r-
FOREWORD Road Engineering Association of Malaysia (REAM), through the cooperation and support of various road authorities and engineering institution, in Muluysia, publishes a series of official documents on STANDARDS, sppcu'tcATloNs, cunnuxgs, MANUAL and TECHNICAL NOTES which are related to road engineering. The aim of such publication is to achieve quality and consistency in road and highway construction, operation and maintenance.
The cooperating bodies are:Public Works Department Malaysia (pWD) Malaysian Highway Authority (MHA) Department of Irrigation & Drainage (DID) The Institution of Engineers Malaysia (IEM) The Institution of Highways & Transportation (IHT Malaysian Branch) The production of such documents is carried through several stages. At the Forum on Technology and Road Management organized u/ewnrnEAM in Novemb er 1997, Technical committe-e 6 Drainage was formed with the intention to review Arahan Teknik (Jalan) t5/97 - TNTERMEDIATE GUIDE To DRAINAGE DESIGN
ROADS' Members
of the committee were drawn from
oF
various gou"*-"rrt departments and agencies, and from the private sector including privatized road operators, engineering consultants and drainage products manufacturers and
contactors.
Technical committee 6 was divided into three sub-committees to review Arahan Teknik (Jalan) 15/91 and subsequently produced ,GUIDELINES FoR R.OAD
DRAINAGE DESIGN' consisting of the ioriowing uolumes, Volume 1 Volume 2 Volume 3 Volume 4 Volume 5 -
i
I
Hydrological Analysis Hydraulic Design of Culverts Hydraulic Considerations in Bridge Design Surface Drainase Subsoil Drainale
The drafts of all documents were presented at workshops during the Fourth and Fifth Malaysian Road Conferences held in 2000 and 2002 reipectively. The comments and suggestions received from the workshop participant, *Jr. reviewed and incorporated in the finalized documents.
i I i I
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ROAD ENGINEERING ASSOCIATION OF MALAYSIA 46-A, Jalan Bola Tampar r3/r4,section 13,40100 Shah Alam, selangor, Maraysia Tel:603-5513 6521 Fax:5513 6523 e_mail:
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TABLE OF CONTENTS
i a.
j
VAAP
i
:
i
4.1
INTRODUCTION
4.2
IMPORTANCE OF SURFACE DRAINAGE
4.3
4.4
...,.4-I
.... COMPONENTS OF SURFACE DRAINAGE 4.3.1 Crowned Roadways 4,3.2 Shoulder Slopes 4.3.3 Toe, Shoulder and Roadside Drain 4.3.4 Discharge Drain 4.3 .5 Interceptor Drain (Catch Drain) 4.3.6 Bench (Cuts) and Berm (Fill) Drains ..... 4.3.7 Outfall (Fi11) and Cascading (Cut) Drains ..... 4.3.8 Median Drain 4.3.9 Gutter 4.3.10 Kerb Opening Inlets 4.3.11 Sumps SURFACE DRAINAGE IN RURAL AREA
... 4-T
..."..4-2 "
..
.. 4-3
....4-3
...4-4 ....4-4 .....
..4-74
..... "..4-14
..".4-I5
.".....4-I5
........4-I5 .....4-16 .........4-26
.,...,..4-26
(FLAT AND ROLLING AREAS) SURFACE DRAINAGE IN URBAN
4.5.1
AREA
Inlets General 4.5.I.2 Types of Inlet
.....4-28
Drainage
4.5.7.1
...4-28
4.5"I.3
........4-34 ......4-36
Recommended Use of
Inlets
SURFACE DRAINAGE IN MOUNTAINOUS
4.6.1 4.6.2 4.6.3 4.7
.....,. .,4-28
AREA
Section Drainage for Fill Section Drainage for Cut
Route Location and Drainage
.......4-36
...... 4-36
....
FLOW CAPACITY DESIGN OF SURFACE DRAINS
.l 4.7 .2 4.1 .3 4.7 .4 4.7 .5 4.1.6 4.1 .1
4.7
..4-36
Analysis Hydraulic Analysis Basic Design Procedures Calculation Worksheet Kerb and Gutter Inlet Spacing Calculation ... Inlet Pits
.....4-36
.
........4-37
Hydrologic
......4-31 ..
..
....4-39
........4-40 ...4-42
....4-44 ....4-50
.....4-50
r I
!
4.1.7.1 Types of InlerFits...
l
........4-51
.2
Allowance for Blockage. .. . 4.7.7.3 Type BKSE3OIntet 4 7 1 4 Type BKLE3O Inlet 4.7 .1 .5 Hydraulic Design of Kerbs and Gutters and Stormwater Inlets. 4.7 .1
... ....4_51 ..4_51 ..
.. .. ...4_52
.....4_52
LIST OF FIGURES
4.1 Typical Road Drainage Layout Cross Section Fig'4'2 Exampleof DrainageLayoutPlanforCutandEmbankment.... Fig.
_ i
Fig.
4.3 Typical
Fig.
4.4 Interceptor Drain
Road Drainage
4.5
Fig.4.9
Fig. 4.12 Outfail
i
.......4_g
...4-g ....4_70
.......4_1tr ..... "..4_12
.......4_I7 .........4_1g
Drain
Fig. 4.13 Concealed Roadside Drain in Rural
I
...4_j
Toe Drain
- Urban Road . Fig. 4.1 1 Median Drain Supereievation Section -
I
.........4-6
Berm
Fig. 4.10Median Drain
-i
.. . .. .4_5
Elemenrs
Drain Fig.4.6 Bench Drain Fig. 4.7 Roadside Drain Fig. 4.8 Shoulder Drain Fig.
...
.
..4_1g
Roads Fig. 4.14 Concealed Roadside Drain (in Cut) in Major Highways Fig. 4.15 Concealed Roadside Drain (in Fill) in Major Highways Fig. 4.16Swale in Roadside/Median Drain Frg. 4.17 Concealed Drain at Median Fig. 4.18 Recommended Type of Kerb Opening Inlet . Fig. 4.19 Typical highway cross Section with Good Drainage Features Fig' 4.20 Guide for Locarions of Kerb openings and Inret pits ... Fig. 4.2I Typical Drainage Elements in Urban Areas Fig. 4.22Types of Storm Drain Inlets Fig. 4.23 Depressed Grared Inlet .
.......4_33
Fig. 4.24 Components of the Stormwater System Network considered for the Sg. Rokam Catchment Analysis
...4_41
Fig. 4.25 Kerb and Gutter showing Half Road Flow
. Fig. 4.26F1owchart for Calculation of Inlet pit Spacing Fig. 4.27 Calculation of Gutrer Flow and pit Spacing Fig. 4.28 Standard Inlet pit Types
.......4_20 "...4_Zl
.
...4_Zz ...4_23
...4_24 .. ..4_25 .
..
..4_21 .
.4-30
..,..4_31 ..4_32
......4_4g ..4_53
.....4_54
......4_54
LIST OF TABLES Table
4.1
Allowable Roadways for Initial Storm Runoff in terms of
Table 4.2
. Allowable Average Velocity
Table 4.3
Suggested Values of Manning's Roughness Coefficient,
Table 4.4
Example of Rational Method Calculation for Small Catchments ...... ....4-46
Table 4.5
Design Acceptance Criteria for Road Gutter
Table 4.6
Mannins's
" '4-29
Pavement Encroachment ..
"4-4I
'n' andFlow Correction
Flow
'
Factor for Gutter
n
'''''"'4-4I ..4-49
Flow... ...." '4-49
APPENDICES
Appendix 4.B
Charts Inlet Pit Capacity Design Chart
Appendix 4.C
Worked Examples
GutterFlow Design
Appendix 4.A
ATTACHMENT Reprint
""""'4-55 " "'4-56
1
of. Chapter 24 :
Stormwater Inlets, Urban Stormwater Management Manual for
Malaysia
F;
111
5...
-
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VOLUME 4. SURF'ACE DR.AINAGE 4.1
INTRODUCTION One of the most important aspects of the location and design of rural highways and city streets ir_,h." necessity for providing adequate clrainage. Ri"quut" and eccnomical drainage is absolutely essential ior the protection of the investment made in a highway structure and for safe-guarding the lives of the persons who use it.
Highway drainage m_ay be generally defined as the process of controliing and removing excess surface and underground water endountered within the limits of the right-of-way and adjacent territory. The flow of surface water with which the highway engineer is concerned generally results from precipitation in the form of rain. A portion of the surface water enters or "percolates" into the soil, while the remiinder stays on the surface of the ground and must be carried on, beside, beneath, o. u*uy from the travelled way. In certain instance the control ;;, (ground water) may be important, as in the case "t "ro"rgr"r; of an undertround flow encountered in a highway cut or in a iocation where tire water table iies ciose to the surface of the ground. Measures taken to control the flow of surface water are generally termed "surface drainage", while those dealing with groundwater in its various forms are called "subsurface drainage". This volume will only discuss the former part ofthe drainage - surface drainage.
The solution of drainage problems should not be regarded as a separate element of highway or street design. Rather, consfoerations relative to drainage must accompany every step in location and design, so that the final design and resulting construction op-ration will provide for optimum drainage
at reasonable cost.
4.2
IMPORTANCE OF SURFACE DRAINAGE one of the major causes of pavement failure in highways is water. It has been appreciated since roads were first built that iheir stability can only be maintained if the surface and foundation remain in a relativety ory condition. Water brings about pavement failures within highways by: _
(a)
hydraulic forces within pavement surfacings;
(b)
softening the road surface when it is constructed of soil or sand-clay or gravel or water bound macadam:
(c)
washing out unprotected areas of the top surface3dsion of side slopes forming gullies, erosion of side drains. etc.:
i E
,E
4-1
4.2
Irnportance of Surface Drainage
-
(Cont'd)
(d)
generally softening of the ground and embankments can give rise to slip failures;
(e)
softening the subgrade soil and decreasing its bearing capacity.
Preventive measures include changing of watercourses, intercepting and disposal of water, bank protection and soil treatment. Drainage works designed to protect the road from these effects may be grouped under the following headings: (a.)
Surface Drainage Works - interception and diversion of the surface water which would otherwise flow across the road or along it and cause erosion.
(b)
o,,L^^:I T\--i.-^ -^ L)r4IIr4tg JLTUSUrI
--^-,: ) *^*^"-! .'^.'j -rapid removai ano lnieicepilJn i-.^,.^^^+i
-.1' oi
.. seepage
oi
ground water. (c)
Cross Drainage Works - interception and disposal of natural drainage water under the road surface.
The cost of drainage is quite expensive; hence careful consideration must be given to determine an economical drainage systems and protection of the road from floods in all phases of its location and design. This in turn will prove to be effective in both construction and on soins maintenance costs. Environmentally, the water quality f}om the surface run-off should also be considered to minimise any adverse impact. Siitation of watercourses, which in turn affect the quality and drainage capacity of the river system, should be discouraged. The concept of using swales (shallow grassed lined drains) to slow down the discharge and trap silt befbre surface run-off discharges into natural watercourse should be encouraged. Alternatively, the surface water can be discharged into a wetland area to enable the water to be filtered prior to the final discharge into the stream.
4.3
COMPONENTS OF SURFACE DRAINAGE The function of surface drainage is to remove excess water brought about by rainfall. Surface drainage systems in built-up areas are generally connected to other drainage systems such as storm sewers, lakes or rivers while that in rural areas are connected to natural drainage channels or watercourses. The main components of surface drainage are: (a)
(b) (c) (d) (e.)
crowned roadways shoulder slopes roadside drains toe drains shoulder drains
l l l
A'
present in all types ofroad present in all types ofroad present in ali types ofroad
4.3
Components of Surface Drainage
(D (g) (h) (i) (t) (k) (l)
- (Cont'd)
interceptor drains
most coffrmon in cut/fill areas most common in cut/fill areas most common in cut/fill areas most common in high class of road most common in urban areas most common in urban areas
bench / berm drains
outfall / cascadins drains median drains gutters kerb openings sumps
A11 drainage systems must be connected
to a natural watercourse or to a storrrr sewer in urban areas subject to negotiations with relevant authorities.
4.3.1
Crowned Roadways Roadway surfaces are normally crowned or superelevated to facilitate the removar of surface water from the wearing iurface. The amount of. crown varies with the type of surfaces; -it is generally 10w for impervious surfaces such -as asphaltic concrete and increases for pervious surfaces such as gravel or earth. For details, please refer to "A Guide to Geometric Design of Roads (REAM - GL 2/2002),,. The common crossfarl used for paved roads is 2.57o for a' singte carriageway and 2.0vo for a duaicarriageway, ho*"u.r, up to 3.\va can be used for coarse surfaces or when trrJ ro"jltuoinat profite of the road is flat eg. less than 0.5Vo.
4.3.2 Shoulder Slopes Road shoulders provide lateral clearances and emergency stopping space and are used to facilitate drainage away from the road surface into roadside drains' To prevent water ponding and edge scour, the shoulders need to be maintiined and graOea,"guiJy. Shoulder slopes vary; unsealed shouiders have a greater slope than the seaied shoulders, a3d. normally srope at 4vo. For more details, 1e please refer to " A Guide to Geometric Design of Roads erana - GL 2/2002).
The unsealed shoulders can affect the water quality and surface water run-off by carrying silts with it and subsequently cause siltation in the stream. Road shoulders for major roads are generally sealed for safety of the motorist as well as for ease of maintenance and grassed areas should be considered to improve the quality of the run_off. F
I
4-3
4.3.3
Toe, Stroulder and trloadside Drains
The function of the toe, shoulder and roadside drains are to coilect water that has fallen on the carriageway and the batters of cuttings or embankments to direct to the edge of the formation. Toe drains are used at the base of embankments wherever the road is in a fiii section and shoulder drains are used along the shoulders. Roadside drains are used along the road edge and can also cater for the drainage of the abutting developed area. Generally, the gradient follows that of road (see Fig. 4.1 and Ftg. 4.2) and is usually shallow (only for toe and shoulder drain) since the catchment area is restricted to the roadway and the cut slope. The most common types of roadside and shoulder drains are detailed at Fig. 4.1 and Fig. 4.8'
built on flat grades to match the road grade, they must either have a large cross-section area or have frequeni discharge points. Depending upon the nature of the material in which they are constructed and their longitudinal grade, the toe, shoulder and roadside drains may be lined with Stone, concrete, or a bitumen seal to resist the action of scouring.
Because toe, shoulder and roadside drains are often
The use of brickside or brickwall drains should be discouraged on major roads due to their lack of structural integrity, drains with vertical walls should be constructed of reinforced concrete. Along minor roads where brickwall drains are used, the height of the brickwall should not exceed 750mm and reinforced concrete stiffeners shall be provided at 3.0m interval. Concealed roadside drains are preferred to exposed drains, examples of which are shown in Fig. 4.13,4.I4 and 4.15'
For environmental considerations, the concept of incorporating swale in roadside and median drainage should be considered and are shown in Fig. 4.16.
4.3.4
Discharge Drain
Discharge drains are located along the boundary line between the embankment and the natural ground to collect the discharge from the toe of shoulder drains that run down the embankment slopes. It can also collect flow from berm drains in high fills. The comrnon types used are generally U-shaped precast or trapezoidal in shape (see Fig. 4.e).
