Volume 19 (2019): Edition 2 (June 2019)

The lakes selected for the analysis are situated in the Kashubian Lakeland which is a proper research area as there is a benchmark lake with a long data series within the region. This lake is located in the central part of the lakeland, in the upper Radunia water catchment area, while the lakes not being hydrometrically supervised constitute part of the upper Łeba water catchment area. The main objective of this study is to determine the relationship between ice cover thickness on the flow-through lake undergoing constant hydrometric supervision and some selected flow-through lakes not being monitored. The following lakes were selected for the study: Lake Raduńskie Górne (the benchmark lake) and four hydrometrically unmonitored lakes: Długie, Wielkie, Reskowskie and Łapalickie. The fieldwork research was done in the period of 2003–2008. Moreover, in order to evaluate the data calculated with the use of empirical formulas, additional fieldwork research was carried out in 2016. The analysis made it possible to develop formulas that allowed the thickness of the ice covering the selected flow-through lakes of the upper Łeba water catchment area to be assessed with decent accuracy.

Wetlands are among the most productive ecosystems in the world. They provide numerous beneficial services for people and wildlife. The most important services are improving water quality and wildlife habitats. The complex, dynamic relationships between the organisms inhabiting the wetland environment are called food webs. Both water quality and high levels of nutrients are crucial for improvement of the food web. Many bird species rely on wetlands for food, water and shelter, especially during migration and breeding. The water quality of Choghakhor Wetland was evaluated from April 2010 to March 2011, by measuring some physicochemical parameters and doing benthic macroinvertebrate analysis. Sampling was done in 3 replicates with alternation of 45 days. The resolute was divided into more than 25 identified macroinvertebrate families which belonged to 5 classes and 12 orders. The correlation between biological indices and water quality parameters showed that bioindicators and community indices could be used for the evaluation of water quality in this wetland. The water quality of Choghakhor Wetland was classified as average or in the severe pollution class, according to these indices. It can be concluded that bird migration is at risk due to the decline in the overall health of the Choghakhor Wetland ecosystem.

Trapa natans (water chestnut) is an aquatic, thermophilic plant whose decline has been observed in many localities in central Europe during the last decades. In this paper, we present a description of two new T. natans subfossil sites located outside its present northern distribution in Poland. High-resolution analysis of plant macrofossils supported by geochemical analysis were undertaken to reconstruct the palaeoecological habitat and examine the cause of the late Holocene decline of T. natans that took place ca. 4000 calibrated years before AD 1950 (cal. yr BP) in a paleolake, presently the Bagno Kusowo bog. Its disappearance was a consequence of terrestrialisation and the development of peatland. In paleolake sediments covered by the peat layer in the Mechacz Wielki bog, T. natans macrofossils were found from before ca. 3300 cal. yr BP. The decline of T. natans could have resulted from the changes and development of other plant communities where the dominant role was played by Stratiotes aloides and Nymphaea sp. In our study sites, T. natans occurred together with Potamogeton crispus, Potamogeton obtusifolius, Nymphaea alba, and Nuphar sp. in eutrophic water dominated by Ca2+, Fe³⁺, and Al³⁺ ions. Our palaeobotanical and geochemical results align with the contemporary conditions of T. natans habitat.

Branching channel flow describes any side water withdrawals from rivers or main channels. Branching channels have widespread application in many practical projects, such as irrigation and drainage network systems, water and waste-water treatment plants, and many water resources projects. Therefore, in this research, a comprehensive analysis of laboratory data has been carried out to discover the best angle of branching. The study also aims to introduce simple, practical equations to help engineers of water resources to fix the percentage of discharge diverted to the branch channel. The study was carried out in the Irrigation and hydraulics laboratory of the civil department, Faculty of Engineering, Assiut University. The laboratory channel consisted of two parts, the main channel, and a branch channel. The main channel was 8.0 m in length, 20 cm wide, and 20 cm in depth. The division corner to the branch channel was sharp edged and located 5.0 m downstream of the main channel inlet. The branch channel was 3.0 m long, 20 cm in depth and its width was changed three times (10, 15, and 20 cm) respectively. A total of 84 runs were carried out. Investigations of the flow into the branching channel show that the branching discharge depends on many interlinked parameters. It increases with a decrease of the main channel flow velocity and the Froude number upstream of the branch channel junction. It also increases with an increase in the Y_b / Y_u ratio. In subcritical flow, water depth in the branch channel is always lower than the main channel water depth. The flow diversion to the branch channel leads to a decrease in water depth downstream of the main channel. In addition, the study showed that the highest discharge rate was obtained when the angle of branching was equal to 45° and then an angle of 60o. While the lowest discharge rate was obtained at an angle of 90°. Furthermore, at B_r = 1.0, using a branching angle equal to 45° the discharge ratio (Q_r) increases from about 4.42 to 19.01%, more than that obtained with using the branching angle equal 90°, while the discharge ratio (Q_r) increases from about 0.52 to 49.18% and 1.51 to 24.79%, at B_r = 0.75, and B_r = 0.5 respectively.