If the Oroville Dam wet “green spot” is caused by lake water flowing through a leak or crack, that flow rate of water and/or particles through the dam must be a function of the driving head, measured by the lake elevation.
The observed phenomena:
1) greening or browning of various vegetative patches within the green spot area, and
2) creation of a high density of long vertical channels weeping out below the green spot area
must both be a function of this lake elevation generated flow.
The highest lake level in recent record was during the spring and summer of 2011, when the lake was within a few feet of topping out for months on end. The only time the green spot flow rate would have ever been higher is for just a few days in Feb 2017. The aggregate volume of green spot flow would have been greater in 2011 than (so far) in 2017.
It appears from the photographic evidence readily available so far that this year’s green spot has been greener than any year within recent photographic record, including 2011, when the aggregate flow to the green spot should been higher. However, DSOD reported wet moisture in February and May of 2011, and there is an unconfirmed report for October.
IMHO, if more evidence comes out that the green spot remained green or wet through the late 2011 summer , then that would be almost conclusive evidence that the water originates from the lake. However, if the green spot dries up as the lake rises this June, then this indicates the green spot is not sourced from reservoir water.
The green areas appear rather uniform in historic imagery and at some point (2009?) it takes on an odd, mottled appearance.
This reminds me of the appearance of railroad embankments in my neck of the woods. Being too steep to mow but very visible to the public in places, they would 'mow the weeds with a hose' in the 80's and 90's. When the sides of the embankments would grow back, they would take on the same kind of toxic waste dump mottled look from herbicide residue and stayed that way for a decade. These herbicides are suppose to be a one-time deal, i.e., they are generally not designed to be persistent.
Yeah, I'm sure they are not suppose to do that and, of course, the green areas serve as a sentinel marker of seepage. But who needs seepage detection anyway? Seepage means the FERC boys will get all riled up and who needs that kind of attention? It's just from a natural spring anyway - hose it down with RoundUp and make the problem disappear.
The source of the water for the green spot is obviously a critical issue. What happens this summer may shed some light on that.
IMHO opinion, however, the CRITICAL issue is the trend. If it is worsening we have a major problem that must be addressed as soon as possible.
The green spot provides a very crude measure of this. If it is worse this year than 2011, especially since the average lake elevation is likely to be less, then we may be looking at a worsening trend.
Worsening water flow will NOT be linear even if it appears to be in the early stages. Once it starts to worsen it will accelerate slowly at first, but the rate of acceleration will increase over time.
The head of water (only that above the leak) pushing water through the dam is variable, hence the volume of water is almost certainly variable as well. The volume of water and rate of flow of that water will impact the time it takes for some of that water to reach the green spot. Put those factors together and you have a very hard to estimate, but nevertheless non-linear, curve.
The acceleration will not follow an easily extrapolated exponential curve, but that is basically what it will be.