Pinal County's new flood study for the San Tan Valley area points to 12 places where new culverts, channels and retention basins could move stormwater away from roads and homes. None of that work has a price tag or a construction date yet.

Engineers presented the San Tan Valley Area Drainage Master Plan on Sept. 9 to the Pinal County Flood Control District board, which is the Board of Supervisors sitting in a second role. No vote was taken. Assistant County Engineer Joshua Plumb said the county hopes to bring the plan back for formal adoption sometime in October.

The study covers 68 square miles, including the roughly 35 square miles inside the Town of San Tan Valley. Ryan Sauer, project manager for Entellus, the engineering firm that did the study, said drainage in the area was built piece by piece as neighborhoods went in. Engineers counted 267 culverts and 74.5 miles of channels, and many of them do not connect. Water leaves one neighborhood's channel, spreads across farm fields and runs on until another channel picks it up.

The computer model found 222 homes and other buildings that would have water against them in a 100-year storm, a storm with about a 1% chance of happening in any year. It found 66 in a much smaller 10-year storm. One cluster the engineers showed sits along Schnepf Road, where water coming from the east has no way across the road and ponds.

Queen Creek Wash is the only place in the study area on FEMA's flood maps. The county now has its own map of where water goes in a 100-year storm across the whole area. That map does not require anyone to buy flood insurance. The county uses it to review property when someone builds.

The study also drew on flooding reports residents sent through a 2021 county survey, which SanTanValley.com shared that June and again after the July storms. The county also held a public meeting at the Town of San Tan Valley's complex earlier this year, which Plumb said drew about 20 residents.

Where the Work Would Go

The largest project would run down the middle of the area. It would carry water from the Copper Basin neighborhoods in a new channel along a planned road to the Bella Vista neighborhoods, then north to a large retention basin that slows the flow before it moves on toward the wash. Sauer said the engineers met with the Arizona State Land Department so the design lines up with the state's plans for its land to the north.

The county's maps show proposed work in these areas:

• Bella Vista Road, from Gantzel Road west toward Gary Road: new channels, box culverts at Bella Vista Road, a pipe culvert under Gantzel Road, an embankment and a retention basin near Gary Road.
• Judd Road, south of Bella Vista Road: a new channel carrying water north from the Copper Basin side, with pipe culverts under Judd Road.
• Skyline Drive, from Schnepf Road east past Sierra Vista Drive: a long run of new pipe culverts, box culverts at Schnepf Road, a channel along the road and a small retention basin.
• Gantzel Road at Queen Creek Wash: a larger box culvert under Gantzel, a flap gate and an embankment.
• Gantzel Road near Skyline Drive: a new channel running east from Gantzel.
• Near Gary Road, from Prospector Way to Foot Hills Drive: new pipe culverts and a regraded basin along an existing channel.
• San Tan Hills Drive near Stone Creek Drive: a pipe culvert with a drop inlet.
• Gary Road, from Gail Road south toward Daniel Road: a box culvert and a new channel along both roads.
• Roberts, Royce and Phillips roads: regraded channels along the roads.
• The west side, from Empire Boulevard south to Skyline Drive: box and pipe culverts where roads cross washes, including Hunt Highway, Sun Dance Drive and Skyline Drive.
• Judd Road, west of Edwards Road: pipe culverts along the wash near Bryce Trail, Royce Road and Joliet Place, and a storm drain along Judd Road.
• Quail Run Lane: two pipe culverts and channels along the road.

Three of those areas, the west side, the Judd Road area and Quail Run Lane, are outside town limits in the unincorporated part of the San Tan Valley area. Several others sit on or near the town line. The SanTanValley.com interactive map shows which side of the line an address falls on. The county's Sept. 9 presentation carries a close-up map of each area.

On Skyline Drive, Sauer said Chris Wanamaker, the Town of San Tan Valley's public works director, is looking to rebuild the road in the next three to five years. That could be a chance to add the drainage work at the same time.

Who Builds It, and When

After the Board of Supervisors adopts the plan, the county will give it to the Town of San Tan Valley, which can choose whether to adopt it too. Plumb said the county serves as the town's floodplain administrator for now and would help the town enforce the plan if it does.

The county's next step is to try to place some of the projects in its five-year capital improvement plan, the schedule it uses for large construction work. Plumb said many of them will land in the later years of that plan, still in the planning stage, because they are large and expensive. The presentation did not include cost estimates.

Plumb said the county focuses its own construction money on unincorporated areas. Inside town limits, it would look to the town to take on most of the projects, with the county as a partner. He said developers are likely to build much of the in-town work as land develops, and the county can make drainage fixes a condition of approving a project, because some of that land is hard to build on without them. The county also looks for grants and partnerships to pay for flood projects.

The Board of Supervisors is expected to consider adopting the plan in October. Continue following SanTanValley.com as the plan moves to that vote and then to the Town of San Tan Valley.