Types of Tailings Dams: Upstream, Downstream, Centerline and Beyond

Tailings dams are classified mainly by how their embankment is raised over time, and that single choice, upstream, downstream or centerline, largely decides how much the dam costs and how safely it behaves in an earthquake or a flood.

Tailings are the finely ground rock and process water left after valuable minerals are extracted from ore. A large mine can produce tens of thousands of tonnes a day, and all of it has to be stored safely, often forever. Most of it ends up behind an embankment called a tailings dam, part of a wider tailings storage facility (TSF).

Unlike a water dam, a tailings dam is usually not built to full height at once. It starts with a starter dam and is raised in stages as the mine produces more waste, sometimes over decades. The direction in which those raises move is what gives each type its name.

1. Upstream construction

In an upstream dam, each new raise is built on top of previously deposited tailings, so the crest moves inward toward the pond with every stage.

Tailings are discharged from the crest to form a beach. Once the beach is firm enough, the next small dyke is placed on it, often built from the coarser fraction of the tailings themselves. The result needs very little borrow material and is the cheapest and fastest option.

The weakness is the foundation. Each raise sits on loose, saturated, fine-grained tailings that can lose strength suddenly through static or seismic liquefaction. Stability depends heavily on keeping a wide beach and a low phreatic surface, and on raising the dam slowly enough for the tailings to consolidate.

Advantages: lowest cost, least fill material, simple to build
Disadvantages: vulnerable to liquefaction and earthquakes, sensitive to water management, limited rate of raise

Two of the worst failures in recent history were upstream dams in Brazil: Samarco’s Fundão dam near Mariana in November 2015, which killed 19 people, and Vale’s dam at Brumadinho in January 2019, which killed 270.

2. Downstream construction

In a downstream dam, each raise is placed on the downstream slope of the previous stage, so the crest moves outward, away from the pond, and no part of the embankment rests on tailings.

The embankment is built from compacted fill, waste rock or cycloned tailings sand. Because it is engineered like a conventional earth dam, it can include internal drains, filters and impermeable liners, and each lift can be compacted to specification.

Advantages: highest stability, best seismic performance, full control over materials and drainage
Disadvantages: needs the most fill, has the largest footprint, and costs the most

Downstream is the standard choice in highly seismic regions. Chile, one of the most earthquake-prone mining countries in the world, banned upstream dams in 1970 after an earthquake triggered the collapse of upstream dams at the El Cobre mine in 1965.

3. Centerline construction

In a centerline dam, the crest stays on the same vertical axis as the dam rises, with each raise resting partly on the tailings beach and partly on new fill on the downstream side.

It is a compromise between the other two. It uses less fill than a downstream dam while keeping most of the structural shell on compacted material. A modified centerline variant shifts the axis slightly upstream to save more material, which brings back some of the upstream risks.

Advantages: moderate cost, good stability, reasonable seismic performance
Disadvantages: the upstream portion still relies on tailings; needs careful beach and drainage control

4. Water-retention type dams

Some facilities use a conventional water-retaining dam built to full height, or close to it, before deposition starts. These are designed like water supply dams, with a low-permeability core and filters, and suit sites that must store large volumes of water or tailings that cannot form a stable beach. They are reliable but expensive up front.

Comparing the main types

Type	Crest moves	Built on tailings?	Fill needed	Seismic performance	Relative cost
Upstream	Toward the pond	Yes	Lowest	Poor	Lowest
Centerline	Vertically	Partly	Moderate	Good	Moderate
Downstream	Away from the pond	No	Highest	Very good	Highest
Water-retention	Built full height	No	High, all at once	Very good	High up-front

Alternatives to conventional slurry dams

The biggest risk in any tailings dam is water. Removing more water before deposition reduces both the chance of liquefaction and the consequences of a breach. That has led to three main alternatives:

Thickened tailings: partly dewatered in thickeners before discharge, forming steeper, more stable beaches and recovering more process water.
Paste tailings: dewatered further into a paste that barely bleeds water, often used as underground backfill.
Filtered (dry stack) tailings: pressed or vacuum-filtered into a moist cake, then trucked or conveyed, spread and compacted like earthfill. There is no large pond to release, but filtration costs much more, especially at high throughput.
In-pit and underground disposal: placing tailings back into mined-out pits or stopes, where the surrounding rock acts as the containment.

Why regulation is moving away from upstream dams

After Brumadinho, Brazil banned the construction of new upstream tailings dams and ordered existing ones to stop receiving tailings and be decommissioned, a process known there as decharacterisation. Later legislation reinforced the ban and also prohibited new tailings dams where communities sit within 10 km or a 30-minute drive downstream.

Chile has prohibited upstream dams since 1970, and Peru also restricts them. At the global level, the Global Industry Standard on Tailings Management (GISTM), published in 2020 by ICMM, UNEP and PRI, does not ban any construction method outright. Instead, it requires facilities to be designed and managed according to the consequences of a failure, with the most demanding requirements applying to the highest consequence classes.

Conclusion

There is no single best tailings dam type. Upstream dams are cheap but unforgiving; downstream dams are robust but costly; centerline sits between them; and dewatered options trade higher operating cost for lower risk. The right choice depends on seismicity, climate, tailings properties, available fill and, above all, who and what lies downstream.

In upcoming articles, GeoMagazine will look at tailings liquefaction in more detail and walk through the GISTM consequence classification.