DRAINAGE DESIGN MANUALprogrammeofficers.co.uk/Preston/CoreDocuments/LCC073.pdf · 2018-07-21 ·...

Revision 0 May 2010

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

Revision 0 May 2010

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.

Revision 0 May 2010

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

Revision 0 May 2010

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.

Revision 0 May 2010


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)

Revision 0 May 2010


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

Revision 0 May 2010


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.

Revision 0 May 2010


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

Revision 0 May 2010


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.

Revision 0 May 2010


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.

Revision 0 May 2010


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.

Revision 0 May 2010


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

Revision 0 May 2010


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.

Revision 0 May 2010


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

Revision 0 May 2010


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)

Revision 0 May 2010


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.

Revision 0 May 2010


(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:-



(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.



(c) Design the rest of the gully spacings on a two year storm intensity.

2. Layout For Summit Points:- (Similar to fig. 22)

Revision 0 May 2010


(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.


NORMAL VALLEY POINT

(Dual Carriageway)

Spacing designed on

10 year storm for 180m.

Spacing designed on

10 year storm for 180m.


Gully at valley point.


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.

Revision 0 May 2010


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.

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


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.

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


APPENDIX 1

BILLHAM'S RAINFALL TABLES

Revision 0 May 2010


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

Revision 0 May 2010


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

Revision 0 May 2010


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.

Revision 0 May 2010


APPENDIX 2

STORM SEWER CALCULATION SHEET - [Rational (Lloyd-Davis) Formula]

Revision 0 May 2010


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

DRAINAGE DESIGN MANUALprogrammeofficers.co.uk/Preston/CoreDocuments/LCC073.pdf · 2018-07-21 ·...

Documents

Transcript of DRAINAGE DESIGN MANUALprogrammeofficers.co.uk/Preston/CoreDocuments/LCC073.pdf · 2018-07-21 ·...