Abstract: Distribution of Suspended Particulate Matter Near Sewage Outfalls in Santa Monica Bay, California

Ronald L. Kolpack

During the past 15 years more than 12 × 10⁸ l/day of primary and secondary-treated sewage effluent and an additional 19 × 10⁶ l/day of sludge have been discharged into Santa Monica Bay in southern California. However, no significant accumulation of particulate material around the discharge sites has been detected by precision-depth and high-resolution seismic-reflection profiles. To determine the distribution and transport paths of sewage particulates within the water column on the Santa Monica Shelf, more than 500 light-transmission profiles were made on 7 cruises between September 1970 and November 1971. Bottom-current meter, temperature, and salinity measurements also were used to interpret the distribution of particulates in the water c lumn. These data show that part of the sludge, discharged near the head of Santa Monica Canyon, moves down canyon as a near-bottom turbid layer. Part of this discharge also is mixed upward into the water column and transported northeast toward shore. The maximum turbidity from the effluent discharge, about 8 km offshore between Santa Monica and Redondo Canyons, is usually in the upper 10 m of the water column. Within several kilometers of the discharge is a sharp boundary with the underlying clearer water at 20 to 25 m. The outer-shelf parts of profile sections also show a characteristic shoreward intrusion of clearer water between the near-surface and near-bottom turbid layers.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC