Design of groynes modified with both alignment and permeability for lowland river problems

Abstract

A groyne is an important river restoration structure. Although its history is for long and widespread use, optimized design of new groynes is not attempted much, which is very important to treat the highly unstable lowland river channels. A completely blocked impermeable groyne suffers from instability of the structure itself; whereas, fully permeable structure can not divert the flow rightly. Considering the present demands, four different groyne structures including modified combined and bandal-structures are examined in the laboratory channel to recognize their fluvial responses, incorporation with some field information. The performance of a groyne is confirmed through three key features: scour near groynes (structure stability), deposition in the groyne field (bank stability) and erosion in channel bed (navigability). Analyses of data show that the combined groynes cause gradual deceleration of flow towards the land and minimize local scour compared with the conventional impermeable ones. Also two other important features: deposition near bank and channel erosion, are better responded from modified bandal-structures and modified combined groyne.