Vegetated Filter Strip: Life Cycle Costs

==Overview==
Vegetated filter strips (i.e., buffer strips, grassed filter strips) are gently sloping, densely vegetated areas that treat runoff as sheet flow from adjacent impervious areas. They slow runoff velocity and filter out suspended sediment and associated pollutants, and provide some infiltration into underlying soils. Vegetated filter strips are generally used as pretreatment to other LID practices. Filter strips also provide a convenient location for snow storage and treatment during the winter months. STEP has prepared a life cycle cost estimate for a vegetated filter strip based on a 2,000 m2 road drainage area, runoff control target of 25 mm depth and 72 hour drainage period, for comparison which can be viewed below. To generate your own life cycle cost estimates customized to the development context, design criteria, and constraints applicable to your site, access the updated LID Life Cycle Costing Tool (LCCT) here.
==Design Assumptions==
Filter strips function by slowing runoff velocities and filtering out sediment and other pollutants. Filter strips may be comprised of a variety of trees, shrubs, and vegetation to add aesthetic value as well as water quality benefits. 										
Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:											
* Filter strip length of 5 metres and width of 100 metres.
* Maximum acceptable impervious drainage area to pervious footprint area ratio of 4:1.
* Swale (0.3 m depth) and ditch inlet catch basin connected to storm sewer as outlet.
* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from curb inlets and outlet catch basin annually, mowing five times a year, removal of weeds twice a year, and core aeration of filter strip surface every 5 years. Verification inspections are included every 5 years to confirm adequate maintenance.
===Notes===
* Design includes pretreatment through stone diaphragms at curb inlets.
* Operation and maintenance cost estimates assume rehabilitation of the filter strip surface is required after 25 years of operation.
* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal. 
** Land value and equipment mobilization and demobilization costs are not included, assuming BMP construction is part of overall development site construction.
** Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.
** The tool adds 10% contingency and additional overhead as default.
* All cost estimates are in Canadian dollars and represent the net present value (NPV) as the tool takes into account average annual interest and discount rates over the 25 and 50 year operating life cycle periods. 														
* Unit costs are based on 2018 RSMeans standard union pricing.							
* Additional costs associated with retrofit or redevelopment contexts is assumed to be 16% of the cost estimate for new (greenfield) construction contexts. 								
** Retrofit construction cost estimates are included in the 'Costs Summary' section for comparison.
==Construction Costs==
thumb|center|950px|Construction Costs Per Unit Drainage Area (CAD$/m2) - Full Infiltration Design, 25 mm Treatment
Note: Please click on each image to enlarge to view associated construction cost estimates.
Above you can find a breakdown of construction costs by expense type for the 500 m2 surface area vegetated filter strip (I:P area ratio of 4:1)
The Material & Installation expenses represent the largest portion of total construction costs (55%).
==Life Cycle Costs==
Below are capital and life cycle cost estimates for the Vegetated filter strip design configuration over 25- and 50-year time periods. The estimates of maintenance and rehabilitation (life cycle) costs represent net present values. Operation and maintenance costs are predicted to represent 46% of total life cycle costs over the 25-year evaluation period, and increase to 60% of total life cycle costs over the 50-year period, due to filter strip surface rehabilitation costs assumed to be required after 25 years of operation.
===25-Year life cycle cost break down===
thumb|center|900px|Vegetated Filter Strips: Full Infiltration
Note: Click on each image to enlarge to view associated life cycle cost estimate.
===50-Year life cycle cost break down===
thumb|center|900px|Vegetated Filter Strips: Full Infiltration
Note: Click on each image to enlarge to view associated life cycle cost estimate.
==Cost Summary Tables==
Total life cycle cost estimate over the 50 year evaluation period for the 500 m2 Vegetated filter strip design configuration is ($105,570.23).
===Full Infiltration===
800px
==References==