Detailed Stormwater Management Practice Design - Tauranga City ...

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SMG-9.4.5.7 Basic <strong>Design</strong> Parameters There are a number of parameters that should be considered when infiltration practices are used as follows: a) Site Characterisation: This must be done to determine the following: i) Topography within 150 metres of the proposed infiltration practice. ii) Site use. iii) Location of any water supply wells within 150 metres of the proposed infiltration practice. iv) Local site geology to gain understanding of soil and rock units likely to be encountered, the groundwater regime and geologic history of the site. v) For infiltration basins, one test pit or test hole should be placed every 200 m 2 of basin invert. vi) For infiltration trenches, at least one test pit per 15 metres of trench length and 2.5 times deeper than the invert depth of the trench. vii) For soakage pits, at least one test pit for each pit. The test pit should be 1.5 times deeper than the invert depth of the soakage pit. viii) For modular permeable pavement, there must be one test pit per 500 m 2 of infiltrating surface and the test pit should be 2.5 times deeper than the invert depth of the filter bed. ix) The depth, number of test holes or test pits and sampling should be increased, if, in the judgment of the geotechnical engineer, the conditions are highly variable and increasing the depth or the number of explorations is necessary to accurately estimate the performance of the infiltration practice. In addition, the number of explorations may be decreased if, in the opinion of the geotechnical engineer, the conditions are relatively uniform and the borings/test pits omitted will not influence the design. x) <strong>Detailed</strong> logs for each test pit or test hole must be prepared along with a map showing the location of the test pits or holes. Logs must include at a minimum, depth of pit or hole, soil description, depth to water, depth to bedrock or impermeable layer, and presence of stratification. xi) Install ground water monitoring wells (unless the highest ground water level is far below the infiltration practice) to monitor the seasonal ground water levels at the site. b) Procedure for conducting an Infiltration Test: The required approach consists of a relatively large-scale infiltration test to better approximate infiltration rates for design of infiltration practices. The following approach reduces some of the scale errors associated with relatively small-scale double ring infiltrometre or "stove pipe" infiltration tests: i) Excavate the test pit at least 1.5 metres below the bottom of the proposed infiltration practice. Lay back the slopes sufficiently to avoid caving and erosion during the test. ii) The surface area of the bottom of the test pit shall be at least 1 square metre. Page 42 Updated 01/11/2012
iii) Install a vertical minimum 1.5 metre long measuring rod marked in 10 mm increments in the centre of the pit bottom. iv) Use a rigid 150 mm pipe with a splash plate on the bottom to convey water to the bottom of the pit and reduce side-wall erosion or excessive disturbance of the ponded bottom. v) Add water to the pit at a rate that will maintain a water level of between 1 - 1.25 metres above the bottom of the pit. A rotametre can be used to measure the flow rate into the pit. vi) Every 15-30 minutes, record the cumulative volume and instantaneous flow rate in litres per minute necessary to maintain the water level at the same point on the measuring rod. vii) Add water to the pit until one hour after the flow rate into the pit has stabilised (constant flow rate) while maintaining the same ponded level. viii) After one hour after the flow rate has stabilised, turn off the water and record the rate of infiltration in mm/hour from the measuring rod data, until the pit is empty. ix) Based on partial clogging, reduce the derived infiltration rate by a factor of 0.5 and reduce this reduced rate in the design calculations. c) Site Data Analysis: Analysis should be undertaken as follows: i) Determine representative site infiltration rate from soil test results and the stratification identified during the site investigation. ii) Determine the textural class from the U.S. Department of Agriculture (USDA) textural triangle in SMG-9 Figure 21 Soil Textural Triangle. Sand is defined to have a diameter between 2000μ and 50μ while clay has a diameter of less than 2μ. Once the textural class has been determined, the infiltration rates can be found. iii) Determine infiltration rates by taking direct in-situ measurements of soil infiltration rates. iv) Long-term infiltration rates greater than one metre per hour (as per steps 8 and 9 above) are considered too rapid to allow significant water quality treatment to occur and pretreatment will have to be provided. Page 43 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 22 and 23: SMG-9.4.3.1 Basic Design Parameters
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
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:
Page 76 and 77: For the purposes of this guideline,
Page 78 and 79: SMG-9.4.8.7 Detailed Design Procedu
Page 80 and 81: This is indicated on SMG-9 Figure 3
Page 82 and 83: SMG-9 Figure 37 - Waitakere City Co
Page 84 and 85: SMG-9.4.9.7.7 Stormwater Management
Page 86 and 87: SMG-8 Figure 8b - Information on ra
Page 88 and 89: SMG-9.4.10.5 Advantages of Water Ta
Page 90 and 91: SMG-9 Figure 39 Calculation of Rood
Page 92 and 93: The 15% wastage factor accounts for
Page 94 and 95:
Commercial and industrial sites wil
Page 96 and 97:
SMG-9 Table 24 Stormwater Managemen
Page 98 and 99:
SMG-9.4.11.2 Separator Size The siz
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VH = Q/1.125 Calculate the surface
Page 102 and 103:
When an outfall is sited in a coast
Page 104 and 105:
SMG-9.5.1.3 Riprap Aprons Outlet pr
Page 106 and 107:
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
Page 112 and 113:
SMG-9 Apx A.3 Sand Filter Case Stud
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SMG-9 Apx A.4 Rain Garden Case Stud
Page 116 and 117:
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
Page 134 and 135:
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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