REAM Guidelines for Road Drainage Design - Volume 2

FOREWORD Road Engineering Association of Malaysia (REAM), through the cooperation and support of various road authorities and engineering institutiorri in Muluysia, publishes a series of official documents on STANDARDS, SppctptcATIoNS, GUIDELINES, MANUAL and TECHNICAL NOTES which are related to road engineering. The aim of such publication is to achieve quality and consistency in road and highway construction, operation and maintenance. The cooperating bodies are:Public Works Department Malaysia (pWD) Malaysian Highway Authority (MHA) Department of Irrigation & Drainage (DID) The Institution of Engineers Malaysia (IEM) The Institution of Highways & Transportation (IHT Malaysian Branch) The production of such documents is carried through several stages. At the Forum on Technology and Road Management organized Uy fWOfnEAM in Novemb er 1997, Technical committee 6 Drainage was formed with the intention to review Arahan

Teknik (Jalan) 15/97 - INTERMEDIATE GUIDE To DRAINAGE DESIGN oF ROADS' Members of the committee were drawn from various government departments and agencies, and from the private sector including privltized road operators, engineering consultants and drainage products manufacturers and

contactors. I

;

Technical Committee 6 was divided into three sub-committees to review Arahan Teknik (Jalan) 15/97 and subsequently produced ,GUIDELINES FoR ROAD DRAINAGE DESIGN' consisting of the foll,owing vorumes: Volume 1 Volume 2 Volume 3 Volume 4 Volume 5 -

Hydrological Analysis Hydraulic Design of Culverts Hydraulic Considerations in Bridge Design Surface Drainase Subsoil Drainale

The drafts of all documents were presented at workshops during the Fourth and Fifth Malaysian Road Conferences held in 2000 and 2002 reipectively. The comments and suggestions received from the workshop participantr *"r. reviewed and incorporated in the finalized documents.

ROAD ENGINEERING ASSOCIATION OF MALAYSIA 46-A, Jalan Bola Tampar l3/r4, Section 13, 40100 Shah Alam, Selangor, Malaysia Tel: 603-5513 6521 Fax:5513 6523 e_mail: ream@po=jaring.m),

TABLE OF CONTENTS Page

2.1

INTRODUCTION

....."..2-I

2.2

GENERAL

CRITER.IA.... 2.2.I Drainage Survey 2.2.2 Site Visit

......2.1 ....2-1 ........2-2 .....2-2

....;..

... Characteristics .. 2.2.2.4Highwaterlnformation.... 2.2.2.5 Existing Structures 2.2.2.6Soiilnvestigation 2.2.3 Culvertlocation 2.2.3.1A1ignment 2.2.3.2 Vertical Profile 2.2.3.3 Structural Consideration... 2.2.2.1Topographical Features 2.2.2.2 Catchment Area 2.2.2.3 Channel Characteristics

2.3

CULVERT TYPE SELECTION

2.3.I

2.3.2

.. .

..

..2-2

.".....2-2 ......2-2 ......-.2-3 ......2-3 ....2-3 ........2-3 ....2-5 ......2-5

.,.......2-8

Type Selection Site Conditions 23.2.f Low Allowab1e 2 .3 .2.2 Depth of Cover for Traffic 2.3.2.3 Settlement of

Headwater.. Loading Culverts 2.3.2.4CulvertJoints

FACTORS TO BE CONSIDERED IN HYDRAULIC DESIGN OF CULVERT . 2.4.1 Hydrological Analysis

Culverts Procedures . 2.4.3 Freeboard 2.4.4 Length of Culvert 2.4.5 Skew of Culvert 2.4.6 GradientofCulverts 2.4.1 Scour and Seepage Countermeasures 2.4.8 Flow Velocities .

2.4.2

. . .. .

Size of 2.4.2.1Design 2.4.2.2 Minimum Size

."...2-8

.....2-8 ........2-8 ..2-9 "..2-lO

.....

......2-I0 ......2-IO ...2-10

......2-I1 .........2-I1

.....2-lI .... ".2-12 "...2-12 ......2-12 ...,......2-13 ..2-13 ..."2-I4

LIST OF FIGURES Figure 2.1 Frgure2.2 Figure 2.3 Ftgure 2"4

StreamRealignment....

Alignment of Culvert in Embankment Across Ravine. Culvert Profile Scour and Seepage Protection

Measures

."..2-4 ....2-6

.........2-7

.....2-I5

''''

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*B e

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r F e

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F -F

LIST OF TABLES

F

F F -F

T^yl"?l Table 2'2

Recommended Minimum Size of Cutvert Maximum Recommended Flow Velocities (m/s) for Various Conduit Materials

p

2-t1 2-16

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LIST OF REFERENCES

.

APPENDIX 1 Reprint of Chapter 27 : Curverts, urban stormwater Management Manual for Malaysia

2-17

E) F q

*

VOLUME 2.0 - HYDR.AULIC DESIGN OF CULVER.TS

2.I

INTRODUCTION The primary purpose of culverts is to convey water under a roadway. They may also be used to restrict flow so that a controlled amount of water is discharged

while the upstream basin of the stream channel is used for detention storage. In road embankments, which traverse across val1eys, culverts are used to convey water from a hisher levei to a lower level. In1et, outiets and joints must be carefully designed so as noi to obstruct smooth

flow of the water. Attention must be paid in detailing of joints to ensure no leakage occurs because it can endanger the embankment integrity by way of washout of the soil mass.

The design of culverts involves hydraulic and structural design. This volume wi.ll

only discuss the hydraulic design of culverts. The method used is generally adopted from the publication "Chapter 27 - CULVERT, Urban Stormwater Management Manual for Malaysia" published by Jabatan Pengairan dan Saliran (JPS), copy of which is reproduced here as Appendix 1.

2.2

GENERAL CRITERIA

2.2.1

Drainage Survey

The design of a culvert begins with the drainage survey. Before the drainage survey is carried out, the designer should check with JPS or the local authorities whether past survey plans are available.

If

a drainage survey needs to be carried out,

it is

suggested that the designer

first

of all estimate the design discharge. If the estimated design discharge exceeds 30 cumec for a 50 years recurrence interval, the survey should cover a minimum of 200 metres upstream and downstream from the centre line of the proposed or existing culvert to obtain:

a) b) c) d)

sufficient channel cross sections, the streambed profile and existing water levels, the horizontal alignment of the existing sffeam channel,

invert levels and crown ievels of any existing culvert, and 11

e)

highest flood levels.

The site survey should be carried out to the extent sufficient for the proper location and design of the culvert.

2.2.2

Site Visit

A

site visit by the designer is a must to determine on site information, such

as

topographic features, catchment area, channel characteristic, highwater information and existing structures should be noted, as it can be useful in the hydraulic design.

