Glacier Hydrology Research Articles

Radio-echo soundings on Icelandic temperate glaciers: history of techniques and findings

AbstractSince the mid-1970s radio-echo soundings have been conducted on Iceland's temperate glaciers. Since then, low-frequency radar technology has furthered the study of most of the island's ice caps. Their masses and volumes have been quantified and detailed subglacial topographic maps produced which demarcate glacial drainage basins and identify subglacial lakes and volcanoes. Even internal tephra layers have been charted. The resulting data have been used to force and validate models of past and future glacier evolution. Many practical applications in glacier hydrology have come into being, including hydropower management, road and bridge planning and the prediction of catastrophic flood paths from subglacial eruption sites. Finally, emerging landscapes can now be foreseen in places where glaciers may soon disappear. These achievements would not have been possible without the advances in RES technology.

How rock glacier hydrology, deformation velocities and ground temperatures interact: Examples from the Swiss Alps

AbstractAn increasing number of studies highlight the controlling influence of water on rock glacier deformation velocities. The link between the concept of water‐driven shearing processes and numerous observations of correlating mean annual air or ground temperatures and rock glacier velocities is discussed here. We present a dataset measured at the Schafberg rock glacier in the Eastern Swiss Alps, complemented by temperature data from three other rock glaciers in the Swiss Alps, which allowed us to reconstruct the processes influencing both mean annual ground temperatures and rock glacier deformation velocity. Rock glacier hydrology is the parameter linking rock glacier temperature and velocities and is a crucial influencing factor. The main external forcing parameter appart from mean annual air temperature is early winter snow coverage. The study shows that the concept of water being a controlling factor for rock glacier velocity is no contradiction to the observed correlations between air or ground temperature and rock glacier deformation.

Surface and subsurface hydrology of debris-covered Khumbu Glacier, Nepal, revealed by dye tracing

While the supraglacial hydrology of debris-covered glaciers is relatively well studied, almost nothing is known about how water is transported beneath the glacier surface. Here, we report the results of sixteen fluorescent dye tracing experiments conducted in April–May 2018 over the lowermost 7 km of the high-elevation, debris-covered Khumbu Glacier, Nepal, to characterise the glacier's surface and subsurface drainage system. Dye breakthroughs indicated a likely highly sinuous and channelised subsurface hydrological system draining water from the upper part of the ablation area. This flowpath was distinct from the linked chain of supraglacial ponds present along much of the glacier's lower ablation area, through which water flow was extremely slow (∼0.003 ms−1), likely reflecting the study's timing during the pre-monsoon period. Subsurface drainage pathways emerged at the glacier surface close to the terminus, and flowed into small near-surface englacial reservoirs that typically delayed meltwater transit by several hours. We observed rapid pathway changes resulting from surface collapse, indicating a further distinctive aspect of the drainage of debris-covered glaciers. We conclude that the surface and subsurface drainage of Khumbu Glacier is both distinctive and dynamic, and argue that further investigation is needed to refine the characterisation and test its regional applicability to better understand future Himalayan debris-covered glacier meltwater delivery to downstream areas.

The influence of glacier meltwater on the hydrological effect of glacial lakes in Mountain Cryosphere

冰川融水通过热量、水、物质传输对山地冰冻圈冰湖水文效应产生影响，引起广泛关注.本文从山地冰冻圈冰湖的水量、物理化学性质、生物等方面系统总结冰川融水对冰湖水文效应的影响.冰川融水被冰湖滞留能在一定程度上延缓区域冰川水资源的亏损，但也直接导致了潜在危险性冰湖数量和危险程度增大.冰川融水对冰湖物理性质的影响主要表现在降低湖水温度、影响透明度/浊度、改变湖水密度、造成湖水热力分层现象等方面，对冰湖化学性质的影响主要表现在增加湖水中的氮素、溶解有机物、持久性有机污染物、各类离子和重金属等，进而影响冰湖生物的分布、组成、结构和功能.深入系统地开展冰川融水及其变化对冰湖水文效应研究，对冰川水文与水资源、山地冰冻圈生态环境研究具有重要意义.;Much attention has been attracted on the glacier meltwater due to its influence on the hydrological effect of glacial lakes through heat, water and material transmission in Mountain Cryosphere. We summarized the impacts of glacier meltwater on the hydrological effects with respects to the water quantity, physicochemical properties and biology of glacial lake in this paper. A certain amount of glacier water resources has been temporarily held resulted by the meltwater direct inflowing into glacial lakes, which retarded the loss water resources in the glaciated area to some extent on one hand, increased the number and hazardousness of the potential dangerous glacial lakes on the other hand. Glacier meltwater affects both physical and chemical properties of glacial lakes. Meltwater normally reduced lake temperature, disturbed lake transparency/turbidity, and facilitated thermal stratification of the glacial lake. Meltwater also increased the contents of nitrogen, dissolved organic matter, persistent organic pollutants, ion concentrations and heavy metals in the glacial lake water, influenced the distribution, composition, structure and function of glacial lake organisms and ecosystem. An in-depth and systematic research on the impacts of glacier meltwater and its changes on hydrological effect of glacial lakes, is of great significant to the glacier hydrology, water resources and ecological environment study of Mountain Cryosphere.

