VOLUME 4 GEOTECHNICS AND DRAINAGE SECTION 2 … · february 2018 design manual for roads and bridges volume 4 geotechnics and drainage section 2 drainage part 4 hd 220/18 vortex separators

February 2018

DESIGN MANUAL FOR ROADS AND BRIDGES

VOLUME 4 GEOTECHNICS AND DRAINAGE

SECTION 2 DRAINAGE

PART 4

HD 220/18

VORTEX SEPARATORS FOR USE WITH ROAD DRAINAGE SYSTEMS

SUMMARY

This document gives requirements on the design and installation of vortex separators as a method of removing sediment and improving the water quality of highway surface water run-off.

INSTRUCTIONS FOR USE

1. Remove existing contents page for Volume 4 and insert new contents page for Volume 4.

2. Insert the new HD 220/18 into Volume 4, Section 2.

3. Please archive this sheet as appropriate.

Note: A quarterly index with a full set of Volume Contents Pages is available separately from The Stationery Office Ltd.


Summary: This document gives requirements on the design and installation of vortex separators as a method of removing sediment and improving the water quality of highway surface water run-off.

Vortex Separators for use with Road Drainage Systems

HD 220/18 Volume 4, Section 2, Part 4

HIGHWAYS ENGLAND

TRANSPORT SCOTLAND

LLYWODRAETH CYMRUWELSH GOVERNMENT

DEPARTMENT FOR INFRASTRUCTURE NORTHERN IRELAND

February 2018

Registration of AmendmentsVolume 4 Section 2Part 4 HD 220/18

Amend No Page No Signature & Date of incorporation of amendments


REGISTRATION OF AMENDMENTS

February 2018

Registration of AmendmentsVolume 4 Section 2

Part 4 HD 220/18



REGISTRATION OF AMENDMENTS

February 2018


VOLUME 4 GEOTECHNICS AND DRAINAGE

SECTION 2 DRAINAGE

PART 4

HD 220/18

VORTEX SEPARATORS FOR USE WITH ROAD DRAINAGE SYSTEMS

Contents

Chapter

1. Introduction

2. Principles & Construction

3. Design and Detail

4. Operation and Maintenance

5. Safety Issues

6. References

7. Approval

Annex A: Generic Detail Drawings

February 2018 1/1

Chapter 1Introduction

Volume 4 Section 2Part 4 HD 220/18

1. INTRODUCTIONBackground

1.1 This document provides requirements on the use of Hydro Dynamic Separators (vortex separators) as a means of removing sediments carried in suspension by flow in road drainage pipelines and floatable debris and oil within the flow. Vortex separators cannot be assumed to be capable of removing soluble pollutants or immiscible liquids of similar density to water. The requirements contained in this document are based on devices commercially available at the time of the trials.

1.2 The term “Roads” used in Scotland and Northern Ireland is synonymous with the term “Highways” defined in the Highways Act 1980. In this document the term highway will be used as the standard terminology, however for clarity, where the term “roads” is used in this document, it should be taken to be equivalent to “highway”.

1.3 This document also contains guidance on the identification of suitable locations, the principles of the device and its operation and maintenance

1.4 Following the introduction of HA 105: Sumpless Gullies (DMRB 4.2.3 Ref 1), the drainage philosophy is to reduce maintenance where practical and improve the quality of surface water runoff from the carriageway. The elimination of the gully sump may lead to an improvement in water quality but may potentially increase the amount of sediment entering the drainage system. HA 219: Determination of Pipe Roughness and Assessment of Sediment Deposition to Aid Pipeline Design (DMRB 4.2.3, Ref 1) provides guidance on the design of the pipe line to transport sediment and the assessment of the volumes of sediment that a road might generate. There is scope to further reduce maintenance costs by reducing the number or frequency of catchpits and instead trap sediment at more centralised locations, remote from the carriageway, where sediment can be removed without recourse to major traffic management associated with lane closures. The vortex separator with its comparatively small footprint would enable these aims to be achieved. To further this, the Highways Agency undertook a full scale trial by installing a vortex separator during M25 widening works. An 18 month long trial monitored the volume of sediment retained and the contaminants present in both the sediment and the water.

