Stormwater calculator

The Benefits of Stormwater Calculator and Green Infrastructure Benefits

Written by: Brandon Hunt

WMEAC and GVSU have spent more than a decade on valuing ecosystem services.  These “ecosystem services” are the benefits that society receives from the environment. Examples of ecosystem services include timber, pollination of crops and flowers, climate regulation, water storage and flood prevention, and riverbank stabilization.

For the last two years, we have been developing an online tool that calculates the costs and benefits of these ecosystem services associated with stormwater green infrastructure in West Michigan and the Great Lakes Basin. We partnered with Michigan Tech to develop the online interface for, which strives to help community leaders and planners, as well as property owners, understand and value the full spectrum of benefits that can be provided to communities via stormwater green infrastructure applications that capture rainwater close to where it falls. This project was funded by the USDA Forest Service through the Great Lakes Restoration Initiative.

Cities, townships, and county drain districts own stormwater infrastructure that is worth millions. Traditionally, grey infrastructure – drains, pipes, water outlets, and storage sites – has been designed to convey water off of productive land intended for development or agricultural uses, and to protect community health and safety against flooding. Across the country, a difficult decade for the economy, along with failures of aging stormwater systems, have called attention to the cost of stormwater infrastructure for our communities. For example, in Grand Rapids, existing stormwater infrastructure is valued at $533 Million. The City is aiming to spend over $10 million annually on maintenance and capital investments from the stormwater budget, with an additional contribution to stormwater infrastructure through the annual streets budget. This level of investment, in comparison to overall need, is graded at a ‘Level of Service C’, indicating that this is a moderately acceptable level of investment.

Best practices in water and infrastructure protection call for the increased use of green infrastructure. Green infrastructure includes things such as porous asphalt, rain gardens, green roofs, natural areas, trees, and rain barrels. These types of installations can provide long-term savings and economic benefits to cities. Long-term savings can include lower maintenance costs, reduced risk of flooding, and better control of stormwater runoff issues like sediment and nutrient pollution. Economic benefits include environmental benefits such as reduced runoff and less pollution, as well as a positive return on investment in some cases.

The Rainwater Rewards stormwater calculator can show on a case-by-case basis which green infrastructure practices work best for different locations or property types. A user simply needs to know the property type or location, the type(s) and size or number of the green infrastructure being considered, and size of the area draining into the green infrastructure practice. The calculator will compute the return on investment which includes costs and benefits of implementing the selected green infrastructure, as well as the reduction in stormwater runoff. Advanced settings offer the opportunity to provide additional details such as implementation cost or specific pollution reduction goals.

“The calculator was designed to help property owners decide if green infrastructure makes sense for their location, depending on what their goals are,” said Elaine Sterrett Isely, WMEAC’s Director of Water Programs. “Rainwater Rewards provides basic information about costs of implementation and maintenance, the benefits to the environment, and the ultimate return on investment over 50 years. Technical details about how the calculator works can be found on our website in our white paper.”

If you or your community are interested in learning more about this tool, WMEAC is developing training workshops, which can be offered for a limited time for free. These workshops will walk users through the basics of the calculator, and provide guidance as to how to use the results. Workshops are currently scheduled in Grand Rapids on May 2nd and in the greater Milwaukee area on June 9th. Registrations for these workshops are available on our website:

If you would like to schedule your own workshop, please contact WMEAC at

1 reply
  1. Taylor Bishop
    Taylor Bishop says:

    Thanks for the interesting read about storm water calculators and green infrastructures. I actually had no idea that this calculator could show what kind of infrastructure practices are the best in different locations. I wouldn’t mind learning some examples of this, like some general calculations in colder or drier climates.


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