October 27, 2015
How much rain can a rain chain drain?BY KEN NENTWIG
Green infrastructure: Storing water in the landscape
This morning I watched the rain fall, and wondered why we don’t have a way to collect and use it instead of letting it run away. And now we see your booth at the trade show! This is wonderful!”
These words were spoken to me at a local home show by a university student, conscious of her water footprint. To spread the message of rainwater harvesting possibilities and to raise rainwater harvesting awareness in the community, the Canadian Association for Rainwater Management (CANARM) entered a booth in several home shows on Vancouver Island this spring. Our booth contained a cutaway 1,125 litre storage tank with piping and a pump, lighted from the inside. On the other side of the booth stood a running vortex filter capable of handling runoff from a 200 sq. m. roof.
Most folks stopping by indicated that rainwater harvesting is a great idea. Many asked why Canadians have not already been practicing this for a long time. After all, England, Germany and Australia have been. Some came specifically looking for information or contacts or help, while a few thought it’s too little too late, or even not necessary since, “We live in a rainforest!” That last phrase is partly true — the west coast of Vancouver Island has some of the highest rainfall and precipitation volumes in Canada. Take Tofino, with over 3,000 mm of precipitation annually — that’s about 10 feet, an awful lot of water. As winter temperatures seldom stay below freezing in the region for long, about 98 per cent of this is actual rainfall.
In virtually every urban centre across the country, water is a problem. Specifically rainwater, which becomes storm water, which in extreme conditions becomes flood water, and which runs away wasted and unused, and can cause physical and economic damage.
Rain capture is needed everywhere
In spite of abundant precipitation, Tofino has a summer drought problem. Based on Environment Canada monthly averages between 1971 and 2000, fully three quarters of Tofino’s rainfall occurs from October through March. All the water that falls is not used, nor is it captured, and during the high-use season, treated water shortages are rampant. In 2006, the town ordered businesses closed on the final long weekend of the summer, throwing tourist plans into complete disarray. This is not so much a problem of poor planning, but of a dependence on infrastructure based on high outdoor usage of precious, treated water supplies.
Water needs are measured by uses, whether landscape/irrigation or flushing or stormwater retention or fire suppression or emergency preparedness. Costs are based on the equipment and installation required to meet the relationships of available rainfall, catchment area and type, demand volumes and seasonality, site characteristics, storage requirements, and water treatment. Guesswork does not have a place, and thankfully there are some guidelines to help get through the calculations.
A roof sheds copious amounts of rainwater during a storm — one litre per square meter for every millimeter that falls. For example, at a rate of 25 mm per hour, on a roof area of 50 sq. m. (that’s about one inch on 535 sq. ft.), a total of 1,250 litres (1.25 cu m, or 275 gal.) will hit, run down, and escape the impervious surface. It can be channeled along a gutter to a downspout — or rain chain — which directs it to ground level. Since water is ‘clingy,’ it runs down the vertical surfaces, either inside the downspout (hopefully!), or on the outside of the sequence of connected bells, links or cups of the rain chain. In this example, that’s about one-third litre, or one-twelfth of an Imperial gallon, per second.
Design for a big storm
That small-seeming volume really adds up. Our building codes dictate the required containment sizes and capacity to manage a deluge. Continuing with the Tofino example, the ‘design storm’ is 13 mm over 15 minutes, about double the example given above. Calculating the volume from the roof area for that period, a total of 650 litres (143 gallons) will be shed. The drainpipe (downspout) required is only 50 mm (2 in.), meaning that the average 75 mm (3 in.) installation is oversized. That’s good.
Which leads back to the title question on rain chains: What about them? Are they useful? The rain chain has a long history (sorry), perhaps beginning with castoff non-sellable cups or bells at the local artisans shop. Suspended vertically where water would normally drip or run from the overhead shelter surface to the ground to splash and make a mess or noise there, rainchains and downspouts become a channel for orderly drip transfer via gravity.
From a design standpoint, the rain chain can have a certain appeal and charm. Speaking practically, light to moderate rainfall events can be handled by the connected modularity of the drip mechanism. It’s the big events, where water escapes the molecular grasp of the chain effect, that we lose control, and lose access to potential collection volumes through splashing and turmoil that can spread water over a fairly wide distance at ground level. One answer could be larger collection structures at the base of the rain chain; another is the lowly downspout.
Green infrastructure makes sense
Rainwater falls on the good and the bad, the plants and the hard surfaces, the flowers and the weeds. How much rain falls is a question of climate, and varies according to the season and the extremes that Mother Nature is showing us. A simple rainwater system introduces water to the soil gently, as originally intended. Redirection or containment for later use opens untold possibilities in ground water recharge and irrigation. Designing the landscape to direct, contain and absorb rainwater requires much thought and preparation, and a commitment to maintain the system over the long term.
Rain chains, downspouts, cisterns and rain gardens all have a place in the landscape, and are individual components of a myriad of possibilities. Designers will take these basic premises to an ultimate end, uniquely formed and created for environmental friendliness, for practicality, and for enjoyment. Installers with practical skills and expertise will build structures that accommodate and enhance rainwater capture. System maintenance personnel will soon become major players in rainwater harvesting as a business operation.
How much rain a rain chain drains is less important than meeting the demand for rainwater — whether at a site or as an entrepreneur. The most fun is in the creativity of solving immediate problems while making a valuable difference in the world.
Ken Nentwig is a B.C.- based horticultural educator specializing in rainwater harvesting, landscape design and organic land care.