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Title:	Improvements for Masonboro Inlet, North Carolina : hydraulic model investigation : Volume 2
Authors:	United States. Army. Corps of Engineers. Wilmington District Seabergh, William C.
Keywords:	Channel improvement Coastal structures Design Shoaling Sedimentation Deposition Shoaling Sediment transport Hydraulic models Tidal inlets Jetties Masonboro Inlet North Carolina
Publisher:	Hydraulics Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Series/Report no.:	Technical report (U.S. Army Engineer Waterways Experiment Station) ; H-76-4 volume 2.
Description:	Technical Report Abstract: Masonboro Inlet, located at the southern end of the important resort area of Wrightsville Beach, is a natural channel through the coastal barrier beach of North Carolina that conducts tidal flows between the Atlantic Ocean and a channelized lagoon. The inlet provides passage from the ocean to the Atlantic Intracoastal Waterway and to various private and commercial docking facilities. Improvements for the inlet were authorized in 1949 and included two jetties, an ocean entrance channel between the jetties, and interior bay navigation channels. Initially, the ocean entrance channel was dredged to authorized dimensions of 14 ft deep by 400 ft wide through the ocean bar. Shoaling of this channel occurred, and in 1965 construction of the north jetty on the apparent updrift side of the inlet began . This 3600-ft-long jetty had a 1000-ft-long weir at an elevation of 0 ft msl at its shoreward end. A deposition basin on the lee side of the weir was dredged to contain the sediments passing over the weir; the entrance channel was reestablished. After construction , the plan functioned well for a year and a half with the deposition basin filling. However, the entrance channel migrated toward the north jetty structure and cut through the deposition basin in the following years, jeopardizing the structural integrity of both the concrete sheet pile weir and the rock rubble portion of the jetty. To aid in alleviating these problems , the Wilmington District submitted plans to the South Atlantic Division for construction of a south jetty. The preconstruction planning and design required hydraulic model testing to aid in determining such design parameters as minimum required jetty length, alignment, spacing, proper channel alignment, entrance current patterns, and currents occurring during construction. The Masonboro Inlet fixed-bed model was constructed of concrete to scales of 1:300 horizontally and 1:60 vertically. The model reproduced an area extending to the -45 ft contour in the Atlantic Ocean and to the extent of the influence of the inlet in the bay. The wetlands were accurately reproduced near the inlet, but those relatively flat areas farther bayward were reproduced schematically and artificially bent into the research flume to provide storage for the tidal prism. Model verification tests assured that the model hydraulic and shoaling regimes were in satisfactory agreement with the prototype. Preliminary testing included the examination of tidal surface current patterns for various structural configurations, including training structures to deflect currents away from the north jetty, offshore breakwaters, and various south jetty alignments. Plan B of the District was selected as the best design and was subjected to detailed testing. This testing indicated that construction of the plan B south jetty would aid in maintaining a channel more centrally located between the jetties, away from the north jetty. The construction of a deposition basin in Banks Channel near the entrance of the inlet was also investigated. It was found that the basin produced velocity increases along the Wrightsville Beach shoulder of the inlet. NOTE This is volume 2 of a 2 volume report series. Volume 1 contains the main text and Appendix A. Volume 2 contains the Photos and Plates.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/13537
Appears in Collections:	Technical Report