Influence of riparian vegetation on flow resistance in mobile bed straight compound channels

Abstract

Riparian vegetation is an important feature in rivers and essential in hydraulic engineering including flood management and river restoration. Deforestation activities have been pointed out as a contributing factor to the severity of flood damages. This shows that the importance of riparian vegetation in river restoration schemes in order to lessen the issues of flood risk and flood protection. The riparian vegetation creates additional resistance to flood flow which resulted in velocity reduction, increasing of flow depth and transportation of sediment in rivers. The hydraulics of flood flows in vegetated floodplain of mobile bed straight channel was experimented in the Hydraulics Laboratory, Faculty of Civil Engineering, Universiti Teknologi Malaysia. Two-lined steel rods with tandem and staggered arrays to simulate as rigid emergent vegetation were placed along the riparian zone of an asymmetrical channel. The flow resistance including Manning’s n, Darcy’s f and drag force, FD were studied. The findings showed that the riparian vegetation had increased the Manning’s n by 20%. Meanwhile, staggered arrangement of vegetation was found to generate the highest Darcy’s f of about 16% as compared to tandem arrangement. The presence of riparian vegetation also found to induce 20% more drag force compared to the main channel roughness effect. The dramatically changes of bed morphology also led to the increase of the flow resistance in the channel.