With this weekend’s pending weather forecast of possible heavy rain check your overflow pipe to be sure it is functioning properly.
This is a crucial step to consider when setting up a rainwater harvesting system.
Although overflowing a rainwater tank may initially seem counter intuitive, it is a benefit for rainwater harvesting as it helps to move water which creates oxygenation and helps prevent stagnation. Using an overflow accomplishes two primary goals: 1.) Creates an exit path for excess incoming water, 2.) helps to remove floating particulate from the surface of the water, and 3.) pushes the overflow water away from the foundation of the catchment.
Creating an exit path for incoming water is important so that you to control where excess water goes and often excess water is routed to a garden or other area for supplemental irrigation. Removing floating particulate from the surface of the water is also beneficial as it is part of the low-maintenance approach that we take to improve the quality of water in your tank.
Overflow can be achieved through standard PVC piping. See photo attached.
A few things to consider when installing an overflow:
Match the overflow pipe size to the inlet pipe size. This makes sure the overflow can keep up with the incoming water if your tank is full of water. Example: If you have a 4" inlet to your tank, you'll want your overflow to be 4".
Ensure that the overflow pipe is installed at a lower elevation than the inlet pipe. In most instances, you want to make sure that the overflow is a minimum of half the pipe diameter below the inlet pipe. This allows for overflow before backing up into the pre-tank filter/inlet pipe.
Make sure the overflow has a lip/bevel. It is recommended to have some sort of angle on the pipe that the water exits through. This creates a siphon effect and helps to draw water into the pipe (think of a pond skimmer). This also helps to siphon the floating particles through the overflow. If PVC piping is used, an angle of 11 or 22 degrees cut across the pipe is recommended.
Prevent mosquitoes/other bugs from entering by placing a knee-high nylon with a rubber band over open ends. Otherwise, the catchment tank is a fresh water lake to lay their eggs and the organic sediment on the bottom is a food source.