Dynamics of a wave-dominated tidal inlet and influence on adjacent beaches,Currumbin Creek,Gold Coast,Australia

Currumbin Creek on the Australian Gold Coast is a wave-dominated tidal inlet which exhibits a particularly active morphology. The recent history of Currumbin Creek entrance has seen rapid growth of the entrance for access to the ocean by fishermen, as a world class surfing site, and as a recreational area. Before the construction of two groynes in the 70's, Currumbin Creek entrance was highly variable in terms of inlet location and sand bar characteristics due to a cyclical behaviour of spit migration. Nowadays, the entrance is stabilised. However, natural processes continue with the entrance infilling causing flood and navigation issues, resulting in a regular dredging program to maintain an open entrance and for regular beach nourishment plans.     

Über einige Innsbrucker Institutsarbeiten seit 1940

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MuSET: A multiparameter and high precision sensor for downhole spontaneous electrical potential measurements

On the basis of an existing multiparameter borehole fluid sensor (p, T, Cw, pH, Eh), a new downhole tool designed for 200 bars and 75 °C was developed to measure the spontaneous electrical potential in situ with great precision (better than a μV). To this end, the new sensor is based on the use of unpolarizable Pb/PbCl₂ electrodes either at the surface or downhole. In situ testing has demonstrated a capacity to identify several subsurface sources of natural electrical potential such as diffusion ones (membrane potential in the presence of clays, Fickian processes due to pore fluid salinity gradients), or else the electrokinetic mechanisms with gradients in pore fluid pressure. As a consequence, Multi-Sensors Electrical Tool (MuSET) might be used as an “electrical flowmeter” sensitive to both horizontal and vertical fluid flow in a vertical borehole.     

Geophysical exploration for geothermal low enthalpy resources in Lipari Island, Italy

Integrated geophysical surveys were performed in two sites, Fossa di Fuardo and Terme di San Calogero in Lipari Island, Southern Italy with the intent of the exploration of low-enthalpy geothermal fluids. Both sites show strong geochemical and geologic evidences of hydrothermal activity. The geophysical methods consist of two microgravimetric surveys, two 2D geoelectric profiles, a seismic reflection profile and a five seismic refraction profiles. The seismic methods allowed us to locate the main subsurface seismic discontinuities and to evaluate their geometrical relationships. The gravity field was used to constraint the seismic discontinuities, while the electric prospecting let discriminate more conductive areas, which could correspond to an increase in thermal fluid circulation in the investigated sites.The results obtained by the different geophysical methods are in good agreement and permit the definition of a reliable geo-structural model of the subsurface setting of the two investigated areas. A low-enthalpy geothermal reservoir constituted by a permeable pyroclastic and lava sequence underlying two shallow impermeable formations was found at Fossa del Fuardo. The reservoir is intersected by some sub-vertical faults/fractures that probably play an important role in convoying the thermal water up to the surface. At the other site, Terme di S. Calogero, the geophysical surveys showed that an intense circulation of fluids affects the subsurface of the area. This circulation concentrates along a ENE-trending fault located at a little distance from the thermal resort. The hot fluids may upraise along the fault if the width of the ascent area is smaller than 20 m.     

Improvement of the solute transfer in a conceptual unsaturated zone scheme: a case study of the Seine River basin

For predicting the evolution of solute concentrations in groundwater and testing the impact of remediation policies, a coupling between the agronomical model STICS and the hydrogeological model MODCOU was implemented. When applied to the Seine River basin, this model accurately represents the temporal evolution of average nitrate concentrations in the aquifer, but with large local errors. We propose an improvement to the simple unsaturated zone (UZ) scheme NonsatSW used in STICS–MODCOU. The modifications are based on a comparison with the mechanistic model Metis considered as a reference as it solves Richards' equation. A more realistic saturation profile and a varying percolation rate are integrated in NonsatSW. This new model, named NonsatVG, is assessed by comparing it with NonsatSW and Metis. In an ideal case, NonsatVG generates a solute transfer and a dispersion closer to that of Metis than of NonsatSW. In real cases, without additional calibration, NonsatVG and Metis simulate better the average transfer velocities of the observed nitrate profiles. Furthermore, modifications in NonsatVG give a direct relationship between the depth of the water table and the saturation profile. We obtain, therefore, as in Metis, an evolution of the solute transfer velocity depending on the piezometric level. These dynamics are not simulated in NonsatSW. Despite a modified water transfer through the UZ, NonsatVG is also as valid as NonsatSW in the modelling of water transfer to the saturated zone. Finally, an application to the Seine basin shows that solute transfer velocities are lower with NonsatVG than with NonsatSW, but are in better agreement with literature. Copyright © 2010 John Wiley & Sons, Ltd.     

Zur Limnologie der Seen Südostlettlands

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A thermodynamic investigation of barium and calcium sulfate stability in sediments at an oceanic ridge axis (Juan de Fuca, ODP legs 139 and 169)

We have used a new thermodynamic model of barium and calcium sulfate solubilities in multicomponent electrolyte solutions (Monnin, 1999) to investigate the stabilities of barite and anhydrite in seawater or in marine sediment porewaters at high temperature and pressure. As a further test supplementing those previously carried out during model development, we have calculated the temperature at which standard seawater becomes saturated with respect to anhydrite. The model predicts that, upon heating at 500 bars, standard seawater becomes saturated with respect to anhydrite at 147 ± 5°C, which compares well with the literature value of 150°C (Bishoff and Seyfried, 1978). At 20 bars the calculated saturation temperature is 117 ± 3°C. This points to a non negligible pressure effect even at moderate pressures.We have calculated the barite and anhydrite saturation indices for the in situ temperatures and pressures, from the composition of porewaters collected at ODP Sites 855, 856, 857, 858, 1035 and 1036 during ODP Legs 139 and 169 (Juan de Fuca and Gorda ridges, NE Pacific). Calculated saturation indices for porewater samples collected at depths corresponding to temperatures between 70° and 110-120°C at an in situ pressure of about 260 bars yield equilibrium values for anhydrite and barite. Saturation indices of samples collected at depths where the temperature exceeds 110-120°C, however, yield values indicating supersaturation with respect to anhydrite and undersaturation with respect to barite. This result is consistent with the redissolution of anhydrite during cooling, leading to the well documented sampling artifact affecting porewater compositions in high temperature marine sediments: anhydrite dissolution increases the porewater sulfate content, which in turn induces a loss of barium from solution through barite precipitation (the common ion effect). We postulate that this redissolution occurs in sediment samples for which the in situ temperature exceeds 110-120°C: below this limit anhydrite remains at equilibrium or does not have time to significantly dissolve before porewaters are sampled.