Results 1 - 10 of 2024
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[en] Multi-model frameworks are widely used to identify the appropriate model structure for the study catchment. However, most frameworks mainly consider the process complexity of the model, and few of them consider the spatial complexity. In this paper, we investigated the appropriate model structure for a karst catchment from the aspect of spatial complexity. The purpose is twofold: (1) to investigate whether the spatial complexity is needed to simulate the spring discharge of this karst catchment and (2) to investigate whether the increase of model’s spatial complexity can make up its deficiency on the process complexity. Three simple lumped models with different process complexities were chosen to gradually increase the spatial heterogeneity of their parameters to investigate the appropriate model structure for simulating the discharge of a karst spring. The results show that the performances of three lumped models highly improve when adding the routing function to them. However, further considering the spatial parameter heterogeneity, only one model shows obvious performance improvement and other two models show limited improvement. Moreover, this model with relatively complex spatial parameter heterogeneity still shows worse performance than another lumped model. This indicates an increase of models’ spatial complexity cannot always make up their process deficiencies. The final comparison results indicated that the lumped model or their semi-lumped version with flexible process complexity is enough to simulate the discharge of this karst spring and no extra spatial complexity is needed. Our studies also indicated that the increase in spatial complexity of the model cannot always fully compensate its deficiency in process complexity.
[en] This study is about the western edge deposits belong to Lavalleja group locataed in the proximity of the Sierra Animas formation. The rocks dominants In this zone are phyllite, calcareous phyllite and limestone magnesian, usually grey or black denoting environment reduce
[en] The MTT (Mean Transit Time) of a catchment without significant surface flow is normally taken to be the sum of mean residence time in the unsaturated zone and mean residence time in the saturated zone. However, the Chalk is a multi-porosity limestone aquifer, with a microporous matrix. This means that the movement of water through the Chalk can occur in complex ways, making the prediction of MTT far from straightforward. Although the Chalk is a regionally-important aquifer, no study of catchment MTT has yet been published. The present study is based on the catchment of the River Lambourn in Berkshire, UK, with an area of 235 km2. Interfluve areas rarely rise above 200 m asl (above sea level), whereas river elevation at the foot of the catchment is ∼50 m asl. Mean annual precipitation is 731 mm. The thickness of the Chalk unsaturated zone reaches a maximum of over 100 m at the water divide at the top of the escarpment on the northern flank of the catchment.
[en] This work brings information of fields and laboratory samples about the outcrop in Treinta y Tres district in the framework of limestones programme carried out jointly with I.G.U and BGR through the geological German mission
[en] An empirical study of luminescence around 360 nm from limestone is presented. Thermoluminescence glow curves from natural limestone show broad peaks at 440 deg. C, 350 deg. C, 530 deg. C and 286 deg. C in order of decreasing amplitude in contrast to the usual observation, for luminescence around 535 nm, of a sharp peak at 286 deg. C with a broader less intense peak at 350 deg. C. Recuperation occurs around 350 deg. C and 525 deg. C, which has a time dependence consistent with quantum tunnelling. Dependent on the history of heating and light exposure of the sample, sharp peaks at about 325 deg. C and 425 deg. C can be observed. Laboratory irradiated limestone shows a peak at 140 deg. C. The stimulation of luminescence by light of 470 nm with preheating at 145 deg. C for 300 s, shows an increasing signal for successive cycles of measurement associated with the heating, light exposure having little influence. Beta irradiation of a sample, with the same measurement conditions, gives a signal which increases in proportion to radiation dose but which does not survive storage for 17 h. Time resolved luminescence spectra, with no preheating, show a luminescence lifetime between stimulation and emission of less than a few μs for natural limestone, and an exponential increase in signal with increase in temperature (over the rang 20-167 deg. C) during stimulation. A signal proportional to laboratory applied beta dose is measurable at room temperature, with lifetime between stimulation and emission of this signal of 35 μs, but it does not survive heating to 100 deg. C
[en] The calibration characteristics of neutron logging instrumentation are discussed. The principles of the rock, plastics, and water models are briefly outlined. Indian limestone of 9% porosity is the primary standard in the neutron logging metrology network, from which secondary standards employed during certification measurements are derived. It is recommended that rock blocks should be used as national standards, and each secondary institution should possess a set of polyethylene cylinders, one of which would serve as the main standard for the institution in question. (J.B.)
[en] Strata-bound large tonnage uranium deposit hosted by the Grey-impure-dolostone of Vempalle Formation of Cuddapah Basin is known in Tummalapalle-Rachakuntapalle sector. Deposition of rocks of Cuddapah Basin commenced with Papaghni Group, which comprises Clastic - Gulcheru Formation and Chemogenic - Vempalle Formation. The Vempalle Formation is developed over 280 km stretch from south to north along the western margin of Cuddapah Basin with maximum thickness of about 2.1 km. Recent studies helped in classifying the Vempalle Formation into five major lithofacies viz. Massive Dolostone, Conglomerate, Grey-impure-dolostone (host rock for uranium mineralization), Purple shale and Cherty Dolostone. The lithofacies studies along selected traverses from Tummalapalle in south to Dhone in north revealed the development of all five facies upto Narpala near Chitravati River whereas towards its north, the Grey-impure-dolostone and Cherty Dolostone dominate. The study also revealed over lapping nature of Cherty Dolostone in North of Nossam-Peddapaya lineament; where it directly rests above the Gulcheru Formation. Environment of deposition for these facies of Vempalle Formation place this in a Shallowing-upward carbonate depositional system with characteristic tidal flat environment. The Grey-impure-dolostone facies hosting uranium is interpreted to be developed in Supratidal environment with a narrow pH range of 7.0 - 7.5 in a reducing environment along with precipitation of phosphate. Since the tidal flats have later extension over several kilometers, favorable environment of Grey-impure-dolostone may exist over wide area in northern part also. The search for Grey-impure-dolostone hosted uranium, therefore has a bearing an understanding the regional facies variations in Vempalle Formation. The paper presents the studies carried out in this direction and results thereof. (author)