GEORADAR CHARACTERIZATION OF GROUNDHOG BURROWS ALONG A SMALL FORESTED CREEK, MILL RUN, SE PENNSYLVANIA

Zoogeomorphic activities play a critical role in stream processes, especially bank stability and resulting channel dynamics. Guided by previous field measurements of more than 20 burrow sites constructed by groundhog (Marmota monax), we present the first attempt to characterize their burrow networks in the riparian zone of Mill Run (Bucks County, Pennsylvania), a small wooded tributary of Neshaminy Creek. These biogenic structures were imaged using high-frequency 800 MHz ground-penetrating radar (GPR) and included: 1) a grid of four parallel 3-m-long transects on the south bank, and 2) an 11-m-long profile on the north bank. Post-processed 2D radargrams showed voids as reverse-polarity anomalies (hollow inclined shafts and tunnels), allowing assessment of burrow depth and orientation. At the southern site, a single-entrance burrow within 1.5 m of the cutbank, exhibited entrance diameter of 0.3 m and a westerly dip angle of ~40°, roughly parallel with the stream flow direction. Based on geophysical data, the maximum depth of this burrow system was 0.9-1.0 m, where partially buried sections were detected based on the characteristics of hyperbolic diffraction. The second study locality traversed three open burrow entrances adjacent to large tree roots. The survey ran parallel to a groundwater sapping channel connected to the creek. Crossover hyperbolics in the records of two adjacent openings indicate that these two groundhog burrows may be connected in a single subsurface network. GPR data show point-source (transverse) hyperbolic signatures connecting approximately 0.4-0.5 m below the ground surface. Along this transect, burrowing activity appears to increase with proximity to the northern bank of Mill Run. Abundant evidence of bank slumping, incision, and treefall along nearby stream segments suggests that burrowing activity likely weakens root systems and enhances groundwater piping, thereby initiating or accelerating a geomorphic cascade leading to slope failure.