News

We have recently made lots of our data newly available in open access format. All the data can be accessed here : These data include

1. 15 minute resolution normalized hydrographs for 6 glaciated basins in south-west Switzerland (search on: Q_1969_2014)
2. Long-term digital elevation models of the Borgne d’Arolla reconstructed from aerial imagery and starting in the 1960s. These are supported by data on flushing of sediment from two intakes (search on: Bakker M)
3. Short-term (daily time-scale) digital elevation models of a braided river (c. 300 m wide, 1600 m long) over a three week period (search on: Bakker M)
4. Data from a monitoring project (SNSF PNR70 Hyroenv) of macroinvertebrate life in the Borgne d’Arolla (search on: macroinvertebrate)

If you want to look for other data available (e.g. glacier recession, DEMs of hillslopes), choose “advanced search”; then unclick all boxes except “data”

Quantification of climate forcing of glacial hydrological systems at the decadal scale is rare because most measurement stations are too far downstream for glacier impacts to be clearly detected. Here we apply a measure of daily hydrograph entropy to a unique set of reliable, high?altitude gauging stations, dating from the late 1960s. We find a progressive shift to a greater number of days with diurnal discharge variation as well as more pronounced diurnal discharge amplitude. These changes were associated with the onset of rapid warming in the 1980s as well as declining end of winter snow depths as inferred from climate data. In glaciated catchments, lower winter snow depths reduce the magnitude and duration of snowpack buffering and encourage the earlier onset of glacier ice exposure, with associated lower surface albedo and more rapid melt. Together, these processes explain the increase in the observed intensity of diurnal discharge fluctuations.

The paper has been published in Water Resources Research and can be accessed here.

Images from specially?commissioned aeroplane sorties (manned aerial vehicle, MAV), repeat unmanned aerial vehicle (UAV) surveys, and Planet CubeSat satellites are used to quantify dune and bar dynamics in the sandy braided South Saskatchewan River, Canada. Structure?from?Motion (SfM) techniques and application of a depth?brightness model are used to produce a series of Digital Surface Models (DSMs) at low and near?bankfull flows. A number of technical and image processing challenges are described that arise from the application of SfM in dry and submerged environments. A model for best practice is presented and analysis suggests a depth?brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low?turbidity and shallow (< 2?m deep) water. The aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18?km reach and three ~1?km long reaches respectively. Dune and unit bar migration rates are highly variable in response to local variations in planform morphology. Sediment transport rates for dunes and unit bars, obtained by integrating migration rates (from UAV) with the volume of sediment moved (from DSMs using MAV imagery) show near?equivalence in sediment flux. Hence, reach?based sediment transport rate estimates can be derived from unit bar data alone. Moreover, it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2D imagery, including from satellite images, so long as informed assumptions are made regarding average bar shape and height. With recent availability of frequent, repeat satellite imagery, and the ease of undertaking repeat MAV and UAV surveys, for the first time, it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low?turbidity rivers that currently have sparse information on bedload sediment transport rates.

The paper is published in Earth Surface Processes and Landforms and can be accessed here.

Shallow rivers provide important habitat for various aquatic and terrestrial species. The bathymetry of such environments is, however, difficult to measure as devices and approaches have been traditionally developed mainly for deeper waters. This study addresses the mapping of shallow waterbathymetry with high spatial resolution and accuracy by comparing three remote sensing (RS) approaches: one based on echo sounding (active RS) and two on photogrammetry (passive RS): bathymetric Structure from Motion (SfM) and optical modelling. The tests were conducted on a 500?m long and ~30?m wide reach of sand-bedded meandering river: (1) during a rising spring flood (Q?=?10–15?m3/s) with medium turbidity and high water color and; (2) during autumn low discharge (Q?=?4?m3/s) with low turbidity and color. Each method was used to create bathymetric models. The models were compared with high precision field measurements with a mean point spacing of 0.86?m. Echo sounding provided the most accurate (ME~?0.02?m) and precise (SDE?=?±?0.08?m) bathymetric models despite the high degree of interpolationneeded. However, the echo sounding-based models were spatially restricted to areas deeper than 0.2?m and no small scale bathymetric variability was captured. The quality of the bathymetric SfM was highly sensitive to flow turbidity and color and therefore depth. However, bathymetric SfM suffers less from substrate variability, turbulent flow or large stones and cobbles on the river bed than optical modelling. Color and depth did affect optical model performance, but clearly less than the bathymetric SfM. The optical model accuracy improved in autumn with lower water color and turbidity (ME?=??0.05) compared to spring (ME?=??0.12). Correlations between the measured and modelled depth values (r?=?0.96) and the models precision (SDE?=?0.09–0.11) were close to those achieved with echo sounding. Shadows caused by riparian vegetation restricted the spatial extent of the optical models.

The paper is published in the journal Geomorphology and can be accessed here.

Publié dans le Bulletin de la Murithienne, 135, 39-53, 2018. Cliquer ici pour l’obtenir

Alors que tous s’accordent dans l’idée de conduire une gestion environnementale optimale, c’est-à-dire de déterminer des mesures efficaces qui permettent à la balance énergie-écologie de couvrir l’ensemble des objectifs, l’enjeu réside parfois dans le manque de connaissances concernant le fonctionnement des systèmes naturels, et des écosystèmes notamment. Les environnements alpins, moins bien maitrisés, devraient faire l’objet d’une attention toute particulière, d’autant plus en cette année des Risques 2018. Cet article expose les principaux résultats de recherche du groupe AlpWISE ( wp.unil.ch / alpenv ) des scientifiques de l’Université de Lausanne, sous la direction du Professeur Dr. Stuart Lane. Il s’agit de déterminer les réponses des éléments du paysage au changement climatique rapide par une approche intégrative regroupant en particulier géographie, géomorphologie et écologie. La figure 1 présente un résumé des interactions du paysage discutées, avec le Val d’Arolla pour terrain d’étude. Die alpine Umwelt angesichts des Klimawandels : Gletscher, Gewässer und Landschaften, wo sind die Herausforderungen ? Obwohl sich alle einig sind, dass wir den Umgang mit der Umwelt optimieren müssen, das heisst, dass wir effiziente Massnahmen zur Herstellung des Gleichgewichtes zwischen Energie und Ökologie ergreifen wollen, besteht das Problem manchmal darin, dass wir zu wenig über die Funktionsweise der natürlichen Systeme und der Ökosysteme im Speziellen wissen. Die alpine Umgebung, welche weniger bekannt ist, besondere Beachtung erhalten, umso mehr in diesem Jahr des Risikos 2018. Dieser Artikel beschreibt die wichtigsten Forschungsresultate der Gruppe AlpWISE der Wissenschaftler der Universität Lausanne, unter der Leitung des Professors Dr. Stuart Lane. Ziel ist es, die Reaktionen verschiedener Landschaftselemente auf den schnellen Klimawandel mit Hilfe einer integrativen Methode zu bestimmen, welche Geografie, Geomorphologie und Ökologie vereint. Abbildung 1 zeigt eine Zusammenfassung der Prozesse in der Landschaft diskutiert, mit Hilfe des Val d’Arolla als Untersuchungsgebiet.

Matthews’ 1992 geoecological model of vegetation succession within glacial forefields describes how following deglaciation the landscape evolves over time as the result of both biotic and abiotic factors, with the importance of each depending on the level of environmental stress within the system. We focus in this paper on how new understandings of abiotic factors and the potential for biogeomorphic feedbacks between abiotic and biotic factors makes further development of this model important. Disturbance and water dynamics are two abiotic factors that have been shown to create stress gradients that can drive early ecosystem succession. The subsequent establishment of microbial communities and vegetation can then result in biogeomorphic feedbacks via ecosystem engineering that influence the role of disturbance and water dynamics within the system. Microbes can act as ecosystem engineers by supplying nutrients (via remineralization of organic matter and nitrogen-fixation), enhancing soil development, either decreasing (encouraging weathering) or increasing (binding sediment grains) geomorphic stability, and helping retain soil moisture. Vegetation can act as an ecosystem engineer by fixing nitrogen, enhancing soil development, modifying microbial community structure, creating seed banks, and increasing geomorphic stability. The feedbacks between vegetation and water dynamics in glacial forefields are still poorly studied. We propose a synthesized model of ecosystem succession within glacial forefields that combines Matthews’ initial geoecological model and Corenblit et al.’s (2007) model to illustrate how gradients in environmental stress combined with successional time drive the balance between abiotic and biotic factors and ultimately determine the successional stage and potential for biogeomorphic feedbacks.

The paper has been accepted for publication in Progress in Physical Geography.

Sediment export from glaciated basins involves complex interactions between ice flow, basal erosion and sediment transfer in subglacial and proglacial streams. In particular, we know very little about the processes associated with sediment transfer by subglacial streams. The Haut Glacier d’Arolla (VS, Switzerland) was investigated during the summer melt season of 2015. LiDAR survey revealed positive surface changes in the ablation zone, indicating glacier uplift, at the end of the morning during the period of peak ablation. Instream measures of sediment transport showed that suspended load and bedload responded differently to diurnal flow variability. Suspended load depended on the availability of fine material whereas bedload depended mainly on the competence of the flow. Interpretation of these results allowed development of a conceptual model of subglacial sediment transport dynamics. It is based upon the mechanisms of clogging (deposition) and flushing (transport/erosion) in sub-glacial channels as forced by diurnal flow variability. Through the melt season, the glacier hydrological response evolves from being buffered by glacier snow cover with a poorly developed subglacial drainage system to being dominated by more rapid ice melt with a more hydraulically efficient subglacial channel system. The resultant changes in the shape of diurnal discharge hydrographs, and notably higher peak flows and lower base flows, causes sediment transport to become discontinuous, with overnight clogging and late morning flushing of subglacial channels. Overnight clogging may be sufficient to reduce subglacial channel size, creating temporarily pressurised flow and lateral transfer of water away from the subglacial channels, leading to the late morning glacier surface uplift. However, without further data, we cannot exclude other hypotheses for the uplift.

