Riverbank stabilization based on the modulation of the near bank turbulence scales

Abstract

Sundarban area of the lower Gangetic plain experiences embankment failure almost every year due to the formation of toe undercuts. Waves generated due to the continuous action of wind and tidal currents are paramount in the growth and development of these undercuts. Existing literature suggests that grids are effective in modulating the scales of turbulence. The present investigation is carried out with the objective of looking into whether grids can be effective in controlling the undercutting process and thereby restraining the failure of these embankments. To explore this artefact, laboratory flume experiments were carried out using cylindrical grid placed near the toe of a cohesive bank. Turbulent 3-D velocity was measured using micro-Acoustic Doppler velocimeter (ADV) at the junction of the grid and at the near bank region to get insight into the governing mechanism of grid-influenced flow on the bank. The present investigation revealed that the installation of the cylindrical grids at the toe region of the bank is effective in modulating the scales of turbulence. The scales of Reynolds shear stress fluctuations showed a reduced magnitude due to the presence of near bank grid. The results show that the grid breaks the large scales (larger eddies) of turbulence into smaller eddies through eddy cascading process and thereby modulate the turbulent shear stresses. This probably slowed down the erosion rate preventing the formation of the undercuts and thus restraining bank/embankment failure. Thus, it is envisaged that the proposed methodology on implementation at the riverbanks would serve as an effective measure in the protection of these embankments.