Garber Schlag (Q-GS) is one of the major springs of the Karwendel Mountains, Tyrol, Austria. This spring has a unique runoff pattern that is mainly controlled by the tectonic setting. The main ...aquifer is a moderately karstified and jointed limestone of the Wetterstein Formation that is underlain by nonkarstified limestone of the Reifling Formation, which acts as an aquitard. The aquifer and aquitard of the catchment of spring Q-GS form a large anticline that is bound by a major fault (aquitard) to the north. Discharge of this spring shows strong seasonal variations with three recharge origins, based on δ
18
O and electrical conductivity values. A clear seasonal trend is observed, caused by the continuously changing portions of water derived from snowmelt, rainfall and groundwater. At the onset of the snowmelt period in May, the discharge is composed mainly of groundwater. During the maximum snowmelt period, the water is dominantly composed of water derived from snowmelt and subordinately from rainfall. During July and August, water derived from snowmelt continuously decreases and water derived from rainfall increases. During September and October, the water released at the spring is mainly derived from groundwater and subordinately from rainfall. The distinct discharge plateau from August to December and the following recession until March is likely related to the large regional groundwater body in the fissured and moderately karstified aquifer of the Wetterstein Formation and the tectonic structures (anticline, major fault). Only a small portion of the water released at spring Q-GS is derived from permafrost.
Rock glaciers are the most prominent landforms of alpine permafrost and comprise complex shallow aquifer systems in (high) alpine catchments. Recession analyses of groundwater discharge of four ...active rock glaciers that contain permafrost ground ice show that they have a base flow component of the order of a few liters per second, similar to that of a relict rock glacier in which permafrost ground ice is absent. This is related to an unfrozen (fine-grained) base layer with a thickness of about 10 m. Based on a threshold analysis of precipitation events and event water discharge, depressions atop the bedrock or the permafrost table seem to play only a minor role in storing groundwater. This important finding has rarely been documented, but is highly relevant for optimal groundwater resources management in sensitive (high) alpine catchments and ecosystems. All the rock glaciers analyzed here are located in the Austrian Alps and represent the nationwide sites where suitable discharge data are available. The analysis highlights the hydrogeological importance of these discrete permafrost-derived debris accumulations as complex shallow groundwater bodies with important—but limited—storage and buffer capabilities.
More than 2,600 relict rock glaciers are known in the Austrian Alps but the knowledge of their hydraulic properties is severely limited. The relict Schöneben Rock Glacier (Niedere Tauern Range, ...Austria), with an extension of 0.17 km
2
, was investigated based on spring data (2006–2014) and seismic refraction survey. Spring-discharge hydrographs and natural and artificial tracer data suggest a heterogeneous aquifer with a layered internal structure for the relict rock glacier. The discharge behavior exhibits a fast and a delayed flow component. The spring discharge responds to recharge events within a few hours but a mean residence time of several months can also be observed. The internal structure of the rock glacier (up to several tens of meters thick) consists of: an upper blocky layer with a few meters of thickness, which lacks fine-grained sediments; a main middle layer with coarse and finer-grained sediments, allowing for fast flow; and an approximately 10-m-thick basal till layer as the main aquifer body responsible for the base flow. The base-flow component is controlled by (fine) sandy to silty sediments with low hydraulic conductivity and high storage capacity, exhibiting a difference in hydraulic conductivity to the upper layer of about three orders of magnitude. The high storage capacity of relict rock glaciers has an impact on water resources management in alpine catchments and potentially regulates the risk of natural hazards such as floods and related debris flows. Thus, the results highlight the importance of such aquifer systems in alpine catchments.
Rock glaciers (RG) are landforms that occur in high latitudes or elevations and — in their active state — consist of a mixture of rock debris and ice. Despite serving as a form of groundwater ...storage, they are an indicator for the occurrence of (former) permafrost and therefore carry significance in the research for the ongoing climate change. For these reasons, the past years have shown rising interest in the establishment of RG inventories to investigate the extent of permafrost and quantify water storages. Creating these inventories, however, usually involves manual, laborious, and subjective mapping of the landforms based on aerial image - and digital elevation model analysis. We propose an approach for RG mapping based on supervised machine learning which can help to increase the mapping efficiency and permits rapid RG mapping in vast and not yet covered areas. We found deep convolutional artificial neural networks (ANN) that are specifically designed for image segmentation (U-Net architecture) to be well suited for this classification problem. The general workflow consists of training the ANNs with orthophotos and slope maps of digital elevation models as input. The output (RG label-maps) is derived from a recently published RG inventory of the Austrian Alps that features 5769 individual RGs and was compiled manually by several scientists. To increase the generalization capabilities, we use live data augmentation during training. Based on this inventory, the ANNs have learned the average expert opinion and the RG map generated by the ANN can be used to increase the consistency and completeness of already existing RG inventories. Moreover, this ANN approach might be valuable for other landform mapping tasks beyond rock glaciers (e.g., other mass movements).
•Artificial neural network based rock glacier mapping support.•Tool to aid mapping of vast areas by delineating rock glacier suspected landforms.•U-Net based image segmentation of orthophotos and digital elevation models.•Deriving average expert opinions by learning from whole rock glacier inventories.
