Gauge Description:

San Joaquin - At Patterson Bend
Show 30 Days ------------- Show 3 Years


Patterson Bend is boatable at a pretty wide range of flows.  The rapids are probably the cleanest at higher flows of 3,000 or 4,000 cfs.   Some paddlers might like it at even higher flows.  At the low end, most of the run is still excellent at 700 cfs, though 3 rapids must be portaged.   

In the spring of wet years, Patterson Bend often gets spill flows, but they are usually very erratic.   Flows can be high one day and off the next, then back on.   If boaters are willing to accept whatever flow there is, then there are a fair number of paddling opportunities.   If one waits for an ideal moderate flow window it is almost impossible to catch this section.   In 2009 and 2010 there were flows for several weeks in the fall.  Flows were highly variable from hour to hour, but mostly within a moderate to low range.

Flows in this reach are diverted by Kerchoff dam. The minimum instream flow released from this dam is mandated to be 25 cfs all year round. Actual minimum flows tend to be a 10 or 20 cfs higher. Optimum boating flows are probably between 1000 and 5000 cfs. Boatable flows are generally only available during the peak runoff of wet years, but sometimes they also occur in late October or November related to powerhouse maintanence. Flows tend to vary dramatically from day to day when it does spill. This section has a much shorter and more erratic flow season than the upstream HorseShoe Bend reach.

The gauging station is a short ways downstream of the dam. If you see this gauge, look at the numbers on the staff gauge and make a note of where the water level is. When you get back home you can translate that water level to cfs with this Rating Table
See also CDEC gauge info, CDEC, and Dreamflows.  Historical records are available at USGS #11246700.  

The PG&E powerhouse that dewaters this section is Kerchoff #2.  It can divert up to 5,000 cfs.  Historical daily flow records for this powerhouse are available from USGS #11247050.   Historical daily flow records for the old PG&E powerhouse, Kerchoff #1 are available from USGS #11246950.

The last few miles of this section often have dependable flows every Autumn. Millerton Reservoir drops low enough every fall to reveal as much as 3 miles of river below a big underground powerhouse, Kerchoff #2. This powerhouse can release up to 5,000 cfs into the Millerton Bottoms section.

Then, typically in late October and November, the big powerhouse turns off and an older, smaller powerhouse, Kerchoff #1, comes online releasing water into the 1.9 mile, class 5, K1 to K2 section. In the past, flows from this powerhouse were typically around 1700 cfs, but in recent years, flows have been lower, around 800 or 900 cfs.    Since 2010, outflows from the powerhouse have been in the 500 cfs range.   The lower capacity of the old powerhouse in recent years has allowed boatable flows in Patterson Bend in the fall. 

The Patterson Bend gauge, linked above varies wildly at times. Even more wildly than seems possible, but PG&E assures us that the gauge is correct.  The following flow information sources can provide some corroboration or correction, but only for looking at previous days flows. Millerton Average Daily inflows, Real Time Reservoir Levels, DailyReport - pdf      


Some of the highest flows in this reach in recent years were during the January 1997 floods.   CDEC has Hourly Inflow to Millerton records for this period.    According to the Friant office of Bureau of Reclamation there is some possibility that a new gauge will be installed at the upper end of Millerton to measure inflows.   It would be a few years off if this did happen (as of 2010). 

Gauge Information

Name Range Difficulty Updated Level
cdec-SJA 700 - 6000 cfs III-V 01h17m 73 cfs (too low)

gauge graph
RangeWater LevelDifficultyComment
700 -6000 cfs barely runnable-high runnable III-V gauge is important or has warning

Reports give the public a chance to report on river conditions throughout the country as well as log the history of a river.