What is the criterion for defining how far downstream the modeling of the dam should be carried out, and what method do you recommend for obtaining the DEM?
It will largely depend on the objective. For example, a criterion could be up to where it is estimated that the arrival time of the peak exceeds 2 hours or after passing an important population center. The DEM can be obtained by restitution of orthophotos generated with drones or from satellite images.
Do you perform fluid tests in the laboratory using a rheometer for rheological analysis?
Yes, some laboratories estimate the rheological parameters using rheometers to measure viscosity and yield stress. On the other hand, the yield stress can also be estimated using Slump tests.
Are the formulations for breach formation directly applicable to the conditions of the high Andean areas of Peru, or do they require some adjustment?
I have not found investigations that relate these simulations to historical ruptures in Peru. These formulations are focused on failures due to overtopping and piping in earth dams, so the erosion or failure of the body and the generation of the breach would be more related to the material of which the dam is composed. However, there could be differences if the trigger for the failure is an earthquake or the activation of a geological fault in the high Andean areas.
How are these variables monitored? Perhaps with inclinometers or video surveillance?
Controls to prevent dam failures include inclinometers (to check for variations in the structure’s inclination), topographic landmarks and scans (to detect possible localized displacements), piezometers (to monitor water levels within the dam body), and pressure transducers or rulers (to check the water level in the tailings reservoir).
In real cases of dam breakage, have hydrographs been recalculated? If the answer is yes, which of the formulations for hydrograph estimation showed the best fit?
The formulations are empirical and only estimate the dimensions of the breach, the formation time, and the peak flows. For hydrograph recalculation, a physical model that more accurately represents breach formation may be necessary.
What are the advantages of performing a 3D analysis compared to a 2D analysis? What criteria do you consider for estimating loss of life, damage to infrastructure, or high risks?
3D models are generally used to evaluate erosion or degradation issues in specific sectors. For example, if you want to know more precisely how a bridge pier would fail, a 3D model would be used, as these models estimate velocities in the water depth or draft of the watercourse (depending on the mesh in the Z-axis depth), which allows for a better representation of the flow’s impact on the pier. In contrast, a 2D model would only obtain an average velocity for the entire water depth or draft, and, in general, these models use only empirical formulations to estimate scour.
How is the discharge hydrograph constructed, how is its duration determined, and when is the peak flow reached? Also, does each failure mode have a specific discharge hydrograph?
To construct the discharge hydrograph and calculate the peak flow, the peak Q must be determined using formulas or by estimating the breach formation time and the volume released, using the triangle area formula. In addition, each failure mode may have a specific discharge hydrograph that reflects its characteristics.
Where should samples be taken from to perform rheological tests?
Samples for rheological tests should be taken from the spigots in the tailings deposit (if it can be sampled safely), as well as from tanks or hydrocyclones that have sampling lines, ensuring that the material corresponds to the tailings destined for the deposit.
What software is recommended to master for performing rupture simulations?
For performing rupture simulations, Riverflow2D is one of the most complete software. Depending on the flow conditions, a Newtonian model could also be used. Other programs used in tailings flow simulations include FLO-2D and Flow-3D.
What methodologies are used to estimate the volume of processes I and II in the generation of the dam break hydrograph?
The most common methodologies for estimating the volume of processes I and II in the generation of the dam breach hydrograph include the statistical approach, which uses formulations by Rico and other authors, estimating the volume released at approximately 35% of the total volume. Another methodology involves assuming a final tailings deposition angle (after the break), which varies between 2° and 5°, both in the transverse and longitudinal direction to the breach.
Currently, emphasis is being placed on the control of sludge and water surface based on Bathymetry.
The volume of water is estimated with bathymetry, and levels are controlled by pressure transducers or rulers. Sludge or beaches can be represented with a DEM that is generated by a drone.
What method would you use to determine the shape of the hydrograph? Although I could estimate a triangular hydrograph based on the peak flow and duration, I have observed that the hydrograph of my simulation shows a steeper rise to the peak.
To determine the shape of the hydrograph, a hydrograph generator such as HMS can be used. However, it is important to edit and adjust the filling curve to suit the specific characteristics of a dam that contains water, taking into account that this may influence the shape of the hydrograph, especially in the rise to the peak.
Is it necessary to implement contingency works, or can only early warning methods be used, which I understand are notifications?
The need to implement contingency works depends on the terrain conditions; in some cases, these structures may be adequate. However, it is essential to always have early warning systems, regardless of whether the contingency structures have been built.
If a large river is incorporated downstream of the spilled tailings, what would be the study limit that can be established?
The study limit will depend on the objective of the analysis, such as establishing an arrival time of the major peak of 2 hours or after passing an important population center. The presence of a large river would increase the travel of the tailings particles, which could have a serious environmental impact, although the incremental effect could decrease, since the greatest impact could be caused by the watercourse.
What would be the steps to follow in the hydraulic model once I have defined the dam break hydrograph?
The steps to follow are:
- Obtain the rheological parameters.
- Generate the digital elevation model (DEM) downstream of the dam.
- Establish the dam failure conditions (according to the CDA cases: 1A, 1B, 2A, 2B).
- Select a representative simulation model for the case.
- Incorporate the data into the model.
- Present the results using maps.
At what stage is it recommended to carry out dam break simulation studies: exploration, feasibility, basic design, or detailed engineering?
According to current standards (GISTM), if a break analysis is not performed, the classification is considered extreme. It is recommended to perform a conceptual break analysis in the early stages of the project. For the feasibility or basic design stages, a semi-detailed analysis of the dam break is necessary.
Are seismic movements also considered in the analyses?
Yes, seismic movements are considered in the analyses, as they can be used to estimate the volume released and/or to evaluate the credibility of the collapse or failure.
What is your opinion, based on your experience, on the construction of a tailings dam on a salt flat?
I have not had the opportunity to participate in the design of a dam on a salt flat, but I believe that, with current technological advances, its construction is possible if appropriate criteria are applied for the foundation and the disposal of the tailings. The disposal of filtered tailings can be effective, but it is essential to evaluate the conditions of the site to ensure an adequate response.