The Comal river is a very constant level. It is fed by underground springs that are very reliable. During major drought, such as in 2009, the river went down by a foot or two, but was never in danger of drying up -- and never any walking.
That said, the river flow information for the Comal is often more about checking on flood-stage conditions. As always, the best information comes from any of our trusted guides on the Comal. They're always willing to give real-time information.
Click this site for up to the minute flow data for the Comal river
The numbers you're looking for are between 300-400 for the Comal. There's little reason that it will change, and if it does, we're all in trouble!