Volumen 17 (2017): Edición 3 (September 2017)

The geometry of weirs is a prime factor influencing hydraulic performance and accuracy. One of the geometric components of weirs, is the situation of its top corners, are they sharp or rounded, and what is the most suitable radius of such rounding curves? The present study was conducted to examine the effect of using five different radius of curvature for both the upstream and downstream top corners of a clear over-fall weir on its hydraulic performance and accuracy. Eleven models of wooden weirs were shaped and prepared with five different values of rounding curvature. The prepared weir models were located in a laboratory tilting flume of 13.50 m length, 0.30 m width, and 0.30 m depth. The study was carried out in the Irrigation and Hydraulic Laboratory of the Civil Department, Faculty of Engineering, Assiut University, Egypt. A discharge ranging from 2.0 to 22.0 dm³ s⁻¹ was used, and through 66 experimental runs, all the necessary hydraulic parameters were measured, and recorded. The obtained data were tabulated, analyzed, plotted, and technically discussed. The main results and obtained conclusions proved that when the front weir top edge is curved the discharge coefficient increases up to 8%. Also, when both front, and behind weir top edges are curved the discharge coefficient increases up to 14%. At the same time the discharge coefficient has a maximum value when the radius of curvature in upstream and downstream top corners equals 20% of the height of the weir.

The largest lakes of the River Tywa basin i.e. Strzeszowskie, Dołgie, Swobnica and Dłużec (north-west Poland, West Pomeranian Lakeland) were studied in the period 2008–2013, usually in a six week cycle. The aim of the study was to determine the degree of anthropogenic pressure on the lakes. Anthropogenic pressure was assessed against the natural vulnerability of lakes to degradation and the actual rate of eutrophication, with particular consideration of the catchment areas. Catchments of the studied lakes were classified as III class – catchment with moderate possibility of matter supply to lakes. Lakes Swobnica and Dłużec are characterised by low resistance to degradation. Lake Strzeszowskie is categorised as having moderate resistance and Lake Dołgie is non-resistant to degradation and highly susceptible to external pressure. The rate of eutrophication of lakes Strzeszowskie and Dłużec was found to be moderate, whereas lakes Dołgie and Swobnica show a high rate of eutrophication. The analysis of nutrient loading reaching the waters of the aforementioned lakes shows that the main area source is arable land, and the fundamental point source is the inflow of river waters to each of the analysed reservoirs. Nutrient loading supplied by the river is several times higher than area load. Such conditions require protective action to be taken within the catchment area and particularly, intensive implementation of good agricultural practice. In the studied lakes, there is a significant predominance of incoming nutrient loadings over dangerous and admissible loads.

The aim of this research was to analyze the horizontal spatial heterogeneity of both water and superficial sediment quality among and within the reservoirs of the Cantareira System (CS), focusing on concentrations of N and P, attributed to the dumping of raw domestic sewage into water bodies, which is the main cause of water pollution in São Paulo State (Brazil). The CS is a multi-system complex composed of five interconnected reservoirs, with water transported by gravity through 48 km of tunnels and channels. From the last reservoir of the CS, with an output of 33 m³ s⁻¹, the water is conducted to a water treatment plant, producing half of the water consumed by 19 million people inhabiting São Paulo city. The upstream reservoirs are more eutrophic than the downstream ones. Data also suggest that the low phytoplankton biomass (ranging from 0.9 to 14.4 μg dm⁻³) is regulated by the low nutrient availability, mainly of phosphorus (TP ranging from below the detection limit, <9.0 μg dm⁻³, to 47.3 μg dm⁻³). For water, the DIN/TP ratios values range from 19 to 380. The upstream reservoirs function as nutrient accumulators and the sediment is the main compartment in which P and N are stored. Although the reservoirs are located in different river basins and are not in sequence along the same river, the results suggest a marked gradient between the reservoirs, with features similar to those of cascade reservoirs. The large volumes flowing through the canals and tunnels could explain the observed pattern. The CS reservoirs can therefore be considered multi-system reservoirs in cascade, constituting a particular case of multi-system reservoirs.

The paper presents the results of the impact of the Tri-City Ring Road on small endorheic catchment basins. Particular attention was paid to pollution discharged from the road to the surface water, as well as changes in hydrological conditions in the vicinity of the road. In the study, surface water samples were analysed in terms of their electrolytic conductivity, pH and content of major minerals. GIS was also used to study transformation of local catchment areas as a result of the road construction, determining their relevance to local conditions of drainage. Moreover, the main directions of transformation of surface waters of the small endorheic wetlands caused by runoff water from the ring road were discovered. Research results have shown a strong influence of the road functioning on surface water properties and changes in hydrological conditions of the studied catchment basins.

Lake sediments are excellent archives of environmental and climate change. Especially important are varved sediments which can provide high-resolution (annual) records of those changes. Process studies including limnological measurements, particle flux monitoring and analyses of sediment structures give an opportunity to explain relationships between meteorological conditions, in-lake processes and varve formation. In our study, three lakes were selected in the Masurian Lakeland: Lake Żabińskie, Łazduny and Rzęśniki. These relatively small and deep lakes contain well preserved biogenic varves. The lakes are influenced by the same meteorological conditions but differ in terms of their catchment size, land use, hydrology, lake basin morphology and trophic status. To explore the relationships between different parameters and preservation/transformation of climate signals in the sediments we started systematic limnological measurements in the water column of these lakes, water sampling for hydrochemical analyses, monitoring of modern sedimentation using sediment traps and analysis of topmost varves from short sediment cores. With this comprehensive and high-resolution monitoring program scheduled for at least four years we are going to verify the potential of varves to track short-term meteorological phenomena in lake sediments.