Inspection and Maintenance: Rainwater Harvesting

Inspection & Maintenance Guidance of Rainwater harvesting/cisterns best management practices. Rainwater harvesting is the practice of collecting, storing and making use of stormwater from roofs. Relatively clean roof runoff water is collected by eavestroughs or other types of roof drains, filtered to remove coarse debris, and conveyed to a structure where it is stored and drawn upon for purposes not requiring potable water (i.e. landscape irrigation, outdoor washing needs, fire suppression and toilet flushing (TRCA, 2018).

Overview

Rainwater harvesting/cisterns uses storage structures that can be installed either:

• Below-ground;
• Indoors that provide a year-round water source; or,
• Aboveground tanks and rain barrels that can only be used seasonally and must be taken out of service for the winter.

Rainwater cisterns can range in size from about 750 to 40,000 litres+ and may be constructed from fiberglass, plastic, metal or concrete. Underground cisterns are most often installed to a depth below the maximum frost penetration depth (generally 1.2 m in Southern Ontario) (Armstrong and Csathy, 1963; Ministry of Transportation, 2013) to ensure they can be used year-round. A pump is used to deliver the stored water to the hose bibs or fixtures where it is utilized. Water that is in excess of the storage capacity of the cistern overflows to an adjacent drainage system (e.g., other BMP or municipal storm sewer) via an overflow outlet structure and pipe. Cisterns that are drawn upon for indoor water uses (e.g., toilet flushing) will also feature water level sensors and the means of adding municipal water during extended periods of dry weather or winter when stormwater does not meet the demand (i.e., make-up water supply system). They may also include in-line devices to filter stored cistern water prior to delivery at hose bibs or fixtures.

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  Frost penetration in southern Ontario shown to be 2 - 4 ft. deep (Armstrong and Csathy, 1963).

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  Design depth showing further detailed frost penetration contour lines for southern Ontario ranging from 1.0 - 2.0m deep (Ministry of Transportation, 2013)

Generalized cross-section view of a rainwater harvesting system showing key components of a commercial configuration of this LID BMP (TRCA, 2018).

Some of the benefits of green roofs include:

• The ability to reduce the quantity of pollutants and runoff being discharged to municipal storm sewers and receiving waters (i.e., rivers, lakes and wetlands);
• Underground and indoor cisterns can be used year-round and located below parking lots, roads, plazas, parkland, landscaped areas or within buildings themselves.
• Can reduce a large commercial building or residential home's water usage significantly if used for non-potable needs
  

Key components of Underground Infiltration Systems to pay close attention to are the:

• Inlets
• Rain Barrel or Cistern|
• Pump
• In-line filters
• Overflow outlets

Associated Practices

• Rain Barrels Rain barrels are an above ground form of rainwater harvesting, typically used in residential settings. The precipitation flows from the roof, to the guttering and down the downspout before being diverted to the rain barrel for storage.
• Downspout disconnection Downspout disconnections are common in many older urban centers. They require that residents retroactively disconnect their downspouts from the municipal sewer system. This is due to older sewer systems being undersized for the combined flow of sanitary waste and stormwater.
• Blue roofs are systems that temporarily capture rainwater using the roof as storage and allow it to evaporate and/or to be used for non-potable requirements (i.e. irrigation, toilet flushing, truck washing) and ultimately offset potable water demands.

Inspection and Testing Framework

Visual indicator to be used when assessing the condition of a pretreatment device (in this case a downspout disconnection with attached filter) so that leaves and detritus from the eaves do not enter the Rainwater harvesting LID feature. Source: (STEP, 2018).

Visual Indicators Framework - Rainwater Harvesting Systems

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Contributing Drainage Area
	CDA Condition	x	x	x	x
Inlet
	Inlet/Flow spreader structural integrity		x	x	x
	Inlet/Flow spreader obstruction	x	x	x	x
	Pretreatment sediment accumulation	x	x	x
Perimeter
	BMP dimensions	x	x		x
Overflow outlets
	Overflow outlet obstruction	x	x	x	x
	Control structure condition	x	x	x	x
Cistern
	Cistern structural integrity	x	x	x	x
	Cistern sediment accumulation	x	x	x	x

Testing Indicators Framework - Rainwater Harvesting Systems

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Testing Indicators
	Sediment accumulation testing	x	x	x	x
Cistern pump testing		x	x	(x)
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

Construction Inspection Tasks

Example of a polyethylene cistern being installed during construction. During construction inspections it's important to note whether or not the depths, slopes and elevations are acceptable (Photo source: Innovative Water Solutions, 2021).

