J. Great Lakes Res. 31 (Supplement 1):64–74 Internat. Assoc. Great Lakes Res., 2005 64 High Resolution Bathymetry and Lakebed Characterization in the Nearshore of Western Lake Michigan James T. Waples 1,* , Robert Paddock 1 , John Janssen 1 , David Lovalvo 2 , Boris Schulze 3 , Jerry Kaster 1 , and J. Val Klump 1 1 Great Lakes WATER Institute University of Wisconsin-Milwaukee 600 E. Greenfield Ave. Milwaukee, Wisconsin 53204 2 Eastern Oceanics, Inc. 25 Limekiln Road West Redding, Connecticut 06856 3 ELAC Nautik GmbH Neufeldtstrasse, D-24118 Kiel, Germany ABSTRACT. The nearshore zone of western Lake Michigan is poorly characterized both in terms of its fine scale bathymetry and its lakebed characteristics. Difficulties in characterizing the lakebed of this region arise in part because of its patchiness as well as the fact that much of the lakebed is not amenable to conventional sediment sampling techniques. With this in mind, high precision bathymetry and the lakebed characteristics of ~17.5 km 2 of the nearshore of western Lake Michigan (near Oak Creek, WI) were mapped using multi-beam and single beam sonar in conjunction with lakebed characterization and surface mapping software. Lakebed features showing nearshore bluff erosion material, glacial scouring, and isolated ridges were revealed in a 1.0 × 1.5 meter resolution map of the survey area. A map of the bottom characteristics, meanwhile, showed a patchwork of four distinct bottom types (area %): mostly rock (12.8%), cobble and sand (21.0%), mostly sand (60.3%), and clay outcrops (5.9%). All predicted bottom types were shown to be accurately characterized by direct observation with an ROV. INDEX WORDS: Lake Michigan, seabed classification, multi-beam sonar, glacial scouring, bottom characterization. INTRODUCTION At 57,750 km 2 , Lake Michigan is the sixth largest lake in the world (Beeton 1984). The lake is divided into two major basins (north and south) with the southern basin occupying approximately one third of the total lake area (18,100 km 2 ; Edg- ington and Robbins 1976.) Morphologically, the southern basin of the lake may be characterized as a relatively simple conical depression with gradual sloped bathymetry leading to a maximum depth in the center of the basin of ~170 meters. Sediment ac- cumulation is highly skewed, with the most rapid rates of permanent deposition occurring not in the * Corresponding author. E-mail: jwaples@uwm.edu deepest portion of the lake, but on the southeastern flank, presumably in response to general circulation patterns which transport material from the western shore to the eastern side of the basin in a counter- clockwise direction (Edgington and Robbins 1990). The nearshore zone of southern Lake Michigan (< 40 meters depth) exhibits little permanent net ac- cumulation of sediment, but rather serves as a tem- porary repository for new inputs of suspended material that are derived from coastal erosion processes, riverine inputs, and autochthonous production. Unlike the eastern side of the southern basin, which consists mostly of sand, the western nearshore of Lake Michigan is characterized by a