Like many old cities in America, Philadelphia has a complicated relationship with rain.  Centuries ago this “greene country towne” was streaked by streams and covered by a thick blanket of vegetation that naturally filtered and absorbed storm water.  But much of the city’s green space has since been covered with pavement and its streams converted into a combined storm water/sewage management system.  The consequence is significantly more runoff from impervious surfaces funneling into a finite system of underground tunnels and pipes.  In other words, too much runoff causes the system to break down, forcing a combination of storm water and untreated sewage directly into the rivers.

Many cities have taken a “gray” approach to this problem, building additional capacity into its existing infrastructure.  But the Philadelphia Water Department (PWD) has opted for an entirely “green” approach and stands to save a lot of green in the process.  The plan?  Phase in policies that charge commercial property owners for the actual impervious area on their parcels and provide financial incentives to adopt storm water management practices (SMP), such as green roofs and porous pavement, to decrease runoff before it even enters a storm drain.

This is a massive undertaking for PWD and Azavea has played an important role in supporting it.  A critical component of this plan is to maintain an accurate record of impervious surface areas and property boundaries for the entire city.  Two Azavea GIS analysts have been working onsite with PWD to validate and make corrections to these extensive spatial data collections.

Philadelphia Water Department's Stormwater Billing Application

One of PWD’s goals was to make this fee restructuring as transparent as possible.  To that end, Azavea built the PWD’s Stormwater Billing application, PhillyStormwater.org, to allow property owners to see exactly how PWD is calculating their new storm water charges.  This web application lets users explore parcels on an interactive map, including high resolution ortho-photography, transparent overlays of impervious surfaces, and tools to do approximate measurements of length and area.  It also provides a charge summary for each parcel, detailing how each component of the bill was calculated and how it will be phased in over time.

Behind the scenes, PWD is running Azavea software to manage each financial credit issued back to its customers for every SMP added, ensuring that land owners are not being overcharged.  Our software is also tracking customer appeals so that data can be promptly corrected when errors are found.

As with so many things, what was old is new again.  It turns out that Mother Nature has been pretty good at managing storm water all along.  It is encouraging to see innovative agencies like PWD leading the way with sustainable, cost-effective solution for managing storm water.

More info:

• http://www.phillyh2o.org/creek.htm
• http://www.philly.com/inquirer/home_top_stories/20100205_A__quot_green_quot__city_plan_to_reduce_storm_water_runoff.html?viewAll=y
• http://www.nytimes.com/gwire/2009/12/24/24greenwire-citys-all-green-stormwater-plan-raises-eyebrow-45258.html
• http://www.nextgreatcity.com/actions/sewer