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Title: Design for prevention of beach erosion at Presque Isle beaches, Erie, Pennsylvania : hydraulic model investigation
Authors: United States. Army. Corps of Engineers. Buffalo District
Seabergh, William C.
Keywords: Beach erosion
Coastal structures
Shore protection
Erosion control
Hydraulic models
Presque Isle, Pennsylvania
Soil conservation
Hydraulic models
Publisher: Hydraulics Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-83-15.
Description: Technical Report
Abstract: Presque Isle Peninsula, Erie, Pennsylvania, is a recurved sand spit with a lakeward perimeter of 9 miles that extends a protective arm around Erie Harbor. The peninsula provides 11 recreational beaches facing Lake Erie which are part of a State Park that occupies almost the entire peninsula and contains an ecological reservation and numerous recreational facilities. Over the past 150 years, the integrity of the peninsula has been threatened by erosion of the beaches due to a decreasing sand supply, and numerous efforts to halt this erosion have been ineffective. A 1:50-scale (undistorted) physical hydraulic model was constructed to aid in evaluating the use of detached offshore breakwaters as a preventive measure against shoreline erosion. The model reproduced a 9,400-ft length of shoreline which included State Park Beaches 4, 5, and 6. These beaches contained a section of shoreline with an existing groin field and a reach of shoreline with few shoreline structures as it was desired to study the interaction of the proposed structures with both types of beaches. Three prototype offshore breakwaters had been constructed at Beach 10 at Presque Isle in 1978. An examination of this reach of shoreline was made with a movable-bed model to determine the suitable modeling materials and techniques to be used in the study. After a series of tests, a 0.78-mm-median-diameter coal sediment (specific gravity = 1.35) satisfactorily reproduced shoreline development in the region of the breakwaters. Tests of the proposed offshore breakwaters at Beaches 4, 5, and 6 then were conducted using coal for sediment tracer tests and in beach-fill tests. Wave-generated current patterns also were observed. Testing of existing conditions indicated that for waves oblique to the shoreline, strong longshore currents were generated within the 1,000-ft groin cells and were deflected offshore by the groins. Sediment tracer tended to move offshore at the groins and then move alongshore on the shoreward face and trough of the main offshore bar. Various offshore breakwater plans were tested. The 350-ft spacing between 150-ft-long offshore breakwaters produced very satisfactory results within the reach of the groin field, outside the groin field, and with the groins removed. Generally, tombolo development was easily initiated. The extent of tombolo development, i.e., whether or not it would attach to the offshore breakwater, was a function of many variables including the proximity to groins, water level, wave height and period, crown elevation of the structure, distance of the breakwater from the initial shoreline, and supply of sediment. Once a tombolo had attached to the breakwater, high water levels and waves overtopping the breakwater were required to erode the tombolo beachline back from the offshore breakwater. The strong longshore current systems noted in the base tests were replaced by slower eddy-like currents behind the breakwaters. Currents moving lakeward between the breakwaters for relatively large wave conditions were diffused. Sediment tracer and beach-fill tests indicated that most sediment was retained shoreward of the line formed by the offshore breakwaters. When tombolos were fully built behind the breakwaters, bypassing on the lakeward side of the breakwater was noted. NOTE: This file is large. Allow your browser several minutes to download the file.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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