J.M. Cahill 1973 <p>Hydraulic sand models are useful physical tools in the&nbsp;investigation of the transition zone that occurs between salt and fresh&nbsp;ground water in coastal aquifers. Such models are used to demonstrate&nbsp;the effects of transport mechanisms that influence the dynamic&nbsp;behavior and the shape of the transition zone. The techniques&nbsp;employed in obtaining in-place measurements of solute concentrations&nbsp;are generally the stumbling block in generating data for two-dimensional&nbsp;dispersion systems. Two in-place measurement techniques&nbsp;were used in the studies described: (1) conductivity probes when salt&nbsp;was used as a tracer; and (2) photoelectric cells when organic dye was&nbsp;used as a tracer. Results indicate that conductivity methods are more&nbsp;reliable; however, care must be exercised inasmuch as the probes tend&nbsp;to disturb the fluid flow.</p> application/pdf en U.S. Geological Survey Hydraulic sand-model studies of miscible-fluid flow article