Naturalized Storm Water Retentions

The increasing frequency and severity of short-duration, high precipitation events are challenging the way we think about sustainable urban surface water management strategies. Today, we are seeing more severe precipitation events in the amount of rain that falls in a storm – even though annual precipitation events are staying the same. This means that multi-day storms are increasing in frequency and extreme precipitation events are becoming more severe and damaging.

The conventional approach to urban surface water management has been to direct runoff into the urban drainage network. While this approach has been successful at removing water from roads and streams, it has contributed to greater stream bank erosion and sediment transport. Urban streams have subsequently been channelized with concrete to push water through the system more efficiently, resulting in increased downstream flooding in the lowland portions of the watershed. The shift away from conventional urban surface water management practices to more innovative and sustainable approaches are essential for mitigating flood risk and building more resilient communities.

Naturalized Storm Water Retentions

Naturalized urban storm water retentions are aesthetically pleasing urban design features, which utilize the ecological functions of wetlands to slow high water flows; reduce surface water runoff from urban and semi-urban areas; and mitigate the effects of downstream flooding. Naturalized wetlands improve water quality as they are vegetated with water loving native plant species. Native plant species contribute to a greater biodiversity in the local area, as well as provide natural habitat to a variety of waterfowl and amphibian species. The native plant species of naturalized systems also provide goose deterrence and management by limiting goose access from the water to grazing areas. Native plant root systems penetrate deep into the ground and clean the water as they absorb nutrients, degrade pesticides, retain sediments, and reduce pathogens as water infiltrates back into the soil for groundwater recharge.

Naturalized urban storm water retentions are a cost-effective alternative to conventional retentions because less soil is removed from a site; rock or soil does not need to be imported to a site; construction time is reduced; basin construction can occur during slower times of the year; maintenance of surrounding native grass uplands is a fraction of the cost of maintaining sod; and there is no maintenance required to remove or manage unwanted algal blooms or submersed vegetation. Conventional ponds require long-term algae management because they are susceptible to algal blooms as nutrients slowly build up in the system. Naturalized storm water retentions mitigate flooding risk in urban areas by utilizing the natural ecological functions of wetlands to reduce peak waters flows for sustainable surface water management in urban areas.

Changes in land use and climate show that conventional urban surface water management strategies must be adapted at the property, neighbourhood, and watershed scale in order to mitigate flooding risk resulting from population growth and development. Innovative next-generation technologies and methods, like permeable surfaces, rain gardens, and naturalized storm water retentions are intrinsic to the sustainability of urban surface water management strategies.

Resources:

Presentation by Native Plant Solutions at the Urban Storm Water Management Workshop, March 16, 2017, Steinbach, MB:

“Part 1: Naturalization Strategies & Solutions” and “Part 2: Naturalized Stormwater Design and Construction”