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 that adequate ESCs and flow diversion devices are in place and confirm that construction materials meet design specifications
2. At completion of excavation and grading, prior to backfilling and installation of cistern and pipes to ensure depths, slopes and elevations are acceptable
3. At completion of installation of cistern and pipes, prior to completion of backfilling to ensure slopes and elevations are acceptable
4. 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)
5. 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
   

Rainwater Harvesting Systems: 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 backfilling and installation of cistern and conveyance pipes	Excavation location, footprint, depth and slopes are acceptable
	Installations of underdrains/sub-drain pipes (location, elevation, slope) are acceptable
BMP Installation – after installation of pipes/sewers, prior to backfilling	Installation of structural components (i.e., pretreatment devices, inlets, cistern, overflow outlet, pump, make-up water supply and backflow preventer valve, control manhole/ access hatch) are acceptable and functioning

Routine Maintenance - Key Components and I&M Tasks

Regular inspections (twice annually, at a minimum) done as part of routine maintenance tasks over the operating phase of the BMP life cycle to determine if maintenance task frequencies are adequate and determine when rehabilitation or further investigations into BMP function are warranted.

Table below describes routine maintenance tasks for rainwater harvesting practices, organized by BMP component, along with recommended minimum frequencies. It also suggests higher frequencies for certain tasks that may be warranted for cisterns that receive flows from large roof drainage areas or roofs with mature trees near them. Tasks involving removal of debris, sediment and trash may need to be done more frequently in such contexts.

Rainwater Harvesting: Key Components, Descriptions and Routine I&M Requirements

Component	Description	Inspection & Maintenance Tasks	(Pass) Photo Example	(Fail) Photo Example
Contributing Drainage Area (CDA)	Roof area(s) from which runoff directed to the BMP originates.	Remove natural debris and sediment annually to biannually; Trim back tree boughs that hang over the roof area to reduce maintenance needs.	CDA has not changed in size or land cover. Sediment, trash or debris is not accumulating and point sources of contaminants are not visible.	Sediment and debris is accumulating on the CDA due to deteriorating roof shingles. Eavestroughs need cleaning.
Pretreatment	Devices prevent debris and sediment from entering the BMP. Includes eavestrough or downspout screens, first flush diverters or filters on pipes leading to or from the cistern. Reduce the risk of obstructing inlets, intakes or overflow outlet pipes and excessive sediment accumulation.	Remove trash, debris and sediment biannually to quarterly or when the device sump is half full; Measure sediment depth or volume during each cleaning, or annually to estimate accumulation rate and optimize frequency of maintenance.	The pretreatment filter of the cistern is free of sediment and debris.	The pretreatment filter on the roof downspout is partially covered by debris which could prevent stormwater from freely entering the BMP (Source: DMR).
Inlets	Pipes connected to eavestroughs or roof drains that deliver water to the BMP. May also include a pipe connected to the municipal water supply line for maintaining cistern water level during dry weather.	Check for obstructions and remove any debris or sediment annually to biannually; For outdoor above-ground cisterns and rain barrels, inlets need to be disconnected in the late fall/early winter, prior to the onset of freezing air temperatures; Reconnect outdoor above-ground cisterns to the roof drainage area in the spring once air temperature remains above freezing.	Inlet pipe and couplings are securely connected to the CDA and cistern. (Source: Lake County SMC)	The roof downspout is disconnected from the eavestrough, preventing runoff from entering the cistern.
Access Hatch	Hatch, manhole or lid that provides access to the interior of the water storage structure.	Inspect for damage, obstruction and accessibility annually.	The access hatch of this cistern is accessible with ladder rungs in place.	The access hatch of this cistern was paved over with concrete and ladder rungs are missing which prevents safe entry for inspection and maintenance tasks. (Source: Miles Golding).
Cistern or rain barrel	The water storage structure (e.g., concrete vault, fiberglass, plastic or metal tank, rain barrel).	Inspect for damage or leaking annually; Drain and remove accumulated sediment as needed (annually at a minimum).	There are no cracks or leaks visible in the cistern structure.	A section of sealing tape over two pieces of the concrete cistern structure is displaced, raising the potential for leaks in the future.
Pump	Pressurized device used to deliver stored rainwater to the hose bibs.	Inspect and test for proper function annually.	Installation of structural components and current operating level are acceptable and functioning in clean and easily accessible condition as seen here (Photo Source: Meir, 2021)	With prolonged usage, the pump capacity declines, causing a reduction in flow rate overall. If the pump is not creating sufficient pressure, and the flow rate is below the design specification, servicing of the pump by a skilled technician should be scheduled (Photo Source: Rapid Plumbing Group Pty Ltd., 2022).
Filter	Cisterns may include an in-line filter device on the intake pipe or prior to delivery of rainwater to hose bibs.	Remove debris and sediment biannually to quarterly or as directed by the system manufacturer.	Very little sediment and no coarse debris has accumulated on the bottom of the cistern and the sediment is not at the level of the distribution system intake structure.	Enough sediment has accumulated in the cistern to cause water delivered from the distribution system to be turbid and discoloured when cistern water levels are low. Intake filyrt must be checked and changed.
Overflow Outlet	Pipe connected to the cistern or rain barrel that conveys overflows to another drainage system (e.g., municipal storm sewer or other BMP).	Check for obstructions and remove any debris or sediment annually to biannually.	The overflow outlet pipe diameter matches what was specified in the final design and is free of damage and obstruction.	The overflow outlet pipe on this rain barrel is undersized and obstructed which impairs its function to safely convey excess water from the BMP. (Source: Melinda Webb)