4-4
r
INTERCIPTOR DRAIN
I
i
uTqvl
BENCH
GROUND LEVIL
r
DRAIN.J
,t-
+
\ " '/
\./ Y I
ROADSiDE DRAIN _-J
(a) cUt
SnCUOt'l
BtRr/ DRA|N--l
i NATURAL GROUND LTVEL
Lro, -t
!
ooo,*
b) Frrr
l t
sEcTroN
i i I t
i
I i
FIG. 4.1
G_
i I
I I
I
-I
+5
-\
suBSorL
DRArN
INTTRCEPTOR DRAIN
BENCH DRAIN
SUI./P
TOE DRAIN PIPE CULVIRT
nn
stoPE
FIG. 4.2 EXAMPTE OF DRAINAGE LAYOUT PLAN FOR CUT AND EMBANKMENT
I
+6
t
t
t-
.L-
OULDER DRAIN
SUMP
TOE DRAIN CULVIRT
FII.L
FIG. 4.2 EXAMPLE OF DRAINAGE TAYOUT
STOPE
PLAN
FOR CUT AND EMBANKMENT
4-6
i I
;t
_-.L
--
INTIRCIPTOR DRAIN
INTERCIPTOR DRAIN
NATURAL GROUND LTVIL l?
Y
r1
[/EDIAN
\
I
BENCH DRAIN-J
ROADSIDI DRAIN SUBSOIL DRAIN
ROADSIDI DRAIN SUBSOIL DRAjN
[/EDIAN
DRAiN
FIG. 4.3
+7
^ \ T\LL GREDWS
CONCRETE LINING
SQUARI MTSH A1 42 DIA. 6 AT 2OO BOTHWAYS
CAST
IN-SIIU
CONCRNTE DRAIN
150mm THICK STONE
PITCHING
GROUTEDWITHl:3
.ues.}ry&
CEMENT MORTAR
50mm
STONE-IIMD DMIN
FIG. 4,4 INTERCEPTOR DRAIN
4-8
CONCRETE BLINDING
SQUART MISH 4142 6 AT 2OO BOTHWAYS
DIA.
CONCRETI
zzffi
I
tsERM pRAIi.i TYPE (EFi) CAST IN-SNU CONCRETE V DRAIN
225mm HALF ROUND GLAZTD EARTHENWARE DRAIN
100mm THK. CONCRITI 100mm THK. CONC.
SURROU
IIALF ROUND GI,AZED
EARTHENTARE
FIG. 4.5 BERM DAAIN
+9
SQUART MESH A1 42
DIA.
c
6 AT
2OO
BOTHWAYS
iy
Svry
1
CAST IN-SITU CO}TCRETE
V
25mm THK
a AVY
CONCRETE
DRAIN
r\U
rq.z 5vry 100mm THK"
CONCRITE
100mm THK. CONC.
SURROUND
HAI,,F ROI'ND GI,AZED EARTHE}ITARE DRAIN
FIG. 4"6 BENCH DRAIN
+10
I
_tI
250 FORMATION LtVtL
500
EARTH DRAIN
250
SUB_BA FORMATION LEVIL
500
125mm THICK C0NCRIIE SQUART MISH A142
DIA.
6 AT 2OO BOTHWAYS
CAST IN-SITU CONCRETE DRAIN
SUB_BASE
250
FORMATION LEVIL
500 CONCRITE BLINDING
150mm
THICK STONE PITCHING
GROUTED WITH
1:SCEMINTMORTAR
STONE-UNED DRAIN
FIG. 4.7
ROADSIDE DRAIN
+11
]275
MINIMUM
)LUTL
R.C. U-DRAIN SQUARE MTSH DIA. AT 1OO BOTHWAYS
6
I f
sEonrJER DRArN
(Spl)
-,\J 1/
+12 - -:Er?ryT":trffg:IlYii,i"-t r.3.. --:@
I
EIIBANKT{Er{T ToE pRAIN EARTE DRAIN
1 (TD
1)
,
125mm THICK CONCRilE SQUART MESH A142
DIA.
6 AT 2OO BOTHWAYS
1000
r-*;;1
fl
|
ETIBANKMENT ToE DRAIN 2 (Tp 2) CAST IN-SrrtJ CONCRETE DRAIN
,
50mm CONCRilE
BLINDING
1000
7*"
fi
,
I
150mm iHICK STONI PITCHING GROUTED WITH
STOM-UNED
DRAIN
FIG. +.9 TOE DRAIN
+13
1
: 3 CtMtNT
MORTAR
4.3.5 Interceptor Drain
(Catch Drain)
Interceptor drains are located along the uppermost edge of cut slopes where the cutting begins, and along the edge of the cut slope descending towards the lowest point of the natural watercourse. Due to the position of the interceptor drain, it must be sufficiently large to account for siltation and debris collection. Water from the cut slope is collected by bench drains which then discharge into the interceptor drain which is usually joined to a main cascading or outfall drain (see Fig. 4.1 to Fig. 4.3). Types of interceptor drains to be used depend upon the type of soil, geographic features and the design flow volume. The common types used in Malaysia are trapezoidal in shape (see Fig. 4.4). T\e use of precast block sections for interceptor drains should be discouraged because of possible seepage problems. Interceptor drains are cofiImon in rural roads involving deep cuts. Problems that might occur due to improper bacldilling resulting in water flowing on either side of the drain instead of within the drain and. can result in erosion or slope failure. At possible problem location, backfilling must be well compacted and strips of ground on either or both sides should be turfed. Interceptor drains should be lined to reduce seepage and prevent scouring and erosion which eventualiy could lead to siope failure. '
4.3.6
Bench (Cut) and Berm (Fill) Drains Bench drains are piaced longitudinally along the bench of a cut section and berm drains are located on the berm of a fill section to intersect water running down the slope. Each bench or berm drain should catch rainwater falling on the slope immediately above. Bench or berm drains are provided on each bench or berm on the inner edge of the cut and embankment slopes respectively. Benches and berms are usually provided at 6m height intervals and are generally shallow with their gradients following the bench and berm gradients (see Fig. 4.5 and Fig. 4.6).
Similar problems may be encountered as those for the interceptor drains"
Bench or berm drains should be continuous and preferably be cast insitu reinforced concrete to overcome dislocation and seepage problems that are normally encountered with precast sections. When precast drains are used, the precast sections should be provided with a concrete surround from the base to the top of the precast section as shown in Fig. 4.5 and Fi-e 4.6.
4-14
4.3.7 Outfall (Fill)
and Cascading (Cut) Drains
Outfall and cascading drains are between the shoulder drain and bench
/ berm drain and the interceptor drain. Outfail drains are provided at the iowest point of a sag curve to cater for water flowing along the roadside and shoulder drains. Cascading / outfall drains also cater for natural drainage path that is cut off on top of a cut or fill section. Outfall drains are necessary where culverts under the road are discharging on to the fill slope. For a small discharge, the common types of outfall drains are the eggshaped precast drains, commonly known as cascade drains (see Fig. 4.12). For a large discharge, it is recommended that the outfall drains should be reinforced concrete cast in-site U-shaped chutes or steel pipes.
Cascade drains or outfall drains should be provided with sufficient depth of side siopes to prevent splashing over of run-off, which can cause scouring or erosion ofthe grassed slopes.
4.3.8 Median Drain Median drains normally are required
in
multiple-lane divided
highways. Median drains are generally a shaiiow depressed area, and at intervals the water is intercepted by transverse channels that discharge into a sewer or storm drain. The function of median drain is to collect surface water'which runs towards the centrai median and are generally of smali section and gentle gradient.
The common types are egg-shaped precast and haif-round glazed earthenware (225mm or 300mm diameter)(see Fig. 4.10 and Fig. 4.11). The use of brickwalls should be discouraged for median drains due to their poor structural integrity; continuous full reinforced concrete drain is preferred. The concealed concept for median drains with intermittent openings should also be considered, please refer to Fig. 4.17 .
.
Median drains are particularly used both in urban and rural roads of high geometric design standards (U5, U6 and R6).
4.3.9 Gutter Gutters are small channels provided at the edge of the roadways or shouiders for drainage purposes in urban areas, they are not covered, and can either be V-shaped or egg-shaped. Whep-used with kerbs, gutters are located in front of the kerbs and tafil5e precast or cast-insitu.
The size and slope of gutter must be carefully designed so as not to cause sedimentation and erosion within the gutter.
4-r5
4.3.9 Gutter -
'
(Cont'd)
Where precast units are used, the precast units should be provided with a concrete surround from the base to the top of the precast section, to ensure continuity of the drain, as well as preventing water seepage and dislocation of the precast units.
4.3.10 Kerb Opening Inlets
Kerb opening inlets are openings at kerbs where stofinwater runoff enters the drainage system. The capacity of kerb opening inlets depends on how efficiently the water changes its course fromlarallel to the kerb to flowing towards the kerb opening inlets. This direction change is primarily due to the crown slope; thus the usage of depressions prior to the openings can significantly increase the intake capacity. Fig. 4.18 shows the common types of kerb opening inlets. practice of forming a round iniet at the end of a pipe is ]he^_common inefficient because: the available inlet area is too small; the head avaiiable to force gutter flow into the inlet is too low; and
when used on grades, the gutter flow simply bypasses the inlet altogether.
As a guideline, it will be necessary to have at ieast 1.0m head height between the road level and the drain invert to ensure the iniets op"*t" correctly. Inlets should be designed and rocated to prevent silt and debris being carried in and become deposited a10ng the watercourse.
In cities or towns where kerbs and kerb opening inlets are placed in conjunction with upgrading the sidewalk pavement, the designer needs to investigate on-site the locations of kerb opening inlets to prevent ponding and localised hazards to road users. In cases where a kerbed intersection is upgraded, careful consideration should be given to locate the kerb opening inlets. Fig. 4.20 can be used as a guide for Iocations of kerb opening iniets.
4-16
CARRIAGTWAY
)
)
-E
E*
CARR]AGIWAY
z. a-
Au)
CARRIAGEWAY
CONC. CHANNEL WITH R.C. SLAB COVER
R.C.
PRECAST CONC. KTRB WITH OPENING
SLAB
COVTR
I
t100 CONC. BEDDING BIDDING
HALF ROUND (22s) GI-AZID EARTHTNWART
DRAIN
CONC. BEDDING
CARRIAGEWAY
MEDIAN
R.C. SLAB COVER
CONC. CHANNEL WITH
R.C. SI-AB
COVTR
rsoSS l:oo RRrso PRECAST CONC. KERB WITH OPENING
225mm
BRICKWALL
50mm
CONC. BEDDING
'100
CONC. BTDDING
300mm P.C. BLOCK
FIG. 4.10 MEDIAN DRAIN +17
-
DRAIN
IEBd
--XO?TD
75mm THK. 225mm HALF
CONC:
CLOSE TURTI ROUND
ZED TARTHiNWARE
^
DRAIN
SUPERELEVATION e<5%
SU
CONC. SURROUND
LOWIR SUBBAST
SUPERELEVATION SECTION
150mm STONE
CLOSI TURFING PITCHING
GROUTED WITH 1:J CEMENT MORTAR SUPIRELEVATION e<5%
raOO*
L-
LowEtr )JDtrA5L
SUPERETEVATION SECTION
STONE IJNED MEDIAN I
|t,{ RGINAI_
VARIES
I
1800
150mm STONE
PITCHING
vaprtrq rr^anr\r^l
CLOSE TURFING
GROUTED WITH l:J CEMTNT MORTAR
SUPERELEVATION SECTION PRECAST BL0CK DRAIN
mfH
FIG. 4.11 MEDI,AN DRAIN
150mm GR0UTED STONE PITCHTNG
-
SUPERETEVATION SECTION
+18
ry-!.-..:
INTERCTPTOR DRAIN
I-AYIRS OF SQUART
MISH 4142
R.C. 0tnFA[L DRAIN SOmm^,;HK. CONC.
IYPE OD3 SCALE
1
:
SQUARE MESH
A142 SQUART A142
75
MESH
L-'l b, "l
INTERCEPTOR DRAIN
f-l
I
^i ol tl
I
,^l iil-l
ro<
N' -L ZZJ
i |
I
ll li llti 150
LAYERS OF SQUARE MESH A142
ROADSIDE
TOE DRAIN
I
DRAI
-l I
50mm THK. C0NC. BLINDING
SQUARE MESH
4142
SQUARE MESH
4142
I
1
| 1qn
200
INTERCTPTOR DMIN
P,
=l---i--l F_=LI 'sl-f 3Nr
40mm DlA.
l|".)l.-t
GALVANISTD
STTTL PIPE HANDRAIL
I
3000
I
.2251 VARIES
225mm THK. STONE PITCHING 50mm THK. CONC. BENCH DMIN
STONE PNCHING OIITT'AII, DRAIN
trTH EANpRAII (TrPE 0p1) ROADSIDE
TOE
DMIN/
DRAIN
suMP (0R rNL$
FIG. 4.12 OUTFALL DRAIN
+19
SUMP
0F cuLVtRT)
F
= z.
o o I
I
a J
I
g KH z.
I
.^
I
o_^
>-
I
dl t''1
v): .{trj
:o_
I
z.
F E U
-
l
=
3r E-l ol
U
o_
l1
o-
=r
EI ul
I
J u
9v i;f,1
?l =l
-?l
Llv Qrn
<=
<. b.e
.
..i
f-.
+20
:.,".-l'il:tlj::::r:,;.::r.,.il:::i,.::.:i,.,:r;,.:::*-:l:,ii.';r:t;..:.:r...i;;;.:,i
r-:r:.
:-:-'::i
J
z
(5 o-
EF <= > t/)
U
z.
= F
T*
.z U
l_
F a
v)l
>l
o_ F
a
) =
z. v.
E
=
=l rtr.l z.
-l
o_
t-=l
l
zl I
-l
o_
E F
z.
FI pl
f,
4 -t U4
F =
(Jl
irJ
(n
E,= t!
zl
I
J
z.
I
E o
zl
I
z.
-< td.
OL! NI ;; i
<.+
v-
I
I
z.
I
= z.?
i
tr]1
(Jl
zl OI
t! =Fq iI= co=
I
-$
I
z.r zz.
I
z.
t,
J
A
u/ lai
J
X U
== z = E F U'' U =
+21
J(J
+
T
(-) I! EE. t! L!
z.
LrJ
E=
-Ln Q-< U
F U) L!
r<
I
C)
u)l
-l
I
I
I
I
EEf l
E
E
ff J z.
F
&=
tJ')
L!
=
Po_<
F
z.
U C)U
t! F
>< LrJ
t!
z, u v.
L!
z.=
:) F
5 Lrl
L!
cn
o_
OJj
d4=
J
aa,Y z.^tn 4 72.H;7==
5P4 E z.o fi o<
):
z.
U tt!
i
E
z.
E.
t!
U
o o z.
0009
z.
E.
o,:5 aZ.
O
Et= <;z:)
=- :-u >
? ,,u3 *F.
,FJF
!(/)6 r-!J za ()
F
4,^ = =- co
= F
(i <{
l=
+22
PAVEMENT
2.52 TA
4%
ROAD
IN
CUT
CROSS-SECNON OF STATE
SAND AND SorL (80:20) MINIMUM COVER 0F 300mm q.
