Spatial and Temporal Distribution of Water in Snow and Soil During Spring Snowmelt in a Small Watershed in Northwest Colorado

Abstract:

The melting of a winter snowpack will often include spatially and temporally variable infiltration across the soil-snow-interface prior to generating streamflow, groundwater recharge, or plant production. During spring snowmelt, moisture distribution is largely driven by hydraulic gradients under variably saturated conditions within the soil and snowpack. In complex mountainous terrain, the variable melt rates across the landscape due to slope, aspect, and landcover add further irregularities to this dynamic system. The aim of this research is gain insight into the distribution of water both within and below a melting snowpack during spring at Dry Lake Study Site near Steamboat Springs, Colorado. This site is a small (0.2 km²) subalpine watershed with a seasonally persistent snowpack each year. Intensive field surveys were conducted to collect snow water equivalent and soil moisture distribution during April and May of 2014 and 2015. Results show the variability in soil moisture consistent with similar studies, suggesting soil moisture distribution follows a similar trend as accumulation of snow depth in relation to topographic and canopy influences. The soil moisture on south facing hillslopes tended to be less than north facing slopes, with flat terrain holding near saturated conditions, particularly in locations with thick layers of organic matter. However, of notable interest is the distribution of snow water equivalent during melt. Early in the melt period at the base of some hillslopes snow water equivalent increased as locations directly upslope decreased suggesting movement of moisture within the snowpack during the transitional period from winter to spring. The hydraulic conductivity of snow has been shown to be greater than that of common soils, suggesting that the timing of water movement from a snowpack to stream will be shortened when considering the flow through the snow layers compared to shallow groundwater on hillslopes. These results have additional implications on the variability of driving hydraulic gradients for groundwater recharge and stream connectivity. This study displays the importance the snowpack as a layered porous medium for purposes of instrumenting, and developing conceptual models of headwater basins