By Wendy Wert, Editor
On June 21, 2007 the Los Angeles Basin Section (LABS) of CWEA hosted a training meeting at Taix Restaurant in Los Angeles. Ben Holt, a Research Scientist in the Oceanography-Atmosphere Group at JPL Pasadena discussed pollution issues for the Southern California Bight (SCB). These include: stormwater runoff plumes, municipal wastewater plumes, and natural hydrocarbon seeps. Due to their small size and episodic nature, these pollution hazards are difficult to sample adequately using traditional in situ oceanographic methods. Complex coastal circulation and persistent cloud cover can further complicate detection and monitoring.
At JPL, Mr. Holt and his team use fine-resolution imagery from satellites, complemented by field measurements, to examine these hazards in the SCB. Examples of these pollution hazards from Santa Monica Bay and San Pedro Bay were shown. Of particular interest were recent observations from the November 2006 Hyperion 1-mile outfall diversion event.
Mr. Holt explained that this NASA-funded study of marine pollution in Southern California concluded space-based synthetic aperture radar can be a vital observational tool for assessing and monitoring ocean hazards in urbanized coastal regions. Using Southern California as a model system, the research team has shown that existing high resolution space-based radar systems can be used to detect and assess marine pollution hazards. This is a means for water quality managers to better protect public health and coastal resources.
Mr. Holt and colleagues from JPL; the University of California, Santa Barbara; and the University of Southern California, Los Angeles, examined satellite radar imagery of the coastal waters of Southern California. The area is adjacent to 20 million people, nearly 25 percent of the U.S. coastal population. The imaging radar data from the European Space Agency’s European Remote Sensing Satellites 1 and 2 and Canada’s Radarsat were complemented by shore-based surface current radar data and other field measurements.
Space-based imaging radar detects pollution deposits on the sea surface consistently irrespective of light or weather conditions, and when combined with field surveys and other observations including shore-based radar data, it improves resolution. The presentation described three major pollutant sources for Southern California: storm water runoff, wastewater discharge and natural hydrocarbon seepage. “During late fall to early spring, storms contribute more than 95 percent of the region’s annual runoff volume and pollutant load,” said Ben Holt. “Californians are accustomed to warnings to stay out of the ocean during and after storms. Even small storms can impact water quality. Radar data can be especially useful for monitoring this episodic seasonal runoff,” he said.
The regional Southern California marine water quality monitoring survey includes JPL and more than 60 other organizations, including the Southern California Coastal Water Research Project. Its goal is to characterize the distribution and ecological effects of storm water runoff in the region. Space radar and other satellite sensor data are being combined, including NASA’s Moderate Resolution Imaging Spectroradiometers. The sensors provide frequent observations, subject to clouds, of ocean color that can be used to detect regional storm water runoff and complement the finer resolution but less frequent radar imagery.
The second largest source of the area’s pollution is wastewater discharge. Publicly owned treatment works discharge daily more than one billion gallons of treated wastewater into Southern California’s coastal waters. Even though it is discharged deep offshore, submerged plumes occasionally reach the surface and can contaminate local shorelines. Natural hydrocarbon seeps are another local pollution hazard. Underwater seeps in the Santa Barbara Channel and Santa Monica Bay have deposited tar over area beaches. Space imaging radar can track seepage on the ocean surface, as well as human-caused oil spills, which are often affected by ocean circulation patterns that make other tracking techniques difficult.
Further research is necessary to determine the composition of pollution hazards detected by radar. “From imaging radar, we know where the runoff is, but not necessarily which parts of it are harmful,” Holt said. “If connections can be established, imaging radar may be able to help predict the most harmful parts of the runoff.”