Topic: Interpretation of ouflow data from BUL, Flows in Lower NF and MF
|Posted: Mar 13, 2007Post Subject: Interpretation of ouflow data from BUL, Flows in Lower NF and MF
|I'm concerned that the data reported by the BUL gauge "Outflows from New Bullards Bar" is very confusing for people not familiar with the hydro plumbing in that part of the world.|
The BUL gauge is misleading, its more of a "virtual gauge" built from amalgamated data, the outflow data is copied from Colgate Power House (CPH) well downstream. YCWA used to have a nice website that showed that better but its gone replaced with lots of useless text crap that says nothing. I believe Flows gaged at CPH includes Colgate Power house outflow, ORH, fish flow generation releases + spill from New Bullards Bar, and some side creeks that are very significant also (most notably Oregon Creek).
New Colgate Power House has a maximum generation flow of 3700cfs and is 5 miles downstream of New Bullards Bar. There is a fish flow release power house at the base of New Bullards Bar that can release 10's of CFS only. The flood gates on New Bullards Bar are below the maximum water elevation, but not by much thus it must be very full for spill to be an option. Colgate Power House has a unique engineering problem that complicates matters further, once in stream flows at the powerhouse start to exceed 10,000 cfs the turbines start to become inundated and generation flows have to be reduced, ceasing completely by 25,000 cfs. Thus this means as high flows increase the ability to drain New Bullards Bar is actually decreased and spill must be increased to compensate. There is an engineering project planned to correct this problem but I don't know if it has started/finished yet. All in all this makes predicting flows in the NF immediately bellow New Bullard Bar and continuing after the MF confluence very complicated and prospective descenders have always relied on a visuall check over the dam at New Bullards Bar.
If we could try to work towards building an estimate of flows bellow New Bullards Bar then that, in conjunction with data from ORH would give the data needed to plan a run on either of these 2 forks.
Anecdotal evidence from the few people I've found who have got on this section suggests that getting to the confluence and finding excessive flows is a big problem.
Brad has suggested 700-800 is ideal after the confluence and 1000 the max.
|Posted: Mar 13, 2007Post Subject: Re: Interpretation of ouflow data from BUL, Flows in Lower NF an
|Dangnabbit! But thanks for the warning and the post, Ian, that seems to sum it up nicely. What I'm hearing from this and other sources is that the reported OUTFLOW from CDEC's BUL is usually very misleading, though higher flows (greater than 3000 cfs) may tell us something useful. So I've suppressed flow reporting for 'No. Yuba - Below New Bullards Bar' for now.|
|If we could try to work towards building an estimate of flows bellow New Bullards Bar then that, in conjunction with data from ORH would give the data needed to plan a run on either of these 2 forks.|
Yes, indeed. I hear this is an outstanding run. All input geared towards getting or estimating reliable flow information much appreciated ...
|You're pretty much right on Ian. Colgate has the capacity to divert around 3000-3700 cfs from the outflow at Bullards so the only time the N Yuba runs below the dam is from spill over the emergency spillway. Seems like this makes it really hard to catch since spill will usually happen when M Yuba has water also. There are lots of stories of people putting on the M Yuba at a good flow and getting to the confluence to see it double. We did it at around 600 on the M Yuba with nothing on the N Yuba which seemed like a good minimum and I imagine 800-900 would be optimum and around 1200 or a little more would be at the top end. I've also heard of paddlers running into a dam operator who gave them spillway flows, etc. You can run shuttle via Moonshine Road but coming back to the put in it is always good to do a visual to see what is coming out of the dam to be sure you don't get the doubling of flow on ya.