Drip irrigation for water conservation

Richmond has had a hot, dry spring. It has rained only twice since class started in mid-May: We had 5 mm on June 2nd, and 3 mm on June 18th. This amounts to zero effective precipitation because 5 mm of rainfall during a dry spell will simply evaporate rather than soaking into the soil to become available to crops.

Meanwhile, unusually high temperatures, clear skies, dry air, and steady winds are combining to create more potential for evapotranspiraton (and greater fire hazard) than this area normally sees in late spring and early summer. If water is available, the plants can use it.

The evapotranspiration model at Farmwest.com currently calculates a 223 mm moisture deficit for south Richmond between May 1st and today, July 8th. The typical moisture deficit for the same period is just a 37 mm.

All of this means we need to irrigate. The campus terrace gardens have a built-in pop-up sprinkler system that has run for an hour each morning since early May. The same system that waters the terrace gardens waters a section of lawn east of the campus entrance.

On July 3rd, Metro Vancouver restricted lawn sprinkler use to once a week to conserve water. The restrictions to not apply to vegetable gardens, but our irrigation system is not designed to separate the vegetable growing area from the lawn.

Sprinkler irrigation systems are typically just 50-70% efficient due to losses from runoff, wind, and evaporation. They also contribute to periods of leaf wetness, which can promote foliar disease.

Last week the class removed six sprinkler heads and replaced them with header lines for drip irrigation. They shut off the remaining sprinklers in the areas growing vegetables. The drip irrigation system should be more than 90% efficient, dramatically reducing water loss due to runoff, wind, and evaporation.

The new system is reducing water consumption without increasing moisture stress in the crops. It has not been without problems, though. During the first few days of operation we saw several blow-outs of irrigation lines and sprinkler heads. The pressure regulators that we used to reduce water pressure in the drip system increased water pressure in the pipes leading to the sprinklers. We've been trouble-shooting these problems one sprinkler at a time.

We excavated the box with a valve for the irrigation system in the west terraces, and reduced the flow to that side. Doing the same thing on the east side of campus will be more difficult because there are several valves, but no single valve controls just the vegetable-growing area.

The crops are looking good, with cucumbers starting to spill over the terrace walls.