Chapter 11: Design Guidance

This chapter provides guidance on the design, construction, and maintenance of the stormwater treatment practices contained in this manual. Table 11-1 lists the individual primary and secondary stormwater treatment practices that were introduced in Chapter Six and are described further in subsequent sections of this chapter.


Table 11‑1. Summary of Stormwater Treatment Practices

Primary (P) Treatment Practice

Secondary (S) Treatment Practice

Stormwater Ponds (P1)

  • Micropool Extended Detention Pond
  • Wet Pond
  • Wet Extended Detention Pond
  • Multiple Pond System
  • Pocket Pond

Stormwater Wetlands (P2)

  • Shallow Wetland
  • Extended Detention Wetland
  • Pond/Wetland System

Infiltration Practices (P3)

  • Infiltration Trench
  • Infiltration Basin

Filtering Practices (P4)

  • Surface Sand Filter
  • Underground Sand Filter
  • Perimeter Sand Filter
  • Organic Filter
  • Bioretention

Water Quality Swales (P5)

  • Dry Swale
  • Wet Swale


Conventional Practices


Innovative/Emerging Technologies



Primary Treatment Practices

This chapter provides the following information for each primary treatment practice:


  • Description: A brief description of the treatment practice. The stormwater management benefits of the treatment practice (i.e., runoff volume reduction, pollutant reduction, stream channel/conveyance protection, and flood control) and effectiveness for removal of specific categories of pollutants are summarized at the beginning of each description for quick reference and screening.


  • Design Variations: Descriptions of common design variations for those treatment practices for which multiple designs have been developed.


  • Advantages: The major beneficial factors or considerations (e.g., environmental, economic, safety) for selecting a specific stormwater treatment practice.


  • Limitations: The major limitations or drawbacks of a stormwater treatment practice that may preclude its use for a given site.


  • Siting Considerations: The site conditions required for implementation of a stormwater treatment practice, such as minimum contributing drainage area, subsurface conditions, and minimum setbacks.


  • Design Criteria: Specific technical requirements and recommendations for designing the major elements of a stormwater treatment practice, including criteria for design variants within each treatment practice category.


  • Construction: Recommended construction procedures and methods to ensure that a stormwater treatment practice functions as designed.


  • Inspection and Maintenance: Routine and non-routine operation and maintenance required for the stormwater treatment practice to function properly over time.


  • Cost Considerations: Approximate capital costs to design, construct, and implement the stormwater treatment practice, as well as approximate annual operation and maintenance costs, where available.

Secondary Treatment Practices

Secondary treatment practices are described in less detail due to their limited applicability for water quality control.  The following guidance is provided for these treatment practices.


  • Description: A brief description and associated stormwater management benefits of the treatment practice.


  • Reasons for Limited Use: Rationale for why the practice generally does not meet the performance standards required for classification as a primary treatment practice.


  • Suitable Applications: The conditions or applications for which the practice is typically suitable (i.e., pretreatment, ultra-urban environments, etc.)


  • Design Considerations: Key factors for siting, designing, and implementing the treatment practice.