1.5 Vortex separators are supplied as a proprietary product; this document contains no guidance on the hydraulic design of the device itself. The units will be sized hydraulically using data provided by the manufacturer, refer to Chapter 3. HD 33: Surface and Sub-surface Drainage Systems for Highways (DMRB 4.2, Ref 1) states the mandatory requirements for the design of the pipeline.

1.6 The trial undertaken has indicated that, when properly maintained, vortex separators offer an effective additional treatment option in any treatment train approach, for example when used in conjunction with isolating devices and other propriety devices. This is particularly important when a high quality of discharge to the environment is needed.

Scope and Purpose

1.7 This document gives requirements on the design and installation of vortex separators as a method of removing sediment and improving the water quality of highway surface water run off. This document applies to all schemes on trunk roads including motorways.


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Design Policy

1.8 HD 49: Highway Drainage Design Principal Requirements (DMRB 4.2 (Ref 1)) describes the policy for the selection and design of road drainage systems for sustainability and the relevant legislation. The design of drainage systems for all trunk roads and motorways in England and Wales is subject to certification and specific guidance on the certification process is given HD 50: The Certification of Drainage Design (DMRB 4.2 (Ref 1))

Definitions, Acronyms and Abbreviations

1.9 The definitions of the various drainage asset types are contained in HD43: Drainage Data Management Systems for Highways England, (DMRB 4.2, Ref 1) whereas environmental definitions are contained in HD 45: Road Drainage and the Water Environment (DMRB 11.3.10, ref 1)

Equality Impact Assessment

1.10 An Equality Impact Assessment is not considered necessary for this document.

Application in Devolved Administration

1.11 In Northern Ireland, this document will be applicable to those roads designated by the Department for Infrastructure Northern Ireland.

Mutual recognition clause

1.12 Where there is a requirement in this document for compliance with any part of a “British Standard” or other technical specification, that requirement may be met by compliance with the Mutual Recognition clause in GD 01 Introduction to the Design Manual for Roads and Bridges

Implementation

1.13 This document should be used forthwith for all schemes currently being prepared provided that, in the opinion of the Overseeing Organisation, this would not result in significant additional expense or delay progress. Design Organisations should confirm its application to particular schemes with the Overseeing Organisation (see HD 33 – DMRB 4.2 (Ref 1)).

Recording of asset inventory and condition data

1.14 Data regarding the inventory and condition of the drainage assets described in this document, and their connectivity with the rest of the drainage system, is to be uploaded and maintained in the drainage data management system described in HD 33 Chapter 10 (DMRB 4.2, Ref 1). This is applicable to England and Wales only; for Northern Ireland and Scotland consult the relevant Overseeing Organisation. All continuous assets must be connected to a point asset at each end, with one point defined as upstream and the other as downstream.

1.15 Vortex separators are recorded as point assets.

Assumptions made in the Preparation of the Document

1.16 Not applicable.

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Feedback and Enquiries

1.17 Users of this document are encouraged to raise any enquiries and/or provide feedback on its contents and usage to the dedicated HA team. The email address for all enquiries and feedback is: [email protected]

1/4 February 2018



February 2018 2/1

Chapter 2Principles & Construction


2. PRINCIPLES & CONSTRUCTIONPrinciples

2.1 The principle operation of the vortex separator is to use tangential flow into the chamber to induce rotational motion in the fluid where a combination of gravity and boundary layer effects separate solids from the liquid. The hydraulic design ensures that the action of the circulating flow exerts a much greater tangential force on the solids than the friction resulting from the centrifugal force generated by the rotating flow. Differential velocities and the low energy of the vortex allow the denser sediment and grit material to settle in the chamber while oil and floatables are retained in circulating flow on the surface. The hydraulic characteristic of the core shape ensures the settled sediments are retained within the base of the device irrespective of the velocities of the flow through the device.

2.2 There are two variations of the hydraulic principle for vortex separators as outlined below. Generic details of these alternative arrangements are shown in Annex A.

Version A: Inflow via central core

2.3 Surface water flow is introduced tangentially into the chamber where it is directed down the central core in a circular motion. A fine screen can be fitted in this central core to retain sediment and floatable objects. Solids within the core remain in continuous motion which prevents clogging of the screens. At the lower end of the core, the flow passes through the coarse screen to spiral upwards in the outer annulus to the chamber outlet. Solids and sediment detained by the screen and the spiral flow fall into the containment area and are retained by the top of the compartment that also forms the base of the central chamber construction.

