Early Implementation Projects on Flood Control and Irrigation in Bangladesh - Review of the programme of closure of tidal channels

A review of the results in the past 5 years regarding the joint-programme of the Bangladesh Water Development Board and the Netherlands Assistance Programme on the Closure of Tidal Channels in Bangladesh. This review is useful after the successful completion of the Amtali Closure. This joint-programme falls within the frame-work of the Early Implementation Projects on. Flood-Control and Irrigation (EIP). A review of the past should enable the determination of the bottle-necks for the success of a possible continuation of the programme. The removal of these bottlenecks could be a pre-requisite for a continuation. The Resident Advisor EIP has thus requested for this review and a glance in the future

Title: Early implementation projects on flood control and irrigation in Bangladesh: Study of methods used for closing tidal channels - Study of methods for closing tidal channels; fifth interim report – Madargong closure

The closure of the Madargong has been undertaken in the winter of 1979/80 as a stage of the "Study of Methods for Closing Tidal Channels". The closure has been taken up as an Early Implementation Project on Flood Control and Irrigation in Bangladesh. A team of four Dutch experts assisted the Bangladesh Water Development Board and also the contractor with the implementation. The closure has already been attempted twice without success by means of the local mata-method. The same fate was ultimately also allotted to the third attempt. The tidal channel has been closed by means of bottom protection mattresses, an underwater sill and a cofferdam filled with clay-filled gunny bags. The tidal range at the site is about 17' at spring tide and 6' at neap tide. The tidal prism during spring tide is about 5800 acre feet (7 million cub.m.). The channel cross-section below the average water level was about 7000 sq.ft. (650 sq.m.) with a width at the water line of 450 feet (140 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 jetty cum coffer dam 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. The execution of the project encountered many problems, which are described in Chapter 4. In spite of these problems, the Madargong has been closed on March 26th, with a delay of one month according to the original time schedule. On 30th of March, however, a breach occurred; a part of the cross-dam washed away resulting in a gap with a width of 80 feet. Chapter 5 deals with the breaching and the planning of the closure of the breach. It was decided that this closure had to be effectuated before May 1lst in view of the deteriorating tidal and weather conditions. The chances to succeed were, however, found to be rather low in view of the amount of work to be done in a very short period, the required quantities of materials, the rather poor management of the contractor, and the approaching rainy season. This could not justify the investment of another 13 Lakh Taka (Tk 1,300,000). It was, therefore, decided to stop the work and to see what is left of the works after the rainy season. The experience obtained is described in a condensed form in Chapter 6. The overall conclusion is that the technical risks involved in a closure with local materials and manual labour can be reduced considerably by using the obtained experience. However, the risks introduced by the lack of management with the contractor are much more difficult to control. These risks must be accepted if the present program is continued. The introduction into the practice of elements of the traditional Dutch methods based on local materials and manual labour is an essential part of the program "Study of Methods for Closing Tidal Channels"

Early implementation projects on flood control and irrigation in Bangladesh: Study of methods for closing tidal channels; third interim report

Methods of closing tidal channels as at present applied in Bangladesh have been developed since many years in an imperical way. As the size of closure gaps in future will increase, a more systematic approach will be required to close those bigger gaps. It was therefore agreed that as a first step bottom protection mattresses should be introduced for the closure of the Madargong. A team of Dutch experts was sent by the end of 1977 to Bangladesh for a few months to advice on the design, the manufacure and the .sinking of the bottom protection mattresses. One team member stayed a little longer and attended the actual closure to review the effects of the mattresses. The application of a bottom protection with mattresses of 50' x 100' made of bamboo gratings and goalpata (palmleaves), posed no real problems and had good results as far as bottom protection is being considered. The closure itself of the Madargong by means of the local mata-method however failed twice, although the flow could be stopped during low water. The failures were the direct result of: - A series of slidings in the preparatory stage, presumably caused- by using of too much clay fill for the cross dam of the right bank. The slidings causing large delays in dumping of matas and giving later rise to further damage during the closure work. - Insufficient mobilization of experienced labourers by the contractor for the closure works, even insufficient mobilization of inexperienced local labour during the critical stages of the closure. - Large delays of a month and more in the execution of the closure work, far beyond the end of the dry season, but also delays of a few days after a neap tide and even a few hours after the lowest water level. - Lack of supervision and management of the contractor, causing shoddy work regarding making of ropes and matas, also causing confused situations during the critlcal stages of closure, and finally causing the missing of two opportunities to still close the gap by forceful attempts

