Culvert

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Steel culvert with a plunge pool below
A multiple culvert assembly in Italy
A stone lintel culvert or stone box culvert.
A culvert under the Vistula river levee and a street in Warsaw.

A culvert is a structure that allows water to flow under a road, railroad, trail, or similar obstruction from one side to the other side. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe, reinforced concrete or other material. In the United Kingdom the word can also be used for a longer artificially buried watercourse.[1] A structure that carries water above land is known as an aqueduct.

Culverts are commonly used both as cross-drains for ditch relief and to pass water under a road at natural drainage and stream crossings. A culvert may be a bridge-like structure designed to allow vehicle or pedestrian traffic to cross over the waterway while allowing adequate passage for the water. Culverts come in many sizes and shapes including round, elliptical, flat-bottomed, pear-shaped, and box-like constructions. The culvert type and shape selection is based on a number of factors including: requirements for hydraulic performance, limitation on upstream water surface elevation, and roadway embankment height.[2]

The process of removing culverts, which is becoming increasingly prevalent, is known as daylighting. In the UK, the practice is also known as deculverting.[3]

Materials[edit]

Culverts can be constructed of a variety of materials including cast-in-place or precast concrete (reinforced or non-reinforced), galvanized steel, aluminum, or plastic, typically high-density polyethylene.

Two or more materials may be combined to form composite structures. For example, open-bottom corrugated steel structures are often built on concrete footings.

Design and engineering[edit]

Construction or installation at a culvert site generally results in disturbance of the site soil, stream banks, or streambed, and can result in the occurrence of unwanted problems such as scour holes or slumping of banks adjacent to the culvert structure.[4][5]

Culverts must also be properly sized and installed, and protected from erosion and scour. Many agencies such as U.S. Department of Transportation Federal Highway Administration (FHWA), Bureau of Land Management (BLM),[6] and U.S. Environmental Protection Agency (EPA)[7] as well as state or local authorities [8] require that culverts be designed and engineered to meet specific Federal, State, or local regulations and guidelines to ensure proper function and protect against culvert failures.

Culverts are classified by standards for their load capacities, water flow capacities, life spans, and installation requirements for bedding and backfill.[9] Most agencies adhere to these standards when designing, engineering, and specifying culverts.


    Pipe culvert construction 

1. Scope

Pipe culverts shall be constructed in accordance with this specification and in conformity with the lines, levels and cross-sections shown on the drawings. The work shall include: the construction of trenches; the supply and placement of bedding; the supply and laying of pipes; the jointing of the pipes; the construction of headwalls, wing-walls, aprons, drops, and intakes and outlet structures where specified; the construction of connecting and outlet drains; backfill of trenches and reinstatement as specified, the supply of all materials, labour, plant, transport and tools required for the proper completion of the work and testing.

Where pipes and are less than 350mm in diameter and laid in a narrow trench, they shall, unless otherwise specified, be laid in accordance with the following standards appropriate for the pipe type: AS/NZS 3725:2007 Design for installation of buried concrete pipes and AS/NZS 2566: Buried flexible pipelines. For PVC pipes use; AS/NZS2032 2006 Installation of PVC pipe systems for PVC pipes. For all polyethylene (PE) pipes use AS/NZS2033 2008 Installation of polyethylene pipe systems.

Where pipe culverts are to be constructed in any natural river, stream, or waterway in such a way that the passage of fish would be impeded, Part 6 of the Freshwater Fisheries Regulations 1983 must be complied with. 2. Materials 2.1 Pipe types

The pipes shall conform to the requirements for the class, type of joints, diameter and length shown on the drawings and defined in the job specification, and shall be one of the following types:

   2.1.1 Concrete pipes
       (a) Concrete pipes shall comply in all respects with the requirements specified in AS/NZS 4058:2007 Precast concrete pipes (pressure and non-pressure) and designed and installed to NZS/AS 3725 2007: Design for installation of buried concrete pipes;
   2.1.2 Corrugated steel or aluminium pipes of any of the following types:
       (a) Aluminium and steel structures (or conduits) complying with AS/NZS 2041 1998: Buried Corrugated Metal Structures, and AS/NZS2041.4:2010 Buried Corrugated structures - Helically formed sinusoidal pipes.
       Aluminium pipes complying with relevant clauses in AS/NZS 2041 as above together with AASHTO M219: Aluminium Alloy Structural Plate for Field Bolted Conduits and AASHTO Standard Specifications for Highway Bridges, Section 12.
       (b) Nestable corrugated steel pipes complying with AS/NZS 2041: 1998 Buried Corrugated Metal Structures, and AS/NZS 2041.4:2010 Buried Corrugated structures - Helically formed sinusoidal pipes.
       (c) Helical lock-seam corrugated aluminium pipes complying with relevant clauses in NZS 4406:1986 as above together with AASHTO M196: Standard Specification for Corrugated Aluminium Pipe for Sewers and Drains and AASHTO M197 Standard Specification for Aluminium Alloy Sheet for Corrugated Aluminium Pipes.
       (d) Helical lock-seam corrugated steel pipes complying with relevant clauses in AS2041 as above together with NZS4406 1986: Helical lock seam corrugated steel pipes design & installation.
   2.1.3 PVC pipes and fittings to Class SN4 or SN6 as defined in AS/NZS 1260 2009: PVC pipes and fittings for drain, waste and vent applications, and UPVC Pipes and Fittings to AS 1254 2010: UPVC pipes and fittings for storm and surface water applications designed and installed to AS/NZS 2566.1:1998 Buried flexible pipelines and AS/NZS2566.2/2002 Buried flexible pipelines.
   2.1.4 Polyethylene pipes manufactured to AS/NZS 4130 2009: Polyethylene (PE) pipe systems for pressure applications and installed to AS/NZS2566.1 1998: Buried flexible pipelines and AS/NZS 2566.2: 2002 Buried flexible pipelines.
   2.1.5 Glass reinforced plastic pipes manufactured to AS 3571: 2009 Glass reinforced thermo plastic (GRP) systems based on unsaturated Polyester (UP) resin – Pressure and non-pressure drainage and sewage and designed and installed to AS/NZS 2566: Buried flexible pipelines (parts 1 and 2).
   2.1.6 Perforated polyethylene pipes manufactured to Type 1 or Type 2 defined in AS 2439:2007 Perforated plastics drainage and effluent pipe and associated fittings and installed to AS/NZS 2566: Buried flexible pipelines (Parts 1 and 2).
   2.1.7 Polyethylene and polypropylene black or black jacket twin wall or plain wall pipes manufactures to NZS/AS 5065:2005 Polyethylene and polypropylene pipes and fittings for drainage and sewerage application (and Amendments) and installed to AS/NZS 2566: Buried flexible Pipelines (Parts 1 and 2).

The Contractor shall produce evidence of the pipes' compliance with one of the above clauses if requested by the Engineer. 2.2 Elastomeric sealed joints

Rubber rings used in flexible joints shall comply with AS 1646 Elastomeric Seals for waterworks purposes (parts 1, 2 and 3) and shall be of a type approved by the pipe manufacturer for use with the particular joint. 2.4 Mortar

Mortar shall consist of one part of cement to two parts of fine, clean, sharp sand that complies with NZS 3103: 1991 Specification for sands for mortars and plasters measured in dry loose volume, and just sufficient water to make it workable. The mortar shall be mixed either by hand or in an approved mechanical mixer, as required. Any mortar which is not used within 30 minutes of mixing shall be discarded. 2.5 Timbering and formwork

The Contractor shall be responsible for providing support to all excavations and for all falsework and formwork. 3. Excavation 3.1 Clearing

The Contractor shall remove sufficient vegetation and topsoil to allow pipe laying to proceed without risk of contamination of bedding or backfilling. 3.2 Trenches

Where trenches are required, they shall be cut in such a manner as will ensure that the pipes will be laid true to the depths, grades and lines shown on the drawings.

The base of the trench shall not be excavated over the specified dimensions unless directed by the Engineer for the removal of unsuitable material.

Unless otherwise specified, trenches shall have a minimum gradient of not less than 1 in 80 and a minimum depth that will ensure that, when the pipes are laid, the distance between the top of the pipes and the finished surface level shall be not less than 1 metre in any place unless otherwise designed for less cover as approved by the Engineer. 3.3 Support for excavations

The Contractor shall be responsible for providing support to all excavations and for falsework and formwork and shall conform with safety practices and codes of practice issued by the Department of Labour. 3.4 Inlet and outlet drains

Inlet and outlet drains shall be cut true to grade and line within the limits of the road reserve or such other limits as are shown on the drawings or directed by the Engineer. These drains shall have a bottom width equal to the external diameter of the pipe or the width of the concrete apron where applicable, and side slopes of one horizontal to two vertical in clay and one horizontal to four vertical in rock. 3.5 Handling of excavated material

To avoid any danger to stability of the trench or adjacent buried services excavated material shall be stacked a sufficient distance away from the edge of the excavation and the size of the spoil bank shall be limited.

Surplus excavated material shall be disposed of as specified in the specific contract documents or as directed by the Engineer. 3.6 Unsuitable foundation material

Where the Engineer considers that the foundation material below the pipes or structures is unsuitable, this material shall be removed to a depth of 600mm or any greater depth as specified by the Engineer. Unsuitable foundation material shall be replaced with approved material placed in layers of 150mm loose depth which shall then be compacted as specified in either the relevant standard or contract documents. 3.7 Saw cutting of existing asphalt surfaces

Existing asphalt surfaces shall be saw cut prior to excavation where pipes are being placed under existing roads. 4. Dewatering 4.1 General

The Contractor shall keep the excavations free from water at all times and shall provide all such pumping plant and drainage systems as may be required for this purpose.

For small diameter rigid pipes upon release of the pumping the bedding material must be stable to ensure a uniform bedding is maintained. Pipe length is an important parameter if broken backs are to be avoided. 4.2 Sumps

Sumps formed for the purpose of dewatering shall be kept outside the line of the trench and away from foundations as far as possible. When finished with, they shall be backfilled and consolidated in layers with suitable fill or concrete. 5. Bedding laying and jointing pipes 5.1 Bedding

Unless otherwise detailed in the specific contract documents or to an appropriate standard as approved by the Engineer, all bedding material shall satisfy the requirements in AS/NZS 3725:2007 Design for installation of buried concrete pipes and AS/NZS 2566 Buried flexible pipelines (Parts 1 and 2).

Irrespective of the method of bedding used, the bedding adjacent to the pipe joints shall be recessed as necessary to ensure that the whole of the barrel length of the pipe makes uniform contact with the prepared bedding. 5.2 Laying and jointing pipes

All pipes shall be laid in accordance with the relevant standards, the manufacturer's instructions and good trade practice.

Pipe jointing shall be carried out in such a manner that the finished joints are watertight and present a smooth invert surface.

For concrete pipes, the spigot and the inside of the socket of pipes shall be clean before jointing. Rubber rings for flexible joints shall be free of dust, grease or dirt. The rubber rings shall be mounted evenly on the extreme end of the spigot and the pipe lined up truly concentric with the pipes already laid. The spigot shall then be forced into the socket leaving a gap between the socket shoulders and the spigot of between 5 and 10mm, or as recommended by the manufacturer, care being taken to maintain the pipes concentric. The rubber ring shall be equidistant from the end of the socket all round and at least 20mm from the back of the socket chamber when the joint is complete. 5.3 Field testing

For concrete pipes, where testing is specified, pipelines shall be tested with an applied hydrostatic head of 2m applied and carried out in accordance with the requirements of the Concrete Pipe Association of Australasia: Field Testing of Concrete Pipelines and Joints Section 1.

For PVC and PE pipes, where testing is specified, pipelines shall be tested as non-pressure pipelines as set out in AS/NZS 2566.2:2002 section 6.4 with an applied hydrostatic head of 2.0m. 5.4 Lifting holes

Most concrete pipes manufactured in New Zealand are lifted using an appropriately fitted lifting anchor. However, where a concrete pipe has lifting holes these shall be closed with a mortar, as specified in Clause 2.4 of this specification, before backfilling. 6. Backfilling 6.1 Commencement of backfilling

Prior to commencement of backfilling the bedding material must comply with Clause 5.1 of this specification. For each installation type, backfilling requirements shall be carried out as specified in the specific contract documents or to an appropriate standard as approved by the Engineer. 6.2 Placement and compaction

Backfilling shall be built up in layers placed and compacted evenly on both sides of the pipes in order to effect balanced loading. Full use shall be made of mechanised hand operated compaction tools on each side of the pipe and within a height of 1.5m above the pipe. Heavy construction equipment and sheep's foot rollers shall not be operated over or near the culvert until the amount of filling required by the job specification has been placed and compacted as specified, around and over the pipes.

Compaction requirements for the fill materials defined in Clause 6.3 in this specification are specified below:

   Selected fill and Ordinary fill unless specified otherwise, shall be compacted to at least 90% of the maximum dry density at optimum moisture content, as determined by NZS 4402:1986 Methods of testing soils for civil engineering purposes Test 4.1.1 in layers not exceeding 150mm thick unless field trials show, to the satisfaction of the Engineer, that the specified compaction is obtained with thicker layers.
   Loose fill unless specified otherwise, shall be compacted (if necessary) to a minimum of 70% and a maximum of 80% of the maximum dry density at optimum moisture content, as determined by NZS 4402 1986 Test 4.1.1 in layers not exceeding 200mm thick unless field trials show, to the satisfaction of the Engineer, that the specified compaction is obtained with thicker layers.

6.3 Fill material

Three types of fill material referred to in the contract documents and drawings, are specified as follows:

   (a) Selected fill shall be any material that does not qualify as either Type W or Type U material as defined in TNZ F/1: 1997 Specification for Earthworks Construction and meets the requirements of the appropriate installation specification.
   (b) Ordinary fill and Loose fill shall be any material that does not qualify as either Type W or Type U material as defined in TNZ F/1: 1997 Specification for Earthworks Construction and meets the requirements of the appropriate installation specification. Ordinary fill placed within 1.5m of the finished surface shall be material suitable for use as a subgrade.

7. Ancillary concrete 7.1 Structures

Ancillary concrete structures required to complete the pipe installation including: headwalls; wingwalls; sumps; sump tops; aprons; drops; and intakes shall be reinforced and constructed as shown on the drawings. No portion of any metal tie permanently embedded in the concrete shall be left within 40mm of any concrete face. Unless otherwise specified, all exposed concrete faces shall be F3 as defined in NZS 3114:1987 Specification for concrete surface finishes.

Ancillary concrete structures shall comply with the durability requirements specified in NZS 3101: Part 1: 2006 Concrete Structures Standard. 7.2 Joints

The jointing of ancillary concrete structures to pipes and other structures shall be in accordance with the relevant standards, the manufacturer's instructions, good trade practice and meet the required performance. 7.3 Concrete and steel reinforcement

All concrete work shall be in accordance with NZS 3109 1997 Concrete Construction. Concrete for headwalls and other ancillary concrete shall have a minimum compressive strength of 25 MPa at 28 days. Steel reinforcement for concrete shall be in accordance with the current version NZS3109:1997 Concrete Construction and AS/NZS 4671:2001 Steel Reinforcing Materials. 7.4 Timbering and formwork

The Contractor shall be responsible for providing support to all excavations and for all falsework and formwork for concrete structures. 8. Maintenance

The work area shall be left in a neat and tidy condition on the completion of the work.

The Contractor shall maintain the culverts and incidental works including the inlet and outlet drains until the end of the maintenance period. He shall make good any subsidence which occurs in the earthworks above the culvert. 9. Basis of payment

The basis of payment shall be in accordance with the specific contract documents. If the basis of payment has not been specified in the contract documents then the following Clauses shall apply: 9.1 General

The scheduled unit rates shall be deemed to include for all materials, labour, plant, miscellaneous items, board, supervision, contingencies, conveyance of plant, sampling and testing required, and incidental work, plus general overhead, administration, profit, quality assurance and maintenance. 9.2 Basic excavation

Payment will be made at the unit rate per cubic metre on the total volume of earthworks excavated as specified to install the culverts. For payment purposes the volume of excavation shall be measured in the solid. The volume shall be calculated from the natural surface of the ground or if in cuts from the subgrade level and specified cross-section dimensions. The volume of excavation for inlet and outlet channels shall be based on specified cross-section dimensions. The volume of excavation for concrete structures shall be based on the net plan dimensions of the concrete to be placed below ground level. The unit schedule rate shall be in full compensation for: clearing; excavating; the removal and disposal of surplus or unsuitable material; the supply, placing, compaction and testing of approved backfilling; removal and stacking of existing pipe culverts and shall include for any temporary drainage control, timbering, etc, necessary to properly install the culvert. 9.3 Rock excavation

Payment for excavation in rock will be made as an extra in addition to payment under basic excavation. Payment will be made on the total volume as either Type R1 or Type R2 as defined in TNZ F/1: 1997 Specification for Earthworks Construction. Measurement of the volume will be made in the solid within the limits specified for basic excavation. There will be separate additional unit rates for both Type R1 and Type R2 material which shall be in full compensation for the increased cost of excavating and handling these materials. 9.4 Supply and install pipes including bedding

Payment will be made under the appropriate schedule item on the total length of each type, class and diameter of culvert pipe, installed as specified. The unit schedule rate in each case shall be in full compensation for: shaping the foundation; provision of the bedding (except when concrete bedding is required); the supply and installation of the culvert pipe; jointing, backfill to levels shown on the drawings and testing where specified. 9.5 Ancillary concrete

Payment will be made on the total volume measured in cubic metres of concrete used for the construction of ancillary concrete (excepting bedding) forming part of the culvert installation. For payment purposes, the volume shall be the net quantity in accordance with the drawings. The unit schedule rate shall be in full compensation for supplying and constructing the structures as specified, including the provision of reinforcement and formwork. Traffic and travel Driver licences Vehicles Tolls, roads and rail Commercial driving Safety Walking, cycling and public transport Planning and investment

Accidents due to culvert failures[edit]

Culvert failures can occur for a wide variety of reasons including; maintenance, environmental, and installation related failures, functional or process failures related to capacity and volume causing the erosion of the soil around or under them, and structural or material failures that cause culverts to fail due to collapse or corrosion of the materials from which they are made.[10]

If the failure is sudden and catastrophic, it can result in injury or loss of life.

Sudden road collapses are often at poorly designed and engineered culvert crossing sites. Water passing through undersized culverts will scour away the surrounding soil over time. This can cause a sudden failure during medium-sized rain events. There are more than 5,000,000 culverts currently in use in the United States alone. Continued inspection, maintenance, and replacement of these structures is crucial for infrastructure and safety.

Accidents due to culvert failure can also occur if a culvert has not been adequately sized and a flood event overwhelms the culvert, or disrupts the road or railway above it.

Ongoing culvert function without failure depends on proper design and engineering considerations being given to load and water capacities, surrounding soil analysis, backfill and bedding compaction, and erosion protection. Improperly designed backfill support around aluminum or plastic culverts can result in material collapse or failure from inadequate load support.[11][12]

Soil and sand carried through a culvert can wear away the galvanizing of a steel culvert, allowing it to corrode and eventually collapse, disrupting the road or railway above it. This happened at a culvert near Gosford, New South Wales in 2007, killing five.

Environmental impacts[edit]

This culvert has a natural surface bottom connecting wildlife habitat. Vermont

Safe and stable stream crossings can accommodate wildlife and protect stream health while reducing expensive erosion and structural damage.

Undersized and poorly placed culverts can cause problems for water quality and aquatic organisms. Poorly designed culverts can degrade water quality via scour and erosion and also restrict aquatic organisms from being able to move freely between upstream and downstream habitat. Fish are a common victim in the loss of habitat due to poorly designed crossing structures. Culverts that offer adequate aquatic organism passage reduce impediments to movement of fish, wildlife and other aquatic life that require instream passage. These structures are less likely to fail in medium to large scale rain and snow melt events.[citation needed]

This culvert cannot accommodate wildlife passage

Poorly designed culverts are also more apt to become jammed with sediment and debris during medium to large scale rain events. If the culvert cannot pass the water volume in the stream, the water may overflow over the road embankment. This may cause significant erosion, washing out the culvert. The embankment material that is washed away can clog other structures downstream, causing them to fail as well. It can also damage crops and property. A properly sized structure and hard bank armoring can help to alleviate this pressure.

Aquatic organism passage compatible culvert replacement in Franklin, Vermont, just upstream from Lake Carmi

Culvert style replacement is a widespread practice in stream restoration. Long-term benefits of this practice include reduced risk of catastrophic failure and improved fish passage. If best management practices are followed, short-term impacts on the aquatic biology are minimal.[13]

Minimum energy loss culverts[edit]

Culvert size relative to a person

In the coastal plains of Queensland (north-east Australia), torrential rains during the wet season place a heavy demand on culverts. The natural slope of the flood plains is often very small and little fall (or head loss) is permissible in the culverts. Professors Gordon R. McKay and Colin J. Apelt developed and patented the design procedure of minimum energy loss culverts waterways which yield small afflux. Colin J. Apelt, (emeritus) professor of civil engineering at the University of Queensland, presented an authoritative review of the topic (1983)[14] and a well-documented documentary (1994).[15]

A minimum energy loss culvert or waterway is a structure designed with the concept of minimum head loss. The flow in the approach channel is contracted through a streamlined inlet into the barrel where the channel width is minimum, and then it is expanded in a streamlined outlet before being finally released into the downstream natural channel. Both the inlet and outlet must be streamlined to avoid significant form losses. The barrel invert is often lowered to increase the discharge capacity.

The concept of minimum energy loss culverts was developed by Norman Cottman, shire engineer in Victoria (Australia) and by Professor Gordon McKay, University of Queensland (Brisbane, Australia) during the late 1960s.[16] While a number of small-size structures were designed and built in Victoria, some major structures were designed, tested and built in South-East Queensland.

Forestry[edit]

In forestry, proper use of cross-drainage culverts can improve water quality while allowing forest operations to continue.

See also[edit]

Notes[edit]

  1. ^ Taylor, Karl (2010). "Thacka Beck Flood Alleviation Scheme, Penrith, Cumbria- Measured Building Survey of Culverts". Oxford Archaeology North. 
  2. ^ Turner-Fairbank Highway research Center (1998). "Hydraulic Design of Highway Culverts" (PDF), Report #FHWA-IP-85-15 U.S. Department of Transportation, Federal Highway Administration, McLean, Virginia.
  3. ^ Wild, Thomas C. (2011). "Deculverting: reviewing the evidence on the 'daylighting' and restoration of culverted rivers.". Water and Environment Journal. Retrieved 2016-04-14. 
  4. ^ Turner-Fairbank Highway research Center (1998). "Hydraulic Design of Highway Culverts" (PDF), Report #FHWA-IP-85-15 U.S. Department of Transportation, Federal Highway Administration, McLean, Virginia.
  5. ^ Alberta Transportation (2004). "DESIGN GUIDELINES FOR BRIDGE SIZE CULVERTS" (PDF), Original Document 1995 Alberta Transportation, Technical Standards Branch, Government of the Province of Alberta
  6. ^ U.S. Department of Interior Bureau of Land Management (2006). "Culvert Use, Installation, and Sizing" Chapter 8 (PDF), Low Volume Engineering J Chapter 8, blm.gov/bmp.
  7. ^ U.S. Environmental Protection Agency EPA Management (2003-7-24). "Culverts-Water" NPS Unpaved Roads Chapter 3 (PDF), "CULVERTS" epa.gov.
  8. ^ Alberta Transportation (2004). "DESIGN GUIDELINES FOR BRIDGE SIZE CULVERTS" (PDF), Original Document 1995 Alberta Transportation, Technical Standards Branch, Government of the Province of Alberta
  9. ^ Turner-Fairbank Highway research Center (1998). "Hydraulic Design of Highway Culverts" (PDF), Report #FHWA-IP-85-15 U.S. Department of Transportation, Federal Highway Administration, McLean, Virginia.
  10. ^ Architectural Record CEU ENR (2013). "Stormwater Management Options and How They Can Fail" (Online Education Course), McGraw Hill Construction Architectural Record-engineering News Record.
  11. ^ Architectural Record CEU ENR (2013). "Stormwater Management Options and How They Can Fail" (Online Education Course), McGraw Hill Construction Architectural Record-engineering News Record.
  12. ^ Turner-Fairbank Highway research Center (1998). "Hydraulic Design of Highway Culverts" (PDF), Report #FHWA-IP-85-15 U.S. Department of Transportation, Federal Highway Administration, McLean, Virginia.
  13. ^ Lawrence, J.E., M.R. Cover, C.L. May, and V.H. Resh. (2014). "Replacement of Culvert Styles has Minimal Impact on Benthic Macroinvertebrates in Forested, Mountainous Streams of Northern California". Limnologica. 47: 7–20. doi:10.1016/j.limno.2014.02.002. 
  14. ^ Apelt, C.J. (1983). "Hydraulics of minimum energy culverts and bridge waterways," Australian Civil Engineering Transactions, CE25 (2) : 89-95. Available on-line at: University of Queensland.
  15. ^ Apelt, C.J. (1994). "The Minimum Energy Loss Culvert" (videocassette VHS colour), Dept. of Civil Engineering, University of Queensland, Australia.
  16. ^ See:

References[edit]

External links[edit]