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Inspection and Maintenance: Enhanced Swales (view source)
Revision as of 16:55, 6 July 2022
, 2 years agono edit summary
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==Tips to Preserve Basic BMP Function==
*Maintain grading of the filter bed (or [[Vegetated filter strips|grass filter strip]] if present) at [[curb cut]] [[inlets]] so at least 5 cm of the back of the curb is visible through regular sediment removal and regrading.
*To avoid over-compaction of the [[Bioretention: Filter media|filter media soil]], any maintenance tasks involving vehicle or foot traffic on the filter bed should not be performed during wet weather.
*For bioretention with sod (i.e., [[Turf|turf grass]]) as [[vegetation]] cover, maintain with a push mower or the lightest mulching ride mower available and core aerate and dethatch annually in the spring to help maintain permeability.
*Pruning of mature [[trees]] should be performed under the guidance of a Certified Arborist.
*Woody [[vegetation]] should not be planted or allowed to become established where snow will be piled/stored during [[Winter]].
*Removal of sediment from the filter bed surface should be done with rake and shovel, or vacuum equipment to minimize plant disturbance. If a small excavator is to be used, keep it off the BMP footprint to avoid damage to side slopes/embankments and over-compaction of the [[filter media]].
==Tips to Preserve Basic BMP Function==
*Maintain grading of the filter bed (or [[Vegetated filter strips|grass filter strip]] if present) at [[curb cut]] [[inlets]] so at least 5 cm of the back of the curb is visible through regular sediment removal and regrading.
*To avoid over-compaction of the [[Bioretention: Filter media|filter media soil]], any maintenance tasks involving vehicle or foot traffic on the filter bed should not be performed during wet weather.
*For bioretention with sod (i.e., [[Turf|turf grass]]) as [[vegetation]] cover, maintain with a push mower or the lightest mulching ride mower available and core aerate and dethatch annually in the spring to help maintain permeability.
*Pruning of mature [[trees]] should be performed under the guidance of a Certified Arborist.
*Woody [[vegetation]] should not be planted or allowed to become established where snow will be piled/stored during [[Winter]].
*Removal of sediment from the filter bed surface should be done with rake and shovel, or vacuum equipment to minimize plant disturbance. If a small excavator is to be used, keep it off the BMP footprint to avoid damage to side slopes/embankments and over-compaction of the [[filter media]].
==Routine Maintenance - Key Components and I&M Tasks==
==Routine Maintenance - Key Components and I&M Tasks==
Technician conducting sediment removal to ensure infiltration rates for the<br>
Technician conducting sediment removal to ensure infiltration rates for the<br>
practice are able to maintain > 25 mm/h. [https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf Photo Source: TRCA, 2018]<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices - Bioretention. Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>
practice are able to maintain > 25 mm/h. [https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf Photo Source: TRCA, 2018]<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices - Bioretention. Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>
==Inspection Time Commitments and Costs==
Estimates are based on a typical partial infiltration bioretention design (i.e., includes a sub-drain); estimates for other designs (i.e., full infiltration and no-infiltration) can be found in the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-7.1-Bioretention-and-Dry-Swales.pdf Low Impact Development (LID) Stormwater Management Practice Inspection and Maintenance Guide]<br>
</br>
[[File:Time commit cost.PNG|thumb|left|400px|General time commitments and costs for inspection of bioretention and dry swale features with partial infiltration (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Bioretention - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>]]
[[File:Cost per maintenance task.PNG|thumb|400px|Per-task cost estimates for maintenance and rehabilitation of a partial infiltration bioretention feature (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Bioretention - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>]]
[[File:Life cycle costs.PNG|thumb|center|400px|Construction and life cycle cost estimates for bioretention and dry swale features with partial infiltration (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Bioretention - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>]]<br>
</br>
Estimates of the life cycle costs of inspection and maintenance have been produced using the latest version of the [[Cost analysis resources|LID Life Cycle Costing Tool]] for three design variations (full infiltration, partial infiltration and no infiltration) 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, [[Inspection and Maintenance: Bioretention & Dry Swales#Routine Maintenance - Key Components and I&M Tasks|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)<ref>CVC and TRCA. 2010. Low Impact Development Stormwater Management Planning and Design Guide. Version 1.0. https://cvc.ca/wp-content/uploads/2014/04/LID-SWM-Guide-v1.0_2010_1_no-appendices.pdf</ref>. 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. [[Cost analysis resources|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, [[Inspection and Maintenance: Bioretention & Dry Swales#Routine Maintenance - Key Components and I&M Tasks|Routine Maintenance - Key Components and I&M Tasks]] above.<br>
</br>
[[File:Life cycle cost for all variations.PNG|thumb|center|900px|Life cycle cost estimates for all variation types of [[bioretention]] and [[Dry swale|dry swales]] under minimum and high frequency scenarios (in 2016 $ figures).<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices. Bioretention - Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>]]
'''Notes:'''
#Estimated life cycle costs represent NPV of associated costs in Canadian dollars per squaremetre of CDA ($/m2).
#Average annual maintenance cost estimates represent NPV of all costs incurred over the time period and do not include rehabilitation costs.
#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.
#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.
#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.
#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.
#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.
#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.
#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.
#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.
#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.
==Inspection Field Data Sheet==
Feel free to '''download''' (downward facing arrow on the top righthand side) and '''print''' (Pinter emoticon on top right hand side) the following [[Bioretention]] and [[Dry swale]] Inspection Field Data Form developed by TRCA, STEP and its partners for the [https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide]<ref>STEP. 2016. Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide. https://sustainabletechnologies.ca/app/uploads/2016/08/LID-IM-Guide-2016-1.pdf</ref>.
The 8 page document prompts users to fill out details previously mentioned above on this page in other sections about various zones associated with [[Bioretention]] and [[Dry swale]] features (i.e. inlets, perimeter of the feature, filter bed, outlets, etc.) and describe why each area is a pass or fail, and if remediate action is required and under what timeframe it would be completed by. Furthermore, the forms prompt the reviewer to determine what type of inspection is being conducted for the feature in question: Construction (C), Routine Operation (RO), Maintenance Verification (MV), or Performance Verification (PV). <br>
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[[File:Continuous monitoring.PNG|thumb|300px|Staff conducting monitoring of bioretention's water level with the use of a [[Digital technologies|continuous water level data logger]] located in the feature's[[Wells|monitoring well]]. [https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf Photo Source: TRCA, 2018]<ref>TRCA. 2018. Inspection and Maintenance of Stormwater Best Management Practices - Bioretention. Fact Sheet. https://sustainabletechnologies.ca/app/uploads/2018/02/Bioretention-and-Dry-Swales-Fact-Sheet.pdf</ref>]]
<pdf width="900" height="800">File:Bio Swale Inspection Sheet.pdf</pdf>
==References==