Monsoon storms, flood zones, and draining a pool in Scottsdale

NOAA's 1991–2020 normals for Scottsdale Airport show 8.73 in. of rain a year. A single storm can still move a lot of water across a yard. Drainage shapes where a pool can sit, what the site plan has to show, and where the water goes when the pool is drained.

Monsoon season and storm rainfall

The National Weather Service in Phoenix says "our 'monsoon season' officially extends from June 15th through September 30th." It lists the hazards as "damaging winds, torrential rainfall, frequent lightning, and dust storms."

NOAA Atlas 14 gives point estimates for central Scottsdale of how much rain falls in 60 minutes at different storm frequencies:

So about an inch of rain in an hour is roughly a 5-year storm at that point. Smaller, more frequent storms still move water across a lot, and a pool deck or wall in the wrong place can push it toward the house.

Where the pool goes

Scottsdale's homeowner drainage guide is direct: "Pools should not be placed in a low spot in the yard, block the natural flow path of a wash, or block the drainage in the yard or the flow of water around or away from your house." The same guide warns that clogged weep holes in block walls can flood backyards and pools. Check the weep holes in your yard walls before the season and after any work near them.

Before you settle on a location, walk the lot after a storm or look at it with whoever drafts the site plan. Note where water enters, where it leaves, and whether a wash crosses the property.

What the site plan has to show

The City of Scottsdale's pool site plan requirements ask for:

• All flood zones, shown and labeled
• A grading and drainage plan if the lot has drainage facilities
• A full grading and drainage plan if the project includes a retaining wall
• Easements, including drainage easements, which the pool, deck, and equipment can't disturb

Custom-lot submittals may need a revised drainage report. Under the city's stormwater and floodplain ordinance, the Floodplain Administrator reviews building permits so that sites are "reasonably safe from flooding." Flood hazard areas include, at minimum, the areas on the adopted FEMA flood insurance rate map.

You can look up the mapped flood zone for an address on FEMA's Flood Map Service Center at msc.fema.gov. A parcel outside a mapped flood zone still has to handle its own runoff.

Other towns

• Paradise Valley handles floodplain and grading permits through its Engineering Department, separate from the Building Department's pool permit.
• Carefree requires a grading and drainage plan of the pool area, stamped by a civil engineer, on its residential pool plan review checklist.
• Unincorporated Maricopa County and the other towns have their own rules. Ask the permit office whether the lot needs a drainage plan.

Draining a pool or spa

Resurfacing, some repairs, and high mineral levels all mean draining a pool. The City of Scottsdale lists three ways to do it.

To your own landscaping. Test the water first. The city calls for a pH between 6.5 and 8.5 and chlorine below 0.1 mg/l. Drain over several days so the water soaks in instead of running off.

To the sewer cleanout. Pump to the property's sewer cleanout at under 12 gallons per minute.

By septic hauler. A hauler pumps the water out and takes it away.

The city says never to drain to streets, alleys, city right-of-way, a sanitary sewer manhole in the street, a storm sewer inlet or drainage channel, adjacent property, drainage easements, or watercourses. Chapter 37 of the city code says "no person shall discharge or cause to be discharged water from a pool or spa into the right-of-way or watercourse." The pool site plan notes add that pools may not be emptied or backwashed into washes, streets, NAOS, scenic corridors, or neighboring lots and tracts.

Those notes cover filter backwash water too. Ask the installer where the backwash line ends, and keep it away from the street, washes, and NAOS.

A drainage checklist

• Find the flood zone on FEMA's map and show it on the site plan.
• Keep the pool out of low spots, wash paths, and drainage easements.
• Ask whether the lot needs a grading and drainage plan, and who prepares it.
• Check yard wall weep holes and keep them clear.
• Plan where drain and backwash water will go before the first fill.

For barrier rules, see the barrier guide. For the full permit process, see how a new pool project runs.