New perspectives on interdisciplinary earth science at the Dead Sea: The DESERVE project

The Dead Sea region has faced substantial environmental challenges in recent decades, including water resource scarcity, ~ 1 m annual decreases in the water level, sinkhole development, ascending-brine freshwater pollution, and seismic disturbance risks. Natural processes are significantly affected by human interference as well as by climate change and tectonic developments over the long term. To get a deep understanding of processes and their interactions, innovative scientific approaches that integrate disciplinary research and education are required. The research project DESERVE (Helmholtz Virtual Institute Dead Sea Research Venue) addresses these challenges in an interdisciplinary approach that includes geophysics, hydrology, and meteorology. The project is implemented by a consortium of scientific institutions in neighboring countries of the Dead Sea (Israel, Jordan, Palestine Territories) and participating German Helmholtz Centres (KIT, GFZ, UFZ). A new monitoring network of meteorological, hydrological, and seismic/geodynamic stations has been established, and extensive field research and numerical simulations have been undertaken. For the first time, innovative measurement and modeling techniques have been applied to the extreme conditions of the Dead Sea and its surroundings. The preliminary results show the potential of these methods. First time ever performed eddy covariance measurements give insight into the governing factors of Dead Sea evaporation. High-resolution bathymetric investigations reveal a strong correlation between submarine springs and neo-tectonic patterns. Based on detailed studies of stratigraphy and borehole information, the extension of the subsurface drainage basin of the Dead Sea is now reliably estimated. Originality has been achieved in monitoring flash floods in an arid basin at its outlet and simultaneously in tributaries, supplemented by spatio-temporal rainfall data. Low-altitude, high resolution photogrammetry, allied to satellite image analysis and to geophysical surveys (e.g. shear-wave reflections) has enabled a more detailed characterization of sinkhole morphology and temporal development and the possible subsurface controls thereon. All the above listed efforts and scientific results take place with the interdisciplinary education of young scientists. They are invited to attend joint thematic workshops and winter schools as well as to participate in field experiments

Variable source areas of bedload in a gravel bed stream

[eng] Bedload texture is dependent on the spatially variable availability of mobile surface bed material, distributed in patches or in other bedforms. We measured bedload transport continuously with an automatic bedload station on the gravel-bedded Tordera River. We also studied bed patchiness from pre-flood vertical aerial photographs in a 40 m section upstream of the bedload station. The results suggest that patches are the main source of sediment during the beginning of the flow event. The median bedload size, in low-magnitude events, depends on the percentage of total area occupied by patches of a given size. Patch areal extent and texture depend on the magnitude and general character of the previous flow event

Continuous monitoring of bedload flux in a mountain gravel-bed river

[eng] An automatic bedload monitoring station has been established on the perennial Tordera River, a Mediterranean mountain gravel-bed stream located in NE Spain. Bedload fluxes were obtained automatically at 1-min intervals using two Birkbeck-type pit bedload samplers aligned across the width of the channel. Flow depth and water-surface slope were both measured continuously and synchronously with bedload. Data for five flow events show that bedload flux varies considerably. Bedload flux is high when it is compared with other perennial streams. For a 15-min interval, maximum channel-average bedload flux was 0.83 kg m−1 s−1. Bedload records also show that there is no direct relationship between bedload flux and grain shear stress. The low correlation between bedload flux and hydraulics arises due to the different thresholds of initiation of motion for each flow event and the variable character of the bed between events. For two individual floods, there is a reasonable relationship between bedload flux and grain shear stress, in part, as a consequence of individual particle entrainment and patch movement over a stable coarse gravel-bed during moderately high discharges. These results demonstrate that the Birkbeck system functions well in a Mediterranean mountain gravel-bed stream with a longitudinal slope of 2%

Flash floods in desert rivers: studying the unexpected

[eng] Flash floods in desert ephemeral streams are unpredictable, infrequent, and shortlived. Although some observations of flood bores have been reported [e.g., Hassan, 1990], there is little quantitative data on the hydraulic and sediment transport dynamics of desert flash floods, despite the fact that desert streams pose many problems for river and reservoir management [Tolouie et al., 19937rsqb;. Furthermore, it has been suspected for some time that rates of sediment transfer might differ markedly in ephemeral and perennial rivers [e.g., Reid and Frostick, 1987; Schick et al., 1987]. Today, because of concern over prospective climate change, water resource issues are the subject of lively debate. Since current understanding and models of sediment dynamics derived from perennial streams may not be readily applicable to ephemeral flows, there is an urgent need for improved understanding of the dynamics of dryland rivers

Bedload transport monitoring in a small upland catchment

International audienceCommunication orale faite lors du 8th IAG International Conference on Geomorphology, Paris, 27-31 August 2013

Premières de charriage dans une rivière à gravier alpine

International audienceIn June 2011, a first attempt for measuring bedload transport in the main channel of an alpine river, the Arc en Maurienne River, was undertaken contemporaneously deploying bedload samplers and hydrophones. The Ehrenberger type bedload basket sampler was unstable at high velocities. Samples were successively taken using a large (152 mm) Helley-Smith type bedload sampler. The considerable temporal variability of bedload flux based on H-S sampling contradicts the generally steady hydrophone signals. The position of the sampler on the river bed may have likely been uneven due to the presence of boulders, thereby decreasing sampler catch in some instances. Apparently when the sampler was evenly set on the riverbed, its efficiency decreased due to the presence of organic matter and large concentration of suspended sediments. A simple hydraulic model was applied to estimate the variation of water depth, velocity and bedload discharge with water discharge, yielding consistent results compared to measured water depths and velocities. The calculated bedload discharge using classical formulae is, however, larger than the average monitored, confirming the relatively low efficiency of the bedload sampler

Processes of Initiation of Motion Leading to Bedload Transport in Gravel-bed Rivers

[eng] Transport processes that lead to the initiation of bedload motion in gravel‐bed rivers have not yet been clarified. We report patch‐ and grain‐scale processes involved in the initiation of bedload motion in a natural gravel‐bed stream as observed through a series of video experiments. With increasing flow strength, the phases of initiation of motion that have been identified are (1) within‐patch grain instability (grain vibration, pivoting, and grain‐scale rolling), (2) within‐patch gyratory step‐and‐rest motion, and (3) general sediment motion involving downstream transport from an individual patch and the throughput of grains inherited from upstream

Bedload transport monitoring at Draix

International audienceConférence invitée lors du International Workshop on Monitoring Bedload and Debris-Flows in Mountain Basins, Free University of Bolzano, Italy, 10-12 October 2012