Plane source injector design for river dispersion studies

A device that injects a planar, spike input of tracer and accommodates irregular stream cross-sections was designed and field tested. The injector is based on a modular support and electrical system that can easily be modified in the field. The tracer is distributed to the water from self-emptying packets made of latex tubing. These packets resist premature breakage and contribute no litter to the stream. The packets empty after applying a current to the electrical system. Instream assembly of the tracer injector is possible from a boat. A two-dimensional input of tracer significantly shortens the initial mixing period for streams that are wide and deep. During the initial period, the tracer cloud becomes well-mixed vertically and laterally. After the initial period is satisfied, the variance of the tracer cloud grows linearly with time, and longitudinal dispersion can be measured easily. The use of a plane source injector significantly reduces the duration of the initial period.