Hydrograph separation of a sub-arctic glacial watershed, Interior Alaska

Abstract:

Glacier melt affect several Alaska rivers and thus far, the contribution to larger-scale watershed runoff has attracted limited attention, and in particular, a quantitative assessment. Geochemically-based hydrograph separation techniques in combination with glacier mass balance and runoff measurements can help refine our understanding of the contributing sources and therefore, support the refinement of both short-term flood forecasts and long-term runoff projections. Our study was designed to quantify the contribution of glacier melt, snow melt and rainfall to lowland streamflow of a sub-arctic basin and to assess hydrologic pathways of glacier wastage. Jarvis Creek watershed (634 km²), Interior Alaska, drains the north-facing Eastern Alaska Range, starting at the Jarvis Glacier (6.7 km²) and flows 69 km to its outlet in the Delta River, Delta Junction. Glacial contribution accounts for at least 15% of total runoff as estimated from measured glacier melt and lowland runoff. Daily stable water isotope samples near the Jarvis Creek outlet show distinct chemical signatures in contributing sources and large seasonal and interannual δ¹⁸O variability. For example, geochemical measurements from 2011 show low rainfall contribution into Jarvis Creek, whereas 2014 show high input of rainfall; and, unlike 2014, spring 2013 show a strong snowmelt contribution in late spring. Stable water isotopes will be the primary signature to inform our end-member volumetric mixing modeling efforts, while dissolved ion concentrations will support a differentiation between glacier- and groundwater sources. Ultimately, the combination of glacier mass balance, hydrological and geochemical measurements will allow us to gain a fundamental knowledge about the current regional hydrologic system.