Design and contract documents for closing of the Madargong in Polder 5 in Khulna District

The Madargong is located in Syamnagar Police Station of Satkhira Division, Khulna District. The closure of the Madargong was approved in 1975 to be executed as part of the Early Implementation Projects, under the Technical Assistance Programme of the Netherlands Government. The work was to be carried out by the Syamnagar SubDivision of the Bangladesh Water Development Board. However, the subseguent attempt to close the Madargong (1977-1978) failed, as was the case in 1970. It should be noted that these two closure attempts failed due to negligence and mismanagement of the Contractor. The 1978 attempt was done after having protected the river bed. The mattresses prevented scouring and another attempt could be made after the first failure. The introduction of bottom protection was done as a first phase of a Study regarding different closure methods suitable to be executed by manual labour. The methods are based on a combination of practices as used formerly in The Netherlands and those used locally at present. The methods should be applicable for closures of larger estuaries, The result of the study and a description of the conducted field experiments are given in three interim reports: "Study of Methods used for Closing Tidal Channels", Early Implementation Projects on Flood Control and Irrigation in Bangladesh, October 1976, August 1977 and August 1978. The report on the Chakamaya closure is still under preparation. It has been suggested to again take up the closure of the Madargong. Technical Assistance would then be provided under the Delta Development Project, while construction costs should be covered by funds originating from Early Implementation Projects. Haskoning has prepared this report, having received the assignment from the Netherlands Authorities to provide technical assistance concerning the closure component of the Delta Development Project. The closure will be designed as a vertical closure with gunny bags and mattresses, more or less similar to the Chakamaya closure, implemented in 1979

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

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

Study of methods for closing tidal channels: Amtali Closure 6th interim report

The closure of the Amtall Khal was executed in the period December '81 to March '82 as a further experiment of the "Study of Methods for Closing Tidal Channels in Bangladesh”. The closure was executed as an Early Implementation Project on Flood Control and Irrigation in Bangladesh, financed by Netherlands Technical Assistance Programme. A team of three Dutch experts of HASKONING Consulting Engineers from the Netherlands, already involved during the past 5 years with introducing new closure techniques in Bangladesh, assisted the Bangladesh Water Development Board - engineers and the contractor with the execution of the work according to the designed closure method. The method was based on a8 gradual build upon an underwater sill on top of the river bottom, which was protected in advance by special mattresses to prevent any scour due to the currents. When the sill had reached a certain level, it s8lso was protected with special mattresses with the same purpose. Then a bridge type cofferdam construction was built across the river on top of the sill and the current was stopped by filling the cofferdam in two stages with clay filled gunny bags. The tidal range at Amtali was 2.4m at spring tide and 0.9m at neap tides. The tidal volume at spring tide was about 4 x 106 m3, and the channel's cross-section at mean water level was 640 m2. The width at the waterline was 123m and the maximum depth of the channel was 7.8m-PWD. More detailed information on the conditions at site are given in chapter 3. In chapter 4 the design and execution method are further elaborated

General Considerations for Improving Photovoltage in Metal-Insulator-Semiconductor Photoanodes

Metal-insulator-semiconductor (MIS) photoelectrodes offer a simple alternative to the traditional semiconductor-liquid junction and the conventional p-n junction electrode. Highly efficient MIS photoanodes require interfacial surface passivating oxides and high workfunction metals to produce a high photovoltage. Herein, we investigate and analyze the effect of interfacial oxides and metal workfunctions on the barrier height and the photovoltage of a c-Si photoanode. We use two metal components in a bimetal contact configuration and observe the modulation of the effective barrier height and the resulting photovoltage as a function of the secondary outer metal. The photovoltage shows a strong linear dependence by increasing the inner metal workfunction, with the highest photovoltage achieved by a MIS photoanode using a platinum inner metal. We also found that coupling a thin aluminium oxide with an interfacial silicon oxide and controlling the oxide thickness can significantly improve the photovoltage of an MIS junction photoanode.ChemE/Materials for Energy Conversion & Storag