Storm water infrastructure – be it pipes, ponds, or rain gardens – is typically designed to convey or capture runoff flows associated with a design storm, the magnitude of which is based on a probability distribution of observed rainfall events (Weather and Climate 101).
One of the underlying assumptions of this design approach is that the rainfall probability distribution is static. However, recent climate trends across much of the country indicate large events are occurring with greater frequency, casting doubt on the notion of a rainfall distribution that is static in time and that storm water infrastructure designed by our current design storm approach can be expected to provide the intended level of service throughout its lifetime. Something that our community experience firsthand in April 2014 with an extreme rain event that caused catastrophic impacts to homes, businesses and roadways. Is this an indication of more things to come?
According to climate researchers from Antioch University, the upper Midwest is one area of the country where large events have been observed with greater frequency in the recent climate record. In response, the University of Minnesota has teamed with the Minnehaha Creek Watershed District, the cities of Minneapolis and Victoria, and climate researchers from Antioch University and Syntectic International to evaluate potential impacts to storm water infrastructure due to climate change. They are using the EPA Storm Water Management Models to examine the effects of a range of midcentury precipitation scenarios, derived from regionally downscaled global climate models, on the existing storm water infrastructure in two case studies: (1) a built-out residential pipe shed in South Minneapolis and (2) the growing community of Victoria located at the urban-rural fringe of the metro area.
According to climate models, the current 10-year storm by which the storm sewer network in these communities was designed is expected to increase 25 percent (5.1 inches) to 150 percent (10.1 inches) by the mid-21st century under moderate to pessimistic emissions scenario.
Using this range as rainfall input in EPA SWMM, they are seeking answers to the following questions: Can we make informed, local-scale infrastructure adaptation decisions in the midst of uncertainty surrounding long-term climate projections? How resilient is the existing storm water infrastructure to projected changes in precipitation? To what extent is flooding expected to increase in these communities? How do we predict changes in climate interact with predicted population growth and development patterns in our communities? Can storm water systems be adapted (e.g., through pipe upsizing or increasing the infiltrative capacity of the landscape through Low Impact Design/Development to provide a similar level of service under mid-21st century climate projections? What are the costs of adapting (or not adapting) storm water infrastructure? These are questions we too have been asking ourselves these last few months.
In addition to examining these questions, they have initiated a public outreach program aimed at engaging local stakeholders in community-driven adaptation planning for storm water management. They've held several workshops in Minneapolis and Victoria, and are developing a framework from which other communities can proceed with their own adaptation planning process. While the adaptive process will hold many commonalities across communities, the actual measures adopted may look very different. For instance, as indicated by their modeling for this project, adapting Minneapolis' existing storm water system to a "most-likely" mid-century precipitation scenario will require a combination of pipe upsizing, detention (likely in the form of underground storage), and infiltration. The projected costs for these upgrades ranged from $40 million to $70 million across the 1,100-acre pipe shed.
In contrast, Victoria's existing storm water network was found to be relatively resilient to projected precipitation increases; even under the most pessimistic climate scenario, excess flooding could be contained completely in streets below the curb elevation or within public open spaces such as parks and golf courses. The resiliency of Victoria's storm water system can be attributed to development policies such as buffer setbacks and wetland conservation that have acted to preserve ecosystem services related to hydrologic regulation.
The point of all this? Well, as we learned with the presentation from David Waggoner at IHMC on July 16 and at the city-county storm water symposium on July 18, we can learn from other communities on how we can implement strategies within our own community and watershed that addresses effective storm water management.
Within the last few months we have made great strides in identifying and addressing key storm water issues and concerns with the implementation of the city-county Storm Water Advisory Team and work currently being conducted by Arcadis.
We have already taken steps to address some of these issues with places like Admiral Mason Park and Corrine Jones Park. We still have work to do, but that's OK, we'll get there. Our approach needs to be multifaceted and holistic; we can't piecemeal our approach or it won't be effective. We need to look at our basins from a big picture view. If we just focus on the southern portion of the basin we will not efficiently address the issue. We start in the northern portion of basin addressing storm water before it even gets to the southern portion of the basin.
And the approach should encompass a multitude of storm water management strategies … rain gardens, pervious pavement and more.
Our initial focus should be on retrofitting and upgrades for existing, grandfathered structures, but not with just a Band-aid approach or the status quo. That no longer works, never has. Let's do things differently. Connecting with the community has been a strategy in help determining the best approach. Kudos to all those who have been involved and engaged in this endeavor; it's important for all us to have a seat at the table.
Here's some food for thought as we move forward with our storm water management issues and growth in general: Perhaps it's time that we revisit how we build (or rebuild). Through the implementation of Low Impact Design/Development we can manage storm water in a way that works better than traditional means. LID is an approach to land development (or re-development) that works with nature to manage storm water as close to its source as possible.
There are several economic and environmental benefits associated with LID.
Some of the ecological benefits include:
The LID site planning process sets aside key natural features and focuses development into clustered patterns on the remaining land.
The LID planning process results in housing that makes more efficient use of land and conserves critical natural features such as wetlands, vegetated buffers, and drinking water protection areas.
The reduction of impervious surfaces reduces the amount of surface runoff and through the infiltration of storm water, recharges the groundwater system, thereby restoring the natural hydrologic cycle. This preserves groundwater supplies and base flow to streams and wetlands.
Economic benefits include:
LID can increase property values.
LID provides important benefits to the municipality, the developer, and the general public.
LID reduces nonpoint source pollution.
LID reduces demand on public storm water infrastructure.
LID promotes recharge to and the preservation of aquifers.
LID reduces building costs.
LID will help considerably with addressing storm water. Improved storm water conditions means improved water quality.
We need a management strategy that sufficiently addresses historical, present, and future (potential) storm water management issues and concerns. The initial cost might be greater upfront, but it'll be worth it to protect people's homes and businesses. It's pay now or pay later. Let's do what's best for the community as a whole.
Gutierrez is executive director of Earth Ethics Inc.