Bioretention: Construction

This section is also applicable to: Bioswale Rain garden

Construction Tasks Table

Construction Task	Bioretention	Bioswale	Rain garden
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Construction Tasks Described

Pre-Construction (KM)

Verification of Siting and LID Design
Installation of ESC and Construction Fencing
ESC Inspection and Maintenance (ongoing)

Excavation and Mass Grading (KM)

Clearing and Grubbing
Excavation
Rough Grade
Verification of Grading/Survey*
Scarification

Backfill Granular and Pipes (JC)

Geotextile
Impermeable liner
Underdrain
Overflow or Overflow Drain
Monitoring well

Backfill Granular and Pipes (SPC)

Storage Reservoir
Stone Choker Layer
Curbing
It is very important to make sure that the contractor responsible for curb construction understands curb cut designs and elevations. This is often a new technique for contractors and they may not understand the overall concept of water in the gutter line being directed behind the gutter.
Common mistakes to avoid:

• Elevated curb cuts and reverse slopes (sloping from back of curb towards instead of depressing from gutter line towards the back)
• Curb cut size (width)
• Placement of curb cuts on steep slopes or the down slope side of a catchbasin

Pre-treatment and Inlet
Pre-treatment structures are most cost effective when they slow down incoming flows, collect sediment for easy clean out, and release water to the bioretention facility in a non-erosive way. Some pre-treatment structures/strategies include:

• Vegetation: If sized correctly, it works more effectively in areas with more dispersed flow. However, in concentrated flow and sediment areas it might not be the best option. Sediment removal can be more difficult in areas of dense vegetation. An advantage of using vegetation as pre-treatment is that it can be easily integrated into the landscape design.

Soil Media / Filter Media

Finishing Grades: Inlet, Outlet, Biomedia, Plants (SPC)

Finish Grading
The finish grading process is anoter critical handoff moment as a number of elements such as curbs, sidewalks, soils and vegetation start to come together to create the functional and aesthetic value of a site. The same supervision and communication that was put into controlling ESC in earlier stages is also required during finish grading. In many cases, more attention to detail is needed for elements in this phase that will create or not the success of the final product.

Riprap (Large Stone)
Plant Material Verification and Installation

Mulch Placement
Stabilizing Contributing Drainage Area - Planting Adjacent Vegetation

Finishing Grades: Inlet, Outlet, Biomedia, Plants (JC)

As-built Survey

Address Deficiencies and Assumption Protocols (JC)

Permanent Fencing
Identify and Address Deficiencies
Assumption/Certification

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

Low Impact Development. A 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.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

Filter 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.

A perforated pipe used to assist the draining of soils.

Box like underground concrete structure with openings in curb and gutter designed to collect runoff from streets and pavement.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.