BY ERIC BOOTH
Fourth in a series
Virtually every discussion around increasing development/density for workforce housing units (WHUs) on Salt Spring revolves around availability of water.
The other three service issues — septic, hydro and roads — pale in comparison, as those are relatively easy to solve.
All water on the island originates from the sky: one metre falls annually. Some is stored in lakes, some in our aquifers and huge amounts run out to the ocean. We “consume” about one per cent of the rain that falls, and deliver that entire one per cent back into the environment via the oceans, aquifers and atmosphere.
The quantity of rainwater stored in our aquifers is entirely dependent upon our underground geology. In generalized terms, Salt Spring is comprised of three land formations. The northern section is primarily sandstone, while the two southern sections are primarily fractured granite.
Sandstone forms on the bottom of an ocean, and then, through tectonic action, is sometimes buckled upwards. If it buckles high enough it will fracture, creating a good aquifer. Channel Ridge, at 220-metres elevation, is an example of such a sandstone ridge. However, travel slightly further north to Sun Eagle Drive, at 160 metres, and the buckling is less. Subsequently, while wells in the Channel Ridge area average three to five gallons per minute, along Sun Eagle you may drill down 500 feet and get nothing.
Fractured granite is an excellent aquifer, and the two southern sections of the island rise to 400 to 600 metres. You can drill virtually anywhere in granite and hit a good water supply.
How much water does the average dwelling use? About 120 gallons per day. Since we have accepted rainwater catchment as one measure, let’s look at its math.
To obtain a CRD building permit for a house, using rainwater for water, you require 1,500 square feet of catchment area. Three feet of annual rainfall x 1,500 = 4,500 cubic feet x 6.22 Imperial gallons (IG)/cu.ft. = 27,990 gal/year. Divided by 365 days = 76.68 IG = 92.08 US gallons (the measure of well output) = .06 USG/min equivalent. Thus the maximum water output you can achieve solely through rainwater catchment is just 63/1000ths of a gpm. In other words, the output of a one gpm well is the equivalent to the absolute maximum yield of 15 rainwater catchment systems as described above.
This means, if you accept/support rainwater catchment as a potential water supply, then any well, with storage, which can sustainably produce one gpm, can equally support 15 homes, and a 10 gpm well = 150 homes.
North Salt Spring Waterworks District’s most recent hydrology study on Lake Maxwell indicates about 30 million gallons per year is safely available, over and above our current usage. Using our rainwater example, that is enough for over 1,000 WHUs.
And, for five months of the year, about 80 million gallons of fresh water overflows Lake Maxwell and drains into the ocean. If the level of the lake was raised just six inches, it could capture half the winter runoff (lake area = 106 hectares = 11,409,745 sf x 0.5 = 35,000,000 IG), which would be enough for another 1,000 WHUs.
So, without even mentioning recycling of grey water, there is a massive, available water supply on the island. All that is required is the vision and political willpower to access/utilize it.
Part 5 of the writer’s workforce housing series will look at the other services required, and how those challenges can be met.