INTRODUCTION 



The turbidity of coastal waters off Southern California 

 has been under investigation for several years from surface 

 ships using a portable hydrophotometer (alpha meter). ■'■ 

 (See list of references at end of report. ) The construction 

 of the USNEL Oceanographic Research Tower, ^ 1 mile off 

 Mission Beach, California, in 6 feet of water, provided a 

 stable platform suitable for studying turbidity. This report 

 describes the first results of turbidity and related studies 

 made from the tower. 



The wide variations in the turbidity structure of sea 

 water in the area around the tower have been verified by 

 previous work, ^ '^ by divers, and underwater television 

 studies. Divers have reported a visibility of about 15 feet 

 at a particular depth and time, but almost zero visibility 

 at the same depth a few minutes later, or at a slightly 

 different depth. At other times visibility extends to distances 

 of over 50 feet. The cause of such changes is as yet largely 

 undetermined. 



An attempt was made to correlate these turbidity fluctu- 

 ations with time, tides, and internal waves or temperature 

 structure. In addition, biological investigations were con- 

 ducted to determine how turbidity is related to organic matter 

 in the water. Living organisms were considered as a possible 

 cause of short-period changes in turbidity and associated 

 acoustic effects. 



MEASUREMENT SITE 



The measurement site was the open sea about 1 mile 

 off Mission Beach (fig. 1). In this area the sandy bottom 

 slopes gently to the west. There was no river runoff nor 

 land drainage in the area during summer when the turbidity 

 observations were made. Although there is a tidal flushing 

 of Mission and San Diego Bays, under normal conditions 

 the bay waters, more turbid than open sea water, do not 

 reach the measurement site since the predominant flow is 

 to the south (fig. 1). There is no significant tidal flushing 

 nor draining of other bays within 70 miles to the north, the 

 usual direction from which the coastal drift comes . Thus 

 the local bays are not an important factor in turbidity changes 

 at the measurement site. 



