Effectiveness of bandalling and dredging for the maintenance of navigational channel in the Jamuna river

Abstract

Inland water tran,port (IWI') has bcen serving Banglade;h as the most important but cheapcst mcans of communicution from long tilllc ago as tbe country is crl8scrossed by hundreds of rivcls. Currcntly, 0111of Ihe 24,000 km of river fOllte, only 25% 1.e arollnd 6,000 km of that remains navigable <.luringmOl1soonand this quantity even reduce, to about 3,800 km during dry scm;OTl, The .r~muna is one of the major rivers in Rangladesh, which imprint, immense importance to national cconomy, The Jamuna River is very dynamic and it~ chaotic behavior oftcn makes it difficult to predict planfonu changes even on medillm term scale. ln the dry season, navigation chal1nels shrink drasltcall} and cOTlsequcntly~ hllge amount of money I>reqUIred to maintain its navigability, The Jamuna River belongs to BJWTA's Class 11Water Ways Category, where Lea,t Available Depth (LAD) 01'2,10-240 m (7"8 It) is to be maintained all the }ear round for safe navigation, 13IWTA is the sole authonty for maintenance of the navigational channel,. Generally, they depend on dredging works to do so hut in ~ome reaches they exeeule il "ith bandalling, The purpose of this study is 10 analyze and compare tile effectiveness of both bandalltng and dredging to keep the navigation~l channel operational dllnng Ihe dry season, The study arcas were selected where b,mdallll1g and dredging - both means wen: 'J<;edto maintain navigability. In Manikdah, BlWT A apply only bandalling, whereas in Aricha only dredging is adopted to serve tile purpo,e. In Char Peehakhola both banda[]ing and dredging were applied simultaneously to maintain the navigational channel. In the year of 2006, it was observed that dunng dry sea~on, dred{ting failed to bring deSired ollteome in Char Pechakhola-Nakalia channel becau,e of high velocity Be~ides, dredged volume \va, dumped in the channel, which ultimately caused huge sediment deposition in the main channel COllsequen!ly, (he authorlly chose banda[[ing as an alternative option to keep the channel navigable Bandals arc comparatively cheap, cost-effective and environment friendly means as compared with dredgmg for maillt~jning navigability, Having installed once III a year, bandalling could su,tain for the entire dry ~easol1wherea, dredging had to be carried out scvcraltimes In each year to ~erve the ,ame purpose, Sincc, Mamkdah is located al 'Ipstream of the JanHllla River, the study indicates thai dredg:mg works might not be effective due to high vciocity and bandalling wOlild be the mo,t ~uitable option in that area. Whereas ln Arieha, only dredging is recommended as remedial mea,ure a, it is a ferry ghat area, From Ihe study, it was found that in the year oflOO], total cost of dredging for around 35,000 mJ dredged volume With 196 IIIreach at Char Peehakhola was Tk. 27 44 lakh, wherea~ ifhad it been carried out by bandalling the required amount would be around Tk. 3 lakh only, ]n Char Pcehakhola, since both bandal1ing and dredging works could be executed simultaneously, the study recommended that bandaUing can be camed out there for small reaches instead of dredging to make it cost effective, On the other hand, when longer reaches arc required to be dredged, tben tile combination of bondailing and dredging seems to be the suitable option to minimize the total cost. Similoily, in areA like Char P""hakhola with shullow water depths but suITicicnt now velocity in dry scason, bandalling alone or in combination wtth dredging is the effectlve option to keep navigational routes operational.