Tonight's scheduled lecture has been postponed. Rescheduled date will be announced soon.

As you walk on many of Philadelphia’s sidewalks, beneath your feet is a hidden world of streams that once crisscrossed the city. Join us tomorrow night, Tuesday September 27 at 7:00 p.m. at the Meadowood Retirement Community in Worcester for a free, fascinating illustrated lecture that will uncover part of Philadelphia’s history that few people ever think about: the drastic changes made in Philadelphia’s landscape since its founding in 1682. Historian and archivist Adam Levine (pictured sewer-spelunking, above) has been digging into the history of the city’s sewers and drainage systems since 1998, and his talk will focus on the systematic obliteration of hundreds of miles of surface streams. Buried deep underground in pipes as large as 20 feet in diameter, these former streams—some of which had watersheds that covered thousands of acres—became main drainage arteries in the city’s 3,000-mile sewer system. These massive alterations to the landscape, undertaken over two centuries, have environmental repercussions that are still being felt today. This lecture is guaranteed to reveal a side of the Philadelphia you have never seen, and change the way you think about cities in general.

Heavy rainfall in Philadelphia today may cause some flooding—try to keep your street's sewer inlets clear of debris and check out some flooded basement tips after the jump.

The Philadelphia Water Department's green infrastructure projects—tree trenches, rain gardens, porous paving and planters, just to name a few—are designed to store and infiltrate stormwater runoff into the ground. By keeping this water out of our sewers, we can prevent sewer overflows that damage the health of our rivers and streams. In the last month, Hurricane Irene and Tropical Storm Lee put our green stormwater projects to the test with periods of intense rainfall.

PWD's stormwater team monitored the performance of stormwater tree trenches, rain gardens, porous pavement, basins and stormwater planters at 10 different sites around the city during one or both of these storms. Some preliminary results are in, and it seems the green infrastructure has performed admirably. At the tree trenches located at Montgomery Avenue between Frankford and Blair streets in Kensington, sensors were placed underground to measure the water depth beneath the system.

The graphs below chart the depth during each storm, which is a rough indication of how much water is entering the system. As the water flows out and infiltrates the soil, you can see the blue line dip down; in the case of Lee, the multiple peaks in the graph indicate intermittent rainfall over the three days. The pink line represents the depth of the tree trench's storage system (i.e., the maximum depth before the system safely overflows into the sewer), which is 4.5 feet.

To find out where PWD has implemented or planned green infrastructure throughout Philadelphia, check out our Big Green Map.