Cities are often constructed from materials which are waterproof, often called gray infrastructure. To offset the negative consequences of large areas of gray infrastructure, we use urban conservation practices to control rainfall runoff and flooding.
Rural conservation practices in Iowa are usually added to private land. Conservation practices allow farmers to protect their soil and water.
Traditional stormwater management, such as gray infrastructure, aim to drain the landscape of rainfall as quickly as possible. Runoff flows into the street, along the curb, and into a gutter where a system of underground pipes whisks it away to the nearest waterbody – regardless if it’s a sprinkle or a major storm event.
Until recently, this was the only approach to stormwater management, which strictly relied on “gray” infrastructure to protect communities from flooding. However, this approach does not address all stormwater concerns, and with innovations in technology, other “green” methods have been developed to address these water quantity and quality issues.
Most communities in Iowa adequately manage the Qp and Qf level storms. In order to improve Iowa’s water quality and provide additional protection from flooding, further management of WQv and CPv classes is needed.
When planning and designing for post construction stormwater management, consideration should be given to both water quality and water quantity (flood control). The Unified Sizing Criteria in the Iowa Stormwater Management Manual (ISWMM) provides a comprehensive approach to managing stormwater, from the more frequent and smaller rainfall events, to the less frequent flooding events. Design specifications for all storm events can be found in the ISWMM posted on the Iowa DNR website.
Site conditions and treatment goals dictate which green infrastructure practices are implemented in series since each method targets different rainfall events. Implementing a train has the potential to greatly reduce the quantity of discharge and pollutants leaving a site.
Long-term inspection and maintenance is critical to ensure proper performance and aesthetics of GI practices. Project plans should include short and long-term maintenance schedules and property owners should be educated about typical design features to perform typical maintenance tasks.
Green Infrastructure (GI) practices, such as bioretention cells, are engineered to capture, infiltrate, cleanse, and detain the rain. The practices are also considered “Best Management Practices” which have available funding for cost-share.
One example of a treatment train might include biocells in a subdivision that drain to a bioswale system, which then discharges to a retention pond or wetland. In an ultra-urban area, where space is at a premium, a treatment train could consist of a green roof, permeable pavers, and plant filter boxes that eventually discharge to an underground detention system for larger rainfall events.
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Polk Soil and Water Conservation District
1513 North Ankeny Blvd., Suite 3
Ankeny, IA, 50023
Polk Soil and Water Conservation District is an Equal Opportunity Employer and Provider.
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