Jaromír Říha

The Influence of Roughness on the Discharge Coefficient of a Broad-Crested Weir

The Influence of Roughness on the Discharge Coefficient of a Broad-Crested Weir The use of environmentally-friendly materials in hydraulic engineering (e.g. the stone lining of weirs at levees) calls for the more accurate estimation of the discharge coefficient for broad-crested weirs with a rough crest surface. However, in the available literature sources the discharge coefficient of broad-crested weirs is usually expressed for a smooth crest. The authors of this paper have summarized the theoretical knowledge related to the effect of weir crest surface roughness on the discharge coefficient. The method of determination of the head-discharge relation for broad-crested weirs with a rough crest surface is proposed based on known discharge coefficient values for smooth surfaces and on the roughness parameters of the weir. For selected scenarios the theoretical results were compared with experimental research carried out at the Laboratory of Water Management Research, Faculty of Civil Engineering (FCE), Brno University of Technology (BUT). Vliv Drsnosti na Velikost Součinitele Průtoku u Přelivu se Širokou Korunou Používání přírodě blízkých materiálů ve vodním hospodářství (např. kamenná opevnění povrchu přelivů v ochranných hrázích) vyvolává požadavek přesnějšího stanovení součinitele průtoku pro přelivy se širokou a hydraulicky drsnou korunou. V dostupných literárních pramenech je součinitel průtoku přelivů se širokou korunou obvykle vyjádřen pouze pro hladký povrch koruny přelivu. Autoři článku shrnuli teoretické poznatky týkající se vlivu drsnosti povrchu koruny přelivu na součinitel průtoku a navrhli metodu pro stanovení způsobu hydraulického výpočtu konzumční křivky přepadu přes přeliv se širokou a drsnou korunou. Postup vychází ze znalosti součinitele průtoku přelivu s hladkou korunou a charakteristik drsnosti. Pro vybrané scénáře byly teoreticky vypočítané hodnoty porovnány s výsledky experimentálního výzkumu uskutečněného v Laboratoři vodohospodářského výzkumu Ústavu vodních staveb, Fakulty stavební, Vysokého učení technického v Brně.

Discharge Coefficient of a Trapezoidal Broad-Crested Side Weir for Low Approach Froude Numbers

AbstractEven though broad-crested side weirs have been subjected to numerous studies, guidance for discharge coefficient determination for broad-crested side weirs still has not been clearly given. Experimental research was carried out to describe the flow conditions in front of a trapezoidal broad-crested side weir at low Froude numbers in the approach channel for various combinations of inflow and overflow discharges. Three side weir variants with different oblique angles were studied. Flow characteristics at the side weir were analyzed and assessed based on the results obtained from extensive measurements performed on a hydraulic model. The empirical relation between the coefficient of obliqueness, the angle of side weir obliqueness, and Froude numbers upstream and downstream of the weir was derived.

Flow characteristics at trapezoidal broad-crested side weir

Abstract Broad-crested side weirs have been the subject of numerous hydraulic studies; however, the flow field at the weir crest and in front of the weir in the approach channel still has not been fully described. Also, the discharge coefficient of broad-crested side weirs, whether slightly inclined towards the stream or lateral, still has yet to be clearly determined. Experimental research was carried out to describe the flow characteristics at low Froude numbers in the approach flow channel for various combinations of in- and overflow discharges. Three side weir types with different oblique angles were studied. Their flow characteristics and discharge coefficients were analyzed and assessed based on the results obtained from extensive measurements performed on a hydraulic model. The empirical relation between the angle of side weir obliqueness, Froude numbers in the up- and downstream channels, and the coefficient of obliqueness was derived.

Harmonisation of Terminology and Definitions on Soil Deformation Due to Seepage

When comparing different literature sources, differences in the terminology concerning soil deformation due to seepage may be found. The distinctions are caused by language barrier (Slavic and Germanic language groups), by the view on the mechanisms and by the way of understanding individual soil deformation processes. These differences in terminology are related to the naming of the phenomenon itself or to translation issues. Clear terminology is important when comparing stability criteria applied in different countries. Here “western” and “eastern” schools may be distinguished. This study provides an overview on terminology for soil deformation due to seepage in English, French, German, Russian, Polish and Czech languages, some suggestions are presented with discussion. The paper is an initial phase for further comparison of criteria for individual soil deformation modes.

Evaluation of groundwater contamination in former military airport area

The analysis of groundwater contamination at the former military airport, due to fuel tanks leakage and other accidental spills, mainly involving polycyclic aromatic hydrocarbons (PAH), is presented in the paper. It was observed by modelling that, after termination of pumping, the contaminant by-passes the slurry wall around its edges and proceeds towards the withdrawal area. The modelling showed that the water contamination hazard is quite low, which is mainly due to pollutant deterioration (decay) and sorption.

Uncertainty in Determining the Critical Hydraulic Gradient of Uniform Glass Beads

One of the local defects in soils due to seepage is heave. This may occur at the downstream toe of hydraulic structures in the case of upward external seepage where particles of uniform soils are subject to uplift and also upward seepage forces. The phenomena starts with gradual liquefaction of soil grains accompanied by gradual loss of shear strength followed by boiling, heave and possible backward erosion and overall collapse of the structure. The problem of heave has been addressed by numerous authors who have published relationships based on the balance of forces and also on results of laboratory experiments. In this paper the results of extensive systematic experimental research carried on glass beads subjected to upward seepage in the vertical Darcy apparatus are presented. Three glass beads’ diameters 0.2 mm, 0.5 mm and 1.0 mm with uniformity coefficient CU from 1.1 to 1.3 and different porosity n from 0.36 to 0.44 were tested. To enable statistical evaluation of the uncertainty in critical hydraulic gradient 177 individual tests have been performed. The results of measurements were analysed and compared with relationships proposed by various authors. The best agreement was provided by the well-known Terzaghi formula relating the critical gradient to the specific mass of grains and soil porosity. Based on the experimental data the uncertainty in the use of Terzaghi formula was expressed via reliability coefficients recommended for use in technical practice.

Assessment of empirical formulae for determining the hydraulic conductivity of glass beads

Abstract Empirical formulae are often used in practice to quickly and cheaply determine the hydraulic conductivity of soil. Numerous relations based on dimensional analysis and experimental measurements have been published for the determination of hydraulic conductivity since the end of 19th century. In this paper, 20 available empirical formulae are listed, converted and re-arranged into SI units. Experimental research was carried out concerning hydraulic conductivity for three glass bead size (diameters 0.2 mm, 0.5 mm and 1.0 mm) and variable porosity. The series of experiments consisted of 177 separate tests conducted in order to obtain relevant statistical sets. The validity of various published porosity functions and empirical formulae was verified with the use of the experimental data obtained from the glass beads. The best fit was provided by the porosity function n3/(1-n)2. In the case of the estimation of the hydraulic conductivity of uniform glass beads, the best fit was exhibited by formulae published by Terzaghi, Kozeny, Carman, Zunker and Chapuis et al.

Assessing stream water quality influenced by storm overflows from sewers

For open channels significant pollution sources during the intensive precipitations are outflows from storm-water overflows on the sewer network. When combined with low discharges in rivers, the water released from overflows can cause high concentration of pollution in receiving open channels. In this paper, the results of computer modeling of the impact of storm-water overflows on the stream water quality in three municipalities in Czech Republic are shown. The local river networks are the main receivers in the cities where storm-water overflows are led in. The results serve as a base for the proposals on the measures, improvements and structural modifications.