Version B: Inflow via external annulus

2.4 The photographs contained in this document are of the trial undertaken by Highways Agency at a location on M25 and are of Version B vortex separator. A general view of the device before locating within the chamber is shown in Figure 2.5.

2.5 Surface water flow is introduced tangentially into the vortex separator (see Figure 2.5) where it is directed around the outside of the central core in a circular motion, spiralling down the internal face of the chamber before entering the central core and continuing to spiral upwards to the chamber outlet. Sediment is directed downwards by the vortex action and is retained by the conical skirt at the base (see Figure 2.11).

2/2 February 2018



Figure 2.5 Vortex unit

2.6 The central core is surrounded by a non-perforated screen which retains floatable material and oils at the top of the chamber, as shown in Figure 2.6. Note that the prime function of a vortex separator is to retain sediment and floating solids and, where required by a spillage risk assessment (HD45: Road Drainage and The Water Environment DMRB 11.3.10 (Ref 1)).

Figure 2.6 Inlet and screen

2.7 Neither version of vortex separator can be deemed to remove dissolved pollutants.

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Construction

2.8 The sump can project several metres below the invert of the pipe line and consequently a deep excavation may be required.

2.9 Vortex separators may be manufactured monolithically utilising plastic chamber units or, for the smaller sizes of separator, integral with pre-cast concrete chamber rings that are supplied in sections. Larger versions of vortex separator, similar to that shown Version B, (Figure 2.5) are sized to fit within conventional precast concrete chamber rings that have been prefabricated to suit the inlet and outlet pipe positions. The trialled example was flanged and stiffened with cross beams and suspended from the upper ring joint as shown in Figure 2.6. When of concrete construction, the chamber base and lower ring are supplied as a homogeneous unit for either version of vortex separator.

2.10 The vortex separator comprises a vertical cylindrical core (Figure 2.10) that either connects to a conical skirt or is suspended above one attached to the lower chamber ring (Figure 2.12). The Version A vortex separator combines the central shaft with a coarse screen that locates in to the floor of the central chamber unit, thereby forming the containment area.

Figure 2.10 Vortex core

2.11 The excavation formation should be blinded with concrete to ensure that the base unit is level and thus the chamber vertical. The thickness of blinding should be in accordance with the manufacturer’s recommendations.

2.12 Dowels or formal markers cast into the rings facilitate correct alignment and butyl gaskets seal the chamber ring joints.

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Figure 2.12 Conical Benching Skirt attached to chamber ring

2.13 The cover slab has a rectangular opening to enable access to the central core and the annulus adjacent to the screen. Further to the experience of the Highways Agency trial, in the absence of alignment markings, it was found that correct orientation of the slab is important (see Figure 2.14) otherwise the oil containment area may be inaccessible. Where the device is fabricated as an integral part of the chamber, there is a lower risk of misalignment.

2.14 Internal components are manufactured from stainless steel and or polyethylene and can be damaged by mishandling. There are no moving components.

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Figure 2.14 Access to core and outer annulus

2.15 Sediments and grit are removed from the sump via the hollow core by vacuum tanker and similarly, floatable materials and oils are removed from the annulus (see Figure 2.14) refer to Chapter 4 for details. Version A of the vortex separator can be supplied with a basket to aid coarse debris removal The presence of a basket in the vortex separator sump may hinder the removal of sediment, hence this is more appropriate where removal of coarse debris is a requirement

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February 2018 3/1

Chapter 3Design & Detail


3. DESIGN & DETAILGeneral

3.1 The vortex separator devices are proprietary products, the internal hydraulic design of the device being undertaken by the manufacturers and outside the scope of road drainage design guidance.

Hydraulic Design

3.2 The principle behind the vortex separator is that there is no minimum velocity through the device, it should continue to operate at all velocities below the design limit, refer to Chapter 2 for the principles of operation.

3.3 The operation of the vortex separator is governed by the flow rate into the device. Consequently vortex separators are designed by their manufacturers on the basis of two capacities, the treatment capacity and the hydraulic capacity. In determining an appropriate device to meet the design requirements, it is the treatment capacity, as advised by the manufacturer that should be used to determine the peak flow capacity limit rather than using the hydraulic capacity. The device is therefore sized for a treatment capacity based on the hydraulic design of the pipeline in accordance with the parameters stated in Design Standard HD 33 (DMRB 4.2 (Ref 1)).

