Produce an engineering design for drainage pipes and culverts


Unit Descriptor

This unit of competency describes the knowledge and skills required to apply principles of design for a minor culvert for a rural road using appropriate drainage standards.

This includes the application of basic concepts in engineering hydrology to estimate flood flow magnitude and basic culvert and drainage design practices.

No licensing, legislative, regulatory or certification requirements apply to this unit at the time of publication.


Employability Skills

This unit contains employability skills.


Application of the Unit

This unit of competency applies to a person working at paraprofessional level in a civil engineering environment where the design of roads using drainage pipes and culverts is undertaken. The unit includes both desk and fieldwork.



Elements describe the essential outcomes of a unit of competency. Elements describe actions or outcomes that are demonstrable and assessable.


Performance criteria describe the required performance needed  to demonstrate achievement of the element – they identify the standard for the element. Where bold / italicized text is used, further information or explanation is detailed in the required skills and knowledge and/or the range statement.

Assessment of performance is to be consistent with the evidence guide.

1. Identify drainage design requirements

  • Occupational Health and Safety/Workplace Health and Safety (OHS/WHS) requirements and environmental requirements for a given work area are obtained and interpreted.
  • Established OHS/WHS requirements and risk control measures and procedures are followed in preparation of the work
  • Safety hazards which have not previously been identified are documented and risk control measures devised and implemented in consultation with appropriate personnel.
  • Design requirements are identified from documentation, work requests or discussions with appropriate
  • Appropriate personnel are consulted to ensure the work is co-ordinated effectively with others involved at the workplace.
  • Resources and equipment needed for the task are obtained in accordance with enterprise procedures and checked for correct operation and safety.

2. Plan design approach

  • OHS/WHS requirements for carrying out the work are incorporated in the design plan.
  • On site reconnaissance to gather surveying data, measurements, photographs and other required information for the design project is
  • Design references and equipment are available to complete the design, to conform to relevant Australian and/or local standards or regulations, in accordance with enterprise
  • Decisions for dealing with unexpected situations are made from discussions with appropriate personnel, job specifications and enterprise
  • Methods for dealing with unexpected situations are selected on the basis of safety and specified work outcomes.

3. Complete the design

  • OHS/WHS requirements for carrying out the work are followed.
  • Design is completed to conform to relevant Australian and/or local standards or regulations, in accordance with enterprise
  • Design references and equipment are used according to relevant Australian standards, manufacturers' manuals and enterprise
  • Design is reviewed with appropriate personnel and amended as required to provide the optimum

4. Compile, document and present results.

  • Design references and equipment are maintained and stored in accordance with enterprise
  • Results are recorded, analysed and reported to appropriate personnel in accordance with enterprise procedures.
  • Results are stored and archived according to enterprise procedures.



This describes the essential skills and knowledge and their level required for this unit.


Required Skills:

    • communicating and working with other team members
    • reading skills to interpret task related documentation, relevant data, job instructions, drawings and OHS/WHS procedures
    • carrying on site reconnaissance to gather surveying data, measurements, photographs and other required information in preparation for the culvert design and drainage task
    • making computations and recording the results

    • assembling gathered information and data and preparing a culvert and drainage design solution
    • reviewing design in consultation with others and finalising the proposal
    • completing required workplace documentation

Required knowledge:

  • hydrological cycle:
    • historic rainfall data
    • flood records
    • availability of data
  • meteorology:
    • elements
    • meteorology measuring gauge results to be recorded and graphed, over the period of duration of the module
  • rain gauging:
    • types of rainfall
    • types of rain gauge
    • networks
    • data adjustment
    • mass curve and hydrograph
    • intensity
  • rain gauging results recorded and graphed over the period of duration of the module
  • stream flow:
    • factors affecting run-off
    • stream flow components
    • stream flow monitoring equipment
    • flood hydrograph
    • use of flood hydrograph software
    • stage discharge
  • stream gauging practical project requiring:
    • suitable site selection with easy determination of stream cross section
    • monitoring equipment
    • work could be completed in liaison with the local authority
  • flood estimation:
    • factors affecting (rainfall, catchment)
    • peak flow
    • run-off hydrograph
    • flood routing
    • flood frequency analysis
    • design flood selection
  • hydraulic structures:


  • retarding basin
  • channel flow regulation (irrigation)
  • reservoir storage
  • erosion control (systems)
  • data collection:
    • recognise the terminology associated with drainage design
  • development of a logical plan of action in approaching design task
  • the information required to undertake design:
    • topographic and base maps, cadastral plans, subdivision plans
    • aerial photographs
    • flood flow, flood level data rainfall data
    • rainfall intensity/ frequency/ duration curves
    • rainfall coefficients
    • drainage design charts, pipes, channels and pits
    • data related to runoff, soil types, geology, stream
    • pattern, vegetation, land use
    • existing drainage lines, outfalls, channels, water-courses, existing drainage locations and levels
    • location and levels of other services
    • state the sources for the design data
  • major and minor floods:
    • average recurrence interval
    • review the Water Cycle
    • Identify factors increasing and decreasing run-off
    • Show relationship between flood magnitude
    • storm event ranking, frequency and Average Recurrence Interval
    • definition of minor, major, rare and extreme floods
    • level of public protection afforded by minor and major flood control design
    • designers responsibility to compromise between ultimate flood protection and economy
    • R.I. appropriate to the design task
  • control measures for floods of greater magnitude:
    • roadway reserves, floodways in footways and reserves
    • retention, detention and retardation techniques
  • rational method for design of peak discharge:
    • theory of method based on completely impervious catchment and continuity of flow
    • (Rainfall in = Discharge out)
    • state rational method formula and define terms
    • direct relationship between discharge area
    • Coefficient of Runoff and Equivalent Area
    • formula in terms of above for litres and cubic metres/second
    • relationship between intensity, frequency and duration


  • peak discharge occurs when design storm duration equals time of flow from most remote point
  • time of Concentration and relation to Design Intensity
  • calculation of design discharge from single use catchment given the area, runoff coefficient and time of concentration
    • intensity/ frequency/ duration for design R.I
  • weighted coefficient of runoff for a multi-use catchment
  • the design discharge from multi-use catchment given areas, coefficient and time of concentration
    • equivalent areas making up the catchment area can be summed to give total area weighted coefficient
  • coefficient of run off based on percentage of impervious area
  • rural catchment areas:
    • state data required for design
    • the topographic plan - ridges, valleys, watercourses
    • properties of contours
    • e catchment boundaries along ridge lines
    • Trace boundary from outlet to ridge line by crossing contours at right angles
    • the catchment area by planimeter, scale and calculation, counting grade squares
    • stream flow lengths, overland flow lengths
    • time of concentration - various methods
    • overland flow time design charts with limits
    • stream time using approximate velocities
    • tortuosity factor to measure length
    • average weighted stream slope
    • stream velocity design chart using weighted slope
    • time as distance/velocity plus overland time
    • time of concentration with Bransby-Williams formula
    • appropriate value for t0
    • state characteristics affecting runoff coefficient relief, retention, infiltration, cover, intensity
    • estimation of values from site data
    • use of Turner’s tables to determine runoff coefficient
    • use of Rural Catchment Runoff Coefficient design chart
    • coefficient C10
    • application of frequency factor obtain Cy
    • comparison of results and selection of appropriate values
  • calculation of design discharge:
    • selection of appropriate recurrence interval
    • determination of intensity from adopted tc
    • calculation of discharge using adopted Cr and area
    • comparison with streamflow flood records if available


  • culvert design:
    • design data - roadway and stream at site
    • determination of depth and velocity of discharge flow in natural waterway
    • derivation of tailwater depth
    • selection of culvert slope compatible with site conditions
    • determination of culvert length through embankment
    • setting of allowable headwater depth - U/S water level
    • establishment of freeboard requirement
    • trial culvert type and cover requirements
    • critical depth of flow
    • use of the Drainage Design Manual (D.D.M.) procedure and design charts to establish maximum headwater level
    • headwater level, cover, outlet velocity for acceptability
    • modification of culvert trail size and recompute as required
    • design data in a form suitable for transfer to working drawings refer Culvert Design Sheet (D.D.M.)
  • urban runoff and flow:
    • rational method
    • partial area effect
    • circumstances when partial area has an effect
    • two values: rational method - full areas, part area
    • time of concentration for various land uses
    • kinematic wave formulation for overland flow
    • variation with intensity, R.I
    • use of overload flow chart (D.D.M.)
  • determination of flow time in gutters or channels (D.D.M. chart)
    • minimum times for design
    • roof to gutter time
  • determination of time of entry:
    • overland (roof) time plus channel time to inlet
    • calculation of full area and part area coefficients
    • coefficient of runoff for project
    • determination of full area and part area coefficients for all internal and external land uses contributing to development outlet
  • pipe and pipe layout
    • location of road drainage lines
  • pit locations:
    • entry pits at upstream side of intersections, low pits, tangent points
    • determination of entry pit spacing based on flow spread and inlet capacity, lot discharge


  • use of design charts and calculation establish entry pits locations. Calculate runoff entry and bypass
  • selection of economical route for road drainage to outlet
  • use of high side of road, avoid easements
  • location of junction pits at direction change, at maximum spacing
  • review and adjustment of road drainage network
  • locate easement drainage:
    • identification of blocks not served by road drainage
    • location of easement pits and inlets
    • economical route to road drains
    • minimum pipe sizes to be used in easements, road reserves and beneath pavements
    • determination of minimum cover required
    • determination of pipe lengths
  • catchment areas:
    • catchment areas contributing to each outlet pipe from pits in the network
    • division of catchment areas into sub areas based on land use
    • identification of sub areas entering gutter inlets
    • recording areas, coefficient of runoff for each sub area
    • calculation of equivalent areas for each sub area
    • sum equivalent areas entering each outlet pipe
  • time of concentration:
    • use of roof and gutter time for house lots
    • use of overland and gutter time for grassed and paved areas
    • use of longest time for full area flow
    • use of impervious entry time for part area flow (minimum 5 minutes)
    • estimation of time in pipe to downstream pit (nearest: ½ minute)
    • sum time downstream from pit to pit
    • adopting longest time at junctions part area and full area
    • in Victoria part area design will predominate
  • calculate peak discharge:
    • use of rational method to calculate part area and full area discharge at each pit
    • part area produces peak discharge in Victoria
    • note that pipe travel time may be amended later when pipe velocities are determined requiring adjustment to discharge
    • calculation of maximum flood discharge at critical points
    • determining gap flow - overflow at critical points
    • consideration of overflow path at intersections, court bowls
    • Pit Water Level and Hydraulic Grade Lines
    • transfer of discharge data to design sheet
  • pipe design:
    • adoption of minimum freeboard at pits


  • insertion of pit design kerb levels in design sheet
  • calculation of maximum pit water level at each pit
  • Bernoulli equation
  • definition of hydraulic grade line at level of water
  • pressure line = total energy
  • velocity head
  • show that H.G.L. is highest allowable obvert level for full pipe flow, pipe located at or beneath H.G.L
  • review of pipeline shock losses.
    • determination of head loss coefficients for pits in network use D.D.M. charts
    • adoption of suitable
    • trial pipe size, calculate velocity as Q/A
    • calculation of water level at downstream pit as U/S
    • W.L. - Head loss at pit - Head loss in pipe



The Range Statement relates to the unit of competency as a whole. It allows for different work environments and situations that may affect performance. Bold / italicised wording in the Performance Criteria is detailed below.


OHS/WHS requirements may include but not limited to:


  • legislation
  • protective equipment
  • material safety management systems
  • hazardous substances and dangerous goods code
  • local safe operation procedures
  • awards provisions


Environmental requirements may include but not limited to:


  • liquid waste
  • solid waste
  • gas, fume, vapour, smoke emissions, including fugitive emissions
  • excessive energy and water use
  • excessive noise

Appropriate personnel may include but not limited to:


  • supervisor
  • leading hand
  • foreman
  • manager
  • site engineer
  • trainer
  • mentor
  • teacher
  • team member

Resources and equipment may include but not limited to:


  • specifications
  • appropriate manuals
  • standards
  • catalogues
  • stationary
  • calculators

Enterprise procedures may include but not limited to:


  • the use of tools and equipment
  • instructions, including job sheets, cutting lists, plans, drawings and designs
  • reporting and communication
  • manufacturers' specifications and operational procedures




The evidence guide provides advice on assessment and must be read in conjunction with the Elements, Performance Criteria, Required Skills and Knowledge, the Range Statement and the Assessment section in Section B of the Accreditation Submission.

Critical aspects for assessment and evidence required to demonstrate competency in this unit

  • Assessors must be satisfied that the candidate can competently and consistently perform all elements of the unit as specified by the associated performance criteria, including required skills and knowledge. Specifically they must be able to demonstrate the ability to:
    • implement OHS/WHS procedures and practices including the use of risk control measures as specified in the performance criteria and range
    • carry out an on-site reconnaissance and gather required data and information for a proposed culvert and drainage system on more than one occasion and in different context
    • design a culvert drainage system solution to meet a specific requirement on more than one occasion and in different contexts

Context of and specific resources for assessment

  • This unit may be assessed on the job, off the job or a combination of both on and off the job. Where assessment occurs off the job, that is the candidate is not in productive work, then an appropriate simulation must be used where the range of conditions reflects realistic workplace situations. The competencies covered by this unit would be demonstrated by an individual working alone or as part of a team. The assessment environment should not disadvantage the candidate
    • Resources required for assessment include:
    • OHS/WHS policy and work procedures and
    • access to workplace or simulated work facility and off site environments
    • access to relevant tools, equipment, materials and consumables
    • access to relevant plans, drawings and instructions and manufacturer’s specifications/manuals




Methods of assessment

  • For valid and reliable assessment of this unit, evidence should be gathered through a range of methods to indicate consistent performance.
  • Evidence must involve demonstration of practical skills and may also include:
    • observation of processes and procedures
    • oral and/or written questioning on required knowledge and skills
    • testimony from supervisors, colleagues, clients and/or other appropriate persons
    • inspection of the final design solutions or outcomes
    • portfolio of documented
  • Where performance is not directly observed any evidence should be authenticated by colleagues, supervisors, clients or other appropriate
  • Questioning techniques should not require language, literacy and numeracy skills beyond those required in this unit of competency.


Software/Hardware Used