Understanding Drainage

Do you understand drainage?  To many people, to drain is to get rid of the water.  The most noticeable water that these people want drained is the water lying in fields and yards.  This type of water is commonly known as  “surface water”.  To most, when the surface water is no longer visible, then the land has been drained.  This is not always the case.  There is also water lying below the grounds surface that needs to be drained.  This type of water is known as “subsurface water”.  Applying good subsurface drainage and good surface drainage practices can keep our land properly drained.

Surface drainage removes excess rainfall from the land surface at a rate, which will prevent long periods of ponding or flooding without excessive erosion so that pasture, hay and cultivated crops will have the best possible moisture conditions.  Common practices used to remove surface water include grassed waterways, surface drains (waterways without grass), surface culverts and open ditches.  Although open ditches handle surface water, they also handle subsurface water.  The subsurface drains (field tile) we have installed in the ground have to outlet somewhere, and the open ditch is the outlet for our subsurface drains as well as the channel for our surface water.

Subsurface drainage removes excessive water from the soil and subsoil below the surface of the ground and lowers the water table for better growing conditions for crops.  Subsurface drainage is applicable to saturated soil conditions where it is physically and economically feasible to use tile drains to remove excessive water from the plant root zone.  The fertility of the soil must be such that drainage will result in additional yields of crops sufficient to justify the expense of installing the drains.  Subsurface drains can act as a helper to drain excess surface water, but only when the drains are designed to handle water in excess to the normal saturated soil conditions.  Excess design should only be done when a satisfactory natural surface outlet is unavailable and when it is economically feasible.  In some cases the financial ability of the farmer may not permit substantial indebtedness, even though returns from increased crop yields and reductions in the cost of production should pay for drain installation within a 5 to 10 year period.

It is important that the current and future stewards of our land understand the differences between surface and subsurface water.  Improper drainage methods could cause serious environmental impact that requires thousands of dollars to repair.  In some cases, these environmental impacts cannot be fully restored.  Forcing surface water down a tile will result in an overload of the tile, which results in blowouts in your field.  Some blowouts start below the ground surface and are not detectible until weight is applied to the surface, allowing the dirt to fall in the hole.  Any tile blowout can cause high risks of bodily injury as well as machinery losses.  Tile discharging on the grounds surface can cause severe soil erosion.  Tile needs to be discharged into a pond, lake, river, or ditch.  A waterway or roadside ditch is not the proper place to outlet a subsurface drainage tile.  You may see tile in a road ditch, but this is not a subsurface drain tile, this is a surface culvert.  Surface culverts are designed to carry only surface water.  If subsurface water is brought to the surface, the surface culvert will be overloaded and back up water (causing additional ponding).

These are just a few examples of what can happen if improper drainage methods are not followed.  If you have a question as to whether your water is subsurface or surface, call your local Soil and Water Conservation District.  The Soil and Water Conservation can inform you on how to handle your water and the proper methods to dispose of your water.  They also assist in finding solutions to correct your current water problems that have developed over a period of time.  If we continue the proper techniques to deal with drainage and correct the existing drainage problems, we will continue to have a safe and healthy environment.