A NEW APPROACH TO MONITORING AND MAPPING CHANGES IN THE GEOMORPHOLOGY OF AN ACTIVELY MIGRATING COASTAL PARABOLIC DUNE AT THE INDIANA DUNES NATIONAL LAKESHORE

Mount Baldy is a heavily disturbed and actively migrating parabolic dune located along the southern coast of Lake Michigan near Michigan City, Indiana within the Indiana Dunes National Lakeshore. The National Park Service declared Moutn Baldy an “impaired landform” in 2011 and has initiated ongoing funding and work to monitor and restore the dune, in an effort to slow its landward migration. In this study, geologic and engineering approaches were combined to develop a reproducible method of monitoring changes in the geomorphology of the dune on an annual to multi-year basis. Previous studies have focused on mapping changes in the position of the base of the slipface. While important, such studies collect point measurements and cannot capture data on the volume of sand movement or changes in the elevation of the dune crest that have accompanied dune-form migration. In this study a map illustrating areas of erosion and accumulation across the entire area was generated by comparing LiDAR imagery from 2009 against a surface generated in summer 2012 from on-the-ground surveying using a Leica Total Station and hand-held survey rods with reflectors. An additional surface was created depicting the distribution of various sediment sizes across the study area. The distribution and mobility of individual sand fractions will be used to provide recommendations for gradations incorporated in to the ongoing beach nourishment plans for the nearshore zone at Mount Baldy. To provide a quick method of monitoring seasonal and annual changes in the foredune and Mount Baldy’s deflationary basin, a surveying grid was established that can easily be reoccupied using a portable Trimble GPS unit, creating a total of 5 N-S and 5 E-W profiles that record changes in elevation across the dune’s form. A total of 4 profile series have been generated between 2009 and 2013. The data records 1.5-2.3 m of change in the elevation of the dune’s crest and approximately 15 m of change in the position of the base of the slipface. Monitoring of the position of the base of the slipface is complicated by interference from trees with the laser surveying methods. Ongoing work will focus on extending the profiles to better capture movement of the slipface and creating a new overall surface comparison using 2009 and recently flown LiDAR imagery from 2013.