ALBANY PARK — If Thursday's rain seemed relentless, it was.
A total of 1.67 inches fell, a record for March 30.
How does less than two inches translate into more than two feet?
According to a report from the U.S. Army Corps of Engineers, the North Branch of the Chicago River has a "flashy" hydrology, meaning the water level goes up very quickly during a storm and down quickly afterward. In 2007, for example, the river hit a record low of .45 feet in mid-July, and then reached 6.36 feet in late August.
Before the Chicago area was extensively settled, the river meandered across a marsh-like geography, dispersing water over a greater space. Precipitation was absorbed by vegetation and stored in the ground, wetlands and flood plains, according to the report.
As the area became more urban, green space was paved over, wetlands were drained and the river was straightened to better collect runoff that would have previously seeped into the ground. The result is a watershed with very little stormwater capacity, the report explains.