Thac Mo Spillway

Most people driving through the Phước Long area pass a structure without a second look. It is the spillway of the Thác Mơ hydropower plant, the part that releases floodwater from one of the largest reservoirs in southeastern Vietnam.

The word spillway makes many people think of a natural waterfall. It is not one. It is an engineered structure with one very specific job, which is to protect the reservoir and the land downstream when the water rises high. The Phước Long ward reports that the Thác Mơ reservoir has five dams in all, and this spillway is the one that releases floodwater.

The Thác Mơ plant sits on the upper Bé River. The company that runs it says the Bé is one of three large branches of the Đồng Nai River. The Bé runs about 300 kilometers, and the land that drains into it, up to the plant, covers about 2,200 square kilometers. Thác Mơ was the first step in using the energy of the whole Bé basin.

Work began on November 20, 1991. On January 6, 1995, the first generating unit produced power. The plant was fully completed on April 30 of the same year. Four years of building laid the foundation for the power and water systems of the whole southeast.

The reservoir does more than make electricity. The company's own documents list three purposes. The first is to regulate the flow of the river through the year. The second is to supply the national grid, with 150 megawatts of installed power and an average output of about 610 million kilowatt hours a year. The third is to supply water for farms, industry and households downstream on the Bé and the Đồng Nai, and in Ho Chi Minh City. So when someone plugs in a lamp at home or turns on a tap, a small share of it may come from this lake.

At its normal water level, the lake covers 109 square kilometers and holds 1.36 billion cubic meters of water. A billion cubic meters of water is a thousand million tons. This is no small pond. It is a small sea in the middle of the forest of the Phước Long region.

Because of its exceptional size, the Thác Mơ lake is on the national list of especially important dams and reservoirs, under a decision of the Prime Minister in 2019. That means every activity around the lake and the dam is closely supervised and managed under the law.

Using the spillway takes careful judgment. Every decision to release water through it has to rest on the weather and hydrology forecast, the level of the lake, the flow of water coming in, the capacity of the spillway, and the actual situation downstream. It is not a tourist event. It is a technical decision made to keep the people living downstream safe.

Life in the lake is worth mentioning too. The company records that the lake has fish and other aquatic resources, and that it has released young fish to restore them, protect the environment and keep the water ecosystem in balance. Beneath the quiet surface in the distance lies a living water world that people are trying to preserve.

The Bà Rá Mountain and Thác Mơ complex has been recognized as a national historic site and scenic area since 1995. Two layers of story sit side by side here. One is a modern energy structure. The other is a landscape of age-old heritage sites.

Standing on the lakeshore, a visitor looks across calm water spread over 109 square kilometers. It is part of a system of water and energy that quietly sustains a great many people downstream, from Đồng Nai all the way to Ho Chi Minh City. Under that still surface lie more than 1.36 billion cubic meters of water, waiting to be sent on to light every home, water every field, and run from every tap each morning.