Features Structures & Equipment Water and irrigation
Inside View: August 2010

Typically, we are now in an age when we are desperately trying to
conserve water. In California, for example, nursery growers are limited
in the number of days per month they can irrigate crops.

Typically, we are now in an age when we are desperately trying to conserve water. In California, for example, nursery growers are limited in the number of days per month they can irrigate crops.

However, 2010 so far seems to have been a cooler, wetter year than most (at least here on the West Coast). This has had a considerable effect on nursery and bedding sales, such that many businesses cut back on labour hours and have been left with more stock on their hands than they’d wish. But rain can do more than just slow things down. Heavy rain caused a landslide in the important fruit production area of the British Columbia interior, and those farms will not be returning to any kind of production for many years to come. (In that area, normal rainfall between May 15 and June 15 is about 40 mm, but hit 109 mm in the same period this year!)

So, what can be done in times of excess water availability?

CONTROL IT OR STORE IT
Runoff water causes devastation if the energy contained in it is not controlled.

It’s not necessarily the total volume that’s the issue, but the volume in a short period of time. So, if you can’t make use of it, and have to let it go, do so expediently. It may be that using green roof technology, swales or other forms of vegetative water control are the way to go.

Alternatively, in areas of high road traffic movements, perhaps investigate the use of porous blacktop to allow rainwater to infiltrate the ground rather than rush off into storm drains. (You’ll find it is quieter to drive on than regular black top too!)

Tanks provide a useful option for storage of relatively small amounts of water. They are unlikely to be able to store all the excess water on a farm property over the year. Tanks can be above-ground or in-ground systems. Either way, be sure to provide mechanisms for preventing tank failure (e.g., corroded joints on above-ground tanks) or tank collapse (e.g., from high water table pressure on empty in-ground tanks). This is especially important, for example, if your tanks are inside a greenhouse next to fertilizer storage.

Lagoons typically provide a better option for storing large volumes of rainwater, but clearly require significant land grading and construction. Make sure they are safe too – exposed butyl liners make it almost impossible to get out of a lagoon if you or someone else is unfortunate enough to fall in.

Underground storage is another option. There are several proprietary systems on the market now, and while expensive, these can provide safe systems capable of storing significant volumes of water for use later.

Maybe you are in a position to consider some form of roof storage. If so, ensure that the roof is suitably engineered to cope with the extra load.

CLEAN IT OR USE IT
Some uses will require cleaning of the water. This can be done in many ways, such as filtration, chemical disinfection, UV sterilization, heat treatment (pasteurization), ozone treatment, membrane filtration or through using biological methods such as reed beds or slow sand filter systems. Whatever the method, again it is likely that water will need to be stored before or after treatment.

It might be totally suitable to simply use the water to irrigate. However, as it will be collected during a precipitation event, it’s most likely that it will need to be stored first! It may also require cleaning before being used on growing crops. Another option is to use it for washing water. This may be for a first wash of field vegetables or machinery.

GET RID OF IT
If all else fails, you may have to let this valuable resource go. This could be slowly into ground water, or quickly into surface run-off (drains and dykes). Either way, once it’s gone, it’s gone.
Whatever you do, it’s best to have a plan to deal with a valuable resource (“blue gold”) that can quickly turn into a liability. Whatever you decide to do, it could save you money.

Gary Jones is chair of production horticulture at Kwantlen University, Langley, B.C. He serves on several industry committees and would welcome comments at Gary.Jones@Kwantlen.ca.