SEDIMENTOLOGY OF A MODERN BRAID BAR IN THE WISCONSIN RIVER NEAR SPRING GREEN, WISCONSIN: ANALYSIS USING GROUND PENETRATING RADAR

A ground-penetrating radar (GPR) survey was conducted over a sand braid bar in the Wisconsin River near Spring Green, Wisconsin to characterize depositional structures within a longitudinal bar. The clean, medium to coarse grained sand in the Wisconsin River provided an ideal environment for GPR surveying, and excellent penetration depth and resolution were achieved. A Sensors and Software PulseEkko 1000 with 250 MHz antennae was used to collect data on a 20m x 20m grid over an area of approximately 40,000 square meters. Aerial photography and detailed topographic surveys were used to characterize the bar externally and to monitor bar migration. USGS gaging stations upstream and downstream of the site provide a history of discharge data that can potentially be linked to depositional patterns within the bar. The radar profiles reveal the internal architecture of the bar which consists primarily of downstream and lateral accretion deposits, however, significant amounts of vertical and upstream accretion deposits are present. Combination and further analysis of the data will be used to determine dominant depositional processes in this reach of the Wisconsin River, and to reconstruct a history of the bar.