Haor

A ( bn, হাওর) is a wetland ecosystem in the north eastern part of Bangladesh which physically is a bowl or saucer shaped shallow depression, also known as a backswamp.MK Alam; ''Wave attack in Haor areas of Bangladesh and cement concrete blocks as structural revetment material''; ''Progress in Structural Engineering, Mechanics and Computation: Proceedings'' (ed. Alphose Zingoni); page 325; Taylor & Francis; 2004; ''Bio-ecological Zones of Bangladesh''; International Union for Conservation of Nature and Natural Resources, Bangladesh Country Office; page 31; The World Conservation Union (IUCN); 2002; Bangladesh & Desertification
, Sustainable Development Networking Programme (SDNP), Bangladesh; ''Retrieved: 2007-12-04'' During monsoon receive surface runoff water from rivers and canals to become vast stretches of turbulent water.

In Bangladesh and in the deltaic part of the Indian state of West Bengal, which lie in the floodplain of three great rivers, the Bengali language has several terms to differentiate between lakes, including , , and .Overview
, Official website of IUCN in Bangladesh; ''Retrieved: 2007-12-03'' All four are types of similar freshwater wetlands. The line of difference between a , a and a is usually very thin.

A is usually a depression or topographic low generally produced by erosion or other geographical process. These are marshy in character. Sometimes are remains of a river that has changed its course. Many of the dry up in the winter but during the rains expand into broad and shallow sheets of water, which may be described as fresh water lagoons. are generally smaller than , but there also are large like

Chalan Beel in Rajshahi Division, through which the Atrai River passes. It has shrunk over the years but still occupies an area of 26 km² in dry season. Sometimes small permanent water bodies within the remain after the dry up. These are also called , which occupy the lowest part of the depressions. A or is an oxbow lake, namely moribund beds of Bhairab, Kaliganga, Gorai and Kumar rivers.

A simple definition was provided by hydrologist Saila Parveen, " – seasonal wetland, – oxbow lake, and – perennial water body." or are found mostly in the moribund delta as in greater Comilla, Faridpur, Dhaka and Pabna districts. The is predominantly a feature of north-eastern Bangladesh. are seen all over Bangladesh and the neighboring districts of West Bengal.

Geography and geology

In a country where one third of all area can be termed as wetlands, the basin is an internationally important wetland ecosystem, spread over Sunamganj, Habiganj, Moulvibazar districts and Sylhet Sadar Upazila, as well as Kishoreganj and Netrokona districts outside the core area. It is a mosaic of wetland habitats, including rivers, streams and irrigation canals, large areas of seasonally flooded cultivated plains, and hundreds of and . This zone contains about 400 and , varying in size from a few hectares to several thousand hectares.Khokon, Leaquat Hossain, ''64 Jela Bhraman'', 2007, p. 79, Anindya Prokash, Dhaka, .

The core area, alternatively referred to as the Haor basin or the Sylhet basin, is estimated to spread over an area between 4,450 km² and 25,000 square kilometres''Communities and forest management in South Asia''; page 32; The World Conservation Union (IUCN); by experts. The total area of -type wetland ecosystem in Bangladesh is 80,000 square kilometres. The basin is bounded by the hill ranges of India – Meghalaya on the north, Tripura and Mizoram on the south, and Assam and Manipur on the east. The basin extends north to the foot of the Garo and Khasia Hills, and east along the upper Surma Valley to the Indian border. The Tippera surface lies directly to the south of the Haor Basin, and is partly low and deltaic and partly higher ground with a piedmont fringe to the east. It includes about 47 major and some 6,300 of varying size, of which about 3,500 are permanent and 2,800 are seasonal.

These area is low because of subsidence of tectonic Dauki fault. In the geological depression of the basin, subsidence is continuing at an estimated rate of 20 mm per year. In some places it has sunk by around 10 m in the last few hundred years. The area, by some experts, is further divided into three zones by standards of morphology and hydrology:

Climate and floods

The basin is a remote and difficult area that is flooded every year during monsoon.

Some of the most extensive seasonally flooded areas in South Asia are situated in bowl-shaped depressions known as located between the natural levees of rivers subject to overflow during the monsoon. The major rivers in the area are Surma and Kushiyara. Some of the tributaries are: Manu, Khowai, Jadukhata, Piyain, Mogra, Mahadao and Kangsha. The hilly rivers coming down from the Khasi and Jaintia hills in Meghalaya carry particularly high volumes of water as they come from some of the rainiest places in the world.

During July to November due to flood these areas go under deep water and look like seas with erosive water surface. During wind storm these waves reach up to 1.5 m in height. It remains under water for seven months of the year, turning settlements mostly built on earthen mounds into islands.

The fight against natural calamity of the locals people, mostly day laborers, relies on traditional and indigenous methods which with limited effect. Many villages have already been washed away, and many more are on the verge of extinction, forcing people to migrate to urban centers.

Flora

The Haor Basin is the only region in Bangladesh where remnant patches of freshwater swamps and reed lands still exists. Once extensive forests of Hijal in the area used to provide an important source of firewood, but these forests are now almost completely destroyed. In recent times, various herbs and aquatic plants are being collected for use as fuel. On top of that, aquatic plants are also being collected for use as fertilizers. Only a few patches remain of the swamp forests that once dominated the area, featuring flood tolerant trees like Hijal (''Barringtonia acutangula'') and Koroch (''Pongamia pinnata'').

Joseph Dalton Hooker (1817-1911) did the original survey of local flora sometime in 1850, recorded in his ''Himalayan Journals'' (published by the Calcutta Trigonometrical Survey Office and The Minerva Library of Famous Books; Ward, Lock, Bowden & Co., 1891). The findings of his travels along the Surma and visiting the wetlands of Sylhet are reflected in his ''Flora of British India''. Three habitat types in the Sylhet region were identified on the basis of botanical records of Kanjilal (U.N. Kanjilal, P.C. Kanjilal & A. Das; ''Flora of Assam''; 1934): Upland vegetation, Emergent vegetation, and Aquatic vegetation.

The hijal or hual, korij or koroch, bhui dumur (''Ficus heterophylla''), nol (''Arundo donax''), khagra ('' Pharagmites karka''), ban golap ('' Rosa involucratia'') and barun (''Crataeva nurvala'') are the main plant species found in the swamp forests. All of them are flood-tolerant species and can survive in the submerged condition for extended periods of time. However, among these, hijal, tamal and koroj trees are of the greatest value to the people and the environment. Other plant species available in the wetlands include madar (''Erythrina variegata''), gab ('' Diospyros peregrina''), makna (''Euryale ferox''), singara ('' Trapa bispinosa''), jaldumur (a kind of ''Ficus''), chitki ('' Phyllanthus reticulatus''), thankuni (''Centella asiatica''), kalmi (''Ipomoea aquatica''), helencha ('' Enhydra flactuans''), hogla (''Typha elephantina''), duckweed, water hyacinth

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