Bench Terracing: A Method for Managing Steep Slopes

Hillside farming is a reality for millions of farmers across South Asia, Southeast Asia, East Africa, and Latin America. On steep slopes, every heavy rainfall event is a potential disaster – runoff accelerates, topsoil washes away, and land productivity declines year after year. Bench terracing is one of the oldest and most effective engineering responses to this problem. By reshaping a slope into a series of flat, step-like platforms, it brings erosion under control, retains soil moisture, and makes sustainable crop production possible on terrain that would otherwise be marginal or unworkable.

What is bench terracing? 🔗

According to the FAO, bench terraces are a series of level or virtually level strips running across a slope at vertical intervals, supported by steep banks called risers. The construction involves cutting into the uphill side of the slope and using that excavated soil to build up the downhill edge – a process known as cut and fill. The result is a staircase-like arrangement of flat platforms, each of which functions as a cultivable mini-field. Greener.Land describes the core purpose well: bench terraces periodically interrupt the slope with flat sections, slowing water runoff and stopping the loss of nutrient-rich topsoil.

This is not a modern invention. The Philippines has evidence of bench terracing going back 2,500 years, and terraced landscapes have been documented in ancient Israel, China’s Shansi province, Lebanon, and southern France. Today, the practice remains central to hill agriculture across the tropics and subtropics.

How bench terracing controls erosion 🔗

The erosive power of water increases with its speed. On a long, unbroken slope, rainwater accelerates as it flows downward, picking up soil particles and carrying them away. Purdue Extension explains that terraces work by intercepting rainfall runoff as it starts down a slope, preventing large accumulations of surface flow. In effect, they break one long slope into a series of shorter ones – each short enough that runoff does not have time to build dangerous velocity.

The flat bench surface also gives water time to slow down and infiltrate into the soil. Rwanda’s Water Portal notes that less-steep slopes mean water runs slower and has more time to infiltrate, with the aim of storing moisture in the soil profile and keeping nutrients from washing away. Research cited in a peer-reviewed review of terracing effects on erosion found that terracing can reduce soil losses by half compared to unterraced slopes.

Types of bench terraces 🔗

Not all bench terraces are built the same way. The choice of type depends primarily on rainfall, soil permeability, and the crops to be grown. ICIMOD’s terracing guidelines describe three main layouts:

Level (tabletop) bench terrace 🔗

The bench is constructed perfectly horizontal with no slope. This design maximizes water retention on the terrace and is best suited to medium-rainfall areas with highly permeable, deep soils. It is the standard design for paddy rice cultivation, where standing water is needed for part of the growing season. A small dyke is typically built along the outer edge to hold water in place.

Inward-sloping bench terrace 🔗

Here, the terrace surface is graded slightly inward – toward the hillside – at around 5% reverse slope. Runoff from the bench drains toward the cut face and into a toe drain running along the base of the riser above. This type is recommended for humid regions with heavy rainfall and less permeable soils. It also suits crops that are sensitive to waterlogging, since water does not pond on the bench surface.

Outward-sloping bench terrace 🔗

The terrace surface slopes gently outward at around 3% gradient, allowing excess water to drain off the front edge of the bench. This is appropriate for arid or semi-arid areas with permeable soils of medium depth, where the priority is draining away whatever little rainfall occurs rather than retaining it. According to FAO watershed management guidelines, this type is used in outward-sloped form specifically for low-rainfall environments.

Suitability and site conditions 🔗

Bench terracing is an engineering-intensive practice, so it should only be applied where site conditions justify the investment. The FAO identifies the following conditions as particularly suited to bench terracing:

• Slopes between 7° and 25° (roughly 12% to 47% gradient) for hand-built terraces, and between 7° and 20° for machine-built terraces
• Areas with relatively deep soils – terracing on shallow soils risks exposing unproductive subsoil or bedrock after the cut
• Sites that are not heavily dissected by gullies and are not excessively stony
• Regions with severe erosion hazards, small landholdings, dense populations, or food security pressures

Bench terraces are not recommended on slopes below 7°, where simpler broad-base terraces or agronomic measures are more cost-effective. According to soil conservation engineer Ted C. Sheng, using machinery on slopes over 20° is unsafe, making hand construction the only viable option on the steepest sites.

Key design parameters 🔗

Designing bench terraces requires calculating several interdependent measurements. Getting these right is critical – poorly designed terraces can fail, causing mass soil movement that worsens erosion rather than preventing it.

Bench width 🔗

Bench width is driven by soil depth, crop requirements, and available equipment. FAO guidelines specify that hand-cultivated terraces typically range from 2.5 to 5 m wide, while machine-cultivated terraces range from 3.5 to 8 m wide. Wider benches require deeper cuts and more earthwork, raising construction costs. However, very narrow benches are impractical for most crops and cultivation equipment.

Vertical interval (VI) 🔗

The vertical interval is the elevation difference between two successive terraces – essentially the height of one “step” in the staircase. It is calculated using a standard formula:

VI = (S × W_b) / 100

Where S is the land slope in percent and W_b is the bench width in metres. A steeper slope or wider bench increases the VI. Greener.Land’s terracing guide notes that this formula is the standard approach for calculating spacing between successive flat bench terraces. To avoid unstable, over-tall risers, the riser height should generally not exceed 2 metres after accounting for soil settlement.

