Dispersion in the Surfzone: Tracer Dispersion Studies
Abstract
Terrestrial runoff and river input dominate urban pollutant loading rates. Often draining directly into the surf zone, this pollution degrades surf zone water quality, leading to beach closures and increased health risks (e.g., diarrhea and upper respiratory illness). This pollution contains both human viruses and elevated levels of fecal indicator bacteria. Surf zone mixing processes disperse and dilute this and other types of pollution. Unfortunately, field surf zone observations of mixing, or turbulence, have been extremely scarce, and much about surf zone small-scale turbulence is not known. On larger scales (10-100 meters), horizontal dispersion is driven by surf zone eddies and meanders associated with shear waves or finite breaking crest length. Understanding the small and large length-scale mixing processes is important to predicting the fate (transport, dispersal, and dilution) of surf zone tracers, whether they are pollutants, bacteria, larvae, or nutrients. The scientific objective of this project is to improve the understanding and modeling of the dispersion of tracers (pollutants, fecal indicator bacteria, fine sediments) within the nearshore (100 meters of the shoreline), and especially within the surf zone, where breaking waves intensify mixing processes and drive strong mean currents. Here the focus is on two components of the HB06 experiment that was performed in the Fall of 2006. The first is an analysis of surf zone cross-shore dye tracer dispersion. The second is an analysis of the small-scale turbulence in the surf zone due to breaking waves. Observations were collected from 15 September to 17 October 2006 (800 hours) at Huntington Beach, California, a site with chronic water quality problems. A cross-shore transect of co-located pressure sensors and acoustic Doppler Velocimeters was deployed spanning 160 meters out to 4 meters mean water depth.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2009
- Accession Number
- ADA527039
Entities
People
- Falk Feddersen
Organizations
- Scripps Institution of Oceanography