Tailings Dam Monitoring: Methods, GISTM Requirements and Satellite Options

Tailings dam monitoring is the continuous measurement of the structural, water and ground conditions of a tailings storage facility (TSF) to catch warning signs of instability before they become a failure. It combines on-site instruments, inspections and, increasingly, satellite data, and it is a core requirement of the Global Industry Standard on Tailings Management (GISTM).

The stakes are high. Tailings failures release huge volumes of mud-like waste in minutes, and they have caused some of mining’s worst disasters.

What is a tailings dam?

Tailings are the finely ground rock and process water left after valuable minerals are extracted from ore. A tailings dam is the embankment that holds them in a storage facility, often for decades and long after the mine closes.

Unlike water-supply dams, tailings dams are usually raised in stages over the life of the mine, often using the tailings themselves. There are three main raising methods:

• Upstream: each new raise is built on top of previously deposited tailings. It is the cheapest method but the most vulnerable to liquefaction and seismic shaking.
• Centreline: raises are built vertically on the crest, giving a moderate risk profile.
• Downstream: each raise moves outward on compacted fill. It is the most stable method but needs the most material and space.

The scale is large. The Global Tailings Review estimated about 8,500 active, inactive and closed tailings storage facilities worldwide in 2020, around 3,250 of them active (E&MJ).

Why tailings dams fail

Most tailings dam failures come from six failure modes, each with its own warning signs:

1. Static liquefaction. Loose, saturated tailings suddenly lose strength and flow. Monitor pore-water pressure, deformation, the phreatic surface and beach width.
2. Water exceeds freeboard during storms or because of poor water management. Monitor pond level, freeboard, rainfall and the water balance.
3. Seepage and internal erosion. Water moving through the embankment carries particles out. Monitor seepage flow and turbidity, and wet zones on the downstream slope.
4. Foundation failure. A weak layer beneath the dam shears and the embankment slides. Use inclinometers, ground deformation data and foundation investigations.
5. Slope instability. The embankment face deforms and slumps. Track surface movement with prisms, GNSS or InSAR, and watch for cracks.
6. Shaking triggers liquefaction or cracking. Use seismic monitoring and post-event deformation surveys.

Lessons from major tailings dam failures

Brumadinho, Brazil (2019). Vale’s Córrego do Feijão upstream-raised dam collapsed on 25 January 2019 and killed 270 people. It was the direct trigger for the GISTM, and Brazil moved to ban upstream-raised dams afterwards.

Fundão (Mariana), Brazil (2015). The Samarco dam failure killed 19 people and sent a mudflow down the Rio Doce to the Atlantic, one of Brazil’s worst environmental disasters.

Mount Polley, Canada (2014). The embankment failed along a weak foundation layer, releasing millions of cubic metres of tailings and water into nearby lakes. There were no deaths, but the failure reshaped tailings regulation in British Columbia.

The common thread: the warning signs (rising pore pressures, slow deformation, seepage) build up over months or years, but monitoring was too sparse or too infrequent to act on them in time.

What GISTM requires

The GISTM was published on 5 August 2020 by the International Council on Mining and Metals (ICMM), the UN Environment Programme and the Principles for Responsible Investment. It sets 15 principles and 77 requirements across six topic areas, aiming for zero harm to people and the environment (SRK).

ICMM members committed to conform by August 2023 for facilities with “Extreme” or “Very High” potential consequences, and by August 2025 for all other facilities (ISOMETRIX). Many non-member miners, lenders and investors now expect the same.

For monitoring, GISTM expects operators to:

• Design monitoring around the facility’s credible failure modes, not a generic checklist
• Set alert levels and trigger action response plans (TARPs) for each key measurement
• Review monitoring data regularly with the Engineer of Record
• Keep consequence classifications and emergency plans current as conditions downstream change
• Disclose facility information publicly, including how risks are managed

Tailings dam monitoring methods compared

• Piezometers measure pore-water pressure in the embankment and foundation, the key early indicator for liquefaction. They give point readings and can fail over time.
• Inclinometers detect deep-seated sliding through subsurface movement, but only at a few locations and often with manual reads.
• Survey prisms and robotic total stations track surface movement at set targets precisely and in near real time, but need line of sight and cover fixed points only.
• GNSS stations give continuous, accurate 3D positions of key points, though each point is expensive.
• Satellite InSAR measures millimetre-scale movement across the whole facility, with years of archived data and no site access needed. Data arrives every few days and needs expert processing.
• Drones and LiDAR capture surface shape, cracks and beach width in detail, but only periodically and at centimetre-level precision.
• Pond level and water balance monitoring controls overtopping risk, but must be paired with structural data.
• Visual inspections provide essential context on cracks, seepage and erosion, but are infrequent and subjective.

No single method is enough. The strongest programmes pair point instruments, which show what is happening at specific locations, with area-wide data that shows where to look.

How to build a risk-based tailings monitoring programme

1. Start from failure modes. List the credible ways your facility could fail and the measurements that would show each one developing.
2. Set baselines and alert levels. Use historical data, including archived satellite imagery, to know what “normal” movement looks like, then define green, amber and red thresholds.
3. Combine instruments with wide-area coverage. Use satellite InSAR to screen the whole embankment, abutments and surrounding slopes, and target instruments where movement appears.
4. Bring the data together. Instrument readings, inspections, survey results and satellite data should sit in one place so engineers see trends, not fragments.
5. Watch downstream as well as the dam. New development below a facility changes its consequence classification and emergency plans.
6. Review and report. Share results with the Engineer of Record and Accountable Executive on a fixed cycle, and document responses for GISTM conformance.

Where satellite monitoring fits

Satellite InSAR is especially useful for tailings because facilities are large, often remote, and change shape as they are raised. It can:

• Measure movement across the full facility, not just at instrument points
• Provide years of historical movement from archived imagery, useful for baselines and legacy sites
• Monitor closed or inactive facilities where instruments have failed or site visits are rare
• Flag areas of change so field teams and instruments go where they’re needed

The same capabilities Rezatec uses for water-supply and hydro dams apply to tailings facilities. Rezatec’s InSAR analytics are validated against GNSS and GPS data, and its Dam Monitoring platform centralises inspection records, ground motion, seepage indicators and downstream hazard data in one place. For more on how failures develop, see Learning from Dam Failures.

See movement across every tailings facility in your portfolio. Book a Dam Monitoring demo.

Frequently asked questions