Basically, all of the water goes thru tunnels and ditches mostly to the flatiron power plant instead of going thru the Big Thompson River. The only time it flows is when they are doing work on the water delivery system (tunnels, power plant, etc). We got lucky last summer when they were having problems with the power plant and had to send a lot of the water down the river and it was freakin awesome, the best class IV boating in the area IMO. Here's a map in case you're interested:
As a side note, I wonder if more water came down the river before the huge flood of 76 when the powerplant in the canyon was destroyed.