Interannual variability in glacier contribution to runoff from a high‐elevation Andean catchment: understanding the role of debris cover in glacier hydrology

AbstractWe present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response, and runoff generation from a high‐elevation catchment in central Chile over the period 2000–2015 to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000 and 2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.

Subglacial Conduit Roughness: Insights From Computational Fluid Dynamics Models

AbstractFlow resistance in subglacial conduits regulates the basal water pressure and sliding speeds of glaciers by controlling drainage efficiency and conduit enlargement and closure. Flow dynamics within subglacial conduits, however, remain poorly understood due to limited accessibility. Here we report the results of the first computational fluid dynamics simulations of flow within a realistic subglacial conduit beneath Hansbreen, a polythermal glacier in Svalbard, Norway. The simulated friction factor is 2.34 ± 0.05, which is around 5 to 230 times greater than values (0.01–0.5) commonly used in glacier hydrological modeling studies. Head losses from sinuosity and cross‐sectional variations dominate flow resistance (∼ 94%), whereas surface roughness from rocks and ice features contributes only a small portion (∼6%). Most glacier hydrology models neglect head losses due to sinuosity and cross‐sectional variations and thus severely underestimate flow resistance, overestimating the conduit peak effective pressure by 2 times and underestimating the conduit enlargement area by 3.4 times, respectively.

Simulation of Runoff and Glacier Mass Balance and Sensitivity Analysis in a Glacierized Basin, North-Eastern Qinhai-Tibetan Plateau, China

Glaciers have been recognized as the most sensitive indicators of climate change. Mountainous areas, with their characteristic snow and glacier cover, have long been recognized as special hydrological environments, receiving above-average amounts of precipitation. The streams originating in the mountains, nourished with distinct seasonal variations, provide water for the populations of the adjacent lowland. Little is known about the effect of climate change on snow and glacier hydrology and glacier mass balance in the Laohugou Glacier Basin (LHGB) over the past 50 years. A study of the glacier basin was performed to quantify the expected impact of climate change on the hydrology in the north-eastern Qinghai-Tibet Plateau. The DEM (Digital Elevation Model) data, daily temperature, daily precipitation, and evaporation data were applied to force the HBV (Hydrologiska Byrans Vattenbalansavdelning)-light conceptual model to simulate runoff depth and glacier mass balance in the historical period (1959–2015). A genetic calibration algorithm approach (GAP method) was used to obtain parameter sets that reproduced observed runoff depth well. The results suggested a drastic increase of the runoff depth from 1995 to 2015 in the Laohugou glacier basin driven by increased temperature. Temperature and precipitation increased by 0.40 °C (10a)−1 and 1.6 mm·a−1 (p < 0.01), respectively, at AWS1 (the automatic weather station at 4192 m a.s.l. near the hydrological station) in the LHGB from 1959 to 2015. The simulated runoff depth increased at 5.7 mm·a−1 (p < 0.01), the glacier mass balance (GMB) of the LHGB was −280.5 mm·a−1, and the overall glacier mass balance was −17.55 m w.e. from 1959 to 2015. The runoff is found to be more sensitive to the variation of temperature than the variation of precipitation. When the glacier area is decreased by 10%, 53%, and 100%, the peak runoff (July) decreased by 20.4%, 54.2%, and 72.3% relative to the baseline, respectively. In the future climate, the function of glaciers in compensating a potential low flow and regulating peak flow will be weakened in the critical months.

