Em4885 irrigation management practices to protect ground water

Possible Effects on Water Diversions
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CHAPTER 4
Minimizing water losses in the distribution system will contribute to increasing overall on-farm
application efficiency and reducing required water diversions to the individual farm. There are
situations where the seepage in the distribution system contributes substantially to recharge of a
usable aquifer and in fact, may be desirable.
Possible Effects on Crop Yields
Crop yields in an individual field could be increased if seepage from the distribution system was
adversely affecting the fields by creating saturated conditions. Total yields from the individual farm
could be increased if the magnitude of losses in the distribution system were such to cause a loss of
cropped land or insufficient irrigations. That is, the water that is saved by achieving this Objective
might be used to bring more land into production or more effectively irrigate currently-cropped land.
Possible Effects on Ground Water Quality
Ground water quality will be affected if the losses were a result of seepage from ditches or
leakage from pipelines. Whether the ground water quality would be diminished or improved
depends on the quality of the irrigation water, the quality of the ground water, and any chemicals
or nutrients in the soil that would be leached by the seepage/leakage.
Pollution is the end result of availability, detachment, and transport. Available contaminants in
earthen ditches would include soil sterilants or herbicides used for weed control. In some situations,
fertilizer is added to water being run through ditches to fields. Also, ground water movement from
adjacent fields could place contaminants under a ditch or pipeline. Then, seepage/leakage would
drive the contaminants deeper.
Normally it would be expected that achieving this OMO would reduce the potential for adverse
effects on ground water quality. However, there are situations where water that seeps from
distribution ditches is of much higher quality than the ground water.
Possible Effects on Surface Water Quality
Surface water quality would not normally be affected by this Objective. It would be expected that
water delivered through the distribution system would be applied through an irrigation system before
returning to any other natural water course. However, there may be cases where there is operational
spill from a farm distribution system directly back to a natural surface water course. In these cases
certain practices, such as lining ditches, could reduce potential contamination by reducing sediment
loads in the spill.