Prediction of Local Scour Depth Around Bandal-Like Structures

Abstract

An analytical model for the prediction of local scour depth around bandal-like structures is developed using the basic features of laboratory experiments under clear-water scour. The developed model is applied to available laboratory data as well as field data along the Jamuna river in Bangladesh. It is found that the model fits the experimental data having relatively shorter length but failed to predict the field data where length of the structure was relatively longer. The underlying reasons of such success and failures of the model for the prediction of local scour depth around BLS is discussed with the future target to develop more generalized prediction model.

Sediment management using bandal-like structures as nature-based solution

“…However, as time passed, both the water levels and discharges increased, resulting increase in sediment transport capacity in the main channel and to some extent close to the end of the BLS field. Initially, the local scour depth around the BLS head was smaller as compared with impermeable structures evidenced in several flume experiments in steady uniform condition (Rahman et al, 2006), but in progress of time as the dimensions (both depth and areal extent) of the scour hole increased, more and more flow was concentrated in a similar fashion as summarized in earlier mobile bed laboratory experiments (Rahman, 1998) and the bed levels around the no.2 to no. 5 BLS exceeded the design level of the structure up to -4 m PWD ( Figure 10; July 27 2018) and eventually structures were washed away and only part of the no.…”

“…High flow velocities with spiral vortices were observed away from the BLS towards the outward direction, while a very low velocity, and nearly stagnant flow was observed behind the structures, resulting in the above observational fact (Figure 9 (Zhang et al, 2016;Hasegawa et al, 2018). Such strong component of near bed vertical flow is responsible for developing local scour depth (Rahman et., 2006) which eventually led towards undermining the structure when it exceeds the design scour depth of BLS.…”

Alternative Method for River Training Works: Bandal-Like Structures

“…However detailed flow features and sediment transport process under different hydraulic conditions are necessary to extend the understanding of the technical characteristics of bandal-like structure 4) . Rahman et al 3) verified the characteristics of flow patterns and sediment transport process around these structures in comparison with conventional impermeable groins. Furthermore, it was studied the applicability of an analytical formula to predict the local scour around the structures including the erosion in the main channel.…”

“…It is made by bamboos or wood pieces and the technique used to its construction is quite easy compared to impermeable groin which uses expensive materials such as concrete. The effects of the bandal-like structures on river morphology were verified through few studies including field investigations 2) and laboratory experiments 3) . However detailed flow features and sediment transport process under different hydraulic conditions are necessary to extend the understanding of the technical characteristics of bandal-like structure 4) .…”