Tips to Preserve Basic BMP Function

• Routinely check the water delivered to hose bibs or fixtures for turbidity or discolouration which could indicate excessive sediment accumulation in the cistern or failure of pretreatment devices or filters.
• Include a filtration device to treat stored water prior to delivery to hose bibs or fixtures as part of the intake/distribution system and clean filters at the same frequency as pretreatment devices.
• If the overflow outlet discharges at grade, the pipe opening should be covered with a coarse screen to prevent entry by insects and animals.
• Provide a means of draining the cistern by gravity to make inspection and maintenance work that requires drainage of the BMP easier to perform.
• Remove accumulated sediment from a large cistern using a pressure washer or hydro-vac truck equipped with a JetVac nozzle to scour and direct sediment to a collection point for removal by vacuuming; for small cisterns, a garden hose and wet shop vacuum may be used.

Rehabilitation & Repair

Table below provides guidance on rehabilitation and repair work specific to rainwater harvesting systems and rain barrels organized according to BMP component. For more detailed guidance on troubleshooting rainwater harvesting systems refer to Ontario Guidelines for Residential Rainwater Harvesting Systems - Handbook (Despins, 2010) and the Canadian Guidelines for Residential Rainwater Harvesting Systems Handbook, developed by the Canadian Mortgage and Housing Corporation (CHMC) (Despins, 2012)

Technician conducting FIT work to ensure cistern tank is in optimal working order. (Photo Source: Pristine Water Systems, 2017)

Rainwater Harvesting Systems: Key Components, Typical Issues and Rehabilitation Requirements

Component	Problem	Rehabilitation Tasks
Inlets	Pipes or fittings are damaged or displaced.	Schedule repairs.
	Ice is accumulating and obstructing inflow to BMP.	Schedule installation of heat trace wire along eavestroughs, around roof drains and in aboveground pipes, or disconnect the system during winter.
Cistern	Cracks are visible or seals between joints in the structure are leaking.	Schedule repairs with oversight by the product manufacturer/vendor.
	Cistern has reached 40 years of age and is due for replacement.	Replace cistern with new one that meets design specifications.
Overflow Outlet	Overflow outlet pipe is obstructed by trash, debris or sediment.	Schedule drain snaking service or pressure/vacuum truck to remove the obstruction.
Make-up water supply	System is malfunctioning (e.g., tops up cistern water level when unnecessary or fails to top up when needed).	Schedule FIT work to determine the cause of system malfunction with oversight by the product manufacturer/vendor or a licensed plumber and electrician.
Pump	Pump is not delivering water to fixtures or not providing adequate water pressure.	Schedule FIT work to determine the cause of system malfunction with oversight by the product manufacturer/vendor or a licensed plumber and electrician.

