Monsoon Season Is Flooding Your Backyard. The Problem Isn't the Rain, It's the Grade.

Las Vegas gets about four inches of rain a year, and much of it arrives in a handful of summer afternoons. That is the defining feature of monsoon season: not volume, but rate. Which is why homeowners who have never had a water problem suddenly find three inches standing against the back of the house in mid-July. Do not shrug it off. Standing water against a foundation is one of the few backyard problems that gets expensive in a structural way.

Why desert yards flood easily

• Caliche. The cemented layer under much of the valley is effectively impermeable, so water soaks in a few inches, hits it, and travels sideways.
• Dry soil repels water. Very dry desert soil sheds the first minutes of a hard storm rather than absorbing it, so it is almost pure runoff.
• Hardscape coverage. A typical lot is mostly house, driveway, walkways, patio, and pool deck, each producing runoff instead of absorbing it.
• Block walls. On nearly every property line, they act as dams, pooling water against the wall or against your house.

Diagnose it yourself in twenty minutes

Standard design calls for the ground to fall away from the foundation, commonly about six inches of drop over the first ten feet, then a continuous path to somewhere it can legally discharge. During or right after a storm, photograph where water stands, which way it moves, and how deep it is, because that is exactly what a contractor needs and it is nearly impossible to reconstruct later. On a dry day, run the hose test at the base of the house at three or four points and watch whether water travels away or hesitates and sits. Escalate if standing water lasts more than 24 hours, if you see white efflorescence on interior garage walls, or if new cracks appear near ground level.

The fixes

• Regrading. Reshaping soil to restore fall. Often cheapest and frequently correct, but you still need somewhere downhill to send it.
• Surface and channel drains. Grated inlets piped out. Effective for a defined pooling area, but they clog with desert dust, and a clogged drain is no drain.
• French drains. Perforated pipe in a gravel trench wrapped in filter fabric. Adequate fall and fabric that keeps silt out are what separate twenty years from three.
• Permeable paving. Joints filled with open-graded aggregate over a deep stone reservoir, so water passes through the surface and is stored below. In a walled backyard with nowhere to send water, this turns the surface from a runoff generator into storage.

One thing not to do: do not solve your drainage by sending water onto your neighbor. It creates real liability and an HOA complaint fast.

"In the desert, low annual rainfall and a flooded backyard are entirely compatible. The problem is rate, and the fix is grade."

Permeable paving is also the detail that can keep a patio eligible for the SNWA turf rebate. Photograph your yard during the next storm and send us the pictures, or browse the project gallery to see how drainage and hardscape get designed together. For the official rules on permeable turf conversions, see SNWA's Water Smart Landscapes program.

Frequently asked questions