Estimating recharge at Yucca Mountain, Nevada, USA: comparison of methods

Obtaining values of net infiltration, groundwater travel time, and recharge is necessary at the Yucca Mountain site, Nevada, USA, in order to evaluate the expected performance of a potential repository as a containment system for high-level radioactive waste. However, the geologic complexities of this site, its low precipitation and net infiltration, with numerous mechanisms operating simultaneously to move water through the system, provide many challenges for the estimation of the spatial distribution of recharge. A variety of methods appropriate for arid environments has been applied, including water-balance techniques, calculations using Darcy's law in the unsaturated zone, a soil-physics method applied to neutron-hole water-content data, inverse modeling of thermal profiles in boreholes extending through the thick unsaturated zone, chloride mass balance, atmospheric radionuclides, and empirical approaches. These methods indicate that near-surface infiltration rates at Yucca Mountain are highly variable in time and space, with local (point) values ranging from zero to several hundred millimeters per year. Spatially distributed net-infiltration values average 5 mm/year, with the highest values approaching 20 mm/year near Yucca Crest. Site-scale recharge estimates range from less than 1 to about 12 mm/year. These results have been incorporated into a site-scale model that has been calibrated using these data sets that reflect infiltration processes acting on highly variable temporal and spatial scales. The modeling study predicts highly non-uniform recharge at the water table, distributed significantly differently from the non-uniform infiltration pattern at the surface. Electronic Publication     

Imagining migration: Placing children’s understanding of ‘moving house’ in Malawi and Lesotho

Research pertaining to children’s geographies has mainly focused on children’s physical experiences of space, with their ‘imagined geographies’ receiving far less attention. The few studies of children’s imagined geographies that exist tend to focus on children’s national identities and their understanding of distant places. However, children’s lives are not necessarily static and they often move between places. Research has not so far considered children’s images of these transitional spaces or how such images are constructed.Through an examination of over 800 thematic drawings and stories, regarding ‘moving house’, produced by children aged 10-17 years in urban and rural communities of Lesotho and Malawi, this paper explores southern African children’s representations of migration. The research considers how ideas of migration are culturally-constructed based on notions of family, home and kinship, particularly in relation to the fluid family structure characteristic of most southern African societies. The results suggest that most children imagine migration as a household rather than an individual process, rarely including micro-migrations between extended family households in their drawings. Further, children’s images of migration are place-rooted in everyday life experiences. Their representations concentrate on the reasons for migration, both negative and positive, which are specifically related to their local social and environmental situations and whether house moves take place locally or over longer distances. The paper concludes by exploring the implications of these conceptualisations of moving house for children’s contemporary migration experiences, particularly in light of changing family structures due to the effects of the HIV/AIDS pandemic.     

Contributions respectives des courants et de la houle dans la mobilité sédimentaire d'une plate-forme interne estuarienne. Exemple : le seuil interinsulaire,au large du pertuis d'Antioche,France

This paper investigates the relative influence of waves, wind-induced current and tidal current on the sediment mobility of a macro-tidal environment belonging to the inner shelf seaward of the ‘pertuis Charentais’ (France). This study, mainly based on three-week hydrodynamic in-situ measurements, shows that, for a water depth of 23 m, the swell (rather than wind waves) orbital velocity is large enough to initiate the motion of medium sands that are then transported by currents. Estimations show that medium sand of 0.2 mm is transported during 92% of the measurements, whereas coarse sand and gravel move sporadically, during storm, synchronously with spring tides. Further more, bedload fluxes appear strongly larger when waves are taken into account (370 times larger for 0.2-mm sands). To cite this article: D. Idier et al., C. R. Geoscience 338 (2006).