Studies were conducted by the San-Francisco District of the U.S. Army Corps of Engineers to determine the effects of dredging and disposal operations on the Main Ship Channel across the San Francisco Bar. Disturbance of a basically sandy substrate causes little eco logical disruption of the marine benthos. Organisms associated with such an environment have evolved with an unstable substrate and are able to survive movements initiated by man as well as nature.
The United States Army Corps of Engineers' primary function since its organization in 1774 has been the maintenance of navigable waterways. In fulfilling this mission the San_ Francisco District annual dredges over 5.2 million cubic meters from channels in the San Francisco Bay region. Part of this dredging includes maintenance of the Main Ship Channel through the San Francisco Bar which is about eight kilometers west of the Gp1denQate. Dredging has been on-going since 1921 when the Bar was first dredged.
In early 1971, work was initiated to provide depths of -1.75 meters mean lower water (MLLW) across the Bar with disposal of the dredged material on the Bar South of the channel. Previously the channel had an authorized depth of -15.25 MLLW, and the dredged material was disposed in deep water outside the Bar about two kilometers southwest of the channel entrance. The new disposal practice was instigated on the recommendations of Professor Hans Einstein, University of California and Professor Raymond McAllister, Florida Atlantic University. The justification for the change was that disposal in deep water prevented the material from re-entering the littoral regime. This procedure has aggravated the beach erosion problem in Florida by depriving the beaches of the nourishment previous afforded by the material (Ref. 1). Therefore, it was resolved that, dispersion of the dredged material on the Bar would retain it in the littoral regime with the possible effect of nourishing the coastline to the south.
While the removal of material from the Main Ship Channel and deposition of that material on the Bar was' within the same localized environment, there was the possibility that the displacement could result in a significant environmental disruption of the indigenousbiota. To examine this possibility the San Francisco District conducted physical, chemical and biological studies on the San Francisco Bar during the period from December 1970 through April 1972 to determine the environmental effects of deepening the Main Ship Channel and disposing on the Bar. The purpose of this paper is to discuss the results of those studies, with particular emphais on the studies employed to investigate the biological impacts of the operation.
