Rain, Rain Everywhere!

I’ve spent weeks talking about water. Water shortages, conservation, rainwater collection, etc. Now that we have finally received significant monsoon rain in most areas, some readers may now be asking, “What do I do with all the runoff?”

From decades of experience, I can tell you a large percentage of all landscape work in this area is for drainage and erosion control. This is one of the primary reasons so many home and commercial landscapes are mostly rock. Rock-filled drainage swales, gravel over fabric to control weeds, and boulders to accent an otherwise boring, flat landscape. All very functional landscape features. Effective too! After all, when a big downpour comes, you don’t want your yard to wash away and become your neighbor’s problem or reward.

 Let’s discuss volume. When a half inch of rain falls in a half an hour, that’s an inch an hour. I know, simple math, but that’s a fair amount of water to deal with in a short time. Especially in a small space like a city lot. And multiple city lots drain into bigger city areas like streets, drainage ditches and creeks. Flooding can be both exciting and dangerous. Let’s not lose our heads though. One of the Phoenix news stations dedicated an entire broadcast a few nights ago to the dangerous results of a dust storm and a half inch of rain that caused about four inches of water to flow through an intersection. The camera crew and reporter stood by this intersection for most of the broadcast watching the water splash out from car tires as they passed through and talked nonstop about how dangerous this was with all that water. Uh, it was 4 inches. Not even enough to reach the hubcap or wheel on most cars. The people who were concerned about the depth of the water were nearly causing accidents by swerving to avoid the deepest water.

 Yes, a half an inch of rain in a short time can cause a little flooding. It’s usually brief and temporary. How about three inches in an hour? Now we’re talking about damaging rain. Not to mention the strong outflow winds that usually accompany these violent monsoons. Comparatively, we hear occasionally about hurricane induced rains in areas around the Gulf that can drop 8 inches in an hour, but there is a significant difference. The natural landscape, and even the built landscape there, consists of mostly vegetation. It’s often said the most effective erosion control on the planet is a blade of grass. Also, the areas surrounding the Gulf are generally flat, or nearly so. This means water tends to collect and not move as quickly, causing flooding issues related to things “filling up” versus moving. Here in our mountainous natural landscape, we tend to have bigger problems with moving water, and all it carries with it.

 We can, and sometimes do, get rains of three inches in an hour. At that point, it’s best to be home with a cup of tea and watch out the window, because there’s nothing you’re going to do to change anything that happens in your yard. Especially if it starts to hail. If your landscape was not designed and built to accommodate such a heavy rainfall, it’s important for you to watch what is happening during the rain and make a careful inspection when it’s over. Did anything wash away? Did an area fill with silt? Is your driveway or foundation undercut? Where did the water come from and where was it going? Water will always flow downhill and will take the path of least resistance, even if it has to make a new path. This is why it’s important to watch it happening. The inspection afterward will guide you to what action to take to make repairs. Unfortunately, it may be a few years before you can test your repairs to make sure they do the job and hold up in a heavy rain.

 If you decide to make adjustments to your landscape as a result of a heavy rain, here are a few suggestions for improving drainage issues. Keep in mind that roofs, driveways, and sidewalks are all impervious surfaces that will increase runoff.

 ·       Use as much pervious surface as possible in your landscaping so water can soak in.

·       Try to reduce impervious surfaces to the minimum necessary for proper drainage.

·       Never drain your property onto someone else's property.

·       Make a few collection areas away from your house for water to pool and soak in.

·       If possible, use permeable concrete or pavers for walks and driveways when you build.

·       Collect as much rainwater as you have space or use for.

·       Use properly placed boulders or plantings to reduce flow in runoff swales.

·       Cover exposed soil areas with mulch to prevent siltation in other areas.

 I hope these suggestions are helpful and of course, if you need assistance figuring out the best path forward, contact The Horticoach.

 See you around the swamp!

The Horticoach