SEALING OF MISSION BAY JETTIES 



SAN DIEGO, CALIF. 



BY 



Robert E. Loudon 

 Assistant Chief, River and Harbor Planning Section 

 U. S. Army Engineer District, Los Angeles 



GENERAL 



San Diego and Mission Bay, California, authorized by the River and 

 Harbor Act approved 2k July 19U6, is a project for the improvement of 

 the lower San Diego River for flood control and the improvement of Mission 

 Bay for small-craft navigation (fig. l). In its natural state, Mission 

 Bay (formerly called False Bay) was a large tidal lagoon formed by a 

 barrier beach across the mouth of the San Diego River. The river flowed 

 mostly into the north end of San Diego Bay proper, until it was diked 

 out of the harbor in I876, and thereafter flowed through the barrier at 

 Ocean Beach. The tidal flow maintained a channel about 200 feet in width 

 and about 8 feet in depth, connecting Mission Bay and the ocean. 



The project plan provides for a river channel between two levees 

 about 900 feet apart which continue through the littoral zone as jetties. 

 The north river jetty separates the flood channel from the entrance 

 channel to the small-craft harbor. A third jetty, parallel to and 918 

 feet north of the common jetty, protects the harbor entrance channel on 

 its north side. Construction of the jetties was completed in 19U9. 

 Dredging of the entrance channel was completed in 1955 and the Federal 

 project was completed in January 1959. 



In December 195U, it was discovered that sand from the littoral zone 

 north of the north jetty was passing through that jetty into the entrance 

 channel. It was apparent that this was taking place over the top of the 

 core of the jetty, the core being composed of small stone impenetrable by 

 sand. In design of the jetties, the top of the core was established at 

 the elevation of mean lower low water (MLLW) (fig. 2). Similar design for 

 jetties at similarly sited harbors at Newport Beach and Point Hueneme had 

 not resulted in such a problem after many years of service. 



In March 1955, a contract was awarded for placement of 3,000 tons of 

 sealing stone on the seaward slope of the north jetty within the limits 

 of the littoral zone, allowing the waves to drive the stone into the inter- 

 stices. Ninety-five percent of the stone was graded in size from 1-1/2 to 

 6 inches. This measure succeeded in retarding the movement of sand, but it 

 was later discovered that infiltration was not entirely stopped. 



During the preparation in 1958 for the final dredging and revetment 

 contract of the project, it was discovered that 70,000 cubic yards of 

 shoaling material had intruded into the entrance channel northward through 