SWALI INVIRT LIVIL
SPOT TURFTNG I
q
1s-
100mm THICK 20mm
SINGLE
SIZE STONE AGGREGATES WMPPED ROUND WITH GTOTEXTILE FILTER FABRICS
RECTANGULAR OR CIRCULAR HIGHLY PERFORATED DMINAGE CONDUIT WMPPED ROUND WITH
CLEAN COMPACTTD SAND 0R GRAVEL
GEOTEXTILI FILTER FABRICS
100
(
5mm
100
DETAIIS OF STAI,E
FIG. 4.16 SIrAlT IN ROADSIDE/MEDIAN
+23
DRAIN
LAMP POST CLOST TURFING
Y/o
____*_____L-
-----------l
DRAINAGE AT UEDHN (cRoss sEcn0N AT taMP PoST) 0
LAMP POST
CLOSI
TURFJNG
PRECAST CONC. CHANNTL
L,J
R.C. SUMP TO
/O
DETAILS
50mm THK LEAN
CONC.
DRAINAGE AT UEDIAIT
(cnoss sncnon
lr sulp)
FIG. 4,17 CONCEALED DRAIN AT MEDIAN
+a+
NOTt: THT STANDARD INLTi IS THI BASIC UNIT FOR USE IN ALL CLASSES OF ROAD. TXTINDED INLilS PERMIT GREATTR CAPTURT WHTRE SPECIAL CIRCUMSTANCIS MAKE THIS DESIRABLI.
IONG HTTENDED INI,ET 48OO IJ}.ITE[
MEDII'U MruEI\TDED INIET 3600 ul.IlEt
FIG. 4.18 RECOMMENDED IYPE OF KERB
+25
4.3.1I Sumps sumps are transition structures used to facilitate changes in level and direction of flow within a drainage system. They may be used as temporary storage so as not to inundate the downstream drains. They are normally rectangular in shape and the invert levels are lower than the joining drains" For cut or fill sections, sumps are iocated at:-
(i)
the intersection of berm
/
bench drains and the outfall /
cascading drain;
of
(ii)
the intersection cascading drain;
(iii)
the intersection of the toe
the toe
/ shoulder drains and the outfall /
/
shoulder drains and the roadside
drain.
For urban areas, sumps are located at:
of
(i)
the intersection point shoulder drain:
(ii)
the intersection point of the roadside discharge drain.
the median drain and the roadside /
/ shoulder
drain and the
Preferably a sump will always have some water retained in it to indicate that there is no seepage occurring. Galvanised steel grating covers hinged to the seating frame are recommended for the sumps, for both safety and retaining debris.
For sumps of depth less than 1.0m, brickwalls of minimum 225mm thick may be used. Sumps exceeding 1.0m internal depth, reinforced concrete should be used. 4.4
SURFACE DRAINAGE IN RTIRAL AREA (FLAT AND ROLLING AREA)
on rural roads, surface water is mainly disposed off by means of drains and the type of drains provided depend upon whether the road is in embankment, cutting or at ground level. when the roadway is built on a low embankment of less than 3.0m and grassed, it is common practice to allow the surface water to flow across the shoulder and down the fiIl slopes to the natural ground level. In cases where surface water from the road is an even sheet of water, erosion is minimal. Where slopes are unprotected and sheet flow is not achievable due to localised pavement or shouider irregularities, slopes can be eroded badly. In these cases, it is necessary to provide protection for the shoulders and side slopes. One type of protective measure is to intercept the water at the outer edgi of the shoulder, as shown in Fig. 4.19(a).
4-26
SLOPI ON LOW FILL (TURFED)
FILL
fIrl,l,u,'o'HIGH (a)RoAp rN EMBANKT{EI'II
NATURAL GROUND LIVTL
lsz to +z
SLOPE
1:J 0R
FLATTTR
(b)RoAp rN cuT
NATURAL GROUND TEVEL
i
-t i
(e)R0AD
0N GR0UND
FIG. 4.Tg
-T
+27
4.4
Surface Drainage in Rural Area
- (Cont'd)
In the case of a long and high embankment, for example bridge
approaches,
the surface water can be collected by shoulder drains and then discharge down the slope by means of paved outfall or cascade drains. When the road is in cut, water is discharged to the roadside drain, as shown in Fig. 4.19(b) and (c), which should then slope towards the nearest watercourse.
4.5
SURFACE DRAINAGE IN URBAN AREA Drainage is usually more difficult and costly in urban areas because of: -
(a) (b) (c) (d)
more rapid florv rates and larger volumes of runoff;
costly potential damage to adjacent properties by flooding; higher overall costs because of more inlets and underground systems; greater restrictions because of urban and large development areas;
(e) (f) (g) (h)
lack of natural bodies and watercourses to receive floodwater; higher volumes of traffic including pedestrians:
impervious character of the area which results in very high runoff;
non-availability or high cost of land prohibits the provision of adequate drain reserve;
(i)
undesirability of open drains due to possible risk to road users and unsightly appearance.
Ftg. 4.27 shows the typical drainage elements for roads in urban areas. There is a greater need to intercept off road concentrated storm water and to remove over-the-curb flow, and surface water, without causing a problem for road users. In urban areas, water from the road surface is usually taken to a system of underground pipes known as storm drain or sewers, which can run ovel a considerable distance and then released again as surface runoff.
4.5.1
Drainage Inlets
4.5.1.1 General
A stormwater inlet is an opening in a drainage system for stormwater runoff. The importance of properly designed, constructed and maintained inlets cannot be over-emphasized as it is not uncommon to find cases where ponding is excessive on a roadway, and yet the drainage system is not operating at its full capacity simply because the inlets are choked up.
4-28
l I,
4.5.1.1 General
- (Cont'd)
Guidelines the design of inlets are provideci in the ,,r]rban for Stormwater Management Manuai For Malayriu guasMA),, published by Jabatan Pengairan dan Saliran Maraysia, volume part _ 1 F Runoff conveyance, chapter 24 - stormwater Inrets is provided as ATTACHMENT 1.
within a catchment, a range of surface flow criteria must be appried to minimise both nuisance floocling and major hazards from flooding of roadways, buildings, and other public areas. It is intended that the surface flow criteria has equal *ilght on the contror of surface flows during storm events as well as the removal of frows from urban
pedestrian and vehicular transport networks.
The surface flow criteria comprises of four basic iiinits:
o An overland flow velocity x a o o
depth limit, which governs the stability of vehicles and the ability of pedestrians to ,walk out, of flood flows A flow width limit A ponding depih limir Design Average Recurrence Interval (ARI)
Please refer to Tabre 4.1 which expresses the maximum overfrow ailowed for a particular road type. Table 4.1
-
Allowarrre Roadways for Pavement Encroachment
Initial storm Runoff in Terms of Road Classification Collector Road
High Volume Road
Criteria
(Single or Dual
Carriaqewrv)
Locations other than Sas poini Design ARI Where the kerbside lane is nor a through lane (i.e. used for n:rkino\
yyrcrs ule KefDstoe lane ls
a
through
Iane
Where parking lane becomes an acceleration, deceleration or turn lane
10 year
i0
Not applicable
Sag Points
Design ARI All locations Major storm check (100
y"* enf;
> 70km/h : no spread < 70km/h: I{< 1.0m > 70km/h : no spread < 70km/h; W< 1.0m
50 year 1.0m One lane in each 4gggtion open to traffic
limit.based on , the product of average flow velociry ;l .lif"y \'/ I.?from W = flow width on road gutter invert, y
:
W
<
Not applicable
1.0m
25m
One lane open to
and gutrer
i""*,
W
W
10 vear
5 vear
w < 25m (not required)
V.D. <0.4m'/s
V.D. <0.6m2/s
flow depth
on major highways and expressways, these standards may not be appiicable flow on the vehicie carriagervay foi safety reasons. Authorities
as it is to limit the resionsiuie for these highways
may specify stricter criteria.
SOURCE : Urban Stormlyafer Nlanagement Vlanual lbr Malavsia
4,29
< 0.45m < 1.0m
traffic V.D.
= fiow depth ut gott",
Note
Not applicable
w<
VD
< 23m
< 15m
< 045m w < 1,0m
I/',<
(1)
5 vear
W
W
W
> 70km/h : no spread < 70km/h : 14 < 1.0m
suesrnan salety
Vehicular safety
year
w < 25m
Not applicable rnrersecuon Kerb refurns
Local Road
INL
T
INLTT POSITION TO SUIT MAX. SPACING EITWEIN
POSITION TO SUIT
MAX. SPACING FROM TOP
OF
CATCHMENT
INLET
PITS
SAG POINT
lrArLl _\ LfI ON TANGTNT OF KERB RilURN
INLII- ON TANGENT OF KIRB RilURN
INLil
UPSTREAM OF PEDTSTRIAN CROSSING
MAX. 450mm
MAX. 1000mm
lN
lN
MINOR STORM
MINOR STORM
BW SMP EOAD
NOAD
(b) AT KERB RETURN
(a) AT BUS ST0P
ITIfi0AGE
(c)
UllE +
A,T DECELERATION LANE
FIG. 4,20 GUIDE FOR LOCATIONS OF KERB OPENINGS AND INLET PITS
+34 .1.
J
z.
z
o_
I F
= @ cY.
Y
o 6 a E
=
o_
oI -2
E
=-
oa< Ug(J :<
c\l $ CJ FE{
z.
o 6 o
J
z.
F ou.
i -l .",.iI
4-31
b GRATED
c(i)
A KERB OPENING INLET
INLET
(a) srorrnn nrnr
C0MBrNATrON INLET
ALTERNATIVE:
SINGLE CROSSFALL
rlonurL
cnGGrI--]*
t
L I
TO OPEN
DRAIN
utom
DRAIN
oR
cRoss-DRATN
(FOR SINGLE CROSSFALL ROAD)
PIPE
FIG. 4.22 TYPES OF STORM DRAIN INLETS
+32
Y
SECNON
A
-
A
FIG. 4.23 DEPRESSED GRATED INLET
I
4-33
4.5.1.2 Types of Inlet There are four (4) types of inlets: -
(a) (b) (c) (d)
kerb opening inlets; grated inlets; combination inlets; and slotted inlets
Fig . 4.22 shows the (a,)
four (4) types of inlets.
Kerb Opening Inlets
A kerb opening inlet is a vertical opening in a kerb through which the gutter flow passes, the gutter may be level or depressed in the area of the kerb opening.
As with ali types of openlngs, a kerb opening iniei may be either on a continuous grade or in a trough iocation. The kerb opening inlet does not clog readily, which is its major advantage, the large dirnension of the clear opening compared to that of a grated inlet allows rubbish to pass into the storm sewer system rather than be trapped at the inlet.
The capacity of a kerb opening inlet is significantly increased by depressing the opening. A characteristic of the kerLr opening inlet is its relative inefficiency on streets of steep grade, which can be improved by the installation of deflector veins in the gutter adjacent to the opening. The veins create a standing wave, which causes the water to flow into the kerb opening.
It is recommended
that kerb opening inlets be used in the design of road drainage systems, particularly when trough conditions exist. Although a kerb opening inlet will not guarantee against clogging, it is the most efficient type of iniet.
(b)
Grated Inlets
The term grated or gutter inlet refers to an opening in the gutter covered by one or more grates through which the water fal1s. As with other inlets, grated iniets may be either depressed or level and may be either located on a continuous grade or in a trough.
Grated inlets can be laid either longitudinal, transverse or combination of the two. The term "longitudinal bar grate" refers to a grate in rvhich the bar are oriented parallel to the direction of flow while "transverse bar grate" are align at some angle, usually perpendicular to the direction of flow. Tests have been conducted to determine various characteristics of grated inlets, these tests have indicated that longitudinal bar inlets are far more efficient and less apt to be blocked by rubbish than the others. A
1/1
T-JA
v (b)
- (Cont'd) The major disadvantage of the grated inlet is a tendency to plug with rubbish, reducing efficiency significantly fiom the theoretical value, and in some cases rendering the inlet inoperable. Some tests indicate that prop"rly designed Arcrcdldels
longitudinal bar grated inlets on u .onti"uous grade are reasonably immune to plugging. The use of a grated inlet in a trough condition with transverse bars virtualiy assures that some blocking will occur to significantly decrease the capacity
of the inlet.
Depressing the grated inlet wiil significantly increase its capacity, but the interference to traffic caused bythe depression may be unacceptabie.
If
depressed grated inlet is requirecl, the width of the galvanised steel grating should be limited to 250mm as shown in Fisure 4.23.
(c/
Combination Inlets
A
cornbination iniet is ccrnposed cf a kerb cpening and a grated gutter opening inlet acting as a unit. usually, G gutter opening is placed directly in front of the kerb opening. As with
other inlets, a combination inlet may be either delressed or undepressed and iocated in a trough o. o.r a continuous grade. Laboratory tests have shown that for a combination inlei on a continuous grade, the kerb opening adds little to the capacity of the inlet when the grate is not plugged. This is due to the high efficiency of the grated inlet, which accepts the water before the kerb opening has a chance to receive water.
In
practice, the kerb opening of a combination inlet on a continuous grade is of benefit because it accepts the flow diverted by rubbish plugging the grating. However, the length of kerb opening on a typical combination inlet is usuailv insufficient to allow acceptance of a large flow.
Under trough conditions, a combination inlet has a high theoretical capacity, the use of which is questionable, extended side inlets, using lintel supports, can be used to increase capacity as shown in Fig. 4.22 c (li). (d)
Slotted Inlets
slotted inlets can be used in areas where it is desirable to intercept sheet flow, their pincipal advantage is their abiliry to intercept flow over a wide section. However, slotted inlets are very susceptible to clogging from sediments and debris, and are not recommended for use in environments where sienificant sediment or debris loads may be present. slotted inlets on a longitudinal grade do have the same hydrauiic capacity as curb openings when debris is not a factor. 4-3J
Y
4.5.7.3 Recommended Use of Inlets
Extra inlets must be provided near the low point of sag vertical curve to cater for flow that might have passed the previous inlets to prevent ponding at the 1ow points. Inlets should be located just upgrade of pedestrian crossings andjust before the change in crossfalls. The key principal in location of inlets is at piaces where concentrated flow and heavy sheet flow is anticipated as shown in Fieure 4.20.
4.6
SURFACE DRAINAGE IN MOUNTAINOUS AREA For proper maintenance of roads in mountainous regions, an effective drainage system is very important. In this case, surface water is mainly drained by the provision of interceptor drains, bench drains, berm drains and toe drains. The previous Frg. 4.2 shows the typical affangement of surface drainage for roads in mountainous region.
4.6.L Drainage for Cut Section Where the surrounding area consists of a higher ground, as in cut, or where the highway is constructed along the side of a hi1l, consideration should be given to the possibility of water flowing towards the roadway either on the surface or at shallow depths through water bearing strata. To intercept and carry the water away, interceptor drains are constmcted at the back of the top of the cut and bench drain on benches in the cut slope usually provided at 6m height intervals. Drains of this type are also effective in preventing erosion or faiiures of the slope. In constructing this kind of drain, care should be taken to prevent the drain from ieading water to the toe of the adjacent fill which may cause erosion. When the roadway has a steep longitudinal slope, a sump and an outfall drain may be placed at the downhill end of the cut to intercept longitudinal flow and carry it safely away from the
hill
slopes.
4.6.2 Drainage for Fill
Section
For high fills, berm drains are necessary to catch surface water
at
regular intervals and these berm drains are again connected to the toe drains, which take the water safely down the slope to a suitable discharge point.
4.6.3
Route Location and Drainage Consideration for surface drainage and erosion control problems must begin with the location survey. Ideal locations from a drainage standpoint would 1ie along the divide between large drainage areas. Then all streams flow away from the right-of-way and the drainage problem is reduced to the water that
+-JO
fa11s
on roadway and back slopes.
