Interpreting some hydropower data. What does DSF mean in this context?
I think the DSF releases are both measures of releases. Neither is a measure of power. They are both a measure of the amount of water released, in day-second-feet, as you say.

The total column is the measure of the total amount of water released (in DSF). The power column is the amount of water released in order to generate power (in DSF). The difference between those two numbers is the amount of water (in DSF) released down the spillways (rather than to generate power), as part of overflow prevention, maintenance, or other activity.

On the realtime feed, the column labelled power looks like mean power to me in MW: the dam rating is 70MW, and the power column maxes out at 70.267, so that does indeed look like MW. So that's the average over the quarter-hour. Multiply by 0.25 to get MWh.

footnote rant:
Feet? Seriously? Feet? Who uses feet? What's wrong with these people?