Terracing

• It can take up to 2 years for the farmer to benefit from terraces, but this is crop-dependent.
• Terraces have significant labour and input costs and create large land and thus ecological disturbances, especially when implemented on a large scale.

Material required:

• Digging equipment
• Sticks and coloured ribbon/paint (or other material) for marking the land
• An A-level (or an automatic level for large properties)
• Optional: 
  • Tractor or other machinery to push or shovel the earth (for larger-scale projects).
  • Stone or timber for building supporting walls, alternatively earth (for earth dam walls)

Steps of implementation:

1. Plan size and number of terraces: Before construction, several factors need to be designed according to the local rainfall, type and permeability of soil, and intended use of the terraces:

• • Type of terrace: Level terraces or graded (sloped) terraces. For example, if an area receives medium rainfall and the soil is highly permeable, the terrace with a level top is best. If a graded terrace is preferred, the specific lateral slope ( which directs water left or right along the terrace) and bench gradient (which directs the water towards the front or back of the terrace) should be decided and informed by the factors mentioned above (introduction of section 1).
  • Length of terrace ridges: This will depend on the length and size of the field. Terrace ridges longer than 100m can be hazardous under certain conditions.  To ensure their safety you can refer to this document or consult an expert.
  • Width of terrace: Consider both farming needs  (i.e. crop needs and tillage tools) and environmental conditions,  such as soil depth and slope. Generally, 2.5 m to 5 m wide is an appropriate width for hand cultivation, whereas for mechanised construction, a width of 3. 5 m to 8 m is appropriate.
  • Spacing of terraces: The appropriate vertical interval (VI) can be calculated based on a formula. The VI is the elevation difference between two succeeding flat bench terraces. The formula VI=S*Wb/100 . Where S is the slope (in %) and Wb is the width of the bench (in m).
  • Slope of riser: The riser is the steep ascending slope of the terrace. Riser material may be compacted earth (covered with grass) or made up and reinforced by rocks or wood. Depending on the type of riser, the appropriate slope will change.
    • For hand-made benches with earth material: a slope of 0.75:1
    • For hand-made benches with rocks:  a slope of  0.5:1  
    • For machine-built benches with earth material: a slope of  1:1

 

 

 

 

 

 

2. Mark out the area: There are two ways to prepare the land for construction. A centre-line method and a two-line method. For hand-made terraces, a centre-line method is more suitable. It involves staking out a line in the centre of a contour or graded contour lines of the property.  Centre lines should be kept and observed as non-cut and non-fill reference lines (See figure below). When using machinery to construct terraces, it is better to use the two-line method,  as a staked-out centre line can impede the use of machinery during construction. For more information on the two-line method, you can read further here

 

 

 

 

 

 

Source 

3. Construct bench terraces

1. • Form the lowermost terrace by cutting and filling the appropriate sections as indicated by the image above. Compact the terrace thoroughly.
   • Remove the topsoil from the area of the (future) terrace immediately above and distribute this over the lower terrace just formed.
   • Next, the second terrace should be formed and covered with the topsoil from the third terrace above. This process is then repeated upslope.
   • Plant grass along the rise of all the terraces

Note that the construction of terraces may take place from the bottom up (described above) or from the top down. Using a top-down method might also be preferable under certain conditions. Consult section 11 of Mesfin (2016) for a discussion on the pros and cons of both methods as well as a visual description of these.

 

