Drain Spacing Calculator
What is the drain spacing required for a 4-inch drain pipe to maintain a minimum water-table depth at midway between drain pipes?

The rate of water movement through the soil into the 4-inch drain pipes (inches per day).

Use the Drainage Intensity calculator to estiamte this value, here.

Scientific research shows that estimating the drain spacing when water table is at the soil surface results in maximum economic return on investment.

Distance from soil surface to bottom of the drain.

This value can be determined from the Drain Spacing Tool, here.
1- Zoom in to the area of interst.
2- Turn on the "USA Soil Survey" layer in the bottom-left corner of the tool.
3- Draw a polygon inside the shaded color of a soil type.
4- Click on "calculate" to run the tool.
5- Find the depth to restrictive layer on the Output page.

Type of lateral drain pipe affects how fast water enters the pipe.
When there is no drain sedimentation problem, use an 8-row regular-perf pipe to lower the water table more quickly than a 4-row regular-perf pipe.
When there is a drain sedimentation problem, use either a sock-wrapped or 8-row sand-slot pipe. A sock-wrapped pipe lowers the water table most quickly because it maximizes water entry into the pipe. An 8-row sand-slot pipe lowers the water table more quickly than a 4-row sand-slot pipe.
For more information click here.

This value can be determined from the Drain Spacing Tool, here.
1- Zoom in to the area of interst.
2- Turn on the "USA Soil Survey" layer in the bottom-left corner of the tool.
3- Draw a polygon inside the shaded color of a soil type.
4- Click on "calculate" to run the tool.
5- Find the equivalent saturated hydraulic conductivity of that soil type on the Output page.

Result: