Sometimes more equals better, sometimes it doesn't. Upstream of Gorge Dam, most of the gravel recruitment comes from Thunder Arm (Creek) and the mainstem upper Skagit River in Canada. The inundated channel behind Ross Dam was supplied with gravel and large wood from the Canadian Skagit. Some of that wood and gravel source would have populated the Skagit downstream of Gorge Dam, but I don't think it would have made a measurable difference because of the plentiful recruitment immediately downstream of the Gorge. Based on assessments made before the 1990 Settlement Agreement (and 1995 license issuance), there is not a gravel shortage between Newhalem and the Sauk River. Therefore, I don't think more would equal better. More large wood would be a benefit nearly everywhere on the Skagit and Sauk. The problem is that the source of large wood is gone and has been gone for many decades now. The source would be the riparian zone along the river banks. It was all logged or few into the river long ago. There isn't much in the way of replacement to be had. Upstream of Ross Dam, there is large wood in the Big Beaver and Little Beaver drainages which supply a small amount to Ross Reservoir. The other drainages are populated with smaller timber, with upper reaches transitioning to lodgepole pine habitat. The Canadian Skagit has been logged similar to the U.S. side, so a significant supply of large wood isn't something I see happening well into the foreseeable future.
An important part of evaluating the benefits of passing gravel and or large wood from upstream of Gorge or the other dams is understanding the geomorphology of the Skagit River channel from Gorge Dam downstream to Marblemount. The area is called the "Gorge" because that is what the landmass and river channel are, meaning over half the river miles in that reach have no floodplain to speak of, where the river can spread out during high flow events. High flow events cause the water level to rise - a lot - and the velocity increases dramatically. Take note that there is very little more than zero farmland between Marblemount and Gorge Dam. The river channel is narrow and surrounded by steep high river bank, with a significant amount of bedrock. My key point is that gorges, or canyons, or any narrow incised river channels are places that do not retain very much large wood or gravel. The preponderance of such material, if there is a source, simply gets blown through during high water events, and is deposited somewhere further downstream. This is why I'm reasonably confident in saying that the river reach from Gorge Dam downstream to Marblemount is not starved for gravel. The non-gorge-like parts would benefit from large wood, if there were a source. There are important spawning areas in the mainstem Skagit between Marblemount and Newhalem. By all accounts that I'm aware of, that reach is well supplied with gravel from Newhalem, Goodell, Bacon, and Diobsud Creeks and a few smaller streams. (Newhalem alone recruits something like 60,000 cubic yards per year on average.)
If anything, benthic invertebrate populations in the reach between the Sauk River and Newhalem should be somewhat better than before 1990 due to the decreased amount of daily flow ramping. I don't know if there are any before and after quantitative surveys for comparison. There were surveys in the 1970s by folks from UW's Fisheries Research Institute. I think I have that report in my basement. Resident fish of fishable size in the mainstem Skagit prior to 1990 were provided mainly by periodic floodwater spill events from Ross Dam (and reservoir). Otherwise, like most streams, catchable sized resident trout get caught and removed by anglers. Fishing restrictions since that time, along with declining steelhead numbers, should have led to an increase in the resident trout population due to decreased fishing mortality. I hear of a few nice resident trout in the Skagit, but not many. The upshot is that I don't see any indication that the gravel supply is limiting the resident trout population. More large wood would help all fish, but as I wrote above, there needs to be a supply of large wood for that to happen.
Fish passage technology, as it stands right now, if developed at the three Skagit dams, is highly unlikely to result in significant increases in the populations of pink, chum, or Chinook salmon or steelhead trout. It could result in significant production of sockeye and coho salmon. This is because pink and chum salmon (with very few exceptions) do not successfully outmigrate as smolts through lakes or storage reservoirs. Nor do Chinook, for that matter. From Snake and Columbia River experience we know that Chinook do outmigrate, with difficulty, through run-of-river reservoirs. Spring Chinook and steelhead were tested at Baker Lake, and from what little I heard, didn't do too well. They were also slated for testing at Lake Cushman, but I haven't heard how that's going either. I'll look into both of those. So no, unless a sockeye plan becomes in the works, I don't expect fish passage at the Skagit dams to do much good for salmon and steelhead.
If I had a billion $$, I'd buy as much riparian land along the Sauk River and Skagit downstream of Hamilton as I could buy and plant massive quantities of red cedar and spruce on the lower reaches of tributaries and the mainstem riparian areas to better achieve that "desired future condition."
