What IS "Green Infrastructure?"
“Lay of the land” is an old idiom that originally refered to the natural features of a geographic area, now used to mean the existing situation. For our ancestors, it was the starting point. We know some farmers changed the courses of small rivers, or dug and installed drain tiles to change the flow of waters from soil below the surface. In our modern day, we pipe storm drains and storm sewers, and dig drainage ditches to direct rainwaters away from areas we wish to keep dry. We have dumped our stormwaters into nearby rivers, lakes and creeks. We have drained our wetlands – our natural sponges – to build houses and commercial buildings, built roads that may or may not block natural drainage. And we tax ourselves in ever increasing amounts to continue to build and maintain these structures. Is there a better way?
According to the U.S. EPA, “Green infrastructure” refers to a variety of practices that restore or imitate natural hydrological processes. While “gray” stormwater infrastructure is largely designed to carry stormwater away from the buildings and pavements, green infrastructure uses soils, vegetation and other media to manage rainwater where it falls through capture and evaporation from soils or transpiration from plants. By integrating natural processes into the built environment, green infrastructure provides a wide variety of community benefits, including improving water and air quality, reducing urban heat island effects, creating habitat for pollinators and other wildlife, and providing aesthetic and recreational value. Green infrastructure is a scientific approach to determine the best use of the land to support both the natural processes that exist on the landscape, and the infrastructure and recreational needs of the people who live there. The best news is that taking advantage of nature’s natural inclinations can reduce the costs of maintaining the infrastructure, and reduce the negative effects of undermining these natural tendences on neighbors or downstream.
The flows of water is a main focus for planning, as flood control and disposition of storm water are major considerations. Knowing the elevation of lands assists in estimating how waters will flow. Hydric soils are soils in which water remains at or near the soil surface for extended time periods, and also favor the formation of many types of wetlands. Wetlands are useful because they generally occupy deptressions in the landscape, so they can trap and detain flood waters, slowing their progress downstream and reducing damages. That’s why there is now regulations focussing on ways to conserve and rehabilitate wetlands, our natural sponges. Because they are formed in association with wetlands, hydric soils are often used to identify the presence and boundaries of wetlands. Of course, over our history, we have drained many wetlands and built on that land. Still it makes sense to understand our soils and topography so that future development can leverage natural systems, rather than investing in infrastructure that tries to prevent water from flowing where it naturally seeks to go. Infrastructure that leverages natural systems are also less expensive to maintain.
It’s useful to know where there are soils that are highly erodible, as those are the areas most susceptible to rainwater runoff, which then pollute our waterways with silt, adding to the total suspended solids, which can block sunlight for desireable water plant growth and cover aquatic spawning areas. A form of erosion called sheet erosion is the washing away of soil in thin layers by raindrop impact and shallow surface flow. It results in the loss of the finest soil particles which contain most of the available nutrients and organic matter in the soil. It can happen very gradually, but over time can result in very large soil losses.
The biggest challenge with developed areas is the amount of impervious surface – roofs, roads, parking lots, sidewalks, patios – that commercial and residential building represents. Impervious surfaces shed water fast – onto lawns, roadside ditches, into stormwater drains and from there, into our creeks, rivers and lakes. That runoff picks up dirt, grime, oil and grease and carries them into our waterways. Infiltration falls – more watering is needed to sustain lawns and plantings, less water trickles down to our aquifers, our area’s source of water.
What should be our strategy? Aside from smarter future development, the name of the game is to SLOW DOWN the water! There are many tools available to do this.