A different group of engineers, planners, and landscape architects came to the same conclusion when evaluating potential improvements for two other interchanges, and suggested that implementation be pursued through multi-stakeholder cooperation and integrating the project into a larger municipal or state construction project. They also explored the option of directing compensatory wetland or stream mitigation, which ODOT may be required to do in the future anyway.
In 2004, Washington State analyzed how roadside vegetation affects pollutant levels. The study found that vegetation cover needs to be at least 80%, and that highway width and hydraulic residence time has little or no impact on discharge concentrations.
Ditches, foreslope areas, pervious infield areas, and other underutilized spaces present the richest opportunities for improving water quality. Solutions range from mowing, rerouting discharge to the area, and introducing potential water quality banking areas to structural BMPs like bioretention basins, rain gardens, vegetated medians, vegetated bioswales, and infiltration planters.
Next Page: ODOT’s interchange opportunities
ODOT’s interchange opportunities
ODOT oversees 43,211 miles of public roads and 1,074 interchanges. The first thing we did was categorize interchange design and the unique ways stormwater enters each:
Clover leaf (about 343). Provides the most space for stormwater management, but further study required to determine water quality potential.
