Terrain and soil analysis tells you whether ground will drain, carry a building and grow crops, using simple field tests rather than a laboratory. The target is a gentle slope of 2-8% grade for natural drainage without erosion, with loam for farming and clay-rich soil within reach for building.
The shape and material of the ground at a candidate site: how steep it is, how it drains, what the soil is made of and what it can carry.
Four Questions About the Ground
The carrier article reduces terrain and soil to four questions, each with its own page:
- What is the soil made of? Sand, silt and clay in different proportions. See Soil Composition Testing.
- How steep is the ground and where does water go? See Slope & Drainage Assessment.
- Can it carry a building? See Load-Bearing Capacity.
- Can it grow food? See Agricultural Potential Mapping.
Why a Gentle Slope Is the Target
A 2-8% grade drains water without enough speed to wash soil away. Less than that, and rain sits: flat valley floors collect floods, cold air and standing water. More than that: steep slopes over 15% bring erosion, difficult building and landslide risk. Grade is the rise divided by the run: 8% means a drop of 8 m over 100 m, an angle of about 4.6 degrees; 15% is about 8.5 degrees.
North-facing slopes in the Northern Hemisphere are cold and have low light in winter, which is why the carrier prefers a gentle south-facing slope. In the Southern Hemisphere the preference is the opposite: north-facing.
What You Need
- A shovel — to dig a test hole at least as deep as your foundation will be.
- A clear jar — for the soil settling test.
- Something to measure slope — an A-frame level or a water level. See A-Frame Level.
- A walk in the rain — watch where water goes.
A First-Pass Routine
Step 1: Walk it Walk the candidate ground slowly in a grid. Note slope direction, wet or soggy patches, rocks at the surface, and what grows where.
Step 2: Dig Dig test holes. The soil is not the same everywhere; dig at several points. Notice color, texture, whether the sides of the hole stand, and when water appears.
Step 3: Wait for rain Walk the site in rain. Where does water pool, where does it run, where does it cut a channel?
Step 4: Combine Mark on a sketch map: good building ground, good farming ground, wet ground, steep ground. See Sketch Mapping.
Common Mistakes
- Choosing flat for convenience — flat ground floods and holds cold air.
- Testing one hole — soil changes within a few meters.
- Looking only in dry weather — drainage problems show up in rain.
Safety
Test holes collapse
Do not stand in an unshored hole deeper than your waist, and keep spoil heaps back from the edge. Cover or fill holes before leaving them, so people and animals cannot fall in.
What’s Next
- Learn next: Soil Composition Testing — what the soil is
- Combine with: Climate & Microclimate — how the same ground behaves in weather