25 PIPE DRAINS

25.1        INTRODUCTION..........................................................................................................25-1

25.2        LOCATIONS AND ALIGNMENTS....................................................................................25-1

25.2.1     Roadway Reserves.........................................................................................25-1

25.2.2     Privately Owned Properties.............................................................................25-1

25.2.3     Public Open Space..........................................................................................25-1

25.2.4     Drainage Reserves.........................................................................................25-2

25.2.5     Clearance from Other Services.........................................................................25-2

25.3        DESIGN CRITERIA.......................................................................................................25-3

25.3.1     Minimum Design Service Life...........................................................................25-3

25.3.2     Diameter.......................................................................................................25-3

25.3.3     Pipe Grades...................................................................................................25-3

25.3.4     Scour Stop Collars..........................................................................................25-3

25.3.5     Vertical Angles...............................................................................................25-3

25.3.6     Curved Pipelines.............................................................................................25-3

25.3.7     Multiple Pipelines..........................................................................................25-4

25.3.8     Dead-end Pipelines.........................................................................................25-4

25.4        PIPE INSTALLATION....................................................................................................25-4

25.4.1     Depth............................................................................................................25-4

25.4.2     Pipe Trenching...............................................................................................25-5

25.4.3     Pipe Materials................................................................................................25-5

25.4.4     Pipe Bedding..................................................................................................25-5

25.4.5     Jointing.........................................................................................................25-5

25.4.6     Branch Connections........................................................................................25-5

25.5        DESIGN  METHOD........................................................................................................25-6

25.5.1     General.........................................................................................................25-6

25.5.2     Hydraulic Grade Line and Total Energy Line......................................................25-6

25.5.3     HGL Calculation Procedure..............................................................................25-7

25.5.4     Friction Losses...............................................................................................25-7

25.5.5     Structure Losses.............................................................................................25-8

25.5.6     Freeboard at Inlets and Junctions....................................................................25-10

25.5.7     HGL for Pipes Running Partially Full.................................................................25-10

25.5.8     Equivalent Pipe Determination.........................................................................25-12

25.5.9     Data Sensitivity..............................................................................................25-12

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25.6        MANHOLES.................................................................................................................25-12

25.6.1     Location.........................................................................................................25-12

25.6.2     Standard Manhole Types.................................................................................25-13

25.6.3     Special Manhole Designs.................................................................................25-13

25.6.4     Deep Manholes...............................................................................................25-13

25.6.5     Maximum Spacing...........................................................................................25-13

25.6.6     Fall Through Structures...................................................................................25-13

25.6.7     Benching........................................................................................................25-14

25.6.8    Vertical Drops.................................................................................................25-14

25.6.9     Access Covers................................................................................................25-14

25.6.10   Cover Levels...................................................................................................25-15

25.7        SERVICE TIES.............................................................................................................25-15

25.7.1     Depth............................................................................................................25-15

25.7.2     Location.........................................................................................................25-15

25.7.3     Marking.........................................................................................................25-15

25.7.4     Size...............................................................................................................25-16

25.7.5     Grade............................................................................................................25-16

25.7.6     Connections...................................................................................................25-16

25.7.7     Maximum Length............................................................................................25-16

25.8        MAINTENANCE............................................................................................................25-16

25.8.1     Design and Construction Stage........................................................................25-16

25.8.2     Drainage Service Stage...................................................................................25-16

25.8.3     Rehabilitation Stage........................................................................................25-17

APPENDIX 25.A HYDRAULIC GRADE LINE DESIGN FLOWCHARTS...............................................25-19

APPENDIX 25.B PIPE DESIGN CHARTS.....................................................................................25-23

APPENDIX 25.C JUNCTION HEAD LOSS CHARTS.......................................................................25-31

APPENDIX 25.D HEAD LOSS DATA FOR OTHER STRUCTURES....................................................25-35

APPENDIX 25.E WORKED EXAMPLE..........................................................................................25-41

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25.1      INTRODUCTION

The use of pipe drains has not been common in Malaysia in the past. This can be attributed to several factors:

      pipe drains have only limited capacity, compared with large open drains;

      it is difficult to provide sufficient inlet capacity to ensure that the pipe capacity is fully utilised;

      pipes are more difficult to clear if blocked;

      design procedures are significantly more complex than the design procedures for open drains; and

      correct pipe installation is more important than for open drains.

In turn, the lack of demand has meant limited pipe manufacturing capability and availability and a lack of design guidelines in the past. These difficulties can now be overcome.

The advantages and disadvantages of pipe drains were discussed in Chapter 10, section 10.3.1.

With an increased understanding of design principles and the availability of improved design procedures, the designer now has the opportunity to utilise pipe drains in suitable locations. This Chapter provides an introduction and outline of the design and installation requirements.

25.2      LOCATIONS AND ALIGNMENTS

Standardised locations for stormwater pipelines are provided to limit the negotiations needed when other services are involved and permit ready location by maintenance crews.

25.2.1 Roadway Reserves

Stormwater pipelines should be located on the high side of road reserves to permit relatively short service tie connections to adjacent properties.

Where there is significant advantage in placing a stormwater conveyance on an alignment reserved for another Authority, it may be so placed provided that both the Authority responsible for maintenance of the stormwater conveyance and the other Authority concerned agree in writing to release the reservation.

UPVC and PE pipes shall not be placed in a reserve designated for another Authority or adjacent to an existing drainage or sewer flexible pipeline within a road reserve.

Table 25.1 provides typical requirements for location of pipe drains and services within road reserves, however these may be varied by the local Authority. The relevant

Authority should be consulted concerning their standard alignments for services.

Table 25.1 Alignments within Roadway Reserves

Pipe Diameter (mm)

Alignment

375 to 675 750 to 1800

under kerb line

within median strip, or centreline of roadway

In selecting pipeline locations, it is necessary to also consider inlet location preferences as outlined in Chapter 24.

25.2.2 Privately Owned Properties

Wherever stormwater pipelines are required along shared property boundaries, they should be located along the high side of the downhill property. Stormwater pipelines are often constructed in parallel to sewers and as the sewerage system is usually deeper, pipes connecting to stormwater ties have less problems in crossing over the sewer.

Alignments shall be offset sufficient distance from building lines to allow working space for excavation equipment.

Acceptable centreline offset alignments from property boundaries in residential, commercial, and industrial areas shall be in accordance with Table 25.2.

Table 25.2 Alignments within Privately Owned Properties

Pipe Diameter (mm)

Rear Side Boundary Boundary

375 to 450 525 to 675

1.8 m 1.2 m (see Note) 1.8 m 1.5 m (see Note)

Note: Where other hydraulic services or power poles are located on the same side of a property boundary, the centreline of the stormwater pipeline shall be located 1.8 m from the property boundary.

25.2.3 Public Open Space

The location of stormwater pipelines within public land such as open space shall be brought to the attention of the operating Authority for consideration. As a guide, unless directed otherwise, stormwater pipelines shall be located not less than 3 m from the nearest property boundary.

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25.2.4 Drainage Reserves

A drainage reserve shall be wide enough to contain the service and provide working space on each side of the service for future maintenance activities. Minimum drainage reserve widths shall be in accordance with Table 25.3.

Pipelines up to and including 675 mm diameter may be located within privately owned properties if satisfactory arrangements are made for permanent access and maintenance. Larger diameter pipelines shall be located within public open space or outside privately owned properties in separate drainage reserves.

Consideration should be given to the multi-purpose use of drainage reserves such as open space or pedestrian corridors.

Table 25.3 Minimum Drainage Reserve Widths

Pipe Diameter, D (mm)

Minimum Reserve Width (m)

Invert < 3.0 m deep

375 to 450

525 to 675

750 to 900

1050 to 1200

1350 to 1800

2.5 3.0 3.5 3.5 not less than 3 x D

Invert 3.0 - 6.0 m deep

375 to 450

525 to 675

750 to 900

1050 to 1800

3.5

4.0

4.5

not less than 4 x D

Note: Where other hydraulic services or electricity services are laid on the same side of the property boundary, the required reserve width shall be increased by 500 mm to provide horizontal clearance between services.

25.2.5 Clearance from Other Services

Where conflicts exist in the alignment and level of services, it will be necessary to ensure that adequate clearance is provided between the outer faces of each service. Minimum clearances have been established to reduce the likelihood of damage to stormwater pipelines or other services, and to protect personnel during construction or maintenance work.

Under no circumstances shall stormwater pipelines be:

      cranked to avoid other services or obstacles

      located longitudinally directly above or below other underground services in the same trench

Minimum clearances between stormwater pipelines and other services shall be in accordance with Table 25.4. The nominated clearance should make due allowance for pipe collars and fittings. Special protection may be provided to protect service crossings by concrete encasing the stormwater pipe for sufficient length to bridge the trench of the other service.

Table 25.4 Minimum Clearances

Service

Clearance (mm)

Horizontal

All services

600

Vertical

Sewers

150

Water mains

75

Telephone

75

High Pressure Gas

300

Low Pressure Gas

75

High Voltage Electricity

300

Low Voltage Electricity

75

Penetration by services through stormwater pipes should be avoided. Where it is necessary for a service to penetrate a stormwater pipe or manhole, allowance should be made for the hydraulic losses in the system resulting from the penetration. In addition, the service should be contained in a pipe or conduit of sufficient strength to resist the forces imposed on it by the flow, including debris, in the stormwater system. Unless agreed to the contrary by the relevant Authority, penetrations should be constructed using ductile iron pipe. To assist in the removal of debris collected on service pipes or conduits passing through a drainage system, it is recommended that a manhole be located at the pipe or conduit penetration.

Where a stormwater pipeline crosses or is constructed adjacent to an existing service, the design shall be based on the work-as-executed location and level of that service. The design documents shall direct the contractor to verify the location and level of the existing service prior to constructing the stormwater pipeline in question.

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25.3 DESIGN CRITERIA

Pipes shall be designed by a "Hydraulic Grade Line" (HGL) method using appropriate pipe friction and drainage structure head loss coefficients. Actual pipe diameters, as opposed to nominal pipe diameters, shall be used for hydraulic calculations.

The HGL method is described in Section 25.5. Drainage structure head loss coefficients may be obtained from the charts provided in Appendix 25.C.

25.3.1   Minimum Design Service Life

Stormwater pipelines shall be designed for a minimum effective service life of 50 years.

In composite PE pipe where steel ribs are used to structurally strengthen and stiffen the pipe, the ribs shall be ignored in determining the long-term vertical deflection, long-term external loading carrying capacity, and long-term buckling resistance of the installation.

25.3.2   Diameter

Minimum diameters for stormwater pipelines shall be in accordance with Table 25.5.

Table 25.5 Minimum Pipe Diameters

Application

Diameter (mm)

Pipe draining a stormwater inlet and crossing a footpath alignment *

300

Any other pipe

375

For a non-self draining underpass, the pipe shall be sized for 10 year ARI and shall not be less than

450

Note: * 300 mm diameter pipes are permitted in this situation only, in order to provide more space in the footpath alignment for other utility services.

The maximum pipe diameter to be used depends on the availability of pipes from manufacturers. The use of large diameter pipes creates problems with clearance for other services. Box culverts or multiple pipes should be used if additional capacity is required.

25.3.3 Pipe Grades

The longitudinal grade of a pipeline between drainage structures shall be calculated from centreline to centreline of such structures.

(a)     Maximum Grade

Pipeline grades shall be chosen to limit the pipe full flow velocity to a value less than or equal to 6.0 m/s. In steep terrain it may be necessary to construct manholes with drops to dissipate some of the kinetic energy.

(b)     Minimum Grades

Stormwater pipelines shall be designed and constructed to be self cleansing, e.g. free from accumulation of silt. The desirable minimum grade for pipelines shall be 1.0%.

An absolute minimum grade of 0.5% may be acceptable where steeper grades are not practical. Such instances shall be brought to the attention of the relevant Authority for consideration before finalising designs.

25.3.4   Scour Stop Collars

Pipelines laid on steep slopes shall be protected from failure due to wash-out of the pipe bedding. Where pipeline grades are greater than 7%, reinforced concrete scour stop collars shall be provided.

25.3.5   Vertical Angles

Stormwater pipelines shall be constructed so that the bore of the pipe has no point where debris can lodge and cause reduction in capacity. The use of vertical angles is not permitted.

25.3.6   Curved Pipelines

Curved stormwater pipelines are only permitted for diameters 1200 mm and above. Curves may be utilised wherever there are significant advantages in their use. Ad hoc curving of pipelines to avoid obstacles such as trees, power poles, gas mains etc. is not permitted. Curved pipelines should be positioned to follow easily identifiable surface features, e.g. parallel to a kerbline.

The curve radii shall be measured from the centreline of the pipe. Curved pipelines shall have a constant radius.

Curved pipelines are permitted provided they are:

      in the horizontal plane only (i.e. no vertical curves)

      in one direction only between successive structures (i.e. no reverse curves)

Curved pipelines shall be achieved as follows:

      curves formed by using rubber ring or flush jointed pipes,

The deflection shall be achieved totally within the pipe joint system so that the rubber ring or flush joint remains effective. Deflection of each joint shall not exceed the manufacturer's recommendation.

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      curves formed by using splayed pipes,

Splayed pipes may be used to construct a curved pipeline provided that the curve is totally formed by the splays. The use of single or double splayed pipes is acceptable.

Splayed pipes shall be either:

° factory formed (preferred), or

° field formed by cutting standard pipes with an approved cutting device, and re-joining

For concrete pipes a bandage joint shall be constructed as shown on Standard Drawing SD F-10.

Design drawings shall show the following information:

      centreline radius

      pipe type (normal or splayed)

      effective length of individual pipes (if other than standard length)

      type of jointing (if other than flush jointed)

25.3.7 Multiple Pipelines

Where multiple pipelines are used, they should be spaced sufficiently to allow adequate compaction of the backfill between the pipes. The clearance between the outer face of the walls of multiple pipes should generally be in accordance with Table 25.6, although the relevant Authority may permit a lesser spacing in special circumstances to reduce structure costs, where reserve width is limited, or for relief drainage works.

Table 25.6 Recommended Minimum Spacing of Multiple Pipelines

Diameter of Pipes (mm)

Minimum Clear Spacing (mm)

Up to 600 675 to 1800

300 600

Notes:

1.    The above minimum spacings may need to be modified to satisfy structural considerations, especially when laid at depth or under traffic loads

2.     Where lean mix concrete vibrated in place or cement stabilised sand is used for backfill, the clear spacing may be reduced to 300 mm for all diameters, subject to structural considerations

25.3.8 Dead-end Pipelines

Dead-end pipelines are those with no surface inlet or manhole on the upstream end. They are only used to provide a connection point for piped property drainage.

Dead-end pipelines shall drain directly to a stormwater manhole or inlet. Connection of a dead-end pipeline to another stormwater pipeline by a branch connection or slope junction will not be permitted.

A dead-end pipeline shall be constructed on a straight alignment and shall have a maximum length of 50 m.

25.4 PIPE INSTALLATION

Pipe class shall be selected to provide adequate strength to meet construction, overburden, and traffic loads. Pipe loadings shall be determined in accordance with the relevant Malaysian or British Standard or manufacturer's recommendations for the selected pipe material.

Designers must be aware of the effect of pipe installation conditions on pipe strength. This applies for all pipe materials, and particularly for flexible materials including PE and UPVC. In assessing pipe loadings, consideration shall be given to bedding support type (or embedment and site soil moduli), specified trench widths, method of installation, and live loads including construction loading.

Where load limits apply, the location and load limitation shall be clearly shown on the drawings.

25.4.1 Depth

In general, stormwater pipelines shall be deep enough to serve the whole of the adjacent block(s) that are to drain to the pipeline (refer Section 25.7.1).

(a) Minimum Depth

Minimum cover over pipelines should normally be 0.6 m as measured from top of pipe to finished surface level. For pipelines under road pavements, the required cover shall be measured from top of pipe to pavement subgrade level.

Minimum cover over FRC and SRC pipes may be less than 0.6 m. The pipe load class for any such design cover shall be in accordance with the relevant Malaysian or British Standard, or manufacturers' recommendations. Minimum cover shall be increased to account for construction loading during pipe installation and traversing over the pipeline particularly when applied at subgrade level. The absolute minimum cover shall be 300 mm, unless the pipeline is protected from superimposed loads by a concrete slab.

Minimum cover over UPVC and PE pipes shall be the greater of 0.6 m or as defined in the relevant Malaysian or British Standard, or manufacturers' recommendations. For pipelines under road pavements, the required cover shall be at least 0.6 m from the top of the pipe to pavement subgrade level.

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(b) Maximum Depth

The maximum depth of stormwater pipelines to invert level shall generally be 6 m. In special cases (e.g. for a short length of pipeline through a ridge), approval must be obtained from the Local Authority to exceed this limit. In this case, design checks shall be required to ensure that the pipeline has sufficient strength for the imposed load.

25.4.2   Pipe Trenching

Trench excavation shall comply with the principles specified in the relevant standard or Manufacturer's specifications for the pipe material used.

The maximum trench width shall be the external pipe diameter plus 300 mm measured at the level of the crown of the pipe. The minimum trench width shall be 600 mm.

In trenches where timbering is necessary, the trench width shall be increased sufficiently to maintain the minimum specified clearance between the pipes and the face of the timbering. The width of curved trenches shall be adequate to allow correct jointing of pipes.

25.4.3   Pipe Materials

Stormwater pipelines shall be constructed from materials proven to be structurally sound and durable and have satisfactory jointing systems. The use of two or more types of pipe material on a single length of pipeline is not acceptable.

Stormwater pipelines may be constructed with any of the following:

      Fibre Reinforced Cement Pipes (FRC)

      Steel Reinforced Concrete Pipes (SRC)

      Unplasticised Polyvinyl Chloride Pipes (UPVC)

      Composite Polyethylene Pipes (PE)

All pipes shall comply with the relevant Malaysian Standards, where applicable, or British Standard.

Alternative pipe materials may be acceptable. Proposals for the use of other materials shall be referred to the relevant Authority for consideration.

25.4.4   Pipe Bedding

Adequate, properly placed and compacted pipe bedding material is essential to allow the pipe to develop its design strength to resist loads.

Bedding material for pipes in trenches shall be a minimum 75 mm thick under the pipe barrel and a minimum of 25 mm under pipe sockets. The bedding shall be shaped and compacted to provide continuous support for pipes

and precautions shall be taken to prevent disturbance or instability of the bedding due to groundwater.

Bedding material shall consist of granular material of low plasticity such as quarry fines, or coarse river sand free from organic matter with a minimum 85% passing the 2.36 mm sieve and not more than 15% passing the 0.075 mm sieve.

25.4.5   Jointing

Pipes need to be capable of resisting root intrusion, hydraulic pressure loadings, and preferably have some flexibility at joints.

Unless otherwise approved by the local Authority, pipe jointing shall be as follows:

      375 mm diameter pipes shall be rubber ring jointed

      450 mm diameter and larger pipes shall be either rubber ring jointed or flush jointed. However, pipes designed to operate under hydraulic conditions that exceed 2.0 m head shall have rubber ring joints

      450 mm to 675 mm diameter pipes located under roadways shall have rubber ring joints

For pipe diameters greater than 1000 mm, adhesive shall not be used to join flexible pipes within the road reserve.

Locations of various joint types shall be shown on the design drawings.

The maximum allowable head for all pipes shall be in accordance with the appropriate Malaysian or British standard.

Where pipes are connected to rigid structures or are embedded in concrete, adequate flexibility shall be provided to minimise damage caused by differential settlement. Pipe connections to structures shall be constructed in accordance with Standard Drawing SD F-12.

25.4.6   Branch Connections

Pipeline junctions except for property ties shall generally occur within a stormwater inlet, manhole, or special structure. Stormwater inlets are described in Chapter 24, and manholes in Section 25.6. Pipe branches are acceptable for property ties.

Branch connections may also be permitted in locations where a surface manhole is undesirable, provided that adequate structural strength can be achieved at the junction. Allowable sizes of branch connections into pipelines of 450 mm to 1800 mm diameter shall be in accordance with Standard Drawing SD F-ll.

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Entry angles for branches shall be between 45 and 90 to the main pipeline. A manhole shall be constructed on the branch pipeline within 20 m of the branch connection.

25.5 DESIGN METHOD

25.5.1   General

All stormwater pipe systems shall be designed by a "Hydraulic Grade Line" (HGL) method using appropriate pipe friction and drainage structure head loss coefficients. The velocity of flow and accordingly the discharge capacity of a pipe are a function of the Hydraulic Grade (slope of the HGL and not the actual pipe grade).

Actual pipe diameters, as opposed to nominal pipe diameters, shall be used for hydraulic calculations.

Flowcharts for the HGL method are given in Appendix 25.A. Design charts for pipe friction loss, pit losses and structure head loss are provided in Appendices 25. B, 25.C and 25. D respectively. A worked example is presented in Appendix 25. E. Chapter 17 provides details of some of the computer programs which can be used for the calculations.

The capacity of a pipe drainage system depends in part on the available inlet capacity (see Chapter 24). If there is insufficient inlet capacity, pipes will not flow full at the design flow. The recommended design procedure is to design the pipe system assuming that there are no constraints on inlet capacity, and then to ensure that a sufficient number of inlets with the appropriate capacity is provided so that the design flow can enter the system.

In general, the hydraulic grade line analysis should proceed upstream through the drainage system commencing at the outlet or some known control point. There will be some exceptional circumstances e.g. in flat terrain where analysis may need to proceed in a downstream direction to ensure that surcharging does not occur at the upstream end of the system. Also, for supercritical flow the calculations should commence at the upstream end (or control section) and proceed downstream. The two methods of calculation are discussed in Section 25.5.3.

25.5.2   Hydraulic Grade Line and Total Energy Line

The HGL is a plot of the pressure head at any point in a pipeline.

The HGL may be thought of as the "effective water level" in the system, the level to which water would rise in an open-topped vertical pipe inserted into the drain line at any point. Note however that at manholes and gully inlets the water surface elevation is normally higher than the theoretical HGL because the latter reflects the HGL

immediately upstream of the structure and its determination does not distinguish between pressure gains or losses at the inlet to or outlet from the structure, but relates to the structure as a whole. Figure 25.1 explains this effect.

Pressure head is normally lost in both pipes and manholes due to friction and turbulence and the form of the HGL is therefore a series of downward sloping lines over line lengths, with steeper or vertical drops at manholes.

In some circumstances there may be a pressure gain and therefore a rise in the HGL at a structure. In these cases the gain should be taken into account in the hydraulic calculations.

The level and grade of an HGL varies with flow. For design purposes the HGL calculated and plotted on the longitudinal section is that applicable to the flow resulting from the design storm. For pressure flow, the HGL will be at or above the obvert (top of pipe). For free-surface flow, the HGL is below the obvert; the pipe runs part-full and the water surface in the pipe is at the level of the HGL.

Pipes which flow under pressure may be located at any grade and at any depth below the HGL without altering the velocity and flow in the pipe subject to the grade limitations outlined in Section 25.3.3. Hence, pipe grade may be flattened to provide cover under roads, or clearance under other services, without sacrificing flow capacity, provided sufficient head is available.

The HGL and the Water Surface Elevation (WSE) must be below the surface level at manholes and inlets, or the system will surcharge. This depth below the surface is termed the freeboard. Minimum freeboard requirements are set out in Section 25.5.6.

The level of the HGL for the design storm should be calculated at the upstream and downstream side of every gully inlet or manhole, at points along a pipe reach where obstructions, penetrations or bends occur, or where a branch joins.

It is recommended that designers check that the elevation of the total energy line falls progressively as flow passes down through the drainage system. This is an important check that should be undertaken where the drainage system is complex and where the configuration of pipes/structures etc. does not conform to the structure loss charts available.

The total energy line under steady flow conditions is located above the HGL by an amount equal to the velocity head. This is shown diagrammatically in Figure 25.1. Note that under quiescent conditions in a pond or storage with no flow the HGL and energy line will coincide.

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Structure Energy Loss Pipe Friction Losses

Actual H.G.L in Structure

OutletChannel (SlopeSo)

Outlet

Figure 25.1 Hydraulics for a Single Pipe Reach (QUDM, 1992)

25.5.3 HGL Calculation Procedure

The procedures for detailed calculation in the two cases of subcritical and supercritical flow are outlined on the Flow Charts contained in Appendix 25.A.

Usually, pipe drainage design by the HGL method is carried out by working upstream from the outlet because:

1.     the outlet is often the only point for which the HGL may be readily determined.

2.     head losses in inlets, manholes and junctions are expressed as a function of the velocity in the downstream pipe. Hence the pipe downstream of each structure must be designed before the head loss in that structure can be determined.

The above method applies in situations of sub-critical flow, which is the usual condition in most drainage systems. Where super-critical flow occurs it is necessary to adopt a procedure of designing from upstream to downstream and this may be essential in parts of the drainage system located in steep or undulating terrain.

The super-critical flow calculation procedure is as follows:

1.     assess the critical start point or points in the system (e.g. sag gully inlet)

2.     allow minimum freeboard to determine the permissible water surface level in that pit, (normally 150 mm)

3.     select pipe diameters and depths to suit hydraulic and economic considerations

4.     calculate hydraulic grade line proceeding downstream from the starting water surface level determined in step 2 above

In either case the procedure is iterative, because the head loss calculations (in particular) depend on the depth of flow. Experience in design should help reduce the number of iterations.

The calculated HGL for the design flow shall be plotted on the design longitudinal section. Where different ARIs for design have been adopted for separate parts of the system, the HGL appropriate to that part of the system shall be plotted.

25.5.4 Friction Losses

Losses due to friction in pipes may be expressed by the Darcy-Weisbacrformula as given in Equation 25.1:

hf

D 2g

(25.1)

where,

hf = head loss in pipe due to friction (m)

f = Darcy-Weisbacrfriction factor (dimensionless)

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L     =    length of the pipe (m)

D    =    diameter of the pipe (m)

V    =    velocity of flow in the pipe (m/s)

g    =    acceleration due to gravity (m/s2)

The friction factor f depends in general upon the flow Reynolds number and the relative roughness as discussed in Chapter 12. The friction factor f is related to a characteristic pipe roughness height k (mm) by the Colebrook-White formula, Equation 12.21 in Chapter 12. Design charts are available giving the solution of these equations for practical applications.

Design Charts 25.Bl to 25.B5 in Appendix 25.B may be used to determine pipe sizes for pipes designed to flow full but not under pressure. These charts are based on the Colebrook-White equation and shall be used for sizing pipes which are designed to flow full.

Some texts use alternative formulae for the pipe friction loss, such as Manning's formula. Manning's equation is not recommended for pipes flowing full or under pressure, which is the usual design case. For cases of free surface flow, use of the Manning's formula is acceptable so as to provide consistency with the design methods for open drains.

Appropriate roughness values (k) for pipes that are in average condition are given in Table 25.7. Also shown for comparison are values of Manning's 'n'. These values are slightly higher than those quoted by manufacturers for new pipes to allow for the effects of pipe joints, and of ageing and deterioration. In the analysis of existing systems, roughness values may need to be further increased to allow for the condition of the existing pipes.

Table 25.7 Pipe Roughness Values (average condition)

Pipe Material

n

k (mm)

Spun Precast Concrete

0.013

0.3

Fibre Reinforced Cement

0.013

0.15

UPVC

0.011

0.06

n = Manning roughness coefficient

k= Pipe roughness height for Colebrook-White equation

Further sources of information on roughness values can be found in textbooks (such as French, 1985 and Chow, 1959).

25.5.5 Structure Losses

Losses due to obstructions, bend or junctions in pipelines may be expressed as a function of the velocity of flow in the pipe immediately downstream of the obstruction, bend or junction as follows:

h5=KxV02/2g                                             (25.2)

where,

hs = head loss at structure (m)

K = pressure change coefficient (dimensionless)

V0 = velocity of flow in the downstream pipe (m/s)

Pressure change coefficients K (sometimes referred to as structure loss coefficients) are dependent on many factors, for example:

      junction structure geometry;

      pipe diameters;

      bend radius;

      angle of change of direction;

      relative diameter of obstruction etc.

(a) Junctions

The pressure head loss is a function of the velocity head (V2/2g) of the flow in the conduit downstream of the junction, thus:

= KuxV2/2g                                            (25.3)

r

where,

AP/y= pressure head change at a junction (m) Ku = pressure change coefficient (dimensionless)

Note that Equation 25.3 gives the pressure head change, not the energy change. The two figures are likely to be different because of different pipe diameters and flow rates upstream and downstream. The pressure head change is convenient for use in HGL calculations (see Appendix 25.E).

Hydraulic model studies are the only means of deriving reliable values of energy losses and pressure changes at different types of pits and junctions. The most significant study has been the work at the University of Missouri by Sangster et al. (1958). This produced a set of design aids known as the "Missouri Charts". In Australia, Hare (1980, 1983) has produced information on other configurations.

As noted in Australian Rainfall and Runoff (1998), the main difficulty in presenting information on pit losses is the almost infinite number of configurations which can occur. The Missouri Charts or similar information are too voluminous to present in this Manual. Appendix 25.C provides pressure change coefficients for some of the most common junction types encountered in urban drainage design. Users requiring data on other pit configurations should consult the above references.

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Note that where a structure has lateral as well as through flow the pressure change coefficient which applies to the through (main) line is in general, different to that of the lateral line.

Some references also list a head loss coefficient for water surface elevation change, Kw For most pit configurations K\s approximately equal to Ku.

The determination of junction pit losses usually requires iterative calculations because the loss coefficient is dependent on the depth of flow. Flowchart 25.A3 in Appendix 25.A can be used to determine both the HGL and the WSE at the junction. The values of Ku and Kw should be applied to the velocity head in the outlet pipe i.e. V02/2g.

Large energy losses and pressure changes can be avoided by attention to simple details in the design of pits and manholes (AR&R, 1998). One principle is to ensure that jets of water emerging from incoming pipes are directed to outlet pipes, rather than impinging on pit walls. Hare (1983) states that changes of flow direction should generally occur on the downstream face of pits, rather than at the upstream face or centre of the pit.

(b)     Inlets and Outlets

Where the inlet structures is an endwall (with or without wingwalls) to a pipe or culvert, an allowance for head loss should be made. Design charts in Appendix 25.D provide entry and exit loss coefficients Ke to be applied to the velocity head.

he=KexV02/2g                                           (25.4)

where,

he = head loss at entry or exit (m) Ke = entry or exit loss coefficient V0 = velocity in pipe (m/s)

(c)      Bends

Under certain circumstances it may be permissible to deflect the pipeline (either at the joints or using precast mitred sections) to obviate the cost of junction structures and to satisfy functional requirements. The requirements for curved pipelines are set out in Section 25.3.

Where pipelines are deflected an allowance for energy loss in the bends should be made. The energy loss is a function of the velocity head and may be expressed as:

hb=KbxV2/2g                                               (25.5)

where,

hb = head loss through bend (m)

Kb = bend loss coefficient

Values of bend loss coefficients for gradual and mitred bends are given in the Design Charts in Appendix 25. D. Note that the head loss due to the bend is additional to the friction loss for the reach of pipe being considered.

(d)      Obstructions or Penetration

An obstruction or penetration in a pipeline may be caused by a transverse (or near transverse) crossing of the pipe by a service or conduit e.g. sewer or water supply. Where possible, such obstruction should be avoided as they are likely sources of blockage by debris and damage to the service. To facilitate the removal of debris, a manhole should be provided at the obstruction or penetration.

The pressure change coefficient KP at the penetration is a function of the blockage ratio. Design Chart 25. D4 should be used to derive the pressure change coefficient, which is then applied to the velocity head.

lip=KpxV2/2g                                               (25.6)

where,

hp = head loss at penetration (m)

Kp = pressure change coefficient of penetration

Where a manhole is provided at an obstruction or penetration it is necessary to add the structure loss and the loss due to the obstruction or penetration based upon the velocity, V in the downstream pipe.

(e)     Branch Lines without a Structure

Where branch connections are unavoidable, appropriate allowance for head loss at the junction should be made. Pressure change coefficients for junctions with branch line connections should be determined from the design charts in Appendix 25.C, with definitions shown in Figure 25.2. Designers should be aware that the pressure change coefficient and therefore the head loss at the junction may be different for the main line and the branch line.

Figure 25.2 Branch Line

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(f) Expansion and Contractions

Sudden expansion or contractions in stormwater pipelines should normally be avoided. They may however need to be installed as part of a temporary arrangement in a system being modified or upgraded, or in a relief drainage scheme.

Expansions and contractions also occur at the outlet and inlet, respectively, of stormwater pipelines.

The pressure change due to the expansion or contraction can be derived using the energy loss coefficients determined from the Design Charts in Appendix 25.D. The entrance loss coefficient should be applied to the absolute value of the difference between the two velocity heads.

25.5.6 Freeboard at Inlets and Junctions

For the design of underground drainage systems a freeboard should be provided above the calculated water surface elevation (WSE) to prevent surcharging and to ensure that unimpeded inflow can occur at gully inlets. Table 25.8 provides recommendations for freeboard for inlets and junctions.

Table 25.8 Minimum Freeboard Recommendations for Inlets and Junctions

Situation

Recommendation

Gully Inlet on Grade

Freeboard = 150mm below invert of kerb and channel. (See Notes 1 and 2).

Gully Inlet in Sag

Freeboard = 150mm below invert of kerb and channel. (See Note 1)

Field Inlet

Freeboard = 150mm below top of grate or lip of inlet

Junction Structure (See Note 3)

Freeboard = 150mm below top of lid.

Notes:

1.     Where the channel is depressed at a gully inlet the freeboard should be measured from the theoretical or projected invert of the channel.

2.     Where an inlet is located on grade the freeboard should be measured at the centreline of the gully inlet chamber.

3.     Where it is necessary for the HGL to be above the top of a manhole or junction structure, a bolt-down lid should be provided. This will, of course, prevent the use of the manhole as an inlet.

The maximum permitted WSE should allow for the head loss resulting from surface inflow through grates etc. into the structure being considered.

Where an appropriate chart is not available it is recommended that the WSE be arbitrarily adopted at the height above the calculated HGL in accordance with Equation 25.7:

WSE - HGL = 0.3 Vu2 / 2g                                   (25.7)

where,

Vu = upstream velocity (m/s)

The freeboard recommendations should be applied as detailed in Table 25.9.

25.5.7 HGL for Pipes Running Partially Full

For established flow in a pipe running partially full the HGL will correspond with the water surface.

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Table 25.9 Application of Freeboard Recommendations

Design Condition

Minor Storm Analysis

Major Storm Analysis

HGL&WSE

Calculations

Required

Freeboard toWSE

HGL&WSE

Calculations

Required

Freeboard to WSE

(a) Underground system designed for minor storm. Overland flow check for major storm requires no increase in size of pipe system

Yes

As per Table 25.8

No

N.A.

(See Note 2)

(b) Underground system designed for minor storm and overland flow check for major storm requires increase in size of pipe system

Yes

As per Table 25.8

Yes

As per Table 25.8 (see Notes 1 and 2)

(c) Underground system designed for major storm

No

N.A.

Yes

As per Table 25.8 (See Notes 1, 2, 3)

Notes:

1.    The major storm HGL may only need to be calculated from the point where the increase in pipe size is required downstream to the outfall e.g. downstream from a trapped sag.

2.     Notwithstanding the presence of overland or street flow on the surface it is recommended that for design purposes the calculated WSE in the underground pipe system not exceed the requirements of Table 25.8.

3.    This situation will only apply where the opportunity for overland flow is nil or extremely limited.

At the upstream end of a pipe reach at a structure the position of the HGL and water surface will depend upon the depth of flow in the downstream pipe and the head loss occurring at the structure.

The following procedures are recommended for determining the HGL and water surface at the structure (refer to Figure 25.3).           Design Chart 25.B6 in

Appendix 25.B should be utilised to determine the flow characteristics of pipes flowing part-full.

MANHOLE

HGL Case 'A' HGL Case 'B'

Assumed HGL if pipe HGL + Structure Loss > Pipe obvert

(a)     Straight through Line

      Determine HGL at point 'S' for pipe running partially full.

      Add structure junction loss (KUV02/2g) where V0 is the velocity in the downstream pipe running partially full and Ku = 0.5.

      (i) Case 'A' : If the calculated HGL at the structure is less than the obvert level (point SO then adopt the calculated HGL as the HGL

(ii) Case 'B': If the calculated HGL at the structure is greater than the obvert level (point Si) then assume that the downstream pipe is running full at the outlet from the structure. A revised HGL at the structure should then be determined using the appropriate head loss chart base upon the velocity in the downstream pipe running full, and with the structure loss added to the level of the obvert (point Si).

(b)      Other Configurations

Figure 25.3 HGL Determination for Pipes Partially Full

A similar procedure should be used for the determination of HGL except that in assessing the trial HGL in step (b) the values of K,, in Table 25.10 are recommended:

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Table 25.10 Trial Values of /fufor use in Determining HGL under Partially Full Flow Conditions

Configuration

Ku

Straight through line

0.5

Change of direction 0° - 45°

0.75

Change of direction 46°- 90°

1.0

Multiple pipes

1.0

(c) Determination of Water Surface in the Structure

It is recommended that the water surface elevation in the structure be determined using the above procedures for establishing HGL in the downstream pipe, then proceeding as follows:

(i) where calculated HGL at the structure is below obvert of outlet pipe, adopt WSE = HGL

(ii) where calculated HGL at the structure is above the obvert, adopt point Si as the starting point and add the value of Kw V02 / 2g determined from the

appropriate design chart, based upon the velocity in the downstream pipe running full.

25.5.8 Equivalent Pipe Determination

Where multiple pipes or combinations of pipes and box culverts occur at a drainage structure, the following procedure may be used for the determination of head losses (QUDM, 1992):

D.

S Qn

[s(<?-kx:

6" T-Qn

(25.8)

(25.9)

Where pipes only are involved, equations 25.8 and 25.9 may be expressed as follows:

Dr

2C?

e                            r- 2

where,

Ve = equivalent flow velocity (m/s)

(25.10)

(25.11)

De   =     equivalent pipe diameter (m)

Dn   =     diameter of pipe 'n' (m)

Qn   =     flow for pipe 'n' (m)

Vn    =     flow velocity for pipe 'n' (m/s)

Note that this method is only applicable for pipes flowing full.

25.5.9 Data Sensitivity

The designer should consider the possible impacts of errors in data or assumptions on pipe roughness, and structure head loss. If water levels are particularly critical then sensitivity analyses should be performed.

25.6 MANHOLES

Manholes are required to gain access to the piped stormwater system for maintenance purposes in pipeline sections where there is no access via inlets. They are to be provided at locations of potential blockage, and at regular intervals for access purposes if there is no alternative access.

Refer to Chapter 24 for guidelines on the location and design of stormwater inlets.

25.6.1 Location

Manholes should be located where maintenance personnel with machinery can have direct access at all times. Preference should be given to siting manholes in public land rather than in privately owned properties.

Manholes shall be located:

       at changes in direction, grade, or pipe size

       at junctions

       at other locations where there is a high risk of blockage, and

       at regular intervals for operation and maintenance access

Manholes shall be constructed in accordance with Standard Drawings SD F-5 or SD F-6 as required.

The order of preference for location of manholes in roadway reserves is:

       roadside verges

       median strips

       centreline of road pavements

Where manholes are located in road pavements, the neck height shall be 100 mm minimum to allow for possible future adjustments.

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Generally, it is not desirable to locate manholes in the following locations due to the potential traffic hazard:

      bicycle or motorbike paths

      road pavements at intersections

25.6.2   Standard Manhole Types

Two standard manhole types are described, and illustrated in the Standard Drawings. The standard types are suitable for use in the majority of situations. However situations may arise where non-standard manholes are required, for example at complex multi-pipe junctions. In these cases, special designs will be required (see Section 25.6.3).

The maximum length of the neck on standard manholes shall be 200 mm.

Standard step irons located over the outlet pipe shall be provided.

(a)          Round Manhole

A round manhole shall be used for pipelines from 300 mm to 675 mm diameter (refer to Standard Drawing SD F-5).

(b)      Chambered Manhole

A chambered manhole shall be provided for pipelines 750 mm diameter and larger (Standard Drawing SD F-6). A chambered manhole may also need to be provided at the junction of two or more large diameter pipelines, depending on the geometry of the junction.

For pipelines 1200 mm diameter and above, it is preferable that straight-through flow be provided at these manholes by taking up angles between pipelines with curved alignments.

25.6.3   Special Manhole Designs

Designers of special manholes shall give consideration to:

      structural strength,

      hydraulic efficiency,

      access requirements, and

      maintenance requirements.

All special manhole designs shall be referred to the relevant Authority for consideration.

25.6.4   Deep Manholes

It is not envisaged that piped drainage systems will be constructed at a depth to invert greater than 6 m. However, should such an occasion arise, the matter shall be referred to the relevant Authority for consideration.

25.6.5 Maximum Spacing

Maximum spacing of manholes and inlets on pipelines shall be in accordance with Table 25.11. The selection of spacing should take into account the ease of access and availability of maintenance equipment.

Table 25.11 Recommended Maximum Spacing of Manholes and Inlets

Pipe Diameter (mm)

Maximum Spacing (m)

Straight

Curved

300 to 600 750 to 1050 1200 to 1800

40 60 100

not allowed

not allowed

80*

* Closer spacing is required on curved alignments due to maintenance considerations. A manhole shall be located on at least one curve tangent point.

25.6.6 Fall Through Structures

The fall through an inlet or manhole on a pipeline not operating under a hydraulic head at maximum design flow should be equal to or greater than the energy loss through the structure. A minimum fall in accordance with Table 25.12 shall be provided through an inlet or manhole (refer to Figure 25.4). In general the pipeline grade should be maintained through the pit or manhole, however in flat terrain this may not be possible.

Table 25.12           Fall and Benching Requirements in

Manholes

Pipe diameter

Minimum fall

Benching

(mm)

(mm)

300 to 525

0

no

600 to 1050 -

0

yes

deflection < 45°

600 to 1050,

25

yes

deflection > 45

1200 to 1800

50

yes

Note: Deflection angle is measured from pipe centreline to pipe centreline.

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25.6.7 Benching

(a)     Inlets

The base of the inlet shall be formed to provide a constant fall to the outlet and to preclude ponding of water within the structure.

(b)     Manholes

Changes in direction at a standard manhole shall be accommodated entirely within the structure. If benching is specified in Table 25.12, the benching shall form a curved channel of uniform radius. The minimum radius shall be three times the diameter of the largest pipe connected to the structure.

Where benching is used, the invert of the benching shall have a minimum fall of 30 mm towards the outlet. A minimum benching side slope of 1(V):50(H) shall be provided. The maximum depth of benching for all manholes shall be half the diameter of the outlet pipe.

(c)      Centreline Offset

To accommodate benching requirements within standard manholes at a change of direction or at pipeline junctions, offsets from the pipeline centreline may be provided as shown in Standard Drawing SD F-7.

Table 25.13 Potential Decreases in Pressure Change Coefficient as a Result of Benching

Manhole Type

Potential Decrease in Pressure Change Coefficient (%)

Half-height benching

Full-height benching

Straight through

30

40

90° bend

20

40

Tee manhole with lateral inflow < 50%

Nil

Nil

Tee manhole with lateral inflow < 50%

Nil

10

Tee manhole with lateral inflow* 100%

20

40

25.6.8 Vertical Drops

Designs where the invert of an inlet pipe is located above the obvert of an outlet pipe should be avoided wherever possible. However, in cases where this is unavoidable, a free fall within the inlet or manhole should be provided.

Where a significant continuous baseflow is likely, consideration should be given to providing an external drop pipe. Such instances shall be brought to the attention of the relevant Authority for consideration.

25.6.9

Access Covers

Minimum fall as per Table 25.12

Benching (where required)

Design I.L outlet

Figure 25.4 Minimum Fall Through Manholes

Benching of the floors of manholes leads to a general reduction in losses and promotes hydraulic efficiency. Table 25.13 provides an indication of the potential decreases in pressure change coefficient that can be achieved in square manholes as a result of benching (Johnston et al., 1989 and Lindvall, 1984). It should be emphasised that these improvements have been measured for square manholes. Testing of circular manholes (but without benching) indicates that these improvements may be less for circular manholes where the shape of the manhole assists in directing flow towards the outlets.

(a)      Concrete Cover

A manhole cover not subject to traffic loads or hydraulic surcharge shall consist of a standard reinforced concrete seating ring and lid in accordance with Standard Drawing SD F-7.

The minimum size opening for access is 600x600 mm.

(b)     Metal Cover

A manhole cover which will be subjected to either internal or external loadings shall be selected according to the following criteria:

      sealed solid top for structures in engineered waterways and other locations subject to hydraulic loads, for

inlet structures, or

surcharge structures (bolt-down locking shall be provided with stainless steel bolts to secure the cover and the seating ring to the structure)

      grated cover, for

inlets subject to traffic loadings, or inlets in paved pedestrian areas

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Ductile iron manhole covers shall be 'GATIC, or other proprietary design as approved in writing by the relevant Authority.

25.6.10 Cover Levels

Manhole covers shall be set at the finished cover levels given in Table 25.14.

3.0 m maximum cover over property drainage pipe at the service tie connection

25.7.2

Location

Wherever practical, a service tie should be connected to a stormwater inlet or manhole in preference to a separate connection into a stormwater pipeline.

Where finished surfaces are steeper than 1(V): 10(H), the sump cover shall be level. An adjacent flat area shall be provided with sufficient space on which to place a removable cover.

Table 25.14 Manhole Cover Levels

Direct connection of service ties to floodway, lowflow pipes or inverts will not be permitted.

A service tie connected to a stormwater pipeline shall be at right angles to the pipeline with the actual inlet made using a 45° junction pipe.

Location

Cover Level

Roads, other paved

Flush with finished surface

areas

Footpaths and

Flush with finished surface

street verges

Landscaped areas,

Flush with finished surface

parks

Elsewhere

100 mm above surface to allow

for topsoiling and grassing (see

note)

Service Tie

Note: Stormwater inlet and manhole tops shall be protected by placing fill against the top. The fill shall be graded down to natural surface at a maximum slope of 1 in 10.

25.7 SERVICE TIES

3.5 m

Kerb & Gutter

Where pipelines are provided for municipal drainage, each property shall be serviced with a service tie to enable stormwater from buildings to be directly connected to the municipal pipe drainage system via a property pipe drainage system.

Service ties for pipe drainage systems shall be provided in accordance with Standard Drawing SD F-ll.

25.7.1 Depth

The service tie shall be deep enough such that the property drainage system can command the whole property at a grade not less than 0.5% with 400 mm minimum cover within the property.

The service tie depth shall be ithin the following limits:

600 mm minimum cover over property drainage pipe at the service tie connection

Figure 25.5 Typical Location for Service Tie

Where a service tie is connected to a manhole or sump, the connection angle shall be greater than or equal to 90° to the centreline of the downstream pipeline.

Where the stormwater pipeline is located outside the property, the service tie shall terminate at the property boundary (see Figure 25.5).

Service ties shall generally be located 3.5 m from the lowest corner of the block.

25.7.3 Marking

Service tie locations shall be identified with a coloured plastic tape. The tape shall be secured to the end of the tie and brought vertically to the surface and attached to a marker stake. The marker stake shall protrude at least 300 mm above the finished surface.

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25.7.4       Size

Service ties shall normally be 100 mm diameter rubber ring jointed pipes.

The size of service ties shall be calculated to provide adequate drainage for the type of development within a property for the ARI of the minor stormwater drainage system as specified in Chapter 4.

25.7.5        Grade

Service ties shall be constructed at a grade between 0.5% and 10.0% and terminate in a sealed pipe socket.

If required, service ties may be connected to the pipeline at a steeper grade by using a suitable branch connection or 45° riser. Such cases shall be brought to the attention of the relevant Authority for consideration.

25.7.6       Connections

Service tie connections into 375 mm diameter pipelines shall be made by means of a rubber ring jointed slope junction, or approved saddle junction, and 45° bend plus an appropriate length of pipe with the branch end sealed.

Service tie connections into 450 mm to 600 mm diameter pipelines shall be made by means of a slope connection made by the pipe manufacturer. The tie piece shall be as short as possible and consist of a 45° angled socket piece epoxy jointed.

Where the stormwater pipeline is 450 mm or larger, service ties may be connected as branch connections in accordance with Section 25.4.

25.7.7        Maximum Length

The maximum length of a service tie shall be 20 m.

25.8 MAINTENANCE

A well-maintained storm drainage system will be ready to convey the runoff from the next storm with minimal damage to the storm drainage facilities. A poorly maintained drainage system may not be able to function at its design conveyance and could be damaged by the runoff.

The owner of storm drainage facilities should establish a routine maintenance inspection program once the facility has been completed and placed in service. The inspections should be conducted on an annual or semi-annual basis, as well as following major storms. The inspections may be accomplished by visual means or by using a television camera, where applicable.

The inspection should be documented. Items to be recorded should include size and type of facility, date of inspection, location of facility, minor deficiencies, major deficiencies and areas of possible future problems. The documentation should be kept current and when any repair work has been accomplish, it should be recorded.

Right-of-way constraints frequently dictate use of a piped drainage system, which in turn create particular maintenance constraints.

25.8.1   Design and Construction Stage

1.     Access - Manpower and equipment access for the length of the piped system must be available. Public owned right-of-way or drainage reserves are normally required.

2.     Erosion protection - The inlets and outlets to piped systems are subject to high velocities. Adequate protection will usually take the form of riprap aprons, energy dissipation structures, or concrete headwalls, wingwalls and aprons. Steep earth slopes at inlet and outlet transitions frequently need short walls to hold the soil in place.

3.     Trash racks - This is one of the most frequent problem areas. Trash racks should be sized in accordance with Chapter 34. The design should consider the potential debris sources upstream. Designers should assume at least 50% blockage of a trash rack when designing for the maximum storm runoff.

4.     Manholes - Most local governments have their own requirements for spacing. Manholes need to be accessible in all weather conditions. Access must be available to all pipes of a multi-barrel system. Drop manholes can be especially difficult when designing for adequate access and safety.

5.     As-built drawings - It is an absolute necessity to obtain as-built drawings of the completed project.

25.8.2   Drainage Service Stage

1.     Kerb inlet cleaning- because of their location and shape inlets often trap sediment and debris. They should be cleaned at least twice a year to insure their proper function. If only one cleaning is possible it should occur prior to the rainy season.

2.     Debris control - Trash racks should be cleaned regularly to keep accumulations from forming. In-pipe debris should be removed if it is large enough to create a flow obstruction.

3.     Overflow channel maintenance - If the pipe system was designed with a surcharge or overflow channel it deserves occasional attention. It must be kept clear of excessive vegetation. In general, it should be maintained as an open channel to be ready to function when called upon.

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4. Inspection - A regular in-pipe inspection of piped drainage systems will detail long term changes and will point out needed maintenance work such as debris removal or joint patching. Special attention is necessary to insure the safety of the inspection team if the pipe is long. Small pipes that carry continuous flow can be viewed with automated equipment. Inspections should be done following major runoff events. Inlet grates should be checked for clogging and catch basins and pipes for sediment/waste blockage.

25.8.3 Rehabilitation Stage

Typical problem areas than can signal the need for rehabilitation of a piped system include:

1.     Inlet and outlet structures - Local erosion to high velocities, lack of protection, or transition turbulence.

2.     Trench backfill - Subsidence of the trench, which can result from poor initial compaction or from pipe or joint failure. Earth settlement around manholes is a frequent indicator of compaction problems.

3.     Pipe joints - The first sign of problems in the system shows at the pipe joints. Spalled concrete, cracks, distorted pipe geometry, backfill movement and water inflow occur at the joints and are precursors of greater problems to come.

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APPENDIX 25.A HYDRAULIC GRADE LINE DESIGN FLOWCHARTS

Flowchart                                                                                                                                                                 Page

25.A1 Hydraulic Grade Line Design Method Flow Chart - Subcritical Flow                                                    25-20 (from downstream to upstream)

25.A2 Hydraulic Grade Line Design Method Flow Chart - Supercritical flow                                                 25-21 (from upstream to downstream)

25.A3 Procedure Flow Chart for Ku and Kw Calculation                                                                                25-22

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(start W----------

INPUT REACH FLOW Q

INPUT QLR,QLl IF ANY

SELECT DOWNSTREAM HGL OR TAILWATER LEVEL - SEE NOTE

SELECT TRIAL REACH PIPE

DIAMETER D0 AND

INVERT LEVEL

CALCULATE PIPE FRICTION LOSS

] <

SELECT TRIAL PIPE DIAMETERS AT UPSTREAM STRUCTURE D, D,, D,,

DESIGN CHARTS

J J

LEGEND

HGL

= Hydraulic grade line

WSE

= Water surface elevation

SL

= Surface level

D/S

= Downstream

U/S

= Upstream

U

= Upstream pipe

LR

= Right lateral pipe

LL

= Left lateral pipe

G

= Grate (inflow)

No

Flowchart 25.A1 Hydraulic Grade Line Design Method Flow Chart - Subcritical Flow (from downstream to upstream)

Notes for Flowchart 25.A1:

1.       The downstream HGL should be derived from the tailwater level in the receiving waters or from the HGL calculated in the structure downstream.

2.       The pipe size selected becomes D0 for the next structure upstream.

3.       The performance of a reach is dependent on the characteristics of the other reaches. Accordingly the most economic design is not that which optimises each reach but which performs best overall.

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Flowchart 25.A2 Hydraulic Grade Line Design Method Flow Chart - Supercritical flow (from upstream to downstream)

Notes for Flowchart 25.A2:

1.      The upstream WSE should not be higher than the surface level less 150mm.

2.      Conditions may be such that regardless of the outlet diameter these conditions cannot be satisfied. To avoid excessive looping check this first.

3.      The final hydraulic grade line level at the downstream pit may be set according to outfall conditions.

4.      The performance of a reach is dependent on the characteristics of the other reaches. Accordingly the most economic design is not that which optimises each reach but that which performs best overall.

Urban Stormwater Management Manual

25-21

Pipe Drains

Flowchart 25.A3 Procedure Flow Chart for K and Kw Calculation

25-22

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Pipe Drains

APPENDIX 25.B PIPE DESIGN CHARTS

Design                                                                                                                                                                    Page Chart

25.Bl          Hydraulic Design of Pipes - Colebrook-White Formula - k = 0.06 mm                                               25-24

25.B2          Hydraulic Design of Pipes - Colebrook-White Formula - k = 0.15 mm                                               25-25

25.B3          Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.30 mm                                               25-26

25.B4         Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.60 mm                                               25-27

25.B5          Hydraulic Design of Pipes - Manning Formula - D= 60 mm to 2000 mm                                          25-28

25. B6         Hydraulic Design of Pipes - Proportional Velocity and Discharge in Part-full Circular Sections           25-29

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25-23

Pipe Drains

HYDRAULIC GRADIENT, percent

o o o o - J\

% 1

o oo o o o o

<& %, ^imgi%.%

7 o o o o o o o c o o

2500

VELOCITY V, m/s

Design Chart 25.Bl Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.06 mm

25-24

Urban Stormwater Management Manual

Pipe Drains

HYDRAULIC GRADIENT, percent

O <? O O O

O O        O O O O O O O O

'1-s&-Q% '& ""> i>         i> i? ■U'oS&v^o.

o o o o o o o o o o

m>%%'%'% % %% %%%%^%%% %

VELOCITY V, m/s

Design Chart 25.B2 Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.15 mm

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25-25

Pipe Drains

HYDRAULIC GRADIENT, percent

O0 O Q O O

o o 0000000 o

O 0 0 0 o 0 0 & o o

o

LU

O DC <

I

o

to

VELOCITY V, m/s

Design Chart 25.B3 Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.30 mm

25-26

Urban Stormwater Management Manual

HYDRAULIC GRADIENT, percent

sOO O O O o

%

% %

o ooo o o c* o

*oo o o o o

%

LU

o

rr <

x o

CO

a

VELOCITY V, rn/s

Design Chart 25.B4 Hydraulic Design of Pipes - Colebrook-White Formula - k= 0.60 mm

Urban Stormwater Management Manual

25-27

Pipe Drains

0.01

XI

re

CO >

QJ 5

- 2000

- 1900

- 1800

o.oz

- 1700

- 1600

- 1S00

0.03

- 1400

T 1300

0.04

E- 1200

- 1L00

o.os

- 10QO

0.06

0.07

~ 900

0.08

-

0.09

- 800

0.10

-

0.2

- 0.3

0.4

NTs

0.6 0.7

0.8

-  0.9

-   1.0

f- 3

to 000 30 000

20 000

rjoo__^2__ p-188--------- He

700

3000 2000

r 500 400 __

r 300 r 250

racy

en

lb 14

12

-  11 -10

9

-  8 7

- 5

L 4

r 3

400 300

200

i- O.OOB c - 0.009^-

t,=*oiir

-^-0.011 0.012 =J -0.013 75 -0.014 > -0.015 L 0.016

>

I

>

-JSX^

- 150

4

5 6

:- ioo

7

Z 90

8 9 10

- 80

-

~ 70

- fifl

.1.9-*

:o.9

r 0.8

r 0.7

0.6

0.5

0.4

0.3

L 0.2

- 1.0 -0.9 0.8 .

NT?

0.6 0.5 0.4

^0.3

0.2 0.15

0.10 -0.09 -0.08 - 0.07

r0.06 L0.05

10

9

8

7

6

5

4

2

1.0 -0.9 L0,8 -0.7

0.6

0.5

r 0A

-

-0.3

- 0.2

>-

0,1

-0.09

-0.08

L0.07

0.06

0.05

0.04

0.03

rO.02

L0.01

Note: For n = 0.012 use the hydraulic gradient scale at right of chart. For values of n other than 0.012 use the inverted hydraulic gradient scale at left of chart by drawing a straight line from the hydraulic gradient scale for n = 0.012 through the appropriate value on the values of n scale (refer Example 2 below).

Examples to show the use of Design Chart 25.B5

1.      Given: n = 0.012, Q = 20 L/s and Hydraulic Gradient = 0.4%; Find: D = 192 mm and V = 0.69 m/s

2.      Given: n = 0.010, Q = 500 L/s and Hydraulic Gradient = 0.5%; Find: D = 572 mm and V = 1.93 m/s

Design Chart 25. B5 Hydraulic Design of Pipes - Manning Formula - D= 60 mm to 2000 mm

25-28

Urban Stormwater Management Manual

Pipe Drains

1.00

0.90

0.80

0.70

Q 0.60

f

$ 0.50

.1

0.40

B

0.30

0.20

0.10

0.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1

20

Legend:

Q = Part-full Discharge, d = Depth of Flow,

Proportional Velocity V/v Proportional Discharge Q/Q

Qo = Full Flow Discharge, D= Internal Pipe Diameter

V = Part-full Velocity,          V0 = Full Flow Velocity,

Example:

Given, Q = 42 L/s, Qo = 100 L/s, Hydraulic Gradient = 0.8% and k = 0.6 mm. Determine flow depth and flow velocity.

From Design Chart 25.B4 for Qo = 100 L/s, Hydraulic Gradient = 0.8% and k= 0.6 mm; D= 300 mm and V0= 1.41 m/s.

For Q/Qo = 0.42, proportional depth (d/DJ = 0.46 and proportional velocity [V/V0) = 0.96 (from Design Chart 25.B6). So, flow depth (d) = 0.46x300 = 138 mm and flow velocity (V) = 0.96x1.41 = 1.35 m/s.

Design Chart 25. B6 Hydraulic Design of Pipes - Proportional Velocity and Discharge in Part-full Circular Sections

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25-29

Pipe Drains

25-30                                                                                                                                                       Urban Stormwater Management Manual

Pipe Drains

APPENDIX 25.C JUNCTION HEAD LOSS CHARTS

Design Chart                                                                                                                                                          Page

25.C1 Headloss Chart for Entry Pit                                                                                                         25-32

25.C2 Headloss Chart for Pit with 0° deflection                                                                                     25-33

25.C3 Headloss Chart for Pit with 90° deflection                                                                                   25-34

Source: adapted from Queensland Urban Drainage Manual (QUDM), 1992

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25-31

Pipe Drains

^ 4

^.

_/t

On

- Vo2

^

- C /

H

=-3»

2gD

o-H

i

r^x

|-[

\/

i

v

A S

V

^^^^^^=-

hg =

_»_

A

o

= Kg.Vo2

i

A

/

7^1

Hr 2g

\

_/_

H

-^

/

\

4

i-t

fN

-At

i

\

Qo=Qg 1 D0

-QZI

/

\

o

-J-/V

/

^

<*)

3^4

/

/

'v>-

T i

i

J

c

^

T _j

\

^

T^ ^

l_C>"

y

/

,o

o

Curve B Outfall at 90° to Inflow

'V

H ^

^*.4P^

C

urve B /

n

'

v;t .

Oi

n

irection as Inflow

V

r.O

,y

\*

^

T^

<-ft

J."

ei

*-

.-

»«

«-

^*

»"

--

*-

Pivot Poir

,^*

,--

**

It i

~~

"'

for HGL

»*

-■»

at Obvert

■**"

-'

^J---

-*■

V

00

Measure H/D0 From Here

Submergence Ratio (S/D0)

^

Dc

Do D

CURVE A

CURVE B

Design Chart 25.Cl Head Loss Chart for Entry Pit

25-32

Urban Stormwater Management Manual

Pipe Drains

AP^=WSE=KU _\/b2

S                     ' 2g

Qg/Qo

t>- AP=WSE=KU V0Z

Qo

NEGATIVE PRESSURE HEAD CHANGE (Ku<0)

Diameter Ratio Du/D0

Design Chart 25.C2 Head Loss Chart for Pit with 0° deflection

Urban Stormwater Management Manual

25-33

Pipe Drains

2.4 2.2 2.0 1.8 1.6

5/D0 = 1.

2.2

Qg/Qo Qg/Qo

= 0.50

2.0 = 0.00

3 1.8

1.6

1.4

0.5          0.6 0.7 0.8 0.9 1.0

Du/Do

Qg/Qo = 0.00 Qg/Qo = 0.50

^

^i-

- *""""'

^""^

S/D0 = 2.0

0.5          0.6 0.7 0.8 0.9 1.0

Du/Do

Qg/Qo

= 0.00

Qg/Qo

= 0.50

1.8 1.6

3

^

1.4 1.2 1.0

0.5          0.6 0.7 0.8 0.9 1.0

Du/Do

Qg/Qo = 0.00 Qg/Qo = 0.50

^\

^

S/D0 = 3.0

0.5          0.6 0.7 0.8 0.9 1.0

Du/Do

1.8 1.6

J>1.4

1.2 1.0

^^

\

s / s

c

5/D0 = 4.(

)

/

/

/

Qg/Qo =0.00 Qg/Qo =0.50

0.5         0.6 0.7 0.8 0.9 1.0

Du/Do

PLAN

Qu

Du

ELEVATION

Qu-

HGL

Do

HGL

Design Chart 25.C3 Head Loss Chart for Pit with 90° deflection

25-34

Urban Stormwater Management Manual

Pipe Drains

APPENDIX 25.D HEAD LOSS DATA FOR OTHER STRUCTURES

Page

Entrance Loss Coefficients                                                                                                           25-36

Bend Loss Coefficients                                                                                                                 25-37

Pressure Loss Coefficients at Mitred Fittings                                                                                25-37

Penetration Loss Coefficients                                                                                                       25-38

Pressure Loss Coefficients at Branch Lines                                                                                  25-38

Expansion and Contraction Loss Coefficients                                                                               25-39

Source: Queensland Urban Drainage Manual (QUDM), 1992

Design Chart

25.D1

25.D2

25.D3

25. D4

25.D5

25.D6

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25-35

Pipe Drains

Type of Structure and Design of Entrance

Coefficient Ke

Concrete Pipe

Projecting from fill, socket end (groove end)

Projecting from fill, square cut end

Headwall or headwall and wingwalls:

Socket end of pipe (groove end) Square edge

Rounded (radius = D/12) Mitered to conforming to fill slope End section conforming to fill slope

Hooded inlet projecting from headwall

0.2 0.5

0.2 0.5 0.2 0.7 0.5 See note 1

Corrugated Metal Pipe

Projecting from fill (no headwall)

Headwall or headwall and wingwall square edge

Mitred to conform to fill slope

End section conforming to fill slope

0.9 0.5 0.7 0.5

Reinforced Concrete Box

Headwall parallel to embankment (no wingwalls)

Square edged on 3 edges

Rounded on 3 edges to radius of 1/12 barrel dimension Wingwalls at 30° to 75° to barrel

Square edged at crown

Crown edge rounded to radius 1/12 barrel dimension Wingwalls at 10° to 25° to barrel

Square edged at crown Wingwalls parallel (extension of sides)

Square edged at crown

0.5 0.2

0.4 0.2

0.5

0.7

Note 1: Refer Argue (1960) and O'Loughlin (1960)

Design Chart 25.Dl Entrance Loss Coefficients

25-36

Urban Stormwater Management Manual

Pipe Drains

y

% o u

to to O

0.3

0.2

0.1

0.0

Radius of (J

Curvature (r) / /

":::r P

^/y//\ ^ -"-"

:f m

/

/ /

/ /

t°AV-

1/

V /

/

/

7 "

/

/ /

/

/

0°            20°            40°            60°          80° 90° 100°

Deflection Angle in oc Degrees

Design Chart 25.D2 Bend Loss Coefficients Source: D.O.T. (1992)

Type

Kb

90° double mitred bend

60° double mitred bend

45° single mitred bend

22.5° single mitred bend

0.47 0.25 0.34 0.12

Source: ARR-1977 (p.327)

Design Chart 25. D3 Pressure Loss Coefficient at Mitred Fittings

Urban Stormwater Management Manual

25-37

Pipe Drains

100.0

0 0.2 0.4 0.6 0.8 1.0 Blockage Ratio

Q.

v 10.0

y

it

QJ

o u

QJ

ro

.c U

QJ

i_

to to QJ

i_ Q.

63

to to O

_l

T3

ro

QJ

X

1.0

0.10

0.01

0.2 0.4 0.6 0.8 Blockage Ratio

1.0

Design Chart 25. D4 Penetration Loss Coefficients Source: Black (1987)

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

0.1 0.0

Ln o

t NO O O O

CM <T (.

doc

o >■

**

1

Nl

\>

Q

/

^0

A.O 6.0

»8.0

0

O,

O

o

<

1-C

9

_

D

tf^

- i

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Flow Ratio QL/Q0

Q

_i O,

i

O

o

<

<

1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

0.1 0.0

o

d

d

o3<

0.6

0.7

0.8

0.9

_

J 90°

t

^0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Flow ratio QL/Q0

Design Chart 25. D5 Pressure Loss Coefficients at Branch Lines Source: A.S. 2200

25-38

Urban Stormwater Management Manual

Pipe Drains

z> U

4-1

c

y

it <L> O U

1.0 0.9

0.8 0.7

0.6 0.5

0.4 0.3

0.2

0.1

0.0

1.0

0.8         0.6          0.4         0.2         0.0

Expansion & Contraction Ratio d/D

Design Chart 25.D6 Expansion and Contraction Loss Coefficients

Urban Stormwater Management Manual

25-39

Pipe Drains

APPENDIX 25.E WORKED EXAMPLE

From the data given in Table 25.El, determine the hydraulic grade line (HGL) for the pipe drain shown in Figure 25. El. All pipe is reinforced concrete pipe (RCP),

Structure 1, 2, 3 and 4 are outlet,

with k = 0.3 mm.

junction with 90° bend with grated inlet, junction with 0°

bend and headwall, respectively.

PLAN

Water Surface

Elevation          = 12-95m

PROFILE

D/S Level 12.95

3) vAea^a*

Inlet

Figure 25. El Plan and Profile of the Pipe Drain System

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25-41

Pipe Drains

Table 25. El Data for HGL calculation

U/S Node

D/S Node

D (m)

L (m)

S (m/m)

Q

(m3/s)

4

3

0.38

60.96

0.047

0.43

3

4

0.53

121.92

0.0075

0.43

2

1

0.61

91.44

0.0070

0.60

Structure 1 Columns 2, 3 & 4

Tailwater level (water surface elevation) = 12.95 m

Pipe size selected = 0.61 m

Calculate pipe friction head loss hf& HGL

Q= 0.60 m3/s

Diameter = 0.61 m

Average discharge velocity of pipe,

0.60

A ;r(0.61)2/4

2.04 m/s

Column 11

Assume, loss coefficient, Ke = 1 for square-edged headwall So, head loss through headwall (Structure 1) is

he=Ke

Column 15

1.0

2.04'

2g         2(9.81)

0.21m

EGL on upstream side of headwall = EGL at downstream side + head loss

(U/S EGL) = 12.95 + 0.21

= 13.16 m

Columns 16 & 17

HGL at upstream side of headwall = EGL - velocity head in pipe

(U/S HGL) = 13.16 m-0.21 m

= 12.95 m

Columns 6 & 7

As discussed in Section 25.4.4, use the applicable Design Chart based on Colebrook-White formula. Use Chart 25.B3 for Ar =0.3 mm

Sf= 0.65 % = 0.0065

Columns 9 & 10

Thus total head loss in the 0.61 m pipe between structures 1 and 2

hf = (0.0065).(91.44) m

= 0.59 m

The previous steps are similar for the other pipes of the system

Structure 2 Columns 2, 3 & 4

EGL on downstream side at Structure 2 = EGL on upstream side of Structure 1 + Head loss in pipe between Structure 1 and Structure 2

(D/S EGL)2 = 13.16 m + 0.59 m

= 13.75 m

HGL on downstream side of Structure 2 = one velocity head below EGL

(D/S HGL)2 = 13.75 - (2,04-) = 13.54 m 2(9.81)

Structure 2

Assume 90° bend and use Design Chart 25.C3

^- = 0.875

Grate inflow,

Qg = Qm= 0.17 m3/s (see Figure 25.El)

Qg 0.17

Qo 0.6

0.28

The pit loss is a function of submergence ratio 5, which is defined on Design Chart 25.C3

Trial 5= 13.75m- 12.88 m

= 0.87 m

Assume S/D0 = 0.87/0.6 = 1.45

From Design Chart 25.C3, by interpolation Ku = 2.2

Column 14

Then/?f = Ku V2/2g= 2.2 =0.47 m

f 2.042 ^ 2(9.81)

For d= 0.61m and Q= 0.60 m3/s,

25-42

Urban Stormwater Management Manual

Pipe Drains

Structure 3

Structure 4

Pipe friction losses are computed in the same way as for pipe section 1-2

Here is 0° bend, so use Design Chart 25.C2

0.71

No grate inflow, so D

Dn

0.0

Trial S= 15.22m- 14.19 m

= 1.03 m Assume S/D0 = 2.0, and use design Chart 25.C2 K=-1.9

Column 14

Then ht = Ku V2/2g = 1.9 = 0.35m

f 1.902 ^

2(9.81)

Pipe friction losses for the pipe section 3-4 are computed in the same way as the previous pipe sections

( 3.792 ^

For the entry structure, ke = 0.5 from Design Chart 25. Dl Then ht = Ke V2/2g= 0.5 = 0.37 m

2(9.81)

The final EGL at Structure 4, 18.51 m, is below the surface level of 18.90 m. Therefore it is concluded that the design is satisfactory.

Detailed calculated results are given in Table 25.E2.

NOTE: the assumptions made during the calculation should now be re-checked. Check that the assumed values of S and S/D0 were reasonable. If not, they should be amended and the calculations repeated.

Urban Stormwater Management Manual

25-43

Table 25.E2 Hydraulic Gradeline Computation Form

PROJECT:

DESIGNED BY:

CHECKED BY:

DESIGN STORM:

DATE:

DATE:

1

2

3 4

5 8

7 8

3

10

11 12

14 15 16 17

18

13

TERMINAL STRUCTURE

PIPE DA Roughne

TA AMD FRICTIOI ssA = 0.3

JLOSS

LOSS

ES

LOSSES

A,

*.

STRUC

D/S

OUT DIS

D

Q

V L

S,

A/

* . I *_

A,

A

UHS

IN

UIS

TOP

FREE-

WO.

EGL

fm) HGL

fml [mVs]

fm/sl fm)

{A

fm)

fm) fm)

(ml

HGL

(m)

EGL

ELEV.

BOARD

1

12.95 0.00 12.95

0.21

1295

0.21 13.18

0.61

0.80

2.04

31.44

1 0.65

0.59

z

13.75 0.21 13.54

2.20

0.47 14,01

0.18 14.19

15.09

103

0.53

0.43

1.30 121.32

0.75

0.31

3

15.10

0.18 14.32

-t.30

-0.35 14.57

0.70

15.27

16.61

2.04

0.38

0.43

3.73 60.36

4.70

2.87

4

18.14

0.70 17.44

0.37

17.31

0.00 18.51

18.30

-

Column

Column

1

Structure identification label

12

Entrance head loss at terminal structure on Ur"S end of run from Design Chart 25.D1(jt', =0 5)

2 EGL elevation at downstream side of structure =

preceding column 17 * preceding column 10

13

Junction head loss coefficient. K, from Appendix 25.C

3

Velocity head at the discharge side of the structur

K *■■_/ ' /&

14

Head loss through the junction = A'. {V* /?}

4

HGL elevation : column 2 column 3

15

HGL on the up; column 4 * cok

tream side of the manhole structure :

5

Pipe diameter (actual)

imn 11.12 or 14

e

Design Discharge

16

Velocity head at the incoming pipe ~ P'* * &g

7 8 3

10 11

Discharge velocity Pipe length betweer

17

EGL on the upstream side of the manhole structure = column 15 * column 16

i structures

Friction slope from (for A z 0.3 mm)

Design Charts 25B4

16

Elevation of top of manhole or inlet structure

19

Freeboard = column 18 column 15

Friction head loss = (column 8 x column 3) /100 Exit head loss at terminal structure on D/S end of

run from

Design C

hart 25.D1

(A', =1.0

>

Pipe Drains

Urban Stormwater Management Manual                                                                                                                                                      25-45