Based on the pictures I have seen the cracks do not appear to be randomly distributed. One testable hypothesis is that location and distribution is related to elastic deformation of the underlying rock. This may or may not be a contributing factor (as you pointed out, concrete will crack, especially under tension).
Given the history of this dam and what is now publicly known about the rock under the spillway, I certainly hope the non-random pattern of cracks have been competently investigated and have been shown to be benign.
Given what we now know about the way the DWR has performed in the past, I have my doubts.
its mid JAN and it has been rather dry....
lake level only at 703 feet....last year at this time it was around 850 feet and they opened up the spillway for the first time on jan 13th
the 8 station rainfall index is at 16.4 inches or 71% of normal to date..last year at this time it was about 50 inches
The max average daily inflow so far has only been about 19,000 cfs back in November...
The daily outflows from the power plant have been 2000-4500 cfs ...
a rather wet medium term pattern but since they can increase the outflow from the power plant to 12,000 cfs if needed....
there is a growing chance the spillway will not have to be used this year since the lake has to rise another 150 feet or so, including with the extra outflow capacity of the power plant, to get to 850ish feet
The only way that is possible is if they get a extreme wet period of about 8 weeks started now like what happened in 1982-83 or 1997-98...the rainfall intensity of those systems were even greater then last year although the duration wasn’t all winter...record inflow of over 240,000 cfs was with the 1997-98 event