After four years of extreme drought, gardeners in drought prone areas have been thinking about using as little water as possible. Then comes the inevitable rainy year. In Southern California, everyone prepared for the big rains of an El Niño year. And it never came. But that doesn’t mean we won’t get rainy winters. Sooner or later, there will be some torrential downpours to deal with – even in drought prone areas. So how do we garden for heavy rain, flooding and erosion as well as serious drought? We factor in proper drainage.
Like anything in life, it’s all about balance. Water-wise means being thoughtful about using water wisely whether there is too much or too little. So, a well-designed garden will make provisions for all possibilities. Drainage, water storage, efficient usage of applied water, smart plant choices, landscape areas that don’t deal with water at all – these are all aspects that combine in a successful, sustainable and good-looking garden.
Before you consider installing a backyard landscape make sure you attend to the drainage. Not only can the most beautiful landscape be ruined by poor drainage, but the integrity of any structures—including your home—can be at risk for water damage. Provisions to improve backyard water drainage should be made at the beginning of landscape installations. You can retrofit drainage, but you will have to dig up your garden to do it. If you find yourself having to retrofit drainage and you do not have time to avoid damage from imminent rains, use stop-gaps. Dig temporary trenches to direct water to a safe exit point, pile sandbags to wall off vulnerable areas where damaging precipitation can rise and flood, and make sure all run-off routes – whether they are pathways, gutters, mud vee-ditches or anything else – are open and clear of debris.
If you are building or retrofitting a landscape, start with placing drainage at the lowest point(s) of your back yard. All general land surfaces should have a slope of at least 2% toward your drainage area. Many backyard properties, especially in more recently built homes are constructed with a gentle swale. A swale is simply a mild depression in the land that will conduct water away from the house. If you have no swale look for the lowest level in the lay of your backyard ground surface. This is where water will normally pool so it is the best place to consider placing a drain. A swale will guide water out of harm’s way. (You can dig your own swale if you need one.) Adding underground drainage beneath the swale offers a pipeline for extra security and to handle large volumes of water.
Dig a trench that follows the existing swale or create your own swale using the low areas of your back yard. This will be the collection area for the water to flow. Make sure the channel you create is at least six feet away from the walls of your house. The drainage needs to cross your back yard and right angle down the side of your house to open onto a street or other acceptable drainage area. Ideally, you should run exiting drainage down both sides of the house making a “U” shape.
Lay 3 inch or 4 inch corrugated, perforated or unperforated pipe made specifically for this purpose into your trench at a depth of six inches or more. You can use prefabricated connectors to extend pipes or to turn corners. (The fewer turns and the wider the angle, the faster water can flow away.)
Slot tee joints along the drainage pipe at least every ten feet, especially where the pipe lines are at their deepest levels. Either end of the tee will join the two parts of the main line pipe together. Point the stem of the tee upward toward the sky. The open end of the tee should rise up level to the bottom of the swale.
Place a pre-formed drainage grid over the open part of the pipe. It will slot smoothly over the top of the pipe. The grid will keep leaves, stones and other materials from pouring into the pipe. Plan on regularly checking the depressed area that conducts water into the grid since blown leaves and other material can collect and clog the drain surface.
Bury the pipe leaving the swale or depression in place above so water will collect there rather than sheeting toward the house or gathering in places where it isn’t wanted. As water from heavy rain pours into the lowest ground levels it will be guided down through the opening into your pipe system created by the upside-down tee joint and safely conducted away.
These are guidelines for setting up a basic drainage line, although some materials and local codes will vary from state to state. There are more involved designs you can use and different materials — like French drain concepts — where broken stone, rock or chopped concrete will form an underground channel to guide water where you want it without using a pipe (or to surround and enhance water flow around an underground pipe). Variations on this can take the form of decorative dry riverbeds, artistic channels cut through outdoor flooring, brick waterways or other passageways. You can make drainage into part of the design of your landscape or hide it so it functions without drawing attention. However you decide to design your drainage, just make sure you include it.
Drainage in drought-prone areas can be easy to overlook, but flooding can happen even without rain. Broken water lines, flooding from over-filled swimming pools and neighbors’ water overflows can lead to disaster if your property is not equipped to handle excess water. Pretty or not, the safety and beauty of your home and garden can be dependent on a good drainage system.