of liquid water content in different snow types during slushflow-inducing weather conditions

Abstract

Slushflows, defined as rapid mass-movements of water-saturated snow, occur when high liquid water content (LWC) causes bonds to melt and the snowpack to lose cohesion, triggering flow. Characterized by their shallow release angles and the potential for extensive runouts, slushflows typically occur during rain- on-snow events or due to significant melting. The presence of an impermeable layer beneath or within the snowpack is normally required for water to accumulate.

An important consideration for the improvement of slushflow prediction is understanding the role snow type has on the development of LWC in the snowpack. To assess this, LWC was measured in snow profiles before and during weather events conducive to slushflow occurrence, using an SLF Snow Sensor. In addition, the SLF sensor was evaluated as a tool to measure LWC and compared with the traditional hand wetness test.

Results indicate that the formation of preferential flow is important for water transport in snow. While precipitation particles and decomposing, fragmented particles may facilitate preferential flow, ripe melt forms tend to promote matrix flow. Thick ice layers can impede vertical water movement and redirect it laterally. Volume and rate of water supply may be as important as grain form in determining the mode of flow.

Comparisons between LWC estimated using the hand wetness test and values from the SLF Snow Sensor align with existing literature, attesting to the efficacy of the hand wetness test as a qualitative method for assessing LWC, especially for internal comparison. When precise values are required, the hand wetness test is insufficient, and use of the SLF Snow Sensor is more suitable. The requirement for an external density measurement to calculate LWC significantly increases the workload.