Storage-discharge characteristics of an alpine active rock glacier
catchment – a multidisciplinary approach applied to the Innere Ölgrube,
The active rock glacier “Innere Ölgrube”, and its catchment area
(Ötztal Alps, Austria) are assessed using various hydro(geo)logical
tools to provide a thorough catchment characterization and to quantify
temporal variations in recharge and discharge components. During the
period from June 2014 to July 2018, an average contribution derived from
snowmelt, ice melt and rainfall of 35,8 %, 27,6 % and 36,6 %,
respectively, is modelled for the catchment using a rainfall-runoff
model. Discharge components of the rock glacier springs are
distinguished using isotopic data as well as other natural and
artificial tracer data, when considering the potential sources rainfall,
snowmelt, ice melt and groundwater. Seasonal as well as diurnal
variations in runoff are quantified and the importance of shallow
groundwater within this rock glacier-influenced catchment is emphasized.
Water derived from ice melt is suggested to be provided mainly by
melting of two small cirque glaciers within the catchment and
subordinately by melting of permafrost ice of the rock glacier. The
active rock glacier is characterized by a layered internal structure
with an unfrozen base layer responsible for groundwater storage and
retarded runoff, a main permafrost body contributing little to the
discharge (at the moment) by permafrost thaw and an active layer
responsible for fast lateral flow on top of the permafrost body.
Snowmelt contributes at least 1/3rd of the annual recharge. During
droughts, meltwater derived from two cirque glaciers provides runoff
with diurnal runoff variations; however, this discharge pattern will
change as these cirque glaciers will ultimately disappear in the future.
The storage-discharge characteristics of the investigated active rock
glacier catchment are an example of a shallow groundwater aquifer in
alpine catchments that ought to be considered when analysing (future)
river runoff characteristics in alpine catchments as these provide
retarded runoff during periods with little or no recharge.