Hidroituango hydropower dam Colombia. Opinion from Dr Ordoñez

Last week we presented time frame of the Hidroituango dam fail emergency (link) in Colombia. Engineers reported that the dam reached the target level. This post in a translation of the communication from Dr. Jaime Ordoñez from the technical commission from Sociedad Colombiana de Ingenieros. The original publication in Spanish is in this link.

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May 25, 2018.

Yes, we should regret that a greater number of members of the Commission had not attended the meeting and helped us in the drafting of this document. Unfortunately, despite the seriousness of the subject we have before us, very few people came. Only those who know the thing well know that the Ituango project is dead and there is no control over it, so the most natural thing is to expect it to fail; we are sure that it is easier for him to fail to fail, and we are truly in a panic, seeing ourselves that nobody seems to understand what is coming, nobody wants to believe that there is going to be a huge tragedy.

We have considered, who we call this meeting, that it is totally absurd that the project managers insist on not letting the Project Engineers speak directly, thereby misinforming rather than informing. That's why you and many other engineers have not heard the seriousness of the situation and still believe there is something to be done, that there is something we can and should help, although it is much clearer that there is nothing to do!

We must know that all the "decisions" taken so far to mitigate the emergency have not really been technical decisions, but solutions forced by the failure of EPM criteria and its engineers to plug the diversion tunnels instead of installing the gates provided for make them work as a background download of the Project. They decided, to gain time and be able to start the project this year, to do more of an "intermediate" tunnel between the detour and the loading, which is the one that failed to start the emergency! From then on being this a strong winter, everything has been to look desperate as the level of the water rises without control, to allow the flooding of the cavern as the only solution so that it does not spill the water on the dam, which would cause its destruction, and now, race, raise the dam 15 to 20 meters, (now they plan to take it to level 415), to see if they can pass the water through the dump of excesses, which is not even finished, and will be a new source of failures when start working, if the floodgates, which have not had time to rehearse, work!

And what to say about the fact that the tunnels below are already filtering water, and there is nothing to do to avoid it! The massif of the right margin, the one that had the failures before the rise of the water, that is to say when it was dry, is now saturated and under pressure, and the pressure continues to rise as the level of the reservoir rises! If water is already filtering through the tunnels, it is because of internal cavities, cavities and dents, caves, because there are several cargo tunnels, two original detours and the "intermediate" all in the same pitiful been and without possibility of arrangement, those cavities as I said, has been enlarged and at any time one or more of them will explode, as happened last Saturday, and through that gap all the water comes and fails the dam the right abutment !.

The approximate calculations we have made reveal a breakthrough rate of more than 100,000 mcs; more than 3 times the flow that destroyed Armero! and that there will be no avalanche is ridiculous! they believe that there will only be an avalanche if the water passes over the dam, but the dam will still go if the breach is by the right-hand abutment; In addition, the avalanche of solids is not due to the volume of material from the dam, it is due to the volume of sediments in the bed and the multiple landslides that would generate an avenue of similar size, on the slopes of a very steep canyon. extraordinarily unstable You must remember that the Farallones project could not be done because the failure of the slopes by itself was enough to fill the glass, together with the 45 million tons a year the river carries. What difference can there be between "Avenue" and "Avalanche"? any avenue of such a flow is in itself an avalanche generator even if most of the dam remains standing !.

And the worst thing is to think that even if there is no fault in these few days until the level of the reservoir reaches the flow through the landfill, there will be no way to make arrangements in the project without emptying the reservoir, which does not it can be done without removing the prey; you can not even know if the tunnel cavities are still working or if they no longer serve as is hardly expected!

And you tell us that our statement can generate panic! Sorry to tell you that the panic is already with those poor people !, that you do not know anymore, if you stay or if you leave their homes, they say that many leave and a few days return, because they simply have nowhere to go, and as every time they tell them that danger is almost over, well, no way, they come back! And if the dam fails tonight, only God knows how many will die while we decide if we speak or we do not speak because the owners of this great project are poor. I remind you that the communities have been pleading for more than 10 years not to do this project, and that no one has ever given them the least care; Now they say that it is what matters most to the owners of the project, and they have even made a truly laughable offer of money, so that they leave the area!