The paper is in press with the journal Earth Surface Processes and Landforms and can be accessed here.

Improved water management strategies necessitate a solid understanding of environmental impacts associated with various flow release policies. Habitat suitability models use hydrodynamic simulations to generate weighted usable area curves, which are useful in characterizing the ecological suitability of flow release rules. However, these models are not conveniently run to resolve the hydrodynamics at the smaller scales associated with macroroughness elements (e.g., individual stones), which produce wakes that contribute significantly to habitat suitability by serving as shelter zones where fishes can rest and feed. In this study, we propose a robust environmental indicator that considers the habitat generated by the wakes downstream of stones and can thus be used to assess the environmental efficiency of flow release rules for impounded streams. We develop an analytical solution to approximate the wake areas behind macroroughness elements, and the statistical distribution of wake areas is then found using the derived distribution approach. To illustrate the concept, we apply our theory to four exemplary river streams with dispersed stones having different statistical diameter size distributions, some of which allow for an analytical expression of the weighted usable area. We additionally investigate the impact of spatiotemporal changes in stone size distributions on the usable area and the consequent threshold flows. Finally, we include the proposed environmental indicator to solve a multiobjective reservoir optimization problem. This exemplifies its practical use and allows stakeholders to find the most favorable operational rules depending on the macroroughness characteristics of the impounded stream.

The paper has been accepted for publication in Water Resources Research and can be accessed here.

Deltas are important coastal sediment accumulation zones in both marine and lacustrine settings. However, currents derived from tides, waves or rivers can transfer that sediment into distal, deep environments, connecting terrestrial and deep marine depozones. The sediment transfer system of the Rhone River in Lake Geneva is composed of a sublacustrine delta, a deeply incised canyon and a distal lobe, which resembles, at a smaller scale, deep?sea fan systems fed by high discharge rivers. From the comparison of two bathymetric datasets, collected in 1891 and 2014, a sediment budget was calculated for eastern Lake Geneva, based on which sediment distribution patterns were defined. During the past 125 years, sediment deposition occurred mostly in three high sedimentation rate areas: the proximal delta front, the canyon?levée system and the distal lobe. Mean sedimentation rates in these areas vary from 0·0246 m year?1 (distal lobe) to 0·0737 m year?1 (delta front). Although the delta front–levées–distal lobe complex only comprises 17·0% of the analysed area, it stored 74·9% of the total deposited sediment. Results show that 52·5% of the total sediment stored in this complex was transported toward distal locations through the sublacustrine canyon. Namely, the canyon–levée complex stored 15·9% of the total sediment, while 36·6% was deposited in the distal lobe. The results thus show that in deltaic systems where density currents can occur regularly, a significant proportion of riverine sediment input may be transferred to the canyon?lobe systems leading to important distal sediment accumulation zones.

The paper has been published in Sedimentology and can be accessed here.

In Alpine streams, humans have strongly modified the interactions between hydraulic processes, geomorphology and aquatic life through dams, flow abstraction at water intakes and river channel engineering. To mitigate these impacts, research has addressed both minimum flows and flow variability to sustain aquatic ecosystems. Whilst such environmental flows might work downstream of dams, this may not be the case for water intakes. Intakes, generally much smaller than dams, are designed to abstract water and to leave sediment behind. Sediment accumulation then results in the need to flush intakes periodically, often more frequently than daily in some highly glaciated basins. Sediment delivery downstream is then maintained through short duration floods with very high sediment loads. Here we tested the hypothesis that sediment flushing, and the associated high frequency of bed disturbance, controls in-stream habitat and macroinvertebrate assemblages. We collected macroinvertebrates over a 17-month period from an Alpine stream as well as a set of lateral unperturbed tributaries that served as controls. In contrast to established conceptual models, our results showed that the stream is largely void of life during summer, but that populations recover rapidly as the frequency of intake flushing falls in early autumn, producing richer and larger populations in winter and early spring. The recovery in autumn may be due to the recruitment of individuals from tributaries. We conclude that intake flushing in summer inverts expected summer-winter macroinvertebrate abundances, and questions the extent to which environmental flows in intake-impacted Alpine streams will lead to improvements in instream macrofauna unless sediment also is managed.

The paper can be accessed here (or email stuart.lane@unil.ch for a copy): https://www.sciencedirect.com/science/article/pii/S0048969718336246