{"id":8389,"date":"2025-12-15T20:06:55","date_gmt":"2025-12-15T23:06:55","guid":{"rendered":"https:\/\/vinq.us\/?p=8389"},"modified":"2026-01-03T20:08:58","modified_gmt":"2026-01-03T23:08:58","slug":"gestao-agua-chuvas-extremas-mudancas-climaticas","status":"publish","type":"post","link":"https:\/\/vinq.us\/en\/gestao-agua-chuvas-extremas-mudancas-climaticas\/","title":{"rendered":"Water Management in the Face of Extreme Rainfall and Climate Change"},"content":{"rendered":"
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The accumulated experience with tailings dam failures and instabilities in waste rock piles converges on an uncomfortable, yet inescapable, conclusion: containment structures generally do not fail because\u2026<\/span>the safety factor was low on paper.<\/span><\/i>"They fail because water, in its different forms, has not been treated as a strategic risk variable. Reservoir levels operating near freeboard, unmonitored pore pressures, drainage systems designed for a climate that no longer exists, underestimated surface and internal erosion, spillways sized based on partially outdated historical data. The pattern repeats itself."<\/span><\/p>

At the same time, the hydrological regime that underpinned intensity-duration-frequency curves, design floods, and traditional concepts of "extreme events" is no longer stationary. In several mining regions in Brazil, the observed reality is a higher frequency of very intense precipitation events, a greater concentration of volumes in short time windows, and greater interannual variability. In other words, more critical events, more abrupt and less predictable by historical statistics.<\/span><\/p>

In this context, the paradigm of \u201c<\/span>meet the standard and the minimum safety factor.<\/span><\/i>"This becomes insufficient. Operators who truly want to reduce structural risk need to migrate from a point-in-time, static drainage model focused on isolated works, to a water resilience model. In this model, tailings dams, stockpiles, pits, processing plants, and intake and discharge systems are treated as a single system, managed under explicit scenarios of climate change, hydrological uncertainty, and increasing pressure from investors, regulators, and communities."<\/span><\/p>

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Water as a critical risk variable<\/b><\/h2>

From a geotechnical point of view, water is the variable that connects virtually all relevant failure modes in rock piles and tailings dams. In terms of rock mass behavior, it modulates the stress state, the degree of saturation, suction in partially saturated zones, and pore pressures at critical interfaces. In hydraulic terms, it controls internal gradients, seepage, seepage, <\/span>piping<\/span><\/i>Surface and internal erosion. In operational terms, it determines the effective freeboard, the hydraulic capacity of spillways and channels, the load on sedimentation basins, and the interaction with natural drainage systems.<\/span><\/p>

In a typical tailings dam, intense rainfall and pressured operating conditions result in three risk fronts. The reservoir may experience a rapid rise in water level, consuming freeboard margins and bringing the system closer to overflow. The dam and foundation may experience increased pore pressure, displacement of the water table, and saturation of zones that, under service conditions, contributed to suction and additional resistance. The discharge system may operate above its designed capacity, generating localized overflows, abutment erosion, and unforeseen flow paths.<\/span><\/p>

In piles, the dynamics are different, but the risk vector remains water. Prolonged rainfall events increase infiltration, raise the saturation front in internal zones, increase the acting self-weight, and reduce resistance at interfaces between materials with contrasting permeabilities. At the same time, the energy of runoff on extensive slopes intensifies erosion, generates deep gullies, carries large volumes of fines, and accelerates the clogging of channels, culverts, and dissipation basins. Structures originally designed as "support drainage" become critical points in extreme scenarios.<\/span><\/p>

By placing water in this central position, the debate ceases to be merely hydrological or hydraulic. It becomes, essentially, a problem of integrated geotechnical risk and the allocation of capital to mitigation measures.<\/span><\/p>

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Climate change and extreme events<\/b><\/h2>

A large part of the tailings dams and tailings piles in operation today were designed under an implicit assumption of stationarity. The basic hypothesis was: the statistical past reasonably represents the future. From this hypothesis, intensity-duration-frequency curves, design return periods, spillway dimensioning fills, and freeboard criteria were defined.<\/span><\/p>

The problem is that this premise no longer holds up comfortably in several mining regions. Certain combined patterns are being observed with increasing frequency. Events with return periods estimated in decades, according to historical statistics, are beginning to occur at intervals of just a few years. Rainfall volumes that were previously distributed over weeks are now concentrated in 24 to 72 hours, generating significantly higher peak flows for the same monthly or seasonal rainfall. Extremely dry years alternate with exceptionally rainy years, forcing the same system to operate under both extreme scarcity and extreme excess.<\/span><\/p>

