Testing and Monitoring:

Optimal Green Infrastructure

Do you know how your green infrastructure is performing? The heart of the problem of underperformance might go all the way back to the initial design. Often traditional green infrastructure designs incorporate engineered soils with high infiltration rates, reducing the risk of standing water by rapidly passing it through the soil media and out the underground piping.

While those fast-draining rates might seem impressive, they often cause the soil around the vegetation to be too dry to sustain plant life — other than those unsightly weeds.

To best sustain your green infrastructure — and avoid costly maintenance, invasive weeds, and poor performance — thorough testing and monitoring, as well as an adaptive design, are critical. Testing during the design phase will estimate the water quantity and quality impacts to the downstream system, as well as ponding depths and soil moisture measurements. Most vegetation for green infrastructure has mature roots up to 3 to 7 feet below the surface, so monitoring the soil at those depths — rather than the filtration rate — will tell what moisture the plants are exposed to and give better insight on the total system’s performance.

It’s important to note that green infrastructure will not fully sustain itself immediately after installation, even with the best initial testing. Therefore, long-range monitoring of ponding depths and soil moisture provides important information on the movement of water in and through the green infrastructure with time. Infiltration performance should improve as maturing plants’ root depths increase and the native vegetation becomes more sustainable.

Knowing the soil moisture in and around your green infrastructure provides insight into how the design is performing for a range of real events. The monitoring process will show if the soil is too dry or moist, identifying any necessary retrofits to current or future designs.