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Source: https://erdc-library.erdc.dren.mil/jspui/ Three separate and distinct (although interrelated) problems exist at Redondo Beach King Harbor, California, at the present time: recurring , but infrequent, structural damage to the breakwater; excessive wave activity in the harbor caused by waves penetrating through and overtopping the permeable rubble-mound breakwater; and shoaling of the harbor navigation channel and boat mooring area . The US Army Engineer Waterways Experiment Station was requested to: (a) perform a water wave refraction/diffraction/shoaling analysis of the 1983 winter storms to determine the wave characteristics and frequencies of occurrence at the breakwater structure site for the extreme storm events of historical record and for the higher sea waves which overtop the lower portion of the breakwater on an average annual basis; (b) determine the magnitude of wave penetration through the permeable rubble mound structure, overtopping of the structure, and total wave transmission into the harbor; (c) evaluate the effect of raising the crest elevation of the structure on wave transmission into the harbor; (d) estimate the structure armor stone required for stability based on the return period of storm waves of various heights; and (e) propose alternative structural measures for reducing excess waves in Basin 3 and reducing harbor shoaling by sediment penetration through the breakwater. The following conclusions were reached: (a) excessive wave damage occurs in the harbor by storm waves overtopping the +11.5-ft Mean Lower Low Water (MLLW) section of the breakwater; (b) storms of the winter of 1982-1983 occurred at extreme high tide elevation (+8.0 ft MLLW), with unusually long periods (conditions for which the structure was not designed to withstand); (c) higher waves of the spectrum overtopped the +20-ft MLLW section of the breakwater at extreme tide level; (d) wave energy also penetrates through all sections of the permeable breakwater; (e) wave energy propagating through the unrestricted entrance channel to the harbor contributes to the damages of Moles C and D and to the damages in Basin 3; (f) structural damage recurs to the breakwater because the structure is underdesigned with respect to the storm wave energy that it is required to withstand; (g) the 1964 design wave was based on only 3 years of hindcast wave data, producing a 1964 design wave height of 17 ft; (h) hindcast storm wave data since 1900 indicate the design wave height for a 50-year recurrence interval should be around 20 ft; (i) stability testing of the 17-ft design wave indicated the stone size for stability should be approximately 15 tons, although the structure was actually constructed with 13-ton stone; and (j) harbor shoaling occurs because of littoral material from upcoast penetrating through the permeable breakwater. To alleviate the extensive damages which periodically occur at Redondo Beach King Harbor, California, the following recommendations are made which will reduce excessive wave activity and shoaling in the harbor; (a) raise the crest elevation of the existing +11.5-ft MLLW section of the breakwater to +22.0 ft MLLW and effectively seal this portion of the structure during rehabilitation work; (b) seal the remainder of the permeable breakwater with chemical grouting materials; (c) extend the south breakwater at least 500 ft into the harbor; (d) install baffles (prestressed concrete sheet-pile groins) at the entrance to Basin 3; and (e) provide additional revetment material to the slopes of Moles B, C, D, and E. Because of potential effects on tidal circulation in the harbor by proposed structural modifications, extensive physical and/or numerical simulation modeling will be necessary prior to major harbor improvements. NOTE: This pdf file is large. Allow your browser several minutes to download the file. |
