Detailed Stormwater Management Practice Design - Tauranga City ...

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SMG-9 Table 2 Stormwater Management Function - Swales Water Quality Metals Sediment TPH Possibly through specific design Flood Protection x Stream Channel Erosion Protection Swales are a very appropriate practice for roads and new development. They can easily occupy a linear corridor without taking up much additional space. They can also take the place of conventional stormwater conveyance systems. Although swales may vary in their purpose in different areas, their overall objective is to slow stormwater flows, capture contaminants and possibly reduce the total volume of stormwater runoff. Water quality treatment can be provided by passing stormwater flows through vegetation. Passage through vegetation and providing contact with organic matter allows physical, chemical and biological processes to occur that reduce contaminant delivery downstream. A key factor in vegetated swale water quality performance is the residence time that the water takes to travel through the swale. Residence time depends on the following items: a) The longitudinal slope of the swale. b) The cross-sectional area of the swale. c) Velocity of the flow. The velocity of flow is a function of the flow area, slope and frictional resistance of the vegetation and a common equation for calculating velocity is Manning’s Equation. V = R0 .67 s 0.5 /n Where: V = Average velocity in metres/sec. R = the hydraulic radius of the swale in metres s = slope of the swale in metres/metre n = Manning coefficient of roughness Residence time can then be determined by the following equation: Page 6 Updated 01/11/2012 x
t = L/V Where: t = residence time in minutes (divide result by 60 sec/m) V = velocity of flow at the design rate of flow in metres/sec. L = swale length in metres SMG-9.4.1.1 Basic Design Parameters SMG-9 Table 3 Swale Design Elements should be used for swale design elements. SMG-9 Table 3 Swale Design Elements Design Parameter Criteria Longitudinal slope < 5% Maximum velocity 0.8 m/s for water quality storm Maximum water depth above vegetation The water quality design water depth should not exceed design height for grass. This is a key criterion for ensuring Manning roughness coefficient is provided. Design vegetation height* 50 - 150 mm Manning coefficient 0.25 for WQ storm, 0.03 for submerged flow (10-yr. Storm) Minimum hydraulic residence time 9 minutes Maximum catchment area served 4 hectares Maximum lateral slope 0% Maximum side slope 5H:1V (shallow as possible for mowing Where longitudinal slope < 2% purposes) Perforated underdrains shall be provided Where longitudinal slope > 5% Check dams shall be provided to ensure effective slope < 5% Where concentrated flows enter the Level spreaders shall be placed at the head of swale (from pipes) the swale to disperse flows 10-year storm velocities < 1.5 m/s unless erosion protection is provided * this applies to normal grasses. Other vegetation, such as Oioi can provide improved performance with reduced maintenance frequency. Page 7 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 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 26 and 27: tf = time required for runoff to pa
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
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SMG-9.4.6.12 Pond Aesthetics and La
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SMG-9 Figure 25 Schematic of a Stor
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When an extended detention orifice
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The forebay should meet the followi
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Requiring, during design, safety fe
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Until recently, the filling and dra
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The most common design priority for
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SMG-9.4.7.1.2 Water Quality Volumes
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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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Detailed Stormwater Management Practice Design - Tauranga City ...

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