- Natural streams in Bangladesh’s southeastern Chittagong Hill Tracts are drying up due to climate change and human activities.
- Rainwater harvesting in man-made ponds holds hopes for the revival of streams and could boost local biodiversity.
- The nature-based solution faces obstacles such as lack of resources and structural vulnerability.
- Experts suggest that co-management with the participation of local communities could bring good results to conserve such natural streams in the region.
Natural streams, the lifeline of Bangladesh’s Chittagong Hill Tracts’ rich biodiversity, are vanishing due to a combination of anthropogenic and climate change-induced stresses.
Aggressive deforestation is wiping out local flora, including the bamboo groves that help the soil absorb water underground. Combined with erratic rainfalls, this has left natural streams completely dry for eight rainless months every year for the last few years. Wildlife and local communities, both dependent on the streams, are suffering from an acute water crisis, as experts have observed.
Having experienced the water shortage, Mahfuz Ahmed Russel, custodian of the community-based initiative (PCI) in Khagrachhari district’s Matiranga region in Chittagong Hill Tracts (CHT), has adapted a customized version of a local practice to pilot the revival of streams.
Traditionally, local people harvest rainwater by damming streams or diverting stream water into ponds for fish farming.
“Instead of disturbing the streams, I harvest rainwater to keep them alive,” Mahfuz tells Mongabay.
In small valleys within the 9.3-hectare (23-acre) privately conserved Pittachhara Forest, Russel has constructed three artificial ponds by building earthen dams at the foot of the valleys. Locally, such gentle-sloping flatlands, surrounded on three sides by hillocks, are called longa.
The ponds collect monsoon runoffs and, over time, water gradually seeps from those into nearby streambeds, helping keep them alive or moist for four to six months during the dry season.
Rainwater-fed ponds boost biodiversity
The Pittachhara Forest, named after the bird Indian pitta (Pitta brachyura), has two streams, locally known as chhara, that originate from the nearby hill Arjun Tilla and flow about 4 kilometers (2.5 miles) to join the nearby Gomti River.
Like other hilly streams, the Pittachhara streams started to run dry during the summer seasons several years ago as unchecked deforestation or denudation of the surrounding hills continued to accommodate commercial cultivation of cash crops such as pineapples and cassava.
Usually, loose sandy soil erodes from denuded hills during the monsoon season, which sediments the streambeds, reducing their water-carrying capacity. Stone quarrying, short-rotation jhum cultivation (a traditional method of agriculture used by Indigenous communities in the region) and shorter monsoons further degraded the streams.
Russel says that although the monsoons have been shorter, heavy rains have become common, often triggering landslides and diverting the direction of stream flow.
To build the first rainfed pond within the Pittachhara area seven years ago, Russel, along with hired laborers, excavated the sloped valley bottom and used the same earth to construct the dam.
That arrangement eventually created an approximately 694-square-meter (7,470-square-feet) pond, which became a reservoir of rainwater the following monsoon. Soon, small fish, crabs and prawns thrived in the water.
“The next scorching summer, I found the nearby streambeds still wet. Growing bushes of green taros and ferns along some shallow and curvy passages proved that water seeped from the reservoir into the streams,” Russel says.
He says he applied the same method in some other ponds in the region, including two in his forest, with the help of local youths.
These streams are vital lifelines for the ecosystem, Russel says: They support the population of freshwater animals like fish fries, crabs and some amphibians, while the surrounding environment provides habitat for butterflies and reptiles like the king cobra (Ophiophagus hannah) and Bengal monitor lizard (Varanus bengalensis).
The streams also support birds. Russel says the stream-rich forest is habitat for, according to his count, 111 bird species, including the colorful pittas and the magnificent kalij pheasant (Lophura leucomelanos).
A recently published study reveals that the particular forest shelters some small and medium-sized mammals, including the Bengal slow loris (Nycticebus bengalensis), northern pig-tailed macaque (Macaca leonina), leopard cat (Prionailurus bengalensis), large Indian civet (Viverra zibetha), common palm civet (Paradoxurus hermaphroditus), crab-eating mongoose (Urva urva), northern treeshrew (Tupaia belangeri) and black rat (Rattus rattus). Moreover, wild fowls (Gallus gallus) and monkeys (Rhesus macaque) are abundant in the forest.
Various streamside plants like chapalish (a wild jackfruit, Artocarpus chama), phanpa dumur (a fig, Ficus fistulosa Reinw. ex Bl.), the shrub bana jam (Ardisia sanguinolenta), the flowering plant bhuiya gachh (Chassalia chartacea), the evergreen tree batna (Castanopsis indica), the flowering shrub kechchua (Glochidion zeylanicum), the evergreen tree atailla (Chaetocarpus castanocarpus) and pipul (a wild pepper, Piper peepuloides) are dependent on these hill streams, says Russel.
