|Posted: Oct 24, 2007Post Subject: Bear River Below Hwy 174 - Misc Flow Info
|Every now and again I get questions about how the Bear River below Hwy 174 works, and NID kindly supplied most of the following information (the remainder coming from the web):|
Water coming down the Bear above Hwy 174 is captured and stored in Rollins Reservoir. During normal operation, Rollins releases water only to meet demand, however they will release as necessary to make room for expected inflows, typically during winter. In what follows, the expression "Rollins is spilling" is used loosely to cover both situations: where they are releasing more than they'd like to make room, or when they can't release enough and it truly does spill.
The diversion canal going off river left from the Bear River at the Hwy 174 bridge is called the Bear River Canal, and under normal conditions none of that water is returned to the Bear River (though it could be made to in an emergency). In normal operation it flows down the canal to PG&E's Halsey, Wise, and Newcastle powerhouses, and is finally diverted off to water districts on a contract basis.
The water which doesn't flow into the Bear River Canal continues down the Bear River to Lake Combie, and is diverted from Combie (through a different canal system than the Bear River Canal), for irrigation and consumption. Fish flow below Combie is very low (10 cfs or so), so normally the only time you can expect boatable flows below Combie is if Rollins is spilling and all irrigation and consumption needs are met.
During winter they release as necessary to keep the Rollins Reservoir at the desired level and to make room for more inflow as mentioned above. This makes the flow schedule unpredictable. The irrigation season starts on April 15 each year. The minimum flow down the Bear River below Hwy 174 is 75 cfs, though usually they release 125 to 150 cfs, according to demand, and the flow can of course be even higher if Rollins is still spilling. Mid-October, they drop the flow back to 75 cfs. On Nov 1 it drops down to 20 cfs; they maintain this flow until the rains start and the cycle repeats. Note that 20 and 75 cfs are required minimums, and in each case actual flows will be 5 to 10 cfs higher. Naturally, in all the above, that's the theory, and they may release more if conditions warrant.
You may recall that in years past they sometimes had fall releases on the Bear. NID can't remember offhand why they had those releases back then, but in any case they don't have them now. So - in general - it's winter boating on the Bear, or not at all.
Edited twice. Last edited by chris Oct 24, 2007.