Inspection and Maintenance: Permeable Pavement

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Inspection & Maintenance Guidance of a built vstormwater best management practices that treats the stormwater that falls on them and can be designed to also receive runoff from adjacent impermeable surfaces (e.g., pavements and roofs) as either sheet flow or from a pipe (e.g., roof downspout) connected to the washed gravel base, where captured water is temporarily stored in the base where it later soaks into underlying native soil or sent to a municipal stormsewer/other BMP via underdrains (TRCA, 2016)[1]

Overview[edit]

Permeable Pavement Permeable pavements contain many small openings (i.e., joints or pores) that allow rainfall and snowmelt (i.e., stormwater) to drain through them instead of running off the surface as it does on impervious pavements like conventional asphalt and concrete. An overflow outlet is needed to safely convey flows during flood events. Depending on the permeability of the underlying soil and other constraints, the pavement may be designed with no sub-drain for full infiltration, with a sub-drain for partial infiltration, or with an impermeable liner and sub-drain for a no infiltration practice. The sub-drain pipe may feature a flow restrictor (e.g., orifice cap or valve) for gradually releasing detained water and optimizing the amount drained by infiltration into the underlying soil.

Associated Practices[edit]

  • Permeable Interlocking Pavers (i.e., Block Pavers) – Precast modular units made of concrete, pervious concrete or rubber/plastic composite designed to create open joints between pavers that are filled with fine, washed aggregate and installed on an open graded aggregate (i.e., clear stone) base and sub-base.
  • Permeable Interlocking Grid Systems (i.e., grid pavers) – Precast concrete or manufactured plastic grids with open cells that can be filled with aggregate or a mixture of sand, gravel and topsoil and planted with grass or low-growing ground covers and are installed on an open-graded aggregate base.
  • Pervious Concrete – a rigid pavement installed on an open-graded aggregate base that uses a cementitious binder to adhere aggregate together, similar to conventional concrete, except that the fine aggregate component is minimized or eliminated which results in the formation of connected pores throughout.
  • Porous Asphalt – a flexible pavement installed on an open-graded aggregate base that uses a bituminous binder to adhere aggregate together, similar to conventional asphalt, except that the fine aggregate component is minimized or eliminated which results in the formation of connected pores throughout.

Inspection and Testing Framework[edit]

Permeable articulated block system at the LSRCA headquarters in Newmarket, ON is designed for heavy loads. This example shows an appropriate pavement surface condition when conducting any of, construction, assumption, routine or verification inspections.
Visual Indicators Framework - Permeable Pavements

Component

Indicators

Construction Inspection

Assumption Inspection

Routine Operation Inspection

Verification Inspection
Contributing Drainage Area
CDA condition x x x x
Perimeter
BMP dimensions x x x
Filter Bed
Standing water x x x
Trash x x
Vegetation
Vegetation cover x x x x
Vegetation condition x x
Vegetation composition x x x
Underdrain & Monitoring Well
Monitoring well condition x x x x
Sub-drain/Perforated pipe obstruction x x
Outlets Overflow outlet obstruction x x x x
Pavement Surface Pavement surface condition x x
Pavement surface sediment accumulation x x x x
Control structure condition x x x x
Control structure sediment accumulation x x x x



Permeable pavement in need of maintenance as excess sediment and unwanted vegetation growth has begun to occur near the perimeter of the installation. Source: (TRCA, 2016).[2].
Testing Indicators Framework - Permeable Pavements

Component

Indicators

Construction Inspection

Assumption Inspection

Routine Operation Inspection

Verification Inspection
Testing Indicators
Surface infiltration rate testing x (x)
Natural or simulated storm event testing x (x)
Continuous monitoring x (x)
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

Construction Inspection Tasks[edit]

Performance Inspection of a Rain garden. Photo source: TRCA.[3]

Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done weekly and include the following:

  1. During site preparation, prior to BMP excavation and grading to ensure the CDA is stabilized or that adequate ESCs or flow diversion devices are in place and confirm that construction materials meet design specifications
  2. At completion of excavation and grading, prior to installation of pipes/sewers and backfilling to ensure depths, slopes and elevations are acceptable
  3. At completion of installation of pipes/sewers, prior to backfilling to ensure slopes and elevations are acceptable
  4. After final grading, prior to planting to ensure depths, slopes and elevations are acceptable;
  5. Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the storm sewer servicing, paving, building and landscaping contractors)
  6. After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure Erosion Sediment Controls (ESCs) and pretreatment or flow diversion devices are functioning and adequately maintained. View the table below, which describes critical points during the construction sequence when inspections should be performed prior to proceeding further. You can also download and print the table here
Bioretention/Swales: Construction Inspections

Construction Sequence Step & Timing

Inspection Item

Observations*
Site Preparation - after site clearing and grading, prior to BMP excavation and grading Natural heritage system and tree protection areas remain fenced off
ESCs protecting BMP layout area are installed properly
CDA is stabilized or runoff is diverted around BMP layout area
BMP layout area has been cleared and is staked/delineated
Benchmark elevation(s) are established nearby
Construction materials have been confirmed to meet design specifications
BMP Excavation and Grading - prior to installation of pipes/sewers and backfilling Excavation location, footprint, depth and slopes are acceptable
Excavated soil is stockpiled outside the CDA
Embankments/berms (elevations, slopes, compaction) are acceptable
Excavation bottom and sides roughened to reduce smearing and compaction
BMP Installation – after installation of pipes/sewers, prior to backfilling Structural components (e.g., foundation, walls) installed according to plans, if applicable
Impermeable liner installed correctly, if applicable
Installations of sub-drain pipes (e.g., locations, elevations, slopes), standpipes/monitoring wells are acceptable
Sub-drain trench dams installed correctly (location, elevation)
Landscaping – after final grading, prior to planting Filter bed depth and surface elevations at inlets are acceptable
Maximum surface ponding depth is acceptable
Filter bed is free of ruts, local depressions and not overly compacted
Planting material meets approved planting plan specifications (plant types and quantities)
Note: for Observation Column: S = Satisfactory; U = Unsatisfactory; NA = Not Applicable*
  1. TRCA. 2016. Fact Sheet - Inspection and Maintenance of Stormwater Best Management Practices: Permeable Pavement. https://sustainabletechnologies.ca/app/uploads/2018/02/Permeable-Pavement-Fact-Sheet.pdf
  2. STEP. 2018. Fact Sheet - Inspection and Maintenance of Stormwater Best Management Practices: Permeable Pavements. https://sustainabletechnologies.ca/app/uploads/2018/02/Permeable-Pavement-Fact-Sheet.pdf
  3. TRCA. 2019. Low Impact Development Stormwater Inspection and Maintenance Guide. https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/low-impact-development/low-impact-development-stormwater-practice-inspection-and-maintenance-guide/