Stormwater Tree Trenches: Maintenance

The following maintenance procedures and preventative measures should be incorporated into a maintenance plan:

An example of a stormwater tree trench system located within the existing street median, Mississauga, ON. Central Parkway retrofit. (Source: STEP, 2016).

• Tree Maintenance: Inspection and maintenance of all municipally-owned trees shall be conducted by municipal staff or its contractors after the warranty period of the construction contract. This work may include, frequent watering and fertilizing as trees begin to establish themselves in the feature, this is especially important during drought-like conditions. Proper tree pruning is also important throughout the life of the tree, but especially during the early life stages of trees to help limit the potential for detrimental deformations or growth habits. This will help reduce costs as the tree matures and attempts at correcting improper growth, or replacement of the tree entirely becomes more costly. Staff involved in inspection and maintenance of these features should be experienced with the designated planting plan, plant species identification, and weed removal and control methodologies enacted by the municipality.

• Planting Beds: Remove invasive species and weeds, trash and organic debris. Ensure to refresh mulch to retain complete coverage and add mulch to correct grade inconsistencies in tree beds flush with the sidewalk (minimum depth of 50 mm to a maximum of 100 mm and an minimum of 40 mm from the base of the tree in the feature). To be completed every 3 - 6 months.

• Pavement / Covered Trenches: Maintain tree surroundings and grates and ensure that the grates themselves are level with the sidewalk, as needed. After 3 - 5 years, dependent upon tree growth, remove inner ring to allow tree to mature and grow unimpeded.

• Inlets: This may include trench drains, curb cuts/openings and pavement edges, all obstructions of trash and debris should be removed twice a year. Any plants within trench drains themselves or 100mm of the entrance or exit of said drains shall be removed twice a year.

• Irrigation System: Maintenance or replacement of these system components shall take place as required, meanwhile winterizing watering systems to prevent damage shall take place twice a year (in the Spring and Fall). To limit excess salt impacts in the feature flushing and/or leaching excess sodium in the soil should be done annually in the spring by fully saturating the passive irrigation system with water.

• Grid Pavers: Paver or grid systems that have been planted with grass should be mowed regularly and the clippings should be removed. Water and fertilize as needed. .

• Soil / Growing Medium: Testing of soil to determine its structure, organic matter and confirm microbial level counts are satisfactory for selected vegetation will take place at installation and during performance diagnostic intervals. Whereas organic fertilizing and soil amendments recommended by testing will be done on an as-need basis.

• Potholes: For porous asphalt or pervious concrete, isolated potholes can be patched with standard patching mixes. Patching can continue until the structural integrity of the pavement has been compromised or stormwater can no longer drain to the aggregate base. Then the surface will need to be torn up and replaced.
• Uneven Pavers: An uneven paver surface can be repaired by pulling up the pavers, redistributing the bedding layer, and then placing the pavers back. New filler stone will need to be swept into the replaced pavers. Typically the pavers are packed very tightly, and breaking one or more pavers will be necessary to pull up a group of pavers. Keeping a set of replacement pavers after construction will be useful for making future repairs.
• Weeds: Over time, weed growth may become an aesthetic problem, particularly on surfaces with infrequent traffic. Keeping the pavement surface free of organic material through regular sweeping and vacuuming can impede weeds from taking root. Ontario has banned the use of cosmetic herbicides for weed control.
• Vacuuming: Annual vacuuming of permeable interlocking concrete pavers can increase the operational lifespan of these pavers.
• Winter Maintenance: Sand should not be spread on permeable pavement as it can quickly lead to clogging. Deicers should only be used in moderation and only when needed because dissolved constituents are not removed by the pavement system. Pilot studies at the University of New Hampshire Stormwater Center have found that permeable pavement requires 75% less salt than conventional pavement over the course of a typical winter season.
• Snow Plowing: Permeable pavement is plowed for snow removal like any other pavement. When groundwater contamination from chlorides is a concern, plowed snow piles and snow melt should not be directed to permeable paver and porous pavement systems
  Also, plowed snow/snow piles should not be stored on top of permeable pavements, since this snow often contains granular materials which can contribute to clogging

Annual inspections of permeable pavement should be conducted in the spring prior to onset of the summer thunderstorm season. These inspections should check for evidence of spills and surface ponding (staining or sediment accumulation on pavement surface), damage and deterioration.

For more detailed guidance, refer to STEP's Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide and Permeable Pavements Inspection and Maintenance Fact Sheet, both of which can be accessed here

Sustainable Technologies Evaluation Program

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

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

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

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

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.

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.

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.

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.

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.