dmrb volume 4 section 2 part 3 - hd 33/06 - surface and

May 2006

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 4 GEOTECHNICS ANDDRAINAGE

SECTION 2 DRAINAGE

PART 3

HD 33/06

SURFACE AND SUB-SURFACEDRAINAGE SYSTEMS FOR HIGHWAYS

SUMMARY

This Standard gives guidance on the selection of thetypes of surface and sub-surface drainage for trunkroads including motorways. It describes the variousalternative solutions that are available to drain trunkroads in the UK, including their potential to controlpollution and flooding. It also includes guidance ondrainage of earthworks associated with highwayschemes and appropriate signing for pollution controldevices.

INSTRUCTIONS FOR USE

This revised Advice Note is to be incorporated in theManual.

1. This document supersedes HD 33/96 which isnow withdrawn.

2. Remove existing Contents pages for Volume 4,and insert new Contents pages for Volume 4dated May 2006.

3. Remove HD 33/96, which is superseded byHD 33/06 and archive as appropriate.

4. Insert HD 33/06 into Volume 4, Section 2,Part 3.

5. Please archive this sheet as appropriate.

Note: A quarterly index with a full set of VolumeContents Pages is available separately from TheStationery Office Ltd.

HD 33/06

Surface and Sub-SurfaceDrainage Systems for Highways

Summary: This Standard gives guidance on the selection of the types of surface and sub-surface drainage for trunk roads including motorways. It describes the variousalternative solutions that are available to drain trunk roads in the UK, includingtheir potential to control pollution and flooding. It also includes guidance ondrainage of earthworks associated with highway schemes and appropriatesigning for pollution control devices.


THE HIGHWAYS AGENCY

TRANSPORT SCOTLAND

WELSH ASSEMBLY GOVERNMENTLLYWODRAETH CYNULLIAD CYMRU

THE DEPARTMENT FOR REGIONAL DEVELOPMENTNORTHERN IRELAND

Volume 4 Section 2Part 3 HD 33/06

May 2006

REGISTRATION OF AMENDMENTS

Amend Page No Signature & Date of Amend Page No Signature & Date ofNo incorporation of No incorporation of

amendments amendments

Registration of Amendments

VOLUME 4 GEOTECHNICS ANDDRAINAGE

SECTION 2 DRAINAGE

PART 3

HD 33/06

SURFACE AND SUB-SURFACEDRAINAGE SYSTEMS FOR HIGHWAYS

Contents

Chapter

1. Introduction

2. Effect of Road Geometry on Drainage

3. Surface Water Collection: Edge Drainage Details

4. Sub-Surface Drainage

5. Earthworks Drainage

6. Detailed Design, Pavement Edge Drainage

7. Control of Pollution and Flooding

8. Signing of Pollution Control Devices

9. References

10. Enquiries


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Chapter 1Introduction

1. INTRODUCTION

General

1.1 This Standard gives guidance on the selection ofthe types of surface and sub-surface drainage for trunkroads including motorways. It describes the variousalternative solutions that are available to drain trunkroads in the UK, including their potential to controlpollution and flooding. It also includes guidance ondrainage of earthworks associated with highwayschemes and appropriate signing for pollution controldevices

Scope

1.2 The guidance given on drainage design isapplicable to all trunk road projects. It provides asummary of design documents available, primarilythose published on behalf of the OverseeingOrganisations. It describes the various alternativesolutions that are available to drain trunk roads in theUK, including their potential to control pollution andflooding. It advises upon selection in principle, andgives advice on the detailed design of the variouspavement edge drainage alternatives with regard toavailable design guides.

Implementation

1.3 This Standard should be used forthwith for allschemes currently being prepared provided that, in theopinion of the Overseeing Organisation, this would notresult in significant additional expense or delayprogress. Design Organisations should confirm itsapplication to particular schemes with the OverseeingOrganisation.

Design Principles

1.4 There are three major objectives in the drainageof trunk roads:

i) the speedy removal of surface water to providesafety and minimum nuisance;

ii) provision of effective sub-surface drainage tomaximise longevity of the pavement and itsassociated earthworks; and

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ii) minimisation of the impact of the runoff on thereceiving environment.

t is also necessary to provide for drainage ofarthworks and structures associated with the highway.

.5 The performance of pavement foundations,arthworks and structures can be adversely affected byhe presence of water, and good drainage is therefore anmportant factor in ensuring that the required level ofervice and value for money are obtained. Highwayrainage can be broadly classified into two elementssurface and sub-surface drainage, but these two aspectsre not completely disparate. Surface water is able tonfiltrate into road foundations, earthworks or structureshrough any surface which is not completelympermeable, and will thence require removal by sub-urface drainage unless other conditions render thisnnecessary.

.6 The necessary objectives can be achieved by:

) combined systems, where both surface water andsub-surface water are collected in the same pipe;or

i) separate systems, where the sub-surface water iscollected in a separate drainage conduit from theone which is used for collection of surface water.Sub-surface water of a separate system will becollected in a fin or narrow filter drain.

ach system has certain advantages and disadvantagesnd one may be more appropriate than the other in anyarticular situation.

.7 Drainage networks incorporating systems such asil separators, sediment traps, filter drains, wetlandsnd other vegetated systems can, by virtue of theiresign, provide a degree of control over pollution andlood control. The three main processes applicable tohe treatment of highway runoff are:

sedimentation – the removal of suspended solids;

separation – the removal of all solids and non-aqueous liquids;

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Chapter 1Introduction

• vegetated treatment processes, includingfiltration, settlement, adsorption, biodegradationand plant uptake, depending on the type andcombination of systems.

The selection and design of systems will depend on thepollution load, the risk of spillage or flood and the siteconditions, particularly if protected species or sites maybe affected. In practice, the network is likely to be acombination of systems. Guidance on the assessment ofthe risk of either pollution or flooding is given inHA 216 Road Drainage and the Water Environment(DMRB 11.3.10). Chapter 7 of this Standard givesexamples of conventional drainage systems that havethe potential to mitigate the effects of runoff. Guidanceon vegetated drainage systems is given in HA 103Vegetated Drainage Systems for Highway Runoff(DMRB 4.2). Guidance on the design of soakaways isgiven in HA 118 Design of Soakaways (DMRB 4.2) andon the design of grassed surface water channels inHA 119 Grassed Surface Water Channels for HighwayRunoff (DMRB 4.2).

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Chapter 2Effect of Road Geometry on Drainage

ETRY ON DRAINAGE
2. EFFECT OF ROAD GEOM
Introduction

2.1 Road surfacing materials are traditionallydesigned to be effectively impermeable, and only asmall amount of rainwater should percolate into thepavement layers. It is important that any such water isable to drain through underlying pavement layers andaway from the formation. Rainfall which does notpermeate the pavement surface must be shed towardsthe edges of the pavement.

Road Geometry

2.2 Drainage is a basic consideration in theestablishment of road geometry and vertical alignmentsshould ensure that:

a) outfall levels are achievable; and

b) subgrade drainage can discharge above thedesign flood level of any outfall watercourses.

These considerations may influence the minimumheight of embankments above watercourses. They couldalso influence the depth of cuttings as it is essential thatsag curves located in cuttings do not result in low spotswhich cannot be drained.

TD 9 (DMRB 6.1.1) and TD 16 (DMRB 6.2.3) containguidance to minimise problems and dangers in sheddingwater from carriageways. The following paragraphssummarise good practice advocated in these documentswith regard to the interaction of geometry and drainageand therefore the minimum standards of road geometrywhich the drainage designer would generally expect.

2.3 TD 9 (DMRB 6.1.1) indicates that considerationof drainage of the carriageway surface is particularlyimportant in areas of flat longitudinal gradient and atrollovers. Where longitudinal gradients are flat it isbetter to avoid rollovers completely by adoption ofrelatively straight alignments with balanced crossfalls.

Drainage can then be effected over the edge of thecarriageway to channels, combined surface water andground water drains or some other form of lineardrainage collector. Gullies may be required at veryclose spacings on flat gradients.

May 2006

Areas of superelevation change require carefulconsideration. Where superelevation is applied orremoved the crossfall on the carriageway may beinsufficient for drainage purposes without assistancefrom the longitudinal gradient of the road. TD 9(DMRB 6.1.1) suggests that a longitudinal gradient of0.5% should be regarded as the minimum in thesecases. This is the nett longitudinal gradient includingthe effects of the application of superelevation actingagainst the gradient where superelevation is:

a) applied on a downhill gradient; or

b) removed on an uphill gradient.

To achieve a resultant gradient of 0.5% may require adesign line gradient of 1.5%. Alternatively thesuperelevation area may be moved to a differentlocation by revision of the horizontal alignment, or inextreme cases a rolling crown may be applied. It isessential that a coordinated analysis of the horizontaland vertical alignments with reference to surface waterdrainage is carried out before alignments are fixed. Itshould also be borne in mind that permissible standardsadopted in design may not be achieved in practice as aconsequence of the construction tolerances permissiblefor road levels. TA 80 (DMRB 4.2) gives furtherguidance.

2.4 TD 16 (DMRB 6.2.3) provides guidance oncrossfall and longitudinal gradients for carriagewaydrainage of roundabouts. Roundabouts are designedwith limited crossfall to provide smooth transitions andreduce the risk of loads being shed from vehiclesturning through relatively small horizontal radii.Consequently areas of carriageways may becomeinherently flat. Careful consideration should be given toroad profiling and the net gradients which result fromcombination of crossfall and longfall. These may bebest indicated by contoured drawings of the requiredcarriageway surface.

Safety Considerations

2.5 Safety aspects of edge details are generallyfunctions of the location, form and size of edge restraintdetail, and any associated safety barrier or safety fenceprovision. Roadside drainage features are primarilydesigned to remove surface water. Since they are placedalong the side of the carriageway, they should not

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Chapter 2Effect of Road Geometry on Drainage

normally pose any physical hazard to road users. It isonly in the rare event of a vehicle becoming errant thatthe consequential effects of a roadside drainage featureupon a vehicle become important. Detailed advice isgiven in HA 83 (DMRB 4.2).

2.6 Whilst the behaviour of an errant vehicleand its occupants is unpredictable and deemed tobe hazardous, the Designer must consider carefullythe safety implications of the design and minimisepotential hazards as far as possible.

