Macatawa Area Coordinating CouncilGreen Infrastructure Suitability
About Green Stormwater Infrastructure
Green stormwater infrastructure (GSI) are practices that manage stormwater (rain water) naturally. Natural pathways for stormwater include evapotranspiration from vegetation, infiltration into the ground and runoff from the surface into lakes and streams. In a natural setting, most stormwater will infiltrate, very little will runoff and vegetation will release water vapor from its leaves (evapotranspiration). However, urban development interrupts these natural pathways. Cutting down trees and building houses, offices, malls, and parking lots reduces evapotranspiration, decreases infiltration and increases the amount of surface runoff.
Image: US Environmental Protection Agency
One thing that remains constant is the amount of water. What changes is the pathways that it takes (see diagram above). There are negative impacts to these changes. More runoff means more water reaches our streams faster. It also picks up pollution from the land as it goes. More water rushing faster down our streams can cause streambank erosion and destroy habitat. Another impact is that less water infiltrates to recharge groundwater. Groundwater provides consistent flows to streams during dry periods. Urban streams may dry up during the summer months and then fill up quickly when it rains. Decreased groundwater recharge also limits our ability to withdrawal it for irrigation and drinking.
Green stormwater infrastructure modifies the urban environment so it behaves more like a natural environment. Green stormwater infrastructure practices capture runoff and allow it to infiltrate. Rain gardens and bioswales use vegetation to infiltrate stormwater. Large underground vaults can also capture stormwater and slowly infiltrate it into the soil beneath. Permeable pavements allow water to infiltrate through them instead of runoff. Some practices, like rain barrels or green roofs, captures water and stores it, reducing runoff without infiltration.
Images: US Environmental Protection Agency (rain garden, bioswale, permeable pavement, green roof) and Flickr (rain barrel)
Pictures from left to right:
- Rain garden – you can install these without an engineered design. Appropriate for residential locations.
- Bioswale – similar to rain gardens, but tend to be linear and require an engineered design. Appropriate for road right of way or commercial/industrial locations.
- Permeable pavement – there are many types, including permeable pavers (pictured), porous asphalt and permeable concrete. Must be engineered, but you can use in many areas, from driveways to parking lots to streets.
- Rain barrel – captures runoff from your roof that you can use to irrigate flower beds and gardens. You can connect multiple barrels together to store more water. Appropriate for residential locations, though large, commercial buildings can install larger cisterns.
- Green roof – highly engineered and best incorporated during the design of a new building. They tend to cost more initially, but last longer than a traditional roof, plus they help save energy.
Learn more about these and other GSI practices from the US Environmental Protection Agency.
Green Infrastructure Suitability
You can install most types of GSI just about anywhere, but there are certain characteristics that make a site better suited for GSI. This is especially true for infiltration practices. Soil characteristics and slope can either encourage or discourage infiltration and runoff. Therefore, it is important to know where conditions are suitable for GSI if we want to make sure they will function correctly. It is possible to engineer GSI to work on less suitable sites, but that could increase the cost.
The MACC, with funding from the Community Foundation of the Holland Zeeland Area, developed a Green Stormwater Vision for the Macatawa Watershed in 2017 (design concepts). As part of this vision, we developed a green stormwater infrastructure suitability model for the watershed. The model was developed in ArcGIS and used soil characteristics, slope and existing building footprints to determine if individual parcels are high, medium, low, or not suitable for GSI (infiltration practices). We updated the model in 2019 to include all of Ottawa and Allegan County. Individual maps for each township and city are below. We also created an instructional guide for anyone that wants to conduct this analysis for another location. This analysis is intended to be an initial screening tool for including infiltration GSI on a site. You should conduct further on-site analysis prior to designing or installing infiltration practices.
