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This paper presents the results of the first comprehensive national analysis of changes in discharge regimes of rivers in Croatia. Seven types of discharge regimes have been defined for rivers in Croatia. We analyzed the changes in discharge regimes of all types, comparing the standard period from 1961 to 1990 with the most recent period from 1990 to 2009. We found evidence of a redistribution of discharge throughout the year, an increase in autumn and winter discharges (especially for rivers dominantly fed by snowmelt), and a decrease in summer discharge values. Furthermore, we detected a change in the month of the appearance of mean discharge maxima and minima. In most cases, the changes can be explained by changes in the regime of climate elements (temperature, precipitation, and evapotranspiration). The results are consistent with those from upstream countries; that is, Slovenia, Austria, and Bosnia and Herzegovina. [ABSTRACT FROM AUTHOR]

Planinsko Polje is the westernmost active polje of Dinaric karst. It is a typical overflow-structural polje, with springs on the southern side feeding the superficial flow of Unica River. The river meanders over the polje towards the terminal outflow area on its northern side, where it sinks back into the aquifer through several ponors. Along the reach in proximity to the eastern border of the polje, the Unica River loses water through several outflow zones into distinct ponors and into a set of small openings and fracture zones. To estimate the outflow rate along these zones, the Unica discharge was measured upstream and downstream to the outflow zone. Seven velocity profiles were recorded with an Acoustic Doppler Current Profiler and the corresponding discharges were calculated. The measurements were taken within four hours during the flow recession following a partial flooding of the Planinsko Polje. Therefore, six outflow zones were evaluated with an outflow rate ranging between 1 m³/s and 5.6 m³/s. The total loss of water along the eastern border summed up to 18 m³/s under the given hydrological conditions. These results give new insight into the functioning of karst poljes and provide an important input for eventual future hydrological modelling of the area. [ABSTRACT FROM AUTHOR]

The pumping and mixing performance of a valveless piezoelectric pump were proposed and studied. A hemisphere-segment group that was fixed in the pump played the role of a valve. Based on the theoretical analysis of the pumping performance, the changes of the fluid velocity field, pressure difference, the coefficient of resistance and flow rate were simulated with FLUENT. Simulation results revealed the relationships among the pressure field, flow rates, row and column numbers, and row and column intervals of the hemisphere-segment group. The simulation results indicated that increasing row and column numbers, increasing row intervals, and decreasing column intervals could all increase the flow resistance difference in pump flow field and thus increased the flow rate. It was a/so found that the pumping effect was significantly improved by increasing row number than increasing column number; the increasing of row and column intervals could increase the size and strength of the vortex, and then improve the mixing and stirring performance of this pump. Finally, simulation results were tested and verified through pump flow-rate experiments. [ABSTRACT FROM AUTHOR]

The paper presents the physical background and the principle of a non contact flow measurement technique of electrically conductive fluids with an electromagnetic force. The explained theory in the paper is supported by an exsperiment given at the end of the paper. The pros of this technique are presented for measuring of aggressive or/and hot fluids. Derivations of the general equations are given for different measurement principles. The measured force is proportional to the fluid electrical conductivity, flow speed and magnetic-field strength. Recent technical advances in manufacturing the rare earth and non-rare earth strong permanent magnets as well as precise measurement of small forces have enabled practical measurement systems although the theoretical background was established already in the 1950s. [ABSTRACT FROM AUTHOR]

An application of data mining for the determination of flooded areas was published in the Journal Geodetski vestnik (no. 54/2010-4). This paper analyses the usefulness of these results for further analyses of hydraulic parameters. The velocity and discharges were computed for six locations. The study showed that the flooded areas determined by satellite images can be used for further analyses. Nevertheless, other layers have to be sufficiently precise, especially the digital terrain model (DTM). DTM 12.5 was used. The study showed that DTM 12.5 is not precise enough. The observed area is very rough and the hydraulic parameters (cross sectional area of flow, wetted perimeter, hydraulic radius, river-bottom slope, flow velocity, discharge) cannot be detected with sufficient precision. Consequently, the calculated hydraulic radiuses, velocities and discharges are out of expectations. In the first part of the article, some basic information about remote sensing and its techniques is presented. Some practical examples of their usage (especially satellite images) for the observation of natural disasters are also given. [ABSTRACT FROM AUTHOR]