-v-
4.6.3
Route Location and Dnainage _ (Cont,d)
In contrast' locations paralleling large streams are far less desirable as they cross every tributary where it is largest. Again, ideal locations are to avoid steep grades and heavy cuts and fi11s, Loth of which can lead to difficult problems in erosion control. Admittedly, surface drainage is only one' among many considerations in location, but it warrants careful attention.
once the location is established, analysis of surface drainage probiems tbllows three basic steps: (a)
hydrology - estimating the peak rates of runoff to be handled:
(b)
hydraulic design - selecring the kinds and sizes of drainage facilities to most economicallv accommodate the estimated flows;
(c)
making certain the design does not create erosion or other environmentally unacceptable conditions.
4.7
FLOW CAFACITY DESIGN OF SURFACE DRAII,{S The flow capacity design of surface drains can be divided into two phases:
(a) (b)
_
hydrologic analysis hydraulic analysis
4.7.1 HydrologicAnalysis The main objective of hydrologic analysis is to estimate the maximum quantity of water (Q) expected .to reach the elenient of the drainage system under consideration. A portion of the rainfall infiltrates into tte ground as ground water and a sma1l portion of water, which flows over the surface, is termed as surface runoff. various factors, which affect the runoff, are intensity of rainfalr, type of soil urra i,. permeability, soil natural moisture condition, topography of the area, type of ground and type of land use. The Rational method has probably been the most popular method for designing storm systems. It has been applied alr ovlr the world and many refinements of the method have been produced.
For small catchment areas, provided that
it continues to be a reasonabie method,
it is used correctly and that results and design conceprs are assessed for reasonableness. For a detailed discussion on the application / limitations of the method, please refer to urban
Stormwater Management N{anual for Malaysia, ctrapter t6.
4-37
Y-
4.7.L Hydrologic Analysis -
(Cont'd)
This section outlines the Rational method procedure for system design calculations for catchment areas less than 80 hectares that do not contain detention or retention storages. This procedure is suitable for small systems where the establishment of a computer model is not warranted.
The steps in the R.ational method calculation procedure
are
summarised below:
o The drainage
area
is first
into sub-areas with to the existing or planned
subdivided
homogeneous land use according development.
c For each sub-area, estimate the run-off coefficient C and the conesponding area A.
.
The layout of the drainage system is then drawn according to the topography, the existing or planned streets and roads and local design practices.
o
Inlet points are then defined according to the detail of design considerations. For main drains, for example, the outlets of the earlier mentioned homogeneous sub-areas should serve as the inlet nodes. On the other hand in very detailed calcuiations, all the inlet points should be defined according to local design practices.
c
After the inlet points have been chosen, the designer must specify the drainage sub-area for each inlet point A and the corresponding mean runoff coefficient C. If the sub-area for a given inlet has non-homogeneous land use, a weighted coefficient may be estimated.
o
The runoff calcuiations are then carried out by means of the general Rationai method equations for each inlet point, proceeding from the upper parts of the watershed to the final outlet. The peak runoff, which is calculated at each point, is then used to determine the size of the downstream trunk drain using a hydrauiic formula for open channel / pipes flowing full. Please refer to Equation 4.1.
After the preliminary minor system is designed and checked for its proximity with the major system, reviews are made of alternatives, hydrological assumptions are verified, new computations are made, and final data obtained on street grades and elevations. The engineer can then proceed with the final hydraulic design of the system.
4-38
t-
Y-
4.7.1 Hydrologic Analysis -
(Cont'd)
This section outlines the Rational method procedure for system design calculations for catchment areas less than 80 hectares that do not contain detention or retention storages. This procedure is suitable for small systems where the establishment of a computer model is not warranted.
The steps in the Rationai method calculation
procedure
are
summarised below:
. The drainage
area
is first
into sub-areas with to the existing or planned
subdivided
homogeneous land use according development.
c For each sub-area, estimate the run-off coefficient C and the corresponding area A.
.
The iayout of the drainage system is then drawn according to the topography, the existing or planned streets and roads and local design practices.
o
Inlet points are then defined according to the detail of design considerations. For main drains, for example, the outlets of the earlier mentioned homogeneous sub-areas should serve as the inlet nodes. On the other hand in very detailed calculations, all the inlet points should be defined according to local design practices.
c
After the inlet points have been chosen, the designer must specify the drainage sub-area for each inlet point A and the corresponding mean runoff coefficient C. If the sub-area for a given inlet has non-homogeneous land use, a weighted coefficient may be estimated.
o
The runoff calculations are then carried out by means of the general Rational method equations for each inlet point. proceeding from the upper parts of the watershed to the final outlet. The peak runoff, which is calculated at each point, is then used to determine the size of the downstream trunk drain using a hydraulic formula for open channel / pipes flowing full. Please refer to Equation 4.1.
After the preliminary minor system is designed and checked for its proximity with the major system, reviews are made of alternatives, hydrological assumptions are verified, new computations are made, and final data obtained on street grades and elevations. The engineer can then proceed with the final hydraulic design of the system.
4-38
4.7.2 ltrydraulicAnalysis when lhe value of design discharge (o is obtained, the next step is the hydraulic design of drains. surfice diains are designed based^on the open channel flow theory.
open channer has advantages in terms of cost, maintenance and capacity, however, disadvantages need to be considered in respect of right-of-way needs, maintenance costs and, hazNds to traffic and pedestrians. Careful planning and design are needed to minimise, where possible the disadvantages and to increase the benefits. Natural channels are normally ideatr because the velocities are usually iow, resulting in longer concentration times and lower down stream peaks; channel storage usually exists which reduces peaks and maintenance is low because the channels are somewhat stable.
An artificial channel that can be constructed with the characteristics of the natural channel will be the next best performing channel. (when right-of-way and /or velocity considerations dictate, a lined channel is normally the choice)
If (o is the quantity of surface runoff (cumec) to be removed by a roadside drain and (v) is the alrowable velocity of flow (m/sec) rn itre roadside drain, the area of cross-section (A) of the channer lsqm; can be computed from the relation: _
a
=
AV
Equation(4.0)
The velocity of flow in any channel should be high enough to prevent silting and it should not be too high as to cause erlsion. The allowable veiocity of flow depends on the soil type (see Table 4.2).
By adjusting the value of srope (s) in Equation 4.r, it is possibre to limit the velocity of flow (v) within peimissible rimits. 'Assuming
uniform cross-section and srope, Manning's formula can be used for determining the velocity of flow, which is liven Uy :' n Yrl'' -!r ii'",., 1/n R2/3 S1/2 Equation (4.1) ir; where V :d average velocity (m/sec) n-
R=
Manning's roughness coefficient hydraulic radius (m) cross-section area of flow divided by wetted perimeter
longitudinal slope of channel
of recommended Manning's roughness coefficient shown in Table 4.3 values
(n)
are
The longitudinal slope (S) of a drain of a known or an assumed cross_ section and depth of flow may be determined using Manning,s formula (Equation 4.1) for the design values of velocity of'flow (v), roughness coefficient (n) and hydraulic radius (R).
4-39
Y
4.7.3
Basic Design Frocedures
Basic steps for the design of longitudinal drains surface water are summarized as follows:-
of a road to
drain
(a)
the total catchment area (A) is usually in units of 10,000 sq.m.
(b)
the values
of coefficients of runoff C1 Cz, Ct, etc., from
drainage areas Ai, Az, At, etc., are read out from the standard table and the weighted value of C is computed.
(c)
from topo maps inlet time for the flow of stormwater from the furthest point in the drainage area to the drain inlet along the steepest path of flow is estimated from the distance, slope of the ground and type of the cover.
(d)
time of flow along ihe longitudinal cirain is determined fbr the estimated distance up to the nearest cross drainage or a watercourse, and for the allowable speed of flow in the drain.
(e)
the sum of the time for inlet flow and the time for flow along the drain is taken as the time of concentration or the desisn value of rainfall duration.
(0
the frequency of return period is decided based on finances available and desired margin of safety, for the design of the drainage system. Usua11y, T = 5 years is used. For more details, please refer to Volume 1 - Hydrology.
(g) from the rainfall intensity duration frequency curves, the rainfall intensity (I) is found in mm/hr.
(h)
the runoff quantity (O is then computed from Q = CIA. For urban area, additional storage coefficient (C,) has been added to account for channel storage. Thus, Q = C, x CIA.
(l)
the required depth of flow in the drain is calculated for a convenient bottom width and side slope of the drain. The actual depth of the open channel drain may be increased slightly to give a freeboard (usual1y 150mm). The hydraulic means radius of flow (R) is determined.
0)
the required longitudinal slope (S) of the drain is calculated from Manning's formula adopting suitable value of roughness coefficient (n).
.
Note
: A11 tables are obtained from Urban Drainage Design Standards and Procedures for Peninsular Malaysia, 1975.
An example of design steps is shown in Section 4.7.4.
1-40
-v
Table 4.2
-
Altowable Average Velocity
Well established grass on any good soil Meadow type of grass with st o.t, pturrt UtuO.s, heavy stand.
Bunch grasses, exposed roit U"twen ptarrts. Grains, stiff-stemmed grasses tt ut Oo not O"na olr", under shallow flow. Earth without vegetation:
(a) (b) (c) (d) (e) (0
Table 4.3
-
Fine sand of silt, little or no clay Ordinary firm loam Stiff clay, highly colloidal Clay and gravel
0.3 - 0.6
0.6 - 0.9 1.2
t.2
Coarse gravel
1.2
Soft shale
1.5
Suggested Values of Manning's Roughness
Coefficient. z Surface Cover urassecl Jwales
z values Minimum IVIaximum -Suggested
r_
i,arln ctraln _ Jnon grass cover _ r all grass cover Ltned Upen l)rains
0.025 0.030 0.035
0.030 0.03s 0.050
LOncrete
Trowelled fini
0.011
Offform
0.013
Stone PitchiogDress"A st
-_
It?noom srones m mo4ar or rubble qerqnry Rock Riprao bncKwork Pt"rurt Muro-y i-
-
4-41
0.015 0.020
0.025 o.012
0.0r2
0.015 0.018 0.017 0.035 0.030 0.018 0.015
-v
4,7.4
Calculation Worksheet
A worksheet for the hand calculation procedure is given rnTable 4.4. This worksheet can be use for open drains or, with minor alterations, for piped systems. The procedure can also be set up on a computer spreadsheet. In this example the network is analysed for the upper catchment only (until Node 6FI/6 of Figure 4.2Q) to make sure that the total catchment area is less than 80 hectares. The procedure is for the average situation, variations may be necessary to fit actual field conditions. (1)
Column 1 - determine design point location and list. This design point should correspond to the sub-catchment illustrated
on the
preliminary layout map.
List
sub-catchments contributing runoff to this point that have not previously been analysed. The sub-catchment at downstream point will only be noted at drainage junction points. The sub-catchment nodes are
numbered as discussed in MASMA Volume System and Computation) Section 16.4.
6
(Network
(2)
Column 2 - The drainage system to be numbered as discussed in MASMA Volume 6 (Network System and Computation) Section 16.4.
r3)
Column 3 - Enter length of flow path between previous design point and design point under consideration.
(4)
Column 4 - The area, A in hectare of the sub-catchments listed column 1 is tabulated here. Subtract ponding areas, which do not contribute to direct runoff.
r5)
Column 5
- Runoff Coefficient, "C", for post development
conditions for the sub-catchments listed in Column 1, should be determined and listed. The C vaiue should be weighted if the sub-catchments contain areas with different C values. (6)
Column 6 - The equivalent area, C x A of each sub-catchment
(1)
Column 7 - Determine the inlet time for the particular design point. For the first design point of a system, the inlet time wiil be equal to the time of concentration (t"). Remember that t" is the wave travel time, and includes both overland flow time and travel time in a discrete channel. For subsequent design points, inlet time should also be tabulated to determine if it may be of greater magnitude than the accumulated time of concentration from upstream sub-catchments, if the inlet time exceeds the time of concentration from upstream catchment, and the area tributary to the inlet is of sufficient magnitude, the inlet time should be substituted for time of concentration and used for this and subsequent sub-catchments.
/1 A')
a'1L
Y
4.7"4 Calculation
of Worksheet _ (Cont,d)
In other words, at each design point in the system, the engineer should ascertain whether the total drainage area with a composite t" or the given indiyiduzl upstream catchment (with a different t. ) produces the higher discharge.
(8)
column
g-
- Enter the appropriate flow time (wave travel time) between the previous design point and the design point under consideration.
(9)
column 9 - The sub-area time of concentration, t" is found by adding columns 7 and g.
(10)
Column 10- The appropriate design return period for the drain, depend on the type of rand use within the sut-catchment.
(11)
column 1i - The total Equivalent Area is the summation of x A of the previous design point
(12)
column 12 - The critical time of concentration, t" is the longer t" summation of the previous design point time of concentration and the intervening flow time.
(13)
Column 13 - The torar time in drain is found by adding the previous time in drain to the time in drain in current section.
(14)
column 14 - The intensity to be applied to the sub-catchments under consideration, is oitained, ^fio- the intensity_duration_ frequency curve developed for the specific ur"u UurJ;O; depth-duralion-frequency information. The intensity is determined from the time of concentration and the return frequency for this particular design point.
(15)
column 15 - Direct runoff from the tributary sub_catchments listed in coiumn 1 is carculated and talurated
multiplying coiumns 11 and 14 together.
t
"r"
c
uy
(16)
column 16 - List the proposed channel/pipe gradient
(r7)
column 17 - List the required channel/pipe size to convey the quantity of flow. For standard open drains or pipes, ,ound up to the next commercially available size.
(18)
column 18 - List the capacity of the channel/pipe flowing furl (with the slope expressed in column 16).
4-43
4.7,4
Calculation Worksheet
- (Cont'd)
(19)
Tabulate the actual velocity proposed channeVpipe for the design Section.
(20)
Column 20 - By dividing the length of the channel/pipe by its velocity, the time of flow in the drain can be determined.
(21)
Column 21 - Proposed drain invert level.
(22)
Column 22
(23)
Additional Column - This column is optional to include any remarks or comments that may affect or explain the design. The allowable quantity of carry-over across street intersections, if any, should be listed for the minor design storm. When routing the major storm through the system, required elevations for adjacent construction can be listed in this coiumn.
Column 19
-
of flow in
the
-
Calculate the discharge for the 100 year ARI to check capacity of the drainage system for major storms.
For turther details, please refer to lviASN4A Volume
6
(Network System and computation). l
4.7.5 Kerb and Gutter l
areas shall generally be provided with an integral (refer gutter Figure 4.25). kerb and
All roads in urban
However, where the volume of gutter flow is negligible as in carparks and on the high side of single-crossfall roads, a kerb only is required.
GABION SC =
Figure
LONGITUDINAL SLOPE
4.25 Kerb and Gutter
Showing Half Road Flow
4-44
4.7.5 Kerb
and Gutter
- (Cont'd)
The location and spacing of inlet pits is governed by the need to provide safe, economical road drainage bi rimiting the amount of gutter flow. The design criteria are shown in Tabre 4.5. Gutter flow may be calcuiated by rzzard'sequation (Equation 4.2):
' +[[ Afur =
66i
-dz-,
F(})tn;*, - d2 667ilr,, EQ (4.2)
where subscripts g.and p refer to the gutter and pavement respectively, F is a flow correction factor. Desigricharts for gutter no*, are given in Appendix 4.A. Recommendei values or "tvtanning,, .oughn"ss coefficient and the Flow correction Factor F for gutter fi'o* u." given in Table 4.6.