3.4 Manufacturer’s requirements may require the inlet pipe to remain submerged in order for the device to function correctly. This would require the inlet pipe to be laid to a steeper gradient than required by hydraulic design, see Fig 3.4 so that the inlet pipe is lower than the outlet. The outlet pipe level relative to the inlet pipe level is set by the manufacturer. For the vortex separator to operate correctly, the level of the outgoing pipe from the vortex separator should still be lower than the outlet level of the upstream chamber in accordance with good hydraulic practice.

Fig 3.4 Relative levels

Some smaller proprietary devices differ from Figure 3.4 by having an internal vertical pipe to introduce the flow at the lower level.

3/2 February 2018



Location

3.5 The depth of excavation necessary to install these devices is generally significantly greater than that to lay the drainage pipeline, possibly by as much as 4 metres. The geotechnical aspects, such as groundwater level and the presence of rock should be taken into account when assessing the suitability of potential locations. The vortex separator should be sited such that the presence of other roadside features does not obstruct maintenance access

3.6 Access for maintenance vehicles, especially larger vehicles such as a vacuum tanker, may require construction of an adjacent hard-standing. The vortex separator should be positioned to be clear of the carriageway and to facilitate safe access and manoeuvring, minimising the requirement for traffic management and shall be designed to withstand the expected loadings relevant to the installed location.

General Arrangement

3.7 Vortex separators may be used in conjunction with other drainage features as part of an overall drainage strategy.

3.8 Contributing pipelines should be connected to an upstream chamber, which should be a manhole rather than a catchpit, to minimise turbulence and maintain stable flow conditions in the inlet pipe.

3.9 Installing vortex separators along the pipeline, rather than immediately upstream of the point of discharge, would remove sediment as close to the source of the sediment in-flow as possible, thereby improving the hydraulic performance of the drain. (HA 219: Determination of Pipe Roughness and Assessment of Sediment Deposition to Aid Pipeline Design (DMRB 4.2 Ref 1) provides advice on the calculation of sediment loads).Siting remote from the outfall may also be a construction expedient where the location of the outfall or topography precludes maintenance access.

Oil interceptors, filters, ponds or soakaways

3.10 A vortex separator may form part of a treatment train for improving the water quality of highway run off (ref HD 45 DMRB 4.2, Ref 1) and the treatment efficiency tabulated in HD33 (DRMB 4.2, Ref 1) may be factored into the treatment process.

3.11 The vortex separator will detain floatable substances such as oils but should not be substituted for a purposely sized oil interceptor where one is required by spillage risk assessment, (see 2.6).

3.12 When using a vortex separator as a treatment system it should be appropriately sized and fitted with an emergency closure device (an isolating device) in order to enable shutting off of the system in the event of a spillage. This will ensure that such spillages are prevented from entering the downstream section of the drainage system and thus prevent discharge to the environment. It is always important to emphasise that regular inspection, cleaning and maintenance is required for all devices’.

3.13 Where the vortex separator can be located adjacent to an oil interceptor and / or spillage containment facility, use of the access and standing area provided for these components will facilitate combined maintenance activities.

3.14 Some versions of the vortex separator contain internal filters to remove more of the suspended solids in the runoff, including smaller sized particles. Alternatively filters can be installed in a chamber immediately downstream of the vortex separator. Filters can be manufactured to remove soluble pollutants such as toxic metals, as well as suspended solids. The inclusion of a filter offers a higher level of environment protection,

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but at the expense of a reduced hydraulic capacity of the vortex separator, as filters are more effective when treating significantly lower flows than vortex separator capacity.

3.15 Applications where low flows from sub-annual rainfall events pass through both the vortex separator and a filter might be the ideal system where the receiving water environment is vulnerable. While an integral filter can be bypassed within the vortex separator chamber, when a downstream filter chamber is installed, a bifurcation arrangement would allow the higher flows from the less frequent rain events to be treated by the vortex separator only and will bypass the filter chamber.

Health & Safety File

3.16 The procedures for the safe operation and maintenance of the vortex separator, together with the known residual risks arising from the design and construction should be inserted into the Health and Safety file for delivery to the Maintaining Organisation.

