There are many demands on California water, and one of them is how much water to leave in streams to protect native fish and ecosystems. A recent approach to this question is to look at "functional flows:" not so much the total amount of water, but when it is flowing and what it is doing. 

In northern California, natural streams get a pulse of water in Fall with the first major storm of the wet season, then a baseline amount of wet season flow punctuated by storm events. Flows drop in the Spring to a dry season base flow. A functional flow approach would attempt to replicate these natural environmental flows. 

Data from Putah Creek, which flows from the coastal ranges past the UC Davis campus and into the Sacramento river, shows that a functional flows approach can support recovery of native species, including salmon, when it moves stream conditions closer to their natural state before dams were put in place. The work is summarized in a new blog post from the Center for Watershed Sciences. 

Putah Creek is held up by the Monticello dam (creating lake Berryessa) and the Putah Creek diversion further downstream. Following a series of droughts and fish kills, the Putah Creek Accord was implemented in 2000 in an attempt to restore the creek's natural habitat. Based on input from UC Davis scientists, especially Prof. Peter Moyle, the Accord included some elements of a 'functional flow' approach, although this specific term is more recent. 

Long term studies show that since the Accord was put in place, native fish have staged a comeback in the creek, including a Chinook salmon run. 

"Essentially, the more the environmental flow regime approached a natural functional flow regime, the greater the likelihood that native fishes would succeed," write researchers Sarah Yarnell, Ethan Baruch, Andrew L. Rypel and Rob Lusardi in their blog post. 

Read more below.