Equivalent roughness of artificial vegetation in subcritical flow.

Eleni Kostidou, George Christodoulou

Thursday 2 july 2015

9:45 - 10:00h at Asia (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 10G. Environment - Impact

Resistance to flow in vegetated rivers is of major importance for flood control, as it determines the stage-discharge relationship and also affects the transport of pollutants and sediments. The paper focuses on determining the resistance characteristics of some selected artificial vegetation elements and patterns in terms of the friction factor f and the equivalent sand roughness ks, based on laboratory experiments. Three types of vegetation elements were used: (a) Thin rigid rods 0.5 cm in diameter and 4 cm high, always submerged; (b) Flexible plastic tubes (20 cm high) adjusted on the same rods, which were submerged or emergent depending on the flow rate; (c) Compound elements, consisting of rigid rods 0.8 cm in diameter and 5 cm high, bearing 3 cm diameter spheres on top, mostly submerged. Three patterns of each type of element were investigated, at plan densities ranging from 100 to 400 stems/m2. By measuring the free surface profiles, the Manning’s n coefficient was evaluated and subsequently the respective friction factor f and equivalent roughness ks were determined. The results are corrected for sidewall effects and presented in dimensionless form. Quantitative expressions are proposed relating f and ks to the density and other geometrical parameters characteristic of the vegetation array. Comparison with previous research is discussed.