Volume 2-05, Chapter 3 - City of Wichita

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Section 3.2.1 - Stomwater Pond 3.2.1.5 Planning and Design Criteria The following criteria are to be considered minimum standards for the design of a stormwater pond facility. Consult with the local review authority to determine if there are any variations to these criteria or additional standards that must be followed. A. LOCATION AND SITING • Stormwater ponds should have a minimum contributing drainage area of 25 acres or more for wet pond or extended detention wet pond to maintain a permanent pool. (See previous discussion.) For an extended detention micropool pond, the minimum drainage area is 10 acres. A smaller drainage area can be considered when water availability can be confirmed (such as from a upstream groundwater spring source). In any case, a water balance must be performed to verify a sustainable source of water (See Volume 2, Chapter 4). Ensure that an appropriate anti-clogging device is provided for the pond outlet. • A stormwater pond should be sited such that the topography allows for maximum runoff storage at minimum excavation or construction costs. Pond siting should also take into account the location and use of other site features such as buffers and undisturbed natural areas and should attempt to aesthetically “fit” the facility into the landscape. • Stormwater ponds should not be located on steep (>15%) or unstable slopes. • Ponds cannot be located within a stream or any other navigable waters of the U.S., including wetlands, without obtaining applicable local, state and federal permits. • No utilities should be located within the reserve boundary for the pond/basin site, if a reserve is required. B. GENERAL DESIGN • A well-designed stormwater pond consists of: • Permanent pool of water for water quality treatment, • Overlying temporary storage zone in which runoff control volumes are detained for quantity control, and • Shallow littoral zone (aquatic bench) along the edge of the permanent pool that acts as a biological filter and wave-action diffuser. • To the maximum extent practicable, the long axis of a pond shall be oriented east-west to minimize erosion from wind waves. • In addition, all stormwater pond designs must include a sediment forebay or equivalent pretreatment at all major inflows to the basin to allow heavier sediments to drop out of suspension before the runoff enters the permanent pool. • Additional pond design features include a principal spillway, an emergency spillway, maintenance access, safety bench, pond buffer, and appropriate native landscaping. Page 3 - 30 Volume 2, Technical Guidance
Section 3.2.1 - Stormwater Pond • Stormwater 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). Thepotential 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). Figure 3-14 through Figure 3-17 provide plan view and profile schematics for the design of a wet pond, extended detention wet pond, extended detention micropool pond and a multiple pond system. C. PHYSICAL SPECIFICATIONS / GEOMETRY In general, pond designs are unique for each site and application. However, there are number of geometric ratios and limiting depths for pond design that must be observed for adequate pollutant removal, ease of maintenance, and improved safety. • Permanent pool volume is typically sized as follows: • Standard wet ponds: 100% of the water quality treatment volume (1.0 WQ v ); • Extended detention wet ponds: 50% of the water quality treatment volume (0.5 WQ v ) with the remaining 50% in the extended detention above the permanent pool; • Extended detention micropool ponds: Approximately 0.1 acre-inch per impervious acre, with the balance of WQ v in the extended detention. • Proper geometric design is essential to prevent hydraulic short-circuiting (unequal distribution of inflow), which results in the failure of the pond to achieve adequate levels of pollutant removal. The minimum length-to-width ratio for the permanent pool shape is 1.5:1, and should ideally be greater than 3:1 to avoid short-circuiting. In addition, ponds should be wedge-shaped when possible so that flow enters the pond and gradually spreads out, improving the sedimentation process. Baffles, pond shaping or islands can be added within the permanent pool to increase the flow path. Volume 2, Technical Guidance Page 3 - 31
Page 1 and 2: 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
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Page 39 and 40: Section 3.2.1 - Stormwater Pond 1'
Page 41 and 42: Section 3.2.1 - Stormwater Pond •
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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 and 54: 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
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Page 75 and 76: Section 3.2.5 - Enhanced Swale 3.2.
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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.
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Section 3.2.6 - Infiltration Trench
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Section 3.2.7 - Soakage Trench 3.2.
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Section 3.2.7 - Soakage Trench •
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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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