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[en] Did the Mediterranean ever become a desert during Messinian or was it a huge hyperhaline water body? According to Selli, the introduction of the concept and name of the Messinian Salinity Crisis in 1954, the second hypothesis was correct, but he did not succeed in preventing the rapid growth of popularity of the first hypothesis, triggered by the DSD Mediterranean campaign during the 1970s. The ensuing desiccation theory became popular enough to be included in elementary text books. The controversy has been revived in the new millennium and much former proof of the theory is now in doubt. The Mediterranean was not totally isolated, but often supplied with normal marine water. Instead of km-deep drawdown, shallower-to-absent level drop is favoured. Exposed canyons at the mouth of major Mediterranean rivers have turned into submarine channels filled by clastic sulphates. The mega-catastrophic potential of the desiccation theory has turned out to be less worrying. Perhaps the text books of our grandchildren should be updated. Within the frame of new evidence regarding normal water supply, even from the Indian Ocean, are discussed, based on two new palinspastic Messinian maps. However, reduced sharpness in the controversy and increasing consensus reached among specialists depend on ongoing inferred correlations between on-land and deep-marine Messinian evaporites. Only drilling across the whole, deep Mediterranean evaporite sequences can back-up the reliability of the correlation and validity of these new views. (Author)
[en] As the number of large reservoirs has grown rapidly, drawdown of water level has become a major factor in inducing landslides. A new simulator was developed to simulate the in-flight drawdown in a centrifuge model test. A series of centrifuge model tests was conducted on slopes with different gradients under drawdown conditions. The failure mechanism was obtained via an integrated analysis of deformation and failure processes according to the displacement histories of the slopes measured by the image capture and displacement measurement system. The slip surface, with slippage failure, was developed from the top downwards due to the drawdown. The displacement histories of the sliding body could be divided into three stages with the increase rate changing from small to large and finally becoming negligible. The deformation of the slope only appeared within a limited zone with a nearly invariable boundary surface during the drawdown. The boundary surface moved closer to the slope surface with the deceasing slope gradient. The drawdown caused a significant coupling process of local failure and deformation localization, which developed from the upper part to the lower part. The upper part of the sliding body behaved as a rigid body, and the lower parts exhibited significant deformation after the slip surface formed, which should be reasonably captured in a stability analysis of a slope under drawdown conditions.
[en] Carbon dioxide (CO2) has been injected in the subsurface permeable formations as a means to cut atmospheric CO2 emissions and/or enhance oil recovery (EOR). It is important to constrain the boundaries of the CO2 plume in the target formation and/or other formations hosting the CO2 migrated from the target formation. Monitoring methods and technologies to assess the CO2 plume boundaries over time within a reservoir of interest are required. Previously introduced methods and technologies on pressure monitoring to detect the extent of the CO2 plume require at least two wells, i.e. pulser and observation wells. We introduce pressure transient technique requiring single well only. Single well pressure transient testing (drawdown/buildup/injection/falloff) is widely used to determine reservoir properties and wellbore conditions. Pressure diagnostic plots are used to identify different flow regimes and determine the reservoir/well characteristics. We propose a method to determine the plume extent for a constant rate pressure transient test at a single well outside the CO2 plume. Due to the significant contrast between mobility and storativity of the CO2 and native fluids (oil or brine), the CO2 boundary causes deviation in the pressure diagnostic response from that corresponding to previously identified heterogeneities. Using the superposition principle, we develop a relationship between the deviation time and the plume boundary. We demonstrate the applicability of the proposed method using numerically generated synthetic data corresponding to homogeneous, heterogeneous, and anisotropic cases to evaluate its potential and limitations. We discuss ways to identify and overcome the potential limitations for application of the method in the field.
