This article is anticipated to appear in the CHS newsletter in 2009
Harvesting water: needs, benefits, and methods
Annual precipitation in Calgary amounts to about 422 mm or about 17 inches: that is, we would be living on "bald prairie" if we did not have city reservoirs. Whether we are looking at issues of cost or environment, we need to look at how to use these resources most effectively in our green areas. A more specific question is how to retain water that might otherwise flow directly and quickly onto our streets and overwhelm the storm system. Our focus should be to reduce evaporation, and slow down run-off. Even in damp maritime climates, 2 litres of water can evaporate from 1 sq. metre of vegetation in one day - imagine how much is lost here! Organic mulching dramatically reduces this water loss and simultaneously improves our soil.
High on my "to do" list is to plant shade trees, re-direct drainage, and utilize more moisture-retaining soil. Using plants that lose less moisture, searching out plants that have drought-resistant characteristics, such as grey or silver foliage, or with leathery, small, preferably long or narrow leaves; succulents store moisture. Lavender is an example of drought tolerant plant. Remove weeds: they use as much water as our more desirable plants. Group pots together for protection from winds that increase desiccation, and use fewer hanging baskets for the same reason. Consider a green roof for your garage (having first checked out its weight bearing strength!). Find ways of directing water into the sub-soil of your yard. If you have a steep slope, terrace it. Use downspouts to optimum benefit - search out rain barrels that fit snugly beside your house: Vancouver provides semi-circular barrels for that purpose \96 we must ask the City here to do likewise.
Thunderstorms can overwhelm the City\92s storm system \96 we can do our part to reduce flooding by slowing down and decreasing run-off from our lots. How? Reduce the area covered by impermeable concrete or asphalt. Plant perennials and trees in mulch-covered, moisture-retaining soil: this slows down water movement. Some trees, such as the Bur Oak, have long tap roots when young and this clearly is good for survival. Trees are valuable in many ways, as can be seen in the way the City assigns values to its boulevard trees: a mature, healthy and attractive 1ft (31cm) diameter conifer could have a value of up to over $ 9000, a deciduous tree of the same girth about $ 6000.
When re-designing or renovating garage pads and driveways, plan to divert water onto the garden, rather than directing it to the gutter (unless you have a high water table, as some of us do). Look for permeable paving stones for driveways and pathways. Their joints also permit vertical drainage in contrast to most concretes. There are lots of choices now for alternatives such as grids of various materials that have honeycomb-like cells in which grass or perennials can grow. If you have a path that does not require snow-shovelling, how about using pebbles, gravel, or bark as a mulch and walkway surface \96 separated stepping stones can be used attractively too, maybe separated by thyme.
Boulevard trees and shrubs \96 and tall grasses - help regulate urban heat, absorb dust, baffle sound, reduce or divert winds, provide berries and other food and shelter for birds, nectar and pollen for insects, and beauty and privacy for us: use them to advantage, and remember, tree-lined streets attract house buyers too. We can\92t lose!