This form of the equation arlows for the pavement and channer to have different roughness and, / or different crossfails. For the definition of terms in the equation, refer to Figure 4.25. The face of the kerb is approximated as being vertical.
using either Equation 4.2 or the chart in Appendix 4.A, suitable
limits for gutter flow can be determined. the averag" pii ,pu"ing is then determined to ensure that this .rimit is not exceeded. A worked example of this calculation is provided in Append ix i.c (based on AR&R - 1937). Note that the inlet capacity of an iniet increases with increasing flow, therefore, provided the flow width rimits are, satisfied, gutter it is an advantage to allow bypass gutter flow on sloping roads, to _some maximise the use of the pit capacity (Sutherla_nd SC, 199)).
4-45
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:!r-
FLOW SPREAD w
Z
LONGITUDINAL SLOPI
FIG.
4.25 KERB AND GUTTER. SHOWING HAIF ROAD FLOTT
448
4.7.5 Kerb and Gutter - (Cont,d) Table 4"5 Design Acceptance criteria For Road Gutter Flow High Volume R.oad (Single or Dual
Criteria
Road Classification Collector Road
Local Road
\ l5r YY
10 year
utrrc Lle Kerosloe lane rs not a
Not applicable
through lane (i.e. rrsed fnr nerrrina\ ry usrtr LrlE KerDsloe lane ls a through lane Where parking lane becomes an acceleration, deceleration or tum lane At pedestrian crossings or bus stous eIurns Sag Points
< l"5m
Not applicable
> /uKfivn : no spread < 70km/h: I7< 1.0m
I/ < 1.0m
Not applicable
Not applicable
W < 0.45m
70km/tr: no spread
> 70km/h : no spread < 70im/h: iV< l.0m
une lane m each direction open to traffic
reoestnan salety'., !q
W
>
I7 <
50 year
Major storm ctr"ct ltObJea. ezu;
D49Ly
5 vear
<
At(l
BIl
l0 year W
2.5m
1.0m
W
w< W
10 year
W < 2.5m One lane open to
5
< 2.5m (not required)
traffic
V.D. <0.4m"/s
V.D. <0.4m"/s
V.D. <0.6m2/s
V.D. <0.6m"/s
V.D. <0.4m'ls V.D. <0.6m'ls
limit.based on v-D', the producr of average flow verocity and guuer flow depth on road from gutt", inu"rt, y iio* depth at gutter = invert
on major highways and expressways, these standards may not be applicable as it is to limit the flow on the vehicle carriageway for safety reasons. Authorities responsiule for these highways may specify stricter criteria.
SOURCE; Urban Stormwater Management Manual for Malavsia
-
Table 4.6 Manning's 'n' and Flow Correction Factor For Gutter FIow Surface Type
n
Concrete
Hot mix asphaltic concrete Sprayed seal Kerb and Gutter tvDe
0.013 0.015 0.018
F
Semi-mountable type Barrier type
0.9 0.9
SOURCE: Urban Stormwater Management For Malaysia
4-49
0.45m
< 1.0m
W
)i]::tr'lflow width \'/W = Note:
< 25m
Y
4.7.6 Inlet Spacing Calculation The average inlet pit spacing is calculated so that allowable gutter flow is not exceeded, as shown in Figure 4.26 andFtgute 4.27 "
The calculation method uses the Rational Method to estimate discharge in the design storm. For simplicity, each pit catchment is assumed to be approximately rectangular as shown in Figure 4.27. If the subcatchments are not rectangular, they should be replaced by equivalent rectangular sub-catchments.
A worked example for the calculation of inlet pit spacing is given in Appendix 4.C.
4.7.7 Inlet Pits 4.7.7.LTypes of Inlet Pits
Three types of inlet pit may be utilised:-
o o
grate only side inlet only combination grates and side inlet
Grates are effective in intercepting gutter flows, and they also provide an access opening for maintenance, in some situations, they are prone to blockage. Side inlets are less affected by blockage and extended side inlets, using lintel supports, can be used to increase capacity"
The Combination Grate and Side Inlet pit (Figure 4.28) is the most efficient, and it should be used wherever possible. Details of the recommended standard inlet pits are shown in Standard Drawing No. SD F-2 given in the Urban Stormwater Management Manual For Malaysia. The Local Authority may determine which types of inlet pits are appropriate for its area. Standardisation of pits is encouraged in the interests of economic efficiency, but if a 1oca1 Authority decides to adopt a different standard design, the design curves given in this volume will need to be adjusted accordinslv Illustrations showing the typical location of inlet pits are given in Fisure 4.20.
4-50
4.7.7.1Types of Inlet Fits
-
(Conr,d)
Inlet pits shall not be rocated on the curve at an intersection of the risk they present to vehicles and the structural design of a side inlet pii oir u .uru", is much more complex. because
Considerarion should arso be given to the position of inret pits relative to property boundaries, pits shourd be rocated clear of existing or known proposed driveways.
(i)
Inlet Pits on Grade Designers should be aware that the inret capacity of pits on grade is controlred by the l0ngitudinal grade andlhe road crossfail. Inlet pit capacity charts forstandard pits are given in Appendix 4.8 of this volume. Bypass gutter flow from an upstream inret pit must be accounted for in the design of the downstream pit, which in turn receives the flow. There is no limit to ihe amount of gutter flow that may be bypassecl, providecl
that the gutter flow restrictions adhered to.
(ii)
in Section 4.7.5 are
Intet pits in Sags Inlet pits in sags must have sufficient capacity to accept the total gutter flow reaching the inlei, including ail bypass flo_*, from upstream. ponding of water at sags must be limited to the limits set in section 4.7:5, particularly at intersections where turning traffic is likely to encounter ponded water.
4.7.7.2 Allowance For Blockage
The design blockage alrowance sharl normalry be 30vo for a prt on grade and 50To for a sag pit or field inret, unless otherwise directed. 4.7.7.3 Type BKSE3O Inlet
This is a combination inlet with a 2.4m extended lintel (refer Standard Drawing SD F-2).
A Type BKSE3O inlet may be used:
t
at changes in direction where entry of water is not
essential (i.e. side entry may be sealed).
o o
in tight radius kerb returns where the length of a type BKLE3O inlet is inappropriare. as a
field inlet
4-51
Y
4.7.7.3 Type BKSE3OInlet
- (Cont'd)
Inlet capacity curves for Type BKSE3O pits are shown in Appendix 4.B. These empirical curves show the combined capacity of the side entry inlet and grate. Allowance must be made for blockase as described in Section 4.7 .l .2.
4.7.7.4 Type BKLE3O Inlet
This is a combination inlet with a 4.8m long extended lintel (refer Standard Drawing SD F-2), all kerbside inlets at low points and on-grade sha1l generally be Type BKLE3O inlets.
Side entry inlet capacity curves for Type BKLE3O pits are shown in Appendix 4.B. These empirical curves show the combined capacity of the side entry inlet and grate. Allowance must be made for biockase as described in Section 4.1 .7 .2.
4.7.7 ,5
Hydraulic Design of Kerbs and Gutters and Stormwater Inlets Design examples for gutter capacity and design of kerb opening inlets are given in the "lJrban Stormwater Management Manual For Malaysia" Chapter 24 - Stormwater Inlets, enclosed as Attachment 1 at the end of the volume.
/1
Y
CALCULATI ALTOWABLE LIMIT OF GUTTER FLOW
CALCULATT ACUAL TLOW FROM CATCHMTNT
OF THE INLET
ADD BY-PASSED FLOW FROM UPSTREAM, IF ANY
TOTAL FLOW WITHIN ALLOWABLE LIMIT?
CALCULATE PIT CAPTURE
AND AMOUNT OF FLOW BYPASSED TO DOWNSTREAM
LAST LOCATION?
PROVIDE FULL REQUIRED CAPACITY AT SAG PIT
URBAN STORMWATER MANAGEMENT MANUAL TOR MAIjYSIA
FIG. 4,26 OF INTET PIT SPACING
+53
xr
SUBCATCHMINT
1
SUBCATCHMENT 2
FIG. 4.27
CALCULATIO
NOTT:
THE STANDARD INLE]- IS THE BASIC UNIT FOR USt IN ALL CLASSES OF ROAD. EXTENDED INLilS PTRMIT GRTATIR CAPTURT WHTRT SPECIAL CIRCUMSTANCIS MAKE THIS DESIRABLT.
FIG. 4,28 STANDARD INTET PIT SOURCT
:
TYPES
URBAN STORMWATTR MANAGTMENT MANUAL FOR
4-54
MATAYSIA
Gutter Flow as a function of road slope
S
200 180 VxD>0.4
160
Flow exceeds crown 1+O
120 E
-c c)
Generol width limit
100
o
80 60
limit
of
intersection
40 20
0.10
0.01
1
Holf rood ftow
.00
(m 7r)
DESIGN CHART 4A,I
USING IZZARD'S EQUATION
BASED ON J% ROAD CROSSFALL, BARRIER KERB ryPt 1 (a50mm), n
p=
ne =
0.015 0.013
APPENDIX 4.A GUTTER FLOW DESIGN CHARTS SOURCI
:
URBAN STORMWATER MANAGTMTNT MANUAL FOR MAHYSIA
+55
-qr
O
z. U
a
n E
1so
-J
U E. = o_
1nn
t--a
z.
cu
100
200
300
ROADWAY APPR0ACH FLOW LTTRES
FIGURE 48.1
INIfiT
CAPACITY
-
/
SECOND
TYPE BIGE 30
O
z.
o
200
U
n E. = u E. =
150
1nn
l-J
z.
JU
ROADWAY APPROACH FLoW LTTRES
FIGURE
APPENDX SOURCE
/
SEC0ND
48.2 INI,ET CAPACITT - TI?E BKSE 30
4.8 INI.TT PIT CAPACITY :
DESIGN CHART
URBAN STORMWATER MANAGEMTNT MANUAL FOR MALAYSIA
4-56
3.C.1
SPACING OF
INIJT
PITS
Problem: The figure shows on ideolised cotchment in lpoh, droining to o gutier with Determine the moximum permissibre iniet pit spocing given thoi
w = 45
Solution: The minor storm is token to be 5 yeor ARl. Eoch subcotchment Assuming o time of concentrotion oi 15 minutes
is
o uniform
longitudinol slope
opproximotely rectongulor so c = 0.g5,
ond lumped runoff coefficient
1)
2)
l=
175 mm/hr from lpoh rDF doto for 5 yeor ARr, 15 minuie duroiion giving
/
Q
=
C.t.A
Q
=
0001859 Lo where Lo is the length of gutter flow in the upstreom subcotchmnet
J60 = 0.85 x 175 x (+5 x Lo
Colculote the ollowoble limit
of gutter
x
10-4)/J60
flow.
Use the Design Chort in Appendix 4.A for n p = 0.015 (hot_mix ospholt povement), ng = 0.01J (concrete kerb ond gutter). The limiting gutter (horf-rood) frow bosed on frow not exceeding the rood crown
Qc
V
=
=
170 litres per second
=
is
:
0.17 mJ/sec.
1.15m/sec.
d x V is within the Therefore Lo
=
0.17
/
ollowobte
0.001959
iimit of 0.4 m/sec.
= 91 metres.
APPENDIX 4.C ITORKED EXAMPLES SOURCE
:
URBAN STORMWATER MANAGEMINT MANUAL FoR MAHYSIA
4-57
of
2%
meires.
A
=wx
L.
T
ATTACHMENT
1
CHAPTER 24 Stormwater Inlets
Acknowledgement The permission granted by Jabatan pengairan dan saliran to to publish rhe whore of rhi' chapter of urban SEAM stormwater Management lv{anual for Malaysia is gratefully acknowledged.
REAM
E
24 STGR.E?WAT€R. SNLETE
24.1 GENEML..... 24.L.t
pavement Inlets
................24-1
..........
inlets 24.2 PAVEMENT DRAINAGE 24.2.t Hydroptaning 24.2.2 Longitudinal S1ope.......... 24.2.3 Cross (Transverse) Slope... 24.2.4 Kerb and Gutter.......... 24.2.5 Design Frequency and Spread... 24.3 LOCATING INLETS........ 24.3.t General Requirements 24.3.2 Gutter Flow.. 24.3.3 Setection of Inlet Type ........... 24.3.4 Inlet Spacing C-alculation 24.3.5 Location of Inlets....... 24.4 INLET CApACrry CALCUTATTON ................ 24.4.L Allowance for Blockage 24.4.2 Combination Kerb Inlet 24.4.3 Fietd Intet 24.4.4 Surcharge In1ets.......... 24.5 HYDMUUC CONSIDEMTIONS ............ 24.6 CONSTRUC[ON.............. ................:.. 24.6.7 Structural Adequacy..... 24.6.2 Materiats...... 24.6.3 Access Covers 24.6.4. Cover Levels 24.7 MAINTENANCE................. Z4.LZ
APPENDIX
24.A
Other
DESIGN CHARTS.......
ESMPLE..... 24.8.L Spacing of Intets (Hatf Road Width)......... 24.8.2 Spacing of Inlets (Combined Catchment and Road) 24.8.3 Inlet Gpacity Calculation
APPENDIX
24.8
WORKED
Urban Stotmwater Management Manual t
.......24_t ....24_t
.....................24_3 ...24_3 ....24_4
.....................244
........244 ..............24_5
...................24-7 .........24-7 ...24_7
."..............24_7 .....24_B
.........24_8
..........24-12 .......24_t2 .......24_12
.......24-L3 .......24_13 ...............24_14
................24_t4 .......24_L4 ...24_74
.24_t4 ...24_14
...............24_15
..:................ ..24-17
...,....,24-23 ...................24_23 .....24_23 ....24_25
Stormwater Inlets
24.I
GFNTRAL
Stormwater runoff presents numerous safety hazards in urban areas. On-road ponding, reduced visibility and
hydroplaning of vehicles are some of the hazards. In an urban setting these hazards are substantially magnified due to the increased traffic and pedestrian density. Stormwater inlets, also known as gully inlets, are mainly
provided
to
collect this stormwater from the paved
surfaces, parks, landscaped and open space areas, and transfer it to underground pipe drains. Even where an open drain system is used, the inlets connect to the open drains by means of pipes. The provisions apply to both types of drainage system.
inlets will not function properly if the downstream pipe or open drain system has insufficient capacrty, causing backwater. The designer of these systems should refer
Chapters desirable
from water-logging and damages. A typical arrangement road drainage and stormwater inleG is shown in
of
Figure 24.1.
The location of inlets on roads is governed by the safe flow
limits in gutters. When selecting and locating inlets,
consideration shall be given to hydraulic efficienry, vehicle, birycle and pedestrian safety, debris collection potential, and maintenance problems. Care is needed to ensure that property access is not impeded. These principles are explained in greater detail in subsequent sections.
Three types drainage:
. . .
grate intet (Figure 24.2a) kerb inlet (Figure Z4.Zb) combined inlet, grate and kerb (Figure 24.2c)
to
25 and 26 respectively. As a guideline it is to have at least 1.0 m height diffeience between
the road level and the drain invert in order for the inlets to operate correctly.
of inlets is encouraged in more highly urbanised areas, for draining more runoff from streets, parking lots and airport facilities although more developed countries are now beginning to shift from hard engineering to soft engineering using roadside swale. This Chaptei does not apply to roads where the runoff should discharge directly to a roadside swale (Chapter 2G and 31). Installing
a
The materials used in this Chapter were adapted mainly from FHWA (1996) and eUDM (1992).
of inlets may be utilised for pavement
Kerb inlets are less affected by blockage. Extended kerb
inlets, using lintel supports, can be used
capacity. The
combined grate
to increase and kerb inlet
(Figure 24.2c) is the most efficient, and it should be used Details of the recommended standard kerb inlets are shcurn in StandarC Drawing No. SD F-1.
on urban roads wherever possible.
