People in Caracas were rightly encouraged last week when the city got some rain. Stories about the Guri Dam reaching critical level have been scaring people for the last two weeks. Unfortunately, as you can see in the rain map above from Monday March 14th. at 1 AM, the rain that poured over the city is nowhere to be seen now. In fact, that rain seemed to come from the Caribbean and did not make a dent on Guri Dam, which the map notes. There is some rainy activity south of the dam in Amazonas state, but it is too far, while it is hopeful to see some.
The question is how bad the problem is or may become. To explain this, I resort to slides I showed in 2010 when a similar threat was present.
Reportedly, the level of the dam is now at 247.5 meters. Within this range, each day without rain implies a drop of 30 cm today, but will accelerate as it drops. The minimum level at which the dam may operate is 240 m. as seeing in the following slide:
What the slide shows is that the minimum level of operation occurs below 240 meters. Below this level, a number of problems begin to take place in which the turbines do not operate well (Cavitation and turbulence). According to the slide, below this level, eight of the turbines (some of which, in red, are not operational, will not work, taking out 5,600 MW of power out of the country´s network. This is about half what Guri can produce and Guri provides 60% of the power in the country. Thus, at this level, we are talking about losing 30% of the power of the country and , of course, the water level could keep dropping.
A more detailed plot of the problems is shown in the following plot (Both plots are official ones from Government’s electrical institutions):
As you can see, slightly below 240 meters, vortices will form and the turbines will have to be stopped. We are talking about 9 meters below current level.
Well, we are close, but the drought will have to last some 46 days, according to predictions made in this post in the comments by a reader in 2010.
This means that we are talking about end of April before in the critical area. Thus, while we have reasons to be concerned, the critical level is still far from where we are, as rains seem to be beginning to appear in the south of Venezuela. The weather is unpredictable, but a catastrophe is still far away and may not happen. Will keep you informed.
Someone sent me this plot. The slope at which it drops is 12-13 cm per day, which is a positive as it gives more time (70 days to be more precise) :