On St. Patrick's Day in 1936, Pittsburgh was greeted with the worst flood in its 171-year existence.

Nearly 2 inches of rain fell on March 16, which added to the 63 inches of snow that came during the winter.

Above-normal temperatures melted the snow, swelling creek beds along the upper Allegheny and Monongahela rivers. On St. Patrick's Day, the rising rivers reached the North Side and washed into the streets of Downtown, wiping out historic businesses within hours.

By night's end, river levels reached a peak of 46 feet at the Point, more than 20 feet over flood stage, leaving more than half of Downtown businesses under water.

By the time the waters receded, the St. Patrick's Day Flood of 1936 claimed 60 lives, with more than 500 Pittsburghers injured and another 135,000 residents left homeless. About 100,000 buildings were destroyed, causing more than $250 million in damage.

Levels of the 1936 flood lines can still be seen on some buildings throughout Downtown. The entire Northeast was badly affected by the flooding.

The U.S. Senate immediately opened hearings on a flood control bill, later known as the Flood Control Act, which was introduced by the House of Representatives the year before. It was passed on June 22, 1936.

Doug Oster writes a blog, "Growing With Doug," exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.