Irrigation dams threaten Thailand’s tiger forests, say conservationists

Irrigation dams threaten Thailand’s tiger forests, say conservationists

CHIANG MAI, Thailand — A plan to construct seven dams in one of mainland Southeast Asia’s last intact forest systems could cause widespread habitat loss and sever important wildlife corridors, activists warn.

The Dong Phayayen-Khao Yai (DPKY) Forest Complex is a vast and biodiverse region that spans six provinces in eastern Thailand. It was declared a UNESCO World Heritage Site in 2005 for its exceptional biodiversity but is perhaps better known as the home of one of Thailand’s two remaining breeding populations of Indochinese tigers (Panthera tigris corbetti).

The Seub Nakhasathien Foundation, a Bangkok-based NGO, says the proposed dams will harm the integrity of the DPKY forest ecosystem, placing its rich assemblage of wildlife at risk. “If every reservoir is built, there will definitely be severe impacts on the ecosystems, especially to wildlife,” Ornyupa Sangkamarn, the foundation’s head of academic affairs, told Mongabay. “A large network of natural forest ecosystems will be cut off and scattered into smaller habitats. Wildlife routes will be altered or cut off, and many plant species will be flooded.”

The proposals come from Thailand’s Royal Irrigation Department, which says the dams will solve flood and drought problems in nearby populated regions, Ornyupa said. Water from the dams is also reportedly planned to serve industrial estates linked with the Eastern Economic Corridor, a centralized project to boost investment in Thailand’s eastern seaboard provinces of Chachoengsao, Chonburi and Rayong.

Planned irrigation dam projects in the DPKY Forest Complex have been contested in the past. In 2017, UNESCO’s World Heritage Committee reported concerns that such proposals were detrimental to the forest’s natural heritage value and explicitly requested the permanent cancellation of two dams planned at the time. In response, Thai authorities said the projects would not proceed.

But according to Ornyupa, the plans were merely shelved. Environmental impact assessment (EIA) processes are underway, and several active plans are being considered, including Khlong Maduea in Khao Yai National Park, and Huay Satone in Ta Phraya National Park.

The Royal Irrigation Department did not respond to multiple attempts by Mongabay to seek comment.

Intact forest corridors within DPKY Forest Complex are important for Asian elephants (Elephas maximus). Image by Rhett Butler/Mongabay.
Intact forest corridors within DPKY Forest Complex are important for Asian elephants (Elephas maximus). Image by Rhett Butler/Mongabay.

A thin green line

The DPKY Forest Complex forms a 230-kilometer (143-mile) strip of green, rising in steep, forested valleys above Thailand’s intensively developed plains to the northeast of Bangkok. It spans Ta Phraya National Park on the Cambodian border in the east to Khao Yai National Park in the west and encompasses Thap Lan National Park, Pang Sida National Park and Dong Yai Wildlife Sanctuary.

As one of mainland Southeast Asia’s last contiguous tracts of forest, the DPKY Forest Complex is widely considered one of the region’s best hopes for wildlife recovery. Indochinese tigers — driven extinct in nearby Cambodia, Laos and Vietnam by habitat loss, poaching and overhunting of prey species — still breed in the forest complex, although the population remains small. Camera trap surveys in 2016 revealed a tiger density of 0.63 tigers per 100 square kilometers (1.63 tigers per 100 square miles). In 2020, surveys in the Thap Lan-Pang Sida Tiger Conservation Landscape estimated the tiger population at around 20 tigers.

Other species suffering regional declines elsewhere continue to hang on in the DPKY Forest Complex, due in part to protection from Thailand’s Department of National Parks, Wildlife and Plant Conservation (DNP), which invests heavily in patrols to curb poaching and the illegal wildlife trade. Asian elephants, Indochinese leopards, gaurs, bantengs, hornbills, white-handed and pileated gibbons and critically endangered Siamese crocodiles still call the forest complex home.

The DPKY Forest Complex, which extends from Ta Phraya National Park on the Cambodian border in the east to Khao Yai National Park in the west, forms a 230-kilometer (143-mile) strip of green northeast of Bangkok.
The DPKY Forest Complex, which extends from Ta Phraya National Park on the Cambodian border in the east to Khao Yai National Park in the west, forms a 230-kilometer (143-mile) strip of green northeast of Bangkok.

Information from the Seub Nakhasathien Foundation suggests that, if approved, three of the dams will cover an area of approximately 2,420 hectares (5,980 acres) — roughly equivalent to nearly 3,000 football fields. The largest dam project is Sai-noi Sai Yai, within Thap Lan National Park, with a reservoir capacity of 334 million cubic meters (11.8 billion cubic feet).

Environmental surveys to support the EIA report on the Khlong Maduea dam project, which is slated to cover 300 hectares (741 acres) in the western part of Khao Yai National Park, recorded 220 species comprising 38 mammals, 116 birds, 43 reptiles and 23 amphibians.

Impacts from the dams will spread wider than the reservoir footprint, disturbing wildlife habitat and crucial corridors further. “Dam construction requires road access and ground to build workers’ quarters [which will involve] excavation of forest areas,” Ornyupa said. “Even after the construction is finished, the dam could be turned into a tourist attraction.”

Blue pitta (Pitta cyanea) in Khao Yai National Park. Image by JJ Harrison via Creative Commons (CC BY 3.0)
Blue pitta (Pitta cyanea) in Khao Yai National Park. Image by JJ Harrison via Creative Commons (CC BY 3.0)

Areas under water

The development proposals seemingly contradict Thailand’s ambitious goal to increase its forest cover to 40% of total land area from around 33%, not to mention Thailand’s national Tiger Action Plan to increase the tiger population by 50% by 2022.

