Detailed Stormwater Management Practice Design - Tauranga City ...

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tf = time required for runoff to pass through the filter (days) The following values should be used. tf = 2 days (maximum) k = 1 metre/day df = 0.3metres (minimum) The following points should be discussed regarding the values that should be used: a) Time Required to Pass the Water Quality Storm b) Permeability Rate Selected SMG-9.4.3.2.1 Time Required to Pass the Water Quality Storm The reasons why this value was selected are: a) Having two days as a limiting value will ensure that the volume is available for the next storm. It should be recognised that these are averages and some fluctuation will occur. b) Having the system drain within a two-day period will prevent the development of biofilms on the surface of the sand, which would reduce permeability rates. SMG-9.4.3.2.2 Permeability Rate Selected This is an issue that has controversy associated with it. Sand has a high permeability rate and the value selected is very low. Experience has shown that the initial high permeability rate rapidly reduces when contaminated stormwater runoff passes through the sand. The rate reduces to a level where it stabilises for a period of time before complete clogging occurs. The value generally accepted internationally is approximately one metre/day. SMG-9.4.3.3 Sizing the Sedimentation Chamber a) Size the sedimentation chamber with the following points in mind: i) Inflow into the chamber must not cause resuspension of previously deposited sediments. ii) The sedimentation chamber outlet must deliver flow to the filtration chamber as sheet flow. iii) The sedimentation chamber must be at least 25% of the filtration area. iv) Flow velocities in the sedimentation chamber are required to be below 0.25 m/s. v) The sedimentation chamber must have a permanent pool with a minimum depth of 400 mm to reduce potential for sediment resuspension Page 24 Updated 01/11/2012
vi) The sedimentation chamber should be configured to avoid short-circuiting of flow. b) The sand specifications are provided in SMG-9 Table 7 Sand Specifications for Sand Filter. SMG-9 Table 7 Sand Specifications for Sand Filter Sieve Size (mm) Percentage Passing 9.5 100 6.3 95-100 3.17 80-100 1.5 50-85 0.8 25-60 0.5 10-30 0.25 2-10 There will be some variation in sand grades from the specified grades. However, a number are close to the lower limit and can be used. It is important to meet as closely as possible the specified limits as coarser aggregate will allow for more contamination migration and finer aggregate will clog more quickly. Recent work done by the Facility for Advancing Water Biofiltration (FAWB) in Australia has indicated excellent TSS and metals removal with soil and sand-based filters that are non-vegetated (FAWB, 2008). Thus, it can be recommended that contaminants of greatest concern in <strong>Tauranga</strong> <strong>City</strong> (sediment and metals) could be effectively removed from stormwater discharges using sand filtration. A key element in the conclusion is that wetting and drying are key elements in treatment. a) An under drainage system shall be provided. The system will normally consist of perforated lateral pipes (150 mm diameter) that are placed in the gravel or stone layer that is under the sand. The depth of the gravel layer shall be at least 200 mm in depth with filter fabric between the gravel and sand to prevent migration out of the system. SMG-9.4.3.4 Sand Filter Case Study Refer to SMG-9 Apx A.3 Sand Filter Case Study. SMG-9.4.4 Rain Gardens Rain gardens are designed and constructed to capture and treat stormwater runoff through: a) Sedimentation b) Filtration Page 25 Updated 01/11/2012
Page 1: SMG-9 - Detailed Stormwater Managem
Page 4 and 5: In the same regard reducing total s
Page 6 and 7: As an example, a stormwater managem
Page 8 and 9: SMG-9 Table 2 Stormwater Management
Page 10 and 11: The following points require some d
Page 12 and 13: e) Select a swale shape. Two shapes
Page 14 and 15: SMG-9.4.1.3 Flows in Excess of the
Page 16 and 17: SMG-9.4.1.6 Swale Case Study Refer
Page 18 and 19: SMG-9.4.2.1 Basic Design Parameters
Page 20 and 21: ) Once the peak discharge is determ
Page 24 and 25: SMG-9 Figure 11 - Diversion Weir SM
Page 28 and 29: c) Infiltration (depending on soils
Page 30 and 31: Rain Garden design differs only sli
Page 32 and 33: SMG-9.4.4.1.1 Filter Media Filter m
Page 34 and 35: SMG-9.4.4.1.5 Transition Layer The
Page 36 and 37: SMG-9 Table 11 Grasses, Ground Cove
Page 38 and 39: Infiltration practices are used for
Page 40 and 41: SMG-9 Figure 19 Schematic of a Soak
Page 42 and 43: Any impermeable soil layer close to
Page 46 and 47: SMG-9 Figure 21 Soil Textural Trian
Page 48 and 49: e) Calculate the practice depth and
Page 50 and 51: SMG-9.4.6.1 Types of Pond Ponds are
Page 52 and 53: A study in the U.S.A (DNR. 1986) in
Page 54 and 55: Where there are downstream flooding
Page 56 and 57: There may be mitigation requirement
Page 58 and 59: SMG-9.4.6.12 Pond Aesthetics and La
Page 60 and 61: SMG-9 Figure 25 Schematic of a Stor
Page 62 and 63: When an extended detention orifice
Page 64 and 65: The forebay should meet the followi
Page 66 and 67: Requiring, during design, safety fe
Page 68 and 69: Until recently, the filling and dra
Page 70 and 71: The most common design priority for
Page 72 and 73: SMG-9.4.7.1.2 Water Quality Volumes
Page 74 and 75: The design steps are the following:
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For the purposes of this guideline,
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SMG-9.4.8.7 Detailed Design Procedu
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This is indicated on SMG-9 Figure 3
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SMG-9 Figure 37 - Waitakere City Co
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SMG-9.4.9.7.7 Stormwater Management
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SMG-8 Figure 8b - Information on ra
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SMG-9.4.10.5 Advantages of Water Ta
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SMG-9 Figure 39 Calculation of Rood
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The 15% wastage factor accounts for
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Commercial and industrial sites wil
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SMG-9 Table 24 Stormwater Managemen
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SMG-9.4.11.2 Separator Size The siz
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VH = Q/1.125 Calculate the surface
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When an outfall is sited in a coast
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SMG-9.5.1.3 Riprap Aprons Outlet pr
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SMG-9 Figure 46 Angled Entry of Out
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SMG-9 - Appendix A Case Studies SMG
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SMG-9 Apx A.2 Filter Strip Case Stu
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SMG-9 Apx A.3 Sand Filter Case Stud
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SMG-9 Apx A.4 Rain Garden Case Stud
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SMG-9 Apx A.5 Infiltration Case Stu
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SMG-9 Apx A.6 Ponds Case Study SMG-
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SMG-9 Table A.6.3 Stage-Storage Rel
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Outflow from ED orifice = Q = 0.62A
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= (Qn/d 1.67 s 0.5 ) - Zd b = ((.04
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SMG-9 Apx A.8.3 Design Water qualit
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SMG-9 Apx A.9 Green Roof Case Study
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Extended detention orifice sizing -
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The minimum width and depth require
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SMG-9 Table B.1.2a Particle Charact
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Particle Diameter (µm) SMG-9 Table
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SMG-9 Figure B.1.3 Wetland Process
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Plants do take up nutrients or meta
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