A slow soak day.

Summary

August 4, 2025. A broad monsoon cell tracked slowly southeast across the central basin between 13:40 and 17:38 MST, depositing a fairly uniform 0.55–0.68 inches of rain across the urban core. NWS Tucson issued no advisories — at no point did the rate exceed 0.3 inches per hour, well below the urban-flood threshold. The El Encanto cooperator gauge logged 0.62″.

This is the storm a basin is designed for. A 1-inch design storm with a 0.85 runoff coefficient and a 600 sf catchment delivers a peak inflow of about 50 gpm to the basin; an 0.62-inch storm at 0.15 inches per hour delivers 7 gpm — well within the soil's percolation capacity even with a moderately compacted Tucson clay-loam profile.

Why we like these

Three reasons we'd take ten of these over one of the bigger 2-inch bursts.

Soil takes it all. Tucson clay-loam will absorb water at roughly 0.2–0.4 inches per hour after it has had a few minutes to wet up. A storm that delivers below that rate goes entirely into the soil, not into the street. The 1.84″ burst of 17 July went into the street even where we had basins, because the rate exceeded soil intake.

Trees grow on these. The 4-hour saturation drive is exactly the slow-water condition mature mesquite, palo verde, and ironwood roots are evolved to tap. We see visible growth in our monitored trees in the two-week window after a slow soak that we don't see after a fast burst of equivalent volume.

No callbacks. The day after a slow soak we get zero service calls. The day after a 1.8-inch burst we get five.

Gauges

Field notes

Crew: full crew on a Catalina Foothills cistern install (the CF-002 build's first follow-up visit, post-commissioning). Sit-down lunch at 13:30, the rain started at 13:40, the crew watched the first hour from the truck. Antón measured infiltration in a freshly opened basin during a break — water sitting in the bottom for about six minutes before disappearing fully into the soil. June Walden had finished the controller installation that morning, ran the first telemetry-driven test of the system at 14:05, and watched the new tank fill from empty to 18% over the course of the storm.

Marisol drove the route across central Tucson at 17:30 to check on three other recent installs. None of the basins had overflowed; all had visible water that had drained completely by the morning of August 5.