Stormwater Tree Pits
Originally a component of the Rosedale Runoff Reduction Project, stormwater tree pits are being more broadly used in the Nine Mile Run Watershed. Street trees are excellent at intercepting rain that falls on their leaves, but with limited pervious space at their base, many are unable to absorb water at the optimum rate. Placed between the sidewalk and street, trees are typically bypassed by water in the street gutter, which is eventually carried to sewer systems with little interference.
Stormwater tree pits attempt to maximize the stormwater capture potential of trees by bringing them to street level and directing water over the pervious surface at their base. This allows water, solids and pollutants to drop out into the soil instead of continuing into the sewer system. Stormwater tree pits often include subsurface storage which further increases their capacity for water retention.
The first stormwater tree pits in the watershed were built in 2017 on Rosedale and Oakwood Streets in Homewood. These tree pits are of two different designs: individual flow-in/flow-out pits and a longer bioswale that includes multiple trees. These tree pits can intercept roughly 2,500 gallons per rain event, a capacity that will increase as the trees mature.
Funding
Richard King Mellon Foundation
Pennsylvania DEP
Cornelia Fund
The Heinz Endowments
PA Commonwealth Financing Authority
Metro 21