Considerations of application

• Terracing can lead to low levels of biodiversity if there is no variation in planted crops. Fertility may also be low in overly exposed soils, thus there may be a need to be supplemented with additional nutrient sources. A solution to this in China is adding juvenile crabs to rice paddies, which benefits both the crabs and the rice as it improves environmental conditions in the paddy by absorbing the nutrients excreted by the crabs while the plants provide shelter and sources of food from weeds and insects for them (more information here). 
• The construction of terraces is most effective when the ground is neither too dry nor too wet. Unexpected rainfall during construction leaves lower terraces vulnerable to excess runoff damage. Thus, drainage ditches or other preventative measures may be necessary,  especially when using the bottom-up method of construction.
• Terraces have significant labour and input costs, and create large land disturbances, especially when implemented on a large scale.
• Terraces should be designed according to the needs of farmers, crops, climate, and tools used for farming.
• Ensuring that the volume cut and fill of the terraces is equal can minimize construction costs.
• The construction of terraces is most effective when the ground is neither too dry nor too wet.
• Ensure the proper compaction of the soil during the filling process. Actively compact soil roughly every 15cm.
• Unexpected rainfall during construction leaves lower terraces vulnerable to excess runoff damage. Thus, drainage ditches or other preventative measures may be necessary,  especially when using the bottom-up method of construction.
• Soil fertility - especially in cut areas where subsoil has been exposed - may be low, thus there may be a need to be supplemented with additional nutrient sources.
• Terracing can lead to low levels of biodiversity if there is no variation in planted crops.
• It can take up to 2 years for the farmer to benefit from terraces depending on the crop.

This intervention contributes to:

Estimated costs and benefits of intervention:

Establishment costs	Very high. Highly variable depending on context. See Mesfin (2016) section 14 for more details and a formula for calculating costs.
Labor time	From 66 to 592 person days/ha depending on slope and soil stability. On farm level data: 279 person days/ha is required.
Maintenance costs	Relatively low (around 5% of investment)
Benefits	Lifespan >15 years
Common products	Wheat, buckwheat, corn, rice, millets, saffron, black cumin, apples, etc..

1. Bench terraces in loess soil, China 

Description
Bench terraces in China are raised, and flat platforms are built on slopes to prevent soil erosion, reduce water runoff, increase rainfall infiltration, and improve agricultural productivity. These terraces create a series of level steps on hilly terrain, slowing down water flow and conserving soil. Constructing terraces on the loess plateau is challenging due to the soft, deep loess soil and severe erosion and water shortages. Initially, terraces were built by hand and were narrow, often damaged by storms. Now, machinery is used to create wider terraces with higher banks, requiring significant investment but offering a long-term solution. Maintenance primarily involves annual improvements to the terrace bunds, making it economically viable. The loess soil in the region is prone to severe erosion, especially during intense summer and autumn storms. Terraces help mitigate this by stabilizing the soil in combination with crop planting. Human activity is intense in these areas as people need to farm on slopes, which increases erosion. Bench terraces are extensively used in the Yanhe River Basin in Shaanxi Province, covering an area of 253.3 km². This region experiences semi-arid conditions with significant rainfall variation and temperature fluctuations, characterized by broken landforms due to erosion-induced gullies and a high density of these gullies leading to severe soil loss. The terraces provide large, flat areas suitable for agriculture in the hilly loess region, helping stabilize the landscape and improve agricultural conditions in the Yanhe River Basin by successfully combining traditional methods and modern technology. For more information about the effects of terracing on soil water and canopy transpiration, please click here.

2. Afforestation and hillside terracing, Eritrea 

Description
In Eritrea's Central and Northern Highland Zone, a common practice involves combining tree plantations with hillside terracing to safeguard upper catchment areas. This approach focuses on establishing terraces on steep slopes to conserve soil and water, facilitating the growth of trees and other plants. The terraces consist of earthen embankments arranged along contours, reinforced with stone risers and equipped with trenches to collect runoff water. These trenches are divided into basins to prevent lateral flow of water. Following the terrace set up, trees are planted, typically eucalyptus spaced 2 meters apart within the trenches, occasionally alongside indigenous African olive trees. The afforested areas are protected until the trees mature, ensuring their growth. In 1995, the Ministry of Agriculture granted user rights to communities, permitting the harvest of grass and trees under government permission. While implementing this technology demands significant expenses, labor, and expertise, it yields numerous ecological and economic benefits, including improved soil cover, water conservation, reduced soil erosion, and protection of downstream dams from siltation. Additionally, trees have become a crucial income source for rural communities, supplying valuable wood for construction and fuel. Since the 1960s, government-led afforestation campaigns, initially incentivized through food or cash-for-work programs, have supported this approach, which is now predominantly driven by local initiatives without external aid.

External Sources 

• For more case studies on terracing, please check this database. 

Guides

• For a A Field Guideline on Bench Terrace: Design and Construction, please click here.