Committed to PEOPLE'S RIGHT TO KNOW Vol. 5 Num 382 Fri. June 24, 2005       Letters to Editor Saltwater irrigation Md. Saeedur Rahman, A retired Chief Engineer of BWDB Irrigation by application of sweet waters is commonly understood. Saline waters are also used in production of solar salts and cultivation of irrigated shrimps. Salt production by solar evaporation (the other being the rock salts) is one of the most ancient industries in the world. The world salt production is estimated at 181.5 million tons per year while that of Asia is said to be 36.5 million tons. Bangladesh produces between 1 and 1.5 million tons of solar salts a year varying with the coastal weather and other influencing factors. Similarly, the world shrimp production is estimated at 500,000 tons, of which approximately one-third is the irrigated shrimps. Asia contributes 80 percent of the world total. Bangladesh produces only 25,000 tons per year, which is only 10 percent of that produced by Thailand. Saltwater irrigation is the key input in production of both the solar salts and irrigated shrimps. In most developing countries including Bangladesh, solar salts and irrigated shrimps are produced along the coastline. The small salt farms and shrimp fields are scattered along the coast and resist coming under any regulatory provisions of the government. Very often, precise figures regarding its location, extent of holdings and production statistics are not available and even if it is, it remain debatable because the data referred to, in most cases, has either been manipulated or documented to be skimpy. Salt farming in the Gangetic delta is probably the beginning of coastal engineering germinated from within the social sciences. The ancient community known as malongis in Chandrdwip, the present Bakerganj-Patuakhali, in the south-western coast of Bangladesh started farming salts by dam-retaining the sea waters at astronomical high tides and then naturally drying by solar heat within the terraced compartments steeped by mud. The wide spread grids of these in series kicked-off the sedimentation processes, eventually triggering the land reclamation engineering. The science that further shared the concomitant development of the nation's coast was raising the lands for secured homesteads and digging the trenches for domestic consumption of sweet water. The human habitation thus gradually surged up the coast resulting in cutting of the natural mangrove for increased settlement. Over time, salt farms continued to be pushed seaward by rice cultivation reversing the direction of habitation settlements towards the coastal potentials. The abundance of upland freshwater flow combined with local run-off in a favourable condition of adequate natural drainage accelerated this process. Shrimp cultivation on the other hand is not as old as salt farming but not a new phenomenon either, in the south-western coast of Bangladesh. Farmers used to construct shallow, seasonal enclosures on the banks of rivers and canals to grow shrimp as an extra source of income. The dynamic version of the modern embanking along the inter-tidal ribbon is the living geometry of the mudflat arising out of these human activities in the coastal regions of Bangladesh.