Inspection Time Commitments and Costs

Life cycle cost estimates are based on two design variations that can be used year-round: underground concrete cistern; and indoor plastic cistern systems. For each design variation, life cycle costs can be found in the Low Impact Development (LID) Stormwater Management Practice Inspection and Maintenance Guide

General time commitments and costs for inspection of rainwater harvesting features features with partial infiltration (in 2016 $ figures) (TRCA, 2018).

Per-task cost estimates for maintenance and rehabilitation of rainwater harvesting features features with partial infiltration (in 2016 $ figures) (TRCA, 2018).

Construction and life cycle cost estimates for rainwater harvesting features features with partial infiltration (in 2016 $ figures) (TRCA, 2018).

Estimates of the life cycle costs of inspection and maintenance have been produced using the latest version of the LID Life Cycle Costing Tool for two design variations (nderground concrete cistern; and indoor plastic cistern systems) to assist stormwater infrastructure planners, designers and asset managers with planning and preparing budgets for potential LID features.

Assumptions for the above costs and the following table below are based on the following:

• Capital costs included within the category of construction include those related to site assessment, and conceptual and detailed design related tasks such as borehole analysis and soil testing. All material, delivery, labour, equipment (rental, operation, operator), hauling and disposal costs are accounted for within the construction costs of the facility. Standard union costs were derived from the RSMeans database in 2010 and have been adjusted for 5 year inflation of 8.79% (2010 to June, 2015).
  • Costs include overhead and inflation to represent contractor pricing. It was assumed the practice is part of a new development (i.e., not a retrofit), thereby excluding (de)mobilization costs unless a particular piece of equipment would not normally have been present at the site. Additionally, it was assumed that excavated soil associated with construction of the BMP would be reused elsewhere on site. Overhead costs were presumed to consist of construction management (4.5%), design (2.5%), small tools (0.5%), clean up (0.3%) and other (2.2%).
• For maintenance frequencies and requirements and the life span of each practice are based on both literature and practical experience. Life cycle and associated maintenance costs are evaluated over a 50 year timeframe, which is the typical period over which infrastructure decisions are made.
• For bioretention, it is assumed that some rehabilitation (e.g., rehabilitative maintenance) work will be needed on the filter bed surface once the BMP reaches 25 and 50 years of age in order to maintain functional drainage performance at an acceptable level. Included in the rehabilitation costs are (de)mobilization costs, as equipment would not have been present on site. Design costs were not included in the rehabilitation as it was assumed that the original LID practice design would be used to inform this work. The annual average maintenance cost does not include rehabilitation costs and therefore represents an average of routine maintenance tasks, as outlined in the Table under section, Routine Maintenance - Key Components and I&M Tasks above. All cost value estimates represent the net present value (NPV) as the calculation takes into account average annual interest (2%) and discount (3%) rates over the evaluation time periods.
• For all bioretention design variations, the CDA has been defined as a 2,000 m2 impervious pavement area plus the footprint area of a bioretention cell that is 133 m2 in size, as per design recommendations. The impervious area to pervious area ratio (I:P ratio) used to size the BMP footprint is 15:1, which is the maximum ratio recommended in the LID SWM Planning and Design Guide (CVC & TRCA, 2010). It is assumed that water drains to the cell through curb inlets spaced 6 m apart with

stone cover on the filter bed at the inlets to dissipate the energy of the flowing water.

• While orientation (i.e., cell versus swale) and choice of components (e.g., inlet/outlet structures etc.) can vary widely, design variations for bioretention practices can be broken down into three main categories. They can be designed to drain through infiltration into the underlying subsoil alone (i.e., Full Infiltration design, no sub-drain), through the combination of a sub-drain and infiltration into the underlying subsoil (i.e., Partial Infiltration design, with a sub-drain), or through a sub-drain alone (i.e., No Infiltration or “filtration only” design, with a sub-drain and impermeable liner). For Full Infiltration systems, an overflow is provided for storms up to 37 mm based on a subsoil infiltration rate of 20 mm/hour. Two standpipe wells are part of the design (one subdrain inspection/flushing port at the upstream end and one sub-surface water storage reservoir monitoring well at the downstream end). Partial Infiltration systems have a sub-surface water storage reservoir with a perforated pipe sub-drain within it. The depth of the reservoir is sized to store flow from a 25 mm rain event over the CDA based on native soil infiltration rate of 10 mm/hour. The No Infiltration system includes an impermeable liner between the base and sides of the BMP and surrounding native sub-soil, to prevent infiltration.
• Estimates of the life cycle costs of bioretention and dry swales in Canadian dollars per unit CDA ($/m2) are presented in the table below. LID Life Cycle Costing Tool allows users to select what BMP type and design variation applies, and to use the default assumptions to generate planning level cost estimates.
  • Users can also input their own values relating to a site or area, design, unit costs, and inspection and maintenance task frequencies to generate customized cost estimates, specific to a certain project, context or stormwater infrastructure program.
  • For all BMP design variations and maintenance scenarios, it is assumed that rehabilitation of part or all of the filter bed surface will be necessary once the BMP reaches 25 and 50 years of age to maintain acceptable surface drainage performance (e.g., surface ponding drainage time). Filter bed rehabilitation for bioretention and dry swales is assumed to typically involve the tasks outlined under section, Routine Maintenance - Key Components and I&M Tasks above.
    

