Over the last two weeks, Northern California has finally seen it's first significant rainfall in almost a year. While we are still in need of a lot more rain and snow pack, the Sacramento River system has risen 10-12ft overnight!
Here is a diagram of the Fremont Weir and how the water flowed during a high river event. In this photo you can see the inflow from the Sacramento River, the existing fish ladder and the scour channel that connects the river to the Tule Canal (eventually leading back down to the Delta).
On Wednesday, December 17th, the Sacramento River at the Fremont Weir was at an elevation of 31 ft. water passively flowed through the existing fish ladder notch in the Fremont Weir, filled the stilling basin, and flowed into the scour channels that lead to Tule Canal.
Without any over-Fremont spilling, juvenile fish moved onto thousand of acres of shallowly-flooded Yolo Byapss floodplain habitat inundated by western tributaries. Nobody was monitoring.
If we had an operational Wallace Weir today, adult winter-run salmon would be swimming upstream through the notch (passing down-stream bound juveniles) and back into the river instead of up the Knights Landing Ridge Cut to their death.
The Take Home: River connectivity is essential. It is beneficial to young juvenile salmon that gain access to the great plethora of naturally produced food on the shallow-flooded bypass and adult salmon, migrating north to spawn, avoid getting trapped in dead end drainage canals. This connectivity is a win for both fish and farms!