expensive real estate and are subject to huge evaporation rates. Many operations now also use large tanks for storage, either above or below ground. Below-ground
installations have the benefit of avoiding any issues with freezing temperatures in the winter, and they also keep the water temperature more moderate.
There are also big plastic blocks that are often assembled into a tank shape underground to collect storm water and release it gradually into
the ground to re-charge the aquifer, treating it as it disperses through the soil.
Those blocks are relatively small and light, so are easy to move and manoeuvre and they can be lined with heavy plastic to prevent infiltration into the ground, so they store water, instead of releasing it slowly.
Barrett figures 50,000 blocks can store 10
million gallons of stormwater. That would be five metres high by 100 metres wide and 500 metres long. Calculating how much rainwater you can collect with your existing roof area is
important before taking the next step of setting up for rainwater harvesting. For instance, a 10,000
square-foot roof can collect 6,230 gallons of water from an inch of rainfall. How useful will that amount of water be for your irrigation needs? Ted van der Gulik is a consultant in water management and is enthusiastic about the use of rainwater harvesting, but also cautious about the need for growers
to ensure it is a viable option for them. “Even if you collect all of the water that falls in May and store it, you could use it all in just one day in July,” he warns.
“You have to do the math,” he states. “Check the figures carefully and make sure it will work for you. Calculate the roof area and runoff capability.”
Tools are available to help you at: bcagriculturewatercalculator.ca
Van der Gulik points out that because regular watering is essential to plant health, it might not be practical to rely on rainwater harvesting as the only water source. However, as a backup to other sources, it could be useful. Even then, so much of it is up to weather and regular rainfall events; and the possibility of a dry summer just when a crop needs water the most, that it’s not practical to rely solely on collection of rainwater for irrigation purposes.
He doesn’t feel it is a useful alternative for mainstream agriculture, although it might work for some small operations, or as a buffer for other sources of water.
British Columbia Berry Grower • Summer 2018
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