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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) i 28/06/2011
LANCASHIRE COUNTY COUNCIL
DRAINAGE DESIGN MANUAL
To be read in conjunction with Road Note 35 – A guide for engineers to the design of storm sewer systems, The Design Manual for Roads and Bridges (DMRB) Volume 4 and the Wallingford Charts.
PAGE AMENDMENTS DATE
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) ii 28/06/2011
SCOPE OF THIS MANUAL:-
The notes in this manual are intended as a guide only, not as absolute standards.
Standards and typical details may change from job to job.
When designing, each problem should be considered on its own merits.
There is no substitute for logical design.
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) iii 28/06/2011
CONTENTS:-
Page
i. Foul Sewers 1
ii. Outfalls 1
iii.A Culverts 1
iv. Primary Carrier Drains 3
v. Secondary Carrier Drains 3
vi. Cross Connections 4
vii. Connections Down Batter Slopes 4
viii. Ditch Connections 5
ix. Concrete Surrounds to Pipes 5
x. External French Drains 5
xi. Cut Off Drains 6
xii. Porous Verge and Central Reserve Drains 7
xiii. Formation Drains 8
xiv. Formation Verge Drains 8
Porous Pipes (Diagram) 10
Porous Pipes in Dual Carriageway (Diagram) 11
Porous Pipes in Side Roads (Diagram) 12
Porous Pipes – Subsidiary Roads (Diagram) 13
xv. Manholes 14
Manhole Types (Table) 16
xvi. Gullies 17
xvii. Dual Carriageway Layout Principles 17
xviii. Single Carriageway Roads Layout Principles 18
Gully Positions (Diagram) 20
xx. General Notes 21
xxi. Impervious Area Tables and Charts 22
Gully Spacings 25
xxii. Appendix 1 - Bilham's Rainfall Tables 30
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 1 28/06/2011
i. FOUL SEWERS
i. Distance between manholes should not normally exceed 90m.
ii. Pipes should run straight between manholes.
iii. Type of pipe is to be specified having been previously agreed with relevant utility
iv. Any sewer diversions should be agreed with the relevant utility and submitted for adoption after completion
ii. OUTFALLS
1. When specifying strength, use the group system where possible.
2. For size and strength design as normal surface water drains.
iiiA CULVERTS
1. The culvert diameter is designed as follows:-
(a) Obtain the catchment area (A) in hectares to be taken by the culvert.
(b) Substitute in the expression:-
Xc = 0.1464 Y A (m2)
Where X c= cross sectional area of the pipe (m2 )
Y = empirical coefficient depending on the nature of the ground i.e.:- rolling farmland 0.80 level ground 0.60 steep ground 1.00 uneven ground 1.00 valleys 1.20
(c) Obtain the theoretical pipe diameter (d) ___________
d = 1000 � Xc x 4 mm
��
The above is an application of the Talbot Formula. It applies to areas not greater than 490 hectares (1200 acres)
The gradient of culverts should be in the order of 1/100 and the culvert sizes in rocky hilly areas should be checked using the Chezy or Manning Formula.
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2. Calculation of Pipe Strength:-
(a) Under embankment, two conditions must be examined and the worst case taken for design:-
(i) the initial condition when the trench has been dug and no embankment surcharge has been added; design using grouping charts.
(ii) The second condition is when the embankment surcharge has been added, and calculations must include for the surcharge.
(b) With pipes laid in fields, design using relevant grouping chart.
Note:- Multiply the fill load by a factor of 1.5 for pipes under high embankments. Each case is to be treated on its own merits, i.e.:- relative height of fill to depth of trench.
3. The invert of the culvert should be placed on or below hard bed level. Hard bed levels should be obtained over the length of the culvert, but soft bed levels should also be obtained as these will give some idea of the silting effect of the stream. For drawing purposes soft bed levels only are plotted. It is usual practice to drop the culvert invert a bit more than is really necessary; and increase the size accordingly, this is a policy which enables regarding of the stream each side of the culvert at some future date.
4. Regrading of existing stream bed upstream and downstream of the proposed culvert is billed and drawn up under the following headings:-
(a) ENLARGE EXISTING WATERCOURSE – where regarding is greater than 225 mm (9") in depth.
(b) CLEAR EXISTING WATERCOURSE – where regarding is less than 225 mm (9") in depth, usually this involves only the clearing or rubbish, vegetation and the silt-mud layer.
(c) NEW WATERCOURSE – completely new excavation.
5. Nearest point (to allow for any skew of the culvert) of standard Inlet and Outlet headwall is 1.4m from the toe of embankment.
6. Most culvert trenches require a porous pipe laid along the invert to aid drainage during construction. Normally these pipes are 100mm dia. but in certain circumstances may be 150 mm dia.
7. In abandoned watercourses 100 mm or larger dia. porous pipes are laid before in filling.
8. Culverts should be designed on the 100 year storm (plus 20'1)
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iv. PRIMARY CARRIER DRAINS
1. The gradient may vary; as flat as 1/1000 (0.1%) is allowable, below which the laying of pipes proves difficult. A minimum velocity of 0.75m/sec (2.5ft/sec) is required for flushing.
150 mm � & 225 mm � pipes are laid at a minimum of 1/250 (0.4%) gradient, which gives the required flushing velocity.
2. Depth of Pipes:-
(a) Invert levels should be designed so that there is 900 mm or more cover to the pipe from formation level. (Formation level is the boundary between earthworks and roadworks, i.e. generally underside of sub-base).
(b) Normally, the Contractor has a choice of road construction materials and thicknesses which means that at design stage, only a depth range is known for formation level. So that (a) above is satisfied, pipe levels are designed from lowest possible formation level, i.e. maximum permissible construction thickness. When taking-off is from formation level, however, the highest possible formation level is used.
3. Classification of Pipes. (Pipe Groups) use tables supplied, always taking the highest pipe strength grouping given by the following loading cases:-
(a) depth – soffit to formation level.
(b) Depth – soffit to finished road or verge level.
4. It is advisable that drains should be laid beneath footway or verge for ease of future access, laying in highway only as last resort.
5. Change in pipe diameter should be made through a manhole.
6. Potentially long pipe lengths should be broken every 90m with a manhole (to facilitate cleaning and inspection) Manholes should be provide at every change of alignment and gradient, at every major junction and at every change in pipe diameter (see item 5 above).
7. Where the proposed road surface uses existing construction as a base (i.e.:- where the proposed road runs into existing) then the proposed drains should be laid at a minimum depth of 1.00m to soffit (to facilitate connection from gullies) below the existing surface).
v. SECONDARY CARRIER DRAINS
1. The gradients must give a minimum flushing velocity of 0.75 m/sec (2.5 ft/sec)
and 150mm� and 225mm� pipes to be laid at the minimum gradient of 1/250 (0.4%).
2. The secondary carrier drain combined with the cross-connection may
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determine the minimum depth of the primary carrier. vi. CROSS CONNECTIONS
1. All connections laid laterally across the highway must be a minimum of
225mm�.
2. Gradients must give a minimum flushing velocity of 0.75 m/sec (2.5 ft/sec)
and 225mm� pipes are to be laid at the minimum gradient of 1/250 (0.4%). 3. Depths for laying pipes are the same as for primary drains. 4. Cross connections should be positioned at the nearest downstream gulley
on the secondary drain (unless there are other limiting criteria). Thus saving an otherwise longer length of secondary drain.
5. Classification of Pipes (Pipe Groups). Use tables supplied for cross- connections.
6. Where pipes occur at substandard depths they should be protected by a concrete arch – see "Concrete Surrounds to pipes" for pipe classification.
vii. CONNECTIONS DOWN BATTER SLOPES
1. Used for bringing French drains and ditch connections into the highway surface water system.
2. Gradients are usually steep, but the minimum flushing velocity and gradients should be adhered to, as previously.
3. Soffit level should be 900 mm below ground level or formation level.
4. Connections steeper than 1/6 (1.67%):-
(a) Pipes up to and including 450mm� -use step bed and surround.
(b) Pipes larger than 450mm� – use anchor blocks.
5. Connections must run perpendicularly down the batters, especially where, peat conditions exist. This is to prevent any slip planes being activated, which might happen if the pipe trench were to run diagonally across the cutting slope, and facilitates digging.
6. In peat conditions the invert of the pipe is to be founded in the stronger strata 1200 mm below the lowest peat level.
7. Classification of Pipes (Pipe Groups) use tables supplied for pipes under fields, even though part of the pipe may be in the verge or hardshoulder.
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viii DITCH CONNECTIONS:-
1. Inlet to be level or below hard bed level.
2. Nominal length between headwall and manhole (where this condition exists) is to be taken as 1.5 m.
3. Classification of Pipes. (Pipe Groups):- use tables supplied for pipes under fields.
4. Ditch connections should be scheduled with surface water drains.
ix. (i) CONCRETE SURROUNDS TO PIPES:-
1. Concrete Bed and Surround (CB & S):- Used on all gulley connections and in conditions where a pipe at substandard depth is laid just above an existing pipe.
2. Concrete Arch. (CA):-
Used where pipes are at sub-standard depths - gives an increased bedding factor over pipe bedding material.
For larger pipe diameters use concrete and calculate the strength using the appropriate bedding factor.
For larger pipe diameters use concrete and calculate the strength using the appropriate bedding factor.
ix. (ii) GENERAL PROTECTION TO PIPES
1. Surface water drains should be laid in the negative trench condition such that when the pipe is laid there is always 900 mm minimum cover immediately available for protection. If 900 mm cover is not available then the trench should be dug from formation level.
2. Culverts and large pipes which cross the carriageway transversely under deep embankment fills are laid on Pipe Bedding Material. If the trench condition gives 300 mm or less of cover then specified back fill protection material is added to a depth equivalent to the external diameter of the pipe above the soffit of the pipe.
x. .EXTERNAL FRENCH DRAINS:-
1. Used to collect any run off from land adjacent to the route. Takes run off from embankments, and cuts off any water getting onto cutting slopes.
2. With land sloping towards the route, not all water falling on the surrounding ground will reach the French drain due to infiltration. It is usual to allow a 100 m strip adjacent to the French drain to be taken into account in the hydraulic
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 6 28/06/2011
calculations, with the relevant permeability factor applied.
3. Gradients as shallow as 1/1000 (0.1%) are permissible but should be steeper wherever possible.
4. Catchpits are required at 90m intervals along the pipe, or at sharp changes in gradient.
5. Minimum depth of laying pipes is 600 mm to invert from ground level where possible.
6. Type of Pipe and Fill – follows the same principle as porous verge drains.
7. Usually French drains are 150 mm ��but where additional flows are present larger pipe-diameters may have to be used.
8. Distance from top of cutting or toe of embankment should be 1.3m.
9. External French Drains are not normally laid in peat.
10. Where French drains are connected into the main drainage system they should be connected into surface water drains, never into verge drains.
11. Trench width for French drains may vary as follows:-
(a) 600 mm when picking up run off from surrounding areas;
(b) 450 mm when picking up batter run-off only.
xi. CUT OFF DRAINS:-
1. Used for collecting existing field drainage in the form of agricultural tiles or stone soughs which may be cut off by the route.
2. Pipe size is usually 150 mm ��but when lengths greater than 180 m are involved the
pipe size is increased to 225 mm ��via a manhole. A Lloyd-Davies calculation may be made to check that this size of pipe can cope.
3. Depth varies depending on the depth of the existing drains to be connected in. Minimum depth – invert of pipe to ground level, are as follows.
(a) Ground Contours showing good fall towards cut off - 1200 mm
(b) Average ground contours - 1400 mm
4. Where cut off drains have to be connected into the main drainage system they should be connected into surface water drains never into verge drains.
5. If the cut off drain is excessively long, i.e. longer than can be coped with by a 225 mm
� pipe, the drain should be connected into the adjacent French drain via a manhole. �������The French drain downstream should then be 300 mm perforated clay French/surface water drain.
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6. Cut off drains are laid 1.5m minimum outside the fence line.
xii POROUS VERGE AND CENTRAL RESERVE DRAINS
A. Positive Drainage System 1. Purpose:- to pick up any water that may get into the construction to prevent water getting into the construction to pick up run off from cutting slopes to pick up any other water that might get onto the verge used wherever the construction is trapped
2. Dependent on their position they may be laid in single or combined (with secondary drain) trenches.
3. There should be a minimum distance of 300 mm between the invert of the porous pipe and the soffit of the secondary carrier (in combined trenches).
4. Laid at a minimum gradient of 1/250 (0.4%).
5. May determine the depth of the secondary drain where they occur in the same trench.
6. Depth of Pipes:-
(a) Normally the invert of the pipe should be 600 mm below formation level (underside of sub-base). This will usually cause the drain to be below the 6.F.5 layer, which is desirable, though not absolutely necessary.
(b) The lowest possible formation level (i.e. maximum allowable construction thickness) is assumed for design.
(c) In sound unweathered rock the depth of the verge drain may be decreased to 300 mm.
7. The downstream ends of verge and central reserve drains are ramped down using clay pipes to soffits level in the manhole except:-
(a) When in combined trench with a surface water drain; (b) When the manhole invert is excessively deep.
8. Porous central reserve drains in P.F.A. embankments are laid in trenches lined with heavy gauge polythene sheeting.
B. Non-Positive Drainage System
1. Purpose:- as for positive drainage system plus the picking up of carriageway run-off.
2. 150mm, 225mm or 300mm Gp IIP pipes with type B fill are used. The pipe size should be designed as for surface water drains in a positive system.
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3. Manholes should be type C with open grating covers which would act as overflows should the filter material be unable to cope.
4. 150 mm and 225 mm pipes are laid to a minimum gradient of 1/250 (0.4%).
5. Normally the soffit of the pipe should be 600 mm below formation level (underside of sub-base). This depth may be increased for increased thicknesses of the 6.F.5 layer.
C. Rock Catcher and Slotted Drainage channel
1. Used in sound, unweathered rock cuttings.
2. Purpose:- as for non-positive verge and central reserve drains plus, in the case of the rock catcher, preventing rock falls from the cutting side slopes reaching the carriageway.
3. Rock catcher is used only in the verge. It may or may not be concrete lined depending on the rock condition. Concrete lined rock catchers have a 150 mm GpIP Sub-drain in type B fill. 150 mm perforated UPVC pipes laid transversely at 30m intervals may be used to drain the formation into the rock catcher.
4. Slotted drainage channel may be used in the verge and central reserve. 150 mm porous concrete pipe sub-drains are always used. These are laid on blinding concrete and backfilled to underside of channel with no-fines concrete. The no-fines concrete allows formation drainage.
xiii. FORMATION DRAINS (SUBSIDIARY ROADS):-
1. Purpose to prevent ingress of water into the formation from the verges and to drain the formation. Used wherever the formation is trapped.
2. Depth to invert is 600 mm below formation level.
3. Type of pipe: - 150 mm � UPVC with type B fill.
4. Due to the often physical impossibility of running formation drains past gully connections, formation drains outfall into every gully connection.
5. Where new construction runs into existing construction, the formation drains are taken to the point where the 6F5 layer is terminated.
xiv. FORMATION VERGE DRAINS (SUBSIDIARY ROADS):-
1. Purpose – to pick up run off from unkerbed minor side roads or track diversions. Also picks up surface water from adjoining ground and also serves as a formation drain.
2. Situated immediately at the edge of the road surface adjacent to the construction.
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3. Depth – minimum depth of 600 mm to invert below formation level.
4. Type of Pipe and fill – follows the same principle as porous verge drains. However that part of the trench above formation level is backfilled with type B granular fill.
30
0m
m m
in.
150
mm
60
0m
m m
in.
6d/
Type B material
Suitable backfill material
Pipe bedding material
Formation Level
150mm dia Porous or Porous Concrete
pipes depending on drainage material
Variable depending onType of drainage media
60
0m
m m
in.
6d/
Type B material
Formation Level
150mm dia Porous pipes
6d/
Formation Level
150mm
Type B material
60
0m
m m
in.
6d/
Type B fill
150mm dia Gp 1
Porous or PC pipes
Waterproof
underlay
Va
ria
ble
6d/
Topsoil
Suitable backfill material
150mm or 225mm dia pipe
30
0m
m
Type B material
150mm above pipe600mm
Clay Puddle
Seal
Clayware
Connection Pipe
fig. 2. COMBINED DRAIN.
RIGID SURFACE WATER AND POROUS VERGE DRAINS.
fig. 3. TYPE B FILLED.
POROUS VERGE AND CENTRAL RESERVE DRAINS
fig. 4. PFA. EMBANKMENT.
fig. 5. FRENCH DRAIN.
fig. 6. CUT-OFF DRAIN.
POROUS PIPES
HIGH EMBANKMENT. Ground sloping towards road.
fig. 7. POROUS DRAINS IN DUAL CARRIAGEWAYS.
FRL
GROUND LEVEL.
PROTECTIVE LAYER
FR
HIGH EMBANKMENT. Ground sloping away from road.
FRL
GROUND LEVEL.
PROTECTIVE LAYER
FR
FR
SHALLOW EMBANKMENT. Ground sloping towards road.
GROUND LEVEL.
FR
FR
SHALLOW EMBANKMENT. Ground sloping away from road.
GROUND LEVEL.
CUTTING. Ground sloping towards road.
GROUND LEVEL.
FR
FR
CUTTING. Ground sloping away from road.
GROUND LEVEL.
FR
GROUND LEVEL.
FR
PROTECTIVE LAYER
SIDE-LONG GROUND CONDITIONS.
KEY :-
VD - VERGE DRAIN.
CD - CENTRAL RESERVE DRAIN
FR - FRENCH DRAIN.
FR
CD
VD
VD
FRL
FRL
FRL
FRL
FRL
CD
VD
VD
CD
VD
VD
CD
VD
VD
CD
VD
CD
CD
HIGH EMBANKMENT. Ground sloping towards road.
fig. 7. POROUS DRAINS IN SIDE ROADS.
FRL
GROUND LEVEL.
PROTECTIVE LAYER
FR
FR
HIGH EMBANKMENT. Ground sloping away from road.
FRL
GROUND LEVEL.
PROTECTIVE LAYER
FR
FR
SHALLOW EMBANKMENT. Ground sloping towards road.
FRL
GROUND LEVEL.
FR
FR
FD
FD
SHALLOW EMBANKMENT. Ground sloping away from road.
FRL
FD
FD
GROUND LEVEL.
CUTTING. Ground sloping towards road.
FRL
GROUND LEVEL.
FR
FR
FD
FD
FR
FR
CUTTING. Ground sloping away from road.
FRL
FD
FD
FR
FR
GROUND LEVEL.
FRL
FD
FR
FR
GROUND LEVEL.
FR
PROTECTIVE LAYER
SIDE-LONG GROUND CONDITIONS.
KEY :-
FD - FORMATION DRAIN.
FR - FRENCH DRAIN.
60
0m
m m
in.
6d/
Type B material
Formation Level
150 or 225 mm dia Porous pipes
fig. 9. TYPE B FILLED.
POROUS PIPES SUBSIDIARY ROADS
FORMATION VERGE DRAINS.
600m
m m
in.
6d/
Type B material
Formation Level
150mm dia Porous pipes
fig. 8. FORMATION DRAINS.
6F5 layer
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xv. MANHOLES:-
1. Manholes must be spaced not greater than 90 m on the primary lengths of drain (to facilitate cleaning and inspection) Manholes should be provided at every change of alignment and gradient at every junction with other pipes (apart from gully connections) and at every change in pipe diameter .
2. Surface Water pipes should enter manholes at soffits level. Porous pipes, and gully connections may be brought into the manhole at any level above the soffit of the outlet pipe, though preferably should also be at soffits level.
3. All manholes not in the verge or carriageway etc. i.e.:- those situated at the top and bottom of batters adjacent to the fence line or in fields, must rise 300 mm above ground level for easy location.
4. Manholes situated in peat areas must have their inverts placed 1200 mm (4' 0") below the lowest peat level to prevent any movement of the pipes etc. during subsequent possible shrinkage of the peat.
5. Vertical Backdrops – use on surface water connections only Ramped Backdrops – use on fouls sewer connections.
6. Type of Cover:-
(a) D400 – on all manholes.
7. Foul Sewer manholes – minimum internal diameter is 1200 mm.
8. Sumps are required on manholes (Type C) only where there is a possibility sailting up occurring. If a surface water pipe passes through a manhole into which there is a porous drain connection, this surface water would flush out any deposited silt, and no sump is required.
9. Catchpit manholes (Type C) the base of the sump is located 450 mm below the outlet invert.
10. Full details of all Manhole Types are shown in the LCC Special Details.
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Table 1. MAXIMUM DEPTH OF MASONARY MANHOLES
WALL THICKNESS (mm) WALL LENGTH
(m) 225 337 450 562
0.675 9.0
0.900 5.5 11.5
1.125 3.5 7.5
1.350 2.5 5.0 10.0
1.575 4.0 7.5 11.5
1.800 3.0 5.0 8.0
2.025 2.5 4.5 6.5
2.250 3.5 5.0
2.475 3.0 4.5
2.700 2.5 3.5
Table 2. SUGGESTED BACKDROP DIAMETERS AND MAXIMUM FALLS
VERTICAL BACKDROP RAMPED BACKDROP
Incoming Pipe Dia. (mm)
Backdrop Dia. (mm)
Incoming Pipe Dia. (mm)
Max. Drop Invert to invert (m)
150 150 150 – 300 1.10
225 225 375 – 600 1.80
300 – 450 300 675 - 900 2.10
525 – 675 450 BACKDROP DIAMETER
750 – 900 600
1050 - 1200 750
SAME AS INCOMING PIPE
DIAMETER
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Table 4. MANHOLE TYPES Using maximum pipe diameter and depth to invert
DEPTH PIPE DIAMETERS (mm) DEPTH
RANGES(m) 150 225 300 375 450 525 600 675 750 825 900 975 1050 1125 1200 1350 1500 1650 1800 2100 (m)
A 0 – 3.05
1050
0 – 3.05
A A A A 0 – 3.35
1050 1050 1050 1050
0 – 3.35
A A A A 0 – 3.65
1200 1200 1350 1350
0 – 3.65
A A A A 0 – 3.95
1500 1500 1800 1800
0 – 3.95
A A A 0 – 4.25
1800 1800 2100
0 – 4.25
A A 0 – 4.55
2100 2400
0 – 4.55
A 0 – 4.85
2400
0 – 4.85
A 0 – 5.15
2700
0 – 5.15
B 3.10 -6.35
1050
3.10 - 6.35
B B B B 3.40 - 6.65
1050 1050 1050 1050
3.40 - 6.65
B B B B 3.70 - 6.95
1200 1200 1350 1350
3.70 - 6.95
B B B B 4.00 - 7.25
1500 1500 1800 1800
4.00 - 7.25
B B B 4.30 - 7.55
1800 1800 2100
4.30 -7.55
B B 4.60 - 7.85
2100 2400
4.60 -7.85
B 4.90 - 8.15
2400
4.90 - 8.15
B 5.20 - 8.45
2700
5.20 - 8.45
B L 6.40 - 12.50
1500
6.40 - 12.50
BL BL BL BL 6.70 - 12.80
1500 1500 1500 1500
6.70-12.80
BL BL BL BL 7.00 - 13.10
1500 1500 1500 1500
7.00-13.10
BL BL BL BL 7.30 - 13.40
1500 1500 1800 1800
7.30-13.40
BL BL BL 7.60 - 13.70
1800 1800 2100
7.60-3.70
BL BL 7.90 - 1400
2100 2400
7.90-1400
BL 8.20 - 14.30
2400
8.20-14.30
BL 8.50 - 14.60
2700
8.50-14.60
DEPTH 150 225 300 375 450 525 600 675 750 825 900 975 1050 1125 1200 1350 1500 1650 1800 2100 DEPTH
RANGES(m) PIPE DIAMETERS. (mm) (m)
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 17 28/06/2011
xvi. GULLIES:-
1. Normally all gullies should be 500 mm X 350 mm or 490 mm X 450 mm.
2. If there is no provision for drainage on large bridge decks, then one gully should be placed as close to the deck as possible at the high end and at the low end place two gullies 1.5m apart to prevent any excess flow reaching the road.
3. Do not place gullies under bridges if possible, so as to avoid fouling the bridge footings.
4. Gullies must be of the trapped type if any amount of foul water is present in the carrier drain. This may occur if a combined drainage system is operating. However if the drain operates as a foul sewer overflow trapped gullies need not be used as the sewage content will be flushed through on the storm flow. If the gullies connect into a surface water system which the enters a foul sewer system, use trapped gullies.
5. Gully connections are usually 150 mm extra strength clay with 150 mm concrete bed and surround.
6. Normally, the top of the gully pot is placed level with underside of sub-base subject to the following limitations:
(a) Maximum distance below FRL is 500 mm) flexible
(b) Minimum distance below FRL is 325 mm) construction
(c) Constant distance below FRL of 300 mm below underside of RC Road slab to prevent any possibility of point loading on the road slab from the top of the gully pot – rigid construction.
7. Gratings to be 10 mm below finished road level.
8. Plastic gully pots may be used, but these must be a former and surrounded with concrete ST4 with a template in the pot to prevent distortion.
9. Full details of all Gullies are shown in the LCC Special Details.
xvii. DUAL CARRIAGEWAY LAYOUT PRINCIPLES:-
1. Layout For Normal Valley Point:-
(a) Place 1 no. gully at the valley point.
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(b) Place 2 no. gullies 10 m each side of the valley point.
(c) Design the rest of the fully spacings on a two year storm intensity.
2. Layout for Trapped Valleys:-
(a) Place 1 no. gully at the valley point.
(b) Place 2 no. gullies 10 m each side of the valley point.
(c) Design the rest of the gully spacings on a ten year storm intensity for 180 m each side of the valley point.
(d) The primary carrier drain downstream of the valley point to the outfall and the secondary drains 180 m each side of the valley point, to be designed using a ten year storm intensity.
3. Layout for Summit Points:- (see fig 22) (a) No gully is required at the summit point.
(b) Design the gully spacings on a two year storm intensity with a minimum spacing of 10 m for the first gully each side of the summit.
4. On long steep grades greater than 2% (1/50) add an additional gully every 180 m positioned 5m beyond the normal gully.
5. Special catch water gullies may be necessary in trapped valleys.
6. Primary drains may have to be "dog-legged" across the highway on dual carriageways at bridge sites to avoid the bridge foundations.
xviii SINGLE CARRIAGEWAY ROADS LAYOUT PRINCIPLES:-
1. Layout for Valley Points:-
Trapped and untrapped valleys have the same gully configuration. This is because for storms of greater intensity than the two year storm, a water channel width greater than the nominal 1 m is allowable and the two year storm spacing can be retained.
(a) Place 1 no. gully at the valley point.
(b) Place 2 no. gullies 10 m each side of the valley point.
(c) Design the rest of the gully spacings on a two year storm intensity.
2. Layout For Summit Points:- (Similar to fig. 22)
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 19 28/06/2011
(a) No gully is required at the summit point.
(b) Design the gully spacings on a two year storm intensity, with a minimum spacing of 10 m for the first gully each side of the summit.
3. Gully positions at no fall points (changeover of cross-fall) for roads with kerbed channel:- see fig. 24 for details.
Spacing designed
on 2 year storm as
normal.
Spacing designed
on 2 year storm as
normal.
10m standard spacing.
Gully at valley point.
10m standard spacing.
NORMAL VALLEY POINT
(Dual Carriageway)
Spacing designed on
10 year storm for 180m.
Spacing designed on
10 year storm for 180m.
10m standard spacing.
Gully at valley point.
10m standard spacing.
TRAPPED VALLEY POINT
(Dual Carriageway)
Spacing designed
on 2 year storm.
Spacing designed
on 2 year storm.
Calculated spacing
10m minimum.
SUMMIT POINT
Calculated spacing
10m minimum.
SUMMIT POINT
(Dual Carriageway)
Ca
lcu
late
d S
pa
cin
g
Overflow Gully.
10m standard
spacing.
CHANGE-OVER IN CROSSFALL.
(Dual Carriageway)
Standard continuation of
channel - 10m.
NO FALL POINT
Ca
lcu
late
d S
pa
cin
g
Ca
lcu
late
d S
pa
cin
g
First gully
placed just
upstream of no
fall point.
10m standard
spacing.
CHANGE-OVER IN CROSSFALL.
(Single Carriageway)
NO FALL POINT
Ca
lcu
late
d S
pa
cin
g
GULLY POSITIONS
Calculated spacing
10m minimum.
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 21 28/06/2011
xx. GENERAL NOTES:-
1. Easement:- the acquisition of land for the purpose of construction with the right to go back at a future date to maintain the structure. (standard colour blue on Land Plans).
2. Licence:- the acquisition of land for the purpose of construction, after which the land is returned to the owner and the maintenance of the structure is up to him. (standard colour – green on land Plans).
1. High Embankment:-
That embankment which is 1.5 m and over in height (i.e. 3 m in plan width). This height means that:-
(a) The construction is not trapped.
(b) The porous verge or formation drains (laid 600 mm below formation level) are approx. at ground level and hence water levels are kept 600 mm below the formation level.
2. Compulsory Purchase Orders (CPO)
Land or property compulsorily purchased from the existing owner for the sole ownership of the LCC. However, at the discretion of the LCC owners of surrounding properties may be allowed access across this land.
3. Oil interceptors must be introduced on all major highway drainage schemes prior
to outfall to a watercourse or culvert. On schemes where it is solely highway drainage, by-pass interceptors can be used, however where there are car parks, depots etc are to be drained, full retention interceptors must be used.
4. Generally, the Environment Agency allows only limited discharge from highway schemes and consequently attenuation is invariably required. This can be achieved in various ways with a hydro brake or similar control restricting the volume of discharge to the watercourse.
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xxi. Impervious Area Charts and Tables
1. Notes:- (a) Carriageway surfaces and hardshoulder P.F. = 1.0
(b) Shallow cuts (3m. wide on plan). P.F. = 1.0
(c) Deep cuts (area measured on plan) including verges P.F. = 0.50
(d) Fields (plan area) P.F. = 0.10 Special investigation may be necessary for steep, rocky or exceptionally large areas. (e) Fields with gradients steeper than 1/5 (20%) to be taken as cutting slopes.
(f) Verges P.F. = 1.0
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 23 28/06/2011
CHART 2. IMPERVIOUS AREA OF CUTTING SLOPES
TABLE 8. IMPERVIOUS AREA OF CUTTING SLOPES
�������������� �������������������� ��������� !"���������
#$%& '$&& %$&& ($&& )$%& #&$&& #*$%& #%$&& #)$%& *&$&& **$%& *%$&& *)$%& '&$&& '*$%& '%$&& ')$%& +&$&&
'& ������ ������ ������ ������ ������ ����� ������ ����� ����� ����� ���� ����� ������ ����� ������ ������ ������ ������
(& ������ ������ ����� ����� ����� ����� ������ ����� ������ ������ ������ ����� ������ ������ ������ ����� ����� �����
,& ����� ������ ����� ����� ������ ������ ����� ����� ������ ������ ������ ����� ������ ������ ����� ������ ������ ������
#*& ������ ����� ������ ������ ������ ������ ������ ������ ����� ������ ������ ������ ������ ������ ����� ����� ������ ������
#%& ����� ����� ������ ������ ������ ������ ����� ������ ������ ������ ����� ���� ������ ������ ������ ����� ����� ����
#-& ������ ����� ������ ������ ������ ����� ������ ������ ����� ����� ������ ������ ���� ����� ���� ����� ���� �����
*&& ����� ������ ������ ������ ����� ������ ������ ������ ����� ������ ������ ����� ���� ����� ����� ����� ���� �����
TYPICAL CALCULATIONS:
1. Less than 6.00m width. P.F. =1.0 - Impervious Area = 410
0.1 xLxwidth Hectares.
2. Greater than 6.00m width P.F. = 1.0 up to 6.00m width, P.F. = 0.5 above 6.00m width.
Impervious Area = 410
00.60.1 xLx +
410
)00.6(5.0 −widthxLx
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 24 28/06/2011
TABLE. 7. IMPERVIOUS AREA PER LENGTH OF ROAD
2 LANE SLIP
ROAD
TWO LANE CARRIAGEWAY
THREE LANE CARRIAGEWAY
FOUR LANE WIDTH
SUBSIDIARY ROAD
10.0m WIDTH
SUBSIDAIRY ROAD
7.3m WIDTH LENGTH
OF ROAD METRES
FULL WIDTH HECTARES
FULL WIDTH HECTARES
HALF WIDTH HECTARES
FULL WIDTH HECTARES
HALF WIDTH HECTARES
FULL WIDTH HECTARES
HALF WIDTH HECTARES
FULL WIDTH HECTARES
HALF WIDTH HECTARES
FULL WIDTH HECTARES
HALF WIDTH HECTARES
30 0.023 0.078 0.039 0.100 0.050 0.122 0.061 0.030 0.015 0.022 0.011
60 0.045 0.157 0.079 0.201 0.101 0.244 0.122 0.060 0.030 0.044 0.022
90 0.068 0.235 0.118 0.302 0.151 0.355 0.183 0.090 0.045 0.066 0.033
120 0.090 0.313 0.157 0.402 0.201 0.488 0.244 0.120 0.060 0.088 0.044
150 0.113 0.392 0.196 0.502 0.251 0.610 0.305 0.150 0.075 0.110 0.055
180 0.135 0.470 0.235 0.603 0.302 0.732 0.366 0.180 0.090 0.131 0.066
200 0.150 0.522 0.261 0.670 0.355 0.814 0.407 0.200 0.100 0.146 0.073
TYPICAL CALCULATION:- Two Lane Carriageway a. Full width. 2 No. c/ways - 26.10m.
b. Length along road. - 30m say.
c. Permeability factor. - 1.0
Impervious Area = 4
10
10.26300.1 xx = 0.078 Hectares.
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 25 28/06/2011
xxii. GULLY SPACINGS
1. Kerbed Channel.
The flow against the kerb is allowed to be 1.00m wide.
a. CALCULATION OF CHEZY COEFFICIENT C:-
For example a crossfall of 1/40 (2.5%) will be assumed. Maximum depth of flow =1 x 1/40 =0.025m Cross sectional area of channel (A) = 0.5 x 0.025 x 1.0 =0.013sq.m Wetted perimeter of channel (P) =1 + 0.025 =1.025m Hydraulic mean depth (m) = A/P =0.013/1.025 =0.013m
Chezy Coefficient C =
m
k+1
87 m1/2s-1 (Bazin's Formula).
Roughness Coefficient K is taken as 0.276 Substituting in Bazin's Formula we get:-
C =
013.0
276.01
87
+
=42.3
87
Chezy Coefficient C = 25.4 m1/2s-1
b. CAPACITY OF CHANNEL (per min):-
1/40 crossfall will be used as an example.
Capacity Q1 = AC mi
Substituting Q1 = 60 x 0.013 x 25.4 i013.0
Q1 = 2.26 i m3/min
Where i the longitudinal gradient (%) (As a decimal i.e. 2.5% or 1in 40 = 0.025)
1.00m
Variable Crossfall
Allowable width of Flow
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CALCULATION OF FLOW (m3/min) PER METRE OF ROAD:-
Two year storm � Intensity (i) at 3 mins (time of entry) = 76.5mm/hr
Generally we may write:-
Area/metre of road (A,) = [width road x 1 metre] m2
Flow/metre Q2 = [A, x intensity x 0.0000167] m3/min.per metre.
Where 0.0000167 is a factor to obtain conformity of units.
Flow/metre Q2 = [A, x 76.5 x 0.0000167] = [A, x 0.00128] m3/min per metre. Where 0.0000167 is a factor to obtain conformity of units
GULLY SPACING = Q1
Q2
CAPACITY OF CHANNEL Q1 (m3/min) AGAINST CROSSFALL AND LONGITUDINAL
GRADIENT
CAPACITY OF CHANNEL Q1
LONGITUDINAL GRADIENT
4% 2% 1% 0.5% 0.33% 0.25% 0.20% 0.17%
CROSSFALL 3.3% 0.710 0.504 0.355 0.252 0.202 0.718 0.160 0.146
CROSSFALL 2.5% 0.452 0.321 0.226 0.161 0.129 0.113 0.102 0.093
CROSSFALL 2.0% 0.278 0.197 0.139 0.099 0.079 0.070 0.063 0.057
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FLOW Q2 (m3/min) per metre of Road
WIDTH OF ROAD METRES
Q2
m3/min per metre
3 0.00384
4 0.00512
5 0.00640
6 0.00768
7 0.00896
8 0.01024
9 0.01152
10 0.01280
11 0.01408
12 0.01536
13 0.01664
14 0.01792
15 0.01920
16 0.02048
17 0.02176
18 0.02304
19 0.02432
20 0.02560
21 0.02688
22 0.02816
23 0.02944
24 0.03072
25 0.03200
26 0.03328
27 0.03456
28 0.03584
29 0.03712
30 0.03840
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THEORETICAL GULLY SPACINGS (KERBED CHANNEL) CALCULATED ON A TWO YEAR STORM INTENSITY
10 METRES WIDTH (0.0128)
LONGITUDINAL GULLY SPACINGS
GRADIENT Full width 1/30
Full width 1/40
Full width 1/50
Half width 1/40
1/ 25 4% 55.5 35.3 21.7 70.6
1/50 2% 39.4 25.1 15.4 50.2
1/100 1% 27.7 17.7 10.9 35.3
1/200 0.5% 19.7 12.6 7.7 25.2
1/300 0.33% 15.8 10.1 6.2 20.2
1/400 0.25% 13.9 8.8 5.5 17.7
1/500 0.2% 12.5 8.0 4.9 16.0
1/600 0.17% 11.4 7.3 4.5 14.5
7.3 METRES WIDTH (0.00934)
Full width
Full width
Full width
Half width
1/30 1/40 1/50 1/40
1/25 4% 76.0 48.4 29.8 96.8
1/50 2% 54.0 34.4 21.1 68.7
1/100 1% 38.0 24.2 14.9 48.4
1/200 0.5% 27.0 17.2 10.6 34.5
1/300 0.33% 21.6 13.8 8.5 27.6
1/400 0.25% 19.1 12.1 7.5 24.2
1/500 0.20% 17.1 10.9 6.7 21.8
1/600 0.17% 15.6 10.0 6.1 20.0
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 29 28/06/2011
10 METRES WIDTH
FULL WIDTH CAMBERED
HALF WIDTH
LONGITUDINAL GRADIENT
GULLY SPACING
1 / 30
GULLY SPACING
1/40
GULLY SPACING
1/50
GULLY SPACING
1/40
4% - 2% 40 30 20 50
2% - 1% 30 20 10 40
1% - 0.5% 20 10 10 30
0.5% - 0.33% 20 10 10 20
0.33% - 0.25% 20 10 10 20
0.25% - 0.20% 10 10 10 20
0.20% - 0.17% 10 10 10 20
7.3 METRES WIDTH
FULL WIDTH CAMBERED
HALF WIDTH
1/30 1/40 1/50 1/40
4% - 2% 50 40 30 50
2% - 1% 40 30 20 50
1% - 0.5% 30 20 10 40
0.5% - 0.33% 20 20 10 30
0.33% - 0.25% 20 10 10 30
0.25% - 0.20% 20 10 10 20
0.20% - 0.17% 20 10 10 20
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APPENDIX 1
BILLHAM'S RAINFALL TABLES
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xxii. BILHAM'S RAINFALL TABLES Table 24.
Table showing the variation of rate of rainfall in millimetres per hour with duration and frequency of recurrence.
FREQUENCY OF RECURRANCE. YEARS TIME OF DURATIONMINS.
1 2 5 10 20 50 100
2.0 69.2 85.8 107.8 124.6 141.5 164.2 181.5
2.5 65.2 80.9 101.8 117.8 134.1 156.0 172.9
3.0 61.6 76.5 96.5 112.0 127.8 149.1 165.5
3.5 58.5 72.7 91.9 106.9 122.3 143.0 159.1
4.0 55.6 69.3 87.9 102.4 117.4 137.7 153.5
4.1 55.1 68.6 87.1 101.6 116.5 136.7 152.4
4.2 54.6 68.0 86.4 100.8 115.6 135.8 151.4
4.3 54.1 67.4 85.7 100.0 114.7 134.8 150.4
4.4 53.6 66.8 85.0 99.2 113.9 133.9 149.4
4.5 53.1 66.2 84.3 98.4 113.1 133.0 148.5
4.6 52.6 65.7 83.6 97.7 112.2 132.1 147.5
4.7 52.1 65.1 82.9 97.0 111.4 131.2 146.6
4.8 51.7 64.5 82.3 96.2 110.7 130.4 145.7
4.9 51.2 64.0 81.6 95.5 109.9 129.5 144.8
5.0 50.8 63.5 81.0 94.9 109.1 128.7 143.9
5.1 50.3 63.0 80.4 94.2 108.4 127.9 143.1
5.2 49.9 62.5 79.8 93.5 107.7 127.1 142.3
5.3 49.5 62.0 79.2 92.9 107.0 126.3 141.4
5.4 49.1 61.5 78.6 92.2 106.3 125.6 140.6
5.5 48.7 61.0 78.1 91.6 105.6 124.8 139.8
5.6 48.3 60.5 77.5 91.0 104.9 124.1 139.1
5.7 47.9 60.1 77.0 90.4 104.3 123.4 138.3
5.8 47.5 59.6 76.4 89.8 103.6 122.7 137.6
5.9 47.1 59.2 75.9 89.2 103.0 122.0 136.8
6.0 46.8 58.7 75.4 88.6 102.4 121.3 136.1
6.2 46.0 57.9 74.4 87.5 101.1 119.9 134.7
6.4 45.3 57.0 73.4 86.4 100.0 118.6 133.3
6.6 44.7 56.2 72.4 85.3 98.8 117.4 132.0
6.8 44.0 55.5 71.5 84.3 97.7 116.2 130.7
7.0 43.4 54.7 70.6 83.3 96.6 115.0 129.4
7.2 42.8 54.0 69.7 82.4 95.6 113.8 128.2
7.4 42.2 53.3 68.9 81.4 94.6 112.7 127.0
7.6 41.6 52.6 68.1 80.5 93.6 111.6 125.9
7.8 41.1 51.9 67.3 79.7 92.6 110.6 124.8
8.0 40.5 51.3 66.5 78.8 91.7 109.6 123.7
8.2 40.0 50.7 65.8 78.0 90.8 108.6 122.6
8.4 39.5 50.1 65.1 77.2 89.9 107.6 121.6
8.6 39.0 49.5 64.3 76.4 89.0 106.6 120.6
8.8 38.5 48.9 63.7 75.6 88.2 105.7 119.6
9.0 38.0 48.3 63.0 74.9 87.4 104.8 118.6
9.2 37.6 47.8 62.3 74.1 86.6 103.9 117.7
9.4 37.1 47.2 61.7 73.4 85.8 103.1 116.8
9.6 36.7 46.7 61.1 72.7 85.0 102.2 115.9
9.8 36.3 46.2 60.4 72.0 84.3 101.4 115.0
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BILHAMS RAINFALL TABLES Table 25
Cont.
FREQUENCY OF RECURRANCE. YEARS TIME OF DURATIONMINS.
1 2 5 10 20 50 100
10.0 35.9 45.7 59.8 71.4 83.5 100.6 114.1
10.5 34.9 44.5 58.4 69.8 81.8 98.6 112.1
11.0 33.9 43.4 57.1 68.2 80.1 96.8 110.1
11.5 33.1 42.3 55.8 66.8 78.5 95.0 108.2
12.0 32.2 41.3 54.6 65.4 77.0 93.4 106.4
12.5 31.4 40.4 53.4 64.1 75.6 91.8 104.7
13.0 30.7 39.5 52.3 62.9 74.2 90.3 103.1
13.5 30.0 38.6 51.2 61.7 72.9 88.8 101.5
14.0 29.3 37.8 50.2 60.6 71.7 87.4 100.0
14.5 28.7 37.0 49.3 59.5 70.5 86.1 98.6
15.0 28.1 36.2 48.4 58.4 69.3 84.8 97.2
16.0 27.0 34.8 46.6 56.5 67.1 82.3 94.6
17.0 26.0 33.5 45.0 54.7 65.1 80.1 92.2
18.0 25.1 32.3 43.5 53.0 63.2 77.9 89.9
19.0 24.3 31.2 42.2 51.4 61.5 76.0 87.7
20.0 23.5 30.2 40.9 49.9 59.8 74.1 85.7
25.0 20.4 26.1 35.6 43.8 52.9 66.2 77.2
30.0 18.2 23.2 31.5 39.1 47.6 60.1 70.5
35.0 16.5 21.0 28.4 35.4 43.3 55.2 65.1
40.0 15.1 19.2 26.0 32.4 39.8 51.0 60.5
45.0 14.0 17.7 24.0 29.9 36.9 47.6 56.7
50.0 13.1 16.5 22.3 27.8 34.4 44.6 53.3
55.0 12.3 15.5 20.9 26.0 32.2 42.0 50.4
60.0 11.6 14.6 19.7 24.5 30.3 39.7 47.8
65.0 11.0 13.9 18.7 23.2 28.7 37.7 45.5
70.0 10.5 13.2 17.7 22.0 27.3 35.8 43.4
75.0 10.0 12.6 16.9 21.0 26.0 34.2 41.6
80.0 9.6 12.1 16.2 20.1 24.8 32.7 39.8
85.0 9.2 11.6 15.5 19.3 23.8 31.3 38.3
90.0 8.9 11.2 14.9 18.5 22.9 30.1 36.8
95.0 8.6 10.8 14.4 17.8 22.0 29.0 35.5
100.0 8.3 10.4 13.9 17.2 21.3 28.0 34.3
105.0 8.0 10.0 13.4 16.6 20.5 27.0 33.2
110.0 7.8 9.7 13.0 16.1 19.9 26.2 32.1
115.0 7.5 9.4 12.6 15.6 19.3 25.3 31.1
120.0 7.3 9.2 12.3 15.2 18.7 24.6 30.2
180.0 5.6 7.0 9.3 11.4 14.1 18.5 22.7
240.0 4.6 5.7 7.6 9.4 11.5 15.1 18.5
300.0 3.9 4.9 6.5 8.0 9.8 12.9 15.8
360.0 3.5 4.3 5.7 7.0 8.7 11.3 13.9
420.0 3.1 3.9 5.1 6.3 7.8 10.2 12.4
480.0 2.9 3.5 4.7 5.8 7.1 9.2 11.3
540.0 2.6 3.3 4.3 5.3 6.5 8.5 10.4
600.0 2.5 3.0 4.0 4.9 6.0 7.9 9.6
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 33 28/06/2011
The "Rational" (Lloyd-Davies) method shall be used for the design of highway drainage as set out in "Road Note 35 - A Guide for Engineers to the Design of Storm Water Sewer Systems", used in conjunction with the "Tables for Hydraulic Design of Storm Drains, Sewers and Pipe Lines" in Hydraulic Research Paper No. 4, all published by HMSO.
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 34 28/06/2011
APPENDIX 2
STORM SEWER CALCULATION SHEET - [Rational (Lloyd-Davis) Formula]
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HEM-RDS-DRAINAGE DESIGN MANUAL (APR '10) 35 28/06/2011
Scheme: Sheet Number of
Storm Freq. once in yrs Drawing Nos:
Roughness Coefficient
STORM SEWER CALCULATION SHEET - [Rational (Lloyd-Davis) Formula]
Time of Entry mins
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21)
MH Nos. or Chainage
Impermeable Area (Hectares)
From To
Length No.
Diff. in Level (m)
Distance (m)
Gradient (1 in )
Velocity (m/sec)
Time of flow (min)
Time of concentration
(min)
Rate of rainfall mm/hr Roads
Side slopes
Fields Total
(11+12+13) Cummu -
lative
col 10 x col 15
Flow (col 16 x 2.78)
lit/sec.
Sewage Flow
(lit./sec)
Pipe Diam. (mm)
Pipe Capacity (lit. / sec)
Remarks
Recommended