[en] The concepts and results presented by the authors emphasize the practical value of geodynamic environment monitoring. The question as to the extent of the displacements to be expected and the consequent deformations arises not only mining advances close to already built-up areas, but also when structures are to be erected on former mining sites. In actual fact the engineering geologist is in a position to answer this question, but the accuracy of data for prognoses on displacement phenomena is limited considerably not only by the possible accuracy of the quantitatively expressed description of the geological and hydrological conditions, but also by the accuracy of the formulation of soil physics parameters. The prognoses of the engineering geologist are far more reliable when soil physics parameters are obtained from check calculations of displacements that are connected with operational sequences of mining, or when prognoses can be extrapolated from the available measurement results, taking the geotechnical conditions into account. In the present paper an initial attempt is made to explain the significance of co-operation between the geologist, the engineering geologist and the geodetic surveyor by means of an example. The authors are well aware that an improvement of such co-operation is certainly possible and also necessary. An interdisciplinary integration of this kind leads one to hope for further progress in this field. Moreover, as a result of the change-over to three-dimensional checking by measurement techniques environment monitoring now qualifies as reliable and efficient. In this connection the use of the modern satellite-aided method of determining locations indicates that a considerable increase in information is to be expected in future, as compared to the conventional methods used hitherto. (orig./MSK)
[de]In der Arbeit wird ein erster Versuch unternommen, das Zusammenwirken zwischen Geologen, Geotechnikern und Geodaeten an einem Beispiel darzustellen. Die Autoren sind sich bewusst, dass eine Vervollkommung solcher Kooperation erheblich moeglich und notwendig ist. Eine solche interdisziplinaere Integration laesst auf weitere Fortschritte hoffen. Daneben ergibt sich eine Qualifizierung des Umwelt-Monitorings durch den Uebergang zur dreidimensionalen messtechnischen Kontrolle. Hier zeigt der Einsatz der modernen satellitengestuetzten Positionierung, dass mit einem erheblichen Informationszuwachs gegenueber herkoemmlichen Verfahren zu rechnen ist. Zur Verbesserung unseres Wissens ueber die in Kippen bei Eigensetzungen und Sackungen infolge Grundwasseranstieg ablaufenden Vorgaenge sowie fuer die Ueberwachung von auf Kippen zu errichtenden Bauwerken (z.Z. vorwiegend Deponien) ist mit der Deformationsanalyse ein effektives Verfahren gegeben. (orig./MSK)
[en] In this study, we developed a parameter estimation method of a reservoir conservation model that was developed by the World Bank for efficient sediment flushing operation in dam reservoirs. The parameters for sediment flushing operation are flushing discharge, duration, frequency, and necessary reservoir drawdown. The parameter estimation method was applied to Shahpur Dam in Pakistan, in which sediment balance ratio and long-term capacity ratio were used as indicators of flushing efficiency. For efficient flushing of Shahpur Dam, we recommended that bottom outlets at the dam be retrofitted to achieve a flushing discharge of 7.5 m3/s. The reservoir water elevation should be drawn to a minimum level of 430 m, and the flushing operation should be performed annually over a 15-day span. Flushing using these parameters would result in 100% sediment balance, with 69% of original dam capacity recovered in the long term. We also assessed constraints on dam site for successful flushing. The drawdown ratio was 0.72, sediment balance ratio at full drawdown was 1.58, flushing width ratio was 0.88, and top width ratio was 1.23. For every increment of 0.5 m3/s in flushing discharge, the amount of sediment flushed increased by 0.020–0.025 million tonnes. This method can provide guidelines for implementation of sediment flushing operations for reservoir sediment management.
