Renata Graf

Integration of a flood risk management and waters protection system on the example of the Warta Valley between Konin and Oborniki

The aim of the study was the analysis of the integration of a flood risk management and water protection system in a selected section of the Warta Valley with taking into consideration the guidelines of the Water Framework Directive and the Floods Directive. The structure of the valley is comprised within a distance of 201.1 km by stretches of: an urstromtal, between the towns of Konin and Śrem, and the Warta gorge stretch between Śrem and Oborniki. High environmental values of the valley are shown, related to the presence of conservation areas and, on the other hand, a high flood hazard risk, resulting e.g. from advancing land development in the valley and its low retention capacity. The Integrated Water Resources Management guidelines conception was used in the analysis, inlcuding pointing out the directions of relations between minimizing flood risk and protection of natural values of the Warta River and its valley. Spatial distribution of the flood hazard and risk in the Warta Valley was also analyzed. A detailed analysis covered activities of a technical and non-technical character intended to stop the growth of flood risk. In the field of water conservation, the considered objectives included: achieving and maintaining a good ecological potential of waters or the risk of failing to achieve it, which is determined by a high urbanisation ratio, draining of an open-pit lignite mine, extensive morphological change in the river bed and pollution discharged into the waters from land used for agriculture. The results proved that one of the most significant factors directly impacting the environmental condition and ecological potential of the waters is the activity related to flood risk reduction. Potential threats to the functioning of NATURA 2000 areas characterized by high natural values were also indicated.

Thermal conditions of the formation and persistence of ice cover on the River Noteć

The article presents the results of an analysis of the impact of cumulated series of negative air temperatures (cumulated degree-days) on the formation and persistence of the permanent ice cover on the River Noteć in the period 1987–2013. When assessing ice phenomena, use was made of observations conducted over 24-hour periods at four IMGW-PIB stations located along the River Noteć: Pakość (upper section), Ujście and Krzyż Wielkopolski (middle section) and Nowe Drezdenko (lower section). The authors determined the nature of the distribution of negative series and 24-hour air temperatures in terms of their duration, increase and distribution in years and months, using data from the Piła meteorological station. The primary objective was to specify the threshold values of cumulated degree-days at which the permanent ice cover starts to appear on the river, and the conditions under which this phenomenon is accelerated. When determining the strength of the relation between cumulated degree-days and the probability of appearance of an ice cover, use was made of the logistic regression model. Research showed that in the majority of instances ice cover appeared on the river at values of cumulated degree-days greater than: –16°C in Pakość, –21°C in Ujście and Krzyż Wielkopolski, and –73.5°C in Nowe Drezdenko. During the analysed period, 306 negative air temperature series occurred in the studief catchment area, with those lasting 5–10 days (76 of all instances) being predominant. As regards the River Noteć in Pakość, the logistic regression model confirmed that, on average, a one-degree increase in the value of cumulated degree-days is associated with an increase in the probability of  appearance of the permanent ice cover of approximately 2.10%, of approximately 1.17% in Ujście, of 2.72% in Krzyż Wielkopolski, and of approximately 5.70% in Nowe Drezdenko. The more rapid the increase in cumulated series of negative air temperatures, the greater the probability of ice cover appearing and persisting on the River Noteć. The  analysis pointed to the usefulness of the cumulated degree-days factor for predicting the appearance of ice cover on the river. The results obtained are significant for maintaining the economic and ecological function of the River Noteć. Information about the icing of the river has a practical dimension, among others as concerns identifying and minimising hazards connected with the occurrence of jams and ice-jam floods, which bring about enormous economic losses and constitute a threat to human life.