Grates are effective in intercepting gutter flows, and they also provide an access opening for maintenance. In some situaUons they are prone to blockage. All grates on road
should be an approved, birycle-friendly design. FHWA (1978) have investigated several grates for inlets and developed bicycle-safe grate configurations. Typical
schematic
of
bicycle-friendly grates
are shown in
Figure 24.3.
24.1.L Pavement Inlets The most common type of inlet is that from a road pavement. Inlets also provide access to pipes for maintenance. Standard sizes and shapes should be used to achieve economy in construction and maintenance. Adequate road drainage helps to protect the road subgrade
24.t.2
Other Inlets
Inlets are not normally required for drainage from private property, because in Malaysian practice this drainage
is
usually discharged into an open drain along the property boundary.
Access Correr
Kerb Inlet
Walkway
Grating
Altemative: Single Cross-fall
Median Drain or Cross{rain (for Single Cross-fall Road)
To Drain
Figure
24.1
Road Drainage System and Stormwater Inlets
Urban Stormwater Management Manual ZA'I
PERSPECTTVE
SECNON
Figure
(a) Rectangular
24.2
24.3
Other stormwater inlets are required
(c) Honey Comb
to
Bicycle-friendly Grates (based on Screen Opening)
collect surface
stormwater runoff in open space, reserves or swales where
the flow is to be introduced to an underground pipe system. These grate inlets are known as 'field inlets'. A field inlet (Figure 24.4) is used in open space reserves, depressed medians and other locations away from pavement kerbs. Grated inlets can also be used in middle
24-2
Pavement Inlets
(b) Rhombus
Figure
of the
(c) CombinaUon Inlet (Kerb and Grate)
(b) Kerb Inlet
(a) Grate Inlet
(Figure 24.5). A surcharge inlet is similar to a field inlet except that it is intentionally designed to permit surcharge for pressure relief in a pipe system.
Details
shown
of standard field inlets and surcharge inlets are in Standard Drawings SD F-2 and 5D F-3,
respectively.
parking lots where kerbs are not required
tJrtan Stomwater Management Manual
Stormwdter Inle&
However this Manual
is not intended to
24.?
preclude the
adaption of other designs by a Local Authority. The Local Authority may determine which standard or. oih"r. types of inlets are appropriate for its area. Standardisation of inlet designs within a local area is recommended in the intereda of economic efficiency. If another design is adapted by a Local Authority, that Authority wiil need to obtain or derive inlet capacity Design Charts in piace of those given
When rain falls on a sioped pavement surface, it forms a thin film of water that increases in thickness as it flows to the edge of the pavement. Factors which influence the depth of water on the pavement are the length of flow path, surface texture, surface slope, and rainfall intensity. A discussion of hydroplaning and design guidance for the
in
Appendix 24.A.
PAWfrM€N? SRASTAGE
following drainage elernents are presented:
. . .
Longitudinal pavement slopes Cross or transveise pavement slope
Kerb and gutter design
Additional technical iniormation
on the mechanics of suface drainage can be found in Anderson et (1995). al
24.2.t
Ftydroptanimg
As the depth of water flowing over a roadway surface increases, the potential for hydroplaning increases. When a rolling tyre encounters a film of water on the roadway,
the water is channelled through the tyre tread pattern and
Figure
24.4
through Grated Sump Field Inlet
the surface roughness of the
HydrcplaninE o€cuis yrhen
pavement.
the drainaEe capacit/ of the tyre tread pattern and the pavement ,rrfu.u is exceeded and the water begins to build up in front of the tyre. As the water builds up, a water wedge is created and this wedge produces a hydrodynamic force which can lift the tyre off the pavement surface. This is considered as furl
dynamic hydroplaning and, since water offers rittre shear resistance, the tyre loses its tractive ability and the driver has a loss of control of the vehicle
(a)
Perspective
Hydroplaning is a function of the water depth, roadway geometries, vehicle speed, tread depth, tyre inflation pressures, and conditions of the pavement surface. It has been shown that hydroplaning can occur at speeds of 89 km/hr with a water depth of 2 mm. The hydroplaning potential of a roadway surface can be reduced by the
following:
. .
Design
the roadway geometries to reduce
the
drainage path lengths of the water flowing over the pavement. This will prevent flow build-up. Increase the pavement surface texture depth by such methods as grooving of cement concrete. An increase of pavement surface texture will increase the drainaqe capacity at the tyre pavement interface. The use of open graded asphaltic pavements has oeen shown to greatly reduce the hydroplaning potential of
the
ii
roadway surface" This reduction due to the ability of the water to be forced through the pavement
tyre.
(b) Figure
24.5
Section
Grated parking Lot Inlet
under the This releases any hydrodynamic pressures that are created and reduces the Dotential for the iyre to hyoroplane. The use of drainage structures along the roadway to capture the flow of water over the pavement will
Uban Stormwater Nanagement Manual z.+-3
Stormwater Inleb
reduce the thickness of the film of water and reduce the hydroplaning potential of the roadway surface.
Additional guidelines related to cross slope are:
Although not widely encouraged, inside lanes can sloped toward the median if conditions warrant.
l.
The Design Acceptance Criteria for surface flow on roads (see Table 4.3 of Chapter 4) have been set to limit the potential for hydroplaning at high speeds, as well as the potential for vehicles to float or be washed off roads at
Median areas should
2.
The number and length of flat pavement sections in cross slope transition areas should be minimised. Consideration should be given 1o increasing cross
3.
24.2.2 Longitudinal Slope
slope in sag vertical curvesr crest vertical curves, and in sections of flat longitudinal grades.
Experience has shown that the recommended minimum values of roadway longitudinal slope given in the MSHTO (1990) Policy on Geometric Design will provide safe,
.
to drain away from the pavement, except with raised, narrow medians and
Shoulders should be sloped
4.
superelevations
In addition, the following
A minimum longitudinal gradient is more impoftant for a kerbed pavement than for an unkerbed pavement since the water is constrained by the kerb. However,
flat gradients on unkerbed pavements can lead to spread problem if vegetation is allowed along the pavement edge.
.
to
Table
Normal Pavement Cross Slopes (FHWA, 1996)
Range in Rate of
Sudace Type
a
Suface Slooe High-Type Surface 2 lanes 3 or more lanes, eaeh direction
for
kerbed pavements with an absolute minimum of 0.3 percent. Minimum grades can be maintained in very flat terrain by use of a rolling profile, or by warping the cross slope to achieve rolling gutter profiles.
.
24.1
build up
Desirable gutter grades should not be less than 0.5
percent
not be drained across travel
lanes.
lower speeds.
acceptable pavement drainage. general guidelines are presented.
be
To provide adequate drainage in sag veftical curves, a minimum slope of 0.3 percent should be maintained within 15 metres of the low point of the curve.
in MSHTO's poliry on geometric design of highways and streets. These cross slopes are a
0.015 minimum; increase 0.005 to 0.010 per lane; 0.040 maximum
lntermediate Surface
0.015 - 0.030
Low-Type Surface
0.020 - 0.060
Shoulders
24.2.3 Cross (Tmnsverce) Slope Table 24.1 indicates an acceptable range of cross slopes as
0.015 - 0.020
Bituminous or Concrete
0.020 - 0.060
With Kerbs
> 0.040
24.2.4 Kerb and Gutter
specified
compromise between the need for reasonabiy steep cross slopes for drainage and relatively flat cross slope for driver comfort and safety. These cross slopes represent standard
practice. MSHTO (1990) should be consulted
before
All roads in urban areas shall generally be provided with an integral kerb and gutter. The current practice of providing a kerb orily on roads is generally not acceptable as there is
no defined gutter to carry stormwater flows, and the road pavement will suffer damage from frequent inundation.
deviating from these values.
of 2 percent have little effect on driver effott in steering or on friction demand for vehicle stability, Use of a cross slope steeper than 2 percent on pavement with a central crown line is not desirable. In areas of intense
Cross slopes
rainfall, a somewhat steeper cross slope (2.5 percent) may be used to facilitate drainage (Gallaway et al, 1979). Where three (3) lanes or more are sloped in the same direction, it is desirable to counter the resulting increase in flow depth by increasing the cross slope of the outermost lanes. The Wvo (2) lanes adjacent to the crown line should be pitched at the normal slope, and successive lane pairs' or portions thereof outward, should be increased by about 0.5 to 1 percent. The maximum pavement cross slope should be limited to 4 percent (refer to Table 24.1).
244
However, where the volume of gutter flow is negligible as in car parks and on the high side of single-crossfall roads, a kerb only is acceptable. Kerbs are normally used at the outside edge of pavement for low-speed, and in some instances adjacent to shoulders
on
moderate
to
high-speed
roads. They
serve the
following purposes:
.
contain the surface runoff within
the roadway
and
away from adjacent properties,
o . .
pr€v€ot erosion on fill slopes, provide pavement delineation, and enable the orderly development
of propefi
adjacent
to the roadway.
lJrban Stormwater Management Manuar
Stornwater Inle?
Gutters formed in combination with kerbs are available in 0.3 through 1.0 metre width. Gutter cross slopes may be same as that of the pavement or may be designed with a steeper cross slope, usually g0 mm per metre steeper than the shoulder or parking lane (if used). MSHTO geometric guidelines state that an go/o srope is a common maximum
cross slope.
The kerb and gutter shail be a standard size to faciritate
economical construction. Recommended standard details for road kerbs and gutters are shown in Standard Drawing No. SD F4. The standard kerb height of 150 mm is basej upon access considerations for pedestrians, vehicle safety
including
the opening of car doors, and
requirements.
A kerb and gutter combination forms a triangular channel
that can convey runoff equal to or less tfra-n tne design flow without interruption of the traffic. When
a design
flow occurs, there is a spread or widening of the conveyed water surface. The water spreads to include not only the
gutter width, but also parking lanes or shoulders, and portions of the travelled surface. Spread is what concerns the hydraulic engineer in kerb and gutter flow. The
distance of the spread is measured perpendicular to the kerb face to the extent of the water on the roadway and is shown in Figure 24.6.
drainage
If a local Authority decides to adapt a different standard, the design curves given in this Chapter wilt need to
adjusted accordingly.
be
24.2.5 Design Frequencry and Spread Two of the more significant variables considered in the design of pavement drainage are the frequency of the design event and the allowable spread of water on the pavement. A related consideration is the use of an event
of lesser frequenry to check the drainage design.
Spread and design frequenqy are not independent. The implications of the use of criteria for spread of
one_half of
a traffic lane is
considerably different for one design freguency than for a lesser frequency. It also has different
implications for a low-traffic, iow_speed roads than for a higher classification roads. These subjects are central to the issue of pavement drainage and important to
traffic
safety.
(a)
Selectbn of Design Frequenq and Design Spread
(a) Uniturm
The objective of pavement storm drainage design is to provide for safe passage of vehicles during the design storm event. The design of a drainaEe system for a kerbed pavement section is to collect runsff in the gutter and convey it to pavement inlets in a manner that provides reasonable safety for traffic and pedestrians at e reasonable cost. As spread from the kerb increase, the
risks of traffic accidents and delays, and the nuisance and possible hazard to pedestrian traffic increase.
(b) Composibe
The process of selecting the ARI and spread for desion
involves decisions regarding acceptable risks of acciderits and traffic delays and acceptable costs for the drainage system. Risks associated with water on traffic lanes are greater with high traffic volumes, high speeds, and higher road classifications.
A summary of the major considerations that enter into the selection of design frequency and design spread follows:
1.
The classification of the road is a good point in the
selection process since
(c) Curved
volume roadways Figure
24.6
it
defines
the
public,s
expectations regarding water on the pavement surface. Ponding on traffic lanes of high_speed, high_
Gutter Sections
is
contrary to the public,s of accidents and the
expectations and thus the risks costs of traffic delays are hioh,
Urban Stormwa ter lrlanagement Man ual z.+-J
Stormwater lnle&
2.
Design speed is impoftant to the selection of design criteria. At speeds greater than 70 km/hr, it has been shown that water on the pavement can cause hydroplaning.
3.
The intensity of rainfall events may significantly affect the selection of design frequency and spread. Risks associated with the spread high in Malaysian conditions.
of water on pavement
is
Other considerations include inconvenience, hazards and nuisances to pedestrian traffic. These considerations should not be minimised and in some locations such as in commercial areas/ may assume major importance.
The relative elevation of the road and surrounding terrain is an additional consideration where water can be drained only through a storm drainage system, as in underpasses and depressed sections. The potential for ponding to hazardous depths should be considered in selecting the frequency and spread ci'iieria and in checking the design against storm events of lesser frequency than the design event.
to greater widths where traffic volumes and speeds are low. Spreads of one-half of a traffic lane or more are usually considered a minimum type design for low-volume local roads. Spread on traffic lanes can be tolerated
The selection of design criteria for intermediate types of facilities may be the most difficult. For example, some arterials with relatively high traffic volumes and speeds may not have shoulders which will convey the design runoff without encroaching on the traffic lanes. In these instances, an assessment of the relative risks and costs of
Table24.2
also given in Chapter 4, Table 4.3.
The
recommended design frequency
(b)
Seledion of Major storm and Spread
A major storm should be used any time runoff could cause unacceptable flooding during less frequent events. Also, inlets should always be evaiuated for a major storm when a series of inlets terminates at a sag vertical curve where ponding to hazardous depths could oeeur"
The frequency selected for the major storm should be based on the same considerations used to select the design storm, i.e., the consequences of spread exceeding that chosen for design and the potential for ponding. Where no significant ponding can occur, major storm are normally unnecessary. Criteria for spread during the check event are
1. 2.
:
one lane open to traffic during the major storm event one lane free of water during the major storm event
These critena differ substantively, but each sets a standard by which the design can be evaluated.
Design Frequency
Design Spread
< 70 km/hr
10 year
1m
Divided or
> 70 km/hr
10 year
No Spread
Bi-directional
Sag Point
50 year
1m
< 70 km/hr
10 year
Vz Lane
> 70 km/hr
10 year
No Spread
Sag Point
10 year
7z Lane
Low Traffic
5 year
7z Lane
High Traffic
10 year
7z Lane
Sag Point
10 year
7z Lane
Local Streets
depressed
depths.
High Volume or
Collector
for
sections and underpasses where ponded water can be removed only through the storm drainage system is a 50 year ARL A 100 year ARI storm is used to assess hazards at critical locations where water can pond to appreciable
Suggested Minimum Design Frequency and Spread (Adapted from FHWA, 1996)
Road Classification
24-6
various design spreads may be helpful in selectino appropriate design criteria. Table 24.2 provides suggeste; minimum design frequencies and spread based on the types of road and traffic speed. Similar design criteria are
lJrban Stormwater Managemeft Manual
Stormwater Inleb
24.3
LSEATING Iru!-F"TS
24.3.1 General Requinements The location and spacing of inlets on roads is governed in part by the need to provide safe, economical road drainage
by limiting the amount of gutter flow. The design
5=
acceptance criteria for road flow is provided in Chapter-4, Table 4.3.
