Description
Similar names: Banquettes, boomerangs, terraces, stone bunds, eyebrow systems, eyebrow basins.
Eyebrow terraces are a form of microcatchment water harvesting system. They are handmade micro basins, in the shape of an eyebrow, and are often made from soil and stones. Their main goal is to facilitate vegetation growth on steep slopes by collecting runoff water from a small catchment area and having it infiltrate the soil. This way, it is stored in the root zone and will be available for crops. They are usually situated on hillsides and can be used on up to 50% of slopes. The steeper the slope, the more the bunds have to be reinforced with stones. Eyebrow terraces work well in areas characterised by 200-600 mm of annual rainfall. Reinforcing eyebrow terraces with stones on steep slopes makes them more resistant to the increased water speed caused by the slope. Instead, they can be some metres apart. After completion, the pit uphill from the eyebrow may fill with sediments and soil, thereby giving rise to terraces.
Some of the main advantages of eyebrow terraces are that they reduce the risk of flooding, while simultaneously increasing the on-site conversion of water through the facilitation of filtration. Furthermore, the intervention improves the yields in the area, by increasing the soil organic content, as sediments are trapped in the terraces.
PRE-CONDITIONS FOR IMPLEMENTATION
- The cost of the implementation can be quite important if there are no stones available in the area.
METHOD OF APPLICATION
- Construction: Eyebrow terraces are usually built by scraping soil and stones together and putting them in place to form a ridge. The centre of each pit functions as a great location for a tree. The catchment area (or the area of the micro catchment intervention, in this case the Eyebrow terraces) should always be larger than the cultivated area, in order to be able to collect sufficient water for the crops. The ratio between the catchment area and the cultivated area can vary between 2:1 and 10:1. For an eyebrow terrace intervention, if the cultivated area is 1-5 square metres, the catchment size should be at least 5-50 square metres. Useful indications about the spacing and dimensions of Eyebrows terraces can be found here.
- Maintenance: The eyebrow terraces need to be maintained as they can break especially the first few seasons after heavy rainfall.
- Monitoring: Soil control, watering and fertiliser must be checked and applied two to three times each week and must be monitored
BENEFITS
This intervention contributes to:
CASE STUDIES
1. Eyebrow terraces (“Boomerangs”) by Perma Atlas, in Morocco
Description
As a result of overgrazing and tree-cutting, the region of Anguelz in Morocco has been facing severe land-related stresses in the past decade. Where once lay lush and vibrant mountains, now the landscape has turned completely arid. With the help of Perma Atlas the people from Anguelz have come together to regreen the landscape and bring it back to its former healthy state. A major issue that the area is facing is the lack of rain and seasonal flooding events. Community members have been taught in workshops hosted by Perma Atlas how to implement three interventions to help mitigate and reduce the impacts of flooding and erosion. Eyebrow terraces, also called Boomerangs are micro-water catchment systems that collect and channel water runoff on steep slopes and help it to infiltrate into the soil. They do this whilst removing sediment and pollutants from the water flows. Boomerangs can help encourage the regrowth of vegetation. They enable water to infiltrate into the soil and surrounding area, providing seeds with the water they need to sprout in such arid and degraded landscapes. The project by Perma Atlas and the village of Anguelz has created a safety from flooding and heavy rains and has given the chance to the local people to learn different techniques used by their ancestors. Additionally, the implementation and maintenance of the techniques have offered job opportunities for the locals.
2. Micro-catchment water harvesting systems in dryland areas in Ethiopia
Description
This study focuses on using micro-catchment water harvesting systems to improve tree establishment in dryland areas, particularly in Gara Adulala, Ethiopia. In these areas, the main challenge for agriculture, especially planting trees, is the scarcity of water. The study suggests that collecting and storing rainwater can help address this issue. Different water harvesting techniques were tested, including semi-circular bunds, eyebrow terraces, contour-bench terraces, and infiltration pits. These structures are designed to collect runoff from rainfall and store it in the soil, providing moisture to tree seedlings during their early growth stages. The study found that semi-circular bunds and contour-bench terraces were the most effective structures for supporting the survival of tree seedlings in dry areas. These structures help retain moisture in the soil, which is crucial for the seedlings' growth. Overall, the research suggests that using micro-catchment water harvesting systems can improve tree establishment in dryland areas by providing much-needed moisture. This knowledge can help minimise the risk of tree loss during drought seasons and contribute to sustainable agriculture in these regions.
