Rapid measurement of surface moisture content on a beach

A simple technique for rapid measurement of moisture content at a point on a beach with a Delta-T moisture probe is described. The sensing elements of the probe consist of four stainless steel rods (6 cm long) which, when inserted into the beach sediments, measure the impedance introduced by the presence of moisture. To provide a realistic measure of surface moisture content, the effective length of the probe was shortened from 6 to 2 centimeters by inserting the rods through a cube (4 centimeters thick) of dielectric foam. Laboratory tests comparing the output voltage of the probe with gravimetric moisture content in sand taken from a field site at Greenwich Dunes, Prince Edward Island, Canada, produced linear best-fit lines (R-2 > 0.97). The tests showed no appreciable difference between the short probe and the original long probe for moisture content of 0-10% and for differing salt content. A calibration produced from 150 measurements in the field over 4 weeks with the short probe and gravimetric moisture content of core samples (2 centimeters thick) was the same as the laboratory calibration, though with more scatter. Field tests within plots (1 meter square) show that surface moisture content can vary by more than 3% within this small area. Measurements within a rectangular grid 50 meters alongshore and 25 meters cross-shore show spatial patterns related to wave run-up and tidal cycles and seepage from the dune, as well as temporal fluctuation related to precipitation events and drying by sun and wind.