Issue 3 [September]( Issue on Water Resources, Hydrology and Hydraulics )Editorial Associations between stream flow and climatic variables at Kizilirmak river basin in TurkeyDadaser-Celik F., Celik M. and Dokuz A.S., Pages:354-361 DOI: https://doi.org/10.30955/gnj.000881Paper Topic: General Issue: Issue 3Get Full Paper AbstractAbstract is currently not available. Regression analysis between sediment transport rates and stream discharge for the Nestos River, GreeceAngelis I., Metallinos A. and Hrissanthou V., Pages:362-370 DOI: https://doi.org/10.30955/gnj.000888Paper Topic: General Issue: Issue 3Get Full Paper AbstractSystematic measurements of sediment transport rates and water discharge were conducted in the Nestos River (Greece), at a place located between the outlet of Nestos River basin and the river delta. This basin area is about 838 km2 and lies downstream of the Platanovrysi Dam. Separate measurements of bed load transport and suspended load transport were performed at certain cross sections of the Nestos River. In this study, relationships between sediment transport rates and stream discharge for the Nestos River are presented. A nonlinear regression curve (4th degree polynomial curve; r2 equals 0.62) between bed load transport rates and stream discharge, on the basis of 63 measurements, was developed. In addition, a nonlinear regression curve (5th degree polynomial curve; r2 equals 0.95) between suspended load transport rates and stream discharge, on the basis of 65 measurements, was developed. The relatively high r2 values indicate that both bed load transport rates and, especially, suspended load transport rates can be predicted as a function of the stream discharge in the Nestos River. However, the reliability of the regression equations would have been higher if more measured data were available. Modeling the effect of vegetation on river floodplain hydraulicsStamou A.I., Papadonikolaki G., Gkesouli A. and Nikoletopoulos A., Pages:371-377 DOI: https://doi.org/10.30955/gnj.000883Paper Topic: General Issue: Issue 3Get Full Paper AbstractVegetation in river floodplains has significant influence on the flood hydraulics and fate of suspended sediments, nutrients and contaminants. In the present, work preliminary 3-D calculations were performed to examine the effect of vegetation on the mean flow in open channels using the CFD model CFX-12.1, employing the RANS k-epsilon turbulence model. Calculated flow velocity distributions were compared against an experiment of free surface uniform flow in a vegetated experimental channel, filled with cylindrical submerged elements representing vegetation; these elements were rigid and arranged in a staggered pattern. Four unstructured numerical grids were employed, ranging from approximately 9.5 to 27.5 millions of tetrahedral elements. The main characteristics of the flow were (a) the formation of small recirculation regions in the wakes of the cylinders and (b) the relative uniform flow conditions throughout the length of the channel. Low flow velocities were observed in the vegetated region, implying the resistance due to vegetation, and higher velocities close to the free surface. The best agreement with experimental data was achieved for the finest grid that also included grid refinement at the top of the cylinders. Grid independence behaviour using relatively very fine grids was rather surprising and requires further detailed investigation. Measuring the turbulent characteristics in an open channel using the PIV methodPechlivanidis G.I., Keramaris E., Pechlivanidis I.G. and Samaras G.A., Pages:378-385 DOI: https://doi.org/10.30955/gnj.000884Paper Topic: General Issue: Issue 3Get Full Paper AbstractInvestigation of open channel flows is very important for a wide range of applications, including restoration and enhancement of river aquatic systems. As a result, the scientific community has focused on providing further insights on the flow characteristics in vegetated channels. Vegetation may be submerged or emerged, rigid or flexible with high or low density. For rigid vegetation, the hydraulic behaviour of the channel is similar to the behaviour of a channel with macro-roughness which could be caused by the presence of geometrical elements (e.g. cylinders, cubes). For flexible vegetation, both the flexibility of the vegetation and the hydrodynamic of the flow contribute to the generation of several formations such as erect, gently swaying, and prone. In this study, the characteristics of turbulent flow in an open channel were studied experimentally using Particle Image Velocimetry (PIV). This method assumes that the particles of a fluid faithfully follow the flow dynamics, hence the motion of these seeding particles are used to calculate velocity information of the flow. The experiments were conducted for both impermeable and permeable beds in a channel of 6.5m length, 7.5 cm width and 25 cm height. Two grass-like vegetation types of different height (2 and 6 cm) were used to represent permeable beds. These conditions are typical of flows encountered in sediment transport problems. Hydraulic characteristics such as distributions of velocities, turbulent intensities and Reynolds stress are investigated at a fine resolution using the PIV. Velocity is measured above the vegetation at different heights. Results show that velocity over the vegetation region is a function of the vegetation height and the total flow depth; velocity decreases as the vegetation height increases. In addition, we show that velocities above the vegetation region are much lower than velocities above an impermeable bed. This is due to the turbulent shear stresses and the existence of turbulence in the vegetation region, which reduce the mean velocity above the vegetation region. In addition, results show a region of zero velocity; between 3 and 6 cm and 1 and 2 cm for a 6 cm and 2 cm vegetation. This result shows that 50% of the vegetation behaves like an impermeable bed. Modeling renewal times in Amvrakikos Gulf, GreeceStamou A.I., Loverdou L., Matsoukis C., Albanis T. and Gkesouli A., Pages:386-392 DOI: https://doi.org/10.30955/gnj.000885Paper Topic: General Issue: Issue 3Get Full Paper AbstractThe Amvrakikos Gulf, located in the northwest Greece, is one of the largest semi-enclosed embayments being about 40 km long and 15 km wide. Water renewal is made via a narrow channel which connects the Gulf with the Ionian Sea having a 3.0 km length, width ranging from 0.8 to 2.0 km and depth from 2.0 to 13.0 m. The most common terms being used to indicate how fast the water of semi-enclosed coastal embayments is renewed are hydraulic retention time (HRT) and residence time (RT). A preliminary estimation of HRT and RT is performed via a 3-D integrated model consisting of the hydrodynamic sub-model FLOW-3DL and the water quality sub-model QUAL-3DL. The models involve the 3-D non-steady state continuity, momentum and convection-diffusion equations expressed in layer formulation. A space-staggered computational grid was used and the following conclusions were drawn: (1) The HRT ranges from 1.86 to 2.42 years. (2) The flow rates of Louros and Arachthos rivers, which gush into the Gulf, reduce the HRT by 0.56 years. (3) The effect of the wind on HRT is minor due to the small size of the entrance to the Gulf. (4) The theoretical RT is equal to 3.85 years. Pages« first ‹ previous 1 2