The use of existing vegetated areas that have surface features that disperse runoff is encouraged, as the use of these areas will also reduce overall site disturbance and soil compaction.A pervious berm and/or retentive grading allows for a reduction in both runoff velocity and volume, thus improving pollutant removal capabilities by providing a temporary (very shallow) ponded area. Filter strip effectiveness may be enhanced by installing berms and retentive grading perpendicular to the flow path.Key Design Considerations for Filter Strips Often require medium-to-large vegetated areas, making them often impractical in an ultra-urban setting.Require preservation and minimization of impacts leading to compaction and/or erosion.Decrease the frequency of required maintenance of associated SMPs.Extend the life of associated SMPs and decrease their hydraulic residence time.Effective at slowing runoff velocities, removing pollutant loads, and promoting infiltration of runoff produced by both impervious and pervious areas.Relatively simple structures that provide effective runoff pretreatment.They are a pretreatment option for SMPs in residential, commercial, and light industrial developments, and for roads, highways, and parking lots. Depending on the site layout and stormwater conveyance design, they may be applicable to subsurface infiltration, subsurface detention, and media filters.įilter strips are typically used for pretreatment of diffuse sheet flow. Successful stormwater management plans will combine appropriate materials and designs specific to each site.Īn example of filter strips in Philadelphia When Can Filter Strips Be Used?įilter strips are a pretreatment option typically applicable to bioinfiltration/bioretention basins and ponds and wet basins. Filter strips are generally a sensible and cost-effective stormwater pretreatment option applicable to a variety of development sites, including roads and highways.ĭesign of filter strip SMPs is not limited to the examples shown within this text. ![]() These systems function by reducing runoff velocity, trapping sediment and pollutants, and, in some cases, infiltrating a portion of the runoff into the ground. Table 4.10‑1: Pretreatment Applicability Guidance SMPįilter strips consist of densely vegetated land that treats stormwater sheet flow from adjacent pervious and impervious areas. The designer is referred to the pretreatment sections within Section 4.5, for cistern pretreatment guidance. The pretreatment systems within this Section are not typically applicable for green roofs, blue roofs, and cisterns treating roof runoff. ![]() Filter strips are typically applicable for diffuse stormwater flow, while forebays and swales are typically applicable for concentrated stormwater flow. Red indicates that the pretreatment type would typically be used with the SMP yellow indicates that the pretreatment type may be used with the SMP in certain circumstances and blue indicates that the pretreatment type would not typically be used with the associated SMP. Table 4.10‑1 below provides guidance on the typical applicability of the types of pretreatment systems covered in this Section. Successful pretreatment systems will combine appropriate materials and designs specific to each site. The design of an effective pretreatment system may incorporate any number of these or other types of pretreatment systems, and the designer should not be limited by the guidance provided in this Manual. In the following Section, guidance is provided on three of the most commonly applied pretreatment practices. Required pretreatment design and material standards are denoted in this Section by easy-to-reference numerals. ![]() The designer should reference the pretreatment sections within the individual SMP Sections of Chapter 4 for SMP-specific guidance regarding pretreatment. Pretreatment beyond these minimum requirements is recommended for SMPs with catchment areas that generate high sediment loads, such as roadways and parking lots. The designer is referred to Section 4.11, Inlet Controls, for guidance on inlets. For all SMPs, the use of sumps and traps or hoods for inlets, and sump boxes with traps or hoods downstream of trench drains, is the minimum requirement. Pretreatment of runoff from all inlets is required. This can be done using a variety of methods, but is most commonly achieved by decreasing peak stormwater velocities to allow sediment to settle or by filtering incoming stormwater through vegetation to remove sediment before it reaches a downstream SMP. The primary goal of most pretreatment systems is to capture sediment, trash, and debris. Properly designed pretreatment systems help to sustain required stormwater management function, extend service life, and reduce maintenance costs of SMPs. ![]() Pretreatment is critical to the design of stormwater management practices (SMPs).
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