The measurement of soil or sediment density in situ by gamma ray attenuation [van Bavel, 1959; McHenry and Dendy, 1964] includes the soil moisture present. The change in total density of a soil with a change in moisture is small with respect to the bulk density of the soil. McHenry [1963] determined the moisture of sediments as a function of total density using the attenuation of transmitted gamma rays. A sensitivity of less than 2% moisture content was reported.