Part 2 · Where These Ideas Come From
Terracing in the Highlands
Terraces from the Andes to Ifugao and Yemen hold soil and water on slopes, and their engineering, drainage, upkeep and labour cost are documented and repeatable.
A slope is where most people who want land end up, and most food-growing advice quietly stops being useful on one. The terrace is the answer, and it is older than the wheel. Every hill-farming culture invented its own version, and the versions differ in their engineering, not their principle. This lesson gives the numbers from systems people actually built, then the cheap version for year one.
The Andes: andenería
The Andean terrace, the andén, is a stair of platforms cut into a hillside. Terracing was underway in the Andes by 2000 BCE, and the Wari culture (500 to 1000 CE) and then the Inca (1438 to 1533 CE) took it to its largest extent. Archaeologists estimate the Inca period covered about 1,000,000 hectares of andenes, land that helped feed roughly ten million people.
The construction is specific. The builder laid a foundation about one metre deep, down to bedrock or a stable layer, to carry a retaining wall that might stand about two metres above the natural slope. Behind the wall went about one metre of large stones, then a layer about one metre thick of sand or gravel, then a cap of topsoil about one metre thick. The result was a surface engineers describe as well drained, rich soil on a level shelf. In the Colca Valley the planting surface averages about three metres wide.
Drainage is the whole game. The stone and sand layers move excess rain out, and in dry valleys such as the Colca the water comes the other way, from snowmelt and springs down canals.
The waru waru of Lake Titicaca
Where the ground floods rather than dries, the answer is the opposite shape: raised fields. The waru waru, also called camellones or suka kollu, are planting beds raised between parallel canals. The technique is dated to about 300 BCE and is most associated with the Tiwanaku culture around Lake Titicaca. The canals took the floodwater off in the wet season, supplied moisture from below in the dry, and stored heat to release at night. In one study near the lake, at about 3,810 metres, the soil on top of 50-centimetre mounds ran about one degree Celsius warmer than nearby ground, which cut the frost risk to potatoes.
Ifugao: the Philippines
The Ifugao rice terraces of the Cordillera cover about 20,000 hectares and rise to roughly 1,500 metres. Estimates of the start date vary, from around 100 BCE to the early first millennium CE, so say about two thousand years. The builders used the simplest hand tools. They cut paddies into the mountain, raised retaining walls of stone and mud, and ran water from forested catchments above down through channels that fed each paddy in turn. Water that passes through one terrace goes to the next, so a single flow irrigates the whole stair.
Yemen and the Mediterranean
Yemen is one of the most extensively terraced countries on earth, with three millennia of documented dryland and irrigated farming. The tenth-century Yemeni scholar al-Hamdani called the dryland farming of his country one of the marvels of the world, and a 1955 FAO mission judged Yemen among the best terraced countries at the time. The terraces held behind check dams and diversion channels that turned flash floods onto the fields. Modern Yemen then expanded tubewell irrigation, drew down the aquifer, and let the terrace land go. Across the Mediterranean, stone-walled terraces carried olives, vines and grain on slopes that would otherwise have eroded, and Morocco's tabia, a low earth bank across a hillside, is the same principle in its cheapest form.
What it costs, and the order you build in
Bench terraces are the most productive slope technology and the most labour, full stop. Every metre of level ground is a metre of hillside cut, moved and walled by hand, which is why so much terraced land was abandoned when populations fell or cheap flat land opened: by the late twentieth century, 60 to 80 percent of Andean andenes were out of crop use.
Exercise
Build an A-frame, mark one contour
Make an A-frame level from three straight poles and a plumb line, or use a clear hose filled with water as a water level. Find and stake one true contour line across your slope, then check it against a second line three metres below. Mark both with stakes you can find after the grass grows.
Exercise
Cut one fanya juu ditch
The fanya juu is Swahili for "throw upwards." Dig a ditch along your marked contour and throw the soil uphill, behind the ditch, to build a shelf of earth at the upper lip. Set it about a spade-depth deep and plant the bank with grass.
Fieldwork
Find a terrace someone else built
Walk the steepest grazed or wooded hillside within reach and look for a step in the slope, a level strip with a bank and a ditch on the uphill side, often under trees where the plough never reached. Measure the height of the riser, the width of the level bench and the fall of the ditch, and photograph the step from below so the profile reads. Then ask whether it still drains and who last repaired it. Bring back the three measurements and the photograph.
Failure mode
A terrace wall that cannot drain becomes a dam, and a dam on a hillside eventually bursts. Build drainage through the wall and through the fill, or the first wet season will move your soil to the bottom of the slope and take the wall with it. Abandoned terraces fail faster than open hillside, because the water is concentrated behind a structure that no longer gets repaired.
Build the cheap terrace first and the permanent one slowly. Run fanya juu ditches across the whole hill in year one, then convert them to bench terraces a few at a time, only where you actually grow the staple. On the steepest, most marginal ground, lay stone lines and half-moons and let that ground heal as pasture. You are not improving a hillside. You are joining a lineage that runs from the Andes to Ifugao to the terraces your grandchildren will repair.
