Observations on the spatial variability of the Prut river discharges

<p>Liquid and solid discharges of the Prut River were analysed based on measurements<br />performed in 7 points from the Romanian national network of water monitoring during a<br />period of 30 years. The analyses were performed on flows for the period after the<br />construction of the Stânca-Costeşti dam and show the influence of the dam for the entire<br />analysed time. The analysis from upstream to downstream of the spatial variability of the<br />Prut River annual discharges showed their steady increase downstream and then a<br />decrease in the sector next to Oancea station. A statistical minority of the annual<br />discharges showed a continuous increase of them until the flowing of Prut into Danube.<br />Knowing that the lower basin of the river is characterized by a low amount of rainfall and<br />a higher evapo(transpi)ration than the remaining basin, the decreasing flows to the river<br />mouth is explicable; but the increasing flows to the river mouth cannot be justified, under<br />these conditions of water balance, than by certain climatological parameters of thermodynamical<br />nature which generate, with increased frequency, more intense and rich <br />rainfall, with a torrential character. The analyses on couples of three months showed that<br />the Oancea flows are higher than the upstream stations (opposite than usual) in years<br />when the flows of the upstream hydrometrical stations are lower than the multiannual<br />average and that supports the mentioned pluviometrical character. A plausible cause for<br />"Oancea phenomenon" is the increase and the decrease of the sunspots number, whose<br />cycles are relatively well fold on the increase and decrease of annual average flow at<br />Oancea hydrometrical station. The strongest increased discharges of the Prut River over<br />the discharges at the upstream stations occur from May to July (MJJ), the months with the<br />highest amount of rainfall. Seasonal analysis of MJJ and other couples of 3 months<br />showed that there are also growing flows at Prisăcani station relative to the adjacent<br />stations, but only in MJJ. This increase at Prisăcani is due to the local influx of water, not<br />to the decrease of the flow at the upstream and downstream stations. Prisăcani influx of<br />water is due to the large volume of rainfall in early summer on Iaşi Coast caused by the<br />numerous orographic convections, volume found then in the permanent flow. The Stânca<br />section has a contrasting variability too, but here is an explicit anthropogenic cause,<br />namely the upstream dam. We conclude the analysis of the Prut river runoff spatial<br />variability by showing that the river doesn’t have a linear model, but one with local<br />deviations whose manifestations can be attributed to the climate and anthropic specificity<br />of the considered sector