The Designer must also give appropriateconsideration to the safety of motorcyclists andnon-motorised road users.

Channel Flow Widths

2.7 The width of channel flow against a kerb facewill generally increase in the direction of longitudinalgradient until the flow is intercepted by a road gully,grating or other form of collector.

Design guidance on determination of spacing of roadgullies is given in HA 102 (DMRB 4.2): ‘Spacing ofroad gullies’.

2.8 A basic criterion in all these studies is the widthof channel flow adjacent to a kerb which is deemed tobe permissible. This is a site-specific considerationwhich should be evaluated against such factors ashighway standard, carriageway width, speed limit,lighting, proximity of footway or cycleway, andcontiguous width of hard strip or hard shoulder.Guidance on design storms is summarised in paragraph6.2.

2.9 Similar considerations of flow width apply to thedesign of surface water channels under surchargedconditions, and are defined in HA 37 (DMRB 4.2).

Surface water channels are formed as an extension tothe basic pavement width of a highway, and comprise adished section within which the selected design stormwill be accommodated. Storms of greater intensity willsurcharge the channel and can be accommodated bypermitting a width of flow to encroach onto theadjacent hard shoulder or hard strip. Differences insafety considerations consequential to flooding adjacentto the offside lane of a superelevated section of dualcarriageway, rather than adjacent to a nearside lane, arerecognised and dealt with in HA 39 (DMRB 4.2).

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rface Drainage of Wide Carriageways and aterges and Diverges

10 Guidance is given in TA 80 (DMRB 4.2) on thesign of drainage for wide carriageways and fornction areas and changes of superelevation. Where ap road or main carriageway crossfalls towards these of a merge or diverge section of an interchange ornction, it will be necessary to provide drainage withine nosing.

ch drainage should intercept all runoff which wouldcumulate in the nosing or flow across the nosing onto adjacent pavement. This can be effected by angitudinal grated or slotted linear drainage channel, by road gullies within a suitably dished cross-section the nosing.

It is essential that such drainage installations mustbe safe and structurally adequate to allow for notjust errant vehicles but also usage which mayoccur during motorway lane closures and thetrafficking of hard shoulders. Particular care mustbe taken in respect of abnormal load routes.

May 2006


Chapter 3Surface Water Collection: Edge Drainage Details

ECTION: EDGE
3. SURFACE WATER COLLDRAINAGE DETAILS
Introduction

3.1 Surface water runoff from the edges of UK roadsis generally collected by kerbs and gullies, combinedkerb and drainage blocks, surface water channels andchannel blocks, linear drainage channels or by directrunoff into combined surface water and ground waterfilter drains adjacent to the pavement edge.

3.2 MCHW and DMRB deal in some detail withkerbs and gullies, surface water channels, both concreteand grassed, channel blocks, combined channel andpipe systems, and combined surface water and groundwater drains. Guidance upon their application is set outin TA 57 (DMRB 6.3), HA 37 (DMRB 4.2) , HA 39(DMRB 4.2), HA 102 (DMRB 4.2), HA 113 (DMRB4.2) and HA 119 (DMRB 4.2). Usage of combined kerband drainage blocks requires that design requirementsbe set out by the designer in numbered Appendices 1/11and 5/5 to the Specification (MCHW 2). This can bebest achieved by consideration of available proprietaryprecast units. The completed appendices should permitusage from as wide a range as possible of acceptablealternatives.

Linear drainage channels comprise closed conduits intowhich water drains through slots or gratings in the tops.Combined channel and pipe systems comprise surfacewater channels having an internal pipe formed withinthe base of the units that is able to carry additional flow.

3.3 Each of these alternative modes of drainage isdealt with in more detail later in this Standard. Generalapplications of their usage are shown in Table 3.1 and alist of documents giving further guidance is set out inTable 3.2. Recommended design selections from thevarious alternatives for verge and central reservesituations respectively are illustrated diagrammaticallyin Figures 3.1 and 3.2.

The location and design of outfalls for highwaydrainage are important considerations. Advice on thedesign of outfalls and culverts is given in HA 107(DMRB 4.2), and guidance on soakaway design can befound in HA 118 (DMRB 4.2). Considerations ofdetention storage and specific pollution controlmeasures may influence selection of drainage solutionsand are described later in this Standard. Advice onvegetated drainage systems is given in HA 103 (DMRB4.2).

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Kerbs and Gullies

3.4 Road surface drainage by kerbs and gullies iscommonly used in the UK, particularly in urban andembankment conditions. ‘Gullies and Pipe Junctions’requirements are set out in MCHW 1. Gully connectionpipes discharge to outfall generally via longitudinalcarrier pipes set within the verge. The function of kerbsis not purely to constrain edge drainage. They providesome structural support during pavement layingoperations and protect footpaths and verges fromvehicular overrun.

3.5 An indirect hazard to vehicles can be presentedby edge details that permit adjacent build-up of widthsof water flow, which may intrude into the hardshoulder, hard strip or carriageway of the highway. Thiscan occur with edge details that do not immediatelyremove water linearly from the adjacent pavement in allstorm situations. The edge detail to which this problemis most pertinent is the raised kerb detail commonlyused on urban roads. Functioning of kerb and gullysystems is dependent upon the build up of a flow ofwater in front of the kerb. Gully spacings will be set outto suit an acceptable width of flow for the design stormas set out in paragraphs 2.7 and 2.8.

3.6 One advantage of kerbs and gullies is that alongitudinal gradient to carry road surface runoff tooutfall is not dependent upon the longitudinal gradientof the road itself, and can be formed within alongitudinal carrier pipe. MCHW 3 illustratespermissible alternative types of gully that provide forvarying degrees of entrapment of detritus.

3.7 Road gullies will generally discharge toassociated longitudinal carrier drains except on lowembankments with toe ditches where it may prove moreeconomical to discharge gullies direct to the toe ditchesvia discrete outfalls. Fin or narrow filter drains woulddrain the pavement layers and formation in suchinstances.

3.8 Cuttings with high ground water flows (HA 39,DMRB 4.2) will require conventional deep filter drainsinstead of fin or narrow filter drains. It is often difficultto provide a filter drain and a separate carrier drain tocollect gully connections within a normal verge width.

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In such circumstances there is justification for theadoption of combined surface water and ground waterfilter drains. Where gullies are required connectionsshould be made directly into junction pipes inaccordance with MCHW 1. Pipe types permitted for thecarrier drains must be able to accommodate thisrequirement.

Surface Water Channels

3.9 Surface water channels are normally of triangularconcrete section, usually slip-formed, set at the edge ofthe hard strip or hard shoulder and flush with the roadsurface. They are illustrated in MCHW 3 andreferenced in MCHW 1. They are the preferred edge-detail solution on trunk roads and motorways, and theirusage is described in HA 39 (DMRB 4.2).

3.10 Significant benefits can include ease ofmaintenance and the fact that long lengths, devoid ofinterruptions, can be constructed quickly and fairlyinexpensively. It may be possible to locate channeloutlets at appreciable spacings and possibly coincidentwith watercourses. However carriageways with flatlongitudinal gradients may necessitate discharge ofchannels fairly frequently into outfalls or parallellongitudinal carrier pipes in order to minimise the sizeof the channels. It will probably be found mosteconomic to design surface water channels such thatoutlet spacings in the verges are coincident with cross-carriageway discharges from the central reserve.

3.11 It is reasonable to assume that the relative risk tovehicles and occupants from impingement on surfacewater channels is lower than would be expected fromimpingement on other drainage features such as kerbs,embankments and ditches, as the channels present amuch lower risk of vehicles losing contact with theground or overturning.

Drainage Channel Blocks

3.12 These are smaller in section than surfacewater channels. They are illustrated in MCHW 3and are referenced in MCHW 1. Guidance on theiruse is also set out in HA 39 (DMRB 4.2). They arenot permitted as edge drains contiguous with hardshoulders, hard strips or carriageways in order tocollect direct runoff from those elements of thehighway.

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3.13 There are potential maintenance difficultiesassociated with the use of drainage channel blocks andthe designers will need to give consideration to thesefactors:

i) any settlement of adjacent unpaved surfaceswould reduce their effectiveness;

ii) they may be prone to rapid build up of silt anddebris in flat areas; and

iii) grass cutting operations by mechanical plant willbe jeopardised adjacent to the channel.

Some roads are drained by ‘grips’ which compriseshallow channels excavated across verges to allowdrainage from road edges to roadside ditches. Thesesuffer many of the same disbenefits. Grips and channelblocks should be avoided in verges subject to frequentusage by equestrians or other vulnerable users.

Combined Kerb and Drainage Blocks

3.14 Combined kerb and drainage blocks are precastconcrete units either in one piece or comprisingseparate top and bottom sections. A continuous closedinternal channel section is formed when contiguousblocks are laid. The part of a unit projecting above roadlevel looks like a wide kerb unit and contains apreformed hole that admits water into the internalcavity. Units are typically 400-500mm long and thepreformed holes thus occur at that spacing. They areillustrated in MCHW 3 B16 and are referenced inMCHW 1.

3.15 They are especially useful where kerbs arenecessary at locations of little or no longitudinalgradient, particularly at roundabouts where their lineardrainage function removes the need for any ‘false’crowning of road-edge channels. They can be usefulwhere there are a number of public utility services,especially in urban areas. They may be economic inrock cuttings, if the high cost of carrier draininstallation in such situations can be thereby avoided.

Linear Drainage Channels

3.16 These are included in MCHW 1 and can bemanufactured or formed in situ. Manufactured unitsmay be of concrete, polymer concrete, glass reinforcedconcrete or other material. They are in all cases setflush with the carriageway and contain a drainageconduit beneath the surface into which surface waterenters through slots or gratings. They can also be of in

May 2006



situ concrete. Manufactured units have beencommercially available for many years, but in situconstruction has been adopted much more recently inthe UK. When used on shallow gradients they may beprone to maintenance difficulties as described inparagraph 3.13. Advice may be sought from theOverseeing Organisation on current experience inmaintaining these systems.

Combined Channel and Pipe Systems

3.17 These are similar to surface water channels, withthe addition of a pipe formed within the system. Thisprovides extra flow capacity for a channel of the samewidth, reducing the number of outfalls from the systemand reducing, or even eliminating the need for aseparate carrier pipe. Where space is limited (forexample, in road widening schemes) they allow anarrower channel to be built than would otherwise bepossible.