One of the worst problems that is faced to save people is that there is no Contingency Plan or Evacuation Plan !. The one that is being executed is that of the NGRD, that is, the government, which is generic and was not made to evacuate cities. Plan of Cotingencia is not to blow a whistle when there is danger, but to establish the materials and means to transfer the population to a safe area: buses, trucks, helicopters, etc. and provide room and food for that population in that safe area. It is not to harass the families in tents, as they are showing us in the news, in a public place in the same town, like the stadium, or a school, or a church, that will be rolled to the bottom of the canyon when the city collapses. hillside to the passage of the "Avenue" or "Avalanche" !!

Our communiqué is a call, (done quite late!), So that those who truly know what the tragedy is going to be pinched, inform the government in a clear way what is going to happen, and stop saying stupid things, that maybe not generate the panic that scares you so much, but that will surely produce the dead that we are all going to regret!

That is the meaning of what we said, to see if our President and Board of the SCI are pinched equally, (something that neither the Space building nor the Chirajara Bridge nor the Lizama spill have done. nor with this problem that some are already saying that it will be the second biggest catastrophe in the world after Chernobyl !!), I have always thought that you 'think like us, Gilberto, that you have to talk about things as they are and not as they sound beautiful! Otherwise, why are we here?

It's my humble point of view, you do not have to accept it!

Regards,

Jaime Iván
Jaime Iván Ordóñez Dr. Eng.


Note. This is a translation from the original post by W radio (Link)
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Importance of fire flows to calibrate water distribution models

Over the years, I have found several engineering projects and journal articles in the topic of modeling water distribution networks. One common mistake that I found in most of them is that they "calibrate" the model (pipe roughness) considering only normal flow conditions instead of high demand conditions such as fire flow tests. Actually, it is not possible to calibrate a model without considering high demand conditions. 

Water distribution modelling: The physics and mathematics

There are several water distribution models (water distribution software) such as EPANET, InfoWater, WaterGEMS, Mike Urban and others. It is important to remember that water distribution models are based on physical processes and they simulate the network by solving a matrix system based on:

• Conservation of mass in every node
• Conservation of energy in every pipe

In the conservation of mass we have 3 variables:

• Flow. This is a known value. Is a boundary condition.
• Area. This value is calculated based on pipe size (known value)
• Velocity. This is a function of flow (known value) and pipe size (known value)

In the conservation of energy we have 4 variables:

• Pressure. This is the value to be calculated
• Velocity. This is a function of flow (known value) and pipe size (known value)
• Elevation. This is a known value
• Head losses. This is a calculated based on the Hazen-WIlliams equation, which is a function of flow (known value), pipe size (known value) and pipe roughness (to be calibrated)

Thus, we have 2 unknown values: pressure and pipe roughness. By assuming a proper pipe roughness we can calculate the pressure. This process of assuming the proper roughness is the calibration of the model. 

Fire flow and pipe head loss

Head losses are calculated based on the Hazen Williams equation. Hazen Williams equation relates the friction head loss as power function of the flow. Thus, it becomes more sensitive to higher flows (you can solve the Hazen-Williams equation online). Let’s show one simple example.

Let’s assume a 1 km pipe reach of a 250 mm pipe, and considering different roughness values from 130 (new pipe) to 70 (pipe in a very bad condition). Let’s calculate the pressure drop for different flows between 1,500 cmd and 5,450 cmd. We are assuming typical flows (1,500 cdm and 5,450 cdm) because:

• Assuming a 300 l/hab day, 1,500 cmd would be enough to supply water to a 5,000 habitants zone
• 5,450 cmd is equivalent to a standard fire demand (1,000 gpm)

As we can see, considering a 1,500 cmd water flow would led to accept a wide range of roughness values. We could assume any roughness value between 70 to 130, and pressure differences would be 1.3 m (about 1.9 psi). On the other hand, those roughness values (between 70 to 130) with fire flow demand produces a 14.5 m pressure difference (about 20.5 psi). Thus, high flows such as fire flow really show the sensitivity of the pipe to roughness. 

