Gauge Description:

Flows in this section of the river are released from Friant Dam. Typical releases are less than 100 cfs in the winter, but around 350 cfs in the summer.  At 100 cfs, boats will run aground in the riffles and rapids.   350 cfs is an excellent flow for beginners with well defined riffles.  Very high flows up to 10,000 cfs can occur in the spring of wet years.   High flows are suitable for experienced swiftwater boaters.  Motor boats will also be seen running up or down the river at high flows.

Millerton Average Daily Flows
Millerton DailyReport (As of midnight)- pdf
Time and Date of changes in release to the river
USGS gauge page. Historical data can be found here.
Hourly Flows   
Daily Regional Snowpack Plots: CDEC

Two small creeks enter the river below Friant.  Normally their flows will be zero to minimal, but they can be high during rain storms. 
Cottonwood Creek enters from the west between the dam and Friant Bridge.
Little Dry Creek enters from the east a few miles downstream of Friant

Since the start of restoration test flows in 2009, a number of new gauges along the river have gone online.
San Joaquin below Friant gauge (shown below) is at the upper end of Lost Lake.
Stage measurement at Highway 41.
Donny Bridge gauge (shown below) is a mile or two west of Highway 99.
Gravelly Ford gauge (shown below), is 5 or 6 miles west of Highway 145.    After the construction of Friant Dam in 1946 till the start of restoration flows in 2009, the river was usually dry at this point.
San Joaquin below Bifurcation gauge is upstream of Mendota, but below the Chowchilla bypass.
Chowchilla Bypass gauge shows flows diverted away from the natural channell into the bypass channell.