# Stream crossing

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:''This article covers crossings over small streams, not those over large rivers.''
'''Stream crossings''' are the numerous instances where small perennial or intermittent [stream](/source/stream)s are crossed by [road](/source/road)s, [pipelines](/source/Pipeline_transport), [railway](/source/railway)s, or any other thing which might restrict the flow of the steam in ordinary or [flood](/source/flood) conditions. Crossings over any dry channel which might carry flood water is included. Any structure over or in a stream which results in limitations on the movement of fish or other ecological elements can be an issue.

==Types==
In addition to [bridge](/source/bridge)s and [culvert](/source/culvert)s streams may be crossed by [ford](/source/Ford_(crossing))s, [floodways](/source/Floodway_(road)), [low-water crossing](/source/low-water_crossing)s or even [stepping stones](/source/stepping_stones).

==Conveyance capacity==
Often expressed in [cubic feet per second](/source/cubic_feet_per_second) (cfs), conveyance capacity is the amount of water a stream crossing structure will pass. The amount of water that can be predicted during flood conditions, such as a [100-year flood](/source/100-year_flood) is one design consideration.

===Failure to convey===
If stream flow exceeds the capacity of the passage through the crossing or it is plugged by debris the crossing may be overtopped or the stream diverted down the road. This may result in substantial [erosion](/source/erosion) as flood water cuts a gully on the side of road. Diversion occurs when a road slopes downward from a crossing and the height of the road exceeds the height of any outlet down the road. A sag (dip) in the road below the crossing may serve as a channel for over flow of excess water and prevent water from continuing down the road but is only practical on gentle slopes.<ref name="FSDiversion">{{cite web|author1=Michael J. Furniss|author2=Michael Love|author3=Sam A. Flanagan|title=Diversion Potential at Road-Stream Crossings|url=https://www.fs.fed.us/t-d/pubs/html/wr_p/97771814/97771814.htm|website=fs.fed.us/|publisher=U.S. Forest Service|accessdate=April 29, 2018|date=December 1997}}</ref>

==Structural integrity==
What happens when a heavy truck passes over, or flood water plugs an opening with debris or overtops the structure.

==Habitat continuity==
Passage of wildlife, particularly fish such as [salmon](/source/salmon) which spawn in streams, is a design consideration as is [habitat continuity](/source/habitat_continuity). In some jurisdictions, such as [Massachusetts](/source/Massachusetts_Department_of_Transportation), these considerations may be incorporated into stream crossing regulations.<ref name="MassDOT">{{cite web|author1=MassDOT personnel|title=Design of Bridges and Culverts for Wildlife Passage at Freshwater Streams|url=http://www.massdot.state.ma.us/Portals/8/docs/environmental/wetlands/WildlifePassagesBridgeDesign122710.pdf|website=MassDOT, Massachusetts Department of Transportation|publisher=State of Massachusetts|accessdate=April 28, 2018|format=PDF|date=December 2010}}</ref>

==See also==
*[Log bridge](/source/Log_bridge)s

==References==
{{reflist}}

==Further reading==
*[https://streamcontinuity.org North Atlantic Aquatic Connectivity Collaborative (NAACC)]
*[https://www.nature.org/ourinitiatives/regions/northamerica/road-stream-crossing-economic-analysis.pdf "An Economic Analysis of Improved Road‐Stream Crossings"] (Adirondack Chapter of [The Nature Conservancy](/source/The_Nature_Conservancy)  August 2013)

Category:River crossings

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Adapted from the Wikipedia article [Stream crossing](https://en.wikipedia.org/wiki/Stream_crossing) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Stream_crossing?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.