If the reservoir is already near full and a storm is predicted they'll lower the pool to accommodate the inflow. But if more water falls then they predict they have two choices:
release as much water needed to prevent overtopping.
allow overtopping and severely damage the power plant and possibly lead to severe structural damage and possible failure.
They'd rather retain as much water as possible and flow it through the turbines. That's how they make money. When it goes through the spill gates it's the same as pouring out money.
If the reservoir is already near full and a storm is predicted they'll lower the pool to accommodate the inflow. But if more water falls then they predict they have two choices:
They'd rather retain as much water as possible and flow it through the turbines. That's how they make money. When it goes through the spill gates it's the same as pouring out money.