Lots of rain is always welcome in Tucson, at least by plant people. Our plants love the moisture, and the rain helps wash excessive salts and minerals out of the root zone. But as welcome as it is, when we get lots of steady rain we may notice some drainage issues in our gardens.
Drainage issues essentially boil down to two basic problems: pooling water or erosion. Pooling water can be an issue if it’s near your house foundation, or near other important structures. It’s also an issue if it’s in walkways, driveways, patios or other traffic areas. This is usually due to not enough slope in an area. The solution in this case is to create a slight slope or, if that’s not possible, divert the excess water away from where it’s pooling and towards your trees, shrubs and other plantings.
Erosion is caused by water running off areas on your property quickly enough to wash away soil, mulch, gravel or other ground coverings. This is usually due to too much slope in a certain area. The solution is to reduce the slope, thereby slowing down the water and preventing it from doing damage.
The common thread in these solutions is to work with gravity and the water falling on your property, and make use of it without causing a problem for another property downstream. You don’t want to fix your pooling or erosion issue only to divert water to your neighbor’s yard, or to the street. In any case, the water that falls on your yard is a precious resource, and it’s free — why waste it?
Keep in mind that this information is quite basic, and is meant to help you deal with minor issues. If you have severe erosion or excessive pooling, or if your yard has a large slope, it’s always best to consult with experts.
Dealing with pooling water in your yard
Depending on your situation, one (or all) of these solutions may be needed:
- Add soil to increase the slope and divert water where you want it. You will need a pretty minimal slope — even 1 inch down for every 12 inches of horizontal run is enough. Gravity will do the rest.
- Create basins with overflows to soak in the water you’ve diverted away from structures. Basins should be around 4-6 inches deep and be filled with mulch. This will help keep the water in the soil. You can (and should) plant around the edges of the basins so that plants can take advantage of the water. One important caveat: large basins should not be within 10 feet of a wall or building foundation, so if you have a small yard this solution won’t work for you, and it’s best to talk to an expert.
- Harvest rainwater from your roof. This can mean using a tank, which is called active rainwater harvesting, or into basins, which is called passive rainwater harvesting. The water flowing off your roof will thus be directed into storage, which will reduce the water volume going through your yard.
- Make sure your gutters are properly installed and aren’t blocked and the runoff is directed away from your house and other structures. Again, avoid creating a problem for your neighbors and community. Water coming off your roof should be directed to a planting area or, as mentioned above, to tanks or basins.
- For any hardscape in your yard, using materials that are water-permeable whenever possible will also help with drainage. Examples include pavers set in sand, gravel and mulch.
Erosion solutions
If you notice soil, gravel or mulch getting washed away in an area of your yard, it’s best to deal with the problem early before it creates a gully. Here are some things you can do:
- Turn your slope into terraces. This creates flat areas that can be filled with plants and which can soak in the water rather than having it run off your slope. These can be small and hand-built, not necessarily masonry structures.
- Divert water into basins for infiltration and storage in the soil. I know I’m like a broken record, but basins are truly some of the most useful structures you can build in your yard. If water is soaking into a basin, it’s soaking into the soil below, and the mulch on top helps keep the water in the soil. Again, remember the caveat mentioned above: do not place large basins within 10 feet of a foundation or wall.
- Create rock structures to slow the water and prevent losing soil. This is a bit more complicated than basin building and should be done with expert consultation. Helpful rock structures include one-rock dams, and Zuni bowls, as well as other structures. These are frequently used in combination, which requires some understanding of the principles. Brad Lancaster’s excellent books "Rainwater Harvesting for Drylands and Beyond, Volume 1" and particularly "Rainwater Harvesting for Drylands and Beyond, Volume 2" will be immensely helpful. For additional guidance, an excellent starting point is our local nonprofit, the Watershed Management Group, which offers residential consultations.
With millions of people living in areas dealing with increasing drought and rising water costs, many are learning how to harvest rainwater.