He adds that the live streams, acting as buffers, also stop the spread of poacher-ignited wildfires.
“Streams are more than just water”
The initiatives for reviving the streams seem vital when the hilly districts are losing natural water sources.
In 2024, the Center for Environmental and Geographic Information Services (CEGIS) in Dhaka prepared a water sources inventory survey in CHT for the Chittagong Hill Tracts Development Board.
The survey found that 15% of the streams in Khagrachhari, which were perennial decades ago, remained completely dry in the summer. Similarly, in Rangamati and Bandarban districts, 22% and 20% of streams, respectively, were found to be seasonal, or alive only during the short monsoons.
However, the board has not yet published the survey report due to technical issues with their servers.
Water resources management specialist at CEGIS, Shakil Ahmed, who was involved in the survey, says that unplanned jhum cultivation, deforestation without reforestation, erratic rainfall, plantation of invasive or non-native commercial species, unplanned development activities, and excessive water use for irrigation and stone quarrying are converting perennial streams into seasonal ones.
The Climate Risk and Vulnerability Assessment, a report exploring climate change in Rangamati and Bandarban districts, published in April 2024 by the local government, identified erratic rainfall as one of the major climate risks for the CHT region of Bangladesh.
In Khagrachhari district, home to Russel’s conservation project, a 2024 study found a 40.5% reduction in forest land, including a 21.11% drop in dense forest cover, between 1990 and 2020. A 2022 study, across three sub-districts in CHT, reported expansion of non-forest areas and shrinking water bodies.
The consequences of disappearing streams are grave. Monirul H. Khan, a professor in the zoology department in Dhaka’s Jahangirnagar University says, “Death of a natural stream means all the creatures, flora and fauna dependent on it are going to face survival challenges.”
Monirul recommends that immediate steps be taken to revive the dying water sources.
CEGIS’s Shakil endorses Russel’s initiative at the Pittachhara Forest as a nature-based solution with no negative downstream impact.
“We recommend the local community build rainwater-fed ponds without interfering with the natural streams,” Shakil says.
He adds that the local people, while responding to CEGIS’s survey questionnaire, also proposed several measures to restore perennial streams.
Local respondents to CEGIS’s survey proposed a range of conservation measures, including promoting bamboo cultivation, planting tree species that aid soil water retention, banning logging, halting farming within 12 meters (40 feet) of streams, banning invasive species, and ending stone quarrying.
Challenges remain
Despite its advantages, the rainwater-fed pond approach faces challenges.
“The first pond almost failed because crabs burrowed holes in the earthen dam, and the leaks released stored water rapidly,” Russel recalls.
Constructing such ponds is also expensive, according to Russel. Labor costs are high in remote hill regions, and rebuilding damaged structures with reinforcement materials increases financial strain.
“The costs of building a dam varies, depending on the location and space, but it is not less than 50,000 taka [$411],” Russel says.
Heavy rains pose another threat. Local entrepreneur Abdul Malek, one of the people inspired by Russel and farms fish in a nearby pond, says “A single day of heavy rain can breach the earthen dam and wash away all the fish.”
Russel says that additional investment to hire guards is required to protect these ponds, especially when they serve both conservation and fish farming purposes.
“Sometimes, goons poison the enclosures to loot fish for maximum profit,” he says.
To sustain these efforts, Russel advocates for co-management models involving local communities. “But the communities need seed funding. Incentives are also essential because such projects don’t bring immediate cash returns.”
Banner image: The Pittachhara Forest, named after the bird Indian pitta (Pitta brachyura). Image by Mahmudul Bari via Wikimedia Commons (CC BY-SA 4.0).
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Citations:
Rahman, M., Haque, T., Rakhi, T.J., Rafi, A.H., & Oishi, S.I. (2024). Carbon consequences of deforestation in Khagrachhari of Chittagong Hill Tracts: A GIS and remote sensing approach. Retrieved from: https://www.researchgate.net/publication/379130772_CARBON_CONSEQUENCES_OF_DEFORESTATION_IN_KHAGRACHHARI_OF_CHITTAGONG_HILL_TRACTS_A_GIS_AND_REMOTE_SENSING_APPROACH
Zahir, R. B. (2022). Assessing land use and land cover changes in the Chittagong Hill Tracts of Bangladesh. Retrieved from: https://www.researchgate.net/publication/361304162_Assessing_land_use_and_land_cover_changes_in_the_Chittagong_Hill_Tracts_of_Bangladesh
Shawon, R.A.R., Rahman, M.M., Iqbal, M.M., Russel, M.A., & Moribe, J. (2024). An assessment of the diversity and seasonal dynamics of small- and medium-sized mammals in Pittachhara Forest, Bangladesh, using a camera trap survey. Animals, 14(24). doi:10.3390/ani14243568
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