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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Some Countries in Asia>

5.1 Bangladesh

From time immemorial, rainwater has been playing a significant role in the socio-economic life of Bangladesh. In fact, the entire agro-economic fabric of the country is built on the particular rainfall pattern (commonly known as the monsoon) occurring ion the country. Nevertheless, very few studies have been carried out on rainwater harvesting. Those that are available are studies by Hossain and Ziauddin (1992), Sarker (1994), and Uttaran (1995). The major constraint on the development of rainwater harvesting technologies is a low education level of the people and the poor economic condition of their households. The past studies have provided few innovations for users in the methods of collection and storage of rainwater. A joint Department of Public Health Engineering (DPHE) and UNICEF programme, that has been working in the southern area of Bangladesh since 1984 to provide better quality drinking water, has been reported that, despite filtering, the water remained salty during the dry season and that people did not want to use it. Of the 90 DPHE-UNICEF sand-filtration facilities serving communities of 50 to 60 users, 45% were found to be idle.

In contrast, rainwater harvesting by the erection of bunds around farms is the most common and one of the earliest methods of rainwater harvesting in Bangladesh. In this method, earthen bunds with height of 30 to 45 cm and width of equal dimensions are constructed around the field. Farmers have learned from experience to match their cropping cycle with rainfall pattern. Rainwater meets around 78% to 97% of land preparation water requirement for aman crops. In saline areas, rainwater is used in the aman paddies to dilute saline river water until the river water becomes sweet. Over the entire aman crop cycle, rainwater meets around 50% of water requirements with the residual being obtained from river water sources.

Variations on this technology exist. In the upland areas of Bangladesh (NC zone- Jhenaighati, Nokla thanas) rainwater is stored in low lying plots usually in between two hills to be used in times of necessary. Plots are irrigated using traditional equipment such as dhoons and hicha. In the CW zone (Jhenaidah thana), rainwater is collected from surrounding lands at higher elevations and carried to storage ponds through a culvert. In saline areas (the Patuakhali, Khulna, Satkhira and Bagerhat districts), lands are located within polders or embankments erected to obstruct intrusion of saline water. In these areas, around three-quarters of the agricultural lands are being used for saline water-based shrimp culture delimiting options for freshwater based agriculture.

The polders also have the potential to revolutionize the drinking water supply systems in the saline areas (the greater Khulna, Satkhira, Patuakhali, Barisal and Noakhali districts) through the construction of "sweet water ponds" which are replenished by rainwater in the monsoon. In southern portion of Hatya and other remote islands in the Bay of Bengal, where there are very few tubewells, rainwater from these ponds is found to meet nearly 80% of the drinking water requirement in the monsoon season. In the saline area of the SW zone, rainwater meets 44% and 7% of drinking water requirement in monsoon and dry season, respectively. Ponds and tubewell water meet remaining 31% and 25% of monsoon season water drinking water requirement. Rainwater meets 49% of cooking water requirement in the monsoon season and is not used at all for bathing. On the other hand, in the NC zone, rainwater is not used for drinking purposes but, instead, is used for cooking (6%) and bathing/washing (11%). The bulk of the drinking, cooking and bathing/washing requirement is met from tubewells. In the NW zone, only 2% of the inhabitants reported using rainwater, for bathing only, as their entire requirement for drinking and cooking water is met from tubewells and, to some extent, from ponds/rivers and other surface waterbodies.

One of the oldest method of rainwater harvesting in Bangladesh is the use of roof-tops for collecting rainwater which is conveyed through a gutter to a pot, or motka, for immediate use or to a storage place for use later on. The water stored retains its colour and taste for around two months after monsoon, after which, the water gradually becomes contaminated with toads, mosquitos, cockroaches, etc. Previously, fish such as Koi, Singh or Magur (Anabas testudinews, Heteropreutes sp., and Clarias batrachus) were grown in the pots to eat the larvae of mosquitos and other insects. However, as these fishes discharge their own excreta in the water, which also degrades the quality of water, use of fish to maintain water quality is fast decreasing. Occasionally, alum or other locally made flocculant aid, like burnt shell, is used to purify the water. Water purifying tablets are very infrequently used. Of the many industrial uses of harvested rainwater, one of the commonest is fish culture. In north Bengal and in Mymensingh, ponds are completely dried prior to the monsoon. The soil is enriched with lime and cow dung, and the water is treated with potash, to prepare the ponds for fish cultivation. In other areas, water is kept in the ponds at levels of 1 to 1.5 m prior to the monsoon. In saline areas like Hatiya, the same pond may be used for drinking water supply purposes. No soil treatments are applied to these ponds. In Sherpur District (Jhenaigati thana), rainwater is stored in embankments and used for fish culture. In the NC zone, excess water flowing out of the embankments passes through a net so that fish cannot escape from the pond.

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