This system is described in HA 113 (DMRB 4.2) andmay be used wherever surface water channels would besuitable. Like surface water channels, they areparticularly suited to in situ construction in concreteusing slip forming techniques. Where they are used insituations that require sub-surface drainage of thepavement, the sub-surface drain will be located betweenthe pavement construction and the channel, as the latterwill form a barrier to the horizontal movement ofmoisture at the pavement edge. This is different fromusual practice for solid surface water channels.

Over-the-edge Drainage

3.18 This method of drainage, applicable toembankment conditions, is illustrated in MCHW 3 B13,and its usage is described in HA 39 (DMRB 4.2). It isinappropriate for usage in locations where footways orsegregated cycleways abut carriageways, on structuresor on embankments constructed on moisture susceptiblesoils. Uncontrolled growth on verges can inhibit freedrainage.

Grassed Surface Water Channels for HighwayRunoff

3.19 Grassed channels are a development of swalesfor use as road edge channels. They have gentle slopesand are often combined with over-the-edge drainage orcombined surface water and ground water filter drains.They are becoming increasingly common due to theirpotential to control both storm water runoff rates and

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llution. HA 119 (DMRB 4.2) gives advice on whereey are suitable and on their design.

ffects of Pavement Overlays on Drainage Edgeetails

Overlays require raising of verge and centralreserve levels, with the following respectiveimplications.

erbs and gullies and combined drains

20 Necessary associated drainage works compriseinging up of filter media and gully gratings to newvels. Neither of these activities presents any greatfficulty. Alterations in level of precast concrete kerb more difficult and expensive than the removal andplacement of extruded asphalt kerbing, but is a matteryond considerations of drainage detail. It may bevisable to consider the relative economics of anternative solution comprising reconstruction of thejacent pavement.

urface water channels

21 Raising of surface water channels may beoidable if the edge of the overlay can be shaped toit the top of the channel without compromising theructural integrity of the pavement. Alternatively theisting channel could be broken out and replaced at agher level. This latter solution would be much morepensive, requiring remedial attention to localeak-out of the surfacing and base coursensequential to removal of the existing channel. Thereould also be a temporary loss of drainage facility ate carriageway edge if the channel was constructedior to placement of the overlay.

orous Asphalt Surfacing Course

22 HD 26 (DMRB 7.2.3) and HD 27 (DMRB 7.2.4)t out the standards for the usage of porous asphalt.dvice on appropriate edge of pavement details andidance on their usage may be sought from the

verseeing Organisation.

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Part 3 HD

33/06Drainage Kerbs and Combined Linear Surface Combined Combined Over the Grassed SurfaceCollector Gullies Kerb and Drainage Water Channel and Surface and Edge Drains Water Channels

GroundwaterFilter Drains

enerally Not generally Not generally Not generallycable applicable applicable applicable

-speed Especially in In verges (not In verges especially cutting verge suitable forbankments embankments

e verge constructed of is limited clayey or silty

soil)

13) (HA 39) (HA 103) (HA 119)

ithin the verge, or safety barriers or parapets are required.

rainage Details

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rainage Details

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Detail (See Note 1) Drainage Channels Channels PipeBlocks

Urban General usage Congested Car park areas Not generally Not gApplications public utility Adjacent to applicable appli

services vertical concreteShallow outfalls barriersFlat long. Nosings ofgradients interchanges

(Reference (TA 57) HA 102documents) HA 104 HA 105 TA 80 HA 78

Rural Footways within Flat long. Nosings of High-speed HighApplications highway verge gradients where interchanges roads especially roads

eg laybys footways within vertical on embankments on emRoundabouts highway verge concrete wher

Roundabouts barriers space

(Reference (See Note 2)documents) (TA 57) TA 80 HA 78 TA 80 HA 78

(HA 39) (HA 1

Notes:1 Kerbs in this context are precast concrete.2 Kerbs and gullies are not recommended for rural roads unless footways are located w

Table 3.1: General Applications of Edge D

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nections have no adverse effect on fin

ural roads.h.

Chapter 3

Surface Water C

ollection: Edge D

rainage Details

Kerbs (with gullies) necessary because of: a) footway within highway verge b) urban conditions c) other site specific considerations

NO

Road on Embankment

Verge Restrictions

Low Embankment of Granular

Material

Adopt SW channel with F/NF

drain

HCD: B9 (B10)

Adopt over-the-edge

drainage and consider use of GSWC

HCD: B13

6

Figure 3.1: Recommended Design Selection Verge-Side Edge Drainage

Note 1: Fin drain usage denoted thus (F) indicates use with road gullies, and should only be permitted if gully condrain.

Note 2: NF denotes alternative Narrow Filter Drain.Note 3: Turf edging between intermittent precast concrete kerb/gully combinations may be acceptable on minor rNote 4: This solution can be useful where lack of space inhibits provision of a separate carrier drain + F/NF trencNote 5: GSWC denotes Grassed Surface Water Channel.

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YES

Road on Embankment

Adopt combined

drain and consider use of GSWC

Adopt NF drain with long. Sealed carrier drain.

and consider use of GSWC

Adopt NF / (F)

Drains with separate gully

connections.

Groundwater Problems

No groundwater

problemsNo Verge

Restrictions

Adopt combined


HCD: B1



HCD: B2,3


drain.

HCD: B12

Groundwater Problems

No groundwater Problems

See note 4 See note 4

Road in Cutting

Road in Cutting

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e Drainage

ves.

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Chapter 3

Surface Water C

ollection: Edge D

rainage Details

Balanced Carriageway Superelevated Carriageway

reserve Central reserveunpaved

(See Note 3)

SW Channel and CombinedF/NF drain filter drain

HCD: B6, 7 HCD: B5

Figure 3.2: Recommended Design Selection Central Reserv

Note 1: A detail like HCD: B8 Type 14 may be judged preferable for the drainage of wide central reserNote 2: F/NF denotes Fin or Narrow Filter Drain.Note 3: This is the preferred solution.

Central reserve Central reserve Centralunpaved paved paved

F/NF drain(See Note 1)

HCD: B8 Type 15 or 16

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May MCHW DMRB

Y VOL 7: PAVEMENTDESIGN ANDMAINTENANCE

N 2: SECTION 3: SECTION 2:ONS HIGHWAY PAVEMENT

FEATURES DESIGN ANDCONSTRUCTION

TA 57: HD 26:c Roadside Pavement Designf Featuresouts HD 27:

PavementConstructionMethods

Chapter 3

Surface Water C

ollection: Edge D

rainage Details

2006

Volume 1:Specification

Volume 2:Notes forGuidance

Volume 3:HCDB – Series

VOL 2: HIGHWAY VOL 4: GEOTECHNICS AND VOL 6: ROAD GEOMETRSTRUCTURES: DESIGN DRAINAGE(SUBSTRUCTURES ANDSPECIAL STRUCTURES)MATERIALS

SECTION 1: SECTION 2: SECTION 1: SECTIOSUBSTRUCTURES DRAINAGE LINKS JUNCTI

BD 30: Backfilled Retaining TA 80: Surface Drainage of Wide TD 9: Highway TD 16:Walls and Bridge Abutments Carriageways Design Link Geometri

HA 39: Edge of Pavement Details Design oHA 37: Hydraulic Design of Road-Edge RoundabSurface Water ChannelsHA 40: Determination of Pipe and BeddingCombinations for Drainage WorksHA 78: Design of Outfalls for Surface WaterChannelsHA 83: Safety Aspects of Road-EdgeDrainage FeaturesHA 102: Spacing of Road GulliesHA 103: Vegetated Drainage Systems forHighway RunoffHA 105:: Sumpless GulliesHA 106: Drainage of Runoff from NaturalCatchmentsHA 107:: Design of Outfall and CulvertDetailsHA 113: Combined Channel and PipeSystem for Surface Water DranageHA 118: Design of SoakwaysHA 119: Grassed Surface Water Channelsfor Highway Runoff

Table 3.2: Surface Drainage – Guidance Documents

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Chapter 4Sub-Surface Drainage

E
4. SUB-SURFACE DRAINAG
Introduction

4.1 Sub-surface drainage of highway pavementscomprises the measures incorporated in the design inorder to control levels of groundwater, and drain theroad foundation (see HD 25, DMRB 7.2).

4.2 Requirements for sub-surface drainage areillustrated in Highway Construction Details, MCHW 3.Sub-surface drainage is normally necessary in order toremove any water which may permeate through thepavement layers of roads in both cut and fill situations.This can be achieved on embankments by provision offin or narrow filter drains illustrated in the B and FSeries Drawings of MCHW 3.

Sub-surface drainage in cuttings must provide notonly for the necessary drainage of pavement layers,but also for the removal, to an adequate depth, ofany groundwater which may be present in thecutting.

Groundwater may be subject to seasonal variationsconsequential to rainfall conditions and soilpermeability, and the best possible analysis ofgroundwater conditions should be undertaken duringground investigation. Water moves partly by gravity andpartly by capillary action, and these movements aresusceptible to control by subsoil drainage.

4.3 Sub-surface drainage is effected by installation oflongitudinal sub-surface drains at the low edges of roadpavements. These serve to drain the pavement layersand the pavement foundation. They also prevent ingressof water from verge areas adjacent to the pavement.

It is also essential that water is not retained withinthe sub-base and for that matter the capping layer.Water reaching the formation and sub-formationmust be drained to longitudinal sub-surface drainsby adequate shaping of the formation and sub-formation such that no undrainable low spotsoccur.

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Circumstances in which sub-surface drainage may beomitted are described in HD 25 (DMRB 7.2) and HA 39(DMRB 4.2), but advice should be sought from theOverseeing Organisation in such instances.

4.4 Table 4.1 sets out the documents which giveguidance on the provision of sub-surface drainage.MCHW 3 indicates alternative acceptable sub-surfacedrains in cross-section, and MCHW 1, in conjunctionwith numbered Appendix 5/1, specifies acceptableconstruction materials. Implications are dealt with indetail in the text following.

