Tualatin Riverkeepers greening parking lot stormwater flows
Tualatin Riverkeepers is working with various partners to initiate a program to plant trees in parking lots for stormwater mitigation. The Tualatin River basin has more than 5000 acres in parking lots that cause runoff that erodes and pollutes streams. One of the goals of this project is to retrofit parking lots without losing parking capacity. Structural soils and linear tree wells designed by Maria Cahill of Green Girl Land Development Solutions a primary feature of the first two proposed project sites.
When it rains on asphalt or concrete, water runs off rather than soaking into the ground. This runoff carries pollutants from brake linings, tires, and automobile fluids, as well as other pollutants from the urban landscape. Nat Scholz at NOAA Fisheries has shown that copper from brake linings is very toxic to our native salmonids. Approximately 20% of impervious area in urban watersheds comes from parking lots.
Storm drains from parking lots are generally connected to a storm sewer system. In many areas, storm sewers dump into the nearest stream. Besides carrying pollutants to these streams, the runoff causes streams to rise quickly during storm events, eroding banks and stirring up sediments and legacy pollutants from the stream bed.
In many larger cities, including Portland, storm sewers connect to the sanitary sewers and go to a wastewater treatment plants. During storms, the combination of sewage and runoff is greater than the capacity of the system and a “combined sewer overflow” occurs, dumping into the nearest river. Text From: http://oregoncommunitytrees.blogspot.com/