Figure 2. Example of spur construction at Siuslaw River, OR

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waves, wind and tidal current. Spurs are usually constructed of rock rubble similar to the jetty it

is connected to (Figure 2). The spur's basic function is to alter the path of the sediment-laden

longshore current and contain the sediment, keeping it away from the navigation channel and

possibly aiding its return to the beach system through rediversion of the longshore current from

going around the ends of the jetties to a 180-deg rotation of the current vector.

Figure 2. Example of spur construction at Siuslaw River, OR

Typically, longshore and tidal currents are turned seaward as they approach a coastal inlet jetty.

Flow is usually seaward along the side of the jetty and typically is drawn into the channel region

during flood flow. The region on the sea side of the jetty is normally shallow because sand ac-

cumulates against the jetty. This sediment moves around the jetty tip and may encroach on the

navigation channel. Figure 3 shows the flood tide entering Grays Harbor, WA. Estimated sedi-

ment transport coming into the inlet from this region is 370,000 cu m/year (Kraus and Arden

2003). Figure 3 also indicates that there is some current movement towards the jetty during ebb

flow (yellow arrows). A submerged 500-m-long jetty spur (Figure 4) has been proposed as one

alternative to limit this large volume from entering the channel and also to protect the beach

behind it.

Spurs also act as a breakwater and provide wave height reduction along the local shoreline. If

added to a weir-jetty system (for information about weir-jetties see Seabergh 2002), it may pro-

vide wave reduction for dredging operations in the deposition basin. Another possible benefit for

a new jetty system with spurs is that the outer tips of the jetties may not need to extend seaward

as far as a system without a weir jetty, because seaward transport along the jetty is minimized

(Bottin 1981).