Groundwater Considerations

4.5 HA 44 (DMRB 4.1) advises upon CBR values ofsubgrade and capping relative to sub-surface drainageconditions. Weak cohesive subgrade material in cuttingswill require replacement by capping layer, and the CBRvalue used to determine the required capping layerthickness required will have been chosen for aparticular water table level. That level will eventuallybe dependent upon the depth of the subgrade drainsbelow sub-formation level. Table 13/2 of HA 44(DMRB 4.1.1) enables CBR values to be assessed fortwo conditions of water table level, a ‘high’ water tableof 300mm below formation or sub-formation level, anda ‘low’ water table of 1000mm below formation or sub-formation level.

4.6 The minimum depth of installation of fin andnarrow filter drains is set out in MCHW 3 as DN +50mm to invert beneath sub-formation level, or 600mmto invert beneath formation level: these levels beingdefined in Clauses 601.9 and 601.10 (MCHW 1).Where there is no capping layer, the drains should belaid to the lower of those two depths. Drains installed atthese minimum depths cannot lower high groundwaterto even the ‘high’ water table level of 300mm belowsub-formation level. To achieve even the ‘high’ watertable level will require the fin or narrow filter drain tobe installed at an appreciably greater depth than theminimum shown in the MCHW 3. In situations wherelarge volumes of groundwater are anticipated filterdrains can provide a better solution than fin or narrowfilter drains.

4/1



A further consideration is that a fin or narrow filterdrain will normally follow the longitudinal profileof the carriageway and it is therefore essential,especially in flat or gently undulating conditions,that the designer ensures that the drains candischarge from all low points to a suitable outfall.

These are important considerations in assessing theapplicability or otherwise of fin and/or narrow filterdrains rather than combined drains.

Sub-surface Drainage of Roads in Cuttings

4.7 The general philosophy of good highwaydrainage is that surface water be kept separate fromsub-surface water in order to prevent large amounts ofwater being introduced into the road at foundationlevel. It is not always practicable to achieve thisphilosophy. For example, in the case of cuttings thereare many benefits that can accrue from the provision ofcombined filter drains. These include:

i) permissible early installation and usage forcollection of drainage runoff during theconstruction stage, provided construction debrisis prevented from blocking the filter media. Thiscould be done, for example, by the use oftemporary sedimentation ponds;

ii) removal of groundwater beneath the pavement toa greater depth than would be possible with fin ornarrow filter drains;

iii) easier construction than with a solutionincorporating both surface water carrier drainsand fin or narrow filter drains;

iv) easier inspection and maintenance than ispossible with fin or narrow filter drains;

v) facility for collection of water from drainagemeasures installed separately in the side-slopesof cuttings.

4.8 Combined drains in cuttings may be constructedusing pipes with perforations or slots laid uppermost,and with sealed joints to minimise surface water inputat trench base level. Trench bottoms may need to belined with impermeable membranes up to pipe soffitlevel to prevent addition of water to the sub-soil thatmay otherwise be dry.

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ub-surface Drainage of Roads on Embankment

.9 Drainage of pavement layers of roads onmbankment is effected by fin or narrow filter drainsontiguous to the edge of the pavement as shown in the-Series Drawings of MCHW 3, and as explained inA 39 (DMRB 4.2).

elative Characteristics of Combined and Separateystems

.10 HA 39 (DMRB 4.2) requires that restraintsposed upon any choice of drain types should be

inimised in order to encourage cost-effectivelutions. It does, however, accept that particular types

f drains or material may be excluded for soundngineering reasons.

.11 The differences in principle between combinednd separate highway drainage systems are defined inaragraph 1.7 of the Introduction to this Standard.hese differences are described in greater detail in thellowing text.

.12 A combined system comprises porous, perforatedr open jointed non-porous pipes within trenchesackfilled with permeable material. These trenches aretuated in verges and/or central reserves adjacent to thew edges of pavements such that surface water can run

ff the pavement directly onto the trench top and thenermeate through the drain trench backfill to the drainipe at the base of the trench. Pavement and cappingyers are contiguous with the side of the trench, and

ny water within these layers is also collected by therain. Such drains contain a number of variables,rimarily pipe types, filter drain backfill material,ench top surfacings and use of geosyntheticembranes and/or impermeable trench treatments as

ecessary in special cases. The function of the drainith respect to surface water runoff and sub-surfacerainage remains identical in all cases. They also haveonsiderable capacity to facilitate the lowering ofroundwater and collection of slope drainage fromuttings.

.13 Separate systems provide for collection of sub-rface water ie drainage of pavement and cappingyers, separately from that of surface water runoff frome pavement. The surface water can be collected byveral different systems such as surface water

hannels, combined drainage and kerb blocks, roadullies and linear drainage channels. Sub-surfacerainage associated with separate collection of surfaceater runoff is effected by either fin or narrow filter

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drains defined in MCHW 1 and MCHW 3 F18. MCHW2 gives advice on the necessary hydraulic capacity offin and narrow filter drains.

Combined Drains

4.14 Combined drains have been a traditional solutionfor many years and possible problems in performanceare commented upon in HA 39 (DMRB 4.2). Theseinclude those of stone scatter, surface failures ofembankments, pavement failures and safety andmaintenance problems. Stone scatter from verge drains,where a hard shoulder of 3.3m width separates theverge from the carriageway, may not normally be aproblem, but they can present a safety hazard when thehard shoulder is used as running lane in contraflow.Stone scatter from central reserve drains presents agreater safety hazard.

Problems can be reduced by implementation of any ofthe following measures:

i) spraying of the top surface of exposed filtermaterial with bitumen;

ii) the use of geogrids to reinforce the surface layerof the filter material;

iii) incorporation of lightweight aggregate for filtermaterial at finished level, as permitted in MCHW3 B15;

iv) possible usage of bitumen bonded filter materialin the top 200mm of the trench.

4.15 Combined drains can be advantageouslyemployed in cutting situations requiring appreciableground water removal. The relatively large hydrauliccapacity required for dealing with surface water duringheavy storms means that combined drains generallycontain sufficient capacity to take any interceptedground water. Separate design estimates of groundwaterflows are not generally necessary.

4.16 Problems may arise with porous concrete pipesused in filter drains. These have lower structuralstrength than other rigid pipes and their adoption mustbe checked against this criteria and local experience.

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parate System: Fin Drains

pes 5, 6 and 7 Fin Drains

7 Detailed guidance is given in Series NG500CHW 2). It is intended that the widest possible

oice of fin drain type should be available to thentractor.

8 It is intended that types 5, 6 and 7 drains betalled in narrow trenches and there can be difficultiesworking in very narrow trenches, depending on thee of ground, and in compaction of backfill.

ese problems should be alleviated by the use oftomatic drain-laying equipment where groundnditions permit. Non-granular materials will permitcavation by continuous trenching machine, providedt the trench remains open sufficiently long for the

ain to be installed. In suitable granular materials,tallation can be effected by plough and simultaneous

ain installation by following ‘box’. Associatedppers and chutes can place backfill where necessary.ither of these techniques is suitable for use in coarsen-cohesive materials such as rock capping layer.stallation by open trench may be unavoidable in suchterials.

9 If it is proposed to use fin drains in conjunctionth kerbs and gully pavement edge drainage, care must taken to ensure that construction of gullynnections will not prejudice the integrity of the finains. The implications of non-restriction innstruction trench width of a Type 5 fin drain should considered. Consequences of the possiblesuitability of trench arisings as backfill materialould also be considered.

pe 10 Fin Drain

0 HA 39 (DMRB 4.2) specifies use of a Type 10ain with rigid carriageways. The designer shouldcide whether particular scheme specific pavementterials warrant its adoption with flexible

nstruction.

parate System: Narrow Filter Drains

1 Narrow filter drains are intended for use as edgeof pavement sub-surface drains and are suitablealternatives to fin drains for that purpose. Guidance issimilar to that for fin drains in MCHW 2, but inaddition requires that for Type 8 drains ‘the filtermaterials should be compatible with the adjacent soil or

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construction layer as the filtration is achieved by thefilter material and the geotextile sock around the pipe’.This can be difficult to predict, particularly in the upperlayer of embankments. Use of 100mm dia pipes withinnarrow filter drains, rather than pipes of smallerdiameter, should provide benefits with respect to futuremaintenance and at little or no additional cost.

Pavement Life

4.22 There are factors pertinent to drainage atconstruction stage that have a bearing upon the life of apavement. The subgrade material may be subjected tomore onerous conditions during the construction stagethan during the service life of the pavement, and somust be sufficiently strong to provide an adequateplatform for construction of the sub-base. The CBRshould not be allowed to reduce from its assumed longterm equilibrium to an unacceptable one as aconsequence of softening due to the presence of water.HD 25 (DMRB 7.2.2) defines requirements of the roadfoundation. It is imperative that groundwater drainageand sub-grade drainage should prevent plasticdeformation of the road foundations, sub-base andcapping layer during construction, and it isrecommended that consideration be given towards pre-earthworks drainage in all projects where this might befeasible.

May 20064/4

Volume 4 Section 2

Part 3 HD

33/06

May 2006

MCHW

Vol 1:Specification

DMRB

VOL 4: GEOTECHNICS AND DRAINAGE VOL 7: PAVEMENTDESIGN AND

ENANCE

N 2:ENT DESIGNNSTRUCTION

D 25ions

2 Subgradeent

3 Capping and

27-3.32)

TRMM(Only applicable inEngland)

VOL 2: ROUTINEAND WINTERMAINTENANCECODE

Part 1:

Chapter 1.7Highway Drainage

Chapter 4

Sub-Surface Drainage

500 – Series

Vol 2: Notes forGuidance500 – Series600 – Series

Vol 3: HCDB – SeriesF – Series

MAINT

SECTION 1: SECTION 2: SECTIOEARTHWORKS DRAINAGE PAVEM

AND CO

Part 1: HA 44 Design and Preparation of Contract HA 39 Edge of Pavement Details Part 2: HDocuments Foundat

Chapter 7 Cuttings: Groundwater Sub-surface drainage (para 3.8) Chapter Assessm

Chapter 8 Embankments: Drainage HA 40 Determination of Pipeand Bedding Combinations for Chapter

Chapter 10 Sub-grade and Capping:Drainage Drainage Works Sub-base(paras 25-27) (paras 3.

Part 3: HD 41Maintenance of Highway Geotechnical Assets

1. Introduction: General (paras 1.1 & 1.2)

Table 4.1: Sub-Surface Drainage – Guidance Documents

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E

Chapter 5Earthworks Drainage

5. EARTHWORKS DRAINAG

Toe Drainage and Cut-off Drains

5.1 It is essential that existing land drainage andrunoff from external catchments be taken intoaccount in the design of highways drainage. SeeHA 106 (DMRB 4.2) for specific advice.

