Jetties: dams in the ‘river of sand’

Jetties: dams in the ‘river of sand’

Text by Paul Jenkin


Jetties: dams in the ‘river of sand’

We have discussed how the beach is like a ‘river of sand’ flowing from west to east along our coastline. This analogy becomes most evident when structures are constructed perpendicular to the shoreline. Just as a dam traps river sediments, jetties interrupt the longshore current and trap beach sand on their updrift sides.

Jetties are coastal structures designed to stabilize an inlet channel or harbor entrance. In our area the harbors at Ventura, Channel Islands, and Port Hueneme all have entrances defined by two parallel jetties that extend from above the high tide line into deep water. These jetties act like dams in the ‘river of sand’ that flows along the beach. Sand accumulates in the harbor entrances and on the updrift side of the jetties. Meanwhile downdrift beaches, starved of their sand supply, experience increased erosion. All of these harbors have ongoing dredging programs that are necessary to keep the harbor entrances open for navigation and to bypass sand around the jetties to the downdrift beaches.

The importance of sand-bypassing became evident this past summer at Hueneme Beach. Located downdrift of the Port of Hueneme jetties, Hueneme Beach relies on the U.S. Army Corps of Engineers to transfer sand dredged from the Channel Islands Harbor entrance. This program normally requires 1.1 million cubic yards of sand every two years, but federal budget cuts only provided for 40% of this amount in 1995. As a result, sand-starved Hueneme Beach receded drastically and required emergency sand replenishment before damage occurred to public and private properties.

At over $4 per cubic yard dredging is expensive, but as we have seen at Hueneme sand-bypassing is necessary when jetties interrupt the ‘river of sand’.




Send feedback to: paul jenkin