Split-Window Algorithm for Retrieval of Land Surface Temperature Using Landsat 8 Thermal Infrared Data

Land surface temperature (LST) plays a vital role in global climate change, radiation budgets, heat balance, vegetation, snowmelt, glacier hydrology, and geo-biophysical processes. It is, therefore, essential to determine LST precisely over large areas. With advancements in remote sensing, LST can now be estimated. In this study, a critical appraisal of various LST inversion algorithms is presented. These algorithms include mono-window (MW), split-window (SW), dual-angle (DA), single-channel (SC), and Sabmao method. The main objective is to derive an SW algorithm to retrieve LST from Landsat 8 satellite data and demonstrate the application to the Beas River basin in India. Located within the Himalayan range, the study area is characterized by heterogeneity and rugged terrain with areas covered by snow and glacier. The satellite imagery is a product of the Optical Land Imager (OLI) with a spatial resolution of 30 m and a thermal infrared sensor (TIRS) having a spatial resolution of 100 m. The SW algorithm requires spectral radiance and emissivity from two bands of the TIRS as input for the estimation of LST. The spectral radiance has been estimated using the TIRS bands 10 and 11. The normalized difference vegetation index (NDVI) and the threshold technique of OLI bands (2 to 5) have been used to derive the emissivity. The estimates of LST from the TIRS and OLI bands using the SW algorithm are found to be accurate and close to the in situ air temperature measurements and the LST values obtained from the MW algorithm. Results obtained show that the values of LST are high in the barren/rocky areas and low in the snow/glacier areas. The study reveals that the LST estimates from SW and MW algorithms are linearly transferable with negligible loss of accuracy. The LST estimates from the SW algorithm differs at most by up to 5 °C with the measured air temperature.

Short-lived ice speed-up and plume water flow captured by a VTOL UAV give insights into subglacial hydrological system of Bowdoin Glacier

The subglacial hydrology of tidewater glaciers is a key but poorly understood component of the complex ice-ocean system, which affects sea level rise. As it is extremely difficult to access the interior of a glacier, our knowledge relies mostly on the observation of input variables such as air temperature, and output variables such as the ice flow velocities reflecting the englacial water pressure, and the dynamics of plumes reflecting the discharge of meltwater into the ocean. In this study we use a cost-effective Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) to monitor the daily movements of Bowdoin Glacier, north-west Greenland, and the dynamics of its main plume. Using Structure-from-Motion photogrammetry and feature-tracking techniques, we obtained 22 high-resolution ortho-images and 19 velocity fields at the calving front for 12 days in July 2016. Our results show a two-day-long speed-up event (up to 170%) – caused by an increase in buoyant subglacial forces – with a strong spatial variability revealing that enhanced acceleration is an indication of shallow bedrock. Further, we used the Particle Image Velocimetry (PIV) method to analyze water flow from successive UAV images taken while flying over the main plume of the glacier. We found that PIV successfully captures the area of radially diverging flow of the plume, and provides information on spatial and time variability as no other remote sensing technique can. Most interestingly, the active part of the plume features pulsating water jets at the time scale of seconds, and is 1 to 5 times smaller than its visual footprint defined by the iceberg-free area. Combined with an ice flow model or a non-steady plume model, our approach has the potential to generate a novel set of input data to gather information about the depth of the bedrock, the discharge of meltwater, or the subglacial melting rate of tidewater glaciers.

Near‐surface hydraulic conductivity of northern hemisphere glaciers

AbstractThe hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day−1, with a mean of 0.185 ± 0.019 m day−1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.

Glacier retreat and its impact on summertime run‐off in a high‐altitude ungauged catchment

AbstractGlaciers are significant freshwater storage systems in western China and contribute substantially to the summertime run‐off of many large rivers in the Tibetan Plateau. Under the scenario of climate change, discussions of glacier variability and melting contributions in alpine basins are important for understanding the run‐off composition and ensuring that water resources are adequately managed and protected in the downstream areas. Based on the multisource spatial data and long‐term ground observation of climatic and hydrologic data, using the remote sensing interpretation, degree‐day model, and ice volume method, we presented a comprehensive study of the glacier changes in number, area, and termini and their impacts on summertime run‐off and water resource in the Tuotuo River basin, located in the source region of the Yangtze River. The results indicated that climate change, especially rising temperature, accelerated the glacier melting and consequently led to hydrological change. From 1969 to 2009, the glacier retreat showed an absolutely dominant tendency with 13 reduced glaciers and lost glacier area of 45.05 km2, accompanied by limited growing glaciers in the study area. Meanwhile, it indicated that annual glacial run‐off was averagely 0.38 × 108 m3, accounting for 4.96% of the total summertime run‐off, followed by the supply from precipitation and snowmelt. The reliability of this magnitude was assessed by the classic volume method, which also showed that the water resources from glacier melting in the Tuotuo River basin increased by approximate 17.11 × 108 m3, accounting for about 3.77% of the total run‐off over the whole period of 1969–2009. Findings from this study will serve as a reference for future research about glacier hydrology in regions where observational data are deficient. Also, it can help the planning of future water management strategies in the source region of the Yangtze River.