2.2.2.1 Topographical

Features

-t

-i

Features such as residential and commercial buildings, croplands, roadways, the lay of the ground and utilities can influence the location of the culvert as it

-l

determines the direction and velocity of the location should be obtained.

I

flow.

Therefore their elevation and

I

I I

i

2.2.2.2

Catchment Area Characteristics

The designer should take note of features such as lakes, land usage, type and density of vegetation and any man-made changes or development such as dams, because these factors could alter run-off.

I

i

I

Future landuse plans of the catchment should be obtained, if available, to study the effects of future landuse changes on run-off and where necessary these effects should be taken into consideration in the culvert desisn.

2.2.2.3

Channel Characteristics

Physical characteristics of the existing stream channel such as, type of soil or rock in the streambed, the bank condition and amount of drift, and debris should also be noted as these factors could affect the durability of the culvert material used and the sizing of the culvert.

2.2.2.4 Highwater Information Highwater information which may be obtained from observation of the high water mark, local residents or Jps can be used to check results of flood estimating

)_)

procedures, establish highway grade 1ines, to locate hydraulic controls, and to check backwater effects arisine from the construction of the new culvert.

2.2.2.5 Existine Structures Considerable importance should be placed on the hydraulic performance of existing structures, some distance upstream or downstream from the proposed culvert site, which can be helpful in the design. Useful data of existins structures includes:

i) ii) iii) iv) v)

date of construction,

performance during past floods, scour indicated near the structures,

highwater elevation with datum and dates of occurrence, and structurai conditions of the structure.

2.2.2.6 Soil Investisation Sub-soil investigation should be carried out to the extent required for the design

of the culvert and soil characteristics should be obtained for design of settlement and protection against soil erosion.

2.2.3

Culvert Location

Culvert location refers to the horizontai alignment and vertical profile with respect to both roadway and stream. A proper location is important because, it affects hydraulics, the adequacy of the opening, maintenance of the culvert and possible washout of the roadway.

2.2.3.I

Alignment

The first consideration of culvert location is to place it in the natural channel to give the stream a direct entrance and a direct exit. Where this is not possible, a direct inlet and outlet can be obtained by means of channel diversion, a skewed culvert alignment or both. Realignment of the natural channel should be designed

properly so as to avoid erosion on the concave side of the channel and siltation on the inner side of the bend. Where following the original channei would result in a very long and skewed road crossing, a cheaper and practical option is to construct a stream realignment, see Figure 2.1 for

'

2-3

illustration.

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(o)

nruttCtPATlNG SEDIMENTATION

(b)

CHANGE FROM CHANNEL GRADE MAY CAUSE SEDIMENTATION OR EROSION

PAVING OR OTHER OPEN SPILLWAY

(c)

CULVERT PLACED BILOW PROPIR GRADE WATERWAY

rYELL-,coMPrcTEo

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FILLING-

IS

REDUCTD

- /GASION UATTRESS

(e)

HTLLSIDE GRADES.

(f) (f) CANTTLTVER

EROSION PR

NOTE:

I. 2.

PROPER CUL\€RT GRADE IS ESSENThL FOR THE PROPER FUNTIONING OF THE SIRUCTURE

3,

DIFFERENThL S€TTLEMENT SHOULD

H LF FrtL (d), (f) rHE CUL\GRT SHOULD BE LAlo ON UNIFORM BEDoINC XATERIAL FOR THE WHOLE LENGTH, TO UINIMIZE DIFFERENTIAL SETTLEMENT

rN FiALF CUl

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CONSIOERED IN THE DESIGN OF THE CULVERT STRUCTURE

FIGURE

2.3

:

CULVTRT PROFILt

2-l

EXTINSTON

tl

CULVERT TYPE SELECTION

2.3.1

Type Selection Types of culverts commonly used in this country are as follows: a)

precast reinforced concrete pipes (refer M.S. gg1: part 1, part

3:1991), b) c) d)

precast reinforced concrete box culverts (refer

2 and.part

M.s. 1293 : part 1 reinforced concrete cast-in-situ box (refer M.s. 11g5:1gg5), and culvert of other material approved by relevant authorities.

:

r99z),

culvert type selection includes the choice of materiai, shape, cross section and the number of culvert barrels that will best fit the waterway of the channel or stream. The following factors shourd be considered in any cuivefi type serection:

a) b) c) d) e) 0

design discharge, site conditions,

design life,

construction period, construction joints, and blockage due to floating debris from upstream.

If

the design discharge exceeds 60 cumecs based on a 50 years recurrence interval, consideration should be given to using a bridge structure taking into

-l

account the site constraints and economic factors.

2.3.2

Site Conditions

2.3.2.1 Low Allowable Headwater

-l I

Headwater is the water depth at the inlet of the culvert. Multiple cells culverts have to be used at places where the headwater should be kept low to get the water through quickly without ponding or flooding of the land upstream. In flat flood plain where there is no well-defined local flow path multiple culverts spread over the width of the flood plain may be more effective than a single large culvert.

2-8

The designer should also take note of the amount of debris in the channel. In be provided areas where solid waste is a problem, trash screen with bypass should a distance upstream of the culvert entrance to prevent clogging of the culvert barrel.

a)

Reinforced Concrete PiPe When two or more pipes are used, the pipes should be separated by a clear distance of about 0.3m to 0.9m to allow space for thorough compaction of

backfilling, which is essential to the side support to prevent collapse of the pipes due to unequal surcharge loading. Backfilling between pipe barrels shouid be with well-graded sancl. Proper headwalis and wing walls should be provided to prevent washouts of the sand back fill. Concrete backfill and haunching may be used in high fill areas where strength is required, and where the founding soii is soft and weak'

b)

Precast Reinforced Concrete Box

Multiple cells precast reinforced concrete box culvert should be laid without a gap between the culverts walls to provide less overall obstruction to the flow of water. Precast box culverts are normally manufactured with butt ends. To prevenr wash-in of fine particles from surrounding soil the butt joints should be wrapped all round with suitable drainage geotextile. The usage of multiple cells culverts should be considered with due care:

o

if clogging by debris is very evident then multiple cells culverts should

be

avoided, and

o

where siltation of cells at the sides of the main cell is very likely then adoption of multiple ceils culverts should also be avoided.

2.3.2.2 Depth of Cover for Traffic Loading The minimum cover over the crown of culverts to the road pavement formation level is normally dictated by traffic load and structural capacity of the culvert. 2-9

i T

-1,

a)

Reinforced Concrete pipe

The minimum cover is 0.4m. If the cover is ress than 0.4m, the pipes should be concrete encased. pipes of higher strength can arso be used but it would cost more. Reinforced concrete pipe below road pavement sharl have adequate structural strength to carry traffic load. b)

Precast Reinforced Concrete Box

Precast reinforced concrete box culverts are designed to withstand direct traffic loading. The minimum cover however is 0.1m. R.einforced Concrete Cast-in-Situ Box

It can be designed structurally to withstand direct traffic loadins.

