A COMPARATIVE STUDY OF SNOWMELT-DRIVEN WATER BUDGETS IN ADJACENT ALPINE BASINS, NIWOT RIDGE, COLORADO FRONT RANGE
Saddle basin is not fed by an extensive seasonal snowpack, but records indicate ablation-season discharge is still closely related to snowmelt in the basin. Martinelli shelters a ~6m thick snowpatch in 8 ha of the basin, even in a low snow year. During much of the ablation season, snowpack mass density (ρ) is 0.5g cm-3 and ablation rates are ~100mm day-1. Since vegetation is shallow-rooted or nonexistent in Martinelli, evapotranspiration (ET) may not be a major factor. Saddle is more heavily vegetated, but only the lower reaches are wooded; ET may be as much as 260mm. Runoff during 2012 was ~270mm yr-1 at Martinelli and ~35mm at Saddle. By monitoring snowpack area changes and longitudinal discharge, we were able to demonstrate that at low flow at least 30% of snowmelt discharge at Martinelli and over 50% at Saddle becomes subsurface flow and is unrecorded by the gages. We believe similar hydrologic budgeting can be applied to a wide range of small alpine catchments with similar “losing stream” characteristics.