Hillingdon SuDS Design & Evaluation Guide

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Detailed Design Bioretention Raingardens A bioretention structure differs from a raingarden in that it employs an engineered top soil and is used to manage polluted urban runoff in street locations and carparks. These features can contribute significantly to the urban scene so should be designed to meet urban design standards. The runoff entering bioretention features will normally carry silt and pollution from vehicles and urban street use. Therefore, some maintenance should be expected to remove the build-up of inorganic silt. The free-draining nature of engineered soils leads to the washing away of nutrients from the soil. The proportion of organic matter should be relatively high and replenished yearly by the application of a mulch layer of well composted greenwaste or shredded plant matter arising from maintenance. Key design aspects for bioretention raingardens include; 1. silt collection in forebays 2. space above the soil profile for water collection and stilling before infiltration through the engineered soil 3. a surface mulch of organic matter, grit or gravel protects the infiltration capacity of the soil 4. a free draining soil, 450 -600mm deep, with 20-30% organic matter cleans, stores and conveys runoff to a drainage layer 5. a transition layer of grit and/or sand protects the under-drained drainage layer that discharges to an outfall 6. a surface overflow for heavy rain or in the event of blockage. 127 1 6 2 3 4 5 London Borough of Hillingdon SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates
Permeable surfaces Permeable surfaces enable SuDS designers to direct rainfall straight into a SuDS structure for cleaning and storage or infiltration into the ground. There are a number of permeable surfaces available. All should have in common: 1. a pervious surface to allow water through the pavement surface 2. an open-graded sub-base layer that provides structural strength to the pavement with about 30% by volume available for water storage. 3. Silt washed off adjacent landscape areas can lead to localised surface clogging. This risk can be managed through design detailing as follows: ■■ ■■ ■■ slope adjacent landscape areas away use paved or turfed surfaces to adjacent areas soil in adjacent planting beds should be min. 50mm below the pavement ■■ ■■ edge adjacent planting should include dense ground cover to bind the soil in place slopes running toward permeable surfaces should have a depression and ideally an underdrain before reaching the pervious surface. The design and construction of pervious pavements are covered by guidance in the SuDS Manual (Section 20) and the Interpave website www.paving.org.uk There are no reported issues with surface clogging under normal use. A dedicated maintenance may be required after between 10 and 20 years of use comprising a brush and suction removal of grit joints and joint replacement. Soft landscape areas are set below kerb level at this permeable paving installation. Almac Car Park, Limerick, Ireland. Detailed Design 128 3 1 2 London Borough of Hillingdon SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates
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Sustainable Drainage Design & Evalu
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Contents 1.0 Introduction 2.0 Under
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This development guide has the supp
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1.2 SuDS today There have been a nu
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2.0 Understanding Rainfall It is im
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Where the ground is impermeable, wa
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Overview 3.0 The Impact of Developm
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Overview 3.3 Consequences of piped
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Overview 4.0 The Role of SuDS Susta
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Overview SuDS schemes offer diverse
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Overview 5.0 The SuDS Design & Eval
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Overview 5.3 The objectives of the
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Local SuDS requirements 21 6.0 Land
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Local SuDS requirements 23 Local Su
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Concept Design for Holyoakes School
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7.4 Concept Design process 7.4.1 Fl
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Modifi Step 2 - Modified Flow Route
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7.4.3 Collection of runoff from har
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7.4.5 Conveyance of runoff between
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A flow control generally defines th
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Additional considerations for infil
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7.4.9 Preliminary flow and volume c
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7.4.11 Managing runoff from site If
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Concept Design 45 7.4.13 Flow rate
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Concept Design Long Term Storage Su
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Concept Design 7.5 Concept informat
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Concept Design 51 7.5.3 Preliminary
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Concept Design 7.5.6 Management and
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5. Quality Confirm ‘treatment sta
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8.2 Objectives of SuDS Outline Desi
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8.4 Design criteria considerations
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8.5.2 Aspects of Health and Safety
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8.8 Outline information required fo
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Detailed Design 9.0 Design and Eval
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Detailed Design 9.3 Typical Detaile
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Detailed Design 71 Plan excerpt: pr
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Detailed Design 73 9.3.4 Detailed D
Page 81 and 82: 9.4 Critical levels Levels are impo
Page 83 and 84: 9.5.3 Calculation processes Calcula
Page 85 and 86: 9.5.4.3 Making allowances for inter
Page 87 and 88: 9.5.4.6 Accounting for Climate Chan
Page 89 and 90: 9.5.5 Calculating storage requireme
Page 91 and 92: Approach 2 Where volumes cannot be
Page 93 and 94: Detailed Design 88 Designers should
Page 95 and 96: Detailed Design Lamb Drove, Cambour
Page 97 and 98: Parameter Modelling of the SuDS lay
Page 99 and 100: 9.6.1 Design flexibility A framewor
Page 101 and 102: 9.6.4 Single, tiered storage compon
Page 103 and 104: 9.6.6 The importance of protected o
Page 105 and 106: the 1 in 100 flow rate - for exampl
Page 107 and 108: 9.7 Water quality Rainfall picks up
Page 109 and 110: For low to medium risk sites, the i
Page 111 and 112: 9.7.5 Water quality design checklis
Page 113 and 114: 9.8.2 Accessibility All parts of th
Page 115 and 116: Firstly the collection and conveyan
Page 117 and 118: 9.9.3 Key design criteria for biodi
Page 119 and 120: 9.10.2 The Principles of SuDS plant
Page 121 and 122: Amenity grass An everyday grass sur
Page 123 and 124: Meadow vegetation Meadow vegetation
Page 125 and 126: Bioretention features are defined b
Page 127 and 128: 9.10.3.4 A place for trees and shru
Page 129 and 130: Source Controls providing collectio
Page 131: Raingardens The raingarden concept
Page 135 and 136: Filter drains Filter drains, someti
Page 137 and 138: Filter strips The hard edge from a
Page 140 and 141: Detailed Design 135 The safety cons
Page 142 and 143: Detailed Design 9.11.5 Storage stru
Page 144 and 145: Detailed Design 9.12 Management of
Page 146 and 147: Detailed Design 9.12.3 Example of S
Page 149: Sheffield Grey to Green : an excell
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Hillingdon SuDS Design & Evaluation Guide

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