Construction stormwater practices - temporary stream crossing Revision as of 16:19, 15 April 2019 by Mtrojan (talk | contribs)(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff) Construction stormwater practices - temporary stream crossing

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A temporary steam crossing is a structure designed for short-term (typically less than one year) use that is installed across a watercourse to allow construction vehicles to safely cross without damaging the stream bed or channel. They may also be referred to as “temporary access” or “temporary access crossings.” The most common types of temporary stream crossings include bridges, culverts (or “pipe crossings”), and fords (or “drive-through crossings”).

Purpose and function

The primary function of a temporary stream crossing is to prevent construction equipment from damaging the stream bed and banks, impeding stream flow, blocking fish migration, and tracking sediment and other pollutants into the stream.

Applicability

Because of the potential disturbance created by construction of a temporary stream crossing, they should be used only when they are completely necessary for construction purposes. Refer to Planning considerations for additional discussion. In general, temporary stream crossings are applicable when heavy equipment must be moved from one side of a watercourse to the other, or where lighter-duty construction vehicles require frequent, short-term access for crossing a stream channel.

Site applicability

Temporary stream crossings should be limited to locations with low erosion potential and should be constructed during dry periods to minimize stream disturbance and reduce costs. Select crossing sites away from trees, steep banks, channel bends, and deep pools. Stream channel conditions, including expected flow rates during the operation of the temporary crossing, should be thoroughly evaluated before choosing the appropriate type of stream crossing. For example, culverts and access fords may not be appropriate for large streams or during high flow conditions, as they may constrict flow and create potential safety hazards. Temporary bridges may be more suitable for these conditions and are also less likely to impede fish and aquatic life passage.

Although bridges are generally the most expensive to design and construct, they are often the preferred method for temporary stream crossings because they provide the least disturbance of the stream bed and constriction of stream flow. Culverts are less expensive than bridges, relatively easy to construct, and able to support heavy equipment loads. Fords are typically the least expensive to construct but are generally not appropriate for construction during rainy periods or on high-flow perennial streams. The table below provides additional information on the applicability of each temporary crossing and limitations of use.

Typical temporary stream crossing methods and their applicability.
Link to this table

Stream crossing type	Applicability	Limitations
Temporary bridge	Results in least disturbance to stream bed and banks compared to other stream crossing methods Typically no time of year restrictions for use Generally most appropriate for streams with high flow velocities or steep gradients	Use in large channels may require pier(s) or other supports, which increase disturbance to stream (see Construction recommendations and specifications)
Temporary culvert (pipe)	Most common temporary stream crossing Most appropriate for short-term use Generally appropriate for perennial or intermittent streams Generally preferred over fords as disturbance to stream is limited to construction and removal	May not be appropriate for large streams or during high flow conditions Causes greatest obstruction to flow May damage channel cross-section; culvert crossings should be planned to limit the number of crossings needed Not appropriate for streams that are vertically degraded or incised
Temporary ford (drive-through)	Most appropriate for short-term use Generally appropriate for ephemeral or low flow perennial streams Used when bridge or culvert crossings are not feasible; typically very shallow streams where stream banks are less than 4 feet above the stream invert	Use should be limited to dry season Use should be limited to streams whose beds are armored May degrade water quality due to contact with construction vehicles and equipment