Builders’ site design decisions, not roof and pavement area alone, drive suburban flooding.

Evidence

But the change in impervious surface was not the only important variable. Though the survey hydrologists hoped to provide a universal method of calculating the effect of urbanization on runoff, the task proved impossible: The increase in flood peaks was never a simple function of the increase in road, sidewalk, and roof area. Instead, the runoff in newly suburbanized watersheds depended on a variety of factors, including the design decisions of developers. Indeed, although the survey’s researchers rarely highlighted the role of builders, the evidence in the runoff reports added up to a serious challenge to the postwar pattern of development. … With the help of bulldozers, builders eliminated the natural drainage channels in subdivision tracts. They filled in creeks, brooks, and runs to create flat construction sites. In a watershed in a rapidly growing county outside of Washington, builders had destroyed 60 percent of the streams by the late 1960s. But the elimination of streams was problematic. “In most conventional urban developments,” a Geological Survey circular explained in 1971, “the land is stripped of much of its vegetation and divided into rectangular lots in a regular grid pattern. This method of development obliterates many of the smaller drainage channels, and they must be replaced by enclosed storm sewers. While the storm sewers are generally adequate to handle the runoff from minor and moderate storms, the sewers overflow during the occasional severe storm and flood streets and basements.” — Adam Rome, The Bulldozer in the Countryside, 805

Categorization

• XREF: connects to: Storm sewers reduce local flooding by worsening downstream flooding. — Adam Rome, The Bulldozer in the Countryside:…, 807; Landslides resulted from specific preventable builder choices, not natural accidents — Adam Rome, The Bulldozer in the Countryside:…, 678