Runoff estimation is a key component in various hydrological considerations. Estimation of storm runoff is especially important for the effective design of hydraulic and road structures, for the flood flow management, as well as for the analysis of land use changes, i.e. urbanization or low impact development of urban areas. The curve number (CN) method, developed by Soil Conservation Service (SCS) of the U.S. Department of Agriculture for predicting the flood runoff depth from ungauged catchments, has been in continuous use for ca. 60 years. This method has not been extensively tested in Poland, especially in small urban catchments, because of lack of data. In this study, 39 rainfall-runoff events, collected during four years (2009–2012) in a small (A=28.7 km2), urban catchment of Służew Creek in southwest part of Warsaw were used, with the aim of determining the CNs and to check its applicability to ungauged urban areas. The parameters CN, estimated empirically, vary from 65.1 to 95.0, decreasing with rainfall size and, when sorted rainfall and runoff separately, reaching the value from 67 to 74 for large rainfall events.

River intermittence was studied based on data from hydrological monitoring in Poland. We screened the entire state database and two another data sources applying the criterion for zero-flow event: discharge less than 0.0005 m ³∙s ^–1, and found five intermittent rivers with catchment area from 9.2 to 303.7 km ². We aimed at finding associations between intermittence and climatic driving forces (temperature and precipitation), and between intermittence and anthropogenic activity. We used the Spearman correlation coefficient, circular statistics, and statistical tests for trend.
The concentration of zero-flow days, mostly in summer, and the decreasing trend in the standardised precipitation evapotranspiration index ( SPEI) in all catchments at various aggregation levels, and an increasing trend in the total number of zero-flow days and in the maximum length of zero flow events in two rivers, were detected. The strong negative correlation (–0.62 ≤ ρ < 0) between intermittence and the SPEI backward lagged in time showed that intermittence resulted from prolonged deficits in climatic water balance due to increasing evapotranspiration. The reaction of the Noteć catchment, amplified by the anthropogenic pressure (brown coal mines), was reflected in the atypical shape of the rose diagram and in inhomogeneities in river discharges.
The results show that the rose diagram can serve as an indicator of the degree of anthropogenic impact on runoff conditions.

Changes of land use, population and climate cause spatial and temporal changes in renewable water resources. For better understanding of the changes and effective management of water resources, hydrological investigations in river catchments are carried out around the world. A special investigation involves a study of hydrological processes in small site-specific catchments. The aim of the study is to analyse three characteristic river flows of a small lowland river on the basis of field surveys over two multiannual periods and to evaluate the applicability of indirect methods for determining characteristic flows in the catchment. Hydrological studies in the small agricultural catchment of the Mławka River, located in the Mławka Hills mesoregion, a part of the North Mazovian Lowland macro-region, have continued since 1966. The recorded data were used to determine daily flows and selected characteristic flows for multiannual periods of 1966–1990 and 1991–2020. To determine characteristic flows with indirect methods, three regional formulae and isorea methods were used. The study showed a decrease in renewable water resources over the period. In the multiannual periods, the average flow at the gauge station of Mławka River decreased by 15.6%. The outflow coefficient decreased from 0.303 to 0.265. The minimum annual flows also decreased by 29.1% and annual maximum flows showed an average increase by 19.7%. The use of indirect methods to determine the mean flow yielded results that converged with those from the second multiannual period.