road drainage design manual - chapter 3

June 2003

Road Drainage Design Manual Chapter 3: Hydrology and Design Criteria

3Chapter 3

Hydrology andDesign Criteria

June 2003


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Chapter 8References

Chapter 7Worked Examples

Chapter 6Maintenance and Remediation

Chapter 5Erosion and Sediment Control

Chapter 4Design

Chapter 3Hydrology and Design Criteria

Chapter 2Site Assessment

Chapter 1Overview

Manual Contents

Table of Contents3.1 Introduction 3-1

3.1.1 Purpose 3-13.1.2 When to use Chapter 3 3-23.1.3 How to use Chapter 3 3-23.1.4 Inputs 3-33.1.5 Applying Design Criteria 3-3

3.2 General Design Criteria 3-33.2.1 Planning 3-3

3.2.1.1 Road Environment 3-43.2.1.2 External Environment 3-4

3.2.2 Environment 3-43.2.3 Maintenance 3-53.2.4 Safety 3-53.2.5 External Criteria 3-6

3.3 Design Standard 3-63.3.1 Introduction 3-63.3.2 Cross Drainage 3-7

3.3.2.1 Standard for State Controlled Roads - Urban Catchments 3-73.3.2.2 Standard for State Controlled Roads - Rural Catchments 3-83.3.2.3 Standard for National Highways 3-83.3.2.4 Practical Application of Standard 3-9

3.3.3 Longitudinal Drainage 3-93.3.4 Surface Drainage 3-9

3.3.4.1 General Standard 3-93.3.5 The Major / Minor System Concept 3-10

3.3.5.1 Urban Areas / Existing Minor Drainage Systems 3-103.3.6 Erosion and Sediment Control 3-10

3.4 Hydraulic Criteria 3-103.4.1 Discharge 3-103.4.2 Velocity 3-10

3.4.2.1 Existing Conditions 3-113.4.2.2 Desirable Velocity 3-113.4.2.3 Maximum Permissible Velocity 3-11

3.4.3 Afflux 3-123.4.4 Gradient 3-123.4.5 Tailwater Levels 3-12

3.5 Hydrology 3-123.5.1 Introduction 3-123.5.2 Methods Available for Runoff Calculation 3-13

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3.5.3 Rational Method 3-133.5.3.1 Catchment Area 3-143.5.3.2 Time of Concentration 3-143.5.3.3 Rainfall Intensity - Frequency - Duration 3-223.5.3.4 Runoff Coefficient 3-27

3.6 Tailwater Levels 3-283.6.1 Introduction 3-283.6.2 Tidal Waters 3-29

3.6.2.1 Tide Levels 3-293.6.2.2 Storm Surge 3-293.6.2.3 The Greenhouse Effect 3-303.6.2.4 Tidal Outlets (Ocean and Bays) 3-303.6.2.5 Tidal Outlets (Rivers and Creeks) 3-303.6.2.6 Design Issues for Tidal Outlets 3-31

3.6.3 Non-Tidal Waters 3-313.6.3.1 Large Storage Areas 3-313.6.3.2 Small Storage Areas 3-313.6.3.3 Open Channels 3-323.6.3.4 Protection of Non-Tidal Outlets 3-32

3.7 Fauna Passage 3-333.7.1 Introduction 3-333.7.2 Identifying Fauna Passage Criteria 3-33

3.8 Ambient Conditions 3-343.8.1 Introduction 3-343.8.2 Specific Design Criteria 3-35

3.8.2.1 Arid Areas 3-353.8.2.2 Mountainous Terrain 3-363.8.2.3 Coastal Regions 3-363.8.2.4 Areas of Inundation 3-373.8.2.5 Urban Areas 3-373.8.2.6 Rural Areas 3-37

3.9 Selection of Drainage Infrastructure 3-373.9.1 Introduction 3-373.9.2 Factors Affecting Selection of Drainage Infrastructure 3-383.9.3 Drainage Decisions 3-383.9.4 Culverts 3-38

3.9.4.1 Culverts or Bridge 3-383.9.4.2 Culvert Size 3-383.9.4.3 Culvert Type 3-38

3.9.5 Bank Protection and Linings 3-403.9.6 Longitudinal Drainage 3-40

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3.9.7 Location 3-403.9.8 Water Quality 3-41

3.10 Pollution Control 3-423.10.1 Introduction 3-423.10.2 Selection Process 3-42

3.11 Erosion and Sediment Control 3-503.11.1 Introduction 3-503.11.2 Review of Data 3-503.11.3 Select Design Standard 3-503.11.4 Select Controls 3-51

3.11.4.1 Introduction 3-513.11.4.2 Erodibility Rating/Soil Type 3-513.11.4.3 Areas of Suitability 3-523.11.4.4 Flow Type 3-523.11.4.5 Life of Controls 3-523.11.4.6 Hierarchy of Measures and Selection Table 3-52

3.12 Design References 3-52

Appendix 3A: Computer Models 3-54

Appendix 3B: Checklist 3-56

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Chapter 3 Amendments - June 2003

Revision Register

Issue/Rev No.

ReferenceSection Description of Revision Authorised

by Date

1 First Issue SteeringCommittee

June2002

2

3.3.2 Section 3.3.2 “Flood Deign Criteria” amendedSteering

CommitteeAug20023.8.2.6 New section - “Rural Areas”

3.10.2 Table 3.16 modified

3

3.1.1 Amendment to 4th paragraph

SteeringCommittee

Oct2002

3.1.2 Additional paragraph

3.4.3 Additional text

3.6.2.4 ‘Outfall’ changed to ‘outlet’

3.6.2.5 ‘Outfall’ changed to ‘outlet’

3.6.3 ‘Outfall’ changed to ‘outlet’

3.10.1 Additional text

4

Minor amendments and corrections throughout chapter

SteeringCommittee

Jun2003

3.3 Expansion and clarification of Design Standard

3.5 Restructing of Hydrology section

3.5.1 Clarification of scope/intention of Hydrology section

3.11.4.6 Table 3.23 has been replaced

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HYDROLOGY ANDDESIGN CRITERIAHYDROLOGY ANDDESIGN CRITERIA

Chapter 3

Introduction

• Purpose

When to use Chapter 3

Inputs

Applying Design Criteria

•

•

•

General Design Criteria

Design Standards

Hydraulic Criteria

Hydrology

Tailwater Levels

Fauna Passage

Ambient Conditions

Selection of DrainageInfrastructure

Selection of PollutionControls

Selection of Erosion andSediment Controls

Chapter 4Design

Chapter 2Site Assessment

3.1 Introduction

3.1.1 Purpose

Chapter 3 of the Road Drainage Design Manualprovides an important link between the collectionof data (Chapter 2) and the design of drainageinfrastructure (Chapter 4). This link establishesthe hydrological conditions and design criteria,and facilitates the selection of the mostappropriate drainage infrastructure at a particularlocation.

The identification of design criteria may also bethought of as the identification of constraints.

This chapter also provides a link between thedetermination of erosion risk, and the selection ofappropriate erosion and sediment controls(Chapter 5).

On this basis, Chapter 3 promotes theconsideration of environmental and hydrauliccriteria in an integrated manner, along with theinfluence of external factors. The structure ofChapter 3 (as summarised below) reflects thisphilosophy.

Section 3.1 provides an overview of Chapter 3,reiterating the importance of using all relevantdata.

In Section 3.2, an overview of several very broadcriteria is presented, including planning,maintenance and safety considerations.

Section 3.3 discusses the selection and practicalapplication of a design standard, with emphasis onflood immunity.

Section 3.4 provides a summary of the keyhydraulic criteria necessary to undertake thedesign of permanent drainage measures. Theseinclude permissible velocity, afflux, gradient andtailwater levels.

In Section 3.5, the Rational Method is adopted asthe Department's standard method for thedetermination of design flows (or discharges) forsmall catchments. A detailed description of thismethod is provided. Whilst this information mustbe utilised during the design phase, its place inthis section of the manual reflects thefundamental importance of hydrology for allaspects of road design.

Section 3.6 provides a discussion of theimportance of tailwater levels in designingeffective drainage infrastructure, addressingtailwaters both within a drainage path and asbackwater from tidal and non-tidal water bodiesdownstream.

Section 3.7 (Fauna Passage) represents the first ofthe “Selection” sections. It provides an overviewas to how fauna passage issues should beconsidered when assessing drainage structures. Insome circumstances, Section 3.7 may be appliedas the primary sizing mechanism for a culvert,with the structure subsequently checked forhydraulic performance.

The influence of ambient conditions on drainageinfrastructure is dealt with in Section 3.8. Thepurpose of this section is to provide anappreciation of the significant influence differentconditions can exert on design.

Section 3.9 guides the user through the selectionprocess in relation to how different types ofdrainage measures are chosen. Its main purpose isto ensure that the user of the manual hasconsidered all relevant criteria and constraintsbefore proceeding to detailed design. The sectionalso recognises that drainage design is an iterativeprocess, with many factors influencing the finallayout of the drainage system.

Section 3.10 deals with the selection of pollutioncontrols, for those situations where water qualityobjectives have been defined, and must besatisfied. The section provides guidance as to

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Chapter 3

Hydrology and Design Criteria

which types of controls will be suitable for thegiven set of conditions.

In Section 3.11, the user is guided as to theselection of erosion and sediment controls, themajority of which will be used during theconstruction phase of the project.

3.1.2 When to use Chapter 3

Use of this chapter should predominantly occurduring the Planning/Preliminary Design phase ofa project. This ensures that the key factorsinfluencing the hydraulic and environmentalperformance of drainage infrastructure areidentified and understood prior to detailed design.

However, it is important to note that drainagedesign, as with all aspects of road design, isfrequently an iterative process. Hence, whilst thischapter of the manual would normally be appliedat the Planning or Preliminary Design phase of aproject, it could also be used to reassess drainageoptions after detailed design had already beencompleted. For example, detailed design mayresult in an unacceptable cost, leading to thesubsequent specification of a reduction in thedesign standard.

An integral part of the design process isknowing when specialist skills are required.The techniques provided in this chapter areappropriate for the majority of small roaddrainage design projects. However, in manyinstances the complexities of the site mayrequire the services of a specialist. Thesesituations are highlighted in the appropriatesections.

3.1.3 How to use Chapter 3

The user of this manual must ensure that theprovisions of Chapter 3 are considered beforecommencing any design process in the followingChapters. The procedure would generally consistof the following steps:

• Determine the general design criteria thatshould apply to the situation;

• Determine an initial design standard to aim for;

• Work out the hydrological conditions of the site(the range of flows) for the desired standard;

• Select possible structure type and sizes thatcould satisfy the hydraulic, environmental andexternal criteria;

• Determine appropriate pollution controls anderosion and sediment controls that may berequired.

• Proceed to the design process in the followingchapters.

It may be necessary to revisit this chapter to refinethe design criteria and hydrology after the firstcycle of the design.

Design criteria relating to road drainage may begrouped into three different types of criteria.These are:

1. hydraulic criteria;

2. environmental criteria; and

3. external criteria.

Hydraulic criteria may be considered asincluding the following:

• flood immunity/design standard;

• discharge;

• permissible velocities; and

• permissible afflux.

Establishing the hydraulic criteria requires anunderstanding of the hydrological conditions ofthe site or project.

Environmental criteria will vary significantlyfrom project to project, and hence it is notpractical to list all potential issues in this section.However, there are two types of environmentalcriteria for which details have been provided.These are provision for fauna passage, and theimprovement of water quality. In many projects,it will be important to ensure that the design ofdrainage infrastructure adequately caters for theexistence of fauna, and also for the maintenance

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(or improvement) of the quality of stormwaterrunoff.

External criteria include a range of factors (eg.economics) which will also play a large role formany projects. The designer must remain awareof these, and how they may influence the ultimatechoice of drainage controls. External criteria (asdealt with in DMR Form F2289) are overviewedin Section 3.2.5.

Finally, it is important to remember that all designdecisions must incorporate maintenance andsafety requirements, as outlined in Sections 3.2.3and 3.2.4.

3.1.4 Inputs

Data to be used in completing this section of themanual should include:

• Specific environmental criteria identifiedduring the REF (Review of EnvironmentalFactors) process;

• A full data set (refer Chapter 2 checklist);

• The results of the soil erodibility assessment(refer Chapter 2); and

• An appreciation of the project budget.

3.1.5 Applying Design Criteria

In order to demonstrate how consideration ofdesign criteria may be incorporated into theselection process, an example is provided as Table3.1.

3.2 General Design Criteria

3.2.1 Planning

The construction of road drainage may lead tochanges in both the natural and socialenvironments. Problems associated with erosionand sedimentation, flooding or water quality areoften of concern to both the road developer/ownerand the local community. The occurrence of theseproblems can be costly to remedy and may lead toreduced amenity.

Effective site planning plays a major role inminimising the potential for adverse impacts tothe environment and to local communities.Further, planning of the drainage system can assistin achieving project objectives such ascompatibility with the natural and socialcharacteristics of the immediate road environmentand its external areas.

For most projects, planning of the drainagesystem can also facilitate the production of a roaddesign that will minimise future maintenance

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Table 3.1 Determination of Design Criteria

Required Input Process Output (Criteria)Type of Road Application of a Standard Design Immunity (ARI)ARI, Catchment Area, Rainfall Intensity Calculation (hydrologic) Design Discharge (Q)Waterway geometry, stream gradient, Q Calculation (hydraulic) Predicted velocities for existing

conditions (Vmax, Vbed)

Existing velocity, REF Specialist advice Permissible velocities to allow fishpassage

Soil Type, Existing Erosion Design Tables Calculate desirable velocity toprevent erosion or calculate velocitythat caused erosion

Existing land use Published Standards or Permissible Headwater level (HW) orAssessment of Potential permissible afflux (H)Damage Costs

REF (identification of sensitive receiving Water quality objectives Need for pollution controlenvironment)

requirements, or will maximise the efficiencywith which specific criteria (eg. pollution control)are incorporated into the design.

Professional Collaboration - Planning

The principles contained in Section 1.4 shall beused to assist in planning the drainage layout.

The two major environments potentially affectedby drainage, and the processes of erosion andsedimentation, are known as the road environmentand the external environment. These are furtherdiscussed below.

3.2.1.1 Road Environment

The Road Environment is the zone which includesthe carriageway, top/toe of batter and the generalarea within the road reserve boundary.

Road Corridor

The Road Carriageway is that area of the roadsystem that includes road pavement, bridges,furniture, surface drainage and piped drainagewithin the extents of the road formation (ie. wherebatter toes match in with natural surface).

Surface Drainage incorporates all open drains,channels, diversion drains, swales, table drains,catch drains and kerb and channel within theextents of the road formation.

Piped Drainage includes all cross drainageculverts, longitudinal piped drains, pits, manholesand outlet structures (eg. energy dissipaters orerosion control devices) located within the extentsof the road formation.

3.2.1.2 External Environment

The External Environment is that zone outside theroad reserve boundary and includes sensitiveareas such as wetland, rainforest, sand dunes,waterways or private property.

Surface drainage and piped drainage also existwithin this zone, which will either receive runofffrom the site or transfer runoff through the site.

Road Corridor - Aerial

3.2.2 Environment

Section 2.2.4 describes the role of the REF/IAS inobtaining and analysing data for the purposes ofidentifying potential environmental impacts of aproposed project.

The REF/IAS also identifies criteria and strategiesfor managing aspects of a project which arepredicted to cause environmental harm. Examplesof issues identified in an REF/IAS, which mayinfluence drainage design, are outlined in Table3.2.

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This table illustrates how an REF/IAS mayrecommend a number of management strategiesto minimise potential environmental harm. Thesemay be in the form of design requirements orimplementation of particular constructiontechniques which minimise potentialenvironmental harm (ie. progressive revegetationto reduce soil exposure). These criteria andtechniques are generally based on therequirements of relevant legislation, policy, codes,guidelines and current Best PracticeEnvironmental Management for the industry.

3.2.3 Maintenance

The provision for maintenance is an integralcomponent of the planning and design phases ofroad drainage. Adequate maintenance is necessaryfor the proper operation of the drainage system.The lack of maintenance is one of the mostcommon causes of failure of drainage systems(and erosion and sediment controls). This may beattributed to reasons such as a significantreduction in hydraulic or storage capacity (eg.blockage by debris or sediment).

Specific details on maintenance procedures andrequirements for road drainage systems areprovided in Chapter 6 of this manual.

To enable maintenance to be properly and safelyundertaken during road construction andoperation, consideration must be given to:

• the provision of adequate access;

• the method of maintenance;

• equipment to be used (eg. vehicles, slashers,backhoe etc.); and

• the method of operation of maintenanceequipment.

3.2.4 Safety

An integral aspect of the detailed design of allroad drainage systems is the underlyingconsideration of safety.

Some of the safety issues that requireconsideration as part of the road drainage designprocess are described below:

• Maintenance Access. Safe access needs to beprovided to all drainage structures that requireeither ongoing (ie. mowing of drains) oroccasional (ie. removal of debris) maintenance.This access is required for vehicles and/ormaintenance crews depending on the type ofmaintenance that will be undertaken. Safe

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Table 3.2 Example of REF/IAS Recommendations Influencing Drainage Design

Potential Environmental Impact Recommended Action Responsibility

Fragmentation of fauna corridor at Ch25000. Design creek crossing at Ch25000 such Zoologist/Detailed Known species using corridor include koala, that fauna movement is maintained. Designersnakes and bandicoots. A suitably qualified zoologist shall be

employed to provide concepts and environmental specifications for a suitably adapted fauna culvert crossing.

Realignment of Sandy Creek at Ch19785 Incorporate stabilisation / hard armour / Detailed Designerassociated with proposed bridge crossing. scour protection measures to minimise Slumping and erosion of sandy-loam banks bank slumping and erosion at bridge may result. abutment.

Disturbance to platypus habitat located in Investigate feasibility of using a single Detailed Designercentre island bank of Four Mile Creek at span bridge design to avoid filling of centreCh9500 as a result of proposed bridge island bank.abutment location.

Discharge of bridge pavement runoff into Incorporate pollution control device(s) to Detailed DesignerJohnson Creek and subsequent impacts on trap heavy metals, oils and greases from aquatic flora and fauna. Upgraded bridge to bridge deck runoff.cater for AADT of 33,500 vehicles with 15% heavy vehicle content.

access to erosion and sediment control devicesduring the construction phase should also beallowed;

• Child Safety. Where long culverts potentiallyprovide a hazard (particularly in urban areas) tochild safety, preventative measures should beconsidered. Safety measures include fencing,swing gates and/or grates at culvert inlets. Anysafety device needs to ensure that it preventsboth access to the culvert and trapping of achild against the grate. The effect of anyproposed child safety measure on culvertcapacity and efficiency needs to be checked;

• Traffic Safety. Projecting culvert ends have thepotential to act as obstructions to out of controlvehicles. Where there are no safety barriersculvert ends should not present an obstruction.If obstructions from projecting culverts or headwalls are unavoidable then safety barriersshould be considered;

• Floodway Safety. The main issues associatedwith safety for floodways are adequate sightdistance for drivers to ensure vehicles can stopbefore entering the floodway. Preferably, thefloodway longitudinal profile should behorizontal so that the same depth of waterexists over the entire floodway length. Thefloodway length should be limited and on astraight stretch of road where possible andadequate permanent and temporary signingmust be erected; and

• Energy Dissipators. Energy dissipation isnecessary due to high flow velocities.Dissipation devices usually consist of largeobstructions to the flow and result in a highdegree of turbulence. For these reasons, energydissipation structures should be avoided inurban areas where possible; otherwise accessshould be limited by appropriate fencing.Energy dissipators are also very costly to buildand changes to the design, such as flattening ofchannel gradient to reduce high velocities, arepreferred.

3.2.5 External Criteria

The selection of road drainage infrastructure maybe influenced by criteria that are neitherenvironmental or hydraulic. Such criteria aretermed external, and may include:

• Project economics;

• Road alignment; and

• Lack of available space.

The Department's Form M2289, RoadInfrastructure Proposal - Project Concept Phasealso lists many other factors which need to beconsidered before a decision is made on thestandard of new infrastructure. These factors mayultimately affect other aspects of road design,which may in turn affect the provision of drainageinfrastructure.

3.3 Design Standard

3.3.1 Introduction

All elements of the drainage system must bedesigned to meet a specified minimum standard.

For a drainage system, the standard isconventionally specified in terms of an averagerecurrence interval (ARI).

This is defined as the average interval in yearsbetween exceedances of a specified event (ie.rainfall or discharge).

The standard will vary in accordance withwhether the design relates to cross drainage (ie.the provision of a certain flood immunity), surfacedrainage, urban drainage, or construction phasedrainage (including erosion and sedimentcontrol).

Guidance as to typical ARIs for each of thesesituations is provided in the following sections.The design standard may be affected by a range offactors, including cost, available space, existinginfrastructure, and public safety.

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For rainfall, the average recurrence interval (ARI)is defined as the average interval in years betweenexceedances of a specified rainfall.

A similar definition may be applied for floods andas explained in the introduction above, it is usualto define the flood arising from a specified rainfallas having the same ARI as the rainfall.

The AEP (annual exceedance probability) is alsoused in relation to flood flows. The AEP is theprobability of exceedance of a given dischargewithin a period of one year. It is commonlyconsidered as the reciprocal of the averagerecurrence interval (ARI) in years expressed as apercentage.

eg. 50 years ARI = 2% AEP

However, reference should be made to Section 1.3of AR&R (1987).

3.3.2 Cross Drainage

The design standard for cross drainage for aparticular project may be set either by the client orby Departmental strategies. These may be basedon any of the following conditions:

• Flood immunity - This is the average recurrenceinterval (ARI) of a flood at the point ofovertopping the crown level or highest point ofthe road if superelevated. This level of floodingis usually critical for afflux calculations and itsimmunity must be calculated as part of thedesign if other design criteria are given. Theflood level is also critical in the design ofculverts and bridges under floodways.

Calculated flood immunities in the BridgeInformation System (BIS) are based on thisdefinition.

• Trafficability - In some instances, it is desirableto allow traffic to continue to use the road whilefloodwater crosses the road surface. The designstandard therefore may be specified in terms ofthe ARI of the flood at the limit of trafficability.This limit is based on a combination of depthand velocity of flow over the road or floodwayand is defined as occurring when the total head

(static plus velocity) across a carriageway isequal to 300mm. Refer to Section 4.2.3.5.

• Pavement immunity - In this instance,immunity is defined with the upstream levelbeing below the pavement base course, whichgives a higher road level. This level will bedefined in future as pavement immunity withthe road grade at 'x' mm above a flood of 'y'yearARI.

• Time of Closure - This is a measure of theexpected time of closure of a road in a majorflood such as a 50 year ARI. This may be in theorder of days. Time of closure is described indetail in Section 4.2.3.5

• Average Annual Time of Closure (AATOC) -This is a measure of the expected time ofclosure of the road due to flooding over thecourse of a year. This may be in the order of afraction of an hour.

Cross drainage culverts under construction

3.3.2.1 Standard for StateControlled Roads - UrbanCatchments

Table 3.3 gives recommended design averagerecurrence intervals for Urban Catchments.

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3.3.2.2 Standard for StateControlled Roads - RuralCatchments

For rural catchments, the generally acceptedstandard for cross drainage is a flood immunity of50 years ARI wherever possible.

This standard also applies to rehabilitation/reconstruction projects where existing structuresare assessed as hydraulically or structurallydeficient and need to be completely replaced.

Designers should check departmental strategiesfor immunity and / or trafficability requirementsfor specific routes and individual projects.

Other than in exceptional circumstances, onlyroads in remote areas of the State and/or with littletraffic are designed outside the 20 year to 100 year

ARI flood trafficability range. However, there areolder roads with lower trafficability.

It is rare to design a new road with trafficability infloods less than 10 years ARI.

3.3.2.3 Standard for NationalHighways

Federal Government requirements are that theprobability of the Highway being closed to trafficby water in any particular year is to be less than:

• 1 in 100 where the AADT is expected to exceed2000 in the next 20 years; or

• 1 in 50 where the AADT is not expected toexceed 2000 in the next 20 years;

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Table 3.3 Recommended Design Average Recurrence Intervals for Urban Catchments

Category ARI

(i) Major System Design ARI (years) 50

(ii) Minor System Design ARI (years)Development CategoryCentral Business and Commercial 10Industrial 2Urban Residential High Density 2-10- greater than 5 & up to 20 dwelling units/haRural Residential - 2 to 5 dwelling units/ha 2Open Space - Parks, etc. 1

Major Road Kerb & Channel 10Flow (See Note 1)Cross Drainage 50(Culverts) (See Note 2)

Minor Road Kerb & Channel As forFlow relevant,

developmentcategory

Cross Drainage 10(Culverts) (See Note 2)

Notes:1. The design ARI for the minor drainage system in a major road will be 10 years for Kerb and Channel Flow and

50 years for Cross Drainage, regardless of the Development Category of the adjacent area.2. Culverts under roads should be designed to accept the full flow for the minor system ARI shown. In addition, for

major roads the designer should aim to ensure that the 100 year ARI backwater does not enter propertiesupstream. Similarly, the 50 year ARI backwater should be used as the check for cross drainage in minor roads.If upstream properties are at a relatively low elevation it may be necessary to install culverts of capacity greaterthan that for the minor system ARI design storm to ensure flooding of upstream properties is not increased. Inaddition the downstream face of the causeway embankment may need protection where overtopping is likely tooccur.

and the average annual time of closure by water isto be less than 12 hours.

3.3.2.4 Practical Application ofStandard

Although highly desirable, it is not alwayspossible to meet the above requirements from thefunds available. Therefore, staged construction atan initially lower standard is sometimes adopted.

Reference should also be made to Section 3.2.5,which lists some of the external criteria, that caninfluence the selection of immunity or designstandard

3.3.3 Longitudinal Drainage

The requirements for longitudinal drainage willvary from project to project. Site constraints andthe adopted design standard will dictate the choicebetween alternative longitudinal drainage optionssuch as kerb and channel, grassed swales, andlined or unlined table drains. In urbanenvironments, kerb and channel has historicallybeen favoured for most roads, though grassedchannels are also common on divided roads. Inrural areas, earth drains are more common.

Consideration of the environmental issues (inparticular, the management of erosion risk, waterquality and maintenance) is also important.

Reference should be made to Chapter 7 of theRoad Planning & Design Manual to determine thecross sectional components of table drains andother drains associated with the formation /carriageway.

The following requirements are to be consideredin determining the design standard forlongitudinal drainage:

• Limit the use of "'V" drains, particularly inerodible soils. Parabolic or flat-bottomed drainsshould be used in preference. The latter maystill require armoring but in thesecircumstances a combination of armoring andvegetation options are more likely to succeed.

• The minimum grade for unlined drains,including table drains, is 0.5% and for lineddrains, 0.2%. This is to ensure flow and, ifapplicable, minimize ponding againstformations and pavements.

• Limit flow velocities for longitudinal drainageto prevent erosion. Limiting flow velocities ispreferred over maintaining high flow velocitiesand providing armouring. An increase in thenumber of outflow points (e.g. turnouts or levelspreaders) from the longitudinal drainageshould be considered.

• Limit flow depths to prevent erosion andinundation of the pavement.

• Median longitudinal drainage will usually havea concrete lined invert to assist maintenanceand reduce the risk of errant vehicles rollingafter hitting ruts caused by tractor mowing.

• Consider collecting road run-off from bridgescuppers and discharging run-off into asediment basin, gross pollutant trap or otherrelevant first flush containment devices. This isparticularly important where the scupper woulddirect bridge run-off into a base flow channel orupstream of a sensitive environment (e.g.wetland, fish habitat reserve).

Reference should also be made to StandardDrawing No: 1178.

3.3.4 Surface Drainage

The requirements for surface drainage relate tosafety (eg. aquaplaning and ponding) and are dealtwith in Section 4.4.4.

3.3.4.1 General Standard

For surface drainage the allowable flow width inthe 10 year ARI flood is specified.

For drainage of bridge decks, a design ARI of 20years is recommended.

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3.3.5 The Major / Minor SystemConcept

The major/minor drainage system or dualdrainage system is a concept that has two distinctcomponents:

The minor drainage system (refer glossary fordefinition) shall be designed to convey thedischarge for a minor design storm (ARI as perTable 3.3) with road flow limited in accordancewith the requirements set out in Chapter 4,Section 4.4.4.4.

The major drainage system (refer glossary fordefinition) conveys the floodwater beyond thecapacity of the minor drainage system and shall bedesigned in accordance with the requirements setout in Chapter 4, Section 4.4.4.4.

Note: With any proposed drainage system designedadjacent to sensitive areas where flood inundation willnot be tolerated, the design of the major drainagesystem should also consider the flow conveyed in theunderground minor drainage system should this systemfail due to malfunction or blockage.

Designers should note that the design dischargefor the major system ARI may require that thecapacity of the gully inlets and underground pipesbe increased beyond that required by the designdischarge for the minor system ARI, in order tomeet the major system design criteria.

The minor design storm and the major designstorm correspond to the rainfall events for the ARIchosen for the design of the minor system and themajor system respectively.

3.3.5.1 Urban Areas / ExistingMinor Drainage Systems

The design recurrence interval in urban areas willoften be influenced by existing standards for thosesituations where new works are being connectedto existing infrastructure.

Designers should confirm requirements of thesesystems with the relevant authority.

3.3.6 Erosion and SedimentControl

Guidelines for the selection of design standards(average recurrence intervals) for erosion andsediment controls are contained within Section3.11.

3.4 Hydraulic Criteria

3.4.1 Discharge

The design discharge for a proposed structure maynot be determined until sufficient hydraulicanalysis is done to define flow patterns, and astructure size is selected.

The determination of the discharge/ARIrelationship is a fundamental requirement for alldrainage designs. Following determination of theappropriate design standard, the discharge mustbe calculated for each proposed structure, and foreach flood ARI that may need to be tested as apossible design condition. This can be undertakenmanually (refer Section 3.5), or with the aid ofcomputer software, as described in Appendix 3A.

3.4.2 Velocity

The velocity of flow (whether in a watercourse oroverland) is one of the most important criteriadictating the performance of a drainage system,the potential for erosion and the subsequentimplications for design.

The presence of high velocities can result in anumber of problems, such as erosion or scour,undermining of a structure, or high afflux.Similarly, in areas where fish passage occurs, highvelocities may inhibit or prevent passage fromoccurring. In each of these situations, the designerhas a responsibility to limit velocities tomanageable magnitudes (preferably below 2 m/s).

However, where high velocities are a naturaloccurrence, or result from the need to confineflows, then it may be necessary to protect awaterway from the impacts of the high velocities.

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Velocity criteria may be specified in terms of theaverage velocity at a location (for a nominateddesign event), or in terms of the maximumvelocity at locations of interest, such as the bed ofa watercourse.

Velocity criteria will typically fit into one of thefollowing three classifications:

1. Existing;

2. Desirable maximum; and

3. Maximum Permissible.

3.4.2.1 Existing Conditions

The existing velocity regime may be consideredacceptable in those circumstances where minimalchanges to a watercourse are proposed, and thatwatercourse is currently stable. However, caremust be taken to ensure that where the bed orbanks of a watercourse are disturbed, thatappropriate restoration occurs. Failure to meet thisrequirement will usually result in erosion, andpossible failure of drainage infrastructure.

3.4.2.2 Desirable Velocity

Where works in a watercourse are required, thedesirable maximum velocity will typically be

dictated by the types of soil and vegetationpresent. The value chosen applies to peakvelocities, but should also be linked to anunderstanding of the duration of flow. For shortduration events, a higher velocity may betolerated than for long duration events.

Table 3.4 provides a summary of typicalmaximum velocity criteria for differentconditions.

Where the desirable maximum velocity cannot beachieved (ie. where it is exceeded), then thedesigner will need to look at the selection ofappropriate linings which can withstand theestimated peak velocities predicted to occur.

3.4.2.3 Maximum PermissibleVelocity

In some circumstances, it will not be possible tooffer bed or bank protection in order to cater for avelocity higher than the desired maximum. Forexample, where fish passage is a requirement,there may be specific velocity criteria that applyto normal and/or low flow. These will typically bedetermined through the REF/IAS process and useof a fish specialist.

In these situations, the specified velocity criteriamust be satisfied, and hence design of the cross

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Table 3.4 Maximum permissible velocities (m/s) for earth channels (SCS, 1982)

Erodability AssessmentCover Channel Low Moderate High Very High

Slope (%)Kikuyu and other dense high- 1-5 2.6 2.4 2.3 2.2growing, prostrate perennials 5-10 2.5 2.3 2.2 2.1

>10 2.4 2.2 2.1 2.0Couch and other low-growing, 1-5 2.1 2.0 1.9 1.7prostrate perennials 5-10 2.0 1.9 1.8 1.6

>10 1.9 1.8 1.7 1.5Perennial improved pastures 1-5 1.7 1.6 1.4 1.2

5-10 1.6 1.5 1.3 1.1>10 1.5 1.4 1.2 1.0

Native tussocky grasses, sparse 1-5 1.4 1.2 1.0 0.8legumes and annuals 5-10 1.3 1.1 0.9 0.7Bare soil 1-10 0.7 0.6 0.5 0.4

Note: Maximum permissible velocities for fish passage are detailed in Section 4.2.2.2 of Chapter 4. These velocitiesare 0.3 m/s for flow depths of 0.2 to 0.5 m and up to 1.0 m/s in isolated locations (i.e. short channel lengths).

drainage system will need to be modifiedaccordingly.

3.4.3 Afflux

In many cases, the existence of a cross drainagestructure, such as a culvert, will cause flood levelsto increase on the upstream side. The increase inwater level compared with that without thestructure is defined as afflux. The distanceupstream that is affected depends on the size ofthe afflux, and the hydraulic gradient of thewatercourse. The acceptability of this increase isdefined by the existence of upstream property orinfrastructure, as assets that cannot cope withincreased flood levels will typically necessitate ahigher capacity culvert.

Additional guidance as to acceptable afflux limitsmay also be obtained from local authority designstandards, or the QUDM (1993).

For major roads the designer should aim to ensurethat any afflux is limited in extent to areas notadversely impacted. Where the 100 year ARIflood currently enters properties upstream, thedesigner must fully consider the impacts of anyafflux generated, and design accordingly.

The 50 year ARI afflux should be used as thecheck for cross drainage in minor roads.

If upstream properties are at a relatively lowelevation it may be necessary to install culverts ofcapacity greater than that for the minor systemARI design storm to ensure flooding of upstreamproperties is not increased. In addition thedownstream face of the causeway embankmentmay need protection where overtopping is likelyto occur.

3.4.4 Gradient

The gradient (or slope) of a watercourse is asignificant factor in determining the hydraulicregime, and in particular, the velocity of flow.This in turn affects the potential for erosion tooccur. Thus, any consideration of drainageinfrastructure is heavily dependent on:

• bed slope; and/or

• gradient of the water surface; and/or

• ground slope (ie. for overland flows).

In all cases, the close links between slope,velocity and erosion require careful considerationof what the governing criteria will be. Typically,these will consist of one of the following:

• stability of the watercourse;

• retention of waterway characteristics(preservation of flora and fauna); and

• protection of existing infrastructure from flooddamage.

3.4.5 Tailwater Levels

The water level at the outlet (tailwater level) of anydrainage or pollution control structure can exert asignificant effect on the functionality of thecontrol. Hydraulic performance will often becontrolled by tailwater levels, and these must beconsidered for all designs. Relevant issuespertaining to tailwater are discussed in Section 3.6.

3.5 Hydrology

3.5.1 Introduction

Hydrology for road drainage design inQueensland conditions may be defined as theestimation of flood (rainfall) runoff from acatchment for specified average recurrenceintervals. The standard method of runoffcalculation used by Main Roads for smallcatchments is the Rational Method.

The Rational Method described in this manual isgenerally applicable for small, single streamcatchments up to 25 km2 in area. However, giventhe many factors which influence rainfall runoff,it is highly recommended that a check byexperienced hydraulic specialists using moredetailed procedures be carried out for catchmentsof 10 km2 or more. Catchments considered ascomplex and therefore beyond the scope of this

3-12 June 2003


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manual, can be of any size and include:

• multiple stream / branched catchments,

• large stream / river systems,

• catchment areas consisting of several differentland uses,

• catchments with highly varied slopes, and

• catchments / streams with storage capacity.

Runoff calculations for these catchments shouldbe undertaken by or in conjunction with hydraulicspecialists.

Variables such as local depressions/storages andinfiltration rates into different soil types aredifficult to quantify and the importance of existingflood information cannot be overemphasised, notonly to calibrate theoretical calculations but alsofor decisions on the magnitude of the design floodand any future legal litigation. The Department’sForm M2759, Field Report - Bridge Waterwaysgives a guide to the information which should besought, such as flood levels, in hydraulicallysensitive locations and for the larger structures.

Calculations based on long term local recordedflood data should be given precedence over moretheoretical calculations, but the reasons for anyinconsistencies should be sought.

Actual rainfall of a given average recurrenceinterval (ARI) does not always lead to a flood ofthe same ARI. Variables such as the magnitude ofantecedent rainfall (ie. wetting of the catchmentprior to the design event) can lead to significantvariation. However, it is accepted as standarddesign procedure to designate a calculated floodwith the same ARI as that of the design rainfall.

The use of recorded data will allow the designer tovary standard parameters for such factors asantecedent precipitation with a degree ofconfidence.

3.5.2 Methods Available forRunoff Calculation

Techniques for flood estimation in the largercatchments, usually associated with majorstructures such as bridges and floodways, are notdescribed in any detail in this manual. Suchprocedures are described in such publications asAustralian Rainfall and Runoff (IEAust, 1987)and Hydraulics Training Course (Department ofMain Roads, 1996) and include unit hydrographmethods, runoff and storage routing andfrequency analysis. Appendix 3A discusses theuse of computer models for hydrological andhydraulics calculations.

Other states use the Probabilistic RationalMethod. However, there are insufficient long termgauging station records in Queensland to compilethe equivalent method.

3.5.3 Rational Method

The traditional Rational Method is describedbelow.

The Rational Method Formula is:

Qy = k x Cy x Itc,y x A

Where

Qy = peak flow rate (m3/s) for an averagerecurrence interval (ARI) of y years

Cy = runoff coefficient (dimensionless) for an ARIof y years

A = area of catchment (km2)

Itc,y = average rainfall intensity (mm/h) for designduration of tc hours and ARI of y years

k = 0.278 and is merely a conversion factor toensure units are consistent for A in km2

k = 0.00278 if A is hectares (ha)

Each of the terms in the Rational Method equationwill be examined in following sections.

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3.5.3.1 Catchment Area

The catchment or watershed area ‘A’ (in hectaresor km2) can be determined from topographicalmapping, from aerial photographs used as stereopairs or the basis of photogrammetric contourplots or by field survey.

Catchments interpreted from aerial photographsin heavily timbered or flat country should beverified by ground inspection or survey to ensurethat major errors do not result frommisinterpretation.

In urban areas, catchment areas are frequentlymodified by roadworks, railway embankments orother earthworks, building works or fences, andcatchment boundaries should be verified by siteinspection.

The term ‘equivalent impervious area’ is used forthe product of coefficient of runoff and catchmentarea.

3.5.3.2 Time of Concentration

In the deterministic interpretation of the RationalMethod, the time of concentration, ‘tc’ for acatchment is defined as the time taken for water toflow from the most remote point on the catchmentto the outlet, or the time taken from the start ofrainfall until all of the catchment issimultaneously contributing to flow at the outlet.

The significance of the time of concentration isthat peak outflow will usually (see also partialarea effect in Section 3.5.3.2) result when theentire catchment is contributing flow from rainfallon the catchment. The most intense rainfall thatcontributes to the outflow will be that with aduration equal to the time of concentration. If therainfall is more intense but of shorter duration notall the catchment will contribute to the peakrunoff. If the rainfall is of longer duration theaverage intensity over that duration will be lessand the peak runoff will be less even though theentire catchment contributes.

The time of concentration is made up of:

• Overland flow time across natural or pavedsurfaces including retardance due to pondage

on the surface or behind obstructions;

• Time of flow in gutters and natural channels;and

• Time of flow in pipes or channels.

The type of flow will vary along the catchment,although once channelised, overland flowconditions do not normally recur. Overland flowto channel flow and pipe flow back to channelflow can be expected to occur. There may also beoverland or channel flow parallel with pipe flowat full capacity. Several flow paths may need to beexamined to determine which is the longest ormost critical in terms of design flows.

The procedure for calculating time ofconcentration varies depending on the version ofthe Rational Method being used and whether thecatchment is urban or rural. The procedures aredescribed later in this section.

The minimum time of concentration to be used indesign is 5 minutes, as the effects of depressionstorage and surface detention do not permitshorter times in practice.

In designing pipes for road crossings, the time ofconcentration used should allow for developmentof the upstream catchment. Consider thefollowing example illustrated in Figure 3.1.

Figure 3.1 Hypothetical Catchment Development

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If the time of concentration to A is calculatedunder existing conditions, it will be made up of:

• a considerable length of overland and channelflow, and

• a short length of flow on pipes.

If the drainage system in the catchment upstreamof the road is improved, the overland flow timewill be reduced and the time of concentration to Aalso reduced. Designers should check the fullrange of possible cases.

Rural

For catchment areas larger than 5 km2 the time ofconcentration is first estimated using the modifiedFriend formula, assuming an estimated peak levelof the design flood. This level is usually themaximum reported flood level or approximatebank level. If later hydraulic calculations showthis to be in error by more than 0.3–0.6m, thevalue is recalculated. The modified Friendformula is:

where

tc = time of concentration (h)

L = length of mainstream (km) from the outlet tothe catchment divide

Ch = Chezy’s coefficient at the site

R = hydraulic radius

= 0.75RS where slope of entire stream is fairlyuniform

= 0.65RS where slope varies appreciablyalong the stream

Rs = hydraulic radius at the initially assumedflood level at the bridge/culvert site (unrestrictedchannel)

n = average Manning roughness coefficient for theentire main stream along length L

A = catchment area (km2)

Se = equal area slope (%) as defined in Figure 3.2.

Figure 3.2 Derivation of the equal area slope ofmain streamReference: IE Aust, 1987.

For catchments less than 5 km2 in area, the time ofconcentration may be calculated using thevelocities in Table 3.9 where there is a definedchannel in most of the flowpath.

Where there is a significant proportion ofoverland sheet flow, use Friend’s equation(directly or via Figure 3.3) for a maximum lengthof 200 m, then, if longer, assume channel flow andvelocities from Table 3.9.

A special allowance is made for small catchmentswith a short but defined channel as shown in thenote below Table 3.9.

)n

R(166.0

=

4.0e

0.1c S A ChL 8.5t =

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Example: A creek is 1500 metres long with a welldefined channel in the flowpath. The top 900metres of its length flows through hilly countryand the rest (600 m) through flat country. FromTable 3.9 for velocities,

tc = 16.7 + 33.3 minutes

tc = 50 minutes

Table 3.9 Velocities for Calculation of tc forAreas < 5 km²

Type of Average Slope Approx. Country of Catchment Velocity of

Surface (%) Stream (m/s)Flat 0 to 1.5 0.3Rolling 1.5 to 4 0.7Hilly 4 to 8 0.9Steep 8 to 15 1.5Very Steep > 15 3.0RockyMountainous

Source: Hee, 1983

Note: For length of catchment less than or equal to1000 metres, add 10 minutes to the calculated time ofconcentration for the influence of overland flow. Toavoid sudden changes, the minimum tc for lengthslonger than 1000m should be the tc for 1000m if this islarger than the tc calculated for the actual length.

Rainfall intensity for duration tc and the designARI of 50 years shall be determined in accordancewith Section 3.5.3.3.

Urban

The time of concentration calculations aredifferent to those for rural catchments.

Flows can reach outlets via overland flow areas,natural or paved surfaces or along gutters, pipes,channels or natural watercourses or by acombination of means.

For single catchment situations, time ofconcentration to a structure site will be thesummation of the times of flow in the variouselements encountered along the longest drainagepath. These elements include:

(a) Overland flow;

(b) Kerb and Channel Flow;

(c) Delays at Inlets or Gully Pits;

(d) Flow in Pipes.

Methods of estimating the flow times in each ofthese elements are given below.

In more complex urban drainage networks, it iscommon for drainage features to be fed by severalcatchments or sub-catchments. This complicates

minutes 600.3

600 600.9

900tc ×+

×=

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Source: IE Aust, 1977.

Figure 3.3 Overland Sheet Flow Times - Shallow Sheet Flow Only

the time of concentration calculations, as itbecomes necessary to follow all the possible pathsand determine the critical time of concentration ateach point throughout the system. A step by stepprocedure for this, illustrated by a workedexample based on a typical catchment andstormwater drainage network introduced inSection 4.4.6.4, is given in Appendix 4E.

(a) - Overland Flow

Overland sheet flow time may be obtained fromFriend’s Equation or the nomograph on Figure 3.3based on this equation.

It should be noted that some Local Authoritiesmay require overland flow times to be obtained byother methods.

In urban residential areas, the typical length ofoverland flow considered is 20 - 50 m with 50 mthe recommended maximum because ofobstructions, minor channels or piped drainage.

In rural residential areas, the typical length ofoverland flow considered is 50 - 200 m with 200m the recommended maximum.

Friend’s Equation is

where

t = overland sheet flow travel time (minutes)

L = overland sheet path length (metres)

n = Horton’s roughness value for the surface

S = slope of surface (%)

Values for Horton’s “n” are similar to those forManning’s “n” for similar surfaces.

(b) - Kerb and Channel Flow

The time of flow in channels depends on a numberof factors including the discharge. Usually, thiscomponent of the total time of concentration isrelatively small and a sufficiently accurateestimate can be obtained from Figure 3.4. Thisfigure has been derived by VicRoads and drawn

from Argue (1986). This figure takes into accountthe length of flow and fall along the gutter onlyand incorporates an assumption about roughnessand flow depth.

(c) - Standard Inlet Times

For small sub-catchments or where detailedoverland flow and channel flow calculations arenot considered justified, the Standard Inlet Timesshown in the QUDM (1993) may be used. Theseare shown in this manual on Table 3.10.

The Brisbane City Council and possibly otherLocal Authorities use Standard Inlet Times ratherthan the kinematic wave equation.

Table 3.10 Recommended Standard Inlet Time ofConcentration to First Inlet

Location Time (Minutes)Road surface and paved areas 5Urban and residential areas where 5average slope of land is greaterthan 15%Urban and residential areas where 8average slope of land is greaterthan 10% and up to 15%Urban and residential areas where 10average slope of land is greaterthan 6% and up to 10%Urban and residential areas where 13average slope of land is greaterthan 3% and up to 6%Urban and residential areas where 15average slope of land is up to 3%

Note: The average slopes referred to are the slopesalong the predominant flow paths for the catchment inits developed state.

2.0

333.0

SL n 107t =

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Source: Argue, J, 1986.

Figure 3.4 Flow Travel Time in Gutters

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Figure 3.5 Analysis of Uniform Flow, Manning’s Formula

(d) - Flow in Pipes

The time of flow in pipes is calculated fromManning’s formula and assumes that pipes areflowing full and not under pressure:

where

v = velocity in pipe, metres per second

n = manning roughness coefficient for pipe

R = hydraulic radius of pipe flowing full,metres (= Area/Wetted Perimeter)

S = slope of hydraulic gradient, metres permetre (= slope of pipe when pipe just runsfull)

A graphical solution of this formula is given on

Figure 3.5. Having determined the velocity andknowing the length of the pipe, the time of travelcan be calculated.

An approximate figure for the time of flow in apipe system may be determined from the values ofvelocity shown in Table 3.11. When the tentativepipe system has been designed, this gives anapproximate check on calculated values.

Table 3.11 Velocities of Flows in Pipes

Type of Country Approx. Velocity for WholePipe System (m/s)

Undulating - Hilly 2.5 to 4.0

Flat (< 1.5%) 1.5 to 2.0

nS Rv

5.0667.0=

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Figure 3.6 Time-Area Representation of Multi-land Use Drainage Unit

Source: Argue, 1986.

Eq

uiv

ale

nt

Imp

erv

iou

sA

rea

Time (mins)

(CA

)h

a

0 10 20 30 40 50 60

0.10

0.20

P

F

ti x C Ap ptc

(CA)part

C Ai i = 0.10 ha

Pave

dC

om

ponent

Pervious Component

(CA)full

C Ap p = 0.08 ha

(CA) =

C A [ xi i C A ]i i

part

titc

ti = 20 tc = 20

The time of concentration most commonly used isthe full area time ie. that required for the runoff toflow by the longest available flow path to thesubcatchment outlet. However, in many cases a“partial area” effect occurs, with the RationalFormula giving a greater flow rate when appliedto a lower part of the catchment, with a time ofconcentration less than the full-area travel time.Partial area effects create a major uncertainty inthe Rational Method and increase the calculationsrequired. The cause may be catchment shape orvariations in slopes and land use within thecatchment. It may be necessary to check a numberof partial areas.

The essence of the part area flow estimate isshown in Figure 3.6 (Argue, J, 1986). The methodinvolves using a time of concentration (ti)corresponding to flow time from the most remote,directly connected paved area of the catchment tothe outfall. Thus, the calculated runoff is that fromthe impervious portion of the catchment plus thatfrom the pervious part of the catchment which hasbegun to contribute up to time ti since the stormbegan. So, from Figure 3.6, the equivalentimpervious area to be used in the rational formula,ie. the product of C and A is given by the formula:

where

C = overall coefficient of runoff with Ci and Cpbeing the coefficients for the imperviousand pervious areas respectively.

A = overall area with Ai and Ap being theimpervious and pervious areas respectively.

ti = time of concentration from impervious area.

tc = time of concentration for the catchment.

For determination of the peak flow rate at thepoint of interest in urban catchments use thefollowing technique:

Figure 3.7 Catchment Example

The areas of the components of the catchment are:

a = area of catchment “a”, ha

b = area of catchment “b”, ha

c = area of catchment “c”, ha

The flow is required at the catchment outlet ie.inlet to pipe YZ:

ta = time of concentration for area a

tb = time of concentration for area b

tc = time of concentration for area c

tp = time of flow in pipe XY

If tb > tc and (tp + tb) > ta

and It = rainfall intensity corresponding to time t,

then the required design flow, the peak flow inpipe YZ is:

QYZ = k × (Cb × b + Cc × c + Ca × a) × I × (tp + tb)

where Ca, Cb, Cc are the runoff coefficients forcatchments a, b, c respectively.

In the common case where:

Ca = Cb = Cc = C

QYZ = k × (a + b + c) × C × I × (tp + tb)

)A C tt(A CA C ppc

iii +=

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3.5.3.3 Rainfall Intensity -Frequency - Duration

Rainfall intensity is defined as the mean rainfallintensity assumed to fall uniformly over acatchment for a given duration and frequency(average recurrence interval).

The normal units for rainfall intensity aremillimetres per hour.

For small catchments, the duration consideredcorresponds to the time of concentration or timeof flow from the top of the catchment to the outletof the catchment.

For the larger catchments, a temporal pattern isapplied so that the rainfall intensity varies overdifferent periods of the storm duration. For thesecatchments also, storms both shorter and longerthan the time of concentration are tested until thatgiving the peak flow is found.

Also for the larger catchments, an areal factor isapplied to point rainfall intensities obtained, toallow for actual non-uniform rainfall over thecatchment.

Rainfall intensity varies with location andtopography as well as duration and frequency, andthis should be considered when using the RainfallIntensity - Frequency - Duration (IFD) tabulationsand curves for many locations in Queenslandobtained from the Bureau of Meteorology.

For design IFD rainfall the computer programRAIN2 already used in most DMR Districts orother suitable programs are recommended.

The use of an IFD programme requires the inputof 9 parameters from Maps in Australian Rainfalland Runoff (IEAust, 1987). These parameters andthe relevant maps are:

• 2i1 (2 year, 1 hr log-normal rainfall intensity)from one of Maps 1.1, 1.2, 1.3, 1.4, 1.5 or 1.6;



• 50i1 (50 year, 1 hr log-normal rainfall intensity)from one of Maps 4.1, 4.2, 4.3, 4.4, 4.5, or 4.6;

• 50i12 (50 year, 12 hr log-normal rainfallintensity) from one of Maps 5.1, 5.2, 5.3, 5.4,5.5 or 5.6;

• 50i72 (50 year, 72h log-normal rainfall intensity)from one of Maps 6.1, 6.2, 6.3, 6.4, 6.5 or 6.6;

• SKEWNESS FACTOR, G from Map 7b or 7c;

• GEOGRAPHICAL FACTOR, F2 from Map 8;and

• GEOGRAPHICAL FACTOR, F50 from Map 9.

A tabulation of IFD values for durations from 5minutes to 72 hours and average recurrenceintervals from 1 to 100 years is a standard outputfrom the RAIN2 program but values for nonstandard times are also readily obtained.

Prior to the publication of Australian Rainfall andRunoff (IEAust, 1987), rainfall IFD curves wereobtained from the Bureau of Meteorology. Typicalcurves indicative of the range of rainfallintensities in Queensland are shown as Figures3.8, 3.9 and 3.10 for Springwood (near Brisbane),Barcaldine and Innisfail.

For a fee, the Bureau of Meteorology will stillgive design rainfall parameters for a givenlocation.

The use of rainfall data different to that obtainedfrom the Bureau of Meteorology may be justifiedby the calibration of actual recorded rainfallagainst recorded floods over a significant periodof time.

The Australian Bridge Design Code, 1996requires that bridges will be structurally sound ina 2000 year ARI flood. Although for most bridgesin Queensland the largest flood forces occur in asmaller overtopping flood, there are occasionswhen the 2000 year ARI flood needs to becalculated. Such calculations are not simple andshould be carried out by the Bureau ofMeteorology or Engineers on the Department’sprequalification register for hydrauliccalculations.

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Figure 3.8

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Figure 3.9

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Figure 3.10

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Table 3.5 Estimation of the Runoff Coefficient for Rural Catchments

Runoff Producing Values (in brackets) as % in calculation of “C” for a 50 year average recurrence interval event

CharacteristicsRainfall 100 mm/h 75-100 mm/h 50-75 mm/h 25-50 mm/h 12-25 mm/h 12 mm/h <12 mm/hIntensity (35) (30) (25) (15) (10) (5) (0)

Relief Very steep Steep country, Hilly, with Rolling with Flat, with rugged country slopes 8-15% slopes of 4-8% slopes 1.5-4% slopes 0-1.5%with averageslopes > 15%(10) (5) (5) (0) (0)

Storage Negligible, few surface Well defined system Considerable surface Poorly defined anddepressions. water- of small depressions, overland meandering stream,courses, steep and thin watercourses flow is significant, some large surface film of overland flow farm ponds, swamps storage. Soil

and contour banks conservation planon 90% catchment

(10) (10) (5) (0)

Ground Rocky, clayey or Open forest or Average Heavily Sands or wellCover non-absorbent grassed land, grassed timbered aggregatedCharacteristics soil with cereal crops timbered land country, closely soil

scanty of medium soil cultivated landherbage texture and garden(45) (40) (35) (30) (10)

Notes:

1. For catchments > 50 km², use with extreme caution.

2. Use values below 50% with caution.

3. Use values above 80% only in very high rainfall areas (absolute maximum of 90%) where the antecedentprecipitation conditions for the design storm is a saturated catchment.

Example:

A catchment has the following characteristics:

(i) Intensity 40 mm/hr

(ii) Hilly, average slopes 4-8%

(iii) Well defined system of small watercourses

(iv) Open forest

Source: Hee (1978).

0.70100

4010515C =

+++=

3.5.3.4 Runoff Coefficient

Rural

This (non-dimensional) coefficient ‘C’ is definedas the ratio of the maximum rate at which waterflows from a catchment area from a given storm tothe mean volume rate at which rain fell on thecatchment for the duration of the storm. Therunoff coefficient is a function of the design ARI.

The value of ‘C’ depends on many features of thecatchment area including:

• Relief or slope of catchment;

• Ground characteristics such as vegetationcover, soil type, and impervious areas; and

• Storage or other detention characteristics.

The runoff coefficient for the 50 year averagerecurrence interval, is determined from Table 3.5.Design coefficients of runoff for other designaverage recurrence intervals should be determinedusing adjustment factors, see Table 3.8.

Urban

Typical values of runoff coefficients used in urbancatchments are given in Table 3.7 with the fractionimpervious parameter obtained from Table 3.6 orby calculations.

Where the proportion of roadway space isunusually high or low, or where more than oneclass of development, soil type, or slope exists inan area, the runoff coefficient is calculated as aweighted average.

In areas where land usage is changing, the valueof the runoff coefficient which is used shouldallow for future upstream development of thecatchment. This is particularly relevant in thesituation where a rural catchment may developinto a partially or fully urbanised catchmentduring the service life of the works beingdesigned.

Where future (hypothetical) development mayrequire an increase to waterways under the road tothat required under existing conditions at the timeof the design of the structures, in some States

there is no legal obligation to try to assess and addthe extra waterways in the initial construction.

If specific development proposals are beingformulated or in the approval process at the timeof the design of road structures, the additionalwaterway area needed to accommodate thedevelopment would be provided at thedeveloper’s cost. However, if the structures arebuilt before the catchment is developed and thereare no development proposals at the time, theadditional cost of the structures is not recoverablefrom the future developer.

Table 3.6 Fraction Impervious Vs DevelopmentCategory

Development Category Fraction Imperviousfi

Central Business 1.00

Commercial and Industrial 0.90

Significant Paved Areas 0.90eg. Roads and Carparks

Urban Residential 0.70 to 0.90High Density

Urban Residential Low 0.30 to 0.60Density (Including Roads)

Urban Residential Low 0.25 to 0.55Density (Excluding Roads)

Rural Residential 0.2

Open Space & Parks etc. 0

Notes:

1. The designer should determine the actual fractionimpervious for the particular development underconsideration, eg. Typically for Urban ResidentialHigh Density developments:• townhouse type development fi = 0.70• highrise residential development fi = 0.90

2. In Urban Residential Low Density areas fi may varyfrom 0.3 to 0.6 depending upon road width,allotment size, house size and extent of paths,driveways etc. Where roads are excluded fi shouldbe adjusted accordingly.

Reference: Queensland Urban Drainage Manual(Neville Jones & Associates and AWE, 1993).

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In making the decision on whether to allow forfuture development in the waterways for the newroad, the disruption to traffic when the additionalwaterways are constructed in the future must beconsidered. Other considerations include therequirements by some Local Governments to notallow any increase in water discharging intoculverts in the road corridor from development ofan upstream catchment. Detention basins aretherefore specified in the design, particularly insmall urbanised catchments. In this case there isno need to consider the effect of development.

Table 3.7 C10 Values

Intensity Fractionmm/hr ImperviousRange fi

I10 0.00 0.20 0.40 0.60 0.80 0.90 1.00

39-44 0.32 0.44 0.55 0.67 0.78 0.84 0.90

45-49 0.39 0.49 0.60 0.70 0.80 0.85 0.90

50-54 0.46 0.55 0.64 0.72 0.81 0.86 0.90

55-59 0.53 0.60 0.68 0.75 0.83 0.86 0.90

60-64 0.59 0.65 0.72 0.78 0.84 0.87 0.90

65-69 0.66 0.71 0.76 0.80 0.85 0.88 0.90

70-90 0.70 0.74 0.78 0.82 0.86 0.88 0.90

I10 = One hour rainfall intensity for a 10 year ARIC10 = Coefficient of Runoff for a 10 year ARIfi = Fraction Impervious

Reference: Queensland Urban Drainage Manual(Neville Jones & Associates and AWE, 1993).

Adjustment Factors

Design coefficients of runoff for other designaverage recurrence intervals should be determinedusing Table 3.8.

Table 3.8 Adjustment Factors for RunoffCoefficients for Other Average RecurrenceIntervals

Average Rural UrbanRecurrence Coefficient Coefficient

Interval (years)1 0.8C50 0.8C10

2 0.8C50 0.85C10

5 0.8C50 0.95C10

10 0.8C50 1.0C10

20 0.9C50 1.05C10

50 1.0C50 1.15C10

100 1.05C50 1.25C10

Notes:1. C50 determined for rural catchments using Table

3.5.2. C10 determined for urban catchments using Table

3.7.3. Where runoff coefficients calculated using the

above table exceed 1.00, they should be arbitrarilyset to 1.00.

3.6 Tailwater Levels

3.6.1 Introduction

When an open channel discharges (or outlets) intoa body of stored water, or to another openchannel, the water level at this point will usuallyact as the controlling level for channel hydraulics.This controlling level is called the tailwater level.There are two types of tailwater levels: tidal andnon-tidal.

A tailwater level is tidal when the channeldischarges into a water body influenced by tides,such as oceans, bays, and rivers and creeks closeto the coast. Tidal tailwater levels are subjected totide levels, storm surges and the rise in sea leveldue to the greenhouse effect (refer Section 3.6.2).

A tailwater level is non-tidal when it dischargesinto a water body that is not influenced by tides,such as lakes, dams, basins, creeks and riversaway from the coast. Non-tidal tail water levelsare independent of tide levels, storm surges andgreenhouse effect (refer Section 3.6.3).

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The hydraulic design of a bridge or culvertrequires the determination of the tailwater leveljust downstream of the structure outlet, even whenit is not affected by a downstream storage or river.In such situations, provided the downstreamchannel is reasonably uniform, the tailwater levelis usually considered to be the normal depth offlow in the stream. This is calculated using theManning Formula (refer Sections 4.3.5 and 4.3.6).

3.6.2 Tidal Waters

When designing tailwater levels for dischargesinto tidal waters, three factors may influence thefinal design level: tide levels, storm surges, andgreenhouse effect.

3.6.2.1 Tide Levels

Annual tide tables published by the Department ofTransport give predicted tide levels at variouscoastal locations in Queensland.

It is important to note that:

• the mean sea level given for the location maybe different to Australian Height Datum (AHD)which is the average mean sea level of 42locations around Australia;

• tide levels are given at or very close to thecoastline; and

• tide levels are often specified in terms of lowwater datum.

It is very difficult to estimate the tide level at alocation in a stream some distance from thecoastline. The time for the tide to rise along thecreek and to then flow back in the oppositedirection is one factor. Another is the existence oflocal sand bars or raised areas of the creek bedcloser to the mouth of the stream, which mayprevent a tide from reaching or falling below acertain level at a particular road crossing.

Although precise tide levels are not usuallynecessary at an upstream road or bridge crossing,tide levels at the mouth of the tidal stream are notsufficient to give tide design parameters at theroad or bridge.

The absolute minimum survey requirements at aroad/bridge site are the times and levels forsuccessive low - high - low tides. Alternativelysuccessive high - low - high tide information maybe found. The more cycles measured the better.

This information when compared with tide levelsat the mouth of the creek will allow experiencedhydraulic engineers to predict approximate designtides such as MHWS (mean high water springs)and MLWS (mean low water springs) at the jobsite.

3.6.2.2 Storm Surge

A storm surge is the rise (or fall) of open coastwater levels relative to the normal water level andis due to the action of wind stress and atmosphericpressure on the water surface.

Storm surges occur in major storms such ascyclones where there are low atmosphericpressures and the wind blows over reaches of theocean.

Some predicted surge heights by the James CookUniversity of North Queensland (1977) are shownin Table 3.12. The estimates are conditional andthe notes for the table are important. The studyalso provides surge levels based on 50 year and500 year cyclones.

There is no correlation with tide levels, nor arethere any predictions for wave break setup andwave runup on the land. These factors will needconsideration for any design with storm surge as afactor.

Storm surges would need to be considered withrespect to coastal developments, the protection ofcoastal roads, route immunity for evacuationpurposes, and for major coastal drainage designs.Local government may also have specificrequirements or data in relation to storm surge.

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Table 3.12 Peak Surges from 100 Year Cyclones

Region Peak Surge in 100 Year(Location) Cyclone (m)

Cooktown 0.70-1.10Cairns (Casuarina Point) 0.80-1.85Innisfail (Flying Fish Point) 1.02-1.84Ingham (Crystal Creek) 1.50-3.04Townsville 2.23-3.32Bowen 0.52-2.20Mackay (Sarina Inlet) 2.02-3.24Rockhampton (Emu Park) 2.12-2.80Gold Coast (Surfers Paradise) 0.41-0.79

Notes:1. These are upper bounds to tropical cyclone surge

levels and cannot be interpreted in terms ofprobability of occurrence of nominated surgelevels.

2 Three cyclones were tested for each location withapproach directions, 0° (parallel), 75°, and 105° tothe defined coastline, giving the range of peaksurges shown.

3.6.2.3 The Greenhouse Effect

The greenhouse effect is a climatic phenomenonwhere part of the solar energy absorbed by theearth and re-radiated is prevented from dissipatinginto space by the greenhouse gases in thetroposphere. This results in a layer of warm airsurrounding the earth, which maintains highertemperatures and evens out the extremes oftemperature between day and night.

The man made gases that mainly contribute to thiseffect include carbon dioxide, methane, nitrousoxide and chlorofluorocarbons. Naturalgreenhouse gases are water vapour, carbondioxide, methane, nitrous oxide and ozone.

Major effects include possible increased summerrainfall (from zero to 40% by the year 2070)throughout Australia, a southward movement ofpredominant summer rain and rise in sea level(CSIRO, 1989).

Sea levels could rise from 5 to 35 cm by 2030(CSIRO, 1989). This range of possible rise in sealevel by thermal expansion of the oceans is alsoshown in the Intergovernmental Panel on ClimateChange (1992).

Appropriate tide levels for the design of long lifestructures near the ocean are indicated in thefollowing Sections 3.6.2.4 and 3.6.2.5.

3.6.2.4 Tidal Outlets (Ocean andBays)

Local government should be consulted for anappropriate design tailwater level for outlets totidal waters in oceans and bays.

Unless otherwise specified an appropriate levelwould be MHWS (mean high water springs) +0.3m to allow for the greenhouse effect.

An allowance for storm surge should be added ifrequired.

3.6.2.5 Tidal Outlets (Rivers andCreeks)

The drainage outlet may be located in the tidalreach of a river or creek.

As stated in Section 3.6.2.1, it is difficult to definetide levels upstream of the mouth of a tidal creekand measured tide levels at the site are required.

Also, an attempt should be made to calculate theeffect of increase in tide levels at the site due tothe greenhouse effect. Tidal effects will extendfurther upstream. However, it is sufficientlyaccurate for calculations to be based on tidalvariations at the site, with the greenhouse effecttaken as a maximum of 0.3 m at the mouth of thecreek reducing with distance upstream.

Approximate tide levels upstream may becalculated by comparing the tidal range in theupstream section to the tidal range in the oceanoutfall.

Based on the tidal range/difference, MHWS -MLWS (mean high water springs - mean lowwater springs), the following procedure isrecommended to allow for the Greenhouse effectat the upstream section of the tidal stream.

(1) Calculate the range MHWS - MLWS = x inthe ocean outfall.

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(2) Calculate the corresponding range, MHWS- MLWS = y at the upstream site.

(3) Calculate the ratio, y/x.

(4) Assume the rise in ocean level due to theGreenhouse effect is 0.3 m.

(5) Calculate the equivalent rise at the upstreamsite equal to 0.3 multiplied by y/x. Adoptthis rise as the Greenhouse effect at the sitefor tidal flows.

3.6.2.6 Design Issues for TidalOutlets

This Section is based on Section 7.07 of theQUDM (Neville Jones and Associates and AWE,1993).

Areas of particular concern where work in tidalareas may need to comply with the requirementsof statutory authorities include:

• All areas below MHWS (mean high waterspring);

• Fish Habitat Reserves;

• Tidal Wetland Reserves;

• National Parks;

• State Marine Parks;

• Great Barrier Reef;

• Area controlled by a Port Authority; and

• Area controlled by a Waterway Authority.

Tidal outlets should be sufficiently elevated tominimise the risk of sand blockage and tofacilitate inspection and maintenance of pipes.

Although aesthetics may dictate that outlets belocated below low tide level, the invert level ofthe outlet should preferably be somewherebetween MLWS (mean low water spring) andMSL (mean sea level). The obvert of the outletshould normally be below HAT (highestastronomical tide).

Not only should there be protection against

scouring downstream where required, but thepossibility of undermining by wave action andlongshore currents, morphological scour andwave impact forces should be considered.

Advice should be sought from the localgovernment and the Environmental ProtectionAgency in regard to the local beach behaviour andlittoral processes.

Flapgates (floodgates) will prevent the intrusionof saltwater upstream of the outlet and may helpto prevent siltation in the pipe system. Theflapgate should be fitted in a chamber justupstream of the outlet to protect its operation fromvandalism, wave attack, debris and sand blockage.Special pipes are required if flapgates are to beinstalled.

3.6.3 Non-Tidal Waters

Non-tidal outlets include lakes, dams, ponds,retardation basins, creeks or rivers and other openchannels. Where the open channel being designedhas an outlet in this category, the tailwater at theoutlet may be selected/calculated from whicheverof the following sections is appropriate.

3.6.3.1 Large Storage Areas

It may be obvious that outlets into large storageareas such as lakes and dams will not raise thewater level of the storage to any significantdegree.

In this case, the storage level is taken as thetailwater level. This does not eliminate the need tocalculate the hydraulic grade line and criticaldepth in culvert outflows.

3.6.3.2 Small Storage Areas

For smaller storages there may be a significantrise in the water level in the storage prior to peakflow in the open channel or culverts discharginginto the storage.

From the discharge hydrograph for the openchannel, the volume of water in the hydrographprior to peak discharge should be calculated. This

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volume of outfall from the channel should beadded to that in the small storage and the newwater level calculated. This water level is thetailwater level for the open channel.

3.6.3.3 Open Channels

The outfall may be into an open channel such as anatural creek or river or a man made channel.

For simplicity, say the open channel beingdesigned is the side channel with discharge, Qs,and that it outfalls into a main channel withdischarge, Qm.

As the two open channels have differentcatchment sizes, they will peak at different times.The combined flow at their junction will give thetailwater level for the channel to be designed.

The design tailwater should be that correspondingto the higher of the following discharges:

(1) peak discharge in the side channel pluscorresponding discharge in the mainchannel; or

(2) peak discharge in the main channel pluscorresponding discharge in the side channel.

The method below assumes the same rainfallstorm on both catchments.

Combination 1

Assume that the peak discharge for the side(smaller) channel occurs at the time ofconcentration for that catchment and the RationalMethod is used, ie. the peak discharge in the sidechannel, Qst is obtained from a storm of duration,t, (for a time of concentration, tc, for the smallcatchment).

For the same design average recurrence interval(ARI) as for the small catchment, calculate thehydrograph for the main channel. Find thecorresponding discharge in the main channel, Qmt,at time, t, on the hydrograph. (A triangular shapehydrograph with the base length 2.7 times thetime to peak may be adopted for somecatchments).

Then

Qct = Qst + Qmt

where Qct is the combined discharge.

Combination 2

For a given ARI, the peak discharge in the mainchannel, QmT, occurs at time T. Find thecorresponding discharge in the side channel, QsT,at time T for a storm of the same ARI as for thecatchment for the main channel. For the RationalMethod for the side channel, use average rainfallintensity corresponding to time T.

Then

QcT = QmT + QsT

where QcT is the combined discharge.

Adopt the higher of Qct or QcT to find the designtailwater level at the junction (outfall).

3.6.3.4 Protection of Non-TidalOutlets

Particular attention should be paid to thepossibility of scour at non-tidal outlets of culvertsor open channels. Bridge abutments, for example,have been badly scoured from the mixing andturbulence from flows from different directionsand the channel discharging into the stream nearan abutment may even be a natural channel notconsidered in design.

Man made flow outlets have the same potentialfor erosion particularly if the bed level/soffit ishigher than the bed level of the stream into whichit is discharging, or if the outlets are in an unstablesection of the stream. Liberal use of dumped rock,rock mattresses or other scour protection isrecommended.

To a lesser extent, outlets into ponds and lakeshave the potential to cause erosion.

Floodgates which are normally only consideredfor outlets into tidal waters, may also be used innon-tidal outlets to prevent back-flooding fromthe receiving waters and to control siltation fromthe receiving waters.

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3.7 Fauna Passage

3.7.1 Introduction

Recognition of the impacts of road corridordevelopment on fauna populations has led tomodifications in the way that roads are nowdesigned.

In recent times, much research has beenundertaken on developing practices that helpfacilitate fauna movement through the roadcorridor in a way that minimises road mortalities.Much of the research has focussed on passagesthat are integral with drainage structures.

As such, the provision of fauna passage is oneof the key environmental factors which mayinfluence the physical dimensions of a drainagestructure. For this reason, it is considered a keydrainage design criteria.

This chapter provides an overview of what stepsneed to be taken when the project REF/IASprocess has identified a need for fauna passage tobe incorporated into drainage design.

Completion of these steps may result in thedetermination of additional design criteria whichmay then influence the selection of cross drainagestructures.

Further reading on this topic is available in FaunaSensitive Road Design (Main Roads, 2000).

3.7.2 Identifying Fauna PassageCriteria

The following steps should be undertaken when aproject REF/IAS has identified fauna passagerequirements. This should be undertaken by theDistrict Environmental Officer.

Step 1 - Identify Terrestrial and Aquatic FaunaPathways

A review of the project REF/IAS should beundertaken to check for the presence of anysignificant terrestrial and/or aquatic faunamovement pathways which could be potentiallyaffected by the proposal.

If fauna pathways have been identified in thestudy area, proceed to step 2. If not, document theoutcomes of the REF/ IAS review and continueidentifying other relevant drainage design criteriausing Chapter 3.

Fauna corridor under bridge

Step 2 - Identify the Species Group

Where fauna pathways have been identified,identify the relevant species group from the listbelow:

• macropods;

• arboreal mammals;

• ground dwelling mammals, reptiles andamphibians;

• chiropteras (ie. bats);

• ratites (eg. Cassowary); and/or

• fish and other aquatic fauna.

Note: Whilst bats may not necessarily have faunapassage requirements, any loss of habitat may result inthe need for constructed habitat such as culverts orsimilar dark drainage areas.

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Rufous Bettong

Step 3 - Consult with the Relevant Authority

The District Environmental Officer shouldconsult with the relevant authority (eg.Environmental Protection Agency or localCouncil) to further discuss the potential impactsof the project on the known fauna species and itsmovement patterns. The publication FaunaSensitive Road Design (Main Roads, 2000)should also be consulted.

A listing of key authorities and relevantlegislation is provided in Table 3.13.

Step 4 - Identify Criteria affecting DrainageDesign

In consultation with the relevant authorities andfrom information provided in the REF/IAS (ie.baseline fauna studies), determine the following:

• specific characteristics and needs of the species(ie. movement patterns, habitat range);

• opportunities to facilitate safe passage of faunathrough the drainage system (ie. bridgingoptions, culvert modifications) (refer Table3.14, the publication “Fauna Sensitive RoadDesign” and to Section 4.2.2.3 of this Manual);

• the economic and engineering feasibility ofpotential opportunities in consultation with theProject Manager and Detailed Designer;

• the need for further preliminary design work(ie. implications to cut and fill balance if adifferent culvert size is required, reviseddimensions, etc); and

• specific design criteria for drainage structures(ie. allowable flow velocity, minimum culvertheight, etc).

3.8 Ambient Conditions

3.8.1 Introduction

Ambient conditions can play a significant role inthe determination of what type of drainagestructure and/or controls may be adopted at agiven location. Structures and controls that areappropriate in one part of the state may not besuitable in other areas. This is also true for theprevention of erosion.

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Table 3.13 Key Environmental Authorities for Protection of Fauna

Species Type Relevant Authority Relevant LegislationMacropods • Environmental Protection Agency • Environmental Protection Act 1994

• Nature Conservation Act 1992• Nature Conservation (Wildlife)

Regulation 1994

Ground dwelling mammals, • Environmental Protection Agency • as abovereptiles and amphibians,ratites, chiropteras

Fish and other aquatic • Department of Primary Industries • as abovefauna (Fisheries) • Fisheries Act 1976

• Sunfish• Qld Fisheries Management Authority

Five different types of ambient condition areidentified below. For each type, designconsiderations have been provided to assist thedesigner in selecting drainage controlsappropriate for the conditions.

Design considerations for different ambientconditions (not identified here) will be added inthe future.

3.8.2 Specific Design Criteria

3.8.2.1 Arid Areas

Key drainage design criteria in arid areas mustfocus on three issues. These are:

• A lack of reliable water;

• Protection of the drainage asset; and

• Expansive soils.

A lack of water will affect the ability to revegetatean area. Hence, the retention of existingvegetation is of paramount importance. Theestablishment of new vegetation should only beconsidered where there is a high probability of

success. Key considerations include soil structureand velocity of flow.

Protection of the drainage asset may be requiredwhere soils are highly mobile or erodible. That is,if soils are mobile upstream and downstream ofthe asset, emphasis on stabilisation of the assetmay be required, rather than prevention of anexisting phenomena.

Expansive soils are also present throughout aridregions. The Department of Main RoadsTechnical Guideline WQ37 “Drainage Structureson Expansive Soils in Western Queensland”should be referenced. Options presented in thisguideline include:

• Replacement of foundation material whereexpansive;

• Use of short span bridges on piles; and

• Use of several banks of culverts across afloodplain rather than a single large bank ofculverts.

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Table 3.14 Confirmed Use of Culverts or Underpass Types by Fauna

Fauna Type Small pipe Large pipe Small box Large box Bridge<0.5m dia >0.5m dia culvert <1.2 m h culvert >1.2m h underpass

Small mammal � � � � �

Medium mammal � � � � �

Large mammal � � � � �

Semi-arboreal mammal � � � � �

Arboreal mammal � � � � �

Microchiropteran bats � � � � �

Reptile � � � � �

Bird � � � � �

Amphibian � � � � �

Introduced predator � � � � �

Source: Queensland Department of Main Roads, 2000.Caution: This table is based on preliminary research only. Although not confirmed at the time, fauna should passthrough all the culverts larger than the minimum ones shown. Recommended minimum sizes for design are shown inSection 4.2.2.3 of this Manual.

Other criteria for consideration in aridenvironments include:

• Planning of the drainage system. For example,where the provision of roadside drainage wouldrequire the removal of remnant trees,negotiations should be initiated with theneighbouring landholders to have the drainagedirected through their property and into astorage dam or contour drain;

• Soil protection. This is very important given thedominance of erosive soils (eg. sodic soils) inarid areas. Existing groundcover must besubject to minimal disturbance;

• Outlets should be located in undisturbed areas,or designed with appropriate erosionprotection. The concentration of flow ontounprotected areas should be avoided;

• Selection of revegetation species should focuson those types which establish and bind thesoil, and which will grow without regularwatering; and

• Where revegetation is not possible, optionssuch as rock mulching may be required subjectto the availability of material on or close to thesite.

3.8.2.2 Mountainous Terrain

In mountainous terrain, the most common factorinfluencing design is gradient. Issues forconsideration where topography is steep include:

• Control of velocities in roadside drains;

• Limited room adjacent to the road;

• Collection and discharge of water from theupslope side of the road to the downslope side;

• Prevention of erosion at outlets onto steepareas; and

• Need for small scale drop structures, weirs ordrop manholes.

Therefore, the key criteria to be aware of willinclude:

• Providing scour protection or energydissipation (where appropriate);

• Controlling runoff so as not to affect naturalstability; and

• Limiting slope length.

In addition, the potential for high rainfall(particularly in coastal regions) brings another setof issues for consideration, though this isgenerally covered in the rainfall erosivity sectionof Chapter 2 of the manual, and in Section 3.5(Hydrology).

3.8.2.3 Coastal Regions

Coastal regions provide unique conditions andhence require special considerations. Conditionsinclude regular inundation, a corrosiveenvironment and sandy soils (ie. soils with littlecohesion). Coastal environments are also highlysensitive to pollution.

Key criteria to consider in coastal environmentsinclude ensuring that:

• Legal requirements with respect to theprotection of marine environments (eg.protection of fish habitats and marine plants)are met;

• Natural flow systems (eg. tidal exchange) areproperly assessed and will therefore not becompromised;

• Corrosion resistant materials are used;

• Potential Acid Sulphate Soils (typically below5m AHD) are identified and managedappropriately;

• Designs allow for the presence of highlyerodible or mobile materials such as sand; and

• Consideration is given to directing drainage tonatural channels or swales rather than to hardstructures.

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3.8.2.4 Areas of Inundation

Locations subject to regular inundation requirecareful consideration of how drainageinfrastructure will operate under a range of waterlevels. The presence of high and low water levelsrequires significantly different approaches.

When downstream water levels (also known astailwater levels) are high, the hydraulic capacityof a structure may be limited.

When tailwater levels are low, high velocities canresult, thereby maximising the potential forerosion to occur.

It is therefore very important that both cases areconsidered during the design of drainageinfrastructure. Additional details are provided inSection 3.9.

Regular inundation (ie. changing water levels) canalso accelerate the erosion process, through thesaturation of banks, which may then fail as waterlevels reduce.

3.8.2.5 Urban Areas

Urban areas often present many constraints thatneed to be considered in the planning and designof road drainage. Constraints may be present inthe form of adjacent infrastructure (includinghousing) or a limit in available space. In addition,local authorities may have prepared catchment orstormwater management plans, which will affectthe future management of stormwater andwatercourses in the area. Reference should bemade to such plans wherever they exist.

Key criteria to consider in urban environmentsinclude:

• Provision for higher peak flows arising fromuncontrolled upstream development (MostCouncils now require flow increases to bemitigated);

• Assessment of the requirements of anycatchment management plan or stormwatermanagement plan prepared for the watercourse;

• Need for pollution control measures;

• Provision of adequate access for maintenance;

• Minimisation of ground disturbance duringconstruction as urban environments often havelimited space for large control measures such assediment basins; and

• Consideration and control of afflux effects. Inurban environments, there is often arequirement that negligible afflux be generatedupstream of the proposed drainage structure.With respect to afflux, it is important that eachcase is assessed fully in keeping with a riskmanagement approach.

3.8.2.6 Rural Areas

Standard practices for the planning and design ofroad drainage should address most issues that willarise in rural areas. Additional issues may include:

• Awareness of local drainage plans;

• Ensuring crops will not be affected by anincrease in duration of inundation;

• Maintaining free drainage, and not causingponding of low flows; and

• Considering seasonal variations in hydraulicroughness linked to changes in vegetationcover.

3.9 Selection of DrainageInfrastructure

3.9.1 Introduction

This section provides guidance towards theapplication of hydraulic criteria with respect tothe selection of drainage measures and focuses onthe selection process for cross drainage structures.

Information is also provided in relation to thosetypes of measures where a decision must be madeon the type of lining required. This is relevant formeasures such as open channels, floodways, andbank protection.

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Finally, details are provided with respect to theincorporation of pollution controls into thedrainage system.

The selection of drainage infrastructure requiresthe user to follow a particular process, in order toensure that all relevant criteria have beenconsidered in making a selection. This process isdiscussed in the following sections.

3.9.2 Factors AffectingSelection of DrainageInfrastructure

A summary of those factors used in selecting theappropriate size and type of drainage structure isprovided below. Relevant factors include:

• The desired level of serviceability or immunity(this defines the relevant ARI);

• Discharge (for the nominated recurrenceinterval);

• Alignment of the road (influences the locationof both longitudinal and cross drainage);

• Topography (including stream geometry);

• Allowable headwater levels (or afflux);

• Soil types (potential for scour);

• Incidence and nature of debris (influencesdecisions relating to size and structuralconfiguration);

• Environmental factors (as identified in the siteassessment and REF); and

• Provision for maintenance.

3.9.3 Drainage Decisions

The following sections of the manual containspecific advice in relation to the selection ofcertain types of drainage structure.

Descriptions provided in the section are supportedby Table 3.15, which is provided at the end of thesection.

3.9.4 Culverts

3.9.4.1 Culverts or Bridge

For the majority of designs, it will be obvious asto whether a bridge or culvert is required at agiven location. This decision will be made on thebasis of serviceability, existing bank height,potential for debris, and in some cases, the need toallow for the passage of large fauna and onwhether the stream is active or not. In the case ofan active stream, building a bridge will be easierand will have less impact on the environment.

In highly reactive or expansive soil conditions orwhere large differential settlements are expectedto occur, culverts should be limited to base slabsnot greater than 10 metres long. This may in someinstances lead to a decision to provide a bridgestructure, provided a clearance of at least 1.2metres is available to the underside of the bridgedeck. Specialist advice should be sort in theseinstances.

3.9.4.2 Culvert Size

The size of culvert required will be dependent ona range of criteria, as discussed previously in thischapter. The choice of culvert size is heavilyinfluenced by the permissible afflux (or headwaterlevel), the likely depth of flow, watercourse shape(ie. channel or floodplain) and, in some cases, theneed to cater for fauna passage, pedestrian orbikeway access, or cattle creeps.

Additional details for sizing culverts are providedin Section 4.2.2 of Chapter 4.

3.9.4.3 Culvert Type

The selection of culvert type is closely linked tothe determination of size, and hence both must beconsidered jointly. In many cases, a number ofiterations will be required before culvertdimensions can be finalised. For the preliminarydesign phase of a project, initial size estimates canbe determined on the basis of permissible velocityand afflux/headwater level.

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Table 3.15 Preliminary Selection of Drainage Infrastructure

Selection Issue Factors Decision

Culvert Type • waterway geometry Box culverts may be favoured:• flat topography • where there is minimal available waterway area.• fauna passage • where insufficient headroom or cover exists to allow pipes.

• for floodplains, or where depths of flow will be low.• where a culvert is to be utilised for the passage of people or large

animals.

Culvert Location • road alignment • Desirable skew is 0° (ie. no skew).• geomorphology • Skew of culvert should not be any more than 45°.

• Do not locate culverts on the bends of actively moving watercourses.

Environmental • sensitive flora or fauna • Consider a bridge rather than culverts.Sensitivity • permanent stream • Control pollutant runoff.

• Maintain a natural stream bed.• Minimise disturbance of bed and banks.• Control runoff during construction.

Need for • soil type • Where dispersive soils are present, a barrier must beChannel Lining • limited available width placed between flowing water and the soil. The barrier can

• steep gradient consist of topsoil and vegetation, blankets, or a permanent• velocity lining such as rock with filter cloth.

• Velocity reductions will often allow a cheaper or more naturallining to be utilised. Velocity reductions may be achieved througha flattening of channel gradient where there is sufficient roomavailable to compensate for the larger flow width. A flattening ofgradient can be achieved through the incorporation of checkdams, drop structures, or a change in alignment.

Type of Bank • soil types • Revegetation. Planting of riparian vegetation is favoured, Protection • flow velocity but there must be a sufficiently high proportion of the bank (where velocities covered to ensure stability during flows.are considered • Erosion Mats. Long term stability will need to be addressed.excessive) • Rock Riprap. Must be properly designed, to ensure diameter and

thickness of rock can cope with design velocity.• Gabions. Can be used on steep banks, but can fail if water gets

between gabion and bank.• Grout Mats. Flexible but will not provide good habitat.• Concrete. Usually a last resort, and would normally only be

utilised where sustained high velocities are likely, and space isconstrained.

Use of Swales • space Swales may be used where:(vs lined table • rainfall • There is sufficient space, and where grade is sufficient to preventdrains or kerb & • water quality permanent ponding of water.channel) • Regular rainfall or watering will occur.

• Water quality benefits are desired.

Need for Outlet • outlet velocities Outlet protection may be required where outlet velocities areProtection • soil type sufficient to cause erosion. Management options include:

• erosion risk rating • reduce gradient;• replace or cover dispersive soils;• reduce velocities through dissipation (subject to safety

considerations);• provide protection.

In addition, ambient conditions can dictate thesuitability of certain culvert types. For example,in corrosive environments (eg. coastal regions),some types of culverts will not be appropriate.(Refer Section 3.8.)

Additional details for selecting culvert types areprovided in Section 4.2.2 of Chapter 4.

3.9.5 Bank Protection andLinings

The choice of bank protection or channel lining(whether natural of artificial) is relevant to thedesign of open channels, chutes, floodways andswales. The decision as to which type of lining isthe most appropriate for the site is dependent onfactors such as soil type, potential for vegetationgrowth, available space and velocity.

Table 3.3 and Chapter 4 Tables 4.5 and 4.9 allprovide indications of permissible velocities fordifferent types of materials.

3.9.6 Longitudinal Drainage

Site constraints and design standards dictate that itis not always possible to choose betweenalternative longitudinal drainage options such askerb and channel, grassed swales, and lined orunlined table drains.

In urban environments, kerb and channel hashistorically been favoured for most roads, thoughgrassed channels are also common on dividedroads.

In rural areas, earth drains are more common.

However, in some cases it will be possible tochoose between the above alternatives. When achoice is available, the designer will need toconsider the following questions:

1. What is the gradient of the channel?

2. What is the available flow width?

3. Is there a need to improve water quality?

4. Will vegetation survive in this area?

5. Will the proposed type of longitudinal drainagerequire regular maintenance?

Responses to the above questions will dictate thefeasibility of the available choices, as discussedbelow.

1. Steep gradients will allow narrower drainagechannels to be used, but can lead to highvelocities, which in turn may require liningswith higher resistance to erosion.

2. The flow width for any option must becompared to the available width forlongitudinal drainage. Flow width is dictatedby gradient, shape of the drainage path, andManning’s roughness of the flowpath.

3. Where water quality improvement is required,use could be made of grass swales, rather thanan impervious lining. For grass swales to be aviable option, there must be sufficient room tocater for shallow flow (refer Section 4.6), andthe designer must consider issues relating to thesurvival and maintenance of the proposedvegetation (see below).

4. In arid areas, it is often not practical to design aflowpath that is reliant on the existence ofvegetation to provide protection to soils. Onlyvegetation suited to the climate of the regionshould be considered.

5. As with all types of drainage and pollutioncontrols, a lack of maintenance will lead tofailure of the design. In those locations wheremaintenance may not be readily available, itmay be necessary to propose a lowmaintenance solution.

In all cases, there is an increasing trend in urbanareas, to adopt a ‘water sensitive’ approach, todrainage design.

3.9.7 Location

For major drainage infrastructure, such as culvertsor bridges, the location of a structure can have asignificant bearing on both environmental impactsand stability. This is also true of several other

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types of drainage infrastructure, including openchannels and drop structures.

Location should be a key design criteria in thoseareas where:

• the watercourse is not stable;

• bed or bank erosion may result from thepresence of new infrastructure;

• soils are highly erodible;

• the area has high environmental sensitivity;

• bed slopes are steep; and

• the face of a structure is not perpendicular tothe watercourse.

Where potential problems have been identified, itis important that:

(a) an alternative location or alignment isidentified; or

(b) appropriate protective measures are put inplace to prevent or mitigate the potentialimpacts.

Option (a) should be the first preference, but willnot always be possible in areas where thealignment is fixed.

In those instances where a river or creek isobviously active (eroding or accreting), ageomorphic analysis may be required.

Reference may also be made to Table 3.15.

Example:

A proposed new road will cross Sandy Creek at apoint where the creek has active bank erosionowing to the existence of a meander. A series ofbox culverts are proposed at this location. Thefollowing courses of action could be considered:

1. Propose a local realignment of the road suchthat the crossing of Sandy Creek will occur at astable location; or

2. Stabilise the meander if constrained for space;or

3. Consider realignment of the creek away fromthe proposed crossing.

Option 1 would be favoured wherever possible,with Option 2 (and the use of a “soft” engineeringapproach) another alternative. The use of “hard”solutions (eg. riprap lining) or creek realignmentis often not favoured, as changes to the creek atone location will often transfer problems to othernearby locations.

AUSTROADS (1994) provides additionalguidelines in relation to the siting of drainageinfrastructure. These guidelines, which will alsominimise the potential for damage to theinfrastructure, are reproduced below.

To minimise environmental impacts the culvertsshould be located:

• Where satisfactory geological and soilconditions exist;

• Away from reaches of highly unstable channel;

• Where possible adverse effects on otherexisting bridges and hydraulic structures can beavoided;

• Where it is possible to minimise the hazardsfrom floods, landslide, cyclones, earthquakeand subsidence;

• Where river banks are stable;

• Where ecological impact is acceptable; and

• Where aesthetic considerations are favourable.

3.9.8 Water Quality

When water quality (pollution) control devicesare required as part of the road drainage system,additional considerations must be taken intoaccount.

For example, the hydraulics of the drainagesystem may not be conducive to efficient pollutantremoval, or conversely, the proposed pollutioncontrol device may compromise the hydraulicefficiency of the system.

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Questions that must therefore be addressed whenincorporating water quality controls into adrainage system include:

• Does the device require a large hydraulicheadloss to operate?

• Will the device lead to upstream flooding in flatareas?

• Is the gradient of the system too steep (resultingin high velocities) to allow effective pollutantremoval?

• Can the device be accessed for maintenancepurposes?

Examples of design implications are offeredbelow:

• Wetlands or sediment basins may not operateeffectively if subject to high velocities duringflood events. A high flow bypass is oftenrequired.

• When trash racks are installed, provision mustbe made for high headlosses associated withblockage of the racks. In this case,consideration of the potential for flooding ofupstream property must also be assessed.

• Pollution control devices placed in areas withhigh tailwater levels may not operate,particularly where there is reliance on a floatingboom to trap litter.

Reference should also be made to Section 3.10.

3.10 Pollution Control

3.10.1 Introduction

A key environmental consideration in relation toroad runoff is pollutant export and the resultantimpact on water quality. Runoff from roadcorridors has the potential to adversely effect thewater quality and aquatic biota of receivingwaters. Impacts may be short or long term.

Wetland area

For a given project, the significance of pollutantexport will depend upon the relative sensitivity ofthe receiving environment, the type and level ofvehicle use and climatic factors experienced in thelocality. The identification of appropriatereceiving water quality objectives from theREF/IAS can influence design criteria for theselection of appropriate drainage infrastructure tomaintain or enhance downstream waterways. Thisin turn may determine the need for pollutioncontrol.

An overview of the steps to be taken, whenpollution control is required, is provided in thefollowing section. Completion of these steps willresult in determination of additional designcriteria that will then influence the selection ofappropriate drainage infrastructure.

3.10.2 Selection Process

The selection and implementation of stormwatertreatment measures involves six major steps.These are:

1. Ascertain environmental issues and waterquality objectives - Identify the sensitivity ofthe receiving environment, appropriate waterquality objectives for the receiving waters andestablish the key design criteria; (eg. to reducethe impact of sediments and heavy metals).

2. Identification of Pollutant Sources andEstimation of Pollutant Loads - Identifypollutant sources and determine pollutant loadsfrom the road corridor to resolve the type andamount of pollutant to be removed (if any).

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3. Identify pollutant transport processes -Identify pollutant transport mechanisms toassist in identifying appropriate capture andcontrol devices.

4. Assess potential pollutant control devices -Identify all applicable treatments on the basisof key site selection criteria. Each stormwatertreatment measure can be accepted or rejectedon the basis of each screening criteria.

5. Assess potential pollutant removal - Compareall potential treatments on the basis ofachieving key treatment objectives.

6. Optimise Potential Treatments - Identify andevaluate tradeoffs between desired treatmentobjectives and key site selection criteria.Determine the most appropriate stormwatertreatment method(s) for achieving objectives.

Step 1 - Identify Environmental Issues andWater Quality Objectives

From the REF/IAS the sensitivity of the receivingenvironment and the potential impact of the roadcorridor will have been identified.

Traffic volumes and heavy vehicle content willhave been identified in the planning report. Thisinformation, in conjunction with the water qualityrequirements documented within the EMP(Planning), will assist in identifying and selectingappropriate key water quality objectives anddesign criteria. These may include objectives suchas:

• capture of gross pollutants upstream of asensitive waterbody; and

• discharges from sediment basin to achieveANZECC water quality levels owing to thesensitivity of downstream aquatic ecology.

Most environmental protection agencies tend torely on the Australian Water Quality Guidelinesfor Freshwater and Marine Waters (ANZECC,2001) developed by the Australian and NewZealand Environment and Conservation Council.These guidelines generally are used as the defaultframework for setting water policy objectives formanaging water resources on a sustainable basis.

The updated guidelines published in 2001 providewater quality trigger values for slightly disturbedAustralian ecosystems, as a function of theecosystem location and the ecosystem type. If apollutant concentration exceeds its trigger value,it will have the potential to cause environmentalharm, and a management response will be set off,or “triggered”. Table 3.16 provides examples ofwater quality trigger values for typical pollutants(nutrients, suspended solids and salts) for variouslocations within Australia and various types ofslightly disturbed ecosystems.

Step 2 - Identify Pollutants and PollutantLoads

Common sources of pollutants in road runoff thatmay adversely effect the downstreamenvironment have been identified in theCalifornia Storm Water Best ManagementPractice Handbook (CDM, 1993). Table 3.17 hasbeen adapted from this reference to representtypical pollutant loads from road corridors.

A review of the project REF/IAS should beundertaken to identify relevant runoff pollutantsfrom the project corridor.

Road pollutant loads can be estimated by:

• analysis of data from a good storm-eventmonitoring program;

• simple computations; and

• an appropriate water quality model.

The method selected will depend on themanagement objective and data availability.Average long-term pollutant loads can beestimated from rainfall data and from simpleinformation about the catchment and roadcorridor. These estimates provide an indication ofthe long-term inputs.

Typical errors in estimating long term pollutantloads are as follows:

• no monitoring - 100 to more than 1,000percent;

• some periodic monitoring - 50 to more than 500percent; and

• detailed event monitoring - 20 to 100 percent.

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Table 3.16 Examples of water quality trigger values for typical pollutants (nutrients, suspended solids andsalts) for various locations within Australia and various types of slightly disturbed ecosystems

PollutantsLocation and TN TP Turbidity Salinity

Ecosystem Type (µg/l) (µg/l) (NTU) (µS/cm)

South East Australia

Upland river 250 20 2-25 30-350

Lowland river 500 50 6-50 125-2200

Freshwater lakes and reservoirs 350 10 1-20 20-30

Wetlands no data no data no data no data

Estuaries 300 30 0.5-10 n/a

Marine 120 25 0.5-10 n/a

Tropical Australia

Upland river 150 10 2-15 20-250

Lowland river 200-300 10 2-15 20-250


Wetlands 350-1200 10-50 2-200 90-900

Estuaries 250 20 1-20 n/a

Marine 100 10-15 1-20 n/a

South West Australia

Upland river 450 20 10-20 120-300

Lowland river 1200 65 10-20 120-300


Wetlands 1500 60 10-100 300-1500

Estuaries 750 30 1-2 n/a

Marine 230 20 1-2 n/a

South Central Australia

Upland river no data no data 1-50 100-5000

Lowland river 1000 100 1-50 100-5001


Wetlands no data no data no data no data

Estuaries 1000 100 0.5-10 n/a

Marine 1000 100 0.5-10 n/a

TN = Total NitrogenTP = Total PhosphorusNTU = Notional Turbidity UnitsµS/cm = Conductivity of water in micro siemens per centimetre

Table 3.17 Common Sources of Pollutants in RoadRunoff (Chiew et al, 1997)

Pollutant SourcesSediment/ Bitumen wear, vehiclesParticulatesNutrients Roadside fertiliser and herbicideBacteria and Source not commonVirusesOxygen Demand Road litter, organic debrisOil and Grease Lubricants and motor fluids (spills,

leaks etc)Heavy Metals Cr, Cu, Pb, Zn, Fe, Cd, Ni, Mn -

emissions, lubricants, corrosion,wear of tyres (filler), bearings,brakes, asphalt, clutch.

Toxic Materials Fuels, herbicides, pesticides, fuelcombustion

Floatables Gross Pollutants (eg. paper,plastics, bottles)

Event Based Monitoring

Event mean concentration (EMC) can beestimated by monitoring pollutant concentrationand discharge over a storm event. EMC withinone catchment can however differ significantlyfrom storm to storm. The EMC depends oncatchment and climate characteristics, and canvary by more than one order of magnitudebetween catchments. A good event-monitoringprogram is essential where accurate estimates ofpollutant loads are required.

Simple Computations

In absence of reliable field data, the range ofvalues presented by Mudgway (1997), Drapper(2001) and McRobert (1997) can be used as aguide to calculate approximate estimates ofpollutant loads.

The average long-term pollutant load of an areacan be estimated using:

pollutant load = runoff × EMC

where EMC = event mean concentration.

Water Quality Modelling

Computer models may be used to estimate runoffquantity and quality from a road corridor toprovide estimates for:

• characterising peak, mean and average annualpollutant loads;

• determining seasonal and spatialcharacteristics;

• study land use change;

• provide inputs to water quality managementmodels.

However, in the absence of reliable data, waterquality models are potentially no better thanestimates calculated using simple analysistechniques.

Drapper (2001) has evaluated the FHWAprediction model from the USA and hasdisregarded the use as a tool for predicting runoffpollutant concentrations. A prediction program iscurrently being developed that may assist indetermining appropriate pollutant loads.

Step 3 - Identify Pollutant TransportMechanism

The determination of additional design criteria toenhance or maintain the downstream waterquality will require the knowledge of relevantpollutant transport mechanisms.

Pollutant runoff from a roadway will be generallytransported by the roadway drainageinfrastructure and will concentrate in gutters,pipes and channels. The pollutants associated withthe stormwater runoff will be transported ascoarse or bottom sediments, suspended particlesor in solution. The rate of pollutant transport isdependent on water velocity, depth and the degreeof turbulence.

Fine particulates and dissolved pollutants canbecome attached to sediments, or flocculate toform larger particles. Most of the pollutants insediments are found attached to smaller particlesowing to their greater surface area relative tolarger particles. Pollutants attached to fineparticles are easily transported because smallflows (and hence low velocities) are sufficient tomobilise and keep them in suspension.

Heavy metals from motor vehicles either directlyfall onto road surfaces or become entrained in air

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flows and deposited some distance awaydepending on their particle size. Particulatematerial on the road surface such as bituminousproducts, rubber from tyre wear and particlescoated with oils, actively absorb heavy metals.The particulates and the associated heavy metalstemporarily bind themselves to the road surfaceuntil they are transported by rainfall runoff events.

Heavy metals contained in road runoff will bedistributed in either bound or soluble forms.Chromium, iron nickel, lead and hydrocarbons arepredominantly absorbed to particulate matterproviding an opportunity for removal bydeposition of sediments. Cadmium, copper andzinc appear at higher percentages in the solublephase and thus are required to be removed bystorage and/or uptake by aquatic biota. (Petersonand Batley, 1992).

Step 4 - Identify Required Pollutant TreatmentProcesses

Stormwater quality improvement measures relyon a range of mechanisms for reducing pollutantlevels within stormwater. The mechanismsemployed may be either or a combination ofphysical, chemical or biological process and theireffectiveness may be dependent on the siteconditions and stormwater characteristics.Stormwater improvement devices can be groupedinto three different categories based on theirdominant treatment processes. These categoriesare:

Primary Treatment - Physical screening or rapidsedimentation techniques (eg. typically retainedcontaminants include gross pollutants and coursesediments).

Secondary Treatment - Sedimentation of finerparticles and filtration/chemical techniques (eg.Typically retained contaminants consist of fineparticles and attached pollutants).

Tertiary Treatment - Enhanced sedimentation andfiltration, biological up-take adsorption ontosediments (eg. typically retained contaminants arenutrients and heavy metals) (Vic EPA, 1998).

In many circumstances a combination oftreatment mechanisms is required to optimise and

achieve the appropriate water quality objectives.The treatment measures may include primary,secondary and tertiary treatment measures usingan ‘outlet’ or ‘distributed approach’.

The outlet approach involves a single treatmentat the road corridor catchment outlet thatdischarges directly into the downstreamenvironment. The distributed approach requiresa number of smaller and potentially differenttreatments throughout the road corridor catchmentbefore discharge to the downstream environment.

The selection of the treatment controls for a roadcorridor catchment under consideration willdepend on a wide range of key selection criteria toenable achievement of the water quality objective.

The selection of the most appropriate stormwatertreatment methods should be assessed against anumber of key selection criteria (eg. catchmentarea, slope etc). Common key site and operationselection criteria are defined as follows:

• Slope: Treatment devices that do not store flowmay require small velocities and hence gentleslopes;

• Hydraulic Head: Head losses in treatmentdevices can exert a minor to large impact uponthe hydraulic grade line. As a result head lossesfrom a treatment device may adversely impactupon upstream flood levels particularly whenretrofitting a device into an area;

• Soil Type: Differing treatment devices may bereliant upon either infiltration or storage ofstormwater runoff. For instance, stormwaterinfiltration will yield better results on highlypermeable soils, whilst the storage ofstormwater will require soils with very lowpermeability.

• Land Availability: The availability ofsufficient appropriate land within a sub-catchment that can be used for a treatmentdevice may be restricted, thereby reducing thesize and effectiveness of the device;

• Habitat Enhancement: Treatment devices thatare able to offer either a wildlife and/or aquatichabitat enhancement may improve aesthetics;

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• Water Table: A high water table depth mayreduce the effectiveness for a treatment devicerelying on infiltration;

• Safety Hazard: Treatment devices mayintroduce new safety hazards that may have notbeen present before installation;

• Water Supply: Treatment devices such aswetlands or ponds may require a permanentwater supply to ensure the long termeffectiveness of the device;

• Pests: Treatment devices such as wetlands orponds may increase the potential for nuisancefrom pests such as mosquitos and weeds; and

• Maintenance: Treatment devices will varysignificantly with regard to their maintenancecost, accessibility, equipment and scheduling toensure the desired effectiveness is consistentlymaintained.

Step 5 - Assess Potential Pollutant ControlDevices

Assess each potential pollutant control device tomeet key site conditions. Each pollutant controldevice can be accepted or rejected on the basis ofscreening criteria to provide a short-list. Table3.18 provides the suitability of common treatmentcontrol devices based on common key siteselection criteria.

Trash Rack and Pollutants

Step 6 - Assess Potential Pollutant Removal

Conduct final selection of potential pollutantcontrol devices on the basis of achieving keytreatment objectives. The final screening can be

achieved by comparing all potential treatments asfollows:

1. Determine the pollutant removal of each short-listed control device based on relevantperformance data or Tables 3.19 to 3.21 (eg.target 90% reduction of Pb through pollutantcontrol device).

2. Determine the area of the catchment for whichthe device(s) can treat runoff.

3. Factor the mean removal rate of each pollutantparameter by the ratio of area treatable by thedevice to total catchment area. ie. if a pollutioncontrol device has a 60% removal efficiencyand will treat 50% of the catchment area thenthe overall pollutant removal efficiency will be30%.

Step 7 - Optimise Potential Treatments

Determine the most appropriate stormwatertreatment control devices(s) for achieving keyperformance objectives. Repeat steps 4 and 5 untilan appropriate system of treatment controldevices has been proposed that will achieve thecorresponding performance objective. Identifyand evaluate tradeoffs between desired treatmentobjectives and key site selection criteria tooptimise the use of treatment control devices.

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Table 3.18 Site and Operation Selection Criteria Associated with Treatment Device

Pollutant Area Slope Head Soil Capital Maintenance GeneralControl Served Require- Type Costs Cost ConfigurationDevice (ha) ments

Oil Grit <1 Note 1 Low NA Moderate ModerateSeparators

Open Gross >2 Note 1 High NA High Moderate-Pollutant Trap <40 High

Closed Gross <15 Low NA High ModeratePollutant Traps

Trash Rack <20 Note 1 Low- NA Moderate Low-40 Moderate Moderate

Downwardly Note 1 High NA Moderate- Low-inclined Screen High Moderate

Extended >5 Note 1 Low All High Moderate- Outlet structures Detention High include weirs or

outlet pipes. Energydissipater at bothbasin inlet and outletto control velocities.

Sand Filter <2 Note 1 High Generally High Moderate- Min filtration depth of can be housed in High 400mm dependent

designed concrete on recommended larger filtration time. Energy

dissipater at inlet.

Filter Strips <2 Note 1 Low All Moderate Low Requires Considerable Land.Length of stripgenerally>6m.

Buffer Zones Note 1 Low All Moderate Low

Grassed <2 <5% Low Sand to Moderate Low Recommended min Swales clay loam length of 30m.

feasible Bottom width Can be used between 0.6m to

in clay 2.5m recommended.

Constructed Note 1 Low- Loam to High Moderatewetlands Moderate clay

Feasible insand to

sandy loam

Water quality >5 Note 1 Low- High ModeratePonds Moderate

Note:1. From 0 - 5% slope preferred but the range can be extended beyond 5%. Buffer zones should only be extended

beyond 5% with careful design.

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Table 3.19 Pollutant Removal Performance of Typical Primary Treatment Devices

Treatment Pollutant Removal Efficiency (%)Control Coarse Fine Phosphorous Nitrogen Oil & Bacteria Litter

Sediment Sediment TP TN Grease

Oil Grit 50-75 10-50 0-10 0-10 50-75 0-10 10-50Separators

Gross 60-100 20-30 20 20 10-20 0-10 50-75Pollutant Trap

Trash Rack 10-50 0-10 0-10 0-10 0-10 0-10 10-50

Derived from: NSW EPA (1997) and Mudgeway et al (1997).

Table 3.20 Pollutant Removal Performance of Typical Secondary Treatment Devices

Pollutant Removal Efficiency (%)Treatment SS Phosphorous Nitrogen Pb Zn Cu Cd Fe BOD COD Bacteria Sample

Control SizeTP org.P sol.P TN org.N sol.N

Extended 50-75 10-66 10-35 70-90 24-62 20-41 50-90 6Detention studies

Sand 60-90 35-80 40-70 -110-0 65-90 10-80 20-60 60-80 35-70 3Filter studies

Filter 5-95 50-79 50-73 10Strips studies

Buffer 100 95 1Strips study

Grassed 4-25 8-24 -4-11 -4-13 -5-22 0-91 34-90 14-60 20-50 3-67 7Swales studies

Legend: SS = Suspended Solids.Shading denotes median value.

From Mudgeway et al (1997).

253529507080954161580

62626674

5370405374<0555780

70304583191864

Table 3.21 Pollutant Removal Performance of Typical Tertiary Treatment Devices

Pollutant Removal Efficiency (%)Treatment SS Phosphorous Nitrogen Pb Zn Cu Cd Fe BOD COD Bacteria SampleControl Size

TP org.P sol.P TN org.N sol.N

Constructed 40-98 -33-97 0-75 -9-43 13-90 6-94 -29-97 40-99 33-99 12-62 18-34 28Wetlands studies

Water 39-98 0-80 70-80 30-85 14-20 24-60 9-95 0-71 0-69 20-70 90-95 13Quality studiesPonds

Legend: SS = Suspended Solids.Shading denotes median value.

From Mudgeway et al (1997).

9330441740516842176075205169

263766665072503225595081

3.11 Erosion and SedimentControl

3.11.1 Introduction

This section provides the user with guidance andtools to facilitate the selection of appropriateerosion and sediment control measures. Referenceto soil types and erosion risk from Chapter 2 willbe required.

The primary tool to be used is a selection matrixshowing the types of permanent and temporarycontrols that can be used to minimise damage tothe environment during runoff events.

The matrix may be used to provide a preliminaryindication of which controls will be most suitablefor a given location, in accordance with the resultsof the site and erosion risk assessments.

Detailed design can then be undertaken using therespective guidelines provided in Chapters 4 and5.

3.11.2 Review of Data

The need for erosion and sediment control willhave been identified in the REF/IAS andsubsequent erosion risk assessment processoutlined in Chapter 2. The information whichshould be available will include details of areas ofthe environment considered vulnerable toenvironmental harm and information pertaining tothe nature of potential erosion and sedimentationrelated impacts.

Depending on the scale of the project, requiredinput from Chapter 2 and the project REF/IASshould include:

• a map of soil types and their erosion potential;

• an erosion risk rating for specific areas withinthe site;

• climate and stream flows;

• topography and natural geographical features(eg. is the site within a floodplain);

• proposed changes to the site topography foreach stage of the project including extent of cutand fill batters;

• a map of existing vegetation identifying areasto be retained;

• details of areas of cleared land at each stage ofthe development, and the period of time thateach area will be exposed for;

• calculation of stormwater flows within micro-catchments within the site, for each stage of theproject; and

• nature and location of works that will occur inclose proximity to natural waterways or othersensitive environmental areas (eg. wetlands).

3.11.3 Select Design Standard

In many cases, erosion and sediment controls arenot designed to a specific standard. Instead, theyare located on site in keeping with the size of thecontributing catchment, available materials, thephysical constraints of the site and a maintenanceschedule.

However, in particular circumstances, such aswhen a site is considered highly erodible, or whenworks are being proposed in an area of highenvironmental sensitivity, a specific designstandard may be required.

Factors dictating the required standard willinclude:

• erosion risk rating;

• environmental sensitivity; and

• duration of construction.

Selection of the appropriate design standard canbe made by:

• referring to Table 3.22, or

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• use of the following equation (Hunt 1992).

where:

ARI = design average recurrence interval (yr)

L = design life (yr)

P = acceptable probability of exceedance(fraction)

ln denotes natural logarithm

For selection of a design standard for sedimentbasins, reference should be made to Section 4.7 ofthe manual.

3.11.4 Select Controls

3.11.4.1 Introduction

A selection matrix has been prepared to assist thedesigner in selecting erosion and sedimentcontrols appropriate to the environmentalconditions of the site and the proposedconstruction program.

It should be noted, however, that this tool is aguide only and the most appropriate controlmeasures may not be fully identified untilconstruction commences and measures areimplemented.

The user should identify each of the following forthe project site:

• erodibility rating/soil type;

• areas of suitability;

• flow type; and

• life of control.

With an indication of the measures most suitablefor the site conditions, detailed design may thenproceed.

3.11.4.2 Erodibility Rating/Soil Type

Erodibility ratings and general soil types of theproject site should have been determined duringthe Chapter 2 site assessment process. Theseshould be reviewed as well as soil/erodibilitymaps for the site.

P)]-(1 [-ln

L= ARI

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Table 3.22 Suggested Design Average Recurrence Intervals for Various Erosion and Sediment ControlMeasures on Construction Sites (Hunt, 1992)

Estimated Design Life (during construction phase)Design ARI (years)

Control Measure 0 - 12 mths 12 - 48 mths > 48 mthsDiversion Bank 1-10 10-20 *Level Spreader 1-10 10-50 *Waterway 1-10 10-50 *Sediment Basin• primary outlet 1-5 5-10 *• emergency outlet 10-20 20-100 *Sediment Trap 1-5 5-20 *Outlet Protection 1-20 20-100 *Grade Stabilising Structure 1-20 20-100 *Detention Basin• primary outlet 1-5 5-10 *• emergency outlet 10-20 20-100 *

* Full design required in accordance with Major/Minor concept (see ARR, 1987 - Section 14.5).

A review of this information will provide the userwith an understanding of the major soil types anderodibility of the site and thus application to theselection matrix.

3.11.4.3 Areas of Suitability

A description of the different types ofenvironments that can affect the selection oferosion and sediment control measures wasprovided in Section 3.8, Ambient Conditions.

The user should assess the control measuresagainst the constraints imposed by thesurrounding environment to gain anunderstanding of the most suitable measures forthe site conditions.

3.11.4.4 Flow Type

The type of flow present will influence both thepotential for erosion and the type of measure toprevent erosion.

Sheet flow occurs as a relatively uniform depth ofwater in the form of a surface ‘sheet’. This type offlow is often characteristic of flat to gentlysloping sites where flow would not tend toconcentrate.

Concentrated flow occurs where depressions areeroded and flow concentrates. It often forms aftersheet flow has travelled some distance. Steep siteswill tend to feature concentrated flow at mostlocations.

3.11.4.5 Life of Controls

Erosion and sediment control measures may betemporary or permanent. The selection of controlswill therefore be dependent on site conditions,duration of construction and available materials.

Temporary measures are often designed,implemented and maintained during construction.They provide temporary protection whilst the siteis exposed to erosive elements, until morepermanent protection is constructed.

Permanent measures provide permanent drainage,velocity, erosion and/or sedimentation control

post construction. They often require formaldesign (refer Chapter 4) and are normally morecostly.

Maintenance of all temporary and permanentmeasures is required to ensure they function tomaximum capability.

3.11.4.6 Hierarchy of Measures andSelection Table

Erosion and sediment control measures listed inTable 3.23 have been grouped into fourcategories. These are:

• drainage control;

• velocity control;

• erosion control; and

• sediment control.

Where practical, the selection of controls shouldfocus primarily on prevention (ie. control ofdrainage, velocity and erosion) prior toconsideration of sediment controls.

3.12 Design References

Additional design information may be obtainedfrom IEAust Australian Rainfall and Runoff(1987), QUDM(1993), Department of MainRoads Hydraulics Training Course (1996),EPANSW Treatment Techniques (1997),Mudgeway et al. (1997).

In many cases, the most effective (andpractical) approach will involve the sitingand design of temporary controls to allowconversion to a permanent measure. Thisshould be investigated as part of the designprocess for all permanent measures.

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June 2003 3-53


3

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.

Appendix 3A:Computer Models

3A.1 Introduction

Computer models are extensively used in all areasof hydrology and hydraulics. These models havethe capacity to allow the design or assessment ofcomplex systems in a much shorter time thanmanual methods. Areas for which mathematicalmodels are routinely used include:

• the estimation of design rainfall;

• the estimation of discharge;

• the sizing and assessment of culverts;

• the design and assessment of pipe networks;

• the design and assessment of open channels;

• the estimation of afflux;

• prediction of flood heights; and

• assessment of the impacts or capacity ofproposed hydraulic structures.

3A.2 When to Use ComputerModels

For many road projects which are small in scope,the use of mathematical models will not berequired. Manual methods (such as the RationalMethod - refer Section 3.5.3) are available for theprediction of design discharges, and culvertnomographs may be used to size cross drainagestructures. It should be recognised however thatenvironmental issues should also be consideredwhen determining the size of cross drainagestructures.

When projects become large in scale, computermodels are often considered essential.Circumstances where a model is recommendedinclude the following:

1. Where a bridge is proposed in largercatchments requiring more sophisticatedmethodology.

2. Where there are significant natural or manmade storage areas.

3. Where there are complex flooding patterns.

4. Where a proposed road may lead to the creationof higher water levels on the upstream side ofthe roadway, and in particular where existingproperty is considered flood prone.

5. For significant pipe systems.

3A.3 Responsibilities of theProject Manager

The use of models for the above types of projectsusually requires significant time at a computer,and therefore the work is often carried out byjunior staff. Because the nature of many programsmakes it more difficult for a reviewer/checker topick up errors than if a manual analysis had beenmade, the use of computer programs thereforebrings enhanced responsibilities to the designer,the reviewer/checker, and the technicalsupervisor. The term project manager belowincludes the checker/reviewer.

Some of these responsibilities are discussedbelow. Project managers must:

• Ensure that the use of the computer model isappropriate and within the limitations of themodel;

• Ensure that the user has a knowledge of thebasic theory and especially how each parameteris selected or calculated; and

• Ensure that an adequate check is made of theuse of the program and that the final results areacceptable. This may involve review of theinput data, comparison with other results andperhaps, approximate manual calculations.

3A.4 Responsibilities of theDesigner

Designers for whom mathematical modelling isbeing undertaken must:

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3

• Ensure that the theoretical basis and limitationsof the program are known and that suchlimitations are not exceeded;

• Ensure the program is calibrated against knownflood data whenever possible;

• Check the input data progressively as it is putinto the computer program in the knowledgethat it would be very difficult and timeconsuming for a checker/reviewer to find asingle error in perhaps, hundreds or thousandsof numbers put into the program;

• Be fully aware that a single error could give anerroneous answer to a design or a number ofdesigns in an iterative process;

• Ensure that it is clear how a parameter wasselected or calculated even if it is necessary toput this data on a separate design sheet; and

• Summarise key findings and results so thatsuch data can readily be placed in a formalreport, if required or not.

3A.5 Computer Programs

A significant number of different computerprograms are available to assist in the assessmentof all aspects of hydrology and hydraulics.

In all instances, computer software should only beused by those who are suitably qualified andsupervised, as the inappropriate use of softwarecan lead to poor design.

Models may be divided into a number of differentcategories. These include models capable ofanalysing or predicting:

• Rainfall (IFD data);

• Flood frequency;

• Hydrology (runoff-routing);

• Stormwater pipe networks (HGL);

• Culverts;

• Backwater;

• Flood level hydrographs (ie. 1D, 2D, & 3Dhydrodynamic models);

• Sediment transport processes;

• Pollutant export; and

• Water quality.

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Appendix 3B: Checklist

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Design Criteria CHECKLIST

District:

Project Name:

Contract/Project Number:

� Conforms, no action required

�� Non Conformance, requires action

N/A Not applicable

Preliminary Design Criteria

Item Check Action Required Has initial site planning considered the drainage layout within the road environment and the external environment?

Has the project REF/IAS been reviewed and the key environmental influences affecting drainage design identified?

Has Form M2290 Road Infrastructure – Project Proposal, been reviewed and relevant factors influencing drainage design identified?

Design Standards

Item Check Action Required What requirements have dictated the design standard?

Has an Annual Recurrence Interval (ARI) been specified and/or is it influenced by standards of existing infrastructure?

Hydraulic Criteria

Item Check Action Required Has the design discharge been calculated for each proposed drainage structure?

Do the combined set of drainage structures cater for flow from the entire catchment?

Have velocity criteria been specified in terms of existing, desirable, or maximum permissible velocities?

Do the calculated velocities comply with the criteria specified above?

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Are culverts flowing full or part full at the outlet? Have velocities been determined accordingly?

Has the potential for erosion due to velocity been determined?

Has the impact of cross drainage structures on flood levels (afflux) been quantified?

Has the afflux been compared with acceptable afflux limits set out by the local authority design standards?

Have watercourse stability, preservation of flora and fauna, and protection of existing infrastructure from flood damage been considered?

Hydrology

Item Check Action Required Has Form F2759 Field Report – Bridge Waterways been used in relation to the collection of flood data?

• For urban catchment, has the Average Recurrence Interval (ARI) been set for both the minor and major drainage systems? • For rural catchment, has the Average Recurrence Interval (ARI) been set in accordance with the required flood immunity and available funds?

Has the Rainfall Intensity-Frequency-Duration (IFD) data been calculated using Australian Rainfall and Runoff (IEAust, 1987)?

Has the catchment area been determined and checked by site inspection?

Has the coefficient of runoff been set according to the characteristics of the catchment?

Has the method for calculating the time of concentration been chosen in accordance with the catchment characteristics?

Has the design discharge been calculated by Rational or other method (specify)?

Tailwater Levels

Item Check Action Required Is the tailwater level tidal or non-tidal?

For outfalls to tidal waters, does the local authority have any storm surge prediction?

Have tide levels been measured at the point of interest?

Has an allowance for the greenhouse effect been added?

Has an allowance for storm surge been added?

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If tidal, is the area protected and does it need to comply with the requirements of statutory authorities?

For outfalls to non-tidal waters, has the possibility of scour at the outlets of culverts or open channels been minimised?

Fauna Passage

Item Check Action Required Has the identification and assessment of fauna passage criteria been undertaken by the District Environmental Officer?

Has the project REF/IAS been reviewed to identify whether there is a need for fauna passage to be incorporated in to the project design?

Have fauna pathways been identified in the REF/IAS?

Have the relevant species group(s) been identified?

Has the District Environmental Officer liaised with the relevant local or state authority to discuss the potential impacts of the project on fauna and management strategies?

Has the Project Manager/Detailed Designer been consulted regarding fauna passage requirements?

Have drainage design criteria (ie. Specifications for culvert size and layout) been determined that will accommodate fauna passage?

Ambient Conditions

Item Check Action Required If the project site lies within an arid, mountainous, coastal, urban or inundated area, have the recommended criteria been considered (Refer Section 3.8)?

Selection Criteria

Item Check Action Required Have all relevant factors used in selecting the appropriate size and type of drainage structure been considered? (Factors include ARI, discharge, road alignment, topography, afflux, soil type, nature of debris, environmental factors, provision for maintenance.)

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Pollution Control

Item Check Action Required Has the REF/IAS/EMP (Planning) been reviewed to identify requirements and objectives for water quality management and the described the sensitivity of the receiving environment?

Have pollutant sources and types been identified for the project?

Has the estimation of pollutant loads been required?

Have the processes for pollutant transport (e.g. pollutant attached to fine sediment) been identified for the project?

Have the required pollutant treatment processes been identified (ie, primary, secondary or tertiary treatment)?

Have the potential pollutant control device(s) been assessed and short-listed?

Have the pollutant control device(s) been assessed for potential pollutant removal?

Have the preferred treatment device(s) been selected based on an assessment for achieving key performance objectives?

Erosion and Sediment Control

Item Check Action Required Has soils and erosion risk information and data from the REF/IAS and Chapter 2 assessment process been reviewed to identify sensitivities and risks associated with the site?

If considered necessary, has a design standard been selected for erosion and sediment control measures?

Has the erosion and sediment control matrix been used to identify the most appropriate control measures based on the site conditions and the construction program?

Other

Item Check Action Required Has the provision of access for maintenance been planned for?

Have relevant safety considerations been identified (e.g. floodway length and potential traffic hazard)?

road drainage design manual - chapter 3

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