:''This article covers crossings over small streams, not those over large rivers.'' Stream crossings are the numerous instances where small perennial or intermittent

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...

s are crossed by

road A road is a thoroughfare used primarily for movement of traffic. Roads differ from streets, whose primary use is local access. They also differ from stroads, which combine the features of streets and roads. Most modern roads are paved. Th ...

pipelines A pipeline is a system of pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countries around the world. The Un ...

railway Rail transport (also known as train transport) is a means of transport using wheeled vehicles running in railway track, tracks, which usually consist of two parallel steel railway track, rails. Rail transport is one of the two primary means of ...

s, or any other thing which might restrict the flow of the steam in ordinary or

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

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 A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

s and

culvert A culvert is a structure that channels water past an obstacle or to a subterranean waterway. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe (fluid conveyance), pipe, reinforced concrete or other materia ...

s streams may be crossed by fords, floodways, low-water crossings or even

stepping stones Stepping stones or stepstones are sets of stones arranged to form an improvised causeway that allows a pedestrian to cross a natural watercourse such as a creek, a small river; or a water feature in a garden where water is allowed to flow betwe ...

Conveyance capacity

Often expressed in 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 A 100-year flood, also called a 1% flood,Holmes, R.R., Jr., and Dinicola, K. (2010) ''100-Year flood–it's all about chance 'U.S. Geological Survey General Information Product 106/ref> is a flood event at a level that is reached or exceeded onc ...

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 Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

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.

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 Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

which spawn in streams, is a design consideration as is habitat continuity. In some jurisdictions, such as

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

, these considerations may be incorporated into stream crossing regulations.

References

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