Stormwater Infiltration in the Highway Environment: Guidance Manual (2019) / Chapter Skim
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1 The purpose of this Guidance Manual is to support evaluation, selection, siting, design, and construction of infiltration best management practices (BMPs) in the highway environment.
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2 Stormwater Infiltration in the Highway Environment: Guidance Manual approaches. This chapter also introduces the decision-making framework that provides structure for the remaining chapters.
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Introduction and Orientation 3 tentative BMP types and locations. This chapter introduces screening-level methods for reaching preliminary determinations and helps determine the need for conclusive methods to confirm feasibility.
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4 Stormwater Infiltration in the Highway Environment: Guidance Manual to deeper groundwater and discharges to surface runoff than would occur in natural reference conditions in which evapotranspiration (ET) tends to have greater influence on the water balance (Strecker et al.
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Introduction and Orientation 5 1.4 Key Limitations to Infiltration as a Stormwater Management Approach Stormwater infiltration approaches have potential limitations. There are five general categories of limits to infiltration.
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6 Stormwater Infiltration in the Highway Environment: Guidance Manual • Project delivery and contracting methods. Successful implementation of infiltration approaches can require careful control through the design, construction, and post-construction phases of the project.
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Introduction and Orientation 7 amount of water infiltrated is a function of BMP size and site conditions. However, these BMPs do not have a design discharge to surface waters except when the system overflows or bypasses.
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8 Stormwater Infiltration in the Highway Environment: Guidance Manual BMP 01 Vegetated Conveyance This BMP type includes engineered vegetated swales and other vegetated drainage features that serve the purpose of conveying stormwater runoff and can also provide treatment and significant reduction of stormwater runoff volume. Variations on this approach can include an amended soil or stone storage layer to increase storage capacity and promote infiltration.
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Introduction and Orientation 9 Table 2. (Continued)
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10 Stormwater Infiltration in the Highway Environment: Guidance Manual Note that this Guidance Manual does not explicitly consider drywells. The use of drywells in the highway environment is rare.
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Introduction and Orientation 11 • Site conditions (e.g., readily available or efficiently obtained information about soil types, sensitive infiltration receptors, groundwater levels, slopes, and contamination) • Local groundwater management criteria and guidance [e.g., wellhead protection programs, source water protection programs, and sole source aquifer (SSA)
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12 Stormwater Infiltration in the Highway Environment: Guidance Manual • Identification of the primary risks and failure modes that could control decision-making for the site, and prioritization of issues for further consideration (e.g., the key factors that need to be resolved) • Scoping and prioritization of the site investigations and analytical efforts necessary to confirm or refine the selected approach (e.g., soil infiltration testing at potential BMP locations, and groundwater and geotechnical analyses)
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Introduction and Orientation 13 Key questions in this step include the following: • Is it physically feasible to infiltrate stormwater at the target levels within the identified potential infiltration areas? Considerations include the following: – Design infiltration rates – BMP sizing calculations – Effect of groundwater mounding on reliable infiltration rates – Topography and space – Reasonable approaches to improve physical conditions for infiltration • Is it desirable to infiltrate stormwater at the target rates?
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14 Stormwater Infiltration in the Highway Environment: Guidance Manual – How will the BMP be maintained? Does the design allow for maintenance to occur?
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