USING GROUND PENETRATING RADAR TO INVESTIGATE THE POSSIBILITY OF PROHIBITION ERA TUNNELS AT CLUB MANITOU

Club Manitou in Harbor Springs, Michigan was a legal nightclub that was in business from the 1920s to 1950s. During the 1920s, the basement of the same property was used by the Purple Gang from Detroit to run a hidden speakeasy during Prohibition. According to stories told by patrons at the time, tunnels were built so workers and alcohol could be moved discretely to and from the basement. These tunnels could also be used if the establishment was raided and gang members and patrons need to escape. Club Manitou stands today as a residential property. The one tunnel still accessible was used to move supplies into the kitchen of the nightclub. A ground penetrating radar (GPR) study was conducted at the Club Manitou property to investigate the possibility of other tunnels. Our pilot study employed 100MHz and 250MHz antennas and determined that the 250MHz antenna had the clearest reflections at the greatest depth. Thus, for all additional data collection the 250MHz antenna system was used. Individual GPR profiles were collected on the north, east and west sides of the old Club Manitou. Data was collected on the south side of Club Manitou Data along 17 parallel lines, each line was 30 meters long spaced 1.5 meters apart and parallel to the south wall of Club Manitou. The GPR data was compiled in GFP edit and processed in EKKO Project. The lines on the north, west, and east sides of the house only show small diffraction parabolas that are probably tree roots and utility lines based on their reflection quality and depth and locations relative to know utilities and trees. The lines on the south side of the house show an anomaly leading away from the house towards the southwest. This anomaly has a strong, clear reflection and a wide parabola. The anomaly’s reflection occurs at about a depth of approximately 1.75 meters near the Club Manitou south wall and increases to 2 to 2.5 meters by approximately 12 meters from Club Manitou. Beyond 12 meters from the wall this reflection is no longer observed possibly because the tunnel goes deeper than the observed GPR reflections or the tunnel may have collapsed or becomes gradually filled in. The results of this GPR study are consistent with the stories that there was a tunnel leading from the Club Manitou speakeasy basement to the south.