Inflow rates.....

Rainbowbridge

Rainbowbridge

Keeper of San Juan Secrets
Question for our WW sages, and apologies if this has been answered before.....

When we see large changes in inflow...IE: 3793 on Tuesday...6974 the next day, Wednesday....almost doubled.....is this runoff from a storm upstream?.....letting more H2O out of upstream reservoirs?.......upstream soil becoming saturated and allowing more flow? Is this large CFS spread manipulated/planned....or just mother nature using her endless female prerogatives?? (I'm envious...) :unsure: 😋
 
I believe that the reported inflow rates are computed rather than directly measured. I think the outflow is known fairly accurately from dam operations. Then the lake elevation is measured from which the change in reservoir content is derived. That change in content adjusted for the known outflow results in the reported inflow. Since small changes in lake elevation result it rather large changes in content that means the computed inflow can jump up or down in error. But over a few days it all averages out, so often an unusually low inflow report is followed by an unusually high inflow report. Actually the inflow was just about the same both days, but a small error in lake elevation measurement on one day results in the two days inflows being out of whack.

I'll try to track down if I'm remembering this correctly, though undoubtedly one of the true gurus knows off the top of their head...

EDIT: Yep, I confirmed that is correct. See here:


Note the asterisk at the bottom of the table which says:
Inflow is computed based on reservoir release and change in reservoir storage (and reservoir evaporation and change in bank storage when these parameters are accounted for).
 
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I'm making an educated guess here but it could be several things.

1. rain runoff upstream from a storm
2. Snow runoff due to some warmer than usual days. You'll notice the SWE chart goes down at times
3. Upstream reservoirs increasing their outflows

So basically all the things you mentioned are possibilities and likely others I think it's just the natural ebbs and flows of mother nature as you pointed out. The other thing to remember is that there may be a gap in how they record the lakes volume and inflows. I think they know how much water they let out, and they know the water level so they are likely calculating for inflow based off that. However, evaporation is not a constant. On warm sunny days, there's likely more evaporation than on cool cloudy days so on a cool cloudy day, you may think you have more inflow than typical when really there's less evaporation. Whether this is enough to make a difference or not, I don't know. I'm not sure anyone truly knows how much water is coming in each day and it's calculated based off of the variables so you'll see some daily ups and downs. The trends are what's important particularly when the spring runoff starts.
 
Releases from Blue Mesa have ramped up a little bit in the past week or so.

I recall seeing negative inflow numbers in the water database charts occasionally, usually when an elevation reading differs greatly from the norm. Look at the average over the past few weeks to get a better idea of what's really happening.
 
Another factor might be if the wind is up and blowing the right direction that may have some effect on the lake level for a short period of time. At least that is my guess in addition to the others already mentioned. :)
 
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