Get the Offline ArchiveFree lifetime updates

Box Design

5 min read

Parent
📦
Spring Box Construction
Enclosing a concentrated spring
Current
🧱
Box Design
Concrete or stone enclosure
Sub-Topics
🔲
Inlet Wall
Permeable back wall design
🚰
Outlet & Overflow
Pipe placement and overflow drain

Size a spring box at about 1 m wide, 1 m deep and 0.8 m tall, with watertight concrete or mortared stone on three sides and a permeable stone or gravel wall facing the spring, and then fix the height of the overflow from the spring eye, not from the top of the walls. In the standard box the overflow sits 0.75 m above the floor, so a floor 0.5 m below the eye puts the overflow 0.25 m above it, which raises the water over the eye and cuts the flow; lower the overflow to eye level by digging the floor deeper or cutting the walls down.

Part of Spring Capture

Box design is the choice of a spring box’s size, materials, openings and levels so that it collects the whole flow of the spring, keeps contamination out and does not choke the spring it serves.

The Standard Box And What Its Dimensions Mean

The Spring Capture guide’s box is 1 m wide, 1 m deep and 0.8 m tall, adjusted to the spring. Its front wall carries an outlet pipe of 32-50 mm set 10-15 cm above the floor, an overflow pipe at least as large as the outlet set 5 cm below the top of the walls, and a drain at the very bottom. The floor is 8-10 cm of concrete on gravel, sloping to the drain, and the lid is a reinforced slab with a lockable hatch, overhanging the walls by 5 cm.

From those numbers:

  • Overflow level above the floor = 0.8 − 0.05 = 0.75 m
  • Water held at overflow = 1.0 × 1.0 × 0.75 = 0.75 m³ = 750 L
  • Dead space below the outlet = 1.0 × 1.0 × (0.10 to 0.15) = 0.10 to 0.15 m³ = 100 to 150 L. This is the sump where silt settles without reaching the outlet

Set The Overflow At The Spring Eye, Not At The Top Of The Wall

The spring pushes water out against whatever water is already in the box. If the box fills above the eye, the flow falls (Gravity Springs works the proportion out), and the water may find a way round the box. The overflow therefore has to be at the eye, or a little below it.

Check the standard box. The guide says to excavate about 0.5 m below the emergence point. If the floor sits at that depth, the eye is 0.5 m above the floor and the overflow is at 0.75 m, so it is 0.75 − 0.5 = 0.25 m above the eye. Two corrections make the overflow level with the eye:

  • Dig the floor deeper: with the overflow at 0.75 m above the floor, the floor must be 0.75 m below the eye
  • Or cut the walls down: with the floor 0.5 m below the eye, the overflow must be 0.5 m above the floor, so the walls are 0.5 + 0.05 = 0.55 m tall

Either way, mark the eye level when you excavate and measure from it. The guide’s dimensions are a starting point to be adjusted to the spring, and this check is part of the adjustment. With the 0.55 m walls the water held at overflow falls to 1.0 × 1.0 × 0.50 = 500 L.

What You Need

  • Mortared stone or poured concrete for the walls (Concrete Making, Hydraulic Lime for a lime mortar that sets wet)
  • Stone or gravel for the permeable wall (Inlet Wall)
  • Pipe and fittings for outlet, overflow and drain (Outlet & Overflow)
  • A reinforced lid with a lockable hatch, with a raised lip so rain runs off
  • A screened vent, so the box can breathe through a pipe that insects cannot enter
  • A level and a plumb line

Method: Mark Levels, Then Build

Step 1: Mark the eye with a stake and a level line on the excavation.

Step 2: Fix the floor depth from the eye and the planned overflow height.

Step 3: Set the floor, 8-10 cm thick on a gravel base, sloping to the drain.

Step 4: Build the walls, the three watertight ones and the permeable one, to the height that puts the overflow at the eye, with the permeable wall on the spring side, pipes cast or sealed in as the wall rises.

Step 5: Cast the lid, hatch and vent.

Step 6: Test by filling and watching for leaks at the walls and pipes, then let the water settle at overflow and check it sits at the eye.

Common Mistakes

  • Taking the wall top as the water level. The overflow, not the wall, sets the water.
  • A hatch that lets rain in. Raise the hatch lip above the surrounding soil.
  • A box too small to clean. Leave room to reach the corners with a brush.

Safety

Closed chambers and heavy lids

The box is a small closed chamber: do not climb into it. Open the hatch, let it air, and clean from outside with long tools. A concrete lid is heavy: use a lever and two people, and keep fingers clear of the hatch edge.

What’s Next