Life cycle cost estimates for all variation types of bioretention and dry swales under minimum and high frequency scenarios (in 2016 $ figures).

Notes:

1. Estimated life cycle costs represent NPV of associated costs in Canadian dollars per squaremetre of CDA ($/m2).
2. Average annual maintenance cost estimates represent NPV of all costs incurred over the time period and do not include rehabilitation costs.
3. Rehabilitation cost estimates represent NPV of all costs related to repair work assumed to occur every 25 years, including those associated with inspection and maintenance over a two (2) year establishment period for the plantings.
4. Full Infiltration design life cycle costs are lower than Partial and No Infiltration designs due to the absence of a sub-drain to construct, inspect and routinely flush.
5. Rehabilitation costs for Full Infiltration designs are estimated to be 26.4 to 28.4% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
6. Rehabilitation costs for Partial Infiltration designs are estimated to be 19.9 to 21.6% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
7. Rehabilitation costs for No Infiltration designs are estimated to be 20.2 to 21.9% of the original construction costs for High and Minimum Recommended Frequency maintenance program scenarios, respectively.
8. Maintenance and rehabilitation costs over a 25 year time period for the Minimum Recommended maintenance scenario are estimated to be roughly equivalent to the original construction cost for Partial Infiltration and No Infiltration designs (96.2% and 97.8%, respectively), and 1.21 times the original construction cost for Full Infiltration design.
9. Maintenance and rehabilitation costs over a 25 year time period for the High Frequency maintenance scenario are estimated to be 1.32 times the original construction costs for Partial Infiltration, 1.34 times for No Infiltration designs, and 1.67 times for Full Infiltration designs.
10. Maintenance and rehabilitation costs over a 50 year time period for the Minimum Recommended Frequency maintenance scenario are estimated to be approximately 1.76 times the original construction cost for Partial Infiltration designs, 1.79 times the original construction cost for No Infiltration designs, and 2.21 times the original construction cost for Full Infiltration designs.
11. Maintenance and rehabilitation costs over a 50 year time period for the High Frequency maintenance scenario are estimated to be approximately 2.40 times the original construction cost for Partial Infiltration designs, 2.44 times the original construction cost for No Infiltration designs, and 3.04 times the original construction cost for Full Infiltration designs.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

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.

The portion of water precipitated onto a catchment area, which then 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.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

Toronto and Region Conservation Authority

Tank used to store rainwater (typically roof runoff) for later use.

Tank used to store rainwater (typically roof runoff) for later use.

A system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

Tank used to store rainwater (typically roof runoff) for later use.

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.

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.

Watercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge.

Any form of rain or snow.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Sustainable Technologies Evaluation Program

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

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.

Structure to control the volume or rate of flow of water through or over it.

Tank used to store rainwater (typically roof runoff) for later use.

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.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

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.

FIT work involves the application of a similar set of inspection and testing indicators as those used in Performance Verification inspections, but focuses on diagnosing suspected problems with the following objectives in mind: (1) Confirm whether or not problems with BMP function exist; (2) Identify the causes of confirmed problems; (3) Determine corrective actions needed.

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

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

Stormwater Management

Credit Valley Conservation

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.

The technique of removing pollutants from runoff as it infiltrates through the soil.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

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 natural ground material characteristic of or existing by virtue of geographic origin.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

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.

The period between the maximum water level and the minimum level (dry weather or antecedent level).

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

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.