Searching for submerged lumber with ground penetrating radar: Rib Lake, Wisconsin, USA

In over 60 years of operation, the Rib Lake Lumber Company processed over 1.4 billion board feet of lumber. The associated Rib Lake was the millpond as well as an industrial waste site. This practice added some 3 to 10 m of organic sediment into the lake, including what is presumed a significant number of sunken logs. Since 1995, the Rib Lake Development Foundation has been searching for ways to efficiently and cost effectively locate these logs for removal. Although there has been SUCCI~SSi n removing logs when found, there is a strong need for a ??tool?? that can consistently locate logs. Ground penetrating radar (GPR) was used to investigate the lake??s depth and probe in the thick sediment pile on the lake??s bottom. Results from the waterborne surveys on Rib Lake indicate: 1) the depth of the lake (0.5 to 2.5 m, bathymetric) can be mapped accurately; 2) geomorphic structures can be imaged (that are now buried by the organic sediment and, in some cases, protrude above the lake bottom into the water column); 3) diffraction patterns interpreted as logs are present along the lake bottom; and 4) diffraction patterns within the organic sediment below lake bottom can be observed. From these initial results, GPR could become the ??tool?? that will enable the location and retrieval of submerged logs in an efficient and cost effective manner.