Combat soil erosion: ‘Malawi dumpy level’ set things straight

The Malawi dumpy level is a simple tool that can be constructed with local materials, which can be used to ensure that contour berms are cut exactly level. Ken Coetzee of Conservation Management Services, based in George, does consultation work for NGOs in Malawi where he teaches locals how to remedy and prevent further erosion.

“Malawi dumpy level” is Ken’s name for an ancient agricultural tool that has been used for setting out contours and water furrows all over the world for a very long time.

What is soil erosion?

Soil erosion takes place when topsoil is washed away by runoff water where protective plant cover has been removed because of deforestation, overgrazing, incorrect land cultivation practices, paths caused by animals and humans, and fire.

Slope stabilisation

In previous articles, Ken provided information on how to take care of different types of erosion, including head-cuts or dongas, gullies and rills, and erosion on slopes, open ground and bare, mostly flat land. The methods used include branch checks with grass fences, and dense packing with brush or grass on the upward side of these and on the steeper downward side of the hollows. The materials needed to create the structures and brush packing are usually freely available in the area. However, care must be taken not to strip the area bare of vegetation as it will create a new erosion problem. Also, the installations must be regularly inspected after rains to ensure they are still in good shape. If not, they must be repaired without delay, otherwise, all the money and labour spent to fix the erosion will literally simply be washed away.

Contour berms

Contour berms are another way of stabilising a slope to stop rainwater from running downhill and causing erosion. A berm is a furrow with an earthen wall on its lower side. These berms can be installed on moderate to steeper slopes where the topsoil is washed away because of the removal of protective plant cover by overgrazing, deforestation, fires, and paths caused by humans or animals.

Aim of a berm

The aim of berms along a slope is to prevent the run-off of fast-flowing water by stopping it and deflecting the water to safe outflow sites. The berm helps the water to infiltrate the soil, thereby improving it and preparing it for planting.

How to create a berm

• Mark out the contour line, making it perfectly level with a Malawi dumpy level (described below), driving pegs into the ground to mark the position of the contour berm;
• the ends of the contour berm must allow water to flow out in a safe site, such as an existing drainage ditch or an area with lots of plant cover;
• dig out a furrow about 45 cm wide at the top and about 25 cm at the bottom;
• dig the furrow about 25 to 35 cm deep;
• pile the soil removed from the furrow on the downslope side of the furrow to form a berm or embankment along the furrow;
• compact or firm down the berm soil by hand;
• construct further contour berms about 50 m apart, depending on the slope. On a steep slope, they must be closer together, while they can be further apart on more gradual slopes;
• pack cut brush or plant trees, or do both, between the contour berms;
• to ensure that the water running from the outflow points at the ends of the berm doesn’t cause new soil erosion, pack some stones or brush on the site, or install an erosion control fence.

How to make and use the Malawi dumpy level can be used to ensure that the contour berms are cut exactly level and on the contour. The furrows and their berms must be level. If not, the runoff water will simply flow out at the lower end and rush down the slope, causing more erosion. The idea is that the water collected in the furrow must remain there so that it will sink into the soil. Once the soil is saturated and the furrow is full, the water will flow out at the exit points that are provided and protected by vegetation, brush, or stones. The makeshift dumpy level consists of an A-frame with a weighted vertical line.

The A-frame can be constructed with thin wooden poles of equal length and firmly tied together at the top with binding wire. A crossbar between the legs of the frame is marked in the centre. A line with a weight, called a plumb bob, at the bottom, is tied to the top of the A-frame. When the instrument is perfectly level, the weight will match up with the middle of the crossbar. If available, two planks can be glued or bolted together at the top of the A-frame and between the legs. The best option would be to construct an A-frame out of metal angle iron or square tubing with welded joints that will not ever come apart. It is important that the top of the A-frame is tightly secured, for when the legs come loose during the operation, it will go out of shape and become inaccurate.

Measurements

Certain measurements are critical for the instrument to be accurate.

‘Walking’ the dumpy level

When marking out the level contour, the instrument is simply ‘walked’ across the ground, making sure the plumb line is exactly on the middle mark with every ‘step’.

Starting a contour berm

To start a contour berm, both feet of the A-frame must be put on the ground and moved around until the plumb line is on the centre mark of the cross-bar.

• Drive wooden pegs into the ground at both feet of the instrument.
• Keeping one leg in place, swing the whole frame over in the direction that you want to go.
• Move the foot around until the plumb line is in the centre of the bottom bar again.
• Mark the position of the foot with another wooden peg.
• Keeping one leg in position, swing the other one around again and continue until the whole contour line is marked with pegs as far as you want to go across the slope.

Contact details: Conservation Management Services Ken Coetzee, Wallie Stroebel and Bruce Taplin Ken: (+27) 76-227-5056 Wallie (+27) 82-493-1441 Website: www.conservationmanagementservices.co.za