Historic water records are pretty skimpy but can be found (or used to be) in USGS. What I heard was that the development of wells in the headwaters, probably coupled with sewers, exported water. Even by the 50s, wells could have been extracting too much. But, into the 80s it was still considered a good producer of steelhead. even intermittent, with good winter flows, could have made it a great stream. The canary grass choking the channel was one of the big issues I heard of.

Chums only need about 6 months flow, at the right time of course. In that system, start flowing in November, be done by April or May and you may really fit the chum. By drying out, the cottids and other predators would be absent meaning more fry make it at least to the mainstem.

I am pretty sure that there is a lot of historic data out there on flows, fish populations, distribution, size, timing, and so on that is not looked at for various reasons.