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Landmark day Saturday, September 5, 1970

September 5, 1970: The Labor Day Flood

A tropical storm turns the dry wash into a mile-wide river, splits the city in two, and settles the flood-control argument forever.

What happened

The remnants of a Pacific tropical storm dropped record rain on central Arizona over the 1970 Labor Day weekend. Indian Bend Wash ran as a huge brown river through the middle of Scottsdale, flooding homes and streets, while the Arizona Canal overtopped. Families canoed intersections; the city was two cities for days. The storm killed nearly two dozen people statewide, most in the high country.

Why it matters

The flood ended debate about whether to engineer the wash — and set up Scottsdale's famous answer: not the Army Corps' concrete channel, but the grass-and-parks Greenbelt, begun in 1973, that became a national model for multi-use flood control.

Two decades of building across a riverbed

Indian Bend Wash was never a secret. It ran diagonally through the middle of town, dry nearly all the time, and every monsoon it reminded the new subdivisions that it was, in fact, a river. Scottsdale had spent the 1950s and 60s growing at a pace few American cities matched — from about 2,000 people at incorporation to 67,841 by the 1970 census — and much of that growth sat squarely in the floodway. By the late 1960s the Army Corps of Engineers had an answer on the table: a concrete channel, Los Angeles-river style, through seven miles of the city. Scottsdale hesitated. The channel would move the water, and it would also plant a fenced dead zone where the town’s geographic heart should be.

Then the sky forced the issue. When the remnants of the tropical storm arrived over the holiday weekend, the wash did exactly what washes do, at a scale nobody had allowed for — a mile-wide brown river where streets had been, the Arizona Canal overtopping its banks, families paddling canoes across intersections. Statewide the storm killed nearly two dozen people, most in the high country. In Scottsdale, for days, there were two cities separated by moving water.

Grass wins

The flood did not decide the outcome; it decided that there would be one. Nobody could argue any longer that the wash could be left alone, so the argument narrowed to concrete versus a counter-idea that sounded almost unserious: make the floodway a park. Citizens organized through the STEP forums, the Chamber, and a crew of insistent local advocates and planners pushed for a wide green channel — turf, lakes, ballfields, golf — that would flood gracefully a few days a year and host the city the other 360. After years of redesigns and bond votes the Corps came around, and construction on the Indian Bend Wash Greenbelt began in 1973.

Built in stages through the 1980s, it worked beyond anyone’s blueprints: eleven-plus miles of connected parks — Eldorado, Vista del Camino, Chaparral — that still carry every flood on schedule, host everyday Scottsdale the rest of the year, and still draw engineers studying how flood control became a city’s best-loved public space. The storm of September 5 is the reason the middle of Scottsdale is green. The rest of the year’s story is on the 1970 page; the full fight is told in the 1970s chapter.