Annual Average Rainfall
Topography
Water Source
Altitudinal Zone
Decision Making
Farming Characteristics
Farm Size
Labour Intensity
Initial Investment
Maintenance Costs
Access to Finance/Credit
Extension Support Required
Access to Inputs
Access to Markets
Gender/Youth Smart
Description
Water spreading bunds are barriers used on gradual slopes to slow down surface water and slow filter runoff, increasing the chance of infiltration, capturing runoff sediment, and decreasing soil erosion. Bunds can be built of different materials including packed earth or stones. Bunds can be spread across fields or used in micro-settings around individual trees or plants and should be applied in semi-arid or arid conditions. Bunds efficiently spread rainwater across the system and prevent streams from developing. Implementing bunds in areas with adequate rainfall or irrigation, may cause waterlogging and adversely affect crop growth.
Different types of bunds include:
- Contour bunds: ridges of soil that follow slope contours and can be implemented at a large scale. Crops are cultivated between bunds.
- Semi-circle bunds: ridges of varying size build in a half-moon or semi-circle. They are generally applied to rehabilitate rangelands and/or in the production of fodder.
- Contour stone bunds: lines of stones laid in a shallow dug out areas that slow down the flow of runoff
Technical Application
To effectively Water Spreading Bunds the following should be carried out:
- Step 1: Farmers should consider making earth bunds by hand, animal ploughs or mechanised ploughs.
- Step 2: Contour bunds:
- Contour lines must be plotted and marked prior to developing the bund.
- A 40 cm deep infiltration pit is dug directly above where the bund will be plotted.
- Bunds should be spread 5 m to 10 m apart.
- Material from the infiltration pit will be piled and compacted to form a 25 cm to 30 cm in height with a base of 75 cm.
- Soil is piled to form a ridge along the contour. The more significant the slope, the closer the bunds must be plotted.
- Step 3: Semi-circle bunds:
- Contour lines must be plotted and marked prior to developing the bund.
- A centre point is chosen as diameter for the bund is selected (this could be 3 m or 30 m depending on the available space). From the centre point a string is used to stake out an even semi-circle.
- Excavate a small trench before the bund and pile the excavated material. Pile and compact a bund wall, wetting it often to form the wall.
- Step 4: Contour stone bunds:
- Developed on less steep slopes.
- Must have access to local stones.
- Dig out a shallow ditch, 10 cm to 15 cm in depth.
- Lay largest stones at the bottom of the ditch and pile smaller stone upward.
- Step 5: Regular monitoring of bunds should take place, especially after rain events or after significant periods of time. Repairs should be done if any damage is found.
Return on Investment Realisation Period
Crop Production
Fodder Production
Farm Income
Household Workload
Food Security
Soil Quality/Cover
Biological Diversity
Flooding
Crop/Livestock Water Availability
Wind Protection
Increase Production
Reduces soil erosion and enables farmers to maintain agricultural productivity.
Increase Resilience
Reduces soil erosion in higher rainfall environments, especially relevant as climates change.
Additional Information
- The Food and Agriculture Organisation (FAO), 1991. Water Harvesting. Rome, Italy.
PDF File
/sites/secondsite/files/tb/CCARDESATechnicalBrief_28_waterSpreading_2019-10-17_0.pdf
Benefits and Drawbacks
Benefits
- Water spreading bunds are implemented on slopes of varying degrees to slow the flow of surface water, increasing infiltration and nutrient capture.
- Bunds capture water and spread it across an area more evenly, preventing streams, erosion channels and gullies from forming at depression points.
Drawbacks
- Developing bunds can be laborious.
- Bunds in areas with adequate rainfall or irrigation may cause waterlogging and affect crop growth.
