Healthy urban trees can reduce the amount of runoff and pollutant loading in receiving waters in the following ways:

• Leaves and branch surfaces intercept and store rainfall, thereby reducing runoff volumes and delaying the onset of peak flows.
• Root growth and decomposition increase the capacity and rate of soil infiltration by rainfall, and reduce overland flow.
• Tree canopies reduce soil erosion and surface transport by diminishing the impact of rain drops on barren surfaces. The roots also secure soil, which would otherwise flow into the sewer system and waterways of Cleveland.
• The expanded tree lawns and tree pits necessary for healthy street trees also decrease the proportion of impervious cement and concrete surfaces in the city, which encourages more rainwater infiltration, reducing treatment costs and downstream pollution.

Findings

Every year, Buckeye-Shaker Square's street trees prevent approximately 638,944 gallons (85,414 ft³) of stormwater from infiltrating into the wastewater treatment system. This values out at $5,710 per year in foregone sewage treatment costs. This amounts to an average savings of about $7.69 per acre and $2.15 per tree. Among all species, Norway maple remediates the highest volume of peak stormwater flow. On a per-tree basis, however, tulip tree remediates the highest volume of peak stormwater (110 ft³ tree/year).

Cudell's street trees prevent approximately 480,587 gallons (64,245.25 ft³) of stormwater from infiltrating into the wastewater treatment system. This values out at $4,295 per year in foregone sewage treatment costs. This is an average savings of roughly $6.15 per acre and $2.72 per tree. Of all the species in Cudell, London planetree is the hardest-working tree with respect to remediating peak stormwater flow. London planetree tops the list both as an overall species and on a per-tree basis (105 ft³ tree/year).

Stormwater Savings