Stormwater planters

From LID SWM Planning and Design Guide
Jump to: navigation, search
ShrubsShrubsPerennialsPerennialsGrassesGrassesForebaysOverflowMulchMulchOverflowBiomediaBiomediaUnderdrainsGrassesPerennialsShrubsLiner
This is an image map of a stormwater planterA vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration., clicking on components will load the appropriate article.
An above ground planter with downspout and overflow illustrated.

Over subsurface infrastructure, soils prone to subsidence, or pollution hotspots, it may be necessary to prevent all infiltration. These BMPsThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. can also be squeezed into tight urban spaces, adjacent to buildings and within the usual setbacks required for infiltrating facilities. Stormwater planters can also be used as a means of providing building-integrated LIDA stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. by capturing a portion of the rainwater from the rooftop. This type of cell can be constructed above grade in any waterproof and structurally sound container, e.g. in cast concrete or a metal tank.

Overview

Stormwater planters are an ideal technology for:

  • Sites which cannot infiltrate water owing to contaminated soils or shallow bedrock,
  • Zero-lot-line developments such as condos or dense urban infill.

The fundamental components of a stormwater planterA vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration. are:

  • a planting bed of storage media,
  • suitable vegetation,
  • decorative aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. or stone,
  • An underdrain

The design may benefit from:

Planning Considerations

Design

A flow-through planter comprises a ponding zone, mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. layer, filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. for planting, and a supporting gravel drainage layer

This article is specific to Flow-through stormwater planters, vegetated systems that do not infiltrate water to the native soilThe natural ground material characteristic of or existing by virtue of geographic origin..
If you are designing a planted system which does infiltrate water, see advice on Bioretention: Sizing.

The dimensions of a stormwater planterA vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration. are largely predetermined according to the function of the component. As they do not contain a storage reservoir the planters rely more upon careful selection of materials. Both the filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. and the perforations of the pipe play critical roles for flow control.

Component Recommended depth (with underdrainA perforated pipe used to assist the draining of soils. pipe) Typical void ratio (VR)
Ponding (dp) ≥ 300 mm 1
Mulch 75 ± 25 mm
  • 0.7 for wood based
  • 0.4 for aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.
filter media (dm)
  • 300 mm to support turf grass (and accept only rainwater/roof runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.)
  • 600 mm to support flowering perennials and decorative grasses
  • 1000 mm to support trees
0.3
Pipe diameter reservoir Is equal to underdrainA perforated pipe used to assist the draining of soils. pipe diameter 0.4
Pipe bedding (db) 50 mm (although commonly omitted altogether). 0.4

Calculate the maximum overall depth

Storage media

filter media

UnderdrainA perforated pipe used to assist the draining of soils.

Stormwater planters differ fundamentally from bioretention in that the storage function is provided only by the water retention capacity of the filter media. As such there is no storage reservoir and the only purpose to the aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. layer is to drain water to the perforated pipe. For this, a medium aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. as described in choker layer is recommended as it negates the need for a separating layer to the filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.. Underdrain

Planting

Stormwater planters routinely capture only rainwater flowing from adjacent rooftops. This means that salt may be less of a concern than in Bioretention: Parking lots or Bioretention: Streetscapes. The plant lists are still a good place to start when selecting species for LIDA stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. in Ontario.

Liners

A liner is sometime incorporated into non-infiltrating practices such as stormwater planters, or has also been applied in permeable paving installations where seperation from the native soils and groundwater was required.

  • Waterproof containment can be created using a plastic membrane/liner (HDPE or EPDM are common materials).
    • When the membrane is being used directly in the ground, punctures from stones can be prevented by compacting a layer sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. (30 - 50 mm) over the soil prior to installing the membrane.
    • Alternatively, a manufactured cushion fabric (geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.) can be employed for this purpose.
    • The top surface of the membrane must also be protected from stone and gravel being used for inside the BMPThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.. Again, sandMineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm. or a cushion fabric may be used.
  • When a pipe is used to provide drainage from the BMPThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. cell, a 'pipe boot' should be sealed to both the pipe and the liner to prevent leaks.

Surface

As stormwater planters are often quite small and receive very rapid flow, both a level spreader and the use of stone mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. are strongly recommended.

Gallery

Performance

Starting after TRIECA (end March) members of STEP will be undertaking a literature review on the performance of our most popular BMPsThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.. The results will be combined with the information we have to date from the development of the Treatment Train Tool and agreed performance metrics established. Until then, please feel free to continue to ask questions via email or the feedback box below.

Water quality [1][2][3]

See Also


Proprietary links

A number of precast modules exist to contain treatment media. As many of these systems are enclosed water balanceThe accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle. calculations may be erroneous where evapotranspiration is constrained. In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.


  1. Macnamara, J.; Derry, C. Pollution Removal Performance of Laboratory Simulations of Sydney’s Street Stormwater Biofilters. Water 2017, 9, 907.;doi:10.3390/w9110907
  2. Lucke, T., & Nichols, P. W. B. (2015). The pollution removal and stormwater reduction performance of street-side bioretention basins after ten years in operation. Science of The Total Environment, 536, 784–792. https://doi.org/10.1016/J.SCITOTENV.2015.07.142
  3. Macnamara, J.; Derry, C. Pollution Removal Performance of Laboratory Simulations of Sydney’s Street Stormwater Biofilters. Water 2017, 9, 907. doi:10.3390/w9110907