Figure 6.2. Placement of flow control structures relative to channel banks, crossing, and
floodplain. Spurs, retards, dikes, and jack fields may be either upstream or
downstream from the bridge (from Brice and Blodgett 1978).
Spurs are also used to protect highway embankments that form the approaches to a bridge
crossing. Often these highway embankments cut off the overbank flood flows causing these
flows to run parallel to the embankment enroute to the bridge opening. Spurs constructed
perpendicular to the highway embankment keep the potentially erosive current away from the
embankment, thus protecting it. Spurs as used in this report encompass the terms dikes,
jetties, and groins, which are also used to describe these structures.
Spurs are also used to channelize a wide, poorly defined stream into a well-defined channel
that neither aggrades nor degrades, thus maintaining its location from year to year. Spurs on
streams with suspended sediment discharge can cause deposition to establish and maintain
the new alignment. The use of spurs in this instance may decrease the length necessary for
the bridge opening and may make a more suitable, stable channel approach to the bridge.
This decreases the cost of the bridge structure.
Recommendations for spur design from Brown (1985) are summarized in HEC-23 (Lagasse et
al. 2001). The major considerations are:
Extent of Channelbank Protection
Spur Crest Profile
Channel Bed and Channel Bank Contact
Spur Head Form