ream guidelines for road drainage design - volume 2
TRANSCRIPT
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FOREWORD
Road Engineering Association of Malaysia (REAM), through the cooperation andsupport of various road authorities and engineering institutiorri in Muluysia, publishesa series of official documents on STANDARDS, SppctptcATIoNS, GUIDELINES,MANUAL and TECHNICAL NOTES which are related to road engineering. Theaim of such publication is to achieve quality and consistency in road and highwayconstruction, 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 onTechnology and Road Management organized Uy fWOfnEAM in Novemb er 1997,Technical committee 6 - Drainage was formed with the intention to review ArahanTeknik (Jalan) 15/97 - INTERMEDIATE GUIDE To DRAINAGE DESIGN oFROADS' Members of the committee were drawn from various governmentdepartments and agencies, and from the private sector including privltized roadoperators, engineering consultants and drainage products manufacturers andcontactors.
Technical Committee 6 was divided into three sub-committees to review ArahanTeknik (Jalan) 15/97 and subsequently produced ,GUIDELINES FoR ROADDRAINAGE DESIGN' consisting of the foll,owing vorumes:
Volume 1 - Hydrological AnalysisVolume 2 - Hydraulic Design of CulvertsVolume 3 - Hydraulic Considerations in Bridge DesignVolume 4 - Surface DrainaseVolume 5 - Subsoil Drainale
The drafts of all documents were presented at workshops during the Fourth and FifthMalaysian Road Conferences held in 2000 and 2002 reipectively. The comments andsuggestions received from the workshop participantr *"r. reviewed and incorporatedin the finalized documents.
ROAD ENGINEERING ASSOCIATION OF MALAYSIA46-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),
2.1
2.2
TABLE OF CONTENTSPage
INTRODUCTION ....."..2-I
GENERAL CRITER.IA.... ......2.12.2.I Drainage Survey ....;.. ....2-12.2.2 Site Visit ........2-2
2.2.2.1Topographical Features ... .....2-22.2.2.2 Catchment Area Characteristics . . .. . ..2-22.2.2.3 Channel Characteristics .. .".....2-22.2.2.4Highwaterlnformation.... ......2-22.2.2.5 Existing Structures ......-.2-32.2.2.6Soiilnvestigation ......2-3
2.2.3 Culvertlocation ....2-32.2.3.1A1ignment ........2-32.2.3.2 Vertical Profile ....2-52.2.3.3 Structural Consideration... ......2-5
CULVERT TYPE SELECTION .. .,.......2-82.3.I Type Selection .. ."...2-82.3.2 Site Conditions . .....2-8
23.2.f Low Allowab1e Headwater.. ........2-82 .3 .2.2 Depth of Cover for Traffic Loading . . . . . ..2-92.3.2.3 Settlement of Culverts "..2-lO2.3.2.4CulvertJoints ......2-I0
FACTORS TO BE CONSIDERED IN HYDRAULIC DESIGNOF CULVERT . ......2-IO2.4.1 Hydrological Analysis ...2-102.4.2 Size of Culverts ......2-I1
2.4.2.1Design Procedures .........2-I12.4.2.2 Minimum Size . .....2-lI
2.4.3 Freeboard .... ".2-122.4.4 Length of Culvert "...2-122.4.5 Skew of Culvert ......2-122.4.6 GradientofCulverts ...,......2-132.4.1 Scour and Seepage Countermeasures ..2-132.4.8 Flow Velocities . ..."2-I4
LIST OF FIGURES
2.3
Figure 2.1Frgure2.2Figure 2.3Ftgure 2"4
StreamRealignment.... ."..2-4Alignment of Culvert in Embankment Across Ravine. ....2-6Culvert Profile .........2-7Scour and Seepage Protection Measures .....2-I5
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F LIST OF TABLESF-F T^yl"?l Recommended Minimum Size of CutvertF Table 2'2 Maximum Recommended Flow Velocities (m/s) for VariousF Conduit Materials
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-: LIST OF REFERENCES .-p'r
ii^i APPENDIX 1
*j Reprint of Chapter 27 : Curverts, urban stormwater Management Manual for MalaysiaI!:.
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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) sufficient channel cross sections,
b) the streambed profile and existing water levels,
c) the horizontal alignment of the existing sffeam channel,
d) invert levels and crown ievels of any existing culvert, and
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e) highest flood levels.
The site survey should be carried out to the extent sufficient for the properlocation 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 astopographic features, catchment area, channel characteristic, highwaterinformation and existing structures should be noted, as it can be useful in thehydraulic design.
2.2.2.1 Topographical Features
Features such as residential and commercial buildings, croplands, roadways, thelay of the ground and utilities can influence the location of the culvert as itdetermines the direction and velocity of the flow. Therefore their elevation andlocation should be obtained.
2.2.2.2 Catchment Area Characteristics
The designer should take note of features such as lakes, land usage, type anddensity of vegetation and any man-made changes or development such as dams,because these factors could alter run-off.
Future landuse plans of the catchment should be obtained, if available, to studythe effects of future landuse changes on run-off and where necessary these effectsshould 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 rockin the streambed, the bank condition and amount of drift, and debris should alsobe noted as these factors could affect the durability of the culvert material usedand the sizing of the culvert.
2.2.2.4 Highwater Information
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Highwater information which may be obtained from observationmark, local residents or Jps can be used to check results of
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of the high water
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) date of construction,
ii) performance during past floods,
iii) scour indicated near the structures,
iv) highwater elevation with datum and dates of occurrence, and
v) 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 illustration.
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Sharp bends in existing stream and new stream diversion, where channel erosion
is likely, should be avoided in the location of culvert.. Where this is unavoidable
then the sharp bends should be iined to minimise the adverse effects of erosion.
The second consideration of culvert iocation is to exercise reasonable precautions
to prevent the stream from changing its course near the end of the culvert. The
use of sumps paving or gabions will help protect the banks from eroding and
changing the channel course.
In hilly and mountainous areas washout of embankment fill materials in ravines is
a cornmon occurrence dr,rring construction. To help protect the environment and
minimise embankment material washout, leading to consequential siltation of
downstreain reaches, a culvert in a ravine shoulC be aligned. such that the
upstream end catches the stream flow directly. The culvert barrel should be
aligned such that its foundation is laid on original ground as much as possible'
The outlet end requires a cascading concrete channel or suitable energy
dissipating structure or chute to convey the flow safely to natural downstream
water course beyond the toe of the embankment. The culvert and its end
connections could be constructed prior to earth filling operation of the ravine to
reduce erosion of the embankment, see Figure 2.2 for iilustration.
2.2.3.2 Vertical Profile
Most culvert locations approximate the natural streambed. Modified culvert
slopes other than that of the natural stream are sometimes used to improve
hydraulic performance of the culvert, shorten the culvert or reduce structural
requirements, see Figure 2.3.
The inlet and outlet levels of a culvert should be the same as that of the existing
channel and the profile of the existing channel should not be modified wherever
possible. This could be achieved by the provision of drop sumps spillways and
flow transition sections. Any abrupt change in grades between the culvert and the
existing channel should be avoided to prevent sedimentation and scouring.
2.2.3.3 Structural Consideration
The culvert should be structuraliy adequate to carry all the imposed vertical and
lateral loads and soil pressures. Laying of culverts should be in accordance to
design requirements, site conditions and manufacturer'S specifications.
2-5
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(o) nruttCtPATlNG SEDIMENTATION (b) CHANGE FROM CHANNEL GRADE MAY
CAUSE SEDIMENTATION OR EROSION
(c) CULVERT PLACED BILOW PROPIR GRADE
WATERWAY IS REDUCTD
(e) HTLLSIDE GRADES. EROSION PR (f)
NOTE:
I. PROPER CUL\€RT GRADE IS ESSENThL FOR THE PROPER FUNTIONING OF THE SIRUCTURE
2. rN FiALF CUl / H LF FrtL (d), (f) rHE CUL\GRT SHOULD BE LAlo ON UNIFORM BEDoINC
XATERIAL FOR THE WHOLE LENGTH, TO UINIMIZE DIFFERENTIAL SETTLEMENT
3, DIFFERENThL S€TTLEMENT SHOULD 8E CONSIOERED IN THE DESIGN OF THE CULVERT STRUCTURE
FIGURE 2.3 : CULVTRT PROFILt
PAVING OR OTHEROPEN SPILLWAY
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GASION UATTRESS
(f) CANTTLTVER EXTINSTON
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2.3.1
If the design discharge exceeds 60 cumecs based on ainterval, consideration should be given to using a bridgeaccount the site constraints and economic factors.
2.3.2 Site Conditions
2.3.2.1 Low Allowable Headwater
a)
CULVERT TYPE SELECTION
Type Selection
Types of culverts commonly used in this country are as follows:
precast reinforced concrete pipes (refer M.S. gg1: part 1, part 2 and.part3:1991),
precast reinforced concrete box culverts (refer M.s. 1293 : part 1 : r99z),reinforced concrete cast-in-situ box (refer M.s. 11g5:1gg5), andculvert of other material approved by relevant authorities.
culvert type selection includes the choice of materiai, shape, cross section and thenumber 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) design discharge,
b) site conditions,
c) design life,d) construction period,
e) construction joints, and
0 blockage due to floating debris from upstream.
b)
c)
d)
50 years recurrence
structure taking into
Headwater is the water depth at the inlet of the culvert. Multiple cells culvertshave to be used at places where the headwater should be kept low to get the waterthrough quickly without ponding or flooding of the land upstream. In flat floodplain where there is no well-defined local flow path multiple culverts spread overthe 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
areas where solid waste is a problem, trash screen with bypass should be provided
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.
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a) Reinforced Concrete pipe
The minimum cover is 0.4m. If the cover is ress than 0.4m, the pipesshould be concrete encased. pipes of higher strength can arso be used butit would cost more. Reinforced concrete pipe below road pavement sharlhave adequate structural strength to carry traffic load.
Precast Reinforced Concrete Box
Precast reinforced concrete box culverts are designed to withstand directtraffic loading. The minimum cover however is 0.1m.
R.einforced Concrete Cast-in-Situ Box
It can be designed structurally
2.3.2.3 Settlement of Culverts
to withstand direct traffic loadins.
when culverts are liable to settle due to a high fi1l, or poor ground condition pipesshould be selected which can withstand the anticipated unequal settlement.Reinforced concrete pipe can withstand anticipated unequal settlement providedrubber ring spigot and socketjoints are used.
2.3.2.4 Culvert Joints
b)
In cast-in-situ box culverts movement joints should be providedlongitudinal intervals. The movement joints should be watertishtprevent wash in of backfill material.
at appropriate
and detaiied to
2.4
For precast box culverts all joints should be wrapped round with non-wovengeotextile to prevent wash-in of backfill material.
FACTORS TO BE CONSIDERED IN HYDRAULICDESIGN OF CULVERT
Hydrological Analysis
Please refer to Volume 1 - Hydrological Analysis
2.4.1
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)
<12
12-18>19
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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.
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2.4.5
Freeboard
Freeboard is the vertical distance from the water surfacelevel. For culverts, the design water surface leve1 shouldformation level.
to the road formation
not be above the road
For high embankments, when the water level at the inlet exceeds 1.0m above thecrown of culvert, the designer must check the stability of the whole embankmentagainst the fluctuations of pore water pressure.
2.4.4 Length of Culvert
The required length of a culvert depends on:
a)
b)
d)
e)
width of the carriageway,
height of fill over the culvert,
slope of embankment,
slope and skew of the culvert, and
type of end finish such as headwall,
transition/tapers or spillway.bevelled end, drop inlet,
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The length of culvert needed can be obtainedthe road embankment along the alignment of
Skew of Culvert
by sketching out the cross section ofthe culvert.
I
a) When the road alignment crosses an existing channel at an oblique angle,as far as possible, the channel should be diverted so that the culverrintersects the road at nearly right angles. It is uneconomical to build' longer culverts due to its skewness. However, it is not desirable either todivert the channel in an abrupt manner to achieve a right angle crossing,especially, if it is a very rapid flowing stream.
b) The headwall of skew culverts should be aligned parallel to the roadwaycentreline. For traffic safety, the headwall should be located a minimumof 4m, away from the edge of the traffic lane.
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2.4.6 Gradient of Culverts
The gradient of a culvert is dictated by the minimum and maximum allowableflow velocities in the culvert. The minimum gradient is the flattest allowable tominimise deposition and accumulation of silts in the culvert, and the maximumgradient is the steepest allowable to control flow velocities to a level notexceeding the scouring resistance of the culvert material:
Minimum gradient = 1:600
Maximum gradient = 1:100
Generally gradients of 1:200 to 1:300 are used for ease of laying and minirnurnvelocity 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 aboveprevious natural stream velocities.
Countermeasures would include rip-rap placed beyond the outlet end or theprovision of 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, couldlead to wash-out of fine material, leading to undermining of the cuivert beddingand side support and eventual failure of the structure. This problem could beminimised by the provision of an impervious bedding and embankment at theinlet end and concrete anti-seepage collar.
Seepage and wash-in of fine material through the joints of precast culvert unitscouid be reduced by wrapping the joints with suitable geotextile drainage fabric.Suitable water-stop should also be provided in movement joints of cast-in-situbox culverts.
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2.4.8
some erosion and seepage countermeasures are illustrated in Fisure 2.4.
When the drop in level from the culvert outlet to the receiving natural streaminvert is more than 1 m then considerations should be given to the provision ofenergy dissipators as described in Chapter 29 - Special Structures of .,Urban
Stormwater Manage Manual for Malaysia',.
Flow Velocities
The flow velocities at the inlet, barrel and outlet of the culvert, are generally notthe same. The inlet approach velocity, vi, is normally low and would not causescouring problem of the embankment material at the inlet. The culvert barrelvelocity, Vc, should not exceed the scouring velocity of the culvert mateial, andto 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 thedownstream receiving channel. For a rough guide of permissible velocities ofdifferent conduit materials, Table 2.2 canbe used. If the outlet velocity is greaterthan the permissible velocity, consideration should be siven to:
reducing the slope of the culvert,
increasing the size of culvert, and
protecting the receiving channel by lining or providing an energydissipator at the culvert outlet.
In all cases' however, a concrete apron shall be provided at the inlet and outletend to prevent scouring.
a)
b)
c)
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Table 2.22 Maximum Recornrnended FIow velocities (m/s)
For Various Conduit Materials
To reduce maintenance the flow velocities in culverts shall be as follows:
Minimum Self Cleansing velocity (to prevent siltation) = 0.7 m/sMaximum velocity (to limit scouring) = 3 m/s
Precast Concrete Pioes 8.0Precast Box Culverts 8.0In Situ Concrete and Hard packed Rock (300mm min) 6.0Beaching or Boulders (250mm min) 5.0Stones (150 - l00mm) 3.0 -2.5Grass Covered Surfaces 1.8
Stiff, Sandy Clav 1.3 - 1.5
Coarse Gravel 1.3 - 1.8
Coarse Sand 0.5 - 0.7Fine Sand 0.2 - 0.5
2-16
LIST OF REFERENCES
LOCAL PUBLICATIONS
Jabatan Pensairan Dan Saliran (JPS)
1. Hydrological Procedure No. 4
- Magnitude and Frequency of Floods in peninsurar Malaysia (19g7)
2. Hydrological Procedure No. 10
- Stage Discharge Curves (I976)
3. Hydrological Procedure No. 11
- Design Flood Hydrograph Estimation for Rural Catchments in Peninsular
Malaysia
Hydrological Procedure No. 19
- The Determination of Suspended Sedirnent Discharge
Hydrological Procedure No. 5
- Rational Method of Flood Estimation for Rural Catchments
Hydrological Procedure No. 1
- Estimation of the Design Rainstorm in Peninsular Malaysia (1982)
Hydrological Procedure No. 16
- Flood Estimation for Urban Areas in peninsular Malaysia
Planning and Design Procedure No. 1
- urban Drainage Design Standards and procedures for peninsular Malaysia
Garispaduan Untuk Memproses Permohonan dan Menetapkan Syarat-syarat BagiJambatan dan Lintasan
Urban Stormwater Management Manual fbr Malaysia
Jabatan Keria Rava (.TKR)
i 1. Intermediate Guide to Drainage Design of Roads
- Arahan Teknik (Jalan) 15/91
1?. Terms of Reference for Survey works and Digital Ground Modelling.
6.
7.
4.
5.
8.
9.
10.
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US PUBLICATIONS
1. Hydraulic Design Series No. 2- Highway Hydrology (Sept 1996)
FHWA_SA_96_061
2. Hydraulic Engineering Circular No. 22- Urban Drainage Design Manual (Nov. 1996)
FHWA_SA_96-078
(us DoT FHA)
3. Hydraulic Engineering Circular No. 14
- Hydraulic Design of Energy Dissipators for Culverts and Channels(Sept. 1983)
(us Dor FHA)
4. Hydraulic Design Series No. 5- Hydraulic Design of Highway Cuvlerts (Sept. 19g5)
FHWA-IP_85_15
(us DoT FHA)
2-18
APPENDTX 1
Chapter 27
Culverts
Acknowledgement
The permission granted by Jabatan pengairan dan Saliran to REAM topublish the whole of this chapter of Urban Stormwater ManagementManual for Malaysia is gratefully acknowledged.
REAM
isclaimer
ery effort and care has been taken in selecting methods and recommendations that are appropriate to Malaysiannditions. Notwithstanding these efforts, no warranty or guarantee, express, implied or statutory is made as to thecuracy, reliability, suitability or results of the methods or recommendations.
re use of this Manual reguires professional interprebtion and judgement. Appropriate design procedures and assessment'lst be applied, to suit the pafticular circumstances under consideration.
re government shall have no liability or responsibility to the user or any other person or entity with respect to any liability,s or damage caused or alleged to be caused, direcily or indiredy, by the adoption and use of the methods and:ommendations of this Manual, including but not limited to, any interruption of service, loss of business or anticipatorycfits, or consequential damages resulting from the use of this Manual.
2000 by JPS Malaysia.
rala Lumpur, Malaysia
I rights reserved. No part of this manual may be reproduced, in any form or by any means, without permission in writingrm the publisher.
'inted in Malaysia
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27 €e3LwffiR?s
27't INTR'oDUcrIoN """"""" ................27-r27.2 DESTGN CONSTDEMTTONS............ .....................27-1
27.2.t Headwater... ...27-t
27.2.2 Culvert in p|an............................27 -r
27.2.3 Verticat profi1e,......... ..........27-2
27.2.4 Muttipte Ceils............ ..........27_2
27.2.5 Increasing Capacity of Cr:hyerts... ..."........27_2
27.2.6 Culverts in Flat Terrain ........27-z
27.2.7 Site Investigation.....,....... ...27-3
27.2.8 Safety.......... ...27_4
27.2.9 Culvert as Flow Measuring Device ...........27_427.2.10 Design Documentation.................
..........27_427.3 HYDRAUUCS ................27_5
27.3.t General........ ...27_s
27.3.2 Control at In1et........ ...........?7_s
27.3.3 Control at Ouflet...... ...........27-627.4 DESIGN PROCEDURE.
,..27-g27.5 COtvtpuTER MODELUNG ..................27_t2
27.6 DEBRIS CONTROL .........27_12
27.6.I General........ ...27_12
27.7
27.6.2 Freeboard .......27_t3
27.6'3 Design Precautions .............27_t3
27.6.4 Relief Culvert ."27_t3
27.6.5 Debris Conkolstructures ....27-13
CULVERT END TREATMENT............. .27-t3
27.7.I Introduction. ...27_!3
27.7.2 Typical End Treatments............... ...........27_13FLow vELocITY
..........27-t327.8.1 Inlet Control.
...27_1327.8.2 Outlet Controt .................
....z7_L427.8.3 Erosion of Conduit
...............27_!427.8.4 Scour at In1ets...........
.........27_L427.8.5 Scour at Ouilets .................27_tq27.8.6 Siltation
..........27-L5
27.8
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Urban Stormwater Management Manual27-i
Cutverts
27.9
27.10 MINIMUM ENERGY CULVERTS... ....... 27-18
APPENDIX 27.A DESIGN FORM, CHARTS AND NOMOGRAPHS .......,.....27-2I
APPENDIX 27.8 WORKED EGMPLE ............ 27-35
?7.8.t Pipe Culvert (Inlet Control) ................ ....27-35
27.8.2 Box Culvert (Inlet Control) ................. ....27-36
27.A3 Pipe Culvert (Outlet Control) ..................27-37
27.8.4 Box Culveft (Outlet Control) .........."........ 27-37
27.8.5 Minimum Energy Culvert.......". ............... 27-38
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CulverE
27.T IruTRCDI.'CTTON
This chapter provides. guidance on the hydrauric design ofculverts, culvert end treatment, the design of scourprotection, debris contror and an introduction to improvedculvert inlets. The procedures for the hydraulic deiign ofculverts are based
- on ..Hydraulic Oeiign of Highway
Culverts', Hydraulic Engineering Circular ru-o S (US FederalHighway Administration, 19g5).
The emphasis in this Chapter is on the design of culvertsfor urban stormwater.drainage. Highway authorities mayhave different or additional requirements, which are notdiscussed herein.
2V.2 DESIGNCONSIDERATTONS
27.2.L Headwater
Any culvert that constricts the natural stream flow willcause a rise in the upstream water surface. The total flowdepth in the stream measured from the invert of theculvert inlet is termed headwater.
The available headwater will depend on the topography ofthe site and the vertical road profile in ieiation to thattopography. In flat or undurating country or where a highstandard vertical road profile is used the availableheadwater may be limited by the height of the surroundingground or the elevation at which the road formation cutsthrough the hydraulic Arade line. Raised levee banks maybe necessary to maintain the headwater depth required asindicated in Section 27.2.6.
The most economical culveft is one which utilise all of theavailable headwater to pass the design discharge, since thedischarge increases with increasing head. However, it isnot always possible to utilise all of the available headwater,because of constraints, which limit the upstream waterlevel. Selection of the design headwater shoutO be basedtherefore, on consideration of the following factors :
. Limits on bachlrater resulting from the presence ofbuildings upstream and/or the inundation ofagricultural land.
. The outlet velocity and the potential for scour.
Potential damage to adjacent property or inconvenience toowners should be of primary concem in the design of allculverts. Expensive court cases and resultant compensationmay result if property owner,s rights are neglected. Inurban areas, the potential for damage to adjacent propefiis greater, because of the number inO value of propertiesthat can be affected.
Culvert installation under high embankments in rural areasmay present the design engineer with an opportunity toadopt a high headwater and allow ponding"upstream to
attenuate flood peaks downstream" If deep ponding isconsidered, the consequences of scour at the outlet andcatastrophic failure of the embankment should beinvestigated. When culverts are installed under highembankments, an appropriate invegrigation shourd bemade to evaluate the risk of a larger iood occurring orblockage of the culverts by debris.
27.2.2 Culvert in plan
Ideally, a culvert should be placed in the natural channel(Figure 27.1.). A culvert in this location is usuaily alignedwith flow and little structural excavation and channel workare required at the inlet and outlet, especially for shorterculverts. In the case, where rocation in the naturalchannel would require an inordinately long culvert, somestream reafignment may be required (FigieZT.Z). Suchmodification to reduce skew and shorten iulverts should becarefully designed, environmental concerns for streamvelocity, flow depth and factors important to the streamecosystem, and hydraulic concerns for stream bed andbank stability make it advisable not to undertake channelmodifications unless there is no practical alternative.
Culvert skew should not generaiiy exceed 45 degreesmeasured from a line perpendicular to the roaclwaycentreline. if the skew is greater than 45 degrees specialconsideration needs to be given to the hydraulic efficiencyof the wingwalls.
culvert alignments square to the road centrerine are notrecommended where severe or abrupt changes in channelalignment are reguired upstream or downiream of theculvert. Small radius bends are subject to erosion on thelon:ave bank and deposition on the inside of the bend.Such changes, upstream of the culverts, result in pooralignment of the approach flow to the culvert with resuitingloss of hydraulic efficiency, subject the embankment toerosion and increase the probability of deposition in theculvert cell. Abrupt changes in channel alignmentdownstream of culverts may also cause erosion ordeposition of material in adjacent properties.
Urban Stormwater Management Manual
Figure 27.1 Culvert Located in Natural Channel
27-tli
,-:i---&
Cu/verB
Channel Change
Altemate Cutvert Location
Relocated Ctannel Channel ChanEe
Recommended Not Recomrnended
Figure 27.2 Methods of Culvert Location in the Natural Channel to avoid an Inordinately Long Culvert
AJ\
2V.2.3 Vertical Profile
Most longitudinal culvert profiles should approximate thenatural stream bed. Other profiles may be chosen foreither economic or hydraulic reasons. Modified culvertslopes, or slopes other than that of the natural stream, canbe used to prevent stream degradation, minimisesedimentation, improve the hydraulic peformance of theculvert, shoften the culvert, or reduce structuralrequirements, Modified slope can also cause streamerosion and deposition. Slope alterations should,therefore, be given special attention to ensure thatdetrimental effects do not result from the change.
Channel changes often result in culverts being shorter andsteeper than the natural channel. A modified culvert slopecan be used to achieve a flatter gradient to preventchannel degradation. Figure 27.3 illustrates possibleculveft profiles.
27.2.4 Multiple Cells
It is impoftant to select a culvert shape that will best fit thewatenany of the channel or stream. In narrow deepchannels, a small number of large diameter pipes or boxculverts are usually appropriate. In flat areas having nowell defined watenray the flood may be larger in volume,but of shallow depth. A number of separate culvertsspread over the width of the flooded area may be moreappropriate for these conditions.
Special consideration should be given to multiple cellculveds where the approach flow is of high velocity,particularly if supercritical. These sites are best suited to asingle cell or special inlet treatment to avoid adversehydra u lic j ump effects.
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27.2.5 Increasing Capacity of Culverts
Changed landuse, such as urbanisation upstream from anexisting crossing may increase the magnitude of floodingand necessitate increasing the culvert capacity toaccommodate additional flow without exceeding a given
headwater elevation. Before deciding that the culvert has
to be replaced by a larger structure, (assuming relief flowis not feasible), the possibility of improving the inlet of theexisting culvert should be investigated (see Section 27.9for details of improved inlet culverts).
27.2.6 Culverts in FlatTerrain
In flat terrain, drainage channels are often ill-defined ornon-existent and culverts should be located and design forleast disruption of the existing flow conditions. In theselocations multiple culverts can be considered to have a
common headwater elevation, although this will not be
precisefy so. Figure27.4 illustrates a design techniquethat can be used to determine the combined capacity ofmultiple culverts with different invert levels and capacities.The total discharge at any point of the headwater elevationfor culverts 1 and 2, on FigureZ7.4, is the sum of the
discharges Ql and Q2.
In flat terrain it may be necessary to construct levee
banks, as shown on Figure 27.5, to achieve the design
headwater at the culvert location. This is only possible if
there is no danger of increased flooding of upstreamproperties. Therefore, approval of the local drainageAuthority must be obtained prior to construction of any
such levee bank.
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27-2 tJrban Stormwater Management Manual
27.2.7 Site trnvestigatlon
A site investigation must be carried out at each proposedculvert site. The extent and complexity of the invesUgationwill depend on the size, importance and cost of theproposed culvert, site conditions, the height of theembankment and the loading that will be imposed on thefoundation material and on the culvert itself.
Survey information should be sufficient to permit theculvert to be located in plan and profile and should includerelevant physical features. In flat terrain the elevation of
irnportani buildings upstream, such as houses, commercialproperty, roads or railways should be recorded, if_tney arelikely to be affected by backwater
At, sites where the stage-discharge curve may have to becalculated by the srope Area l.rettroc, as is often the casein urban.or developing areas and for all major culverts, thesurvey should include a cross_section of the channel andfloodplain and a water surface profile extending a sufficientdistance upstream and downstream to est Otirn tf,elongitudinal siream gradient.
IRepr€ed r-tF...-
Dlsdrarge ToblDisdrarge (er = er + ez )
Figure 27 '4 Stage-Dixharge Curue for Multiple Cutverts with Different invert Levels
Streambed l-ma$on
Deposftion
Rffi
Perfonnance CurveCulvert 1
Use ChuteWhere Necessary
Stable Channel Gradient
Degndlng Channel
Figure 27.3 possible Culvert profiles
Perbrmance CurveCutuert 2
Cornbind Performance CurveCuh/eft 1 plus Culvert 2
Discfiarge
Urfun Sbrmwater lvlanagement Manual27-3
Culverts
Levee Bank b Maintain Design Headwater- Shculd be Extended Far Enough Outfiom Embankment to Match Nahrnl Surface. Zt
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Figure 27.5 Development of Headwatera(
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In scour prone areas, soil characteristics should beassessed to enable stream protection strategies to beformulated. The design engineer should also know thenature of the subsoil material underlying the stream bed,unless it is obvious that it is sound bed-rock or othermaterial, which will not cause foundation problems.Detailed foundation investigations should be carried out forall large culverts, unless it is certain that thev will befounde on sound bed-rock.
27.2.8 Safety
Traffic safety - An exposed culveft end (projecting fromthe plane of the batters) acts as an unyielding obstruction,which is likely to bring an out of control vehicle to anabrupt stop, causing considerable damage to the vehicleand high deceleration forces on the occupants.
Where a road safety barrier is not provided, culvert endsshould be designed so that they will not present anobstruction to vehicles running off the road. This can beachieved by covering exposed sides with fill, providingheadwalls or wingwalls which will not present anobstruction, or mitrering culveft ends flush with theembankment surface.
The location of culvert ends placed flush with theembankment slope should be indicated by markers toreduce hazards to equipment operators and others. Highculverts in populated areas should be fenced wheneveroossible.
The hazard presented by culverts under private and side-road entrances should be minimised by placing them as faras practicable from the roadway and avoiding the use ofheadwalls.
Child safety - Culverts can also be an attradion foradventurous and inquisitive children. At locations wherelong culverts could a hazard, especially in urban areas,fencing, swing gates or grates at upstream ends should be
considered to prevent entry. However, this may causeblockages and reduce the efficiency of the culvert.
27,2"9 Culvert as Flow Measuring Device
As stream flow records for small catchments are veryscarce, any reliable supplementary data gathered during orafter major floods are of considerable value. A convenientway of deriving such data is to measure high water marksat culverts after major floods and then to estimate theactual flood flows, which pass through the culvert (seeSection 27.4). The calculated discharge can then berelated to the catchment characteristic and used to verifoor improve existing runoff estimation methods. Carefulidentification and measurement of high water marks is
essential and should be carried out as soon as possible
after the flood, before the evidence disappears.
27 .2.1O Design Documentation
Records of culveft designs should be retained for at leastthe lives of the culverts. The amount and detail ofdocumentation should be related to the importance of thestructure. The following data would normally be retainedfor large culverts:
. Field notes and data
. Site plan, profiles and cross-sections
. Soildata
r Summary of calculations
. Design flood frequency
. Headwater depth
. Outlet velocity
r Culvert drawings
. Rationale for culvert choice
. Photographs of site and developments, if there is a
possibility of future claims resulUng from the hydraulicperformance of the culvert.
. Flood data observed during and after construction ofthe culvert.
274 utban Stcrmwater Management Manual
j,
-'!
Culverts
2V.3 STYDRAT.Ii_ICS
2V,3.L General
The flow hydraulics in the culvert is normally either undercondition of full flow in closed conduit or part full flowunder uniform flow or non-uniform flow. The fundamentalhydraulic principles under these two flow conditions weredescribed in Chapter 12.
The most irnportant consideration in culvert hydraulics iswhether the flow is subject to inlet or ouflet control.Figures 27.6 and 27.7 show the range of flow typescommonly encountered in culverts. For inlet control twodistinct regimes exist, depending on whether the inlet issubmerged or not submerged. Outlet control occurs inlong culverts, laid on flat grades and with high tailwaterdepths. In designing culverts, the type of control isdetermined by the greater of the headwater depthscalculated for both inlet control and outlet control.
For the two fypes of control, different factors and formulaeare used to calculate the hydraulic capacity of b cutuert.Under inlet control, the cross-sectional area of the culvertcell, the inlet geometry and the amount of headwater orponding at the entrance are of primary importance. Ouiletcontrol involves the additional consideration of theelevation of the tailwater in the outlet channel and theslope, roughness and length of the culvert cell.
2V,3.2 Contnol at Inlet
For cul.reds subjeC to inlet control, the important factorsare entrance conditions, including the entrance type,existence and angle of headwalls and wingwalls and theprojection of the culvert into the headwater pond.
For one dimensional flow, the theoretical relation betweendischarge and upstream energy can be computed by aniterative process or by the use of nomographs.
A. Projecting End - Unsubmerged Inlet
B. Projecting End - Submerged Inlet
C. Mitred End - Submerged Inlet
Figure 27.6 Flow Profiles for Culvert under Inlet Control
- ..-3
Urban Stomwater Management Manual 77-5
Inlet control can occrJr with the inlet submerged and theoutlet not submerged (Figure 27.6). Sketches of inletcontrol flow for both unsubmerged and subrnergedprojecting €ntrances are shown on Figure 27.6(a) and27.6(b). Figure 27.6(c) shows a mitred entrance flowingsubmerged with inlet control. Under inlet control, the flowcontracts to a supercritical jet immediately downstreamfrom the inlet. When the tail water depth exceeds criticaldepth f. and the culvert is laid on a steep grade, flowremains supercritical in the cell and a hydraulic jump willform near the outlet. If the culvert is laid on a slope lessthan critical, then a hydraulic jump will form within theculveft.
In inlet control the roughness and length of the culvert celland the outlet conditions (including depth of tail water) arenot factors in determining culvert capacity. An increase inthe slope of culvert reduces headwater only to a smalldegree and can normally be neglected for conventionalculvefts flowing under inlet control.
27.3.3 Contro! at Outlet
Culverts flowing with outlet control can flow with theculvert cell full or with the cell part full for all of the culvertlength. With outlet control and both inlet and outletsubmerged (Figure 27.7(a)) the culvert flows full underpressure. The culvert can also flow full over part of itslength, then part-full at the ouUet (Figure 27.7). The pointat which the water surface breaks away from the culvertcrown depends on the tailwater depth and culvert gradeand can be determined by using backwater calculaUons. Ifthe culverts is laid on a flat gnde, outlet control can occurwith both inlet and outlet not submerged (Figure 27.7) andpart full flow throughout the cell is subcritical. Minorvariations of these main types can occur, depending on therelative value of critical slope, normal depth, culvert heightand tailwater depth.
The procedure given in Section 27.4 provides methods orthe accurate determination of headwater depths for the fullflow condition and for the case of the cell paft-full overpart of the culvert length. The method given for thecondition of the celi part full, over the total length, gives asolution for headwater depth that decreases in accuraqy asthe headwater decreases.
(a) Determination of Energy Head (H)
The head, H (Figure 27.7) or energy required to pass agiven flow through a culveft operating under outlet controlis made up of three major parts. These three parts areusually expressed in metres of water and include a velocityhead, Hn an entrance loss, H, and a friction loss, ff,. Theenergy head is expressed in equation form as:
H=Hr+H"+H1
The velocity head, H" is given by,
where /is the mean velocity in the culvert cell and g is theacceleration due to gravity. The mean velocity is thedischarge, Q divided by the cross-sectional area .4 of thecell.
The entrance loss is expressed as,
rt2
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H,=H*,#
u l,. - .zgnztlvzlz=Lrr""tnru )ZS
(27.2)
(27.3)
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The entrance loss coefficient, K" , depends on the inletgeometry primarily through the effect it has on contractionof the flow. Values of K. determined from experiment,range from 0.2 for a well rounded entrance, through 0.5for a square edged inlet in a vertical headwall to 0.9 for asharp pipe (e.9. corrugated steel) projecting from anembankment. Ku coefficients are given on Design Chart27.2.
Since most engineers are familiar with Manning's n, thefollowing expression is used to calculate the friction loss, H,.
aiong ihe conduit:
(27.4)
where,
n = Manning's friction factor
t- = length (m) of culvert cell
V = mean velocity (m/s) of flow in culvert cell
g = acceleration due to gravity
= 9.80 m/sz
R = hydnulic radius (m) = 4WpA = area (m2) of flow for full cross-section
We = wetted perimeter (m)
Substituting in Equation 27.t and simplifying, we get fortullflow:
(27.s)
Figure 27.8 shows the terms of Equation 27.5, the energy
line, the hydraulic grade line and the headwater depth,
HW. The energy line represents the total energy at any
point along the culvert cell. The hydraulic grade line ls
defined as the pressure line to which water would rise in
small veftical pipes attached to the culvert wall along its
length. The difference in -elevation
between these b/vo
lines is the velocity nead Y1"6'
27-6
(27.1)
lJtban Stormwater Management l'lanual
Cu/verb
By referring to Figi:re 27.g and using the culvert invert atth€ outlet as datum, we get:
rt2tl*ii+LS=hr+H,+H"+H,
zg
Then,
tt2hr**+LS-h2--H,+Hu+H,
2g
and,
H=ht+fi"U-hz=H,+H,+H, (27.8)
(27.5)
(?7.7)
(a) Culvert Flowing Full, Sr.lbmerged Oudet
(b) Culvert Flowing tull, Unsubmerged OuUet
FiEure 27.7 Flow Profiles for Culvert under Outlet Control
Frorn the development of this energy equation andFigure 27.8, ff is the difference between the elevation ofthe hydraulic arade line at the outiet and the energy line atthe inlet. Since the velocity head in the entrance poot isusually small under ponded conditions, the water sr:rfaceof the headwater pool elevation can be assumed to equalthe elevation of the energy line.
Equation 27.5 can be readily solved for # by the use ofthe fulf flow nomographs in Design Charts 27.3 to 27.5.
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(d) Culvert Not Floruing Full
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Urban Stormwater Nanagement Manual27-7
CulverE
- .: -. aqgv-li1. - \- - IYqE@gld€r,j_"e
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Figure 27.8 Hydraulics of Culvert Flowing Full under Outlet Control of hsfor High Tailwater
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JN(b) Determination of Headwater Depth (HWo)
Headwater depth, HW6 can be determined from anequation for outlet control:
HWs=H+ho-LS t27.s)
where,
H = head (m) determined from Design Charts 27.3 to27.5 or from Equation 27.8
h0 - greater of TW and (hc + D)IZ, in which D < D
hc - critical depth (m) from the Design Charts inAppendix 27.A
D = culvert height (m)
l- = length (m) of culvert
S = slope (m/m) of cell
(c) Determination of ho
The determination of hs is an important factor incalculating both the headwater depth and the hydrauliccapacity a culveft flowing under outlet control.
Tailwater depth, TWis the depth from the culveft invert atthe outlet to the water surface in the outlet channel.Engineering judgement is required in evaluating possibletailwater depths. Tailwater is often controlled by a
downstream obstruction or'by water levels in anotherstream. A field inspection should be made to check ondownstream conditions and flood levels. The Slope AreaMethod can be used to calculate flow depths, ifdownstream conditions do not provide an obvious control.
Foftunately, most natural streams are wide compared tothe culveft and the depth of water in the natural channel isconsiderably less than critical depth in the culvert section.In such cases the natural tailwater does not govern.
Two tailwater condiUons can occur with culverts operatingunder outlet control, (i) tailwater above the top of theopening and (ii) tailwater at or belsw top of opening:
(i) Tailwater above the top of opening - when thetailwater, TWinthe outlet channel is above the too ofthe culvert ouUet Figure 27.7(a),
ho--TW (27.10)
The relationship of hs to the other terms in Equation27 .9, for this situation, is illustrated on Figure 27.9.
(ii) Tailwater at or below top of opening - when thetailwater in the outlet channel is at or below the top ofthe culvert ouUet, as on Figure 27.7(b), 27.7(c) and27.7(d), fa is more difficult to determine.
Full flow depth at the outlet, Figure 27.7(b), will occur onlywhen the flow rate is sufficient to give critical depths equalor higher than the height of the culveft opening. For allsuch flows the hydraulic arade line will pass through thetop of the culveft at the outlet and the head, H can beadded to the level of the top of the culvert opening in
calculating HWq
When critical depth is less than the height of the culvertopening, the water surface drops as shown on Figures
27.7(c) and /7.7(d), depending on the flow. For thecondition shown on Figure 27.7(c), the culvert must flowfull for of its length. Flow profile computations show thatthe hydraulic arade line, if extended as a straight line fromthe point where the water breaks away from the top of theculvert, will be at a height approximately halfway betweencritical depth and the top of the culvert, at the culvertoutlet. i.e.:
n" =(tg:ro) (27.r1)
This fevel should be used if it is greater than TW.
Ut27-8 Uftan Starmwater Management Manual
Culverts
The head, Hcan be added to this level in calculating f/llla.The relationship of hs to the other terms in Equation 27.9for this situation is illustrated on Figure 27.10.
As the discharge decreases the situation approaches thatof Figure27.7(d). For design purposes, this method issatisfactory for calculated headwater depths above 0.75D.For smaller values of headwater, more accurate result canbe obtained by flow profile calculations or by the use of thecapacity charts from Hydraulic Engineering Circular No 10(US Federal Highway Administration, t972).
27.4 DESIGN PROCEDURE
The design engineer should be familiar with all theequations in the previous Section before using theseprocedures. Following the design method without anunderstanding of culvert hydraulics can result in an
inadequate, unsafe, or costly structures. The proceduresdoes not address the effect of storage. The designprocedure is summarised on the Culveft Design fbwcha-4Figure 27.11.
1. Assemble Site Data
r Site survey and locality map.. Embankmentcross-section.
. Roadway profile.
" Photographs, aerial photographs.
e Detaiis from field visit (sediment, debris and scour atexisting structure).
. Design data for nearby structures.
. Studies by other authorities near the slte, includingsmall dams, canals, weirs, floodplains, storm drains.
" Recorded and observed flood data.
D S--+
Figure 27.9 Determination of hs for High Tailwater
Figure 27.10 Determination of hsfor Tailwater Below Top of Opening
f atl
Dt-
lb = Greater of h. + D and TW2
Urban Stcrmwater Management Manual27-9
2. Determine Design Flood Discharge
Determine ARI of design flood - see Chapter 4.Deterrnine design flood discharge, Q - see Chapter 14.
3. Commence Summarising Data on Design Form
See Design Chari 27.1 in Appendix 27.A.
4. Select Trial Culveft
(i) Choose culvert material, shape, size and entrancetype.
(ii) Determine the initial trial size of culvert, either byarbitrary selection or by assuming a velocity (say3 m/s) and calculating a culvert area from A =o/v
5. Determine Inlet Control Headwater Depth, flft- Useinlet Control Design Charts 27.3 to 27.5.
The nomographs cover various culvet types and inletconfigurations. Each nomographs has an example on itwhich is self-explanatory. Using the trial culvert size, therelevant nomograph can be used to calculate l7W1 given aknown O. They can also be used in reverse to calculate egiven a known HWi
It should be noted that where the approach velocity isconsidenble, the approach velocity head can be calculatedand deducted from the calculated HWi to give the actualphysical head required.
6. Determine Depth, f4for Outlet control
(i) Calculate both (r. + D)12 and the tailwater, Il,/from known flood levels, downstream controllinglevels or from the Slope Area Method. If it is
clear that the downstream tailwater conditlons donot control, take f4 = ftc + D)/2. 11, can becalculated from Design Chafts 27.8 or 27.9. If hcexceeds Dthen take D.as D.
(ii) h0 is the larger of TWor (h, + D1/2
7. Determine Outlet Control Headwater Depth at Inlet,HW
(i) Determine entrance loss coefficient, Ku fromDesign Chart27.2.
(ii) Glculate the losses through the culvert, H usingthe outlet control nomographs, DesignCharts 27.10 to 27.tZ (or Equation 27.5 if outsidethe range). As with the inlet control nomographs,these nomographs cover various cuivert types andeach nomograph has an self-explanatory exampleon it.
(iii) If the Manning's n value of the culvert underconsideration differs from the Manning n valueshown on the nomograph, this can be allowed forby adjusting the cuivert length as follows:
(27.12)
wnere,
lr = adjusted culvert length
I = actual culved length
,t = desired Manning n value
rl = Manning n value given on the nomograph
(iv) Calculate HW = H + ho- LS
As with inlet control, where the approach velocityis considerable, the approach velocity head can beealeufated and deducted from the calculated HWoto give the actual physical head required.
(v) It HWo is less than 0.75Dand the culvet is underouflet control, then the culvert may be flowingonly part full and using (/t. + D)12 to calculate famay not be applicable. If required, more accurateresults can be obtained by flow profile calculationsor the use of Hydraulic Engineering Circular No 10(as discussed in Section 27.3.3 under (ii) tailwaterdepth at or below top of opening).
B. Determine Controlling Headwater, Hl1/,
Compare HWland HWsand use the higher:
It HW > HWo the culvert is under inlet control ?nd HW, =HW
lf HWy > HWithe culvert is under outlet control and HW, =HWo
9. Calculate OuUet Velocity, 1,24
The average outlet velocity will be the discharge divided by
the cross-sectional area of flow at the culvert outlet. The
cross-sectional area of flow depends, in turn, on the flowdepth at the outlet.
If inlet control is the controlling headwater, the flow depth
can be approximated by calculating the normal depth, yn,
for the culvert crogs-section using Manning's Equation.The flow area, A is calculated using yn and the outletvelocity:
(27.13)
L = L(!L\- \n )
v" =n
27-LA tlrban Stormwater Management lutanual Url
Culverts
TRY CULVERT SIZE D
HWo=Ho+H-SoL
OF CULVERT CELLS; REPEATDESIGN STEPS
HW=HWi(TNLET CONTROL)
CONSIDER OPTIONS:SCOUR PROTECTIONENERGY DISSIPATORIF CHANGE OF CULVERT SIZE.
REPEAT DESIGN STEPS
'Yl HEADWATER, FOR IIttET COi{TNOI
r/rr. H€ADWATER FO8 OLfTIET COr.mOt
ADOTT DESIGN ANDRECORD CALCUUTIONS
a.. 6,d
Urban Stormwater Management f"fanual
Figure 27.11 Design Flow Chart
27 -t1
The outlet velocity computed utilising the normal depth, y,will usually be high, because the normal depth is seldomreached in the relatively short length of average culvert.
if outlet control is the controlling headwater, the flowdepth can be either critical depth f., the tailwater depthTW (if below the top of the culvert), or the full depth D ofthe culvert depending on the following relationships:
. Use hc,if hr> TW
. Use TW,if hc< TW< D
. Use D,if D< TW
Calculate flow area using appropriate flow depth and thenoutlet velocity using Equation 27.13.
10. Review Results
Compare alternative design with the site constraints andassumptions. If any of the following conditions are notmet, repeat steps 4 to 9:
. The culvert must have adequate cover.
. The final length of the culvert should be close to theapproximate length assumed in design.
. The headwalls and wingwalls must fit the site.
. The allowable headwater should not be exceeded.
. The allowable overtopping flood frequency should notbe exceeded.
The performance of the culvert should also be considered,(i) with floods larger than the design flood to ensure suchrarer floods do not pose unacceptable risks to life orpotential for major damage and (ii) with smaller floodsthan the design flood to ensure that there will be nounacceptable problems of maintenance.
If outlet velocity is high, scour protection or an energydissipater (see Section 27.8.5) may be required.
11. Improved Designs
Under certain conditions more economic designs may beachieved by consideration of the following:
. The use of an improved inlet for culverts operatingunder inlet control (see Section 27.9).
. Allowing ponding to occur upstream to reduce thepeak discharge, if a large upstream headwater pool
exists.
12. Documentation
Prepare report and file background information. See'Design Documentation' in Section 27.2.10.
27.5 ESMPI.|TER MODFLLIEVG
HEC-2 Water Surface profiles, (Hydrologic EngineeringCentre, US Army Corps of Engineers) is a widely_usejgeneral purpose program with advanced culvert designfeatures which is available in the public domain. ftrerevised version, September 1991, includes the hydraulicdesign of culverts using the US Federal HighwayAdministration culvert design methods. A commercialdevelopment, HEC-MS, is also available.
Several computer programs have been developedspecifically for the hydraulic design of culverts, including:
" XP-Culvert200O, distributed by Xp Software, Canberra,Australia.
' Waterflow, Hydraulic Design of Culvefts, Distributedby Roads and Traffic Authority, lVagga Wagga, NSWAustralia.
Further information on computer modelling is given inChapter 17.
2V.6 DEERIS CONTROL
27.6.! General
All too often floods have clearly demonstrated how theperformance of culverts can be affected by anaccumulation of debris at inlets. This accumulation cancause failure of the drainage structure, possibly resulting inovertopping of the roadway by floodwaters, with ensuingdamage to the embankment or to the properties upstreamand downstream of the culvert.
Experience has shown that in non-urban areas, thefollowing stream characteristics tend to produce the mostserious debris problems:
o Susc€ptibility of stream to flash flood, i.e. relativelyimpervious watersheds with moderate or steepgradients.
n Actively eroding banks bordered by trees or large
shrubs
. Relatively straight unobstructed stream channels with
no sharo bends.
. Cleared land upstream with fallen trees on the ground"
In urban 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.
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27.6.2 Freeboard
Ail culverts with a waterway area of 1.0 m2 or more shouldbe designed with a minimum of 300 mm freeboard abovethe design water level. For large culverts the designershould consider increasing this freeboard to allow for thesize of debris anticipated, up to a maximum of 1000 mm.
27,6.3 Design precautions
Where debris accumulation is considered to be a problem,other design precautions should be taken, such asproviding a smooth well designed inlet, avoiding multiplecells and increasing the size of culvert. if multiple cells areunavoidable, provision of a sloping cutwarer on theupstream pier (wall) ends may help to align floating debriswith the culvert entrance.
2V.6,4 Relief Culvert
A relief culvert passing through the embankment at ahigher level than the main culvert permits water to by_passthe latter, if it becomes blocked. The relief culvert couldalso be placed at a low level some distance away from themain culvert where it is not likely to be blockeo. tu thisrelief culvert is an additional requirement, the cost of bothculverts should be compared with that of a larger culvertthat will be less subject to blockage.
27.6.5 Debris Control Structures
These can be cosfly both to construct and maintain.Details of the various types of debris control structures
.TaV 6" found in Hydraulic Engineering Circular No 9,nDebris Control Structures,, (US federat HighwayAdministration, L97L). The choice of structure typedepends upon size, quantity and type of debris, the costinvolved and the maintenance proposed. However, forexisting culverts, which are prone to debris clogging, itmay be worthwhile to construct a debris control structurerather than replace or enlarge the culvert.
27.7 CULVERT END TREATMENT
27,7.1 Introduction
The term "end treatment,, encompasses the shape of theculvert ends, end structures such as wingwalls, cut_offsand anchorages and erosion control measures for theadjoining fill and channel (see Standard Drawini;s SD F_21to SD F-24). The design of hydraulically improved inleb isdisdssed separately in Section 27.9.
Culvert end treatment may be required to perform one ormore of the following functions:
r To increase the hydraulic efficiency of the culvert;r To prevent fill from encroaching on the culvert
opening;
" To prevent erosion of the fill and adjacent channel;. To prevent undermining of culvert ends;
" To inhibit the seepage and piping through the beddingand backfill;
. To ineet traffic safety requirements (see Section27.2.8);
. To improve the appearance of large culverts;
. To resist hydraulic uplift forces on corrugated metalpipe culverts; and/or
. To strengthen the ends of large flexible culverts,especially those with mitred or skewed ends.
Cut-offs in the form of a vertical wall, constructed belowthe end apron of a culvert, should always be provided atculvert inlets to prevent undermining and piping. Forcorrugated metar pipe curverts, the cut-off wails arso act tocounteract uplift at the culvert inlet.
27.7"2 Typieal End Treatnnenf-s
and wingwalls _ are the most common encltreatment in overseas countries. An apron is generallyincorporated between the wingwals to rimit scour of thestream becl. They are usually constructed from reinforcedconcrete, but can be formed from masonry, or rock filledgabions and mattresses, or concrete filled mattresses.
Mitred ends - these are generally limited to corrugatedmetal pipe culverts, where the end of the pipe is cutparallel to the slope of the embankment. The area ofembankment around the ends of the culverts is usuallypaved with concrete or rock.
Projecting ends - where the ends of the culvert projectfrom the face of the embankment. Although they are theleast costly end treatment, they .r" hydraulicallyinefficient, do not meet safety requirements and arevisually objectionable. For these reasons their use inMalaysia is not recommended.
27.8 FLOW VELOCITY
Culverts usually increase the flow velocity over that in thenatural water course. Except when the culverts flow full,the highest velocity occurs near the ouflet and this is thepoint where most erosion damage is likely to occurs.
A check on outlet velocity, therefore, must be carried outas part of the culvert design if the outlet discharqes to anunlined watenaray.
27.8.1 Inlet Control
For a pipe culvert flowing with inlet control the outletvelocity can be determined from Figure 25.81 to 25.84 inChapter 25, Appendix 25.B (k = 0.6) in combination withcharts for part full flow in Chapter 12.
l
Urban Stormwater lvlanagement l,lanual
Figures 25.81 b 25.84 were derived from *te Cdebr@k -White equation (in Chapter 12) for k = 0.06 to 0.6. Thisapproach assumes that the depth of flow at the outletequals the depth corresponding to uniform flow, but thesholc length of the average culveft mostly precludes this,making this approach conservative
The depth of flow should be checked against critical depthas determined from Design Charts 27.8 or 27.9. If theflow is supercritical the effed of a hydraulic jump must beconsidered.
27.4.2 Outlet Control
For outlet control the average outlet velociV will be thedischarge divided by the cross-sectional area of flow at theoutlet. This flow area can be either that corresponding tocriticai depth, tailwater depth (if below the crown of thecuivert) or the full cross section of the culveft barrel.
27.8.3 Eroslon of Conduit
Flow of the water subjects the conduit material toabrasion, and too fast a velocity for a given wall materialwill cause erosion to the conduit. Very fast flows cancause cavitation unless the conduit surface is very smooth,and this results in erosion taking place at a rapid rate.However, cavitation damage does not occur in full flowingpipes with velocity less than about 7.5 - 8 m/s and aboutt2 mls in open conduits.
The maximum velocity b,eyond which erosion will takeplace depends on factors like smoothness of conduit,quantity and nature of debris discharged and frequen{ ofpeak 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, forcingthe flow through a reducing opening. As the flowcontracts, vortices and areas of high velocity flow impingeagainst the upstream slopes of the embankment adjacentto the culveft. Scour can also occur upstream of theculveft, as a result of the acceleration of the flow, as itleaves the natural channel and enters the culvert.
Upstream wing walls, apronsr cut-off walls and
embankment paving assist protecting the embankment and
stream bed at the upstream end of a 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
bar across the stream, while finer material will be carriedfurther downstream. Depending on the supply bfsediment the scour hole may gradually refill until after thenext major fiood occurs.
Table 27.1 Ma;imum Recommended Flow Velocities ,(m/s) for various conduit materials
Material
Precast concrete pipes
Precast box culverts
In situ concrete and hardpacked rock (300mm min)
Beaching or boulders(250mm min)
Stones (150 - 100mm)
Grass covered surfaces
SUff, sandy clay
Coarse gravel
Coarse sand
Fine sand
Maximum V (m/s)
8.0
8.0
o.u
5.0
3.0 - 2.5
1.8
1.3 - 1.5
1.3 - 1.8
0.5 - 0.7
0.2 - 0.5
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 whetherfurther 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 towhich type of scour protection is suitable for the site. The
options available include the following:
. Local protection of the stream bed material, in the
case of unlined drains and waterways.
. Flow expansion structure.
. 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
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under the rock riprap. Seour protection is discussed indetail in Chapter- 29"
An important parameter in the selection of an appropriateenergy dissipater is the Froude Number, f, of the outletflow. Where an outlet has 4 < !.7, a simple apronsb'ucture, riprap, or a flow expansion structure will suffice.Where 1.7 < n< 3 a riprap basin or hcrizontal roughnesselements basin is appropriate. Where E > S a hydraulicjump basin wlll be reguired. Energy dissipaters arediscussed in detaii ln Chapter 29.
27.8"6 Siltation
If the flow velocity becomes too low siltation occurs. Flowvelocity below about 0.5 m/s will cause settlement of fineto medium sand particles.
To be seif-cleansing cuive*s must be graded to theaverage grade of the water course upstream anddownstream of the culvert, and levels must represent theaverage stream levels before the culvert was built.
Culvert locaUon in both plan and profile is of particularimportance to the maintenance of se,jiment_free culveitcells. Deposition can occur in culverts when the sedimenttrcnsport capacity of flow within the culvert is less than inthe stream. The following factors may cause deposition inculverts:
. Culverts often provide a wider flow width at low flowsthan natural streams. This results in the flow depthand sediment transport capacity being reduced.
. Point bars (deposition) form on the inside of streambends and culvert inlet placed at bends in the streamwill be subjected to deposition in the same manner.This effect is most pronounced in multiple-cell culver8with the cell on the inside of the curve often becomingalmost totally plugged with sediment deposits.
o Abrupt changes to a flatter grade in the culvert or inthe channel upstrearn of the culvert will inducedeposition. Gravel and sand deposits are commondownstream from the break in grade because of thereduced transport capacity in the flatter section.
Deposition usualiy occurs at flow rates smaller than thedesign flow rate. The deposits may be removed duringlarger floods, depending upon the relative transportcapacity 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 areinstailed at incorrect levels, creating pcnding areas. Suchgrading should generally be avsidecj.
?7"9 TMPR,SVSF gruL€T'EL'LVER.TS
27.9.t General
The capacity of a culvert operating under inlet control canbe significanUy increased by providing a more efficientinlet, which reduces the flow concentration at the entranceand increases the flow depth in the cell. In outlet control,the entrance losses form oniy a minor part of the totalhead losses and major inlet improvement are not justified.
various vpes of inret improvements are discussed in thisSection. A nurnber of these are aimed merely at improvingthe inlet efficiency by reducing the entrance loss, r(*These focus on headwalls, wingwails and the end of theculvert cell. Other major types of improvement, includethe provision of a fall (or steep slope) In the bed of theinlet or tapers in the end section of the cell, orcombination of these improvernents. The aim of thesernajor improvements is to increase the velocity head or theeffective headwater depth.
The material in this Section is based on ..Hydraulic Design
of improved inlets for Culvertsi ttydrauiic EngineeringCircular i,io. 13, (i.iS FerJerai Highway Administration,ISTZ)and the "Hydraulic Design of Culverts,, (Ontario Ministry ofTransportation and Communications, 19g5, which includesmetric design nomographs). These references may needto be consulted for further inforrnaticn when undertakinothe design of improved inlet culverts.
27.9.2 Bevelled Inlets
Adding bevels to a conventional culvert design with asquare-edge at the periphery of the inlet opening increasesculvefts capacity by 5 to 20 percent. The greatest benefitoccllrs with high headwaters.
Bevelled inlets increase the hydraulic efficiency of theculvert (4 = 0.2). Details of typical bevels are shown onFigure27.t2. They should be considered for all boxculvert installations, which operate under inlet controi.Bevelled inlets can be provided on both pre-cast and castin-situ culverts.
The 1.5:1 bevel (33.7 degrees) is more efftcient than the1:1 bevel (45 degrees), but the latter is easier to constructand more practical. Bevels should be provided on the topand side edges of the opening.
27.9.3 Frovision of Depre*sed Inlet
Provision sf a fall or steep slope upstream from the culvertinlet may innprove the capacity of a culvert operating underinlet control by increasing the veiocity head. The fall maybe achieved by flattening the cell slope. This may tend toinduce sedimentation during low flows, but the deposit willin most c:ses be washed out during floods.
,---3,
Urban Stormwater Management Manua!27-15
Culverts
PI.AN
Side BevelAngle
b = 0.(X2 B for 45o (1:1)b = 0.083 B for 33.7o (1.5:1)
Side BorelAngle
(a) Side Berels
LOT{GITUDINAL SECTION
Side BevelAngle
d = 0.(X2 D for 45' (1:1)d = 0.083 D for 33.7o (1.5:1)
(b) Top Eorel
NOTE:
1. Dimensions of Bevels Shall Not be Les than Shorrn.
2. Dimensions b and d are Basd on the SquarcDimensions of the Opening.
3. To Obtain BsrelTerminaUon in One Plan on aRectangular Box, either Increase d b Equal b,or Deoease the Top Bevel Angle.
4. For Multiple Cells Calanlate b from Total CIearWidth or 3D, whidtener is Smaller.
Figure 27.12 Bevelled Inlet for Box Culvert
The fall may be constructed within the limits of the flaredwingwalls, 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.
2V.9.4 Tapered Inlets
A tapered inlet is a culvert inlet with a side-taper or a slopetaper within the end section of the culvert cell. This resultin an enlarged face section and a hydraulically efficientthroat section. A tapered inlet may have a fall,incorporated into the inlet structure. The fall is used toprovide more head on the throat section for a givenheadwater elevation.
A tapered inlet can sometimes greatly improve theperformance of a culvert operating under inlet control.This may permit the use of a cell size considerably smallerthan would be required for a conventional culvert. Thegreatest savings are achieved with long culverts, but thepossibility of increasing the capacity of an existingundersized culvefc by adding an improved inlet should notbe overlooked, since it may eliminate the need for a costlyreplacement structure.
A disadvantage of a tapered inlet culvert is the high outletvelocity, which in some cases may necessitate anexpensive outlet structure or downstream channel erosioncontrol works. Cost comparisons between variousirnproved inlet designs and conventional designs should bemade to select that with the least overall cost.
Side Tapered Inlet - Side tapered inlets are illustrated inFigure27,L4. In some cases, they may increase flowcapacity by 25 to 40 percent over that of conventionalculverts with a square edge-inlet. The side tapered inlethas an enlarged face area with a tapered transition to theconstant culvert cell section. The inlet face has the same
height as the cell and its top and bottom are extensions ofthe top and bottom of the cell. The intersection of thesidewall tapers and the cell is defined as the throat section.Side-tapers may range from 6:1 to 4:1 taper beingrecommended as it results in a shorter inlet.
For a side-tapered inlet, there are two possible controlsections the face and the throat. H; shown on
Figure27.14, is the headwater depth measured from theface section invert and l{ is the headwater depthmeasured from the throat section invert. The weir crest isa third possible control section when a fall is used.
Slope Tapered Inlet- The slope tapered inlet, like the side-
tapered 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 ofthe inlet intersects the flatter slope of the cell, a thirdsection, designated the bend section, is formed.
The slope-tapered inlet is the most complex inlet
improvement. This type of inlet can in some instancesprovide a capacity more than 100o/o greater than that of a
conventional culvert with square edges. The increase in
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27-76 Urban Stomwater Management Manual Itt
Culverts
capacity depends largely upon the amount of fall availablebetween the invert at the face and invert at the throatsection. Construction difficulties are inherent, but thebenefits in increased performance can be great. Withproper design, a slope tapered inlet passes more flow at agiven headwater elevation than any other configuration.
Pl-Aftl
Slope-tapered inlets can be applied to both box culvertsand circular pipe culverts. For the latter application, asquare or round transition is normally used to connect therectangular slope-tapered inlet to the circular pipe.
NOTE:
Weir Slope to be Paved tohevent Upstream Degradationwhere Necessary.
ELEVATION
Suggested Slope for Fall 2:1 to 3:1
s----->.
Figure 27.13 Fallfor ConventionalCulvert with Flared Wingwalls
Urban Stormwater Management Manual
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27.TO MINIMUM EI{ER.GY C!.'LVERTS
In the coastal plains the natural slope of the land is oftenlittle more than a fraction one per thousand, which inconcrete conduits laid on natural grade, grass coveredchannels 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.
The aim of \he Minimum Energy Culvert" concept is toconcentrate the flow in a narrow, deep cross sectionflowing with critical velocity under maximum design flowthus taking advantage of the minimum specific energyunder critical flow condition (see Chapter 12). Thismaximises the flow per unit length of waterway crossing.By keeping the flow outside the supercritical region thedesigner avoids the energy loss in a hydraulic jump and
the cost of having to protect against the erosion associatedwith the jump.
Throat Section
Weir C,rest
Figure 27.14 Side-Tapered Improved Inlet
PI.AN
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q
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Bend S€ction
Throat Section
Figure 27.75 Slope-Tapered Improved Inlets forBox Culverts
Taper (4:1 To 5:1)
27-18 Urban Stormwater Management Manual
Culverb
The design requires knowledge of:
. 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 longitudinalsection of the culvefi is drawn up. (Figure 27.16). in doingso the following assumptions are made :
0 The energy line panllels the natural fall of theterrain
(iD Energy losses at enty and exit of cufuert aredisregarded
T[re justification for the ratter assumpton is that rosses atsrmth fansitions are generally small.
In his ontext it is warth nc$ng that $e exit expansion of Sesfeam bed needs to progress at a smaller angle than theenby angle if the formation of Snding eddies is to beavrided.
Using the equations:
Hr, = 1.5d, and
Q=Mrr[4 (27"14)
d, and H, en be bied and
PLAro
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coneponding values of b,ornpared.
Figure 27.16 Characteristic Flow Line of MinimumEnergy Culvert
One problem witi minimum-energy culvefts is that they arelocated in a dip below the drain or waterway inveft, creating apdential site for ponding and sediment deposition. Thepotential for ponding can sometimes be minimised by asmall diameter pipe drain or a channel connecting theculvert to a suitable point downstream. However thisapproach is not feasible if there are high sediment loads.
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Urban Stormwater Management f"lanualzl'!>
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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 pipeFlow
Relative Discharge, Velocity and Hydraulic Radius in part_full BoxCulvert Flow
Critical Depth in a Circular pipe
Critical Depth in a Rectangular (Box) Section
outlet control Nomograph - concrete pipe curvert Frowing Fuil withn = 0.012
ouuet control Nomograph - concrete Box curvert Frowing Fuil withn = 0.012
Outlet Conhol Nomograph - Corrugated Metat pipe (CMp) FtowingFullwith n = 0.024
Urfun Stormwater Management Manual27-27
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coefficient K" to apply velocity head v,2/2g for determination of head loss at entrance tocontrol. Entrance head loss Hu: K" V2,/2ga culvert operating under outlet
TYPE OF BARREL AND INLET
Pipe, Concrete
Projecting from fill, socket end
Projecting from fill, square cut end
Headwallor headwall and wingwalls
Socket end of pipe
Square-edge
Rounded (radius = t/LZ D)
Mitred to conform to fill slope
End-section conforming to fill slope (standard precast)Bevelfed edges, 33.7o or 45. bevels
Side-tapered or slope-tapered inlets
Ke
0.2
0.5
0.2
0.5
0.2
0.7
0.5
0.2
0.2
Pipe, or Pipe-Arch, Corrugated Steel
Projecting from fitl
Headwall or headwall and wingwalls, square edgeMiUed to conform to fill slope
End-section conforming to fill slope (standard prefab)Beveffed edges, 33.7" or 45" bevels
Side'tapered or slope-tapered inlets
0.9
0.5
0.7
u.5
0.2s
0.2
Box, Reinforced Concrete
Headwall
Square'edged on 3 edges 0.5Rounded on 3 edges to radius of I/12 barreldimension,
Or bevelled edges on 3 sides O.2Wingwalls at 30" to 75" to barrel
Square.edged at crown 0.4
Crown edge rounded to radius of Ut2 baneldimensionOr bevelled top edge
O.zWingwalls at 10. to 25" to banel
Square'edged at crown 0.5Wingwalls parallel (extension of sides)
Square'edged at crown 0.7Side-tapered or slope-tapered intet 0.2Projecting
Square.edged 0.7*
Bevelled edges, 33.7" or 45. bevels O.jo* Esiimated
Urbn Sbrmwater Management Manual
Design Chart27.2 Entrance Loss Coefficients
27-23
Culverb
D (m) $r*tl.l4.50
4.00
3.50
3.00
2.50
2.00
0.90'
0.80
0.70
0.60
0.50
0.40
0.30
300
200 F:omple
(3)
6
5
4
3
0.5 0.5
(1)
HWD
(2)
F6rrsrl4Ft-F-3
10080
605040
30
20
51.50
1.0
0.9
0.8
1.0
0.9
0.8
sl,F"1
0.8
0.60.50.4
0.3
0.2
0.15
8.H0.050.04
0.03
0.02
D=0.80m Q=1.7m3lsN
Inlet Ut' HW(m)D
(1) 2.60 2.08(2) 2.18 r.74(3) 2.20 t.76
-&',*o9-/
^Ey'\]./9*'j'
Inlet Type
(1) HeadwallwithSquare Edge
(2) HeadwallwithSod<et End
(3) Projectng wilhSocket End
5
5
4
3
10
8
3
t.oooa$)/
Design Chart 27.3 Inlet Control Nomograph - Concrete Pipe Culvert
Un27-24 Urban Stormwater Management lvlanuar
Cu/verts
D (m)
4.00
3.50
1.50
HWD
2) (3)109I76
5
4
3
_d")'1.00
o.st'
0.80
0.70
0.60
0.50
0.40
1.0
0.9
0.8
o.7
0.6
0.5
0.4
0.35
1.0
0.9
0.8
0.7
0.5
0.5
0.30
0.4
0.35
E1'Design Chart 27.4 Inlet Control Nomograph - Box Culvert
S f*Vr per mebe span)
r7O Example
h60 2.00 x 0.80m Box e = 8.0m3/s
rso n (1) (
f <o ffi= 4.0m3/s per m f g
F" In'|et ry il$ t:
F" til i'E i:,ffi,'+'E *,.s r, F,
Fy^ ,'#)" F IlZuu>" ^F' I1,7' $ F,, Iz I Angleofl . :f I/ f'H'JlE""'i\_gF tel_a l__ El. I5l ,/- E i-'.0 i:t- '/ ,FLo.ni
FF*g F[.' IFFi,i g [" I-ho'o E l-ou tt-0.3 r | |Erl
[ 0., l- 0., trltF[.$9 [04 |[-o.oe I IFo.os I I
L o.o+ B = span per cell L o.s L
xIos.9(u
WingwallFlare HWD Scale
30" - 75"90o (headwall)
0o (parallel)
1
2
3
z/-tJUrban Stormwater Management Man ual
Culverts
D (m) $t"lr14.614.30
3.0s
2.742
2.432.282.L2
1.97
l.ol
1.65
1.50
4.50
4.00
3:883.30
3.00
2.70
2.40
2.20
2.00
1.80
1.50
1.501.40
300
200
HW
D
(2) (3)
10080
605040
30
20
Fxample
D=0.90m Q= 1.8m3/sn
Inlet !W Hw(m)D
(1) 1.73 1.s8(2) 2.03 1.83(3) 2.10 1.8e
*.$o- -t9'>1l' '/
^$$'- -
\ z->-/'*- -
gu',
i
I
II
i_
1.0
0.9
tn
8
65
1
0.8
0.60.50.4
0.3
Inlet Edges
(1)Headwall(2)MiEed(3)Prcjecting
Design Chart 27.5 Inlet Control Nomograph * Conugated Metal Pipe (CMP) Culvert
Utt27-26 Urban Stormwater Management t lanuar
Culverb
-< I /-a/q
v/vrF/& ,(
,(
1 .7I
I
YI
Y
I I /v
I
,1'/
0.9
0.8
o 0.7
>
F 0'6
# o's
E 0.4
Q = Part - full Disdrarge
Q = Full Flow Discfrargev = Part - full Velocityvr = Full Flor VelocityR = Part - tull Flow Hydraulic RadiusPv= Full How l-ldraullc Radius
0.1
Q/Qr vive VRr0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 t.2
Relative Discharge Q/QF , Relauve Velocity v/v, , Relative Hydraulic Radius R/R,
Design Chaft 27.6 Relative Discharge, Velocity and Hydraulic Radius in Part-full pipe Flow.
Uban Stormwater Management Manual27-27
Culverts
vlD
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
n
0.40.1
UQr vtvr0.6 0.7 0.8 0.9 1.0 1.1 L.2 1,3 L.4 1.5
Q/Qr and vTvo
Design Chaft.27.7 Relative Discharge, Velocity and Hydraulic Radius in Part-full Box Culvert Flow.
NOTE:
Q/Q, = 1 ConesPonds to Full Flowwith Top Slab Fully Wetted
UQ, t 1 Disregards All Effectsof Top Slab
Part - Full FlowBox Culverts
k_E___t
27-?8 IJrban Stormwater Management Manual
*"-!:--+:t:"4
Culverts
1.0
6 1.2o O,n rt
0.30
1.5
Disctrarge $ f*?.1
10 20 30 40 s0 60 70 80
Discharse ft f*rlO(h.lD)
E
EI
a u.5c)oE(J
00.50.0
3.0
2.4
2.0Eus
cE. l.sE
cu 1.0
0.6
4.0
E-, 3.0t
I
tCL
EtoE 2.0Lu
1.2
rn\J/CriticalDepthCircular Pipe
Ufuan Stormwater Management Manual
Design Chart 27.8 Critical Depth in a Circular pioe
27-29
Culverts
$ tr'lrlg 1000l-800
FMFsoo
200
150
1008060504030
20
rs Q/N
10I654!J
2
1.5
0.60.50.4
0.20.15
0.10.080.060.05
(m)-20
-15
2
1.5
10
9
I7
6
5
'4
3
= 1.50 rtlm3ls
hs= 11.5
n=2'00fiv-
1.00.9
0.80.7
0.6
0.5
0.4
0.3
0.2
0.r5
:-Th. = 0.q67(r,rQsl* | l. l;
fttD) p- s---+,
CriticalDepthRectangular Section
Design Chart 27.9 Critical Depth in a Rectangular (Box) Section
27-30 Uhan Stormwater Management Manual
Culverts
0.2
0.3
0.4
0.5
0.6
0.8
1
/s)(m3
:80:70-60
:s0-40
-30
-20
109876
5
4
IN
"^
u'-'o ,"
" t-u.t
{tfr6"
0.70
0.60'oc
J
Q"9o
0.50
0.,10
Oudet ControlConrete Pipe Culvert
Flowing Fulln = 0.012
Design Chart 27.10 Outlet Control Nomograph - Concrete Pipe Culvert Flowing Full with n = 0.012
t40.90.80.70.6
0.5
0.4
0.3
0.2 rG Winswall Anole FEdoE-ffiifr-0.2
0.5
- Socket enO lerolectingE neaawaiij-- Bevelled Inlet (33.70 or 45o)- gqu-ap (Cut). EId (Proj. or Headwalt)- HabricaEd End Section
l*ban Stormwater Management Manual27-31
Cu/verts
m3/s)
-200
A (mz)-100 40_1 '
:90 J: 30t:60 Iso 2ol.40 l: 151:30 rgf. ttl:20 E]t1. oi: sJ,10 4l-8o 3-j'--\- I-Ul/:- r I_l< {(7rzl' \]:4 $-l-l
,t t+''.2 0.8 ]: 0.7 -l
: 0.61
, o'sl;1 0.O l-0.8 0.3 -l
-o.u l- 0.21
=o'4 I: 0.1 -j; o.z
::: O.t
ftt
TD
_tB
A = Ocs-sectionalArea per Cell
NOTE:
If BID = 0.5 to 2.0Glculate H from87.5
Design Chart 27.11 Outlet Control Nomograph - Concrete Box Culvert Flowing Full with n = 0.012
@
}rk"
.- =t_iq
IG WnswallAnqle & Edqe Finistl
0.2
0.5
0.7
- 0o or 90o Bodled Edge- 30o to 75o Banelled Edge- 90" Squre Edge- 10o to 25o Square Edge- Projectirg Square Edge
Urban Stormwater Management Manual27-32
Culverts
(rn3/s
:s0:40
:to.zo
D (m)
4.00
1 fln
0.90
0.70
0.60
o.eol-*
:10.8.6.5'4
3
2
aF=1+-0.8
0.60.5
0.4
0.3
0.3
0.4
0.5
0.5
0.8
I
t--9Pu-){PJ99 - -K" s'
1o
A$ 6,Lso %,\,p ?l Lrol Vso
SIl.rH=2.29 m
ocorccLfF
r50
3
4
5
6
OuUet ControlCorugated Steel Pipe
Flowing Full
n=0.024
Design Chart 27.12 Outiet Control Nomograph - Corrugated Metal Pipe (CMp) Flowing Full with n=0.024
as
-a$
-!e-0.20.250.5
o.70.9
WingwallAngle & Edge Finish- Side-tapered or Slope-.tapered- Bevelled Edge- leajygtt or Wingwails, Square Edge- Prefabricabd End Section- Iitred Paraltetb Fiil Stope- Projecting
Urban Stormwater [vlanagement Manua/27-33
Culvefts
APPEi{DIX 27.8 WOR,KED EXAMPI-E
27.8.1 Pipe Cutvert (Intet Control)
Given the following data, carcurate a suitabre curvert sizeand check the ouflet velocity to see if erosion will be aproblem.
Step 1 : Data
Flow = ?= 5.00 m3/s
Culvert lengfr = l. = 90m
Natural watenrrray invert levels :
Inlet: R.1.50.00m
OuUet: R.1.49.00m
Aaepbble upstream flood level: R.1.52.50
Desinble road pavement level : R.L. 52.00Minimurn height of pavement above head water : 0.30Btimated downstream tailwater level : R.L. 49.g0Maximum headwater height, HW, is the lesser of:i) Maximum practicalculvertheight:
52.00 - 0.30 - 50.00 = 1.70m, andii) Acceptable u/s flood level
52.50-50.00=2.50mTherefore maximum HW= t.70m
Step 2 : Assume Inlet Control
E*imate required waterway area assumin g V = 2.0 mls
Estimated area A = UV = 2.5 m2
D Try 1550mm pipe, D = 1.65m
Enter Design Chart 27.3 with e = 5.00m3/s.
HffD= t.09
HW = t.80 > 1.70m maximum. Not acceptable
ii) Try 1800mm pipe, D = 1.8m
Obb,in Hl/r//D = 0.93
HW= L.67m
But maximum culvert height available is only 1.70m
iii) Try twin lines, 2/1050mm
D = 1.05m g/N = 2.5m3/s
Qbhin HIU/D = 1.62
HW= L.70m
Use 2/1050mm diameter pipes
Step 3 : Check for Oufiet ControlHeight of tailwater above invert:TW = 49.80 - 49.00 = 0.g0 < proposed1.05m
pipe diameter of
Diagram in Figure 27.7(c) depicts actual conditions, flowingfull for part of the tength.
Now enter Design chart 27.g to determine criticar deprth
4 = 0.83m
d, + D _ 0.83+1.052 0.94 > TW = 0.g0
as ouflined in Section 27.3.3 enter Design Chart 27.10 withI=90mD= 1.05m
Ke= 0.2 (socket end of pipe upsiream)
Then use A-/N = 2.50 m3/s and obtain f/r= 1.15mFall of culvert invert, L, = 50.00 - 49.00 = 1.00 hence:
HW =( dc : Dl* s-rs = 0.94+1.15-1.00 = 1.09mt2l'
HW(inlet control) = 1.70m greater thanHl1/ (outletcontrol) = 1.09m
Therefore inlet control governs.
Step4:FlowVelocity
For 1050mm diameter pipes:
-n2A="1 =0.87 and s= 1/90 = 0.01114
From Colebrook-White's Chart for k = 0.6mm (Figure 25.84in Chapter 25, Appendix 25.B):
Qr= 3.1msls
Vr= 3.6 m/s
Because the culvert does not flow full it is necessary to usethe part-full flow relationships ptotted in Design Chart 27.6.
UQr= 2.5/3.t = 0.81 and from Design Chart27.6,
V/Vr= L.0 and r= 1.0 x 3.G = 3.G m/s
y/D=0.75and y= 0.75x 1.05
= 0.79 < d. = 0.83
Unless the drain, which receives the culvert discharge,flows at supercritical flow a hydraulic jump will form at theculvert outlet.
Step 5 : Surrnnaly
Use 2/1050 mm diameter concrete pipes with socket endfacing upstream.
Uban Stamwater Management l4anual27-35
Pipes will flow with inlet control with a headwater height of1.70m and headwater R.L. = 51.70m.
Outlet velocity = 3.6 m/s and the possibility of scour or theformation of a hydraulic jump at the outlet must bechecked.
27,8.2 Bor Culvert (Inlet Control)
Step 1 :
Using the same data as provided for the previous pipeculvert, calculate a suitable box culvert size and check forthe effects of the ouUet velocity.
Step 2 : Assume Inlet Control
Estirnate required waterway area assuming V = 2,0 mls
Estimated areaA= W= 2.5m2
Try 1800 (wide) x 1200 (high) box culvert.
Enter Design Chaft27.4 with Q= 5.00 m3/s.
n-Y- - 1 1qNB - 1,te
Draw line and obtain HffD = I.30HW = t.30 x 1.2 = 1.56 < 1.70m, which is acceptable
Step 3 : Check for Outlet Control
TW=0.8 < 1.2m
Enter Design Chart 27.9 with
dr= 0'92m
d.+D 0.92+1.20-:- = 1.06, which exceeds the22tailwater depth of 0.80m
As outlined in section 27.3.3 enter Design Chart 27.11 withl=90mA=t.2x1.8=2.16m2ku = 0'5
Draw line with Q = 5.0m3/s then draw the other line toobtain H= 0.45m
Fall of culvet invert, l, = 50.00 - 49.00 = 1.00m hence:
rJ +DHW=-c'-+H-L
2"-s
=1.06 + 0.45 - 1.00 = 0.51m
HW(inlet control) = 1.56m which is greater than
HW(outlet control) = 0.51m
Therefore inlet control governs.
Step4:FlowVelocity
Hydraulic radius R = ffit'ffi*;
R=--?:ltr- =o.36m2(1.8 + 1.2)
Equivalent D= 4x 0.36 = 1.44m and s= 1/90 = 0.011
From Colebrook-White's Chart for k = 0.6mm (Figure 25.84in , Appendix 25.8) we get:
Vr= 4.4mls
Qr= 2.!6 x 4.4 = 9.5 m3/s
Eecause the culvert does noi fiow full it is necessary to usethe paft-fullflow relationships plotted in Design Chart27.7.
I -s'o=0.526.Q, 9.5
and from Design Chart 27.7 for B/D= L.5
V; = t.O2 and y = L.02 x 4.4 = 4.5 m/s
= 0.53 and y = 0.53 x 1.2 = 0.64 <d. = 0.92m
Hence the same remark about hydraulic jump applies asmade for pipes (see example 1: step 4).
Step 5: Summary
Use 1800 x 1200mm concrete box culvert with souareedges.
Culvert will flow with inlet control with a headwater heightof 1.5m and headwater R.L. = 51.5m
Outlet velocity = 4.5 m/s and the possibility of erosion or a
hydraulic jump must be checked.
27.8.3 Pipe Culveft (Outlet Control)
Given the following data calculate a suitable pipe size and
check the outlet velocity for the possibility of erosion.
Step 1 : Data
Flow P= 0.5 m3/s
Culvertlength, l=120mNatural waterway invert levels : inlet R.L. = 100.0m
: outlet R.L. = 99.0m
Acceptable upstream flood level : R.L. = 103.0m
I
I
-l
I
-1C
r
i
-t(
vD
I
,lI
I
I
i
-i,
I
s
I
I
f
I
-ic
I-2
I(
27-36 Urban Stormwater Management f,lanual
Cutverts
Desirable road pavement level : R.L. = 102.5mMinimum height of road above headwater level : 0.5mRquired freeboard : Nil
Estimated downstream tailwater level : R.L. = 100.5mMaximum headwater height, HW, isthe lesser of:iii) Maximum practical culveft height:
102.5- 0.5 * 100.0 = 2.0m, andiv) Acceptable u/s flood level
103.0-100.00=3.0mTherefore Maximum HW= 2.Om
Step 2 : Assurne Intet Control
Estimate required waterway area assumin g V = Z.O m/s
Estimated area A = AV = 0.25 m2
Try450mmpipe,D=0.45m
Enter Design Chart 27.3 with e/N = 0.5 m3/s
Draw line and obtain for Inlet Type 2:HWD= 2.8
HW= 2.8 x 0.45 = 1.26m for inlet control
This depth is tess than the limit of 2.0m.
Step 3 : Check for Outtet Controt
Height of tailwater above inveft:
W= 100.5 - 99.0 = 1.50 > 0.45m
Diagram in Figure 27.7(a) depicts flow condition, i.e. pipe isflowing full with a submerged outlet. Now enter DesignChart 27.10 with:
D= 450mm
I = 120m
ke = 0.2 (socket end of pipe upstream)
Then use ? = 0.5 m37s to draw line and obtarn
H = 3.4m
Fall of culvert invert, 1., = f OO.O - 99.0 = 1.00 hence:
HW= TW+ H- Lr= 1.5 + 3.4 - 1,0 = 3.9m
Note that because 3.9m > HWfor inlet control (1.26m), theculvert is under ouflet control.
However the design is unacceptable because HWr., =2.0m.
Return to step 2 using 525mm pipe diameter in DesignChart 27.3 and obtain HW/D = L.6Z
HW= 1.62 x 0.525 = 0.g5m for inlet control
Now check for ouflet control. Re_enter Design Chart 27.10with D = 0.525m and obtain H = L.Sm hencJ:
HW= L.5 + 1.5 _ 1.0 = 2.0m
This headwater depth is acceptable.
and since 2.0m > 0.95m = HW(inletcontrol) ouflet controlgoverns.
With HW and TW both well above the crown of the pipeand a _moderate slope of 1A/e0 = 0.0083 the pipe witlflow full hence:
v= UA
,. 4x0.5" =;oE = z'3m / s
This velocity must be checked against erosion danger atoutlet (Tabte 27.1).
Step 4 : Summary
Use a single line of 525mm diameter concrete pipes withsocket end upstream.
The pipe wiil flow full under outlet control and with a HWheight of 1.3m giving a HW R.L. of 101.3m and an oufletvelocity of 2.3m/s.
27,8.4 Box Culvert (OuUet Control)
Step 1 : Using the same data as provided for the previouspipe culvert calculate a suitable box culvert size ancl checkfor the effects of the outlet velocity.
Step 2 :Assume Inlet Control
Using the previous estimate of required area, try 600mm x300mm box culvert.
Enter Design Chart27.4 with e= 0.5 m3/s
UNB = 0.5/0.6 = 0.83 m37s7m
Draw fine and obtain HW/D = 4.3
Hl,1/= 4.3 x 0.30 = 1.29m < 2.0m
Step 3 : Check for Outlet Control
TW = 1.50m (see example 3) > 0.30m hence diagram inFigure27.7(a) depicts flow condition, i.e. culvert is flowingfullwith a submerged outlet.
A=0.6x0.3=0.18m2
Urban Stormwater Management Manual27-37
Cu/verts
Calculate H from Design Chart 27.11, noting that B/D =2.0so the chart is applicable.
H= lAm
then HW= TW+ H- l, =1.5 + 1.4 - 1.0 = 1.9m
Note that 1.9m > 1.29m, the headwater depth for inletcontrol, so outlet control appties.
However the design is not acceptable because of the risk ofclogging of the 300mm deep culvert due to debris.
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, and
H= 0.95m and HW= 1.45m for outlet control.
This is acceptable because 1.45 < HW ^", = 2.0
And the culvert flows with outlet control since:
1.45m > 0.9m = HW(inlet control)
As the culvert flows full,
,,- rt/A- Q'5v=tJ/A=m=2.2m/s
Step 4 : Summary
Use a single 600 x 375 concrete box culveft with square
edges.
The culvert will flow with outlet control with a HW height of1.45m giving a HW R.L. of 101.45 and an outlet velocity of2.2mls.
27.8.5 Mlninrum Energy Culveft
Given a required design flow of 25 m3/s and referring toFigure 27.16 with chosen widths b as set out in thefollowing table, calculate suitable levels for the bottomprofile of the flared culvert entry at the given sections toachieve critical flow through the culveft. Choose an
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.
Section 1-1 2-2 3-3
width b t4 9 4
q= Q/b 1.79 2.78 6.25
dr=1'[m u.ov 0.92 1.59
trial depth D 1.10 1.30 1.58
v= Qr/A 1A? 2.t4 3.96
v2/29 0.13 0.23 0.80
Hr= D+ v2/2g t.23 1.53 2.38
The depth of flow is required to be critical in the culvert
and unchanged subcritical at the start of the flared entry.
Intermediate depths are interpolated.
For chosen values of d, H, can be calculated and the
bottom level of the culvert and approach is located 4metre 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
culvert with a flow area 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.
27-38 lJrban,stormwater Management Manual
ACKNOWLEDGEMENTS
TECHNICAL COMMITTEE 6 - DRAINA.GE
Main Committee Member.s
Nafisah Hj. Abdul Aziz
Ahmad Fuad Emby
Wan Suraya Mustaffa
Normala Hassan
Teh Ming Hu
Lim Kim Oum
Alias Hashim
Low Kom Sing
Nor Asiah Othman
Johan Les Hare Abdullah
Chairman
Deputy Chairman
Secretary
Alternate Secretary
Committee member
Committee member
Committee member
Committee member
Committee member
Editor
Lim Kim Oum
Normala Hassan
Yeap Chin Seong
Chin Kok Hee
K. Nanthakumar
Chia Chong Wing
Ng Kim Hooi
Chairman
Secretary
Committee member
Cornmittee member
Committee member
Committee member
Committee member
ACKNOWLEDGEMENTS
Volume 2 is a review of the Arahan Teknik (Jalan) 15197 - INTERMEDIATEGUIDE TO DRAINAGE DESIGN OF ROADS, the chapter was authored originallyby Mustafa Shamsudin of Public Works Department Malaysia.
Volume 2 now provides guidelines to the practical design of culverts, with a fewworked examples provided in Appendix 1, which is reprinted from Jabatan Pengairandan Saliran publication - Urban Stormwater Management Manual for Malaysia(MASMA 2000).
Thanks are due to:
- 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 theguidance and encouragement given in the preparation of Volume 2.
- Members of the Technical Committee 6 - Drainage and Sub-Committee forHydraulic Design of Cuiverts for their untiring efforts to ensure timelycompletion of Volume 2.