Figure
These criteria are based on pedestrian safety and vehicle stabirity. They assume that traffic wiil srow to a safe speed in the major flood when the road is flooded. They do not appry to expressways because ponding on expressways would cause a risk of vehicle aquaplaning. The design of expressway drainage is outside the scope of this Manuar.
24.7
Table
Kerb and Gutter, Showing Half Road Flow
24.3
Manning,s 'n' and Fiow Correction Factor, F,,for Gutter Flow (eUDM, 1992)
Suface Type
24.3,2 Gutter Flow Many pavement dralnage problerns occur
because
Longitudinal Slooe
in
Malaysia
of a failure to give due attention to gutter flow In many cases gutters are poorly formed or
Concrete
0.013
llot nix asphaltic conc:ete
c.015
Sprayed seal
0.018
Kerb and Gutter type
Ff
and inlets.
absent, inlets are too widely spaced, and the design of the inlets is inadequate to capture gutter flow and convey it to the drainage system.
Senn I - m o u nta b
In particular, the common practice of forming a round or half round inlet at the entrance of a pipe is unacceptaOte
I
e
-r y*pe
Barrier type
rJ.>
0.9
because:
r . o . r
the available inlet area is too small to be effective, the design is hydraulically inefficient,
water must pond on the road
to
produce sufficient
head available to force gutter flow into the inlet, it is prone to blockage, and
This form of the equation allows for the pavement and channel to have different roughnesses and/or different crossfalls. For the definition of terms in the equation refer to Figure 24.7. The face of the kerb is approximated as being vertical.
when used on grades, gutter flow simply bypasses the inlet altogether.
It
is vital that proper hydraulic design principles Oe applied to the design of stormwater inlets. These principles are discussed in this Chapter.
Parameters required to calculate gutter flow from the pavements are shown in Figure 24.7. Knowing those parameters, gutter flow capacity may
be calculated by
Izzard's equation given below (lzzard, 1946):
Using either Equation 24.1 or the Design Chart in 24.A, suitable limits for gutter flow can be
Appendix
determined. The average inlet spacing is then determined ensure that this limit is not exceeded. A worked
to
example
of this calculation is provided in
Appenctix 24.8
the inlet capacity of an inlet
increases with
(based on AR&R, 1997).
Note that
increasing gutter flow. Therefore, provided the flow width limits are satisfied, it is an advantage to allow some bypass
gutter flow on sloping roads to maximise the use of the inlet capacity (Sutherland, 1992).
24.3,3 Selection of trnlet Type (24.1) where, subscripts g , p and c refer to the gutter, pavement and road crown, respectively. F,.is a flow iorrection factor, Zis the cross slope, 5is the longitudinal slope and dis the runoff depth over the pavement. A Design Chart for gutter flow calculation is given in Appendix Z+.n. Recommended values of Manning,s roughness coefficient n and the Flow Correction Fador F1 for gutter flow are given 24.3.
in Table
Kerb inlets on gracle shall normally be type .S, with a Z.4m long lintel as shown on Standard Drawing SD F_1. The capacity of these inlets is shown in Design Chart24.2. Type 'M'or 'L' lintels may be used at sag points to provide
additional capacity if space and kerb geometry permits. A
Type'S'inlet may also be used:
o
Bt changes in direction where entry of water is not essentiai (i.e. side entry may be sealed)
Utban Stormwater f,fanagement Manual 24-7
Stormwater Inlets
. I
in tight radius kerb returns where the length of a type M or L iniet is inappropriate as a field inlet
o on grades, with average spacing calculated in accordance with Section 24.3;
o
Bt the tangent point of intersection kerb returns such that the width of gutter flow around the kerb return in the Minor Design Storm Coes not exceed 1.0m;
"
immediateiy upstream of pedestrian crossings, access ramps, taxi or bus stops;
"
imrnediately upstream of any reverse crossfall road pavement, where flow would be directed across the
24.3.4 lnlet Spacing Calculation Inlet spacing calculation uses the Rational Method to estimate discharge in the design storm. For simplicify each inlet subcatchment is assumed to be approximately rectangular as shown in Figure 24.8. If the subcatchments are not rectangular they should be replaced by equivalent rectangular su bcatchments.
The average inlet spacing on grade is caiculated so that allowable gutter flow is not exceeded, using the procedure shown in Figure 24"9.
A worked example for the calculation of inlet spacing on grade is given in Appendix 24.83.
Illustrations showing the typical location of inlets for roads are given in Figure 24.10. General
Kerb inlets for all roadways shail be spaced such that gutter flow widths do not exceed the previously discussed limits. Inlets should also be located such that the quantity of gutter flow entering an intersection kerb return is minimised.
along the high side of islands or medians so as to meet the gutter flow width limitations in Section 24.3. and at the downstream end of the island or median to
prevent gutter florry continuing onto
the
road
pavement.
inlers shail nor be iocateci on the curve at an iniersection because of the risk they present to vehicles. Also, the structural design of a side inlet on a curye is much more
Kerb inlets vrithin an island or median strip should, where possible, be a normal inlet. However if the space available v;ithl:l a ::'ledien st'ip is insufficient, a median drain design similar to Figure 3.10 of JKR "Guide to Drainage Design of Roads" can be used. Because this alternative is less
hydraulically efficient, appropriate modifications shall be made to the inlet spacing. If the depth and velocity of gutter flow are within acceptable limits, a median opening may alternatively be used to allow runoff to flow to the downhill kerb drain.
Where sufficient width is available, grated inlets can be recessed into the kerb or island so that the grate does not project onto the road pavement. However this also reduces their effectiveness,
Inlets shall be provided:
.
"
complex.
24.3.5 Location of Inlets
(a)
pavement;
in the low points of all sags;
Fall
\ Subcatchment
LEGEND
Pipe,
Inlet -....o-
Gutter
Flow -----> Flow \-v
Figure
24-B
24.8
Calculation of Gutter Flow and Inlet Spacing on Grade
tJrba n 5 torm wa ter Ma naaemeil Man
u al
Stormwater In/ets
CALCUTATT ALL*WAEIE
ii,*
ut4IT *F 6rlTTr* rL&W
:;::.qi :):::':i,i
]fi
CATCL{FISF*T
*F THg i
iLTT
AOD SY'PA55CD FLOIV Fn0t'l UP5'iRf,,\i"i " iF Ai{"1
T*TAL FLOW WiTl'{:f,{
CALCi.ILAYE iFILg-N CAF"I1J&€ A}J* AMOtJf iT 0F rLQW SY-PASgfp
To **wil$TnrAr4
pROVIDE FUil_ &EQUIR.c* CAPAC:TY AT 5A$ IIiLTT
Figure
Urban
S torm wa
ter Manag em en t plan ua/
24.9
Flowchart for Calculation of Iniet Spacing
74-9
Stormwater Inlets
Inlet posfion to suit maximum spacing from top of catchment
,I r/
*"/
Inlet on
"paOng
tangent of kerb return
Inlet on tang€nt
I/ /
;to*r*'^ I
I
Inlet upstream of pedestrian crossing
Max. 450 mm in
Max. 1000 mm
in Minor Storm ROAD
(a) at Bus Stop
(b) at Kerb Return
Max.1000 mm
in Minor Storm
Through
Lane --D
(c) at Deceleration Lane
Figure
24-L0
24.10
Typicai Location of Inlets for Roads
ltrba n Storm wa ter f,lana ge men t Man ua /
Stormwater InteE
Locations are also influenced by {AR.&R, 199g):
. . . . "
If the longitudinal grades of the kerbs approaching
superelevations
and other changes to road
an
intersection are steep, it may be necessary to check for the effect of flow super-elevation on the gutter flow spread around the kerb return.
the positions of other utility services; the posiiions of driveways; cross_
sections, which cause flow to cross roads; maintenance requirements, such as clear access; and
(c)
the need to limit flow depths on the low side of roads below crest levels of driveways serving properties
Inlets in sags must have sufficient capacity to accept the total gutrer flow reaching the inle! including ail bypass flows frorn upstrearn. ponding of water at sags must be lirnited to the limlts set in Section 24.3, particularly at intersections where tuming trafflc is likely to encounter
below road level.
(b)
InleE on Grade
Inleb in Sags
ponded water. Designers should be aware that the inlet capacity of pits on grade is controlled by the longitudinai grade and the road crossfall. Inlet Capacity charts for standard inlets are given in Appendix 24.A of this Chapter.
Bypass gutter
fiow from an upstream inlet must
be
acccunted rfcr in the Cesigit of ihe downsti-earn inlet which receives the flow. A design procedure which satisfies this requirement is given in Chapter 16. There is no limit to the amount of gutter flow that may be bypassed, provided that the gutter flow restrictions in Section 24.3 are adhered
(d)
Inleb for Parking Lot
Parking
lot inlets should be lccated
outside
of
heavily
traveled pedestrian areas (e.g. crosswalk, kerb ramps, and lead walks to the building and between parked vehicles). Inlets should be placed in areas where people can access
their vehicles without stepping around the Figure 24.11 shows recommended placement parking areas.
inlet.
of inlets in
Kerb Inlet
Prefuned Kerb Inlet
l-ocaUon
Locauon Not Recommended
Drop Inlet Accepbble Location
Figure
Urban Stormwater Management Manuat
24.11
GIN .*ow
Typical Location of Inieis for Parkinq Lots
24-rr
__lr_ Stormwater lnlets
24.4
INLETCAPACTTY CALCIJLATICII'{
24,4.1 Allowance for Blockage Inlet interception capacity has been investigated by several agencies and manufacturer of grates. Hydraulic tests on grate inlets and slotted inlets were conducted by Bureau of Reclamation for the U.S. Federal Highway Administration. Normally the longitudinal bars are veftical and the
transverse bars (vanes) are fixed in different angle and
orientation
to get
maximum hydraulic efficiency with minimum blockage from litters. Few typical arrangement
of vanes in the grates are shown in Figure 24.12. The design blockage allowance shall normally be 30yo for an inlet on grade and 500/o for a sag inlet or field inlet, unless otherwise directed.
to be handled by the inleG shall be determined from network design calculations as
The gutter flow required described in Chaoter 16.
24.4.2 Combination Kerb Inlet Combination kerb inlets can have 2.4 m, 3.6 m or 4.g m long lintels (refer Standard Drawing SD F-1 types .S,, 'M, and'L', respectively).
The inlet capacity of combination kerb inlets can be taken
to be approximately equal to the sum of the kerb openino and grate capacities.
fhe
kerb apening capacity depends on the inlet throat geometry (see Figure 24.13). The inlet throat acts as an orifice and the orifice flow equation applies (FHWA, 1gg4). Qt =o.67hLtl2gd,
(24.2)
where,
Or = flow through the inlet throat, l. = length of kerb opening, do = effective head at centre of the orifice throat, and
11 = orifice throat
width
For inlets on grade, this theoretical capacity is
reduced
of fast-flowing water to bypass the inlet opening. The efficiency f of a kerb opening on because of the tendency
Flow Direct'on
grade is given as:
r (a) Parallel Bar
(24.3)
=Q,
a
where,
Tranwerse Bar (Vane) Flow Drcction
(b) Curved Bar
Flow Direction
O = total incoming flow through the gutter side O = flow captured by the inlet The efficiency of an inlet on grade depends on the length of the opening, longitudinal slope, cross-fall, and whether there are any deflector bars to divert flow into the grate.
The grate capacity depends on pavement geometry, the direction and depth of flow and the grate configuration including the spacing and size of bars. For shallow depths, up to approximately 200 mm, the weir equation can be applied.
Qe -- F, x !.66 x luh3t (c) 45'Tilt Bar
Figure24.L2 Typical Arrangement of Vanes for Grates
11'L Z
2
(24.4)
where,
Le =
effective length of grate opening in the direction of flow,
Fa = blockage factor, pn = grate capacity
lltban Stormwater Management Manual
lnleb
Stormwater
In practice, it is not worthwhile or practical to perform these calculations for each inlet. Instead the capacity is estimated from empidcar curves which shourd be based on prototype testing. Empirical iniet capacity design curves for combination kerb inlets are shown in Appendix 24.A. These curvd:s based on eUDM (1992), show ihe comOined capacity of the kerb and grate inlet. Allowance must be made for blockage as described in Section 24.4.1.
24.4.3 Fietd
(a) Horizontal
InNet
The inflow capacity of a field inlet depends on the depth of
water over the
inlet.
For shallow depths. up
to
approximately 200 mm, the flow will behave as a sharp_
crested
weir. For greater depths the inlet will become and will behave as an orifice. The
submerged
discharge/head characteristics of the two flow types are different (see Equations 24.5 and 24.6).
The capacity of the inlet should be checked using both formulae and the lesser inlet capacity adapted.
(i)
under weir flow eonditions
(b) Indined
Qe = Fe xL.66 x Lh3t2
(ii)
(24.s)
under orifice flow conditions
Qo=Fa x0.60,46
(24.6)
"Jegh)
where 246
is the area of the grate opening.
24.4.4 Surcharge Inlets Surcharge inlet structures shall be provided:
. (c) Verticat
in floodways
. Figure
24.13 Throat Configuration of Kerb Opening (FHWA,1996)
where branch pipelines connect to low flow pipelines
Inlets
where there are shallow points in the system to form an emergency overflow relief path in times of acute hydraulic overload or blockage of the pipe system
The need for a surcharge inlet on pipelines shall
The effective length of the grate opening will depend on its width, the width of the grate bars and on the approach direction of flow. On grade, Lu (W_W6) and = in sags,
be
deterrnined by Hydraulic Grade Line Analysis, as described in Chapter 25. If the HGL analysis indicates the tiketihood of surcharge but the location does not permit surcharge
L"= 2(W-Wt), where, Wis the overall width of the grJte
water to flow away safely, a sealed manhole lid with
At dipths greater than 200 mm, grate inlets in sags can function under orifice flow concJitions as discussed in the
To
and
W6 is
the total width of the longitudinal bars.
following section.
lock-down cover shall be provided.
a
the risk that the surcharge opening will becorne partially or fr:lly blocked by debris and titter in the minimise
surcharged flow, the surcharge capacity of the inlet structure should be twice the total design inflow from all
pipes connected
to the structure.
Details
of
the
Urban Stormwater Management Manual
24-t3
Stormwater Inle&
recommended standard surcharge iniet
are shown in
24,6,3
Aceess Cowess
Standard Drawing SD F-3.
24.5
HYDRAIJLIC COfqSIEER.ATTSNS
The type sf inlet cover shall be selected according to the following criteria:
o
sealed solid
top for
structures
in
The calculations given in this Chapter assurne that there is no downstream constraint to inlet flows. This means that
waterurays and other locations subject
or downstream open channel is sufficient to convey the flow from the inlet(s).
' "
loads, for
the capacity, level and grade of the pipe drain
In order to achieve this condition, the downstream system must be properly designed and have sufficient freeboard
the HGL. A number of older existing drainage systems do not meet this criterion. The designer of these systems is referred to Chapters 25 and 26, respectively. As a guideline it will be necessary tc have at least 1.0 nr height difference between the road level and the drain above
engineered hydraulic
to
.
inlet structures, or surcharge structures (bolt-down locking shall be provided with stainless steel bolts to secure the cover and the seating ring tc the structure)
grated cover, for
" inlets subject to traffic loadings, or o inlets in paved pedestrian areas (a) Concrete cover
in practice, the stormwater inlets and pipe drains must be
An ungrated inlet not subject to traffic loads or hydraulic surcharce shall be orovided with a standard reinforeed concrete seating ring and lid in accordance with Standard
designed together because the two systems interact:
Drawing SD F-7.
