Technical Abstract: Sediment concentration measurement in high concentration runoff waters is highly problematic. A method was developed with the goal of characterizing a sediment concentration measurement system for monitoring bed material concentration during monsoon runoff events at the USDA-ARS Walnut Gulch Experimental Watershed in Southeast Arizona. Using a model and the empirical function describing pure water, the sensor's concentration output was calculated. Data were obtained using a 55 cm, three-prong, embedded time domain reflectometry probe and sediments in a range of size classes under laboratory conditions; then installing the probe in the base and center of a flume. Basal (0-2 cm depth) sediment concentrations were monitored in three flows with peak discharges of 5, 90, and 130 m3/s representing small, intermediate, and large events. Without sediment specific calibration, laboratory validation indicated agreement between sensor and gravimetric concentrations within about 0.02 Kg/L for suspended sediment and within 0.2 Kg/L when the probe was completely buried in coarse (<2.5 cm) channel bed material. For the large and intermediate events, basal sediment concentrations rose from 0.4 - 0.12 Kg/L to a plateau of 0.15-0.19 Kg/L after the flow peak. The plateau extended through much of the tail of the hydrograph before falling to 0.04-0.12 Kg/L. The small event had a similar progression but lower overall concentrations of 0.02-0.08 g/L. These observations are consistent with a period of high sediment transport and channel erosion in the tail of monsoon runoff hydrographs. The dielectric method provides in-situ measurements in high concentration and bed transport environments where traditional methods fail.