<P>The Military Engineer ? No. 66669 S mall Boat Stations of the U.S. Coast Guard are, by their very nature, lo- cated near some of the most dif- ?cult, high-incident coastal waters in the United States. Coast Guard Station Indian River in Rehoboth, Del., is no exception. Located near the mouth of the swiftly- moving Indian River, the stations area of responsibility stretches north to the Maryland-Delaware border and south to the southern side of the Delaware Bay. The same treacherous conditions that threaten boater safety also threatened the units wa- terfront structures. Attempts to stabilize the shoreline in- cluded both traditional steel sheet pile bulkhead sections and riprap toe ar- moring around the perimeter. Despite these efforts, the structural stability of the southern and western bulkheads, as well as the safety of the operations buildings behind them, was still in jeopardy. Since the construction of the Indian Riv- er inlet jetties in the late 1930s, properties along the banks of the inlet have had on- going localized accelerated erosion. When Station Indian River was constructed in 1964, the bulkhead shoreline on the north side of the river was aligned with the adjacent existing shorelines; the stations southern boundary is now 350-ft south of its closest neighbor. The shoreline erosion and high ?ow rates have been studied by federal agen- cies including the Coast Guard and the U.S. Army Corps of Engineers (USACE) as well as the Delaware Department of Transportation. Both the Coast Guard and Delaware Department of Transportation have maintained a compressed cycle of underwater structural inspections and hy- drographic surveys at their sites to keep a close watch on their structures stability. Urgent Action Required A recent USACE hydrographic survey identi?ed a large scour hole just offshore of the southwest corner of the stations bulk- head. The scour hole measured approxi- mately 50-ft wide and 90-ft deep, scouring at about 2-ft to 3-ft a year. A smaller scour hole measuring 20-ft by 50-ft deep also was identi?ed adjacent to the stations west wall. This location was coincident with a steel sheet pile bulkhead section that had been added to the west wall in 2005 in reaction to the shoreline erosion. The sections were driven to a toe elevation of 32-ft while the scour holes elevation was not yet affecting the depths along the toe of the bulkhead. Shortly after the project completion, station personnel identi?ed sinkhole formation and a tilting light pole along the west bulkhead. The light poles were removed promptly and their con- crete foundations soon began to descend into the sinkholes. An underwater inspec- tion of the bulkhead con?rmed that the unarmored toe of the west bulkhead had Underwater Acoustical Imaging By Lt. Cdr. Jorge Martinez, USCG, Lt. Colleen Symansky, PMP, M.SAME, USCG, Lynn Stock, P.E., and Elizabeth Burkhart, P.E., LEED AP, M.SAME Acoustical scanning technology was employed to help avoid a large-scale failure of the shoreline surrounding Coast Guard Station Indian River, Del. Water Planning and Management Structural failure along the bulkhead near Coast Guard Station Indian River, Del., alerted person- nel of the possibility of a more widespread, potentially catastrophic shoreline failure. Photo by Lynn Stock</p> <UL><LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/1/1/">Front-Cover</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/2/2/">Inside-Front-Cover</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/3/3/">Page-1</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/4/4/">Page-2</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/5/5/">Page-3</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/6/6/">Page-4</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/7/7/">Page-5</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/8/8/">Page-6</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/9/9/">Page-7</a></LI> <LI><a href="http://www.stallionpublishers.com/publication/609/tofzxaosm/10/10/">Page-8</a></LI> 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