From a technical standpoint, this implies revising central design assumptions. Intensity-duration-frequency curves calculated solely based on long historical series can mask recent intensification trends. Design floods associated with return periods of 50 or 100 years may not adequately reflect current risk, especially when they do not incorporate extreme value techniques and climate scenarios. Concepts such as Maximum Probable Precipitation cease to be merely a regulatory requirement for dams with high damage potential and become a useful reference for testing the robustness of drainage systems in sensitive projects.<\/span><\/p>

In practice, the operator who continues to design and make decisions solely based on historical data is accepting to run their business with an increasing level of uncertainty. And, often, without knowing exactly where the new boundaries of safety and failure lie.<\/span><\/p>

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Structural implications for TSFs in more extreme rainfall regimes.<\/b><\/h2>

When observing a radioactive stream (RTS) system under the lens of a more aggressive climate, three structural elements deserve special attention: the reservoir, the embankment, and the discharge and diversion system.<\/span><\/p>

In the reservoir, the combination of intense events with operations generally under pressure to maximize water reuse and volumetric capacity results in increasingly narrow freeboard margins. A single high-intensity event in a few days can consume a large part of this margin, especially if the pumping and recirculation system does not have the capacity to quickly lower the level or if the operation works close to the approved volumetric limit. The central risk ceases to be just the design flood and becomes the sequence of events, the reservoir's starting level, and the system's response speed.<\/span><\/p>

In the rock mass and foundation, the challenge lies in the hydraulic and geotechnical response under transient loads. Tailings with contractile behavior and low relative density are sensitive to abrupt increases in pore pressure and stress paths that bring them closer to static liquefaction. Horizontal drains, toe filters, crest drains, and other elements designed in the project may be partially clogged or underperforming as expected, resulting from fine deposition, variations in particle size distribution, or insufficient maintenance. Under extreme events, the system as a whole may respond very differently from that predicted in analyses. <\/span>steady-state<\/span><\/i>.<\/span><\/p>

In the discharge and diversion system, the problem is less visible, but equally critical. Diversion channels, spillways, dissipators, and transition devices were often designed considering smaller contributing basins, lower sediment loads, and original cover and roughness characteristics. Years of operation, vegetation suppression, access road construction, and stockpile expansion alter the local hydrology. In extreme events, the combination of higher flow and higher sediment load quickly exceeds design capacities. The result can be overflow at fragile points, regressive erosion, loss of lateral containment, and, in more severe scenarios, the onset of erosion failures on abutments or the crest itself.<\/span><\/p>

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Structural implications for fuel piles in high rainfall regions<\/b><\/h2>

Waste rock piles, especially in regions with high rainfall and rugged topography, present a combination of risks that is still underestimated in many portfolios. They accumulate large volumes, significant heights, extensive surface drainage structures, and often foundations with residual or colluvial soils that are sensitive to saturation.<\/span><\/p>

Surface erosion is often the first sign that the system is out of balance. On extensive slopes, even small concentrations of flow can evolve into deep gullies when subjected to high-intensity rainfall. These gullies expose inner layers, redirect runoff, destabilize berms, and carry large volumes of fine material. The resulting sediment load tends to rapidly clog channels, culverts, and sedimentation basins. With each event, the useful drainage section is reduced a little more, which worsens the behavior in the next event. The cycle is cumulative.<\/span><\/p>

Infiltration and internal saturation are another significant risk factor. In piles with heterogeneous materials, preferential flow planes form along contacts between materials with different permeabilities. Under prolonged rain, these planes become zones of high pore pressure, close to potential rupture surfaces. In foundations with low drainage capacity, accumulated water can generate base settlement, slope rotation, and a progressive reduction in the safety factor. In many cases, the pile was designed assuming predominantly unsaturated behavior, with a significant contribution from suction. This contribution disappears under saturation, reversing the safety logic conceived in the design.<\/span><\/p>

The sum of these effects creates an asymmetrical risk profile. The system operates, for much of the time, with an appearance of acceptable stability. However, in high-intensity events, especially those that occur after prolonged rainy periods, the behavior enters a different regime, closer to a limit condition. Without instrumentation and models that capture this state, management operates practically blindly at these times.<\/span><\/p>

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From \u201csufficient\u201d drainage to water resilience.<\/b><\/h2>

Responding to this context with the traditional logic of simply increasing diameters, uniformly raising freeboards, or adopting arbitrarily longer payback periods is a partial strategy. It increases CAPEX without necessarily maximizing risk reduction per unit of investment. International experience in climate adaptation in mining suggests another path, based on four pillars:<\/span><\/p>