[en] Analysis of water-level trends in well hydro-graphs can be used to better understand and conceptualize a groundwater-flow system. A water-level trend reflects the summation of all natural and anthropogenic stresses acting on the aquifer at the well location. Common stresses include recharge, evapotranspiration, barometric pressure, earth tides, and pumping. A water-level model (WLM) can be used as a tool to distinguish which stresses are affecting the trend and quantify the impact of each stress on the trend. A WLM is an analytical model that fits measured water levels to a synthetic curve representing the sum of one or more time-series components that explain the water-level trend. Time-series components include recharge pulses simulated with Gamma transforms of precipitation; long-term climatic trends and barometric-pressure responses simulated with moving averages of barometric pressure and water levels in background wells; tidal responses computed from theoretical tidal signals; and pumping drawdown simulated with Theis models. WLM examples are presented to show how to: (1) determine and decompose stresses affecting long-term water levels in wells; and (2) estimate short-term draw-downs in observation wells where drawdown is masked by environmental water-level fluctuations. (authors)
[en] In 1921-1923 a precise levelling network, with more than 200 km of lines, was set up and measured in the Tuscan geothermal region comprising the Larderello area. In 1985-1986 this topographic network was rearranged and levelling measurements were repeated. Negative elevation changes reaching a maximum of about 170 cm were observed across the areas of maximum fluid withdrawal and maximum fluid pressure decline. Levelling measurements carried out in 1989 show that elevation changes are no longer evident in the central Larderello area, but subsidence of less than 3 cm can still be observed in some nearby areas exploited recently. The measured subsidence values cannot be ascribed solely to the compaction of reservoir rocks, as this would entail a pressure decline down to about 10 km depth. In this paper since this figure seems excessive the authors hypothesize that compaction of the cover terrains is also involved
[en] Tunnel excavation causes geological, hydrological, environmental and social changes. The effects of groundwater level changes caused by tunnelling on tree growth have been poorly understood. Dendrochronology was used to evaluate the impact of groundwater level drawdown on tree growth. Tree cores of Masson pines were collected from the areas affected by tunnel construction in the Zhongliang Mountains of Chongqing in south-western China to study the effects of tunnel excavation on the growth rate of trees by comparing with tree cores collected from unaffected areas. Excavation and early operation of the first tunnel in the Zhongliang Mountains from 1968 to 1984 caused a groundwater table drawdown in both karst aquifer and non-karst aquifer. The lowered groundwater table significantly reduced the growth rate of pine trees, and the low growth rate remained for 15 years. The effect was experienced up to at least 1 km from the tunnel axis. The decline in tree growth was higher in karst than in non-karst areas, though the effects on the trees of the karst areas were lagging. The high precipitation in 1998 contributed to groundwater recovery, after which the tree growth recovered moderately but not to the original level. Groundwater leakage of the recently excavated tunnels did not affect pine trees heavily, probably because the pines had adapted to the new hydrogeological conditions and new strategies in tunnel inflow management were adopted in the recently excavated tunnels. The use of tree growth rate as an indicator of groundwater table change in tunnelling areas offers a new option to study environmental impacts and the extent of tunnelling effects.
[en] The minimum water level of Lake Pend Oreille was raised from 625.1 m to 626.4 m elevation during the winter of 1998-99 in an attempt to recover the impacted kokanee Oncorhynchus nerka fishery. This report covers the third year of testing higher winter levels. Hydroacoustic surveys and mid-water trawling were conducted in the fall of 1999 to assess the kokanee population. We estimated the abundance of each age class of kokanee as: 6.023 million age-0 (wild and hatchery fry), 883,000 age-1, 409,000 age-2, 579,000 age-3, 861,000 age-4, and 87,000 age-5. Wild fry abundance was estimated at 2.57 million fish. These originated from 43.1 million eggs spawned in the wild during the fall of 1998. The survival from wild spawned eggs to wild fry was, therefore, 6.0%. This was lower than the 9.6% survival rate calculated last year but was much higher than the 1.4% calculated in 1995 prior to changing lake levels. To date, years of higher winter lake elevations have out-performed years of full drawdown. Based on data collected during trawl sampling, the total number of eggs laid in the lake in the fall of 1999 was 74.8 million. Mean fecundity per female was 379 eggs. Hatchery personnel collected 22.4 million eggs, leaving 52.4 million eggs to be laid by wild fish in tributary streams and along the lake shoreline. These eggs will be used to assess wild kokanee survival during 2000. Peak counts of spawning kokanee were 3,500 fish on the shoreline and 16,400 fish in tributary streams. This represents only a fraction of the total kokanee spawning population. Opossum shrimp Mysis relicta increased slightly in the southern two sections of the lake but decreased in the northern end. Immature and mature shrimp (excluding young-of-the-year shrimp) densities averaged 302 shrimp/m(sup 2), down from 426 shrimp/m(sup 2) the previous year. The relatively stable shrimp population was not thought to affect the outcome of the lake level testing