The Alva B. Adams tunnel goes from Grand Lake to Estes Park and that water heads to various locations after that. I think it mostly goes down the Big Thompsom but gets redirected at several points for irrigation and probably some drinking water. Granby reservoir holds water that is pumped back up to Grand Lake so that it can be pumped out all summer long and keep the northern front range watered down.
Williams Fork is for replacement water that Denver pulls out of the Colorado River drainage. They also have the new Wolford Mountain reservoir outside of Kremling to replace water as well.
As for a guage out of the Moffat tunnel, click on this link http://www.dwr.state.co.us/Hydrology...&MTYPE=DISCHRG