Suggestions to calibrate water distribution models

Basic suggestions for calibrating water distribution models are:

• Use normal conditions data to verify connectivity issues only. Do not use it to verify roughness. 
• If you want to calibrate the model, then perform fire flow tests or collect data during high demand equivalent or greater than 1,000 gpm.
• If is not possible to collect high flow data, do not say that your model is calibrated (because it is not). In this case perform a sensitivity analysis.

Hidroituango dam fail emergency

A dam fail does not necessarily mean a total collapse of the dam. A dam fail refers to any unexpected or uncontrolled water flow. Therefore, the recent emergency at the Hidroituango dam in Colombia could be referred as a dam fail.

On May 2018, Colombia faced one of its worse dam fails in history in the Hidroituango hydropower dam construction. Hidroituango hydropower dam is supposed to be the most important hydropower project in Colombia. With a 220 m high dam and 8 turbines it will have an installed capacity of 2 400 MW. On May 2018, some landslides locked some water detour tunnels, thus creating an unexpected fill and unexpected water flows. Dr. Ordoñez from the technical commission expressed his concern about the critical situation. In order to safe the dam, it was necessary to sacrifice the machines room by using it as an emergency spillway.

In this post we present a time frame summary of this event. 

• April 28^th. Water detour tunnel gets locked due to internal landslide
• April 30^th. Water naturally unlocks the tunnel
• May 1^st. Another water detour tunnel gets locked due to internal landslide. Water begins to accumulate and to fill the reservoir
• May 4^th. Water fills about 50% of reservoir capacity.
• May 10^th. It is decided to use the machines room as bypass. Machines room gets flooded.
• May 12^th. River flow downstream increases. Some towns are flooded and some bridges collapse
• May 16^th. Emergency is declared. Several towns and thousands of people are evacuated. One filtration is reported; there is possibility for a dam break. Emergency works continue.
• May 19^th. Dam works reach level 405 masl (target level to use the cofferdam is 410 masl). Although there is hope for reaching the target, rains are forecasted.

The video and the infographic shows a time frame of this event

Infographic of Hidroituango dam crisis 2018

New HEC-RAS v 5.0.4

A new version of HEC-RAS was released; HEC-RAS 5.0.4. The first question to HEC-RAS user's is What are the main improvements of this version?

Actually, there are several improvements. Moreover, considering the software versioning standards, I think it would have been better to call it version 5.1. I will not go into the detail of all the improvements (the release notes is a 19 pages document), but I will summarize the most important ones.

●       Computational speed. Computational speed is crucial in selecting a 2D model. I remember my first experience with HEC-RAS 5 beta took several days to perform a simulation; that same simulation took just about 2 hours using other models. Fortunately, HEC-RAS has been improving its computational speed. This new version has a fully parallelized engine that doubles the computational speed. If your previous simulation required X hours, with this new version it will only require 0.5 X hours.

●       Ras Mapper tools. This one is a major improvement. Previous version still required ArcGIS and GeoRAS for preparing geometric data, especially for 1D cross sections and 1D profiles. This new version includes full GIS geometric processing capabilities. This video shows the creation of a 1D river geometry with the new Ras Mapper.

●       2D nested mesh. Previous version performed 2D simulations on a nearly regular non staggered grid. That means the 2D DX was the same for all the grid. The new version allows to refine the grid at specific locations. Hence, a coarse grid can be used for big floodplains, while a more refined grid can be used for particular areas requiring more detail.

●       More sediment options. New linear scaling factors and granulometry options are available

●       64 bit processor. Most users may not be deep into computer science and may neglect the importance of this improvement. Let me tell you that this is an important improvement with BIG benefits. It allows working with bigger data files and faster processing. You will easily realize this benefits when working with the 2D; you will see how the mouse movements and the clicks are faster and your work is more comfortable.

Image 1. Print screen from the video showing 1D creation with the new RasMapper

Nevertheless, there is one disadvantage that you have to consider before using this new version. Although this 5.0.4 version is compatible with previous versions, previous version are not compatible with models saved under 5.0.4 version.

As I you can see, this new version is not limited just to fixing bugs. It has important add-ons and improvements. Therefore, considering the software versioning standards, I consider that it could have been  more appropriate to call it version 5.1.