Terrace length 🔗

Longer terraces are more efficient for farming operations, but they come with a trade-off. FAO recommends a maximum length of 100 metres in a single draining direction for humid tropical conditions, since longer terraces can cause accelerated runoff and increased erosion risk toward the outlet end.

Riser construction 🔗

The riser is the steep face between two terrace levels. It can be made of compacted earth protected by grass cover, or reinforced with rocks or other materials. Grass-covered earth risers are the most common choice for cost and ecological reasons – the root systems bind the soil and resist erosion at the riser face. Any break or collapse in the riser must be repaired immediately to prevent progressive failure.

Construction process 🔗

Construction typically begins at the lowest terrace and proceeds upward, though a top-down sequence is sometimes preferred depending on local conditions. The standard cut-and-fill sequence involves:

1. Removing and stockpiling the topsoil from the cut and fill zones before any earthwork begins, so it can be redistributed over the finished terrace surface
2. Cutting soil from the uphill portion of each future bench and moving it downslope to form the fill section and riser
3. Compacting the filled material thoroughly – for bulldozer construction, this means driving along the outer edge of each bench repeatedly
4. Checking grades with a dumpy level during construction to ensure horizontal and drainage gradients are correct
5. Shaping the riser slope by hand to the required ratio (typically 1:1 for earth risers)

Soil Management India notes that the topsoil replacement step is especially important – the subsoil exposed during cutting is typically less fertile and harder to cultivate, so redistributing the original topsoil is essential for maintaining productivity on the newly formed bench.

Benefits beyond erosion control 🔗

While controlling erosion is the primary purpose, bench terracing delivers a range of additional benefits that make it a comprehensive land management tool:

• Soil moisture conservation: By slowing runoff and promoting infiltration, terraces increase the amount of water stored in the soil profile. This is especially significant in rainfed farming where crops depend entirely on stored soil moisture between rain events.
• Improved water quality downstream: Purdue Extension notes that sediment and contaminants settle out behind terrace ridges before they can reach downstream water bodies, reducing agricultural pollution.
• Expanded arable land: Terracing converts slopes that are too steep for conventional cultivation into productive farmland. This is particularly valuable in densely populated hill regions where flat land is scarce, such as Uttarakhand in India or the hill districts of Nepal and the Philippines.
• Support for intensive cropping: By stabilizing the land and enabling irrigation delivery, terrace systems increase food production and allow farmers to move away from shifting cultivation toward permanent, more intensive agriculture.

Limitations and maintenance requirements 🔗

Bench terracing is not without drawbacks. Construction is labour-intensive and costly, particularly on steep slopes – this remains a significant barrier for smallholder farmers without access to equipment or credit. Initial productivity on the cut zone of each bench can be lower than expected because the fertile topsoil layer is thinner after levelling. The scientific review by Dorren and Rey also points out that the foot of a terrace riser is a zone of concentrated erosion risk due to steepness and sparse vegetation, and that poorly managed toe drains are a common cause of terrace failure.

Regular maintenance is non-negotiable. This includes keeping toe drains clear and properly graded, repairing any breaks in risers immediately, maintaining grass cover on riser faces, and preventing livestock from trampling on risers. FAO’s watershed management manual stresses that correct gradients must be reshaped after each cropping season, and that any obstacle to water flow in the toe drain must be removed to prevent water from backing up and saturating the terrace fill.

Bench terracing in practice: global examples 🔗

The longevity and geographic spread of bench terracing reflects how reliably it works when properly designed and maintained. China’s Loess Plateau – a landscape once devastated by severe gully erosion – has seen large-scale terrace construction since the 1950s transforming millions of hectares of degraded hillside into productive farmland. In Eritrea’s Central and Northern Highland Zone, bench terracing is combined with tree plantations on upper catchment slopes to protect watersheds from runoff. Across the terraced landscapes of Nepal, Rwanda, and the Philippine Cordilleras, the same basic principle – steps carved into the hillside – continues to sustain food production for millions of people on land that would otherwise be too steep and erosion-prone to farm.

What do you think? Given that bench terracing requires substantial upfront investment in labour or machinery, what kinds of support systems – financial, technical, or community-based – would make it more accessible to smallholder farmers on steep slopes? And as climate change intensifies rainfall variability in hilly regions, how might the design criteria for bench terraces need to evolve to remain effective?

References

1. https://www.fao.org/4/ad083e/ad083e07.htm
2. https://www.greener.land/terracing/
3. https://www.extension.purdue.edu/extmedia/ae/ae-114.html
4. https://waterportal.rwb.rw/toolbox/466
5. https://www.ecorisq.org/docs/Dorren_Rey.pdf
6. https://www.larimit.com/mitigation_measures/1026/
7. https://topsoil.nserl.purdue.edu/isco/isco12/VolumeIV/BenchTerraceDesignMadeSimple.pdf
8. https://www.soilmanagementindia.com/soil-erosion/terracing/how-to-design-and-construct-bench-terrace-soil-management/15303
9. https://eos.com/blog/terrace-farming/