Hydrological controls on glacially exported microbial assemblages

AbstractThe Greenland Ice Sheet (GrIS) exports approximately 400 km3 of freshwater annually to downstream freshwater and marine ecosystems. These meltwaters originate in a wide range of well‐defined habitats that can be associated with very different physical environments within the ice sheet, ranging from oxygenated surface environments that are exposed to light and supplied with nutrients from atmospheric/aeolian sources to subglacial environments that are permanently dark, isolated from the atmosphere, and potentially anoxic. Hydrological conditions in the latter likely favor prolonged rock‐water contact. The seasonally evolving hydrological system that drains meltwaters from the GrIS connects these distinct microbial habitats and exports the microbes contained within them to downstream ecosystems. The microbial assemblages exported in glacier meltwater may have an impact on downstream ecosystem function and development. We explored how the seasonal development of a glacial drainage system influences the character of microbial assemblages exported from the GrIS by monitoring the seasonal changes in hydrology, water chemistry, and microbial assemblage composition of meltwaters draining from a glacier in southwest Greenland. We found that the microbial assemblages exported in meltwaters varied in response to glacier hydrological flow path characteristics. Whether or not meltwaters passed through the subglacial environment was the first‐order control on the composition of the microbial assemblages exported from the glacier, while water source (i.e., supraglacial or extraglacial) and subglacial residence times were second‐order controls. Glacier hydrology therefore plays a fundamental role in determining the microbial exports from glaciated watersheds.

Impact of Climate Change on Water Resources in View of Contribution of Runoff Components in Stream Flow: A Case Study from Langtang Basin, Nepal

Observation and model-based studies suggest substantial hydrological flow pattern changes in mountain watershed where hydrology is dominated by cryospheric processes (IPCC 2007). The response of cryospheric processes to warming climate in mountain areas can be analysed by examining the responses in the seasonal and annual hydrologic regimes of rivers where snowmelt contributes significantly to the runoff. This study is carried out in Langtang basin, which aims to assess the impact of potential warming on snowmelt contribution and river discharge utilizes a Snowmelt Runoff Model (SRM), which is one of a very few models in the world today that requires remote sensing derived snow cover data as a model input. In this study, snow cover and hydrometric data were derived from Moderate Resolution Imaging Spectro-radiometer (MODIS) snow product and Snow and Glacier Hydrological Unit (SGHU) of Department of Hydrology and Meteorology, Government of Nepal. The model is calibrated for the year 2006 and validated in 2005. Different climatic scenarios are used (only change in temperature) to run the model in order to understand the impact of changing climate on runoff component and river discharge. In 2006, snow and glacier melt component contributes 35% in winter, 18% in summer and 19% annually in the stream flow. In this study, model predicts that snow and glacier melt contribution in stream flow will increase approximately at the rate of 2% in winter, 5% in summer and 4% in annual flow per 1°C temperature rise. Due to increase in snowmelt contribution, river discharge will also increase at the rate of 2% in winter, 6% in summer and 5% in annual flow under the projected temperature rise of 1°C.Journal of Hydrology and Meteorology, Vol. 9(1) 2015, p.74-84

