SPATIAL VARIABILITY OF LOW-FLOWS IN THE UPPER WARTA RIVER CATCHMENT

Low-flows are an important component of the river regime. Their identification advances our knowledge about the formation of water resources in drought conditions. The analyses that we have carried out aimed to indicate the spatial structure of these flows. Our study area was the Warta River catchment up to the water-gauge at Sieradz. The input research material consisted of a sequence of daily discharge data for 12 gauging stations located in this catchment, in the period of 1971-2000, made available by IMGW-PIB. At the first stage, periodic flows based on flow time-duration curve and annual minimum flows were determined. Their values have been converted into specific flows, which facilitated the conduct of comparative analyses. On the basis of the obtained results, the spatial variability of low-flows in studied catchment was evaluated. The annual number of days with low-flows was identified for all gauge sections. The dynamics and distribution of low flow appearing in the multiannual period were evaluated. The analyses we have carried out made it possible to identify the factors, which determine the structure of low-flows. Research results have been illustrated with relevant maps and graphs.