A dam can have floodgates to control the flow of water (and therefore the water level in the reservoir to a degree), not just a weir with a fixed elevation where water flows over the crest, so I suspect that you might confuse a dam with a weir. I read that a professor said this particular dam had 26 gates. If you expect a flood, you’d want to open the gates beforehand, as to make room in the reservoir, and to reduce the peak flow that an uncontrolled flood would give, for example.
A dam can have floodgates to control the flow of water (and therefore the water level in the reservoir to a degree), not just a weir with a fixed elevation where water flows over the crest, so I suspect that you might confuse a dam with a weir. I read that a professor said this particular dam had 26 gates. If you expect a flood, you’d want to open the gates beforehand, as to make room in the reservoir, and to reduce the peak flow that an uncontrolled flood would give, for example.