Stormwater Infiltration in the Highway Environment: Guidance Manual (2019) / Chapter Skim
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Pages 79-98
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From page 79... ...
79 4.1 Overview Surveys and interviews with DOTs (see Project Summary Report) have provided the research team with insights into the challenges DOTs face in design, construction, and O&M of infiltration BMPs.
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From page 80... ...
80 Stormwater Infiltration in the Highway Environment: Guidance Manual 4.1.1 Role of BMP Selection in Managing Uncertainty and Reducing Risk If data are not available at the time of design to ensure feasibility, then BMPs should be selected and designed so that they do not depend on uncertain design parameters (e.g., a certain infiltration rate) for the system to remain operable, or additional investigation should be undertaken during the construction phase to achieve the necessary level of confidence.
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From page 81... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 81 • Sediment loading from the drainage area • BMP footprint relative to sediment loading • Soil and media characteristics • Presence of vegetation and type of vegetation • Use of pretreatment • Road salting and sanding Some factors can be beyond the control of the project designer (e.g., sediment concentrations in roadway runoff, footprint available for BMPs, and soil properties) , but the remaining project design decisions can have a large effect on clogging risks, including the following: Routing of Non-Roadway Runoff.
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From page 82... ...
82 Stormwater Infiltration in the Highway Environment: Guidance Manual within the DOT ROW. Where open space or off-site areas drain through the same drainage system as roadway runoff, a key design decision is whether to hydraulically separate these or provide a high level of pretreatment so that they do not contribute loads to infiltration or filtration BMPs.
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Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 83 0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 1 2 3 4 5 6 7 8 9 10 Ap pl ie d Lo ad (l b/ ft2 )
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84 Stormwater Infiltration in the Highway Environment: Guidance Manual In these cases, the use of adaptable design approaches (e.g., infiltration BMPs with a built-in contingency plan) can have an important role.
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Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 85 construction. Examples of adaptable design features are described in Table 27.
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From page 86... ...
86 Stormwater Infiltration in the Highway Environment: Guidance Manual This could potentially include changing the size of the facility. This may require primary and contingency calculations to be included in the project permitting and design documents.
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Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 87 layer before it approaches the limiting rate of the underlying layer. Additionally, if this material is significantly coarser than incoming sediment, it is more likely that the depth filtration processes will prevail in the media rather than surface filtration (also known as cake filtration)
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From page 88... ...
88 Stormwater Infiltration in the Highway Environment: Guidance Manual mixing during blending; compaction during installation; weathering and breakdown of media materials; types and maturity of plants; amount of clogging from particulates in runoff; and other factors. An alternative, passive, non-proprietary design approach (e.g., outlet control)
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From page 89... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 89 4.6.1 Construction Phasing to Reduce Sediment Risk In accordance with federal and state rules, construction sites must implement effective erosion and sediment control BMPs. This Guidance Manual does not cover how these should be done; however, with respect to infiltration and filtration BMPs, several common-sense approaches should be followed.
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From page 90... ...
90 Stormwater Infiltration in the Highway Environment: Guidance Manual • If local climate prevents pervious areas from being stabilized prior to commissioning of infiltration facilities, then route these areas separately so they do not pass through the infiltration BMP until they are stabilized. • Stabilize the side slopes of BMPs so they do not contribute sediment to the infiltrating surface.
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From page 91... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 91 • Restrict heavy equipment and traffic from traveling over the proposed location of infiltration BMPs. • Use construction fence and temporary erosion and sediment control BMPs to demarcate areas proposed for infiltration BMPs.
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92 Stormwater Infiltration in the Highway Environment: Guidance Manual 4.6.4 BMP Vegetation Establishment Vegetated systems are most susceptible to declines in permeability during the period immediately after construction and before plants have been able to establish root structures. Several practices can be used to help mitigate these risks: • Where possible, develop construction phasing to allow time for plant establishment before BMPs are brought on-line to receive stormwater inflow.
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From page 93... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 93 This tends to result in BMPs that require less maintenance or simpler maintenance. Approaches include following: • Utilize design approaches that limit clogging risk (Section 4.2)
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From page 94... ...
94 Stormwater Infiltration in the Highway Environment: Guidance Manual 4.8 O&M Manual The development of a facility-specific O&M manual may be beneficial for communicating maintenance needs to the entity that will be responsible for maintaining the facility. 4.8.1 O&M Manual Contents Table 28 provides suggestions for the contents of a facility-specific O&M manual.
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From page 95... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 95 Routine O&M Activities. These are activities conducted at regularly scheduled intervals to sustain long-term performance of each BMP, including inspections and normal upkeep.
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96 Stormwater Infiltration in the Highway Environment: Guidance Manual local outline. Oregon DOT policies call for a draft O&M manual to be prepared as part of the design phase and finalized after construction.
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From page 97... ...
Key Considerations for Design, Construction, and Maintenance of Infiltration BMPs 97 4.9 Post-Construction Monitoring Monitoring of constructed infiltration BMPs can address a range of questions and current data gaps. Monitoring can serve a range of purposes: Guidance Improvement.
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From page 98... ...
98 Stormwater Infiltration in the Highway Environment: Guidance Manual Purposes of Monitoring Potential Monitoring Questions G u id an ce Im p ro ve m en t M ai n te n an ce P la n n in g P er fo rm an ce E va lu at io n Im p ac t A ss es sm en t Potential Study Elements Water level monitoring How reliable were the methods used to estimate design infiltration rate? Did methods have a high or low bias compared with full-scale performance?
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