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February 2018 4/1

Chapter 4Operation and Maintenance


4. OPERATION AND MAINTENANCEGeneral

4.1 The vortex separator works due to the hydraulic properties of the device and has no moving parts or power requirements, hence there is no reason to enter the chamber and all operations can be carried out from above ground.

Safety

4.2 There should be no reason to enter the chamber, consequently no means of access or egress is provided. Safety issues are detailed in Chapter 5.

Operation

4.3 There should be no operational requirements beyond the maintenance inspections, emptying and cleaning.

4.4 Although there are no moving components, ensure that the internal features of the separator, especially the coarse screen, where fitted, are not damaged especially by the vacuum tanker hose nozzle.

4.5 Replacement or repair of any components that may be damaged during cleaning operations will, generally, necessitate the partial disassembly of the chamber.

Maintenance

4.6 Maintenance Procedures should be in compliance with those stated in the Health and Safety File and the manufacturer’s instructions.

4.7 Some proprietary products may incorporate a fine screen around the top of the device as the means of capturing coarse floatable material. The manufacturer’s instructions should be followed and this may require the use of a pressure water jet to clear debris.

4.8 In versions of the vortex separator that contain internal filters to remove additional suspended solids or soluble pollutants, the filter material must be checked for signs of damage or blockage and must be cleaned or replaced in accordance with manufacturer’s instructions. In some devices, this may mean entry into the chamber is necessary. Filter maintenance and / or replacement should be planned in accordance with the manufacturer’s recommendations.

4.9 Maintenance should be undertaken in accordance with the Maintaining Organisation’s safe working practices and the manufacturer’s recommendations.

4.10 Note that if a suitable inspection or monitoring regime and resulting emptying and cleaning operations are not put in place then a loss of material from the sediment containment area may occur if organic matter, such as leaves, decompose and resulting organic compounds dissolve and are lost in the circulating flow.

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Chapter 4Operation and Maintenance


February 2018 5/1

Chapter 5Safety Issues


5. SAFETY ISSUESGeneral

5.1 Vortex separators may be located adjacent to the highway and fast moving traffic.

5.2 The Health and Safety File should identify residual risks and state procedures, which shall be recorded in the relevant asset management system.

5.3 The covers shall be lockable and kept locked when not in use.

Placard

5.4 The cover shall be marked ‘Vortex Separator’ and a placard should be attached to the chamber opening just below the cover that warns against attempting to access the chamber. Note that if filters are used then access may be required in order to replace the filter. The wording of the placard should acknowledge this and warn against unplanned access to the chamber.

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Chapter 5Safety Issues


February 2018 6/1

Chapter 6References


6. REFERENCESInformative

6.1 Design Manual for Roads and Bridges (DMRB) (The Stationery Office)

HD 33 Surface and Sub-surface Drainage Systems for Highways (DMRB 4.2)

HD 49 Drainage Design Policy (DMRB 4.2.1)

HD 45 Road Drainage and the Water Environment (DMRB 11.3.10)

HD 50 The Certification of Drainage Design (DMRB 4.2.1)

HA 105 Sumpless Gullies (DMRB 4.2)

HA219 Determination of Pipe Roughness and Assessment of Sediment Deposition to Aid Pipeline Design (DMRB 4.2.4)

HD 45 Road Drainage and the Water Environment (DMRB 11.3.10)

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Chapter 6References


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Chapter 7Approval


7. APPROVALApproval of this document for publication is given by:

Department for InfrastructureClarence Court10-18 Adelaide StreetBelfast P B DOHERTY BT2 8GB Director of Engineering

Welsh GovernmentTransport S HAGUECardiff Deputy DirectorCF10 3NQ Network Management Division

Transport Scotland8th Floor, Buchanan House58 Port Dundas RoadGlasgow R BRANNENG4 0HF Chief Executive

Highways EnglandTemple Quay HouseThe SquareTemple QuayBristol M WILSONBS1 6HA Chief Highway Engineer

All technical enquiries or comments on this Document should be sent to [email protected]

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Chapter 7Approval


February 2018 A/1


Annex AGeneric Details

ANNEX A: GENERIC DETAILS

A/2 February 2018


Annex AGeneric Details

Documents

VOLUME 4 GEOTECHNICS AND DRAINAGE SECTION 2 … · february 2018 design manual for roads and bridges volume 4 geotechnics and drainage section 2 drainage part 4 hd 220/18 vortex separators