Turbulence intesity in open-channel flows with submerged flexible vegetation.

Nina Nikora, Vladimir Nikora

Friday 3 july 2015

13:45 - 14:00h at North America (level 0)

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

Parallel session: 16F. Environment - Ecohydraulic

Turbulence intensity is a major measure of turbulence structure that remains a hot topic of basic research, particularly for unconventional conditions such as flexible roughness elements. Over the last few decades there have been numerous studies of this parameter for wall-bounded flows over smooth and rough beds. The formulations for vertical profiles of turbulence intensity that resulted from these studies can be grouped into three main categories: (1) exponential; (2) logarithmic; and (3) power type distributions. In most cases, these formulations have been obtained empirically, with a few exceptions of semi-empirical or physically-justified relationships. Among wall-bounded flows, the open-channel flows over flexible vegetation represent the least studied case. The information on turbulence intensity within vegetation canopy is particularly scarce. The objectives of this paper therefore are: (1) to provide a brief comparative overview of the existing turbulence intensity approximations; (2) to propose a new concept where vertical turbulence intensity profile, covering both canopy region and vegetation-free overlying region, is modelled using a multi-segment approach; and (3) to test the proposed formulation and compare it with currently available relationships. Tests of these relationships are conducted employing extensive laboratory experiments covering wide ranges of background flow and vegetation parameters. The analysis also includes the identification of the effects of flow and roughness parameters on the model coefficients as well as the assessment of their interdependence. Finally, potential applications of the proposed model in fluvial hydraulics and eco-hydraulics are discussed.