Hetch Hetchy Water and Power reports as follows:

 

There have been a number of questions about Tuolumne River flows after August 28. The latest forecast (and flows to date) at Cherry Lake are shown in the plot below. We anticipate low releases from Cherry until 8/31, at which point we will increase valve releases to ~1500 cfs on 9/1. We will continue to draft full at Holm PH through this period. According to this forecast, we will be at our desired elevation at Cherry on 9/6, at which point we will close the valves, and reduce HPH generation to ~500 cfs. From this point on, HPH + Cherry Valve releases will be less than 500 cfs. If weather results in increased inflows to Cherry, timing and magnitude of releases will change.