Rock glaciers are capable of storing water in solid (permafrost ice) as well as in liquid form (groundwater within the unfrozen base layer). The latter is relevant no matter the actual state of the ...rock glacier (intact, containing ice versus relict, no more ice present). A nation-wide comparison of the water equivalent of glacier ice within the Austrian Alps is conducted to evaluate the role of rock glaciers in the hydrological cycle at its current state and potentially in the future. Estimates of ice volumes and their uncertainties, especially related to thickness estimates of permafrost-ice bodies, are discussed in the light of available data and need to be seen as order-of-magnitude estimates. With intact rock glaciers covering almost 123 km2 and an assumed ice content of 40% within the permafrost body, ice volumes are estimated to be 0.93 Gigatons. This corresponds to 8.3% of the ice volume estimated for the most recent glacier inventory of the Austrian Alps. Thus, with the currently available data, a water equivalent ratio of ~1: 12 for rock glacier ice versus glacier ice is estimated.
In addition to the solid water storage, the dynamic storage potential within rock glaciers in liquid form needs to be considered. While this volume is relatively small compared to the ice volume in glaciers and rock glaciers (ratio of ~1: 20), the time-scales of hydrological relevance (when they become runoff due to ice melt) are very different. This dynamic liquid water storage is replenishable and therefore available over shorter time scales (seasonal drainage pattern), and moreover relatively stable and may potentially even slightly increase as pore space becomes available due to increased melting of permafrost ice.
In the light of climate warming and projected glacier recession, the relative hydrological importance of rock glaciers as water stores (in solid as well as in liquid form) in the European Alps is expected to increase and their storage-discharge patterns need to be accounted for in water management considerations.
Display omitted
•Intact rock glaciers store 1/12th of glacier ice volume as permafrost ice.•The unfrozen base layer of rock glaciers may store 1/20th of the total ice water equivalents.•Potential liquid water storages in rock glaciers are replenished seasonally.•Mean residence times of liquid water storages are in the order of months.•Liquid water storage capacities are relatively stable and outlasting ice stores.
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 longer stored 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.
Seasonal variations in input (“recharge”) and output (discharge) of an active rock glacier catchment are quantified by rainfall‐runoff modelling and analysing natural and artificial tracer data; thereby contributing to a better understanding of storage‐discharge characteristics of high alpine catchments that ought to be considered when analysing (future) river runoff from alpine catchments. The provided steady baseflow and delayed release of water within such catchments is crucial to understand and critical to sustain ecological diversity in the light of climate change.
A multidisciplinary approach focusing on the integration of diverse and non-invasive investigations is presented to define the hydrogeological conceptual model of the complex Fontana Cornia landslide ...in the Northern Apennines, Italy. The results of seismic refraction tomography and electrical resistivity tomography investigations indicate that the landslide has a curvilinear sliding surface dividing the shallow calcarenite debris layer from the deeper pelitic bedrock. The surface presents undulations in which water can be stored and supports the application of the fill and spill hypothesis that is seldom used in landslide studies. The joint interpretation of the geophysical outcomes and of the hydrogeological and hydro-chemical analyses of a spring located on the slope allows the definition of the landslide hydrogeological conceptual model. Four specific hydrologic stages with different groundwater flows though the landslide body were identified. The developed hydrogeological model may explain the displacements of the landslide that were detected with In-SAR monitoring. The isotopes analyses, the displacement monitoring, and the hydrogeological measurements confirm that periods with significant precipitations and snowmelt can cause an increase in landslide saturation that in turn triggers larger displacements. Conversely, the landslide slowly moves at a steady rate during periods with limited recharge water.
The validity and applicability of various methods to infer hydraulic properties of sloping aquifers in alpine settings using the power law relationship between the discharge recession and its first ...time derivative is explored. For this purpose, a synthetic spring catchment implemented in the numerical groundwater flow model MODFLOW as well as the example of a relict rock glacier in an alpine setting is examined. The various approaches are found to differ particularly in the late time domain, whereas most of them agree fairly well in the early time domain and at the transition point between the two time domains. As the early recession may be affected by uncertainties from inappropriate initial conditions, it is proposed to use the transition point for estimating aquifer thickness and transmissivity. Using only prolonged winter recessions in the analysis of the field data from the relict rock glacier yields estimates of aquifer thickness and hydraulic conductivity consistent with results from a geophysical survey and tracer tests, respectively. In the other seasons, the recession is frequently interrupted by minor recharge events, and using the lower envelope of the entire data is found to yield estimates that are too high in the given case. It is thus recommended to focus on the winter recession in the analysis of hydrograph data from alpine settings.
Key Points:
Analytical solutions are compared to a numerical model for sloping aquifers
Estimated hydraulic properties for steep slopes are in a reasonable range
No kinematic wave condition observable at steeply sloping relict rock glacier
Relict rock glaciers are complex hydrogeological systems that might act as relevant groundwater storages; therefore, the discharge behavior of these alpine landforms needs to be better understood. ...Hydrogeological and geophysical investigations at a relict rock glacier in the Niedere Tauern Range (Austria) reveal a slow and fast flow component that appear to be related to the heterogeneous structure of the aquifer. A numerical groundwater flow model was used to indicate the influence of important internal structures such as layering, preferential flow paths and aquifer-base topography. Discharge dynamics can be reproduced reasonably by both introducing layers of strongly different hydraulic conductivities or by a network of highly conductive channels within a low-conductivity zone. Moreover, the topography of the aquifer base influences the discharge dynamics, which can be observed particularly in simply structured aquifers. Hydraulic conductivity differences of three orders of magnitude are required to account for the observed discharge behavior: a highly conductive layer and/or channel network controlling the fast and flashy spring responses to recharge events, as opposed to less conductive sediment accumulations sustaining the long-term base flow. The results show that the hydraulic behavior of this relict rock glacier and likely that of others can be adequately represented by two aquifer components. However, the attempt to characterize the two components by inverse modeling results in ambiguity of internal structures when solely discharge data are available.
PDF