2.3.2.3 Settlement of Culverts when culverts are liable to settle due to a high fi1l, or poor ground condition pipes should be selected which can withstand the anticipated unequal settlement. Reinforced concrete pipe can withstand anticipated unequal settlement provided rubber ring spigot and socketjoints are used.

2.3.2.4 Culvert Joints In cast-in-situ box culverts movement joints should be provided at appropriate

longitudinal intervals. The movement joints should be watertisht and detaiied to prevent wash in of backfill material.

For precast box culverts all joints should be wrapped round with non-woven geotextile to prevent wash-in of backfill material. 2.4

FACTORS TO BE CONSIDERED IN HYDRAULIC DESIGN OF CULVERT

2.4.1

Hydrological Analysis Please refer to Volume 1 Hydrological Analysis -

I

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i

I

2-rc

2.4.2

Size of Culverts

2.4.2.1

Design Procedures

The hydraulic calculations of culverts shall be in accordance to the design procedures and worked examples as described in Chapter 27 CULYERT of "IJrban Stormwater Management Manual for Malaysia".

2.4.2.2 Minimum

Size

For the purpose of maintenance, the minimum size of a culvert is related to the length of the culvert even if the flow to be conveyed is much lesser than the discharge capacity of the culvert. The recommended rninimum sizes of culverts are as shown in Table 2.1.

Where there is a high possibility of accumulation of debris in the culvert, some reserve in cross sectional area is necessary i.e. the pipe size should be larger than

the required hydraulically adequate size.

If

an embankment with a culvert is

located on soft ground, some reserve area may aiso be necessary to compensate for a possible loss in cross sectional area due to long term settlement. Table 2.1: Recommended Minimum Size of Culvert

Length of Culvert (m)

Minimum Diameter or lleight of Culvert (m)

19

1.5

At private access road

crossing

of roadside drainage, to reduce

depth of

downstream roadside drainage channel, the culvert size for the access road may not have to be in accordance to those in Table 2.I,blt it should be hydraulically adequate to convey the roadside drainage

runoff and compatible with the roadside

channel and shall not be less than 0.6m diameter.

L-I] ^

11

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4Aa

/.-+._)

Freeboard

Freeboard is the vertical distance from the water surface to the road formation level. For culverts, the design water surface leve1 should not be above the road formation level.

For high embankments, when the water level at the inlet exceeds 1.0m above the crown of culvert, the designer must check the stability of the whole embankment against the fluctuations of pore water pressure.

2.4.4

Length of Culvert The required length of a culvert depends on: a)

width of the carriageway,

b)

height of

fill

over the culvert,

slope of embankment, d)

slope and skew of the culvert, and

e)

type of end finish such as

headwall,

bevelled end, drop inlet,

transition/tapers or spillway.

I I

The length of culvert needed can be obtained by sketching out the cross section of the road embankment along the alignment of the culvert. 2.4.5

Skew of Culvert

a)

-l

'

I

divert the channel in an abrupt manner to achieve a right angle crossing, especially, if it is a very rapid flowing stream.

I b)

;tr

When the road alignment crosses an existing channel at an oblique angle, as far as possible, the channel should be diverted so that the culverr intersects the road at nearly right angles. It is uneconomical to build longer culverts due to its skewness. However, it is not desirable either to

The headwall of skew culverts should be aligned parallel to the roadway centreline. For traffic safety, the headwall should be located a minimum of 4m, away from the edge of the traffic lane.

1 1a -- \L

2.4.6

Gradient of Culverts

The gradient of a culvert is dictated by the minimum and maximum allowable flow velocities in the culvert. The minimum gradient is the flattest allowable to minimise deposition and accumulation of silts in the culvert, and the maximum gradient is the steepest allowable to control flow velocities to a level not exceeding the scouring resistance of the culvert material:

gradient = Maximum gradient = Minimum

Generally gradients

1:600 1:100

of 1:200 to 1:300 are used for ease of laying and minirnurn

velocity requirements.

2.4.1

Scour and Seepage Countermeasures

The inlet and outlet ends of the culvert should be protected against scour, particularly at the outlet end where design flow velocities have been raised above previous natural stream velocities. Countermeasures would include rip-rap placed beyond the outlet end

provision

of

or

the

energy dissipating devices such as baffle-apron, drop spillway,

cascading drop, etc. Seepage in the direction of culvert

flow, in the soil mass around the culvert, could lead to wash-out of fine material, leading to undermining of the cuivert bedding and side support and eventual failure of the structure. This problem could be minimised by the provision of an impervious bedding and embankment at the inlet end and concrete anti-seepage collar. Seepage and wash-in

of fine material through the joints of precast culvert units couid be reduced by wrapping the joints with suitable geotextile drainage fabric. Suitable water-stop should also be provided box culverts.

z^

in movement joints of cast-in-situ

1a I) L

some erosion and seepage countermeasures are illustrated in Fisure 2.4.

When the drop in level from the culvert outlet to the receiving natural stream invert is more than 1 m then considerations should be given to the provision

of

energy dissipators as described

in

Chapter 29

-

Special Structures

of

.,Urban

Stormwater Manage Manual for Malaysia',. 2.4.8

Flow Velocities The flow velocities at the inlet, barrel and outlet of the culvert, are generally not the same. The inlet approach velocity, vi, is normally low and would not cause scouring problem of the embankment material at the inlet. The culvert barrel velocity, Vc, should not exceed the scouring velocity of the culvert mateial, and to minimise silting it should not be less than the self-cleansing velocitv.

The allowable outlet velocity can vary to prevent scouring the soil type of the downstream receiving channel. For a rough guide of permissible velocities

of

different conduit materials, Table 2.2 canbe used. If the outlet velocity is greater than the permissible velocity, consideration should be siven to: a)

reducing the slope of the culvert,

b)

increasing the size of culvert, and

c)

protecting the receiving channel

by lining or providing an

energy

dissipator at the culvert outlet.

In all

cases' however, a concrete apron shall be provided at the

end to prevent scouring.

a 1A zr+

inlet and outlet

UC

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Qoa E6>

9:9 -

Use TW,if Use

TW

size

the US Federal Highway A

!7,

commercial

wh

XP-Culvert200O, distributed by Xp Software, Canberra, Australia.

Further information on computer modelling is given

outlet velocity is high, scour protection or an energy

dissipater (see Section 27.8.5) may be required.

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in

ig

_te

27.6.!

unacceptable problems of maintenance.

