Construction

Overview

• Importance of construction inspections
• Contractor familiarity
• What you can expect from STEP guidance: practical advice, specific to LID, practical advice on how to ensure successful construction
• LID types and construction sequencing

Construction stages

STEP divides the construction process for LID practices into five over-arching stages:

1. Pre-construction
2. Excavation and grading
3. Sub-surface components
4. Finishing grades: inlet, outlet, and surface layer
5. Post-construction]

Stages 1-3 and 5 of the LID construction process are fundamentally similar for all surface-level LID types (bioretention, bioswales, enhanced grass swales, permeable pavements, infiltration chambers, infiltration trenches, soakaways, etc.). To illustrate, STEP's recommended processes for excavation do not differ depending on the practice type. Excavation is excavation, whether it is for a bioretention garden or a permeable pavement parking lot. On the other hand, stage 4 sub-tasks will vary substantially from LID type to LID type, as do some sub-tasks in stage 3. The following gives a brief description of each over-arching stage and links to the page dedicated to each construction stage.

Green roofs, blue roofs, and rainwater harvesting systems have specific construction requirements. One day we will write guidance for these LID practices as well

Pre-construction

Pre-construction activities set the stage for the successful construction of an LID practice. The pre-construction page gives guidance on:

• design verification and site walk-through
• LID construction notes
• tendering and contract
• communication, inspection plan, and utilities coordination
• erosion and sediment control measures
• mobilization, access, staging, and perimeter controls

Excavation and grading

Excavation and grading are necessary for installing LID practices with sub-surface components, re-grading land to hold more water, and re-routing overland flow routes into an LID practice. The excavation and grading page gives guidance on:

• clearing and grubbing
• excavation and rough grade
• sub-grade
• final excavated grade and verification

Sub-surface components

Many LID practices rely on sub-surface features--gravel storage reservoirs, liners, underdrains, monitoring wells, etc.--to function. The construction process for sub-surface components works from the ground up. While some LID practices include all the sub-surface components listed below, most designs will not include one or more of these layers. Also, permeable pavement types can have different construction requirements at this stage, mostly regarding compaction of sub-surface layers.

The backfill granular, utilities, and pipes / sub-surface components page gives guidance on:

• geotextile
• underdrain
• impermeable liners
• overflow
• monitoring wells
• storage reservoir
  • sub-base reservoir (permeable pavements)
  • base course (permeable pavements)
• stone choker layer
• curbing
• pre-treatment and inlet

Finishing grades and surface layer installation

This construction stage differs between LID practice type. The finishing grades and surface layer installation page has guidance for vegetated LIDS (bioretention, bioswales, enhanced grass swales, and vegetated filter strips; can also include infiltration chambers/trenches/soakaways, depending on the design) and permeable pavements.

• soil media installation and soil amendment
• finish grading
• large stone and riprap
• plant verification and installation
• mulch placement
• stabilizing contributing drainage area and planting adjacent vegetation
• as-built survey

Stage 4 guidance for vegetated LIDs and permeable pavements

LID practices with vegetated surfaces	Permeable pavements
*geotextile (if applicable)	PP
*underdrain	PP
*impermeable liners	PP
*overflow	PP
*monitoring wells	pp
*storage reservoir	PP
stone choker layer	PP
curbing	PP
*pre-treatment and inlet

Post-construction

If you assume the works too early, u make an ass out of me.

LID practice pages

Each construction page listed below :)

8008

Sustainable Technologies Evaluation Program

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.

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 shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

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.

Open space floodway channels, road reserves, pavement expanses and other flow paths that convey flows typically in excess of the capacity of the Minor Drainage System.

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.

An underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

The practice of adding organic material, such as mulch or compost to topsoil to improve fertility, and tilling of the native soils to reverse compaction and restore its water retaining capacity.

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

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.