Characterisation of the transmissivity field of a fractured and karstic aquifer, Southern France

International audienceGeological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests.We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the transmissivity fields in both synthetic and field studies.By following the above approach, transmissivity fields that produce similar hydrodynamic behaviours to the real head measurements were obtained. The inverted transmissivity fields show complex, spatial heterogeneities with highly conductive channels embedded in a low transmissivity matrix region. The spatial trend of the main flow channels is in a good agreement with that of the main fracture sets mapped on outcrops in the vicinity of the Terrieu site suggesting that the hydraulic anisotropy is consistent with the structural anisotropy. These results from the inverse modelling enable the main flow paths to be located and their hydrodynamic properties to be estimated

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Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND DEWEY.Bibliography: leaves 115-116.by James G. Cosgrove anf Ubiratan N. Guzzi.M.S

Persistence of perennial ryegrass, tall fescue and cocksfoot following annual sowings: Influence of grass species, ryegrass cultivar and pasture age on yield, composition and density

Persistence is an important component of perennial pasture-grass productivity. Defining traits that affect persistence is essential for improving pasture longevity through plant breeding and for identifying persistence traits that should be included in cultivar ranking indices. Compared with conventional longitudinal studies, where a single sowing is monitored over time, repeated annual sowings allow the effects on persistence of sowing year and the ensuing interactions between environment and age of pasture to be identified. An experiment was commenced in 2015 under sheep grazing in Canterbury and in 2016 under cattle grazing in Waikato, where eight cultivars of perennial ryegrass representing different ploidy, flowering date, and cultivar age (release date), and one cultivar each of tall fescue and cocksfoot were sown in four randomised complete blocks in autumn each year. This paper reports interim data on spring and autumn pasture yield, composition, and density of 3-year-old, 2-year-old and 1-year-old pastures exposed to the same environmental conditions within the same, single year. There were significant effects on yield, botanical composition, basal cover and tiller density due to cultivar, pasture age, and their interaction. When the confounding effect of year-to-year variation was removed by comparing each age cohort in the same year, the underlying differences among grass species and cultivars, and ages of pasture, is starting to reveal the nature of this influence on pasture persistence

Partial Preference of Grazing Cattle for Contrasting Legume Swards

Yearling heifers in groups of 3 grazed 405 m2 plots made up of alternating 2.4m wide strips of white clover/birdsfoot trefoil (WC+BT) or red clover (RC) in the proportions of 80:20, 67:33, 33:67 and 20:80 for periods of 3 days over four replicates in time, balanced for effects of previous treatment. Observation of the distribution of grazing activity and biting rate were made over 3 hour periods each evening. Biting rates were consistently higher on (WC+BT) than RC (52.3 vs 46.3 ± 0.59 bites.min-1 P(0.0001). Animals initially showed partial preference for the minor sward component in each treatment but regression of the proportion of grazing activity on proportion of total area for (WC+BT) approached unity with time, indicating the development of essentially neutral behaviour as herbage on minority strips was depleted

Species Preference Influences on Cattle Grazing Behaviour

Lotus corniculatus offers specific nutritional benefits to animals, but exploiting these advantages in grazing systems depends on the proportion of lotus in the feed offered and the animals\u27 preference, hence desire to select for it. To determine preference for lotus, heifers were offered free-choice in contrasting, spatially separated but adjacent monocultures of ryegrass-lotus or red clover-lotus. Following a one-week period to adjust to the species offered and their arrangement, 10 young heifers were observed at 10-minute intervals during daylight hours, and the species they were on and whether or not they were grazing was recorded. This procedure was conducted in summer (February) and autumn (May). Partial preference was determined from the proportion of time spent grazing each species. Preference for lotus was higher when the alternative species was ryegrass, than when it was red clover, in both summer (75:25 vs 53:47) and autumn (67:33 vs 54:46), although this preference for lotus in the ryegrass-lotus contrast reduced in autumn compared with that exhibited in summer. Total grazing time, which was similar for each contrast, was lower in autumn (6 hrs) than in summer (9 hrs). For the ryegrass-lotus contrast, the reduced grazing time in autumn resulted from reduced time grazing lotus, whereas on the red clover-lotus contrast they reduced grazing time equally on both species