Drain Spacing Calculator Guide

The drain spacing calculator estimates the required drain spacing between parallel drains necessary to promote trafficability and prevent crop damage from excess water in the root zone by using the Hooghoudt[1] equation. The drain spacing calculator gives the recommended drain spacing given the choice of drainage coefficient and the soil and system parameters. However, actual choices for spacing and drainage coefficient should be based on balancing the costs with the expected benefits.

The required parameters for the drain spacing calculator, with typical values for the Upper Midwest, and a reference diagram are as follows:

Average Saturated Hydraulic Conductivity Values

Saturated Hydraulic
Soil Texture Conductivity (ft./day)[2]
Sand 49.9
Loamy sand 44.2
Sandy loam 9.84
Silt loam 2.04
Loam 1.97
Sandy clay loam 1.79
Clay loam 0.694
Silty clay loam 0.482
Sandy clay 0.615
Silty clay 0.292
Clay 0.363

Source: Clapp and Hornberger (1978)[3]

  1. Hooghoudt was a drainage researcher from the Netherlands who developed a steady-state drain spacing equation with wide applicability and relatively simple structure in 1940. The Hooghoudt equation is commonly used to develop drain spacing recommendations.  ↩

  2. Based on analysis of 1845 soils.  ↩

  3. Clapp, R.B. and G.M. Hornberger. 1978. Empirical equations for some soil hydraulic properties. Water Resources Research 14:601–604.  ↩