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Title: Evaluation of downdrift shore erosion, Mattituck Inlet, New York: Section 111 study
Authors: Batten, Brian K.
Kraus, Nicholas C.
Keywords: Breaching
Coastal inlets
Long Island Sound (N.Y. and Conn.)
Longshore sediment transport
Navigation channel
Sediment budget
Shoreline change
Coastal Inlets Research Program (U.S.)
Publisher: Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (Engineer Research and Development Center (U.S.)) ; no.ERDC/CHL TR-06-1
Abstract: This report was prepared for the U.S. Army Engineer District, New York, to evaluate shore erosion in response to construction of the Federal navigation project at Mattituck Inlet, NY, under the authority of Section 111 of the River and Harbor Act of 1968, Public Law 90-483, approved August 1968. The original navigation project was authorized in 1896 and modified in 1935 and 1964. The report is organized into seven chapters and two appendixes. Chapter 1 gives an introduction to Section 111 authority and the physical setting at the study site. Chapter 2 discusses shoreline change and change rates in the vicinity of Mattituck Inlet. Shoreline change rates are calculated for the region and compared for shorelines adjacent to the inlet. Chapter 3 describes numerical simulations of waves, wave-induced and tidal currents, and sediment transport pathways at the inlet. Chapter 4 develops the sediment budget for the site and region. Chapter 5 describes estimated future conditions without a project. Chapter 6 evaluates the responsibility of the Federal government for downdrift shore erosion, and Chapter 7 presents alternatives for mitigation. Appendixes A and B document analysis results for shