A culvert is a structure that channels water past an obstacle or to channel a subterranean Waterway. 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.
Culverts are commonly used both as cross-drains to relieve drainage of ditches at the roadside, and to pass water under a road at natural drainage and stream crossings. When they are found beneath roads, they are frequently empty. A culvert may also 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, open-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, limitations on upstream water surface elevation, and roadway embankment height.
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
Construction or installation at a culvert site generally results in disturbance of the site's soil, stream banks, or stream bed, and can result in the occurrence of unwanted problems such as scour holes or slumping of banks adjacent to the culvert structure.
Culverts must be properly sized and installed, and protected from erosion and scour. Many U.S. agencies such as the Federal Highway Administration, Bureau of Land Management, and Environmental Protection Agency, as well as state or local authorities, require that culverts be designed and engineered to meet specific federal, state, or local regulations and guidelines to ensure proper function and to 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. Most agencies adhere to these standards when designing, engineering, and specifying culverts.
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.
If the failure is sudden and catastrophic, it can result in injury or loss of life. Sudden road collapses are often the result of poorly designed and engineered culvert crossing sites or unexpected changes in the surrounding environment cause design parameters to be exceeded. Water passing through undersized culverts will scour away the surrounding soil over time. This can cause a sudden failure during medium-sized rain events. Accidents from 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, hydraulic flow, surrounding soil analysis, backfill and bedding compaction, and erosion protection. Improperly designed backfill support around culverts can result in material collapse or failure from inadequate load support.
For existing culverts which have experienced degradation, loss of structural integrity or need to meet new codes or standards, rehabilitation using a reline pipe may be preferred versus replacement. Sizing of a reline culvert uses the same hydraulic flow design criteria as that of a new culvert however as the reline culvert is meant to be inserted into an existing culvert or host pipe, reline installation requires the grouting of the annular space between the host pipe and the surface of reline pipe (typically using a low compression strength grout) so as to prevent or reduce seepage and soil migration. Grouting also serves as a means in establishing a structural connection between the liner, host pipe and soil. Depending on the size and annular space to be filled as well as the pipe elevation between the inlet and outlet, grouting maybe required to be performed in multiple stages or "lifts". If multiple lifts are required, then a grouting plan is required which defines the placement of grout feed tubes, air tubes, type of grout to be used and if injecting or pumping grout then the required developed pressure for injection. As the diameter of the reline pipe will be smaller than the host pipe, the cross-sectional flow area will be smaller. By selecting a reline pipe with a very smooth internal surface, with an approximate Hazen-Williams Friction Factor, C, value of between 140–150, the decreased flow area can be offset and hydraulic flow rates potentially increased by way of reduced surface flow resistance. Examples of pipe materials with high C-factors are high-density polyethylene (150) and polyvinyl chloride (140).
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, as well as restrict the movement of aquatic organisms 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. 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, then the water may overflow the road embankment. This may cause significant erosion, ultimately 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.
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.
While the culvert discharge capacity derives from hydrological and hydraulic engineering considerations, this results often in large velocities in the barrel, creating a possible fish passage barrier. Critical culvert parameters in terms of fish passage are the dimensions of the barrel, particularly its length, cross-sectional shape, and invert slope. The behavioural response by fish species to culvert dimensions, light conditions, and flow turbulence may play a role in their swimming ability and culvert passage rate. There is no simple technical means to ascertain the turbulence characteristics most relevant to fish passage in culverts, but it is understood that the flow turbulence plays a key role in fish behaviour. The interactions between swimming fish and vortical structures involve a broad range of relevant length and tine scales. Recent discussions emphasised the role of secondary flow motion, considerations of fish dimensions in relation to the spectrum of turbulence scales, and the beneficial role of turbulent structures provided that fish are able to exploit them. The current literature on culvert fish passage focused mostly on fast-swimming fish species, but a few studies argued for better guidelines for small-bodied fish including juveniles. Finally, a solid understanding of turbulence typology is a basic requirement to any successful hydraulic structure design conducive of upstream fish passage.
Minimum energy loss culverts
In the coastal plains of Queensland, 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. Researchers developed and patented the design procedure of minimum energy loss culverts which yield small afflux.
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 the 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 a shire engineer in Victoria and a professor at the University of Queensland during the late 1960s. 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.
- Bridge – structure built to span physical obstacles
- Clapper bridge – Bridge formed by large flat slabs of stone
- Drainage – Removal of water from an area
- Fish ladder – Structure to allow fish to migrate upriver around barriers
- Low water crossing
- Sanitary sewer – Underground pipe or tunnel system for transporting sewage from houses or buildings to treatment facilities or disposal
- Subterranean river – River that runs wholly or partly beneath the ground surface
- Taylor, Karl (2010). "Thacka Beck Flood Alleviation Scheme, Penrith, Cumbria – Measured Building Survey of Culverts". Oxford Archaeology North.
- 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.
- Wild, Thomas C. (2011). "Deculverting: reviewing the evidence on the 'daylighting' and restoration of culverted rivers". Water and Environment Journal. 25 (3): 412–421. doi:10.1111/j.1747-6593.2010.00236.x.
- Alberta Transportation (2004). "DESIGN GUIDELINES FOR BRIDGE SIZE CULVERTS" (PDF), Original Document 1995 Alberta Transportation, Technical Standards Branch, Government of the Province of Alberta
- 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.
- Environmental Protection Agency EPA Management (2003-7-24). "Culverts-Water" NPS Unpaved Roads Chapter 3 (PDF), "CULVERTS" epa.gov.
- Architectural Record CEU ENR (2013). "Stormwater Management Options and How They Can Fail" (Online Education Course), McGraw Hill Construction Architectural Record-engineering News Record.
- Plastic Pipe Institute-Handbook of Polyethylene Pipe, First Edition Copy 2006
- 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. arXiv:1308.0904. doi:10.1016/j.limno.2014.02.002.CS1 maint: multiple names: authors list (link)
- Chanson, H. (2004). The Hydraulics of Open Channel Flow: An Introduction. Butterworth-Heinemann, 2nd edition, Oxford, UK. ISBN 978-0-7506-5978-9.
- Nikora, V.I., Aberle, J., Biggs, B.J.F., Jowett, I.G., Sykes, J.R.E. (2003). "Effects of Fish Size, Time-to-Fatigue and Turbulence on Swimming Performance: a Case Study of Galaxias Maculatus". Journal of Fish Biology. 63 (6): 1365–1382. doi:10.1111/j.1095-8649.2003.00241.x.CS1 maint: multiple names: authors list (link)
- Wang, H., Chanson, H. (2017). "How a better understanding of Fish-Hydrodynamics Interactions might enhance upstream fish passage in culverts". Civil Engineering Research Report No. CE162: 1–43.CS1 maint: multiple names: authors list (link)
- Lupandin, A.I. (2005). "Effect of flow turbulence on swimming speed of fish". Biology Bulletin. 32 (5): 461–466. doi:10.1007/s10525-005-0125-z. S2CID 28258800.
- Papanicolaou, A.N., Talebbeydokhti, N. (2002). "Discussion of Turbulent open-channel flow in circular corrugated culverts". Journal of Hydraulic Engineering. 128 (5): 548–549.CS1 maint: multiple names: authors list (link)
- Plew, D.R., Nikora, V.I., Larne, S.T., Sykes, J.R.E., Cooper, G.G. (2007). "Fish swimming speed variability at constant flow: Galaxias maculatus". New Zealand Journal of Marine and Freshwater Research. 41 (2): 185–195. doi:10.1080/00288330709509907. S2CID 83942063.CS1 maint: multiple names: authors list (link)
- Wang, H., Chanson, H., Kern, P., Franklin, C. (2016). "Culvert Hydrodynamics to enhance Upstream Fish Passage: Fish Response to Turbulence". 20th Australasian Fluid Mechanics Conference, Perth, Australia. Paper 682: 1–4.CS1 maint: multiple names: authors list (link)
- Cabonce, J., Fernando, R., Wang, H., Chanson, H. (2017). Using Triangular Baffles to Facilitate Upstream Fish Passage in Box Culverts: Physical Modelling. Hydraulic Model Report No. CH107/17, School of Civil Engineering, The University of Queensland, Brisbane, Australia, 130 pages. ISBN 978-1-74272-186-6.CS1 maint: multiple names: authors list (link)
- Wang, H., Chanson, H. (2017). "Baffle Systems to Facilitate Upstream Fish Passage in Standard Box Culverts: How About Fish-Turbulence Interplay?". 37th IAHR World Congress, IAHR & USAINS, Kuala Lumpur, Malaysia. 3: 2586–2595.CS1 maint: multiple names: authors list (link)
- Wang, H., Chanson, H. (2018). "Modelling Upstream Fish Passage in Standard Box Culverts: Interplay between Turbulence, Fish Kinematics, and Energetics" (PDF). River Research and Applications. 34 (3): 244–252. doi:10.1002/rra.3245.CS1 maint: multiple names: authors list (link)
- Chanson, H. (2019). "Utilising the Boundary Layer to Help Restore the Connectivity of Fish Habitats and Populations. An Engineering Discussion" (PDF). Ecological Engineering. 141 (105613): 1–5. doi:10.1016/j.ecoleng.2019.105613. S2CID 207901913.
- 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.
- Apelt, C.J. (1994). "The Minimum Energy Loss Culvert" (videocassette VHS colour), Dept. of Civil Engineering, University of Queensland, Australia.
- Apelt, Colin. (2011). "The Minimum Energy Loss Culvert, Redcliffe" (prepared speech: Award of Engineering Heritage National Landmark By Engineering Heritage Australia on 29 June 2011). https://www.engineersaustralia.org.au/sites/default/files/shado/Learned%20Groups/Interest%20Groups/Engineering%20Heritage/EHA%20Queensland/McKay%20Landmark/CJA%20Speech-MEL%20Redcliffe.pdf
- CHANSON, H. (2003). "History of Minimum Energy Loss Weirs and Culverts". 1960–2002. Proc. 30th IAHR [The International Association for Hydro-Environment Engineering and Research] Biennial Congress, Thessaloniki, Greece, J. GANOULIS and P. PRINOS, ed.s, vol. E, pp. 379–387. Available on-line at: University of Queensland.
- Chanson, Hubert, Web page: Hydraulics of Minimum Energy Loss (MEL) culverts and bridge waterways.
- Oxford English Dictionary, ISBN 0-19-861212-5
- Oxford English Dictionary, ISBN 0-19-861212-5 http://www.fhwa.dot.gov/engineering/hydraulics/pubs/11008/hif11008.pdf
- Impact of culverts on salmon
- Culvert fact sheet
- Culvert Analysis
- Bottomless Culvert Scour Study
- Culverts for Fish Passage
- Hydraulics of Minimum Energy Loss (MEL)
- Hydraulics engineering circular
- Culvert use, installation, and sizing
- Design guidelines for culverts
- Upstream fish passage in box culverts