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For proper nutrient control, bioretention cells must not be fertilized unless a soil test from a certified lab indicates nutrient deficiency. The one exception is a one-time fertilizer application during planting of the cell, which will help with plant establishment. Irrigation is also typically needed during establishment. | For proper nutrient control, bioretention cells must not be fertilized unless a soil test from a certified lab indicates nutrient deficiency. The one exception is a one-time fertilizer application during planting of the cell, which will help with plant establishment. Irrigation is also typically needed during establishment. | ||
− | Pre-treatment devices need to be maintained for long-term functionality. Accumulated sediment in the forebay will need to be cleaned out at a minimum when it is half-full, which should be approximately every 10 to 20 years. In an especially dirty watershed, the frequency may be increased to every 2 to 3 years. Sediment should also be cleaned out of rip rap and sumps. A vacuum truck is typically used for sediment removal. If a grassed filter strip or swale is used as pre-treatment, they should be mowed as frequently as a typical lawn. Depending on the contributing watershed, grassed | + | Pre-treatment devices need to be maintained for long-term functionality. Accumulated sediment in the forebay will need to be cleaned out at a minimum when it is half-full, which should be approximately every 10 to 20 years. In an especially dirty watershed, the frequency may be increased to every 2 to 3 years. Sediment should also be cleaned out of rip rap and sumps. A vacuum truck is typically used for sediment removal. If a grassed filter strip or swale is used as pre-treatment, they should be mowed as frequently as a typical lawn. Depending on the contributing watershed, grassed BMPs may also need to be swept before mowing. All grassed BMP’s should also be swept annually with a stiff bristle broom or equal to remove thatch and winter sand. The University of Minnesota’s [http://www.sustland.umn.edu/maint/maint.htm Sustainable Urban Landscape Series website] provides guidance for turf maintenance, including mowing heights. |
− | Maintenance of vegetation after establishment is similar to adjacent gardens (except for application | + | Maintenance of vegetation after establishment is similar to adjacent gardens (except for application of fertilizer). Weeding is especially important during the plant establishment period, when vegetation cover is not 100 percent yet, but some weeding will likely always be needed. It is also important to budget for some plant replacement (at least 5 to 10 percent of the original plantings) during the first few years after planting, in case some of the plants that were originally planted die. Rubbish and trash removal will likely be needed more frequently than in the adjacent landscape, since the hydraulic loading ratio is high. Trash removal is important for prevention of mosquitoes. Mulch renewal will be needed two or three times after establishment (first five years). After that, the plants are typically dense enough to make it difficult to mulch, and the breakdown of plant material will provide enough organic matter to the infiltration/filtration device. It is recommended that bioretention performance evaluations follow the four level assessment system in ''Stormwater Treatment: Assessment and Maintenance'' (Gulliver et al., 2010). More detailed information about maintenance procedures, a maintenance schedule, and estimated maintenance costs are also available in Gulliver et al. 2010. |
Owner’s Representatives may wish to consider deducts and liquidated damages for bad construction practices. Regulating authorities may wish to consider fines for bad construction practices. | Owner’s Representatives may wish to consider deducts and liquidated damages for bad construction practices. Regulating authorities may wish to consider fines for bad construction practices. |
The most frequently cited maintenance concern for bioretention is surface and underdrain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include
Recommendations described below are aimed at preventing these common problems.
Implicit in the design guidance for bioretention is the fact that many design elements of bioretention systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include
Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of bioretention practices, the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line.
Inspections during construction are needed to ensure that the bioretention practice is built in accordance with the approved design and standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided here.
BIORETENTION - Construction inspection checklist
Effective long-term operation of bioretention practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards.
For proper nutrient control, bioretention cells must not be fertilized unless a soil test from a certified lab indicates nutrient deficiency. The one exception is a one-time fertilizer application during planting of the cell, which will help with plant establishment. Irrigation is also typically needed during establishment.
Pre-treatment devices need to be maintained for long-term functionality. Accumulated sediment in the forebay will need to be cleaned out at a minimum when it is half-full, which should be approximately every 10 to 20 years. In an especially dirty watershed, the frequency may be increased to every 2 to 3 years. Sediment should also be cleaned out of rip rap and sumps. A vacuum truck is typically used for sediment removal. If a grassed filter strip or swale is used as pre-treatment, they should be mowed as frequently as a typical lawn. Depending on the contributing watershed, grassed BMPs may also need to be swept before mowing. All grassed BMP’s should also be swept annually with a stiff bristle broom or equal to remove thatch and winter sand. The University of Minnesota’s Sustainable Urban Landscape Series website provides guidance for turf maintenance, including mowing heights.
Maintenance of vegetation after establishment is similar to adjacent gardens (except for application of fertilizer). Weeding is especially important during the plant establishment period, when vegetation cover is not 100 percent yet, but some weeding will likely always be needed. It is also important to budget for some plant replacement (at least 5 to 10 percent of the original plantings) during the first few years after planting, in case some of the plants that were originally planted die. Rubbish and trash removal will likely be needed more frequently than in the adjacent landscape, since the hydraulic loading ratio is high. Trash removal is important for prevention of mosquitoes. Mulch renewal will be needed two or three times after establishment (first five years). After that, the plants are typically dense enough to make it difficult to mulch, and the breakdown of plant material will provide enough organic matter to the infiltration/filtration device. It is recommended that bioretention performance evaluations follow the four level assessment system in Stormwater Treatment: Assessment and Maintenance (Gulliver et al., 2010). More detailed information about maintenance procedures, a maintenance schedule, and estimated maintenance costs are also available in Gulliver et al. 2010.
Owner’s Representatives may wish to consider deducts and liquidated damages for bad construction practices. Regulating authorities may wish to consider fines for bad construction practices.