Contour Trench & Catch the Run-off
Plans trenches
“This tool gets better every time someone says what confused them.
Enter the slope area, trench spacing and cross-section to get the total trench length, the water-holding capacity and the area treated for your patch.
Lay out contour trenches
Next: dig ~405 m of staggered trenches on the contour and divert the spoil to the downhill bund; check the cross-section holds after the first big rain.
Spacing follows the vertical interval (steeper slopes need closer trenches); staggered (discontinuous) trenches reduce breaching on long slopes.
Contour trenches — key facts
- Runs
- Along the contour (level)
- Purpose
- Catch run-off, cut erosion, recharge
- Trench length
- Area ÷ spacing × run
- Capacity
- Cross-section × total length
- Spacing
- Closer on steep, wet slopes
- Spoil
- Piled downhill as a planting bund
- Types
- Continuous (CCT) or staggered
- Privacy
- Runs in your browser; nothing uploaded
Cut across the slope and the water stays put
Run-off on a bare slope picks up speed and soil with every metre it travels. A contour trench dug across that slope breaks the journey: it intercepts the flowing water, slows it to a stop and holds it in a long shallow reservoir that follows the land’s contour. The water then soaks in instead of racing to the valley, the topsoil it was carrying drops out, and the hillside loses far less of both. From the spacing between trenches and the cross-section of each one, you can plan exactly how much trench to dig and how much water it will hold.
This tool computes the total trench length to excavate, the combined water-holding capacity, the area treated and the spacing for your slope. Use it to estimate earthwork, labour and recharge benefit before you start. Pair it with the Percolation Tank, Recharge Pit and Check Dam tools to design a complete ridge-to-valley watershed treatment.
Stop run-off in its tracks
Trenches intercept and hold flowing water.
Keep your topsoil
Trapped sediment stays on the land, not the river.
Recharge the aquifer
Held water percolates down to refill wells.
Plan the earthwork
Know the trench length and volume before you dig.
Frequently Asked Questions
What is a contour trench?+
A contour trench is a long, narrow ditch dug across a slope along the contour — the line of equal elevation — so it runs level rather than downhill. Because it cuts across the direction water flows, it intercepts run-off, slows it down, holds it and lets it soak into the soil instead of rushing off the hillside.
How does the calculator find total trench length?+
For a given area treated and the spacing between successive trenches down the slope, the number of trench lines is the slope length divided by the spacing, and the total length is that multiplied by the run of each trench. The tool works this out from your area and spacing so you get the metres of trench to excavate for the whole patch.
How is the water-holding capacity worked out?+
Each trench has a cross-section — set by its top width, bottom width and depth — which gives the area of water it can hold per metre of length. Multiply that cross-sectional area by the total trench length and you get the total water-holding capacity (storage volume) of all the trenches across your area.
What spacing should I use between trenches?+
Spacing depends mainly on slope and rainfall: steeper slopes and heavier rain need closer spacing so no single strip sheds too much run-off before it reaches a trench. As a rough guide, gentler slopes might use 10–20 m vertical-to-horizontal spacing while steep ground needs trenches much closer together. Use a locally recommended figure where you have one.
What is the difference between continuous and staggered trenches?+
Continuous contour trenches (CCT) run as one unbroken line across the slope and are used where you want to hold the maximum run-off. Staggered (or intermittent) trenches are broken into shorter sections offset between rows; they suit steeper or rockier ground, reduce the risk of a breach cascading, and use less earthwork.
Do contour trenches really reduce soil erosion?+
Yes. By breaking the slope into shorter run-off lengths and trapping flowing water and the soil it carries, trenches sharply cut the velocity and erosive power of run-off. The trapped sediment stays on the land and the held water soaks in, so the slope loses far less topsoil over a season.
How do trenches recharge groundwater?+
Water held in a trench has time to percolate down through the soil profile instead of running off in minutes. Over many trenches across a watershed this adds up to a large volume that recharges the aquifer, raises the water table and improves the yield and reliability of wells and springs downstream.
Can I plant on the trench spoil?+
Yes — the excavated soil is usually piled on the downhill edge as a bund, and tree seedlings or grasses are planted on or just below it. The trench keeps the planting line moist, which is why contour trenching is a standard first step in afforestation and watershed treatment on degraded slopes.
Are the results here exact engineering figures?+
They are sound planning estimates from your area, spacing and trench cross-section. Real ground is uneven, slopes vary and trenches are rarely a perfect prism, so treat the length and capacity as a guide for material and labour planning, and confirm against a field survey before major earthwork.
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