The requirements of the appropriate water and drainageauthorities should be established to ensure that theirrights are accommodated and their reasonable interestssafeguarded. Information on ground water conditionsmust be included in the data obtained from siteinvestigations for proposed major roadworks.

5.2 Where surface water and sub-surface water fromadjoining land will flow towards the road, it willgenerally be necessary to construct intercepting drainsat the tops of cuttings and the toes of embankments. Inrural areas these may be ditches rather than filter drainsbecause of their greater capacity and comparativecheapness. It is imperative that the geotechnicalengineer evaluates the effect of such proposed ditchesat an early stage, as large off-sets may be necessaryfrom the toes of embankments to associated toe-ditches.This may affect land acquisition requirements in thedraft Compulsory Purchase Order (CPO) for a scheme.It may also affect adjacent land management and thechoice of drainage solution. Landscaping measures,especially the inclusion of noise bunds, may influencedrainage design.

5.3 It is good practice to carry out drainage works atthe earliest possible stage in the construction of anynew road. Longitudinal drains should be sufficientlydeep to collect whatever drainage is necessary at cut/fillzones and it will be necessary to give special attentionto the treatment and collection by sub-soil drains ofwater from any water-bearing seams which areintercepted by cuttings. Intercepting drains or ditchesmust be sufficiently deep to intercept any system ofsevered agricultural under-drainage.

5.4 Watercourses and ditches crossed by a majorhighway are generally culverted, with the consent of theland drainage authority. It may be more economical tocollect flows from minor ditches into longitudinalhighway drains, but such decisions are complex andinvolve considerations of relative levels, availability ofan adequately large outfall watercourse, land drainage

May 2006

authority consents, and possible compensation for lossof water downstream of the road. HA 106 (DMRB 4.2)provides specific advice on dealing with the drainage ofnatural catchments and HA 107 (DMRB 4.2) givesdetailed advice on outfall and culvert design.

5.5 Where it is necessary to provide slope drainagein cuttings a longitudinal piped drainage system will berequired in the verge. This will be able to collect theslope drains without the possibility of any detrimentaleffect to sub-surface drainage of the pavement. Adrainage system comprising a surface water channelwith an associated fin or narrow filter drain, and nolongitudinal pipe drain, could not be used to collectslope drainage. It would be necessary to provide, inaddition, a longitudinal carrier drain, or dispense withthe fin or narrow filter drain and provide a filter drain,or alternatively use a combined surface and groundwater drain without a surface water channel.

5.6 The need for slope drainage should bedetermined prior to the start of construction in order tominimise difficulties in the future connection of slopedrains into longitudinal verge drains.

Drainage to Retaining Structures

5.7 Requirements for drainage of retaining structuresare set out in BD 30 (DMRB 2.1).

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MENT EDGE DRAINAGE

Chapter 6Detailed Design, Pavement Edge Drainage

6. DETAILED DESIGN, PAVE

Introduction

6.1 Detailed design of pavement drainage comprisesfive basic aspects:

i) determination of the design storm that should beused in the design of the drainage elementswithin the catchment under consideration;

ii) calculation of the flows from the design storm ateach drainage element within the catchment;

iii) establishment of the hydraulic adequacy of eachdrainage element within the catchment;

iv) determination of the location of the outfalls orsoakaways; and

v) determination, where necessary, of structuralloadings upon drainage conduits, and verificationthat each conduit will withstand the loadingplaced upon it.

Storm Return Period

6.2 Longitudinal sealed carrier drains must bedesigned to accommodate a one-year storm in-borewithout surcharge. The design must be checkedagainst a five-year storm intensity to ensure thatsurcharge levels do not exceed the levels ofchamber covers.

Combined surface water and groundwater drainsmust also be designed to accommodate a one-yearstorm in-bore without surcharge. A design checkmust be carried out to establish that a five-yearstorm intensity will not cause chamber surchargelevels to rise above the formation level, or sub-formation level where a capping layer is present. Incarrying out this check it should be assumed thatpipes are sealed and that back flow from pipes intothe filter media does not take place.

6.3 Guidance on the design of surface waterchannels is given in HA 39 (DMRB 4.2). Thefundamental philosophy of this document is that adesign storm with a return period of one year must

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be contained within the channel, and that surchargeconsequential to a storm of five-year return periodshould not encroach into the carriageway.

Channels must be designed to accommodate a 1 in1 year storm with the flow contained within thechannel cross section without surcharging. Theallowable surcharge widths must then be checkedfor 1 in 5 year storm.

In verges, surcharges under a 1 in 5 year stormmust be limited to a width of 1.5m in the case ofhard shoulder and 1.0m in the case of hard strip.

In central reserves, surcharge under a 1 in 5 yearstorm must not be permitted to encroach thecarriageway, but flooding within the non-pavementwidth of the central reserve is permissibleproviding there is safeguard against flows from thesurcharged channel overtopping the central reserveand flowing into the opposing carriageway.

Allowance for climate change: The rainfallintensities used to calculate the design storms mustinclude an allowance for the effects of climatechange. Where rainfall data exclude such anallowance, a sensitivity test on the design of thedrainage system must be carried out by increasingrainfall intensities of the design storm by 20%.

6.4 Application of storms of other return periodsshould be tempered by considerations of geography andparticular highway geometry. Examples of criticalsections of road are quoted in HA 37 (DMRB 4.2) as:

i) applications of superelevation that cause crossfallto be locally zero; and

ii) sections of road draining to longitudinal sagpoints where it is important to prevent flooding.

This is especially important for longitudinal sags incuttings, where it may for example be deemed prudentto design outfall drainage to a design storm returnperiod of say ten years (i.e. having an annualprobability of 10%). These are matters for engineeringjudgement relative to the drainage elements under

6/1



consideration, and the consequences of surcharge of thesystem in its unique situation.

Calculation of Runoff Flows

6.5 Having determined the relevant design stormfrequency that should be used, it is necessary todetermine the storm that will give maximum runoff atthe various locations within the catchment.

6.6 Over the years, drainage designers have beenusing a number of established procedures (ref . 7) forcalculating runoff. However, the most commonly usedprocedure in the UK is the Wallingford Procedure firstpublished in 1981 (ref. 9). This comprises a number ofmethods and one of these, the Modified RationalMethod, gives a value of peak discharge only and noindication of runoff volume or hydrograph shape. It isrecommended within the Wallingford Procedure thatcatchments to be analysed by this Method should notexceed 150 hectares, with times of concentration of upto about 30 minutes and outfall pipe diameters of up toabout one metre.

The Wallingford Hydrograph Method is a computer-based hydrograph method incorporating separatemodels of the surface runoff and pipe-flow phases.Storm overflows, on-line and off-line tanks andpumping stations may be represented. The Method isappropriate to the majority of applications. Peak flowdischarges obtained by the Modified Rational Methodand Wallingford Hydrograph Method are of comparableaccuracy. Data input requirements are similar for bothmethods.

6.7 A number of commercial programs based uponthe Wallingford Procedure are available and suitable forhighway drainage design. Programs selected for useshould be able to design a system to a particular stormintensity, and permit analysis of the system undersurcharged conditions. Details of these programs andtheir use are given in DMRB 11.3.10.

Gully Systems

6.8 Gully systems are based upon the collection, byroad gully, of surface water runoff which has been shedtowards the edges of a road pavement and which flowsalong a road channel in front of a raised kerb until it iscollected by a gully.

The spacing of road gullies is determined byconsiderations of the maximum width of flow that canbe permitted in a channel fronting a raised kerb. Advice

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n gully design spacing is set out in paragraphs 2.7 and.8. It is necessary for the Designer to include details ofully grating specifications in the Contract in Appendix/1, and the comments in 6.9 are pertinent to structuralonsiderations of traffic loadings to which gullies arebject.

.9 The nose sections of junction merge and divergepers commonly have low points in cross-section due the direction of crossfalls of the slip roads and main

arriageways and because of similar correspondinghannel levels. Drainage elements placed within thesepers should be designed to withstand trafficking of theard shoulder during maintenance operations.

urface Water Channels

6.10 Design of surface water channels isdescribed in principle in HA 39 (DMRB 4.2).Design of the channels in cross-section to achievethe necessary hydraulic capacities is set out inHA 37 (DMRB 4.2); cross-sections are illustratedin the MCHW 3 B Series Drawings. The designtechnique is essentially a method by which therequired size or distance between outlets forchannels is determined taking into account localrainfall characteristics.

.11 Surface water channels generally occupy a largerroportion of the available verge or central reserveidth than do other common drainage systems. This isarticularly the case for wide motorways with a vergeidth of 1.5 metres, where transverse areas ofpermeable pavement are proportionately larger and

e unpaved width of verge much less than that of trunkads. Other features within verges and central reservesch as safety fences, services, lighting columns andgns impose further restrictions upon maximumhannel sizes which can be constructed. Thechievement of long channel lengths may also berevented by necessary discontinuations at piers,butments, slip roads, junctions, laybys, central reserverossover points or emergency crossing points. Changesf superelevation also constitute points of terminationf channels. The surface drainage of wide carriageways described in TA 80 (DMRB 4.2).

.12 It is necessary to outfall surface water channelshenever they reach capacity, and if suitable outfalls

re not available carrier pipes become necessary.ischarge into carrier pipes will be unavoidable in

uttings more than a few hundred metres in length.

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When discharge into a longitudinal carrier pipe hasbecome necessary, access chambers are normallyrequired at 100m intervals. These provide convenientdischarge points for channel outfalls via suitable apronsand gratings within the channel invert. They also enableincorporation of smaller channel sections that can bemore easily accommodated within the availablehighway cross-section.

6.13 The design method of HA 37 (DMRB 4.2) isbased on kinematic wave theory and takes account ofvariations in rainfall and flow conditions with time. Forthe purpose-built surface drainage channels, HA 37(DMRB 4.2) should be used to determine the spacingbetween the outlets, which, in turn, should be designedaccording to the recommendations of HA 78 (DMRB4.2).

