ROLE OF GROYNES IN CONTROLLING RIVER EROSION

Abstract

The main objective of Installation of groynes in rivers is to save the destruction of river banks caused by sediment erosion in the form of flood. The hydraulic features (the water level, the velocity of flow, flow of main stream, depth of sand) depend on the groyne that affects the bank protection. The design factors, the spacing, length of groynes & thickness of groynes also affect the flow in a river. If length of groyne increases, it helps in increasing bank protection but if it is increased over a desired limit, it leads to chocking of flow in a river. If simultaneously net head of groyne & velocity in the main channel change considerably, this will result in risk of causing severe local scours on structures. Recirculation flow between groynes develops because of launching of groyne series. It is necessary that groynes should be designed with appropriate spacing to save banks as erosion of banks may take place depending on spacing between groynes that may generate strong reverse flow. The experimental analysis provided information about the following: (i) The X-stream distribution of the velocity (ii) The cross stream distribution of the depth of sand (iii) The depth of water for all cases for plain sand bed as well as well as groyne bed (iv) The morphological developments in the groyne fields in different flow conditions The results lead to the following conclusions: (i) The depth of sand curves, the velocity distribution curves & the Froude number curves are analysed all along the length of the flume in main river channel, along the centre line & in the groyne field for all tested cases. (ii) In all tested cases, there was net import of sediments into the groyne fields V (iii) We chose that case in which there is least erosion of soil and that was determined from the depth of sand curves and also from the weight of sediment sample taken from each set of experiment during flow condition In our case of submerged groynes, the sediment is transported to the groyne fields across the whole length of normal line. Diffusion through the mixing layer & secondary flow circulation play a role.