Analysing the Effects of Climate Change on Wave Height Extremes in the Greek Seas

Climate Change, Adaptation and Long-Term Prediction

3-D Numerical computations of turbulence in a partially vegetated shallow channel

River hydrodynamicsTurbulent open channel flow and transport phenomen

Reynolds Stress Modeling of Flow in Compound Channels with Vegetated Floodplains

Experimental and Computational Hydraulic

Modeling of Climate Change Effects on Coastal Erosion

Sediment Transport and Morphodynamic

Assessment of Coastal Vulnerability for Present and Future Climate Conditions in Coastal Areas of the Aegean Sea

Mini-Symposium: Impacts of Climate Chang

Gravity Currents in a Vegetated Valley of Trapezoidal Shape

In this study lock-exchange experiments are performed in a tank of rectangular upper cross section and a lower vegetated valley of trapezoidal shape to study the effect of drag resistance, due to vegetation, on gravity currents. Many natural and man-made channels are approximately trapezoidal. For the simulation of the vegetation the bed is covered by flexible grass vegetation (height of vegetation, hv=2.0cm) of different submergence ratio hν/H (hν=height of vegetation, H=water depth). The motion of the gravity current is monitored with a digital video of high definition, the front velocity is measured and the height of the front is captured. Twenty four experiments are performed, twelve inside the trapezoidal section (H/Htr=0.4, 0.6 or 0.8) and twelve over the trapezoidal section (H/Htr=1.2, 1.4 or 1.6). The initial Reynolds number, based on the height of the valley and the reduced gravity, is greater than 10000 for all cases indicating that the gravity currents are turbulent. Results are compared with those of similar experiments without vegetation (Keramaris and Prinos, 2010) and hence the effect of the vegetation drag resistance on the motion of the current is investigated. The main conclusion of this study is that the shape of the tank plays a significant role in the propagation of gravity currents. The presence of trapezoidal increases the velocity of gravity currents in comparison with triangular or orthogonal shape

Vegetation turbulence: from RANS micro-computations to macro-analysis

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732In this work turbulent flow in a vegetated channel is studied numerically for various submergence ratios and vegetation densities. The submergence ratio, H/h (H=flow depth, h=vegetation height) varies from 1.17 to 5.0 and the vegetation density α (α= A/V , A= frontal area of the cylinder and V= volume influenced by a single cylinder ) from 2.46 to 4.3. The vegetation is considered rigid, simulated as cylindrical roughness and arranged in a staggered or a non-staggered pattern according to experimental data (Dunn et al., 1996 and Poggi et al., 2004). The 3D flow around a single cylinder is computed with the 3D RANS, a turbulence model of the k-ε type and appropriate boundary conditions. Based on detailed, “micro” flow characteristics (mean velocity, turbulent kinetic energy, shear stress etc.) the distributions of the respective “macro”, spatial-averaged characteristics are analysed and are compared with respective experimental data (Dunn et al., 1996). Implications for the macroscopic modeling of such flows are discussed and the significance of additional terms, resulting from volume-averaging, is analysed