Combined Kerb and Drainage Blocks

6.14 Combined kerb and drainage blocks werecommented upon in principle in Chapter 3.Specification for these blocks is set out in MCHW 1.This requires the Designer to specify particularrequirements with respect to dimensions and strength ofthe units and their hydraulic design parameters, and theContractor to design the system. The Designer shouldobtain the approval of the Overseeing Organisation tothe content and inclusion of the Specification which herequires. Proprietary combined kerb and drainageblocks should be examined, and in the interests ofcommercial benefit the specification should be as wideas possible to maximise competition.

6.15 Each manufacturer produces comprehensiveliterature of the product and this will include statementsand a design guide to the hydraulic capacity of hisproduct. The Designer should be aware that the claimedhydraulic capacities may have been derived on asimplistic basis, normally based on the Colebrook-White equation for open-channel flow. The effect ofturbulence from the entry of flow at each inlet to theblocks will be detrimental to the flow conditions andmay or may not have been taken into account. Forseveral reasons an equable comparison of the relativepractical performance of kerbs and gullies, surfacewater channels and combined kerb and drainage blocksis not possible. Different flow theories are used in eachcase, the most extreme disparity being that part floodingof the carriageway is accepted and essential in theoperation of a kerb and gully system, whilst no suchflooding is taken into account in manufacturers’ claimsfor capacities of combined kerb and drainage blocks.The Designer will need to be satisfied with the design

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ommendations provided by the manufacturers.wever, it is unlikely that outfalls designedordingly will give rise to under-performance inctice. The designer should examine the basis ofmed hydraulic capacities and the correspondingfall spacings.

nufactured Linear Drainage Channels

6 MCHW 1 sets out the specification for linearinage channels. Manufactured units have beenilable in the UK for a number of years and haven used extensively for the drainage of large pavedas, notably car parks. One of the two common typesystem is based on a trough or channel made ofcrete, polymer concrete, glass reinforced concrete orer similar material. Cast iron and steel systems are available. Troughs are covered by some form of

ting, which will be either integral with the channel separate element which is bolted or otherwise fixedhe channel. The other common system comprisescrete blocks, typically 300mm square in section andmm to 900mm in length. These are cast with anrnal cylindrical cavity such that a continuous pipe ised when units are laid together. Water is admitted

ugh either a continuous slot or through frequentlyced holes in the top face. Side entry inlets may alsopecifically incorporated for use as edge drainage

h porous asphalt surfacing.

6.17 Use of linear drainage channel units in trunkroads or motorways will require the approval ofthe Overseeing Organisation.

h approvals have generally only been granted for in nosings and crossover situations and in locationsich are unlikely to be trafficked. Restrictions will beced upon the usage of manufactured units whichuire the mechanical interlocking of a grating to thegh section of a unit. Some units may also beuitable for areas of pedestrian and cyclist usage.nufactured units have been more extensively used on Continent than in the UK and it is possible to obtainprietary products with comprehensive ranges ofngs. Manufacturers will claim hydraulicracteristics and performance of their products.formance of the units must be compatible withulated design runoffs from the pavement into the

posed linear drainage systems and the proposedfalls from those systems.

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In Situ Concrete Linear Drainage Channels

6.18 This form of construction has been extensivelyused, primarily by slip forming, on major roads on theContinent. Development and practice in the UK hasbeen more recent, and has only been trialled on limitedschemes. These channels comprise formation of alongitudinal cylindrical conduit within an in situconcrete block approximately square in cross-section.Longitudinal slots formed in the block above theconduit transmit surface-water run-off into the conduitbeneath, and the form of these units is thus very similarto one of the manufactured types of channel describedearlier. These units are normally constructed by slipforming, the longitudinal conduit being generallyformed by inflated plastic tubes which are laterremoved, or by a PVC pipe which is left in position.The longitudinal slots overlying the conduit are formedby slip-forming.

6.19 Specification in practice is based primarily uponthe 1100 Series (MCHW 1) clauses and the Code ofPractice ‘BS5931. Machine laid in situ edge details forpaved areas’ (ref 4). It is necessary that the constructionbe structurally adequate, and the slip formed channelsgenerally incorporate longitudinal reinforcement.

6.20 There are considerable differences in thetolerances and quality control that can be achieved within situ construction relative to pre-cast. In themeantime, in situations where a linear drainage slot-type channel is desired, the Overseeing Organisationwould be able to provide guidance on current best-practice. It is possible that this form of construction willbe well suited for installation alongside slip formedvertical concrete barriers (VCBs) as construction ofthese becomes more common.

Combined Channel and Pipe Systems

6.21 Guidance on the hydraulic and structural designof combined channel and pipe systems is given inHA 113 (DMRB 4.2). They comprise surface waterchannels with an internal pipe formed within the baseof the units that is able to carry additional flow. Thesystems are particularly well suited to in situconstruction in concrete using slip forming techniques,although they can also be constructed using othermethods. Use of such systems can remove the need fora separate carrier drain in the verge and can enable flowto be carried longer distances between outfalls. If nocarrier drain is required, more space can be madeavailable in the verge for other services.

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ipe Design

ydraulic

22 Hydraulic design of a pipe network is generallycomplished by computer application of the principlesscribed earlier in this Chapter. Cross-carriagewaypes, which discharge flows from the central reserve toe verge and thence to outfall, should have sufficientare capacity to ensure that storms in excess of thesign storm will not cause surcharges of the centralserve drainage. Cross connections should beequately sized to avoid this. Considerations ofovision of some spare capacity are relevant to alltfall pipes, which, in surcharge conditions, mayherwise jeopardise the safety of the highway.

ructural

23 Guidance on the structural design of pipes is sett in two publications:

A Guide to Design Loadings for Buried RigidPipes (ref. 5); and

) Simplified Tables of External Loads on BuriedPipelines (ref. 8).

Guidance on permissible combinations of pipe andbedding materials applicable to MCHW is set outin HA 40 (DMRB 4.2).

his document guides the selection of pipes in trenchesith cover depths between 0.6m and 6.0m, and withameters from 100 to 900mm in carrier drains andom 100 to 700mm in filter drains. Pipe materialsvered within the document include rigid pipes oftrified clay, precast concrete and asbestos cement, andexible pipes of upvc. MCHW 2 guides upon necessaryecifications for plastics pipes, and also uponclusions or special treatments necessary to withstandemical attack because of groundwater conditions.

24 Analysis of pipes outside of this range willquire recourse to other guidance documents, but thisould not generally be necessary at design stage.here it is necessary to lay pipes beneath carriagewaysith very shallow depths of cover the characteristics ofctile iron pipes should be borne in mind. These aremi-flexible and able to withstand high loadings, notst in the permanent situation, but also duringnstruction. Guidance on structural strength and

loadings can be obtained from manufacturers. A useful

May 2006



recent publication guiding upon characteristics anddesign of a broad range of pertinent drainage materialsis the “Materials Selection Manual for Sewers,Pumping Mains and Manholes” published in January1993 by the Foundation for Water Research (ref. 6).

6.25 MCHW Volume 1 permits the use of other typesof pipe, such as twin-walled PVC, provided that theyare supported by a British Board of Agrément Roadsand Bridges (BBA R&B) Certificate. Beddingcombinations for such pipes are not included in HA 40,but will be specified in the BBA R&B Certificate.

CCTV surveys of drains

6.26 MCHW 1 specifies requirements for testing andcleaning of drains, and includes for testing by sphericalmandrel. It also requires that unless otherwise requiredin Appendix 90/1, carrier, foul and filter drains (butexcluding fin and narrow filters drains) shall besurveyed by Closed Circuit Television (CCTV) inaccordance with the relevant requirements of SD 15(MCHW 5.9).

Discharges to Outfalls and Soakaways

6.27 A balance needs to be struck when consideringwhether road runoff should be discharged to surfacewaters or to ground. In some cases the effect onreceiving surface waters could be such that discharge toground may be appropriate. This could apply where thedischarge would aggravate an existing flooding risk, orwhere it could have a potentially disproportionate effecton pollution within the receiving waters. Advice on thedesign of outfalls and culverts is given in HA 107(DMRB 4.2).

6.28 Advice on the design and construction ofsoakaways is given in HA 118 (DMRB 4.2). Anumber of factors must be considered in theirdesign:

i) soakaways must not allow direct dischargeto groundwater, for example via boreholes;

ii) soakaways must not be sited within 5m of abuilding;

iii) soakaways must not lead to a risk ofinstability, either by washing out of fines, orof saturation of road foundations due toinadequate capacity;

iv)

6.29safeopeall mwith

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soakaways must not increase the risk ofgroundwater flooding.

Designers must ensure there is adequate, access to soakaways for maintenance for bothratives and plant. Provision must be made for

aintenance operations to be carried outout disruption to traffic.

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N AND FLOODING

Chapter 7Control of Pollution and Flooding

7. CONTROL OF POLLUTIO

General

7.1 Whilst the primary aims of drainage systems areto provide rapid removal of surface water from the roadsurface and to provide effective sub-grade drainage, thesystems should also provide some degree of controlover the risk of either pollution of the receivingwatercourse or flooding elsewhere in the catchment.Guidance on the assessment of these risks is given inHA 216 (DMRB 11.3.10). Table 7.1 shows whichsystems can provide some form of control over theserisks, as well as their compatibility with vegetateddrainage systems.

7.2 Systems with the potential for control ofpollution or flooding include:

• Spillage control: Oil Separators, Lined Ditches,Penstocks, Baffles, Kerbs and Gullies, SurfaceWater Channels, Filter Drains;

• Other pollution control: Filter Drains, UnlinedDitches, Oil Separators, Sediment Traps;

• Flow control: Filter Drains, Carrier drains(oversize), Ditches, Combined Kerb andDrainage, Permeable Pavements;

• Vegetated systems: Ponds, Infiltration basins,Wetlands, Grassed channels, Swales.

7.3 Where risks of potential pollution or floodinghave been identified and the need for controlsidentified, the use of vegetated drainage systems shouldbe considered in the first instance. Guidance on thesesystems in given in HA 103 (DMRB 4.2). Guidance ongrassed surface water channels for highway runoff isgiven in HA 119 (DMRB 4.2). There may be situationswhere limited space restricts the use of vegetatedsystems and in these cases, the use of conventionaldrainage systems, either independently or incombination with vegetated systems should beconsidered. Designers should ensure that systems suchas oil separators and lagoons, that may be remote fromthe highway, are provided with safe means of access formaintenance.

