A note on diffusion from a continuous line source in a time varying flow

This note describes approximate techniques for calculating the transient concentration field resulting from horizontal diffusion from a continuous source in a time varying flow. Using these techniques, calculations could be performed either by hand or very economically by machine. The analyses are based on a model for two‐dimensional horizontal diffusion in which the field for a continuous source is represented as the superposition of the fields for instantaneous patches; the spread of an instantaneous patch is characterized by a diffusion velocity. The specific case considered is an oscillating flow characteristic of a tidal estuary, but the techniques should be of practical value in the description of concentration fields of passive quantities introduced into a variety of time varying flows.