Bart Schultz
Bangladesh is located in the world's largest delta, formed by three enormous rivers: the Brahmaputra, Ganges and Meghna. These rivers drain the excess water from a basin of approximately 172 million hectares, only 7% of which lies within Bangladesh. The remaining areas are in China, India, Nepal, Bhutan and Myanmar. Besides water, the rivers transport large quantities of sediment into the country.
The coastal areas are divided into distinct landmasses by a complex network of rivers. Most areas have a surface below mean sea level, rarely more than three metres above, and are generally above high neap tides but below high spring tides.
Bangladesh has a tropical climate with a warm rainy season from June to October. Floods, tornadoes, cyclones and tidal waves occur almost annually, along with the consequences of deforestation, soil depletion, and erosion. In 1998, two-thirds of the country was flooded. This was one of the worst floods in modern world history, killing 1,000 people and 135,000 cattle, and leaving 30 million people homeless. 300,000 houses, 9,700 kilometres of roads, 2,700 kilometres of dikes, and 5,000 hectares of land were also destroyed. Damage totalled approximately US$ 2.8 billion. Earthquakes can also pose a threat, as they can cause rivers to suddenly change course.
The oldest known dike was constructed in the thirteenth century. Since the seventeenth century, most of the flood prone area has been reclaimed and developed by large landowners. They built and maintained low dikes with wooden cylinder discharge sluices. Later, farmers began building dikes. Subsequent government projects focused more on the development of polders. Large-scale land reclamation began in the 1950s.
After the country suffered from major floods in 1954 and 1955, the East Pakistan Water and Power Development Authority (EPWAPDA) was established in 1959 to develop water and energy resources. This organization developed a Master Plan containing 58 land reclamation projects covering 5.8 million hectares of agricultural land. These polders were drained by natural gradients, sluices, and pumping. In 1961 and subsequent years, EPWAPDA reclaimed 1.4 million hectares.
In the early 1970s, various projects focused on river improvement, drainage, and flood control. For dikes along the rivers, a crest height based on the highest observed level was required, and for dikes along the Bay of Bengal or large estuaries above it, an additional height of 1.5 metres was required. These projects were followed by the construction of 92 polders with approximately 4,020 kilometres of dikes and 780 discharge sluices.
After independence in 1971, the EPWAPDA was split into the Bangladesh Water Development Board (BWDB) and the Bangladesh Power Development Board (BPDB). Since then, the BWDB has played a key role in water management. To protect rice from early river flooding, prevent salt intrusion and provide storage of water during wet periods, more dikes and sluices were built.
Much has been written internationally about improving the management of irrigation systems. This has resulted in suitable management models for these systems. This was not the case for polders, and water management lagged far behind that of irrigation systems. Due to differences in elevation within the polders, the landowners' interests differ. The multitude of water management options makes management quite complex, resulting in frequent conflicts in almost all polders.
As water management in the polders gradually improved, farmers saw new opportunities for high-yielding crops. This led to an increased need for water during the dry season. Therefore, water management in many polders was adapted to enable water storage. The sluices, which until then were only equipped with valves for discharge, were modified by installing vertical gates on the landward side. Watercourses were deepened and widened to store water in the polders. With the possibility of retaining water within the area, the need for lifting devices to bring water from the watercourses onto the land developed. Many traditional lifting devices, as well as mobile and non-mobile pumps, were and are still used.
Due to the numerous demands placed on the management, maintenance and adaptation of the country's water management and flood protection facilities, Bangladesh will always remain a highly vulnerable country. Furthermore, climate change can lead to more erratic river flows, rising sea levels, and more severe cyclones. Therefore, it will be crucial to take the necessary measures in a timely manner.
