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The Impact of High Densities on Watersheds

Feb 13


The Portland Tribune reports that Portland’s mania for high densities is imposing significant costs on the region’s watersheds. This has been an open secret in Portland for a long time.

Back in the 1960s, Oregon’s Willamette River was an open sewer. Cities like Eugene and Salem and various pulp mills and other industries poured untreated pollution in the river, so by the time it got to Portland, it was not safe to swim in and the fish were dead or dying. Before he ever ran for elective office, Tom McCall (who started out as a television news reporter) famously called on the state to clean it up, and it did, passing legislation requiring all cities and other point-source polluters to make the water they put in the river cleaner than any water that might take out. By 1980, the fish were back and no one hesitated to swim in the river.

The Environmental Protection Agency threw a monkey wrench into this when it required cities to treat storm sewer runoff (normally considered non-point source pollution). The EPA gave cities the option to tie their storm sewers into their sewage treatment plans knowing that major rain storms would overwhelm the plants, forcing the cities to dump storm sewage and untreated human sewage into the river. This is what Portland did, which meant that the Willamette is now clean only when it hasn’t rained recently.

Portland is now spending $1.4 billion to expand its sewage treatment capacity so that “combined sewage overflow” does not take place during rain storms. But, says the Tribune, this won’t be enough thanks to all the new residents Portland is packing in to its New Urban high-density neighborhoods. Density not only means more people flushing more sewage down the drains, it means less permeable area, such as lawns, to absorb the storm runoff.

A few years ago, the National Marine Fisheries Service published guidelines saying that, for watershed protection, new development should render no more than 10 percent of any acre impermeable. This demands low-density development; probably no more than one home every two acres. Portland simply ignored this rule because it did not fit into planners’ preconceived notions of “environmentally friendly development.”

High-density development is not a prescription for a cleaner environment. In many ways, it is harmful to the environment, and its impact on watersheds is one of them.


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Reprinted from The Antiplanner