Volume 2-05, Chapter 3 - City of Wichita

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Section 3.2.2 - Extended Dry Detention Pond 3.2.2.1 General Description Dry extended detention (ED) ponds are surface facilities intended to provide extended periods of detention for water quality and channel protection control, and may also serve to control peak flood flows. 3.2.2.2 Pollutant Removal Capabilities The following design pollutant removal rates are average pollutant reduction percentages for design purposes derived from sampling data, modeling and professional judgment. In a situation where a removal rate is not deemed sufficient, additional controls may be put in place at the given site in a series or “treatment train” approach. • Total Suspended Solids – 60% • Total Phosphorus – 35% • Total Nitrogen – 25% • Heavy Metals – 25% • Fecal Coliform – Insufficient data to provide pollutant removal rate For additional information and data on pollutant removal capabilities, see the National Pollutant Removal Performance Database (2nd Edition) available at www.cwp.org and the National Stormwater Best Management Practices (BMP) Database at www.bmpdatabase.org. 3.2.2.3 Design Criteria and Specifications Location • Extended dry detention ponds must combine with other structural stormwater controls to provide treatment of the full WQ v . They may be part of a treatment train which treats the WQ v . General Design • Extended dry detention ponds are sized to provide 24 hours of extended detention of the WQ V . • Extended dry detention ponds are sized to provide 24 hours of extended detention of the CP V . • Extended dry detention ponds can also provide additional storage volume for conventional detention (peak flow reduction) of the 2 through 100-year storm event. • Routing calculations must be used to demonstrate that the flood storage volume and outlet structure configuration are adequate. See Volume 2, Chapters 4 and 5 for procedures on the design of detention storage. Page 3 - 48 Volume 2, Technical Guidance
Section 3.2.2 - Extended Dry Detention Pond • Design may be subject to the requirements of the Kansas dam safety program based on the volume, dam height, and level of hazard. • Earthen embankments shall have side slopes no steeper than 3:1 (horizontal to vertical). • Vegetated slopes shall be less than 20 feet in height and shall have side slopes no steeper than 4:1 (horizontal to vertical). Riprap-protected slopes shall be no steeper than 3:1. Geotechnical slope stability analysis is recommended for slopes greater than 10 feet in height. • Areas above the normal high water elevations of the detention facility should be sloped toward the basin to allow drainage and to prevent standing water. Careful grading is required to avoid creation of upland surface depressions that may retain runoff. The bottom area of storage facilities should be graded toward the outlet to prevent standing water conditions. A low flow or pilot channel across the facility bottom from the inlet to the outlet (often constructed with riprap or a concrete flume) is recommended to convey low flows and prevent standing water conditions. • Ponds cannot be located within a stream or any other navigable waters of the U.S., including wetlands, without obtaining applicable local, Kansas and federal permits. • Dry extended detention ponds located in floodplains or backwater areas must perform as specified for peak flow control for any tailwater condition, up to the Base Flood Elevation (BFE). The potential for back flow into the pond must be addressed with flap gates or by providing sufficient volume to receive backflow up to the BFE, and still provide peak flow control surcharge volume in the pond (above the BFE). Inlet and Outlet Structures • Discharge into the pond from inflow channels or pipes are to be stabilized with flared riprap aprons, or the equivalent. A sediment forebay or equivalent upstream pretreatment with a volume of 0.1 inches per impervious acre of contributing drainage shall be provided upstream of the pond. The pre-treatment storage volume is part of the total WQ v required. • An orifice capable of detaining the WQ v for 24 hours must be provided. The orifice shall be adequately protected from clogging using designs found in chapter 5. • Likewise, the outlet structure must have an orifice capable of detaining the CP v for 24 hours. Orifice protection requirements are the same as for the WQ v . • For peak flow control, discharge is controlled by a principal spillway, typically consisting of a riser and outlet pipe. The WQ v and CP v orifices are usually incorporated into the riser. Additional orifices and weirs are incorporated into the riser to control the 2 through 100- year design storms. • Small outlets that will be subject to clogging or are difficult to maintain are not acceptable. • See Volume 2, Chapters 4 and 5 for more information on the design of outlet works. • Seepage control or anti-seep collars should be provided for all outlet pipes. Volume 2, Technical Guidance Page 3 - 49
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CHAPTER 3 STORMWATER CONTROLS TABLE
Page 3 and 4: Chapter 3 - Table of Contents 3.2.8
Page 5 and 6: Chapter 3 - Table of Contents LIST
Page 7 and 8: Section 3.1 - Stormwater Management
Page 31 and 32: Section 3.2.1 - Stormwater Pond 3.2
Page 33 and 34: Section 3.2.1 - Stormwater Pond Fig
Page 35 and 36: Section 3.2.1 - Stormwater Pond For
Page 37 and 38: Section 3.2.1 - Stormwater Pond •
Page 39 and 40: Section 3.2.1 - Stormwater Pond 1'
Page 45 and 46: Section 3.2.1 - Stormwater Pond 3.2
Page 47 and 48: Section 3.2.1 - Stormwater Pond Ste
Page 53: Section 3.2.2 - Extended Dry Detent
Page 57 and 58: Section 3.2.2 - Extended Dry Detent
Page 59 and 60: Section 3.2.3 - Vegetative Filter S
Page 67 and 68: Section 3.2.4 - Grassed Channel 3.2
Page 73 and 74: Section 3.2.4 - Grassed Channel max
Page 75 and 76: Section 3.2.5 - Enhanced Swale 3.2.
Page 77 and 78: Section 3.2.5 - Enhanced Swale Chan
Page 79 and 80: Section 3.2.5 - Enhanced Swale B. G
Page 81 and 82: Section 3.2.5 - Enhanced Swale High
Page 83 and 84: Section 3.2.5 - Enhanced Swale Side
Page 85 and 86: Section 3.2.5 - Enhanced Swale 3.2.
Page 87 and 88: Section 3.2.6 - Infiltration Trench
Page 99 and 100: Section 3.2.7 - Soakage Trench 3.2.
Page 101 and 102: Section 3.2.7 - Soakage Trench •
Page 103 and 104: Section 3.2.8 - Surface Sand Filter
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Section 3.2.8 - Surface Sand Filter
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Section 3.2.9 - Bioretention Areas
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Section 3.2.10 - Stormwater Wetland
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Section 3.3 - Secondary TSS Treatme
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Section 3.3.1 - Proprietary Treatme
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Section 3.3.1 - Proprietary Treatme
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Section 3.3.2 - Gravity (Oil-Water)
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Section 3.3.3 - Alum Treatment 3.3.
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Section 3.3.3 - Alum Treatment •
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Section 3.3.4 - Underground Sand Fi
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Section 3.3.5 - Organic Filter 3.3.
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Section 3.3.5 - Organic Filter •
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Section 3.4 - Other Stormwater Mana
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Section 3.4.1 - Conventional Dry De
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Section 3.4.2 - Underground Dry Det
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Section 3.4.3 - Porous Pavement 3.4
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Section 3.4.3 - Porous Pavement The
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Section 3.4.3 - Porous Pavement com
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Section 3.4.3 - Porous Pavement Fig
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Section 3.4.4 - Modular Porous Pave
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Section 3.4.5 - Green Roof 3.4.5 Gr
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Section 3.4.5 - Green Roof Signific
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Section 3.4.5 - Green Roof 3.4.5.3
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Volume 2-05, Chapter 3 - City of Wichita

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