Denman Island, British Columbia
Rainwater Irrigation System |
We live in a "Mediterranean" climate - rainy winters and dry summers. Lately, the summers have been getting even drier. Our well does not supply enough water for garden irrigation. The obvious solution is to collect enough rainwater in winter to see the garden through a rainless summer.
Rain is collected off the roof of the house using standard gutters. Instead of using a standard downspout, I used 2-inch PVC pipe. This easy to work with, and is better able to be routed to the tanks and valves as required. A standard eavestrough strainer basket fits into a 2-inch PVC elbow very nicely. It doesn't have to be a tight fit.
Below the deck, the downspout leads to a T-fitting above a valve. The side branch of the T-fitting is always open, and leads to the fill opening of the collection tank. This branch slopes upward to form a trap, the purpose of which is to prevent pollen from being washed into the tank. The down branch of the T-fitting leads to a valve. When open, the valve allows water to go straight down, bypassing the tank, from where it drains away onto the ground. When the valve is closed, the drain branch is blocked, and the water is diverted into the tank.
There are two primary collection tanks, located under the deck. Each primary tank receives the water from one downspout. Tank 1 is fiberglass, and holds 1000 gallons. Tank 2 is polyethylene and holds 1500 gallons. Water from the respective downspout enters the top of each tank. An overflow near the top of each tank allows excess water to flow into the drain line, where it drains away onto the ground.
Water for irrigation is drawn from the bottom of each tank. A shutoff valve allows this supply pipe to be closed off for maintenance. A Fire Department connection is cheap and easy to install, and will allow the Fire Department to access the water in an emergency.
A secondary storage tank, located in the garden is filled through the irrigation piping from the primary tanks. This tank holds 2000 gallons. It is not connected directly to the downspouts. Instead, it is filled by gravity flow from tanks 1 and 2. An overflow near the top of the tank allows excess water to flow into a drain line, where it drains away onto the ground. This tank is also fitted with a fire department connection.
A pipe from each primary tank runs to a common manifold, from which an underground pipe connects to the garden and the secondary tank. Water flow from the primary tanks to the garden and to the secondary tank is by gravity. When water is drawn from the secondary tank, it must be pumped, as the tank is located downhill from the garden.
In the garden, a solar-powered pump provides pressure for watering the garden. It draws its water from the Irrigation Supply Pipe, and delivers it to garden hoses at several locations via more underground pipes.
Water is pumped by a 12-volt Shur-Flo diaphragm pump, which is powered by a Canadian Tire 12-volt marine battery. The battery, in turn, is charged by a 15-watt solar panel, also from Canadian Tire. The pump, battery and switches are protected from the weather in a cedar box covered by metal roofing.
The solar panel is mounted on a rotating post made of galvanized pipe. The pipe is mounted onto the fence post using large eyelets that allow it to rotate freely. A thrust bearing at the bottom of the post, made from a furniture caster, supports the weight of the post and the solar panel. A short length of pipe was attached at right angles part-way up the post to serve as a handle for rotating the post and panel towards the sun.
The water outlet of the pump runs through a mechanical clockwork timer valve before going to the garden hose connections. When the timer shuts off, the integral pressure switch in the pump detects the rising pressure and shuts off the motor.
A problem developed in that the inertia of the rotating pump motor would continue to turn the shaft for a few strokes of the pump after the electrical supply was shut off. With rigid piping between the pump and the valve, there was nowhere to absorb the volume of these pump strokes, and the pressure would go from low to astronomically high in a split second. This had potential to damage all the components, including the pump. As it was, I had to replace some plastic pipe connectors. I mitigated the problem by adding a pressure tank between the pump and the shutoff valve. The pressure tank is simply a large body of pipe connected above the water line. Being higher than the water level, it traps a volume of air. Now, when the valve closes, the air can be compressed slightly, absorbing the volume of the last few strokes of the pump as it stops.
Home
Copyright © 2010 Keith Walker
Last modified: 2-Jan-2010