,-

Chapter 17.

The headwalls and wingwalls must fit the site. The allowable headwater should not be exceeded.

potential for major damage and (ii) with smaller floods than the design flood to ensure that there will be no

wit

Australia.

2V.6

The allowable overtopping flood frequency should not

ni

_ps

Waterflow, Hydraulic Design of Culvefts, Distributed by Roads and Traffic Authority, lVagga Wagga, NSW

The final length of the culvert should be close to the approximate length assumed in design.

alg

DEERIS CONTROL

la :li,

General

iuh

All too often floods have clearly demonstrated how the performance of culverts can be affected by an accumulation of debris at inlets. This accumulation can

rha

t7

cause failure of the drainage structure, possibly resulting in overtopping of the roadway by floodwaters, with ensuing

ltr )et

damage to the embankment or to the properties upstream and downstream of the culvert.

ma

-D( ,dt

Experience has shown that in non-urban areas, the following stream characteristics tend to produce the most

ttel

jnv

serious debris problems:

o

xil

of stream to flash flood, i.e. relatively impervious watersheds with moderate or steep

Susc€ptibility

--na rat

gradients.

11. Improved Designs

n

Under certain conditions more economic designs may be achieved by consideration of the following:

The use of an improved inlet for culverts operating

Actively eroding banks bordered by trees

large

-)7

.

Relatively straight unobstructed stream channels with no sharo bends.

L7

.

Allowing ponding to occur upstream to reduce the peak discharge, if a large upstream headwater pool

In urban

exists.

12. Documentation

file

background information. See 'Design Documentation' in Section 27.2.10.

or

shrubs

under inlet control (see Section 27.9).

Prepare report and

,th

cell

"

The culvert must have adequate cover.

The performance of the culvert should also be considered, (i) with floods larger than the design flood to ensure such rarer floods do not pose unacceptable risks to life or

.

culverts using

ne - _hc

development, HEC-MS, is also available.

'

Results

be exceeded.

.

of

Cleared land upstream with fallen trees on the ground"

areas there is additional potential for debris to enter waterways and cause blockage. The risk of debris blockage is very high in all urban areas in Malaysia. Precautions to be taken range from providing freeboard, and taking design precautions to providing elaborate debns control structures.

-

fn, :ul ln(

"dj to lis Cul

nc

a

z/-r1

r

be

specifically for the hydraulic design of culverts, including:

Compare alternative design with the site constraints and assumptions. If any of the following conditions are not met, repeat steps 4 to 9:

If

design

ell

Several computer programs have been developed

outlet velocity using Equation 27.13.

. . .

HEC-2 Water Surface profiles, (Hydrologic Engineering Centre, US Army Corps of Engineers) is a widely_usej general purpose program with advanced culvert design features which is available in the public domain. ftre revised version, September 1991, includes the hydraulic

hc< TW< D

Calculate flow area using appropriate flow depth and then

. .

\'7,

ESMPI.|TER MODFLLIEVG

Administration culvert design methods.

D,if D< TW

10. Review

27.5

Urban Stormwater Hanagement l,lanuat

Culverts

27.6.2 Freeboard Ail culverts with a waterway area

of 1.0 m2 or more should be designed with a minimum of 300 mm freeboard above the design water level. For large culverts the designer should consider increasing this freeboard to allow for the size of debris anticipated, up to a maximum of 1000 mm.

27,6.3 Design precautions Where

debris accumulation is considered to be problem, a other design precautions should be taken, such as providing a smooth well designed inlet, avoiding multiple cells and increasing the size of culvert. if multiple cells are unavoidable, provision of a sloping cutwarer on the upstream pier (wall) ends may help to align floating debris

with the culvert entrance.

To prevent erosion of the fill and adjacent channel; To prevent undermining of culvert ends; To inhibit the seepage and piping through the bedding and backfill;

To ineet traffic safety 27.2.8);

. . .

requirements (see Section

To improve the appearance of large culverts; To resist hydraulic uplift forces on corrugated metal pipe culverts; and/or

To strengthen the ends of large flexible especially those with mitred or skewed ends.

culverts,

Cut-offs in the form of a vertical wall, constructed below the end apron of a culvert, should always be provided at culvert inlets to prevent undermining and piping. For

corrugated metar pipe curverts, the cut-off wails arso act to counteract uplift at the culvert inlet.

2V.6,4 Relief Culvert

A relief culvert passing through the embankment at

a

higher level than the main culvert permits water to by_pass the latter, if it becomes blocked. The relief culvert could also be placed at a low level some distance away from the main culvert where it is not likely to be blockeo. tu this relief culvert is an additional requirement, the cost of both culverts should be compared with that of

a larger culvert

that will be less subject to blockage.

27.6.5 Debris Control Structures These can

27.7"2 Typieal End Treatnnenf-s and wingwalls _ are the most common encl treatment in overseas countries. An apron is generally incorporated between the wingwals to rimit scour of the stream becl. They are usually constructed from reinforced concrete, but can be formed from masonry, or rock filled gabions and mattresses, or concrete filled mattresses.

Mitred ends - these are generally limited to corrugated metal pipe culverts, where the end of the pipe is cut parallel to the slope of the embankment. The area of

be cosfly both to construct and maintain. of the various types of debris control structures 6" found in Hydraulic Engineering Circular No 9, .TaV nDebris Control Structures,, (US federat Highway Administration, L97L). The choice of structure type depends upon size, quantity and type of debris, the cost involved and the maintenance proposed. However, for existing culverts, which are prone to debris clogging, it may be worthwhile to construct a debris control structure

inefficient, do not meet safety requirements and are visually objectionable. For these reasons their use in

27.7

27.8

Details

rather than replace or enlarge the culvert.

CULVERT END TREATMENT

27,7.1 Introduction The term "end treatment,, encompasses the shape of the culvert ends, end structures such as wingwalls, cut_offs

and anchorages and erosion control measures

for

the

embankment around the ends paved with concrete or rock.

of the culverts is

usually

Projecting ends - where the ends of the culvert project from the face of the embankment. Although they are the

least costly end treatment, they

.r"

hydraulically

Malaysia is not recommended.

FLOW VELOCITY

Culverts usually increase the flow velocity over that in the natural water course. Except when the culverts flow full, the highest velocity occurs near the ouflet and this is the point where most erosion damage is likely to occurs.

adjoining fill and channel (see Standard Drawini;s SD F_21 to SD F-24). The design of hydraulically improved inleb is disdssed separately in Section 27.9.

A check on outlet velocity, therefore, must be carried out as part of the culvert design if the outlet discharqes to an

Culvert end treatment may be required more of the following functions:

27.8.1 Inlet Control

r r

to perform one or

To increase the hydraulic efficiency of the culvert;

To prevent fill from

encroaching

opening;

Urban Stormwater lvlanagement l,lanual l

" . " .

on the

culvert

unlined watenaray.

For a pipe culvert flowing with inlet control the outlet velocity can be determined from Figure 25.81 to 25.84 in Chapter 25, Appendix 25.B (k = 0.6) in combination with charts for part full flow in Chapter 12.

b

-

25.84 were derived from *te Cdebr@k Figures 25.81 White equation (in Chapter 12) for k = 0.06 to 0.6. This approach assumes that the depth of flow at the outlet equals the depth corresponding to uniform flow, but the sholc length of the average culveft mostly precludes this, making this approach conservative

bar across the stream, while finer material will be carried further downstream. Depending on the supply bf

lal

sediment the scour hole may gradually refill until after the next major fiood occurs.

1n :nl

Table

27.1

The depth of flow should be checked against critical depth

-rlo Ma;imum Recommended Flow Velocities (m/s) for various conduit materials

,

as determined from Design Charts 27.8 or 27.9. If the flow is supercritical the effed of a hydraulic jump must be

str tlJt

:le

jur

considered.

Material

27.4.2 Outlet Control

Precast concrete pipes

8.0

Precast box culverts

8.0

In situ concrete and hard

o.u

For outlet control the average outlet velociV will be the discharge divided by the cross-sectional area of flow at the outlet. This flow area can be either that corresponding to criticai depth, tailwater depth (if below the crown of the cuivert) or the full cross section of the culveft barrel.

Maximum V (m/s)

Jis

-1? ,l

-,F

packed rock (300mm min) Beaching or boulders (250mm min)

5.0 dv

Stones (150

27.8.3 Eroslon of Conduit Flow

of the water subjects the conduit

-

100mm)

3.0

Grass covered surfaces

material to

-

2.5

1.8

abrasion, and too fast a velocity for a given wall material will cause erosion to the conduit. Very fast flows can cause cavitation unless the conduit surface is very smooth,

SUff, sandy clay Coarse gravel

- 1.5 1.3 - 1.8

and this results in erosion taking place at a rapid rate. However, cavitation damage does not occur in full flowing pipes with velocity less than about 7.5 - 8 m/s and about

Coarse sand

0.5

t2 mls in open

conduits.

The maximum velocity b,eyond which erosion will take place depends on factors like smoothness of conduit, quantity and nature of debris discharged and frequen{ of peak velocity. Commonly adopted maximum values based on experience are listed in Table 27.1.

27.8.4 Sceur at Inlets A culvert normally constricts the natural channel, forcing the flow through a reducing opening. As the flow contracts, vortices and areas of high velocity flow impinge against the upstream slopes of the embankment adjacent to the culveft. Scour can also occur upstream of the culveft, as a result of the acceleration of the flow, as it leaves the natural channel and enters the culvert.

27.a.5 Scour at Outlets If the flow emerging from a cuivert has a sufficiently high velocity and the channel is erodible, the jet will scour a hole in the bed immediately downstream and back eddies will erode the stream banks to form a circular elongated scour hole. Coarse material scoured from the hole will be deposited immediately downstream, often forming a low

zl

- L.+

0.2 -

0.7

Cr

u( !L

0.5

Ltl

CU

The provision of wing walls, headwall, cut-off wall and apron is generally all the protection that is required at culvert outlets. The judgement of design engineers, working in a particular area is required to determine the need for any further protection. Investigation of scour and outlet protection at similar culverts in the vicinity of the culvert being designed may provide guidance on whether further protection is required. Periodic site visits and inspection after major flood events will also confirm whether the protection is adequate or further protection is required.

In

urban areas,

the risk of outlet scour is

generally unacceptable and therefore a choice must be made as to which type of scour protection is suitable for the site. The

options available include the following:

.

Upstream wing walls, apronsr cut-off walls and embankment paving assist protecting the embankment and stream bed at the upstream end of a culvert.

1.3

Fine sand

lc

. .

Local protection of the stream bed material, in the

n

-dr

case of unlined drains and waterways.

IA

Flow expansion structure.

c)

An energy dissipating structure

Stream bed protection can be achieved with a concrete apron, rock riprap, or rock mattresses, or concrete filled matFesses. It is important that mattresses are anchored to the cut-off wall or apron at the culvert outlet, to stop them moving downstream. A geotextile filter is usually provided under the mattresses and may also be required

llrban Stormwa ter Managemen t Manual

ta

-o p

ir n

under the rock

riprap.

detail in Chapter- 29"

Seour protection is discussed in

An important parameter in the selection of an appropriate energy dissipater is the Froude Number, f, of the outlet flow. Where an outlet has !.7, a simple apron sb'ucture, riprap, or a flow expansion structure will suffice. Where 1.7 < n< 3 a riprap basin or hcrizontal roughness elements basin is appropriate. Where E > S a hydraulic jump basin wlll be reguired. Energy dissipaters are discussed in detaii ln Chapter 29.

4<

27.8"6 Siltation If the flow velocity becomes too low siltation occurs. Flow velocity below about 0.5 m/s will cause settlement of fine to medium sand particles.

To be seif-cleansing cuive*s must be graded to the average grade of the water course upstream and downstream of the culvert, and levels must represent the average stream levels before the culvert was built.

in both plan and profile is of particular importance to the maintenance of se,jiment_free culveit

Culvert locaUon

cells. Deposition can occur in culverts when the sediment trcnsport capacity of flow within the culvert is less than in the stream. The following factors may cause deposition in culverts:

. .

o

Culverts often provide a wider flow width at low flows than natural streams. This results in the flow depth and sediment transport capacity being reduced.

Point bars (deposition) form on the inside of stream bends and culvert inlet placed at bends in the stream will be subjected to deposition in the same manner. This effect is most pronounced in multiple-cell culver8 with the cell on the inside of the curve often becoming almost totally plugged with sediment deposits. Abrupt changes to a flatter grade in the culvert or in

the channel upstrearn of the culvert will

induce

deposition. Gravel and sand deposits are common downstream from the break in grade because of the reduced transport capacity in the flatter section.

Deposition usualiy occurs at flow rates smaller than the design flow rate. The deposits may be removed during

larger floods, depending upon the relative transport capacity of flow in the stream and in the culvert, compaction and composition of the deposits, flow duration, ponding depth above the culvert and other factors.

Siltation can also occur upstream of culverts if they are instailed at incorrect levels, creating pcnding areas. Such grading should generally be avsidecj.

Urban Stormwater Management Manua!

,---3,

?7"9

TMPR,SVSF gruL€T'EL'LVER.TS

27.9.t

General

The capacity of a culvert operating under inlet control can be significanUy increased by providing a more efficient inlet, which reduces the flow concentration at the entrance and increases the flow depth in the cell. In outlet control,

the entrance losses form oniy a minor part of the total head losses and major inlet improvement are not justified.

various vpes of inret improvements are discussed in this Section. A nurnber of these are aimed merely at improving the inlet efficiency by reducing the entrance loss, r(* These focus on headwalls, wingwails and the end of the culvert cell. Other major types of improvement, include the provision of a fall (or steep slope) In the bed of the

inlet or tapers in the end

section

of the cell, or

combination of these improvernents. The aim of these rnajor improvements is to increase the velocity head or the effective headwater depth. The material in this Section is based on ..Hydraulic Design

of improved inlets for Culvertsi

ttydrauiic Engineering

Circular i,io. 13, (i.iS FerJerai Highway Administration,ISTZ) and the "Hydraulic Design of Culverts,, (Ontario Ministry of

Transportation and Communications, 19g5, which includes metric design nomographs). These references may need to be consulted for further inforrnaticn when undertakino the design of improved inlet culverts.

27.9.2 Bevelled Inlets Adding bevels to a conventional culvert design with a square-edge at the periphery of the inlet opening increases culvefts capacity by 5 to 20 percent. The greatest benefit occllrs with high headwaters. Bevelled inlets increase the hydraulic efficiency of the culvert (4 = 0.2). Details of typical bevels are shown on

Figure27.t2. They should be considered for all box culvert installations, which operate under inlet controi. Bevelled inlets can be provided on both pre-cast and cast in-situ culverts.

The 1.5:1 bevel (33.7 degrees) is more efftcient than the 1:1 bevel (45 degrees), but the latter is easier to construct and more practical. Bevels should be provided on the top and side edges of the opening.

27.9.3 Frovision of Depre*sed Inlet Provision sf a fall or steep slope upstream from the culvert inlet may innprove the capacity of a culvert operating under inlet control by increasing the veiocity head. The fall may be achieved by flattening the cell slope. This may tend to induce sedimentation during low flows, but the deposit will in most c:ses be washed out during floods.

27-15

Culverts

r t

2V.9.4 Tapered Inlets

PI.AN

A tapered inlet is a culvert inlet with a side-taper or a slope taper within the end section of the culvert cell. This result

Side BevelAngle

in an enlarged face section and a hydraulically efficient throat section. A tapered inlet may have a fall, incorporated into the inlet structure. The fall is used to provide more head on the throat section for a given

)?r

l,v

sectir

f'arle

tlp gr?€l

headwater elevation.

b = 0.(X2 B for 45o (1:1) b = 0.083 B for 33.7o (1.5:1)

A

tapered inlet can sometimes greatly improve the of a culvert operating under inlet control. This may permit the use of a cell size considerably smaller than would be required for a conventional culvert. The greatest savings are achieved with long culverts, but the possibility of increasing the capacity of an existing performance

Side BorelAngle

undersized culvefc by adding an improved inlet should not be overlooked, since it may eliminate the need for a costly replacement structure.

(a) Side Berels LOT{GITUDINAL SECTION

A disadvantage of a tapered inlet culvert is the high outlet

velocity, which

in

some cases may necessitate

an

expensive outlet structure or downstream channel erosion Side BevelAngle

control

works.

Cost comparisons between

various

irnproved inlet designs and conventional designs should be made to select that with the least overall cost.

Side Tapered Inlet

-

Side tapered inlets are illustrated in

Figure27,L4. In some cases, they may increase flow capacity by 25 to 40 percent over that of conventional

d = 0.(X2 D for 45' (1:1) d = 0.083 D for 33.7o (1.5:1)

culverts with a square edge-inlet. The side tapered inlet has an enlarged face area with a tapered transition to the constant culvert cell section. The inlet face has the same height as the cell and its top and bottom are extensions of the top and bottom of the cell. The intersection of the sidewall tapers and the cell is defined as the throat section.

Side-tapers may range

(b) Top Eorel

from 6:1

to 4:1 taper being

recommended as it results in a shorter inlet. NOTE:

1. Dimensions of Bevels Shall Not be

Les than

Shorrn.

2. Dimensions b and d are Basd on the Squarc Dimensions of the Opening. To Obtain BsrelTerminaUon in One Plan on a 3.

Rectangular Box, either Increase d b Equal b, or Deoease the Top Bevel Angle. 4. For Multiple Cells Calanlate b from Total CIear Width or 3D, whidtener is Smaller. Figure

27.12

Bevelled Inlet for Box Culvert

The fall may be constructed within the limits of the flared wingwalls, as illustrated in Figure 27.13. The drop may also form an integral part of a slope-tapered inlet. The fall slope should be paved to prevent upstream bed degradation and an upstream cut-off wall provided.

For

a

side-tapered inlet, there are

sections

two

possible control

the face and the throat. H; shown

on

Figure27.14, is the headwater depth measured from the

face section invert and

l{ is the headwater depth

measured from the throat section invert. The weir crest is a third possible control section when a fall is used.

Slope Tapered Inlet- The slope tapered inlet, like the sidetapered inlet, has an enlarged face section with tapered side walls at the throat section (Figure 27.LS). In addition, a steep fall is incorporated into inlet between the face and throat section. This fall concentrates more head on the throat section. At the location where the steeper slope of the inlet intersects the flatter slope of the cell, a third section, designated the bend section, is formed.

The

inlet is the most complex inlet This type of inlet can in some instances

slope-tapered

improvement.

provide a capacity more than 100o/o greater than that of a conventional culvert with square edges. The increase in

27-76

Urban Stomwater Management Manual

Itt

Culverts

capacity depends largely upon the amount of fall available between the invert at the face and invert at the throat

Slope-tapered inlets can be applied

section. Construction difficulties are inherent, but the benefits in increased performance can be great. With

square or round transition is normally used to connect the rectangular slope-tapered inlet to the circular pipe.

to both box culverts and circular pipe culverts. For the latter application, a

proper design, a slope tapered inlet passes more flow at a given headwater elevation than any other configuration.

Pl-Aftl

NOTE: Weir Slope to be Paved to hevent Upstream Degradation

where Necessary.

ELEVATION

Suggested Slope for Fall 2:1 to 3:1

s----->.

Figure

Urban Stormwater Management Manual

27.13

Fallfor ConventionalCulvert with Flared Wingwalls

CulverE

? PI.AN

a a

t{

WeirCrd

1s'to s07

a

--n

{-

st s{

Flare Angle

15"

b So

(,4) With Fall

(B) Wirhour Fatl (Wingwalls Not Shown)

n ST

fr ELEVATION

ELEVATION

t{-Face

$ -'-el

lV.--Faesection

section

a\ I

Throat Section

Throat Section

Weir C,rest

q Figure

27.14

c

Side-Tapered Improved Inlet

PI.AN

27.TO MINIMUM EI{ER.GY C!.'LVERTS In the coastal plains the natural slope of the land is often little more than a fraction one per thousand, which in concrete conduits laid on natural grade, grass covered channels and natural water courses resulb in b-anouil flow (see Chapter 12).

To reduce the coSs of bridging these waterways the concept of the 'The Minimum Energy Culverf'was developed.

Taper (4:1 To 5:1)

ET.S/ATION

\he Minimum Energy Culvert" concept is to concentrate the flow in a narrow, deep cross section flowing with critical velocity under maximum design flow thus taking advantage of the minimum specific energy

The aim of

Face Secdon

Bend S€ction

under critical flow condition (see Chapter 12). This maximises the flow per unit length of waterway crossing. By keeping the flow outside the supercritical region the designer avoids the energy loss in a hydraulic jump and the cost of having to protect against the erosion associated

Throat Section

with the jump. Figure

27-18

27.75

Slope-Tapered Improved Inlets for Box Culverts

Urban Stormwater Management Manual

Culverb The design requires knowledge of:

. . , .

PLAro

Design disdrarge Average nafural slope of ternin Flood levels

Survey details of floodplain adjacent to culvert

On the basis

of this information a plan and

section of the culvefi is drawn up. (Figure so the

following assumptions are made

0

longitudinal

27.16). in doing

:

The energy line panllels the natural fall of the terrain

EIEI/ATTON

(iD Energy losses at enty and exit of cufuert are disregarded

T[re justification

for the ratter assumpton is that srmth fansitions are generally small.

rosses at

In his ontext it is warth nc$ng that $e exit expansion of Se sfeam bed needs to progress at a smaller angle than the enby angle if the formation of Snding eddies

is to

avrided. Using

be

Figure

27.16 Characteristic Flow Line of Minimum Energy Culvert

the equations:

witi minimum-energy culvefts is that they are located in a dip below the drain or waterway inveft, creating a

One problem

Hr, = 1.5d, and

pdential site for ponding and sediment deposition. The

Q=Mrr[4 coneponding values

(27"14)

of

b,

d, and H,

ornpared.

en

be bied

and

potential for ponding can sometimes be minimised by a small diameter pipe drain or a channel connecting the culvert to a suitable point downstream. However this

approach is not feasible if there are high sediment loads.

't

n tol

Urban Stormwater Management f"lanual

zl'!>

Cu/verb

A''ENDIX 27.A

DESIGT{ FORM, CHARTS Ar{D

NOMOGRA**'

Design Form for Culvert Calculation Entrance Loss Coefficients

Inlet Control Nomograph

-

Concrete pipe Culvert

Inlet Control Nomograph -Box Culvert Inlet Control Nornograph

-

Comrgated Metal pipe (CMp) Culvert

Relative Dixharge, Velocity and Hydraulic Radius in part_full pipe Flow Relative Discharge, Velocity and Hydraulic Radius in part_full Box

Culvert Flow

Critical Depth in a Circular pipe Critical Depth in a Rectangular (Box) Section

outlet control Nomograph

-

concrete pipe curvert Frowing Fuil with

ouuet control Nomograph n = 0.012

-

concrete Box curvert Frowing Fuil with

Outlet Conhol Nomograph

-

Corrugated Metat pipe (CMp) Ftowing

n = 0.012

Fullwith n = 0.024

Urfun Stormwater Management Manual

27-27

CulverE

I

s

)tl

= = o U

T_

t!

N

--+l f.-

;

v) F z.

F F F

V1

1l

I

;uJ

I

tri

z l! (' F z. TIJ

t

h 8

I

__l I

tl ll

ArIf,O-r3A

-|jnrno

UJ

lltl

p = tr v tJ)

tl tl iltl

(Jf!

I

Ill

Er XLJ

i I

\

j

I

Lr.l

I

-t,

I

JY

\-

=E E-

ll I

;r< =lu

t;

I

/uH 9NntourNof,

r^s

t,h

!

z.

!ry

=E

P +

{

fi{

I

;!

as

\

sa

z.

\1

\t

\

F lo-

= o U

E pr

k

tl

F

s\-

N

J

al 1l\

F z.

s']

o d.

I F l! J

{.s

F

o = o tu

z.

o F

'l-

F

= o TL

z. J IJ.J

z. z.

illl

ss

Eh

Eg oi5

E't E8 lt

(J

z.

\'

ge

\\-

F z (J

b

il"

-) z,

ll

ss

J

s

I

9

(t,

z F

l.lJ

N

VI

z.

trl

o

E

a

T

z U

Iu

&

2.6

;L) ut

lt

il

cts

r-9 * dFF tu a>= I :f L) oaE

z

o) (q

= = (t

og,

Design Chart

z7-22

27.1

Design Form for Culvert Calculations

lJrban Stormwater Management lvlanual

Ut1

Culvefts

coefficient K" to apply velocity head v,2/2g for determination of head loss at entrance to a culvert operating under outlet Hu: K" V2,/2g

control. Entrance head loss

TYPE OF BARREL AND INLET

Pipe, Concrete

Ke

Projecting from fill, socket end

0.2

Projecting from fill, square cut end

0.5

Headwallor headwall and wingwalls Socket end of pipe

0.2

Square-edge Rounded (radius

0.5

= t/LZ

D)

0.2

Mitred to conform to fill slope

0.7

End-section conforming to fill slope (standard precast) Bevelfed edges, 33.7o or 45. bevels

0.5 0.2

Side-tapered or slope-tapered inlets

0.2

Pipe, or Pipe-Arch, Corrugated Steel Projecting from fitl

0.9

Headwall or headwall and wingwalls, square edge MiUed

0.5

to conform to fill slope

0.7

End-section conforming to fill slope (standard prefab) Beveffed edges,

u.5

33.7" or 45" bevels

0.2s

Side'tapered or slope-tapered inlets

0.2

Box, Reinforced Concrete Headwall

Square'edged on 3

edges

0.5

Rounded on 3 edges to radius of Or bevelled edges on 3

I/12 barreldimension,

sides

O.2

Wingwalls at 30" to 75" to barrel

Square.edged at

crown

0.4

Crown edge rounded to radius

Or bevelled top

of Ut2 baneldimension

edge

O.z

Wingwalls at 10. to 25" to banel

Square'edged at

crown

0.5

Wingwalls parallel (extension of sides)

crown or slope-tapered intet

Square'edged at Side-tapered

0.7 0.2

Projecting

Square.edged Bevelled edges, 33.7" or

45.

0.7*

bevels

O.jo

* Esiimated

Design

Urbn Sbrmwater Management Manual

Chart27.2

Entrance Loss Coefficients

27-23

Culverb

D (m)

$r*tl.l

4.50

300

4.00

200

3.50 3.00

2.50

HW D

(1) F:omple

D=0.80m Q=1.7m3ls 100 80 60 50 40 30

Inlet (1) (2) (3)

Ut'

HW(m)

2.60 2.18 2.20

2.08

(3)

F6 r

6

rs r

5

l4

4

F t-

D

F-3

r.74

t.76

5

4 3

3

-&'

20

,*o9

2.00

-/

10

8 1.50

5

N

(2)

^Ey' 9*'j'\]./

5

3

sl,F" t.oooa$)/ 1

Inlet Type

0.90'

0.8

(1) Headwallwith

0.80

0.6 0.5 0.4

(2) Headwallwith

0.70 0.60

0.3

1.0

1.0

0.9

0.9

0.8

0.8

0.5

0.5

Square Edge Sod 0.45m

Diagram in Figure 27.7(a) depicts flow condition, i.e. pipe is flowing full with a submerged outlet. Now enter Design

with:

Chart 27.10

Step 2 :Assume Inlet Control

D= 450mm

Using the previous estimate of required area, try 600mm x 300mm box culvert.

I = 120m ke

Then use

H Fall

= 0.2 (socket end of pipe upstream)

? = 0.5

m37s

of culvert invert, 1., = f

Note

Enter Design Chart27.4 with

to draw line and obtarn

UNB = 0.5/0.6 = 0.83

= 3.4m

HW= TW+

OO.O

-

H- Lr= 1.5 + 3.4 -

99.0 = 1.00 hence:

culvert is under ouflet control. 2.0m.

the design is unacceptable because HWr., =

Return to step 2 using 525mm pipe diameter in Chart 27.3 and obtain HW/D

=

e=

0.5 m3/s

m37s7m

Draw fine and obtain HW/D = 4.3 Hl,1/= 4.3 x 0.30 = 1.29m < 2.0m

1,0 = 3.9m

that because 3.9m > HWfor inlet control (1.26m), the

However

pipe culvert calculate a suitable box culvert size ancl check for the effects of the outlet velocity.

L.6Z

Design

Step 3 : Check for Outlet Control TW = 1.50m (see example 3) > 0.30m hence diagram in Figure27.7(a) depicts flow condition, i.e. culvert is flowing

fullwith a submerged outlet.

A=0.6x0.3=0.18m2

HW= 1.62 x 0.525 = 0.g5m for inlet control

Urban Stormwater Management Manual

27-37

Cu/verts

Calculate H from Design Chart 27.11, noting that B/D =2.0 so the chart is applicable.

27.8.5 Mlninrum

Energy Culveft

a required design flow of 25 m3/s and referring to Figure 27.16 with chosen widths b as set out in the following table, calculate suitable levels for the bottom profile of the flared culvert entry at the given sections to achieve critical flow through the culveft. Choose an Given

H= lAm then HW= TW+

H- l,

=1.5 + 1.4

-

1.0

=

1.9m

Note that 1.9m > 1.29m, the headwater depth control, so outlet control appties.

for inlet

However the design is not acceptable because of the risk of clogging of the 300mm deep culvert due to debris.

appropriate box culveft size for the culvert.

The widths b are chosen with regard to the survey data, and then q and d, can be calculated for each section as shown in the table below.

Try 500mm x 375mm box culvert. A = 0.225m2 Repeating the above steps gives:

HLI/D = 2.7 and HW =

t.1lm for inlet control,

H= 0.95m and HW=

1.45m for outlet control.

This is acceptable because 1.45

< HW

^",

and

As

1-1

2-2

3-3

width b

t4

9

4

1.79

2.78

6.25

dr=1'[m

u.ov

0.92

1.59

trial depth D

1.10

1.30

1.58

1A?

2.t4

3.96

v2/29

0.13

0.23

0.80

Hr= D+ v2/2g

t.23

1.53

2.38

q=

Q/b

= 2.0

And the culvert flows with outlet control since: 1.45m > 0.9m

Section

= HW(inlet control)

the culvert flows full,

,,rt/A- Q'5 v=tJ/A=m=2.2m/s Step 4 : Summary

v=

Qr/A

x 375 concrete box culveft with square

The depth of flow is required to be critical in the culvert and unchanged subcritical at the start of the flared entry.

edges.

Intermediate depths are interpolated.

The culvert will flow with outlet control with a HW height of 1.45m giving a HW R.L. of 101.45 and an outlet velocity of

For chosen values of d, H, can be calculated and the bottom level of the culvert and approach is located 4

Use a single 600

2.2mls.

metre below the energy line in each section. From the table it will be noted that a box culvert flow area of 4m.x 1.58m is required hence a 4.0m wide x 1.8m high

of 7.2m2 will be suitable. This culvert must then be checked for the risk of debris blockage and sediment deposition in the depressed section.

culvert with a flow area

27-38

lJrban,stormwater Management Manual

ACKNOWLEDGEMENTS TECHNICAL COMMITTEE

6

- DRAINA.GE

Main Committee Member.s Nafisah Hj. Abdul Aziz

Chairman

Ahmad Fuad Emby

Deputy Chairman

Wan Suraya Mustaffa

Secretary

Normala Hassan

Alternate Secretary

Teh Ming Hu

Committee member

Lim Kim Oum

Committee member

Alias Hashim

Committee member

Low Kom Sing

Committee member

Nor Asiah Othman

Committee member

Johan Les Hare Abdullah

Editor

Lim Kim Oum

Chairman

Normala Hassan

Secretary

Yeap Chin Seong

Committee member

Chin Kok Hee

Cornmittee member

K. Nanthakumar

Committee member

Chia Chong Wing

Committee member

Ng Kim Hooi

Committee member

ACKNOWLEDGEMENTS Volume 2 is a review of the Arahan Teknik (Jalan) 15197 - INTERMEDIATE GUIDE TO DRAINAGE DESIGN OF ROADS, the chapter was authored originally by Mustafa Shamsudin of Public Works Department Malaysia.

Volume 2 now provides guidelines to the practical design of culverts, with a few worked examples provided in Appendix 1, which is reprinted from Jabatan Pengairan dan Saliran publication - Urban Stormwater Management Manual for Malaysia (MASMA 2000). Thanks are due to:

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Jabatan Pengairan dan Saliran for permission to reprint Urban Stormwater Management Manual for Malaysia - Chapter 27 , CuIveft.

REAM Standing Committee on Technology and Road Management for the guidance and encouragement given in the preparation of Volume 2.

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Members of the Technical Committee 6

Hydraulic Design of Cuiverts for completion of Volume 2.

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Drainage and Sub-Committee for their untiring efforts to ensure timely