Interactive lesson

Slopes and terraces, step by step

Interactive lesson: measure the slope, find the contour, spot erosion, build a terrace and lay a dry-stone wall that lasts.

Free sample Chapters 1 and 2 (8 steps) are free. The full lesson comes with the Slopes and terraces module. Already bought? Unlock

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The whole lesson as text

1. Measure the slope

Before any digging, find out how steep the slope is.

Board and spirit level — You need a 2 m straight board, a spirit level on it and a tape measure. Put one end of the board on the ground, uphill.
Lift it to level — Lift the other end until the spirit level reads level. Then measure the height from the ground to the board in centimetres.
Slope % = height ÷ 2 — The height in cm divided by 2 gives the slope in percent. Repeat at 5–10 points down the slope.
Water level for longer runs — For longer distances, use a clear hose filled with water. The water in both ends stands at the same height, so you can measure the difference between two stakes 10–20 m apart.

Why: Everything depends on the gradient: up to 15 %, working across the slope, mulch and grass strips are enough; from 15 to 30 % you need terraces; above 30 % it is woodland, pasture and fruit trees. Slope is expressed as a percentage: how many metres the ground drops over 100 metres of horizontal distance.

Percent is not degrees: 20 % is roughly 11°, and 100 % is 45°.
Enter the results in the slope and erosion survey from the module.

2. A-frame and contours

A contour line joins points of the same height. Beds, terraces, swales and hedges follow it.

Join two battens — Join two 2 m battens at the top and nail a crossbar on halfway up. Spread the legs about 2 m apart.
Hang a plumb line — Hang a plumb line from the top so it swings across the crossbar. On level ground, mark where the string crosses the bar, turn the frame round 180° and mark again. Halfway between the marks is level.
Find the middle on the slope — Keep one leg in place and move the other up or down until the plumb line hangs at the middle mark.
Stake, then move on — Drive in a stake there and move the frame on. Stakes every 2 m give you the contour.

Why: Everything on a slope is done across it, along the contour. The simplest tool for finding it is an A-frame made of two battens, a crossbar and a plumb line.

The plumb line can be a string with a stone or a nut.
Stretch a string between the stakes or run a hoe along them, and you have the line to work to.