Volume 2-05, Chapter 3 - City of Wichita
Volume 2-05, Chapter 3 - City of Wichita Volume 2-05, Chapter 3 - City of Wichita
Section 3.1 - Stormwater Management Controls Overview 3.1.6 Using Structural Stormwater Controls in Series 3.1.6.1 Stormwater Treatment Trains The minimum stormwater management standards are an integrated planning and design approach whose components work together to limit the adverse impacts of development on downstream waters and riparian areas. This approach is sometimes called a stormwater “treatment train.” When considered comprehensively, a treatment train consists of all the design concepts and nonstructural and structural controls that work to attain water quality and quantity goals. This is illustrated in Figure 3-6. Runoff & Load Generation (Source Control) Pretreatment Control Standard Treatment and/or Quantity Control Figure 3-6 Generalized Stormwater Treatment Train Runoff and Load Generation: The initial part of the “train” is located at the source of runoff and pollutant load generation, and consists of pollution prevention practices and optional “Preferred Site Design” practices that reduce runoff and stormwater pollutants. Pretreatment: The next step in the treatment train consists of pretreatment measures. These measures typically do not provide sufficient pollutant removal to meet the overall TSS target reduction goal, but do provide calculable water quality benefits that may be applied towards meeting the WQ v treatment requirement. In addition, pre-treatment may reduce maintenance and/or improve the performance of downstream facilities. These measures include: • Structural controls that achieve less than the overall TSS target removal rate, but provide pretreatment for sources such as hotspots. • Pretreatment facilities such as sediment forebays. Standard Treatment and/or Quantity Control: The last step is standard water quality treatment and/or quantity (channel protection and flood) control. This is achieved through the use of structural controls to achieve overall water quality and quantity goals. 3.1.6.2 Use of Multiple Structural Controls in Series Many combinations of structural controls may be used for a site. The following are descriptions of some examples of how controls and other practices may be combined to achieve the goals of the integrated design approach. • Stormwater ponds are often used to achieve overall target TSS removal as well as channel protection and flood control, thus meeting all of the requirements of the integrated site design approach in a single facility. Page 3 - 20 Volume 2, Technical Guidance
Section 3.1 - Stormwater Management Controls Overview • The other structural controls achieving overall TSS target removal each (bioretention, sand or organic filters, infiltration or soakage trenches, and enhanced swales) are typically used in combination with other water quality controls and with detention flood controls to meet the integrated site design goals. The detention facilities are located downstream from the water quality controls either on-site or combined into a regional or neighborhood facility. • Where a structural control does not meet the overall TSS target removal criteria, one or more additional downstream controls must be used. For example, urban hotspot land may be fit with devices adjacent to parking or service areas designed to remove petroleum hydrocarbons. These devices may also serve as pretreatment devices removing the coarser fraction of sediment. One or more downstream structural controls are then used to meet the full TSS removal goal, as well as water quantity control. • An environmentally sensitive large lot subdivision may be designed and developed so as to waive the water quality treatment requirement altogether. However, detention controls may still be required for downstream channel protection and flood control. WQ V reductions (See Volume 2, Chapter 2) may be employed to reduce the WQ V requirement. In this case, for a smaller site, a well designed structural control may provide TSS removal while a dry detention pond provides flood control. Direct discharge to a large stream and local downstream floodplain management practices may eliminate the need for channel protection and flood control storage altogether. (See Volume 2, Chapter 4) The combinations of structural stormwater controls are limited only by the need to employ measures of proven effectiveness while meeting regulatory and physical site requirements. Figure 3-7 through Figure 3-9 illustrate applications of the treatment train concept to a moderate density residential neighbourhood, a small commercial site, and a large shopping mall site. In Figure 3-7, runoff from yards and driveways reaches roadside grass channels. Then, all stormwater flows to an extended detention micropool stormwater pond. Volume 2, Technical Guidance Page 3 - 21
- Page 1 and 2: CHAPTER 3 STORMWATER CONTROLS TABLE
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- Page 53 and 54: Section 3.2.2 - Extended Dry Detent
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- Page 75 and 76: Section 3.2.5 - Enhanced Swale 3.2.
Section 3.1 - Stormwater Management Controls Overview<br />
• The other structural controls achieving overall TSS target removal each (bioretention, sand<br />
or organic filters, infiltration or soakage trenches, and enhanced swales) are typically used<br />
in combination with other water quality controls and with detention flood controls to meet<br />
the integrated site design goals. The detention facilities are located downstream from the<br />
water quality controls either on-site or combined into a regional or neighborhood facility.<br />
• Where a structural control does not meet the overall TSS target removal criteria, one or<br />
more additional downstream controls must be used. For example, urban hotspot land may<br />
be fit with devices adjacent to parking or service areas designed to remove petroleum<br />
hydrocarbons. These devices may also serve as pretreatment devices removing the<br />
coarser fraction <strong>of</strong> sediment. One or more downstream structural controls are then used<br />
to meet the full TSS removal goal, as well as water quantity control.<br />
• An environmentally sensitive large lot subdivision may be designed and developed so as<br />
to waive the water quality treatment requirement altogether. However, detention controls<br />
may still be required for downstream channel protection and flood control.<br />
WQ V reductions (See <strong>Volume</strong> 2, <strong>Chapter</strong> 2) may be employed to reduce the WQ V<br />
requirement. In this case, for a smaller site, a well designed structural control may provide<br />
TSS removal while a dry detention pond provides flood control. Direct discharge to a large<br />
stream and local downstream floodplain management practices may eliminate the need for<br />
channel protection and flood control storage altogether. (See <strong>Volume</strong> 2, <strong>Chapter</strong> 4)<br />
The combinations <strong>of</strong> structural stormwater controls are limited only by the need to employ<br />
measures <strong>of</strong> proven effectiveness while meeting regulatory and physical site requirements.<br />
Figure 3-7 through Figure 3-9 illustrate applications <strong>of</strong> the treatment train concept to a<br />
moderate density residential neighbourhood, a small commercial site, and a large shopping<br />
mall site.<br />
In Figure 3-7, run<strong>of</strong>f from yards and driveways reaches roadside grass channels. Then, all<br />
stormwater flows to an extended detention micropool stormwater pond.<br />
<strong>Volume</strong> 2, Technical Guidance Page 3 - 21
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