Morphological dynamics of an englacial channel

Abstract. Despite an interest in the hydraulic functioning of supraglacial and englacial channels over the last 4 decades, the processes and forms of such ice-bounded streams have remained poorly documented. Recent glaciological research has demonstrated the potential significance of so-called "cut-and-closure" streams, where englacial or subglacial flow paths are created from the long-term incision of supraglacial channels. These flow paths are reported to exhibit step-pool morphology, comprising knickpoints and/or knickzones, exaggerated in dimensions in comparison to supraglacial channels. However, little is known of the development of such channels' morphology. Here, we examine the spatial organisation of step pools and the upstream migration of steps, many of which form knickzones, with repeated surveys over a 10-year period in an englacial conduit in cold-based Austre Brøggerbreen, Svalbard. The observations show upstream step recession to be the dominant process for channel evolution. This is paralleled by an increase in average step height and conduit gradient over time. Characteristic channel-reach types and step-riser forms are consistently observed in each of the morphological surveys reported. We suggest that the formation of steps has a hydrodynamic origin, where step-pool geometry is more efficient for energy dissipation than meanders. The englacial channel system is one in rapid transition towards a quasi-equilibrium form within a decadal timescale. The evolution and recession of knickzones reported here result in the formation of a 37 m deep moulin shaft, suggesting that over time an incising supraglacial channel may evolve towards an englacial channel form exhibiting a stable end-point characterised by a singular vertical descent, which potentially can reach the glacier bed. This challenges the prevailing notions that crevasses or hydrofractures are needed to form deep moulins. Our observations highlight the need to further examine the adjustment processes in cut-and-closure channels to better understand their coupling to supraglacial meltwater sources and potential significance in cold-based glacier hydrology and ice dynamics.

Inversion of a glacier hydrology model

ABSTRACTThe subglacial hydrologic system exerts strong controls on the dynamics of the overlying ice, yet the parameters that govern the evolution of this system are not widely known or observable. To gain a better understanding of these parameters, we invert a spatially averaged model of subglacial hydrology from observations of ice surface velocity and outlet stream discharge at Kennicott Glacier, Wrangell Mountains, AK, USA. To identify independent parameters, we formally non-dimensionalize the forward model. After specifying suitable prior distributions, we use a Markov-chain Monte Carlo algorithm to sample from the distribution of parameter values conditioned on the available data. This procedure gives us not only the most probable parameter values, but also a rigorous estimate of their covariance structure. We find that the opening of cavities due to sliding over basal topography and turbulent melting are of a similar magnitude during periods of large input flux, though turbulent melting also exhibits the greatest uncertainty. We also find that both the storage of water in the englacial system and the exchange of water between englacial and subglacial systems are necessary in order to explain both surface velocity observations and the relative attenuation in the amplitude of diurnal signals between input and output flux observations.

Numerical simulation of the flow velocity and change in the future of the SG4

Based on glacier dynamic theory, a two-dimensional velocity field model is developed to apply for the Qilian Shuiguan River glacier no. 4 (SG4). Our analysis shows that the glacier bedrock slope and shape affect the ice flow velocity together. The hydrological parameter k was adjusted in the model to fit the measured average flow velocities in summer and winter. The simulated results show that parameter k has a considerable impact on the glacier surface velocity, indicating that the water pressure under the glacier’s base is a major factor leading to basal sliding and ice velocity. The simulation shows that the glacier thickness, bedrock slope, bedrock shape, and basal slide jointly effect the glacier movement. The annual average mass balance was used to forecast the changes over the next 50 years based on the continuity equation. The results forecast the shrinkage of nearly 400 m in the terminus and glacier area over the next 50 years; the longitudinal section will diminish by nearly 29.2 %, and the average thickness will decrease by 47 %. If the effective glacier hydrology and geothermal temperature changes are taken into account, the actual retreat will be more substantial than that shown in our model.

Stable oxygen isotope variability in two contrasting glacier river catchments in Greenland

Abstract. Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of δ18O variations in Greenlandic rivers, we examined two contrasting glacierised catchments disconnected from the Greenland Ice Sheet (GrIS). At the Mittivakkat Gletscher river, a small river draining a local temperate glacier in southeast Greenland, diurnal oscillations in δ18O occurred with a 3 h time lag to the diurnal oscillations in run-off. The mean annual δ18O was −14.68 ± 0.18 ‰ during the peak flow period. A hydrograph separation analysis revealed that the ice melt component constituted 82 ± 5 % of the total run-off and dominated the observed variations during peak flow in August 2004. The snowmelt component peaked between 10:00 and 13:00 local time, reflecting the long travel time and an inefficient distributed subglacial drainage network in the upper part of the glacier. At the Kuannersuit Glacier river on the island Qeqertarsuaq in west Greenland, the δ18O characteristics were examined after the major 1995–1998 glacier surge event. The mean annual δ18O was −19.47 ± 0.55 ‰. Despite large spatial variations in the δ18O values of glacier ice on the newly formed glacier tongue, there were no diurnal oscillations in the bulk meltwater emanating from the glacier in the post-surge years. This is likely a consequence of a tortuous subglacial drainage system consisting of linked cavities, which formed during the surge event. Overall, a comparison of the δ18O compositions from glacial river water in Greenland shows distinct differences between water draining local glaciers and ice caps (between −23.0 and −13.7 ‰) and the GrIS (between −29.9 and −23.2 ‰). This study demonstrates that water isotope analyses can be used to obtain important information on water sources and the subglacial drainage system structure that is highly desired for understanding glacier hydrology.