“The Royal Irrigation Department says that it needs to expand the supply of water available for irrigation to much-needed farmland,” said Pianporn Deetes, Thailand and Myanmar campaigns director of the NGO International Rivers. “But the proposals in Dong Phayayen-Khao Yai, alongside many proposals in other parts of Thailand, are in reality largely driven by the construction industry and other non-public benefits.”

Recently, Thailand has faced some of its worst droughts in decades. But experts say dams will not provide a quick-fix solution. “What we need to do is to talk about how to effectively manage the water that we have, how to be responsible with it and how use it wisely,” Pianporn said. “Where there is a lack of water, we must find the root cause and solve it ideally at the local level so that everybody can participate rather than from above through centralized large-scale environmentally destructive construction projects.”

High annual rainfall makes the DPKY Forest Complex an important watershed that feeds into five of Thailand’s major rivers, including the Mun River, which flows into the Mekong. The proposed dams within the complex are chiefly located in steep valleys, where they will collect water from tributaries.

“The Royal Irrigation Department claims that nobody uses these tributaries, that the water just flows uselessly to the sea … but the water is crucial to sustain ecosystems and for migratory fish, aquatic wildlife and flooded wetlands,” Pianporn said.

A representative of Freeland, a counter-trafficking NGO that works alongside the DNP, says the Huay Satone dam proposed within Ta Phraya National Park, which borders Cambodia, is of particular concern. The national park offers a narrow, forested route through which elephants and other wildlife can pass to reach remaining habitat in other countries. “Ta Phraya has recovered well from past disturbances associated with refugee camps,” said the representative, who asked to remain anonymous due to the political sensitivity of the issue. “It now seems a shame to put the last 20 years of work in jeopardy by putting areas under meters of water.”

The EIA for Huay Satone dam confirmed that the project will flood deciduous dipterocarp forest and sloping grassy glades that are important foraging habitat for banteng, an endangered species of wild cattle and key tiger prey animal. “Some wildlife can be rescued, while some wildlife … may not be able to escape by themselves in time,” said a representative of the DNP, who also asked to remain anonymous. “DNP has worked very hard to explain those impacts to the Royal Irrigation Department and relevant stakeholders.”

The DNP is concerned that assessing the impacts of each of the seven plans in isolation will not give a clear picture of the overall development impacts. It has recommended the irrigation authority undertake a Strategic Environmental Assessment to look at combined impacts before any decision or commitment be made.

Gaur (Bos gaurus) are key prey species taken by Indochinese tigers in DPKY Forest Complex. Image by Rhett Butler/Mongabay.
Gaur (Bos gaurus) are key prey species taken by Indochinese tigers in DPKY Forest Complex. Image by Rhett Butler/Mongabay.

World heritage at risk

Campaigners from the Seub Nakhasathien Foundation say the development proposals could endanger the DPKY Forest Complex’s World Heritage status, which is due for review by the World Heritage Committee in July this year.

The assessment will take into account the renewed plans for the seven dams, together with threats from illegal poaching of rosewood and encroachment from road upgrades.

In the past, the World Heritage Committee has requested the Thai government permanently cancel plans for any construction of dams with reservoirs inside the World Heritage Site boundaries. The fact that several of the planned dams positioned within the World Heritage Site are now being actively considered via EIA processes is likely to raise significant concerns.

The IUCN’s World Heritage Programme provides technical advice to the World Heritage Committee to inform its decisions. “The IUCN has not received detailed information for all seven proposed dams but considers that any proposal to construct dams with reservoirs inside the World Heritage site will be contrary to the Committee’s request [to cancel previous plans], and will pose potential negative impacts on the Outstanding Universal Value of DPKY-FC,” a spokesperson from the IUCN World Heritage Programme told Mongabay in an email.

At a time when climate change is taking its toll on water resources across Southeast Asia, Thailand is looking for solutions to diminishing water supplies and unrelenting demand across all sectors. But conservationists say that destroying irreplaceable ecosystems in the process will ultimately lead to far graver problems. “We have always believed that without forests, there is no water,” Ornyupa said.


Ash, E., Hallam, C., Prawatsart, C., Kaszta, Z., Macdonald, D. W., Rojanachinda, W., … Harihar, A. (2020). Estimating the density of a globally important tiger (Panthera tigris) population: Using simulations to evaluate survey design in Eastern Thailand. Biological Conservation, 241, 108349. doi:10.1016/j.biocon.2019.108349

This article by Carolyn Cowan was first published on on 14 June 2021. Lead Image: Asian black bear (Ursus thibetanus) in Khao Yai National Park. Image by Tontan Travel via Creative Commons (CC BY 2.0).

What you can do

Support ‘Fighting for Wildlife’ by donating as little as $1 – It only takes a minute. Thank you.


Fighting for Wildlife supports approved wildlife conservation organizations, which spend at least 80 percent of the money they raise on actual fieldwork, rather than administration and fundraising. When making a donation you can designate for which type of initiative it should be used – wildlife, oceans, forests or climate.

Dive in!

Discover hidden wildlife with our FREE newsletters

We promise we’ll never spam! Read our Privacy Policy for more info


Founder and Executive Editor

Share this post with your friends

Leave a Reply

Notify of

1 Comment