Archive for March 6th, 2010

An attempt to answer the question of whether the critical level of the Guri dam will be reached

March 6, 2010

Recent Picture of the Guri dam

All week, I (we) have been worrying about whether the Guri dam will or not reach the “critical” level of 240 meters above sea level at which point it will have to be shut down. In El Nacional there was an article on Friday in which one person talked about simulations and another gave a very definite date of something like April 4th.

This post is an attempt to answer that question. I start by looking at a graph I already published once:

This is the historical behavior of the flow of Rio Caroni that feeds Guri. As you can see, the minimim historical flow, shown in the green line, had a low around May 10th. Thus, unless this year represents a minimum in historical flow, this should be the worst possible scenario we may expect.

As usual, friend Moses came to the rescue yesterday linking to this post in Noticiero Digital which has a table of the level of Guri day by day since January 1st. This is how the water level has dropped so far this year and until Feb. 25th.

You can see that the daily drop is accelerating, which I noted yesterday because in January the daily drop was 8 or 9 centimeters and Chavez quoted 14 centimeters in February. Thus, because of a number of factors, conical shape, lower water inflow, lower levels, the change in not linear, the water drops faster as the days go by.

Instead of lloking at the level, it is better to look at the daily change as a function of time:

as you can see, there is a lot of scatter in the plot, due mostly to the fact that the data only has two significant digits. I did a fit to it and it looks quite good with a simple linear fit, the water level dropping accelerating its drop by about 0.594 mm. per day, that is it takes about 16 days to add  a centimeter to the daily drop.

This is the the data for the first two months of the year extrapolated all the way to June 16th.:

As you can see, the fit is pretty good and looks linear. In any case we can monitor in the upcoming days whether the model predicts the correct level day after a day and adjust accordingly.

Of course, I can now extrapolate using the model what would be the level into the future and how the date compares to the May 10th. cut off of the first graph above. Using the model, I get:

The plot above shows the orignal data in red below the water level data in blue generated by the model. The crossing of the 240 mts. level (I am not sure the exact number) takes place on May 29th. two weeks after the historical minimum. To give you an idea, I only used data up to the 25th. of February and today, the OPSIS page says that the level is at 254.20 and my model says 254.22, not bad at all, it does not seem to be accelerating or changing.

Given that May 10th. is the historical minimum for the water flow and the model says May 29th. it seems quite unlikely that Guri will have to shut down.

Comments are welcome.

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