|
Stormwater Control & Detention
Stormwater control is an important aspect of site design. Stormwater is naturally gathered, channeled, detained, absorbed or dispersed, and recycled through the watershed. Site development (e.g., the introduction of large expanses of buildings or impervious pavement, as well as topographic changes) impacts this cycle by interrupting or altering the water’s natural course. Effective stormwater control strategies can work with the site’s natural ecosystem, aiding in the return of stormwater from developed areas to its natural course of flow. Stormwater is efficiently channeled and dispersed, while pollutants are filtered, isolated, and disposed of responsibly. Good stormwater control measures result in less soil erosion, standing water, and impervious ground covering (e.g., large parking areas). These methods frequently result in lower development costs.
|
|
Natural drainage pattern, Central Lake, Antrim County
|
|
Natural Drainage Patterns
Maintaining natural drainage patterns and minimizing disturbances to a site’s vegetation can reduce the total runoff volume. Stormwater management techniques can incorporate natural features and designed systems to retain and manage stormwater on-site. Retaining existing vegetation, especially near wetlands and water bodies, helps minimize runoff; natural vegetation can also be used to filter stormwater on-site, making it available for reuse (e.g., irrigation).
|
|
|
Restored stream, Garfield Township, Grand Traverse County
|
|
Stormwater Runoff Reduction, Retention, & Reuse
Site design should include elements to reduce, retain, and reuse stormwater runoff on-site. This helps prevent flooding, as well as contributes to more affordable development costs and lower taxpayer contributions to stormwater system maintenance. Attractively landscaped, shallow basins retain stormwater and can be aesthetic assets to a site.
To reduce stormwater runoff, developments can incorporate natural drainage patterns, minimize impervious surfaces including roads and parking, and whenever possible include porous asphalt, pervious concrete, or other alternative paving. Since trees with large canopies catch ninety (90) percent of rainwater before it reaches the ground, preserving a site’s existing vegetation – especially mature trees – contributes significantly to a reduction in stormwater runoff. Refer to Critical Design Practices: Natural Landscape Character and Water Resource Protection for more information.
Methods for retaining stormwater include sedimentation basins, rain gardens, rain barrels, and engineered systems.
|
|
|
|
|
Rain Gardens
Rain gardens offer an attractive, low-maintenance method for collecting and filtering water, and they can be sized to fit a site’s specific conditions. Rain gardens are constructed with special soils and planted with native species that flourish in wetland conditions. Excess water from roofs, sidewalks, yards, streets, and parking areas is directed to the rain garden where the water seeps through the soil, and pollutants are filtered out.
|
|
|
Sedimentation Basins
Sedimentation basins can be used to retain stormwater runoff. Following a rainstorm, stormwater enters the basin – allowing the sediment to sink to the bottom of the standing water. If enough stormwater enters the basin, the “clean” water flows out via a drain. Otherwise, the water will percolate through the soil.
|
|
|
Plaza with pervious paving, Elk Rapids, Antrim County
|
|
Infiltration Techniques
Incorporating infiltration techniques into a site design minimizes stormwater runoff and assists in maintaining the natural drainage of a site. Infiltration techniques include swales, pervious paving (refer to Critical Design Practices: Parking for additional information), strategic grading, and bioretention islands.
Swales are open, vegetated channels which temporarily store water and allow pollutants to settle out, especially sediment. Depending on the site, they can be lined with vegetation or rocks, wet or dry. Swale design can include check dams to reduce the speed and thus the erosion potential of stormwater runoff, as well as enhance infiltration into the soil.
Bioretention uses plants and soils to capture, filter, and infiltrate stormwater runoff on-site at the source. Bioretention methods include specially designed parking lot islands, rain gardens, large vegetated retention areas, and small stormwater planters. Incorporating bioretention techniques improves water quality on- and off-site, something of critical importance to our region.
|
|
|
Filtration Techniques
In some instances, removing particles from stormwater is necessary and a site should incorporate methods for treating stormwater runoff on-site before it enters a storm sewer system or local watershed. Techniques include perimeter filters around paving areas, surface and underground sand filters, swirl technology, and sediment chambers.
|
|
|
Underground stormwater infiltration system beneath a parking lot
|
|
Engineered Systems
On larger sites or those with unique characteristics, engineered systems can be designed for below-ground stormwater runoff storage, infiltration, or both. Engineered systems can be more costly than traditional retention basins; however, they can reduce the space required for stormwater infrastructure and provide more buildable space on a site.
|
|
|
Key Points:
- Retain wetlands and existing drainage patterns as part of a natural stormwater and open space system to accommodate the natural flow of water. This will help reduce infrastructure costs and flooding frequency, as well as increase open space and wildlife habitat.
- Incorporate natural stormwater control systems to reduce development costs.
- Reduce the total amount of impervious surfaces and increase areas of vegetation. Driveways and parking areas should be designed to be as small as possible and constructed with alternative paving whenever possible.
- Select a method for retaining stormwater based on a site’s natural characteristics and intended usage.
- Include on-site detention and infiltration of stormwater runoff.
- Rainwater should be allowed to infiltrate into the ground as near as possible to where it falls.
- Include proper infiltration measures in site design. Swales channel stormwater above ground and facilitate stormwater infiltration on-site. Similarly, bioretention areas are both environmentally beneficial and aesthetically pleasing. Trees, shrubs, perennials, and grasses combined with different filtering layers (e.g., soil, sand, gravel) can enhance on-site stormwater infiltration.
- Incorporate filtration techniques to treat stormwater runoff on-site.
|
|
