Early implementation projects on flood control and irrigation in Bangladesh

Early implementation projects on flood control and irrigation in Bangladesh: Study of methods used for closing tidal channels - Chakamaya closue; fourth interim report

Smith, E.C.
Zwets, J.
Visser, R.

Bangladesh Water Development Board

1979-08

The closure of the Chakamaya Khal was executed in the winter of 1978/79 as a stage of the "Study of Methods for Closing Tidal Channels". The closure was executed as an "Early Implementation Project on Flood Control and Irrigation in Bangladesh". A team of three Dutch experts assisted the Bangladesh Water Development Board and also the contractor with the implementation. The tidal channel has been closed using bottom protection mattresses and a cofferdam filled with clay-filled gunny bags. The tidal range at the site is about 10' at spring tide and 5' at neap tide. The tidal volume at spring tide is about 8,000 acre feet (10,000,000 cub.m). The channel cross-section below the average water level was about 9,000 sq ft (800 sg m) with a width at the water line of 700 feet (210 m). More detailed information concerning tides, soils, cross-sections and work activities is given in Chapter 3. Vertical closure was implemented in two phases. Phase One consisted of the construction of a bottom protection and an underwater sill formed by dumping clay-filled gunny bags from barges which were subsequently covered with mattresses. Phase Two involved the construction of a cofferdam with walls of bamboo piling. The actual closure was achieved by filling the cofferdam with clay-filled gunny bags. Chapter 4 gives more extensive information concerning the design and the execution of the closure works. In Chapter 5 the behaviour of the mattresses and the gunny bags is discussed. The execution of the project encountered no serious problems although small problems did occur because of the fact that this was the first such project to be implemented in Bangladesh. The method employed proved to be a reliable closure technique. The closure was controlled throughout. Closure must be achieved before the middle of March when weather conditions begin to worsen. Closure at the Chakamaya as late as April 22nd was possible however due to an exceptional dry spring in Bangladesh. The actual execution of the closure should ideally start in the beginning of December. The contract should therefore be awarded by the end of October, so that the Contractor has at least 5 weeks available to collect materials and to manufacture the anchor ropes etc. The practical experience acquired in this project suggests that much larger closures can be executed with this method. It would however be necessary to improve the management of the execution of larger closures. The direct construction cost of the closure method employed are higher than that involved in the mata-method (local horizontal method). The success of the mata-method is however uncertain and there are chances of failure, so that the chances of a delay in the realisation of the indirect economic benefits are greater. The total of the indirect and direct costs for the method employed is therefore in general lower than the costs with the local mata-method so far as larger closures are concerned.

Bangladesh
Chakamaya
Closure works

TPN4000

http://resolver.tudelft.nl/uuid:0319f185-fe7f-4cc0-9603-5a34a8330f06

Bangladesh Water Development Board

Hydraulic Engineering Reports

report

(c) 1979 Netherlands Technical Assistance Programme