Modelling suspended sediment concentration using artificial neural networks for Gangotri glacier

AbstractThe dynamics of suspended sediment involves inherent non‐linearity and complexity because of existence of both spatial variability of the basin characteristics and temporal climatic patterns. This complexity, therefore, leads to inaccurate prediction by the conventional sediment rating curve (SRC) and other empirical methods. Over past few decades, artificial neural networks (ANNs) have emerged as one of the advanced modelling techniques capable of addressing inherent non‐linearity in the hydrological processes. In the present study, feed‐forward back propagation (FFBP) algorithm of ANNs is used to model stage–discharge–suspended sediment relationship for ablation season (May–September) for melt runoff released from Gangotri glacier, one of the largest glaciers in Himalaya. The simulations have been carried out on primary data of suspended sediment concentration (SSC) discharge and stage for ablation season of 11‐year period (1999–2009). Combinations of different input vectors (viz. stage, discharge and SSC) for present and previous days are considered for development of the ANN models and examining the effects of input vectors. Further, based on model performance indices for training and testing phase, a suitable modelling approach with appropriate model input structure is suggested. The conventional SRC method is also used for modelling discharge–sediment relationship and performance of developed models is evaluated by statistical indices, namely; root mean square error (RMSE), mean absolute error (MAE) and coefficient of determination (R2). Statistically, the performance of ANN‐based models is found to be superior as compared to SRC method in terms of the selected performance indices in simulating the daily SSC. The study reveals suitability of ANN approach for simulation and estimation of daily SSC in glacier melt runoff and, therefore, opens new avenues of research for application of hybrid soft computing models in glacier hydrology. Copyright © 2015 John Wiley & Sons, Ltd.

An overview of GPR investigation in the Italian Alps

Different applications of Ground Penetrating Radar (GPR) in glaciology are discussed through examples of mapping bedrock or internal features of glaciers or the characterization of snow properties and frozen materials’ physical parameters like electromagnetic velocity and density. A first example focuses on the appli¬cation of GPR to the estimate of snow water equivalent, density at scale of basin, of interest for the analysis of the hydrological behaviour during the snow melt. Examples on the radar survey to map bedrock, investigate the inner features of glaciers and monitor its evolution with time are herein discussed. We focus particularly on the radar survey of the Cevedale glacier, to get information on the thickness of glacier. Another example shows the result of geophysical characterization of iced-bodies in the Canin massif, located in the north-east part of the Italian Alps. Moreover, an example of a 4D GPR data survey is provided, demonstrat¬ing the applicability of GPR as an efficient tool to estimate the seasonal mass balance of a glacier, with a higher overall accuracy than direct methods. Ground Penetrating Radar (GPR) is generally used for locating targets in ice, determining ice and snow thickness, glacialogical studies and crevasse detection. In glaciology, the low electrical conductivity and reduced water content of glaciers allows penetration depths sufficient to detect the bedrock in most glaciers, with frequency ranging from 50 MHz to 200 MHz or even higher. The variations of electromagnetic properties of the inner features causes reflections that are well detectable (Godio and Rege, 2015) and provide extremely valuable data in glaciological studies of the hydrology and structural evolution of glaciers, for mapping and monitoring permafrost evolution (Carturan et al., 2012; Colucci et al., 2014).

Estimating Subglacial Water Geometry Using Radar Bed Echo Specularity: Application to Thwaites Glacier, West Antarctica

Airborne radar sounding is an established tool for observing the bed conditions and subglacial hydrology of ice sheets and glaciers. The specularity content of radar bed echoes has also been used to detect the hydrologic transition of a subglacial water system from a network of distributed canals to a network of concentrated channels beneath the Thwaites Glacier. However, the physical dimensions of the distributed water bodies in these networks have not been constrained by observations. In this letter, we use a variety of simple radar scattering, attenuation, and cross-sectional models to provide a first estimate of the subglacial water body geometries capable of producing the observed anisotropic specularity of the Thwaites Glacier catchment. This approach leads to estimates of ice/water interface root mean square roughnesses less than about 15 cm, thicknesses of more than about 5 cm, lengths of more than about 15 m, and widths between about 0.5 and 5 m.