Description

FLOAT TRACING
Float tracing is an inexpensive Lagrangian method of giving an indication of the dispersion characteristics of effluent at a particular location. A series of floats, consists of a cruciform canvas square approx 1 metre square, attached to a small float, are released at pre-determined locations; these are tracked until they reach the edge of the survey area, or get washed ashore or turned by the tide.

DYE TRACING
A number of different techniques are available to measure the rate of dispersion of effluents released into the marine or reverie environment. The most commonly used is the dispersion of dye, typically using Rhodamine or Fluoroscein. Quantities of dye are released and tracked for periods of up to 12 hours, although the length of the track will be dependent on the water clarity and dispersive properties of the receiving waters. Additional information on the movement and dispersion can often be obtained through the use of longer-term tracers such as spores.

FLOAT TRACING
Investigation of a regional flow regime. Typically a number of drogues are released and followed for a full tidal cycle (12.5 or 25 hours). This provides information on residuals in an area as well as the typical flood and ebb excursions.
Can also be used to produce a Tidal Atlas showing the spatial distribution of the currents in an area at different stages of the tide.

DYE TRACING
The use of a combined dye and spore release in conjunction with a numerical model is a good way to investigate pollutant dispersion. The use of longer-term tracers can also be used to determine whether a pollutant released from a particular outfall will reach a specific location. This method has been used regularly when assessing the possible impact of a wastewater discharge on bathing waters.

Float tracing is a much simpler technique than dye tracing, without the potential difficulties attached to dye tracing of permitting and contamination. There can be difficulties in using dyes such as Rhodamine, due to the requirement in some countries for licensing of releases.