7.4 The degree to which drainage systems and acombination of systems can reduce the pollution inroutine runoff is illustrated in Table 7.2, which is taken

May 2006

from a study carried out by The Water Research Centre(WRc) (ref. 10) to determine treatment efficiencies of arange of systems. The table highlights the performanceefficiencies of individual components of a drainagesystem as well as overall system efficiency for 5 sites inEngland. It will be noted that in some instances anegative efficiency was recorded within a discretecomponent of the system. This indicates the potentialfor pollutants to remobilise within component systemsas a result of high velocity flows entering a system.Whilst the findings from this study are instructive thescope of the study was limited and the figures are givento indicate rather than prescribe the range of treatmentefficiencies of certain systems.

Drainage Systems

Kerbs and Gullies

7.5 Gully pots can have both beneficial and negativeimpacts on water quality for receiving watercourses.The main benefit from gully pots is their ability tocapture potentially contaminated sediments duringnormal rainfall events prior to discharge into areceiving watercourse. They are more effective attrapping the coarse sediments than the finer ones. Theycan also provide a good first line of defence in the eventof an accidental spillage.

7.6 High inflow rates can cause re-suspension ofsediments within the gully pot and subsequentdischarge of the liquor from the gully pot can result in apollutant flush into the receiving drainage network orwatercourse. It has been found turbulence in the sumpcauses mixing of any trapped oils with the water beingdischarged. The best way of avoiding suchre-suspension or mixing of oils is to ensure that thegradient of the pipe leading to the gully is as shallow aspossible, consistent with adequate hydraulicperformance. Where this cannot be achieved, sumplessgullies may be an option to be considered. HA 105(DMRB 4.2) provides specific advice on this type ofgully.

Surface Water Channels and Drainage ChannelBlocks

7.7 In situations where channels are not self-cleansing, deposition of gross pollutants and sedimentsis likely to occur. Increased sediment build-up

7/1



potentially poses a safety threat to the travelling public,due to runoff ponding behind deposited materials. Toavoid this, gradients of long lengths of these channelsshould be designed to ensure that they are selfcleansing, with sediments being deposited in adownstream system. Channels can be designed to allowfor pollution control by emergency response kits, suchas those used by Environment Agency personnel. Thesecan be rapidly deployed to form a watertight seal atgully gratings, preventing discharge of runoff to thedrainage network.

Combined Kerb and Drainage

7.8 Combined kerb and drainage systems canattenuate flow, mainly due to the high storage capacityof the design. Where storage or balancing ponds areproposed as part of the design, the use of combinedkerb and drainage systems can help to reduce the sizeof, and sometimes eliminate the need for, an attenuationpond.

Piped Systems

7.9 In the event of accidental spillage, piped systemscan provide a form of spillage containment if adequatedownstream control is provided. This could take theform of a penstock, handstop, or an orifice that can bereadily blocked in emergency.

Ditches

7.10 Ditches have the potential to control pollution,due to infiltration of the runoff through any vegetationpresent. Ditches with gentle side slopes can beconsidered to have similar properties to swales, whichare described in HA 103 (DMRB 4.2). Ditches withconcrete or similar facing will not have the samepotential, but can be adapted to contain spillages. Alined ditch can act as a containment basin if locatedbetween the road drain and the receiving watercourse. Itshould have a minimum of 25m3 capacity and have adownstream control that can be shut or blocked in theevent of accidental spillage of pollutants on the road.Where ditches are located above permeable strata, thereis a risk that highway runoff will infiltrate andcontaminate any underlying aquifer. This can beprevented by facing the ditch with concrete/impermeable liner or placing the impermeable linerbeneath it.

Over-the-edge Drainage

7.11 Over-the-edge drainage can provide, in somecircumstances, an effective form of pollution control as

7/2

highway runoff is allowed to filter through vegetationon the slope. As with ditches, however, there is the riskof infiltration and contamination of groundwater. Insuch locations the toe ditch should be lined to preventsuch pollution. Pollution control is also possible withthis drainage system using a downstream control.

Combined Filter Drains

7.12 Combined drains offer some protection againstrelease to receiving water of accidental spillages, asthey can delay the release of pollutants. However oncepolluted effluent has entered the carrier pipe, pollutioncontrol is very limited without downstream controlssuch as penstocks. The filter media can also adsorbsuspended solid pollutants and heavy hydrocarbons,reducing downstream pollution risk from routine runoff.In locations where the routine runoff causes a build-upof pollutant in the filter media, it may be necessary torenew the filter material every ten years to ensure itremains sufficiently permeable. This will probably beneeded if contaminated by a serious accidental spillage.

7.13 The use of combined filter drains should alwaysbe assessed in conjunction with the risk to groundwaterpollution. Impermeable trench liners may beappropriate where groundwater pollution risks are high.

Oil Separators

7.14 There are two main types of oil separator: the fullretention separator and the bypass separator. Theirprimary function is to remove oil from the watercolumn, but they are less effective at removing solubleoils or other water-soluble liquids.

7.15 Full retention separators are used where all therunoff has to be treated. Their application will be veryrare on highways, and their use is usually reserved forlocations such as garage forecourts. Exceptionally, theymay be used in maintenance depots or constructionsites, and where the receiving environment is especiallysensitive.

7.16 Bypass oil separators are designed to capture andcontrol flows from rainfall events of up to 5mm/hour,which is about 10% of the typical peak rainfall intensityin the UK. They rely on the greatest pollutant loadbeing carried by the “first flush” of a runoff event. Only1% of all rainfall events in the UK have a rainfallintensity exceeding 5mm/hour, so such interceptors willcater for the large majority of events.

May 2006



7.17 On rural highways, oil separators may not be theoptimum solution, due to their requirement for frequentmaintenance. Consideration should be given toinstalling a vegetated drainage system, as described inHA 103 (DMRB 4.2), or to a less expensivecontainment facility.

Other Containment Facilities

Sedimentation Lagoons and Tanks

7.18 These structures should be constructed aboveflood plain level, if they are required to provide stormwater control. Aquatic growth in lagoons will act as afiltering mechanism for suspended particles andpollutants. Incorporation of by-pass facilities may bepossible such that only the first flush runoff is given fullsettlement, subject to consultation with the regulatoryauthority. For more advice on the design and selectionof settlement lagoons see HA 103 (DMRB 4.2).

Pollution Control Devices

Penstocks

7.19 Penstocks comprise a flat plate, fitted to a pair ofguide slots on a headwall or chamber wall, which israised and lowered using a screw thread operated by awheel. During routine highway operation, penstocksshould be in the fully raised position, and have noinfluence on flow passing through the drainage system.The primary function of penstocks is to control spillageincidents. If lowered in time prior to discharge ofsignificant quantities, penstocks can potentially retain100% of spilled material, which are then relativelyeasily removed by suction or other methods, dependingon the material involved. Operation of penstocks shouldonly be by either emergency or EPA personnel, orhighway maintenance contractors. Designers mustensure that such devices can be readily located and thatthey are provided with safe and easy means of access(see Chapter 8).

7.20 If the penstock is lowered over the pipe openingfor any other reason, potentially due to vandalism,failure of the screw thread or plate, or not being raisedafter an incident, the penstock will retain storm waterflow, which is likely to result in flooding, or scouringfollowing a breach of the headwall or ditch. Regularinspection and maintenance will be required to ensurethey do not become inoperable through long periodswithout use and to check they are not being vandalized.

Ha

7.2plathrbeThaswiwi

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7.2floredwisacoweatt

7.2to distheaccoco

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ndstops

1 Handstops are similar to penstocks except thete is raised and lowered directly, not using a screwead. The design should ensure that their use will not compromised by the need to lift the plate manually.ey will generally be cheaper than penstocks, but not

suitable for locations requiring a larger system. Asth penstocks, regular inspections and maintenancell be required.

eirs, baffles

2 Weirs and baffles can act as both pollution andod control devices. Where they are required touce spillage pollution risk, they should be designed

th a notch or orifice that can readily be blocked by andbag in an emergency. Weirs can act as a flowntrol device by allowing excess flows to overtop theirs. These flows can then be channelled toenuation ponds or other flood storage systems.

3 Baffles can be placed in open channels or ditchesslow down the flows, and therefore attenuate thecharge. Like weirs, they can be adapted to allowm to be blocked in emergency, thus retaining

cidental spillages. Where baffles are used for spillagentrol, there should always be at least 25 m3 ofntainment.

nging Walls

4 Hanging walls comprise simple bafflesnstructed across open ditches, so that oils and othern-miscible pollutants are retained. The ditch willve a reduced invert level downstream, so that thew is siphoned beneath the baffle. Careful attentionll need to be given to the location, ditch gradient andtential storage capacity of the system. Access forergency or maintenance personnel will be required.

ow Control Devices

5 Where attenuation of a flow is required, a devicech as a vortex chamber can be installed downstream a pond, ditch, drain or other storage facility, whichll have to be designed with adequate storage capacity.ese flow control devices should be designed for theecific job they are required to perform.anufacturers are usually able to provide designtails. For some locations, an orifice plate will suffice.

7/3



Permeable Pavements

7.26 Full depth permeable pavements allow surfacewater to infiltrate into the subgrade or to be capturedfor controlled release off site. With proper design andinstallation, they can provide an economical solutionfor management of storm water.

7.27 Traffic levels on motorways and trunk roadsrequire strong pavements and permeable pavements canonly be constructed as a departure from standard. Theremay however be paved areas remote from the runninglanes that can be constructed using permeablepavements.

7.28 Permeable pavements are becoming increasinglycommon in the construction of estate roads and carparks because of their ability to allow surface water toinfiltrate into the sub-grade or to be captured forcontrolled release off site. These pavements areconstructed with porous asphalt surfacing overlying athick gap-graded sub-base, which can temporarily storewater. Where infiltration directly into the sub-grade ispermitted, no special collection system will be required.As with all such proposed infiltration, the risks to theground water regime should be carefully assessed.

7.29 Where the existing sub-grade is impermeable, orwhere infiltration into the ground would lead tounacceptable risks, the water held in the sub-base willhave to be drained using appropriate sub-surfacedrainage adapted to cater for the larger flows expected.Impermeable linings are likely to be required to preventwater reaching sensitive ground waters, unless there is asufficient existing thickness of impermeable material.The design should ensure that the water will not lead tolong term deterioration of the foundation.

7.30 It should be noted that permeable pavements areprone to blockages by debris and this may have arequirement for frequent cleaning. Proper considerationshould be given to the provision of safe and convenientaccess for suitable machinery to carry out this task. Theuse of permeable pavements on major highways is anew technology. Where their use is being considered,further guidance should be obtained from theOverseeing Organisation.

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May 20

Compatibility with Vegetated Drainage Systems

Balancing/ Ponds HybridSedimentation Systems

Ponds

♦ ♦ ♦

♦ ♦ ♦

♦ ♦ ♦

♦ ♦ ♦

♦ ♦ ♦

♦ ♦

♦ ♦ ♦

♦

♦ ♦ ♦

♦ ♦ ♦

♦♦♦♦♦ ♦♦♦♦♦

♦♦♦♦♦ ♦♦♦♦♦ ♦♦♦♦♦

ith Vegetated Drainage Systems

Chapter 7

Control of Pollution and Flooding

06 Conventional Drainage Systems Potential Potential Potential Grassed Constructedfor for for Channels Surface

Spillage Pollutant Storm (Swales) WetlandsControl Removal Water

Control

Distribution Systems

• Kerbs and Gullies ♦ ♦ ♦

• Surface Water Channels ♦ ♦ ♦

• Combined Kerb and Drainage ♦ ♦

• Piped systems ♦ ♦ ♦

• Ditches (Unlined) ♦ ♦ ♦ ♦

• Combined Filter Drains ♦ ♦ ♦ ♦

• Ditches (Lined) ♦ ♦ ♦

Separators

• Oil Separators ♦ ♦ ♦ ♦

Pollution Control Devices

• Penstocks ♦

• Weirs and baffles ♦ ♦ ♦

Flow Control Devices

• Flow Regulators ♦♦♦♦♦ ♦♦♦♦♦

Soakaways ♦♦♦♦♦ ♦♦♦♦♦ ♦♦♦♦♦

Table 7.1: Runoff Management Capabilities of Conventional Drainage Systems and Compatibility w

7/5



% Reduction: Inlet to Outlet

Road Site/Treatment Devices Initial Second TotalForm of Form of System

Treatment Treatment Treatment

A34 Bypass oil separator/surface flow wetland/wet Metals 15 11 24balancing pond PAHs -1 99 99

TSS 37 73 83

A34 Filter Drain Metals 7 7PAHs 52 52TSS 38 38

M4 Oil trap manhole/Sedimentation Tank Metals -7 41 30PAHs -30 -26TSS -19 43 33

M40 Full retention oil separator/wet balancing pond Metals 19 35 48PAHs 13 50 57TSS -9 62 58

A417 Bypass oil separator/dry balancing pond Metals 27 39 56PAHs 4 16 22TSS 56 -37 40

Table 7.2: Indicative Treatment Efficiencies of Drainage Systems

May 20067/6


Chapter 8Signing of Pollution Control Devices

8. SIGNING OF POLLUTION

Introduction

8.1 This chapter gives guidance to the signing ofpollution control devices. The sign is intended to enablethe emergency services to locate the pollution controldevice as quickly as possible. It is not a traffic signwithin the meaning of section 64 of the Road TrafficRegulation Act 1984 and the Roads Traffic Regulations(Northern Ireland) 1997.

The Design of Pollution Control Device Signs

8.2 The sign must be designed in accordancewith BS EN 12899-1 ‘Fixed, vertical road trafficsigns Part 1: Fixed Signs’ (ref 11).

8.3 The location of the sign must be within thehighway boundary and must be referenced in thedrainage database described in HD 43 (DMRB4.2).

8.4 The sign should be located at least 600mm fromthe edge of a single carriageway or at a hardened vergeand 1500mm on high-speed dual carriageway ormotorway. Locations other than at the edge of thecarriageway are subject to approval by the OverseeingOrganisation. The mounting height of the sign shouldbe at least 900mm above the highest point of thecarriageway and can be increased up to 1500mm whereexcessive spray is likely to occur around the sign.

8.5 As this sign is regarded as a notice for theemergency services, the sign face is to have a lightgreen background with white legends and a yellowborder (see Figure 8.1). The X-height of the sign is tobe 50mm.

8.6 Illumination of the sign is not required. However,the sign face shall be made of retro-reflective Class 1material.

8.7 The sign should give details of the location of thepollution control device as referenced in the datamanagement system. HD 43 (DMRB 4.2) gives detailsof how such systems should be managed.

Ma

8.9discInscarsigngivSigtheSig

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CONTROL DEVICES

intenance of Pollution Control Device Signs

8.8 The sign must maintain its visibility to beeffective.

It should be checked at least annually for signs ofolouring or deterioration of the sign face.

pections of such signs should include inspectionsried out after dark and replacement and/or repairs ofs should be initiated if necessary. Further advice is

en in TD 25 ‘Inspection and Maintenance of Trafficns on Motorway and All-Purpose Trunk Roads’ and Traffic Signs Manual Chapter 12: Maintenance ofns.

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99-1:2001

X-Height 50mm Width 320mm

Height 410mm Area 0.13 sq. m

Diagram No. 1.4 Legend WHITE X-Height 50mm Background LIGHT GREEN Width 320mm Border YELLOW Height 410mm Material CLASS 1 Area 0.13 sq. m

25m

ollution Control Devices

8/2

Chapter 8

Signing of Pollution Control D

evices

May 2006

NOTES The sign shall be designed in accordance to BS EN 128



Diagram No. 1.3 Legend WHITE Background LIGHT GREENBorder YELLOW Material CLASS 1

25m

X X

Figure 8.1: Signing of P


Chapter 9References

9. REFERENCES

1 Trunk Road Maintenance Manual: Volume 2Routine and Winter Maintenance Code(TRMM2)

2 Manual of Contract Documents for HighwayWorks (MCHW)

Specification for Highway Works (MCHW 1)

Notes for Guidance on the Specification forHighway Works (MCHW 2)

Highway Construction Details (MCHW 3)

3 Design Manual for Roads and Bridges(DMRB)

BD 30 Backfilled Retaining Walls and BridgeAbutments (DMRB 2.1)

HA 37 Hydraulic Design of Road EdgeSurface Water Channels (DMRB 4.2)

HA 39 Edge of Pavement Details (DMRB 4.2)

HA 40 Determination of Pipe and BeddingCombinations for Drainage Works(DMRB 4.2)

HA 44 Design and Preparation of ContractDocuments (DMRB 4.1.)

HD 41 Maintenance of Highway GeotechnicalAssets (DMRB 4.1)

HA 71 The Effects of Highway Constructionon Flood Plains (DMRB 4.2)

HA 78 Design of Outfalls for Surface WaterChannels (DMRB 4.2)

HA 83 Safety Aspects of Road Edge DrainageFeatures (DMRB 4.2)

HA 102 Spacing of Road Gullies (DMRB 4.2)

HA 103 Vegetated Drainage Systems forHighway Runoff (DMRB 4.2).

HA 104 Chamber Tops and Gully Tops for RoadDrainage and Services: Installation andMaintenance (DMRB 4.2)

4

5

May 2006

HA 105 Sumpless Gullies (DMRB 4.2)

HA 106 Drainage of Runoff from NaturalCatchments (DMRB 4.2)

HA 107 Design of Outfall and Culvert Details(DMRB 4.2)

HA 113 Combined Channel and Pipe System forSurface Water Drainage (DMRB 4.2)

HA 118 Design of Soakaways (DMRB 4.2.)

HA 119 Grassed Surface Water Channels forHighway Runoff (DMRB 4.2.)

HA 216 Road Drainage and the WaterEnvironment (DMRB 11.3.10)

HD 25 Foundations (DMRB 7.2)

HD 26 Pavement Design (DMRB 7.2)

HD 27 Pavement Construction Methods(DMRB 7.2)

HD 43 Drainage Data Management Systemsfor Highways (DMRB 4.2)

TA 57 Roadside Features (DMRB 6.3)

TA 80 Surface Drainage of WideCarriageways (DMRB 4.2)

TD 9 Highway Link Design (DMRB 6.1)

TD 16 Geometric Design of Roundabouts(DMRB 6.2)

TD 25 Inspection and Maintenance of TrafficSigns on Motorway and All-PurposeTrunk Roads (DMRB 8.2)

BS 5931: 1980 ‘Machine laid in situ edge detailsfor paved areas’

A Guide to Design Loadings for Buried RigidPipes. O C Young and M P O’Reilly. Transportand Road Research Laboratory. Department ofTransport. HMSO, 1983

9/1


Chapter 9References

6 Materials Selection Manual for Sewers, PumpingMains and Manholes. Foundation for WaterResearch, 1993

Manual of Sewer Condition Classification. WRc

Model Contract Document for Non Man EntrySewer Inspection. WRc

7 Road Note 35. A guide for engineers to thedesign of storm sewer systems. Transport andRoad Research Laboratory. Department ofTransport. HMSO

8 Simplified Tables of External Loads on BuriedPipelines. O C Young, G Brennan and M PO’Reilly. Transport and Road ResearchLaboratory. Department of Transport, HMSO1986

9 The Wallingford Procedure: Design and analysisof urban storm drainage. National Water Council,1981

10 Long Term Monitoring of Pollution fromHighway Runoff. F Moy, R W Crabtree, TSimmes. WRc report ref. UC 6037

11 BS EN 12899-1:2001 ‘Fixed, vertical road trafficsigns Part 1: Fixed Signs’

May 20069/2


May 2006 10/1

10. ENQUIRIES

All technical enquiries or comments on this Standard should be sent in writing as appropriate to:

Chief Highway EngineerThe Highways Agency123 Buckingham Palace RoadLondon G CLARKESW1W 9HA Chief Highway Engineer

Chief Road EngineerTransport ScotlandVictoria QuayEdinburgh J HOWISONEH6 6QQ Chief Road Engineer

Chief Highway EngineerTransport WalesWelsh Assembly GovernmentCathays Parks M J A PARKERCardiff Chief Highway EngineerCF10 3NQ Transport Wales

Director of EngineeringThe Department for Regional DevelopmentRoads ServiceClarence Court10-18 Adelaide Street G W ALLISTERBelfast BT2 8GB Director of Engineering

Chapter 10Enquiries