A collection chamber is a sealed chamber at the end of drains that gather water from a seep or from several small spring eyes: perforated pipe is laid in gravel-filled trenches 0.5-1 m deep across the wet ground, sloping towards the chamber, and the chamber has an outlet, an overflow and a drain like a spring box. Use it where water comes out over a broad area, because a spring box only works where the water comes from one point.
Part of Spring Capture
A collection chamber is the sealed collecting point of a system of drains. It does for a seep or a group of eyes what a spring box does for a single eye: it collects the water, protects it and sends it on.
Where A Spring Box Cannot Work, Drains Gather The Water
When water seeps from a wide area, no single place has enough flow to build a box around. Instead you lay lines of perforated pipe in trenches across the wet ground, each draining to a chamber where the water is collected. The same approach works for a cluster of small eyes close together: each drains to the chamber by a short pipe. The Spring Capture guide describes the system in six steps, below.
What You Need
- Perforated or slotted pipe — PVC or other pipe with holes or slots cut in it (Slot Cutting shows how)
- Clean gravel, 10-20 mm
- Geotextile fabric, or layers of progressively finer gravel, to stop fines clogging the drain
- Clay — for the cap
- A sealed chamber — built like a spring box (Box Design)
- Pipe for the outlet, overflow and drain (Outlet & Overflow)
Method: The Six Steps
Step 1: Dig a trench across the seep zone, 0.5-1 m deep, perpendicular to the slope, so that it catches the water flowing down through the ground.
Step 2: Lay the perforated pipe in the trench, sloping towards a collection point.
Step 3: Surround the pipe with clean gravel, 10-20 mm.
Step 4: Cover with geotextile (or progressively finer gravel) to prevent clogging.
Step 5: Backfill with clay on top, to keep surface water out.
Step 6: Connect the pipes to a sealed chamber with an outlet, overflow and drain.
Details of each trench are in French Drain Collection; the longer, deeper collectors in Gallery Trenches.
How To Choose Between The Two Structures
| What you see | Use |
|---|---|
| Water flowing from one place, with a visible flow | A spring box (Spring Box Construction) |
| A broad wet patch with no flow | Collection drains and a chamber (Seep Springs) |
| Several eyes near each other | A chamber with a short drain from each |
Common Mistakes
- Trench along the slope instead of across it. It collects only a narrow strip of the flow.
- A level pipe. Without a fall it silts up and water stands in it.
- No fabric or graded layers. Fine soil clogs the gravel.
- An unsealed chamber. It lets the surface in.
- No clay cap. Surface water runs straight into the drain.
Safety
Trenches in wet ground
Wet trenches collapse. Slope or shore any trench deeper than 1.2 m, keep spoil at least 0.6 m back from the edge, and do not work alone. The chamber is a small closed space: do not climb into it (Excavation).
What’s Next
- Learn next: French Drain Collection — building the drains
- Combine with: Seep Springs — measuring what a seep gives