Though lake water started flowing through the drainage channel from Saturday morning, its volume was far below the inflow.
Only after soldiers fired massive missiles into the bottleneck created by boulders on Monday that the volume increased substantially.
Flight to safety
Meng Shunyou "officially" bade farewell to his past to begin a new life as the lake water flooded parts of Beichuan, under the jurisdiction of Mianyang city.
The 42-year-old man and a number of other Beichuan residents made a rush for the Sandaoguai mountains, the closest place they can call home for now. They jumped into buses or walked from their resettlement zones.
They watched in silence as the water submerged what was once their home.
"Today we start things from scratch," said Meng, who lost his 14-year-old son, a million-yuan restaurant and three houses in the quake. His son died when his Beichuan Middle School collapsed.
Meng had moved into downtown Beichuan from deep in the mountains at the age of 16, and had lived there ever since. The debris of his restaurant that collapsed too went under water yesterday.
Experts and many officials say the county has to be rebuild - but on another site.
The news of Beichuan going under watery has spread fast through word of mouth. And even 66-year-old He Yixing now knows that he will have to start life afresh in another place.
He has lived in the mountains on the southeastern part of the county all his life. But now he is looking to move to a new Beichuan. As a man of the soil, the only work he really knows is farming.
Though he has two sons, both migrant workers, they have not returned home for a long time.
"I have been living on government relief after the quake," he said. "They were delivered at my home daily during the first few days after the quake.
"Now, they come after every five days because the only way to reach where I live is a mountainous road, unfriendly to any vehicle That is why I want to move to a new place," he said.
Xinhua contributed to the story