Drainage Guidelines

Drainage recommendations

Illinois has a wide variety of soils, and each differs in some way from all the others. The guidelines will help you determine what drainage practices are best suited to your particular soil. These guidelines are based upon field tests and upon past experience with drainage practices on various soils.

The soils listed in the guidelines are grouped according to the soil characteristics that are most relevant to the design of man-made drainage systems. The two primary characteristics are the rate at which water will move through the soil (referred to as soil permeability or hydraulic conductivity and measured in inches per hour) and the degree of wetness before any drainage practices have been applied (referred to as natural drainage) Two other important characteristics, which help determine subgroups in the guidelines, are soil depth and topographic position. Some soils are shallow to bedrock, shale, or sand. Others occur on bottom lands and have stream flooding problems. And some are located in saucer-like depressions where they have no natural surface outlet. Other factors, such as land use, affect drainage design but are not dealt with in the guidelines.

In the guidelines, the drainage groups are assigned a number (1 to 4) and a capital letter (A or B). The number indicates the degree of soil permeability:

1 Rapidly permeable More than 6 inches per hour
Moderately rapidly permeable 2 to 6 inches per hour
2 Moderately permeable 0.6 to 2 inches per hour
3 Moderately slowly permeable 0.2 to 0.6 inch per hour
4 Slowly permeable 0.06 to 0.2 inch per hour
Very slowly permeable less than 0.06 inch per hour

The capital letter indicates the natural drainage of that group of soils.

A Poorly drained The water table is at or near the surface during the wetter seasons of the year
Very poorly drained The water table remains near, at, or above the surface much of the time
B Somewhat poorly drained The water table is near the surface only during the very wettest periods

Natural drainage is a good indicator of the relative yield increase you can expect from most crops if you install an adequate drainage system. The yield increase will probably be greater for the soils with the poorest natural drainage.

Landowners and operators, farm managers, drainage contractors, and others can determine the soil type and number from county soil survey reports, the conservation plan of the farm, or unpublished soil maps that are available at the local soil and water conservation district office.

Some small areas of wet soils cannot be shown on maps on the scale commonly used for soil surveys. A few very minor soils that need drainage and that are shown on soil maps are omitted from the alphabetical and numerical lists.  Information and publications on soils can be obtained from the Natural Resources Conservation Services  or Local Extension Offices.

Recommendations on drainage depth and spacing may be obtained by running the General Recommendations program. In addition, the County Specific Simulations program combines soil information with historic weather data to produce simulated yield response for specified depth/spacing combinations.

Construction near utilities

Illinois has centers of high population that are serviced by many miles of public and private utilities such as telephone, telegraph, and electric transmission lines, pipelines, railroad tracks, and highways. In designing and constructing a drainage system, it is extremely important that you know the location of any utility (especially pipelines) near the drainage project. Many utilities are well marked, but some are not.

If a buried utility line or a highway is to be added to an area, landowners should obtain information about the engineering design work. This information is needed to assure them that the installation will not interfere significantly with present and future drainage work. Information can be obtained from the utility company or highway authority.

Whenever possible, avoid building drain lines across buried cables, pipelines, and other facilities. You can keep the number of crossings to a minimum by installing special lines (called interceptor lines) parallel to the facilities. Find out from the owner of the pipeline or cable its exact location and depth. Perhaps the owner can also inform you of any special construction requirements and supervise work in the vicinity of the line. You may have to obtain a special permit and meet certain other requirements to install drain lines across a county, state, or federal highway.

In working around a buried pipeline, the landowner and contractor are naturally subject to some safety hazards. They may also be liable for the cost of interrupted service and repair if they damage the buried utility and have not properly notified the owner of their plans to work near it.