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

road A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation. There are many types of ...

s, pipelines,

railway Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...

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

flood A flood is an overflow of water ( 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 an area of study of the discipline hydrol ...

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 a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

s and culverts streams may be crossed by

ford Ford commonly refers to: * Ford Motor Company, an automobile manufacturer founded by Henry Ford * Ford (crossing), a shallow crossing on a river Ford may also refer to: Ford Motor Company * Henry Ford, founder of the Ford Motor Company * Ford F ...

s, floodways,

low-water crossing A low-water crossing (also known as an Irish bridge or Irish Crossing, causeway in Australia, low-level crossing or low-water bridge) provides a bridge when water flow is low. Under high-flow conditions, water runs over the roadway and preclu ...

s 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 river; or a water feature in a garden where water is allowed to flow between stone steps. U ...

Conveyance capacity

Often expressed in

cubic feet per second Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...

(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 is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.Holmes, R.R., Jr. ...

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 water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...

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 () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus '' Oncorhy ...

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

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, these considerations may be incorporated into stream crossing regulations.

References

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