.
The minimum size opening for access is 600x600 mm.
inveft in order for the inlets to operate correctiy.
if there is insufficient lnlet capacity the pipes wil! not flow full, and
.
backwater effects from the pipe drainage system rnay reduce the effectiveness of the inlets, or cause them to surcharge instead of acting as inlets.
The complexity of these interactions is such that in all but the simplest situations, the design task is best handled by
computer models. Some suitable computer models are described in Chapter 17.
24.6
CONSTRUCTION
24.6.L Structural Adequacy Stormwater inlets shall be constructed so that they are structurally sound and do not permit ingress of water through the walls or joints. Materials shall be resistant to erosion and corrosion. Where necessary, corrosion resistant cement shall be utilised.
24.6.2 Materials
(b)
MetalGrates
An inlet grate which will be subjected to vehicle loadings shall be designed to support those loads in accordance with the relevant Malaysian or British Standard. Ductile iron covers shall be :GATIC:, or other proprietary design as approved in writing by the Local Authority.
24.6.4
Cover Levels
Stormwater inlet grates and access covers (if used) shall be set at the finished cover levels given in Table 24.4. Table
24.4
Location
Flush with finished surface
Footpaths and
Flush with finished surface
Stormwater inlets may be constructed from:
r r . .
Landscaped areas, parks
precast concrete,
cement rendered brickwork, or
Elsewhere
24-14
Flush with finished surface 100 mm above surface to allow
for topsoiling and grassing
mortared blockwork
The lintels for type S, M and L Bits shall be preeast, to comply with appropriate Malaysian or British standards.
Grate/ Cover Level
Roads, other paved areas
street verges
in-situ concrete,
Grating Cover Levels
(see Note)
Ncte:
Stormwater inlet tops shall
be
protected The fill shall
placing fill against the top. graded down ta natural suface slope of 1 in 10.
at a
bY
be
maximum
Utban Stormwater Management f"lanual
Stormwater
Where finished surfaces are steeper than 1(V):10(H), the level. An adjacent flat area shall be provided with sufficient space on which to place a removed access cover shall be
cover.
24.V
MAINTENANCE
InleE
an accumulation of litter and debris, which may cause blockage. Sag locations are particularly susceptible to
blockage.
Chapter 25 provides more detail maintenance required for maintenance required for drainage qystem, which involves inlets.
Inlets shall be checked and cleaned regularly, to prevent
Urban Stormwater Management Manual
24-t5
--;+_--.*+:
Stormwater Inlets
APPENDIX 24.A DESIGN CHARTS
Design
Description
Chart 24.L
Gutter Flow
24.2
Combination Kerb Inlet Gpacity _ Type S
Page
24-18
24.3
24.4 24.5
Combination Kerb Inlet Capacity _ Type M CombinaUon Kerb Inlet Capacity Sag Inlet Capacity
-
Type
L
24-19 24-L9 24-20 24-21
Urban Stormwater Management Manual 24-17
-
:I
Stormwater Inlets
Longitudinal Road Slope, 5(%)
0.5 t
200
2 461015
)./5
ti 180
4.73 160
3.73
140
ly it:
xQ OJ
ff
120
T
=
E
\
''-i'1-
80
'ft/z1ffi: ; 'tl' //4 i'." ,,i:
50
i;:-;;';
i :tiit
7.73
(
T:';114,=
100 o)
o
7l
ts d=
; 3
tr
:
t.73
i' ,i'
ydhiLI
1'i'r'';'l'i.'
n7?
*"i-,*---*--l*,* i:..i.-
40
ri.
20
0.10
0.01
i"tl i ,' ,r,
-u.l/ 10.00
1.00
Gutter Flow, Q (m 3/s)
Design Chart
Based on Znand
24.1
Gutter Flow using lzzard's Equation (QUDM, 1992)
Zo= lo/o (Road Crossfall),
aartiei kerb type 81 (450mm), flo ne
= 0'015, = 0.013
Note:
A number of similar set of curves can be prepared using different combination of variables in lzzard's Equation.
24-18
Urban Stormwater Managemen t Man ual
Stormwater ln/eE
E c vt s-' o h '-1
E
I
CL
(u
E
Roadway' Approaeh Flow (l_lbes/Seeond)
Design Chart
24.2
Combination Kerb Intet Capacity: Type (QUDM, S 1992)
E c
8
E
E E
:t
I
CL
o,
E
.w)
3Ut]
400
Roadway Approadr Flow (LitreslSecond)
Design chart
Urban Stormwater Managemen t
fulan
ual
24.3
Combination Kerb Inret capacity
-
Type M (QUDM, 1992)
24-t9
Stormwater InleE
E
c o (J
E 6
g J
E
:t
CL
I
n
=
100
200
300
400
Roadway Approadt Flow (Litres/Second)
Design Chaft
74-20
24.4
Combination Kerb Inlet Capacity
-
Type L (QUDM, 1992)
Urban Stormwater Management Manuat
Starmwater InleE
E E
o cc |E
150
6 o J
iE
100
s E zo tg
g CL dl
50
Inlet Capture (Litres/Secondl
Inlet Capture vs Wdth of Fonding 1:30 Crossfall
1:zl0 Cros#all
Inlet Capture Litres/Second Flow
600
800
WidUl
L?00
x300
800 x500
inlet Capture l_itres/Second
800
800
2@
x500
x5@
8CIo
Flow
6S0
800
WdEl
v30O
x30C
800 x500
800 lc500
800 x500
800
2@
m
OE
OE
5tr
ME
LE
2.0
x500
rn
103
OE
118
OE
13s
SE
ME
Itr
144
159
165
xs00
2.0
91
104
120
126
191
134
198
139
2.s
102
It7
134
193
226
143
234
157
163
3.0
113
130
148
219
262
27l
?E
160
181
188
125
1.14
163
179
206
214 247
2.5
3.0 3.5
118 135 152
136 155
174
155 175 196
168
4.0
159
194
217
245
300
310
4.5
r87
4.0
138
215
158
240
273
t79
197
339
232
351
4.5
150
173
194
717
302
259
380
?qd
259
5.0
164
188
210
237
288
298
258
377
328
5.0
206
237
263
5.5
226
259
287
332
2#
48
438
5.5
6.0
t77
203
282
227
312
363
467
483
6.0
5.5
191
219
266
244
306
337
279
34V
395
359
s30
6.5
205
235
267
300
37V
391
579
7.0
287
330
353
42V
s12 qqa
7.A
7.5
220
309
252
355
279
389
323
450
409
607
424
629
7.5
234
269
298
345
495
457
657
680
42
8.0
250
287
316
369
475
492
8.0
331
381
416
Inlet casures shown Above^are Independant of capture by the Grated Area. The 2 @ g00x500 configuration Requires Two sbndardini"E;;n;ed by 2.4 rn Lengr'of pipe.
Design Chart
24.5
Sag Inlet Capacity
Urban Stomwater Management l4anua/
24-21
Stormwater !n/e6
APPErutr3X
24.8.1
24.S
ltrSR.KgP FX.AS€PLtrS
Spaeimg of gclgets {ffialf R.oad WEdte!}
Problem:To determine inlet spacing to cater runoff frorn half rcaei catchment in lpoh, perak. Following data are given:
{f Rainfall intensity, 5/5 Half road widih Longitudinal slope Cross slope
= = = =
0.5
=
?o/^
The minor system design
5 rninutes 300 mm/hr
9m
= 5 year
The outer lane is a through lane,
7o
ARI
!,/<
4 r\ 1.5m \/T*Li^ | i:utc t,J,
Solution:
1)
From Design Chart L4.3, C 0.91 = [Category From Equation I4.7;
(t)],
Qnna = (Cx5lrxe;7360 = 0.91 x 300 x (9 x /7x 10-4)/360 = 0.000693 /.1 where
2)
{,
is the length of gutter flow in the upstream subcatchmeni.
Calculate the allowable limit of gutter flow. Using the Design Chart 24,1 and
Q= 0.018
W= 1.5 m;
m3/s
= 1g Vs and Vx Dis less than 0.4 m/s. Therefore, spacing for the first inlet is,
l;
=0.018/0.000683
=26.3m-26m
3)
Use a Type's'inlet as recommended in section 24.4.3. Refer to Design chart 24.2 for a Type.s, inlet with a gutter approach flow of 18 l'/s, the inlet capture is 18 gs is giving a capture efficiency of 100 o/o.
(BKSE3o).
Therefore, bypass gutter flow is zero and ihe inlet spacing to be adapted is 26 m.
24.8.2 Spacing of Inlets (Combined Catchnnent and Road) Problem: Figure 24'81 shows an idealised catchment and minor road system in lpoh. In this case the surface catchmenr drains to a gutter with a unifcrm longitudinal slope of 2o/o, Determine the maximum permissible inlet spacing from residential/road catchrnent combined wldth of 45 nr (half road width is g m). Time of concentration is 15 minutes and lumped runoff coefficient for the combined caichment is 0.g5. Manning n for paveme nt, no = e.g15 (hot-mix asphalt pavement), and for gutter, ns = 0.013 (.on.r"t" fur6lj'nJ cros. stope is 3%.
il;;|.'=Road
solution: The minor storm A
=
Wx
l.
is taken to be 5 year ARI (Table 4.1). Each subcatchment '- approximateiy rectangutar so area, ---- is Time of concentration is assumed as 15
Urban Stormwater Managenent Manual
minutes.
-rr'-'
24-23
Stormwater Inlets
Subcatchment
I Subcatdlment 2
Subcatchment 3 J
LEGEND
Flow ----| Flow \-t Pipe, Inlet --r-
Gutter
Eypass
Figure 1\
Adapt
/=
Example for Catchment and Road Drainage
175 mm/hr from Ipoh IDF data for 5 year ARI, 15 minute duration storm,
Qconb,nd= C.I.A.
I
360
= 0.85 x I75 x (45 = 0.001859 2)
24.81
l;
x
L1x 10-4)/360
where l1 is the length of gutter flow in the first upstream subcatchment
Calculate the allowable limit of gutter flow.
4.3). Note that the cross-fall is 3olo and the runoff depth at 0.075 m. So, the flow will not overtop the kerb. Using Design Chart24.l in Appendix 24.Afor S = 2o/o, n, = 0.015 (hot-mix asphalt pavement), spread of 2.5 m width, and ,c = 0'013 (concrete kerb and gutter). The limiting gutter (half-road) flow based on flow not exceeding the road crown is: For a minor road the allowable flow width is 2.5 m (Table
gutter, dn is given by 0.03 x 2.5
O
=
= 170 litres per second = 0.17 m37sec with
/xD
is within the allowable limit of 0.4 m/sec.
or 0.001859 Lt= 0.17
Therefore, Lt = 0.t7
=91
/
0.001859
m
As in the previous example, adapt
3)
type'S'inlet. Determine the capture efficiency on a 2olo slope.
Capture efficiency of a Type S inlet. Use the Design Chart
24.2. With a gutter approach flow of 170 Lls, the inlet capture is 125 Us giving a capture
efficiency of about 73%. Therefore, bypass gutter flow
=
170
-
725
=4\l/c
24-24
n n4q
m3/s_
lJrban Stormwater Management Manual
Stormwater Inlets
4)
This bypass gutter flow reduces the capacity of the next and subsequent inlets to accept inflow from their own subcatchments. The spacing reguired between subsequent inrets is given by:
L1= (0.170
-
0.045)
/
0.001859
=67m
5)
For design purposes, adapt a maximum inlet spacing of 70
m. The adapted design is shown in figure below.
Note: This example ignores the fact that roof drainage would normally be connected directly to the piped drainage system, therefore the result is likely to be conseryative.
24.8.3 Inlet Capacity Catculation Problem: Determine the inret capacity and anaryse the hydraurics of Line 38, part of an open drainage system for a similar idearised catchment in Ipoh (Figure 24.Bz). Inret numbers 3A/5p, 3A/10P,38//1P and 3Bl2p are Type-S. Inlets 3A/7P and 3Al8p are Type-M or L (depends on capacity required). The road has a uniform longitudinal slope of 2o/o.
I
E tc}
r)
LEGEND
Flow -----> Flow \_t inlet E Gutter
Bypass
Open Drain
Figure
24.82
Example for Road and
Solution:
1)
The required calculations are tedious to perform by hand. As such, RatHGL software is used for the analysis. The RatHGL network layout is shown in Figure 24.83:
Urban Stormwater Management Manual
24-25
Storrnwater Inlets
:igure
2)
24.83
Example for Road and Catchrnent Drainage to an Open Drain
The preliminary design shown above was preoared based on calculations sirnilar to Appendix 24.8.2, taking care to account for the catchment areas draining to each section ci drain. The analysis is perforrned with Ipoh rainfall IDF data. a o
Runoff coefficients 0.90 (impervious), 0.60 (pervious)
inlet rating curve used for Type S, M and L inlets on grade as mentioned in the problem. For nodes on the open drain, the capacity is set to a large value (5 m3/s) so that there is no constraint on inflow.
3)
Hydrology input data and results for the network in the 5 year and 100 year ARi storms are shown in Table 24.81.
4\
Hydraulic input data and hydraulic grade line resulis for the network in the 5 year and 100 year ARI storms are shown in Table 24.82.
z.+-ztl
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Stormwater Inle6
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Urban Stomwater Management Manual 24-27
Stormwater Inlets
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Urban Stormwater Management Manual
Standard
STAI{DARD DRAWINGS
Title
Drawilro No,
Kerb Inlets
SD F.1
Field Inlets
SD F-2
Surcharge Inlets
SD F-3
Kerbs and Gutters
SD F.4
Structures
Urfun Stormyyats Management Manuat
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Miscellaneous Details
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ACKNOWLEDGEMENTS TECHNICAL COMMITTEE
6
- DRAINAGE
Main Committee Members Nafisah Hj. Abdul Aziz
Chairman
Ahmad Fuad Emby
Deputy Chairman
Wan Suraya Mustaffa
Secretary
Normala Hassan
Alternate Secretary
Teh Ming Hu
Committee member
Lim Kim Oum
Committee member
Alias Hashim
Committee member
Low Kom Sing
Committee member
Nor Asiah Othman
Committee member
Johan Les Hare Abdullah
Editor
Teh Ming Hu
Chairman
Wan Suraya Mustaffa
Secretary
Ahmad Fuad Emby
Committee member
Lam Kok Hong
Committee member
Yap Lee Chor
Committee member
Letchumanan Aliagappan
Committee member
ACKNOWLEDGEMENTS Volume 4 is a review of the Arahan Teknik (Jalan) 15197 - INTERMEDIATE GUIDE TO DRAINAGE DESIGN OF ROADS, the chapter was authored originally by Soon Ho Sin and Muhamad Amin Mahmud of Public Works Department Malaysia.
Volume 4 now provides guidelines to the practical design of surface drainage, with worked examples provided in Appendix 4-C, which is reproduced from Jabatan Pengairan dan 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 24, Stormwater Inlets.
-
REAM Standing Committee on Technology and Road Management for the guidance and encouragement given in the preparation of Volume 4.
-
Members of the Technical Committee 6 - Drainage and Sub-Committee for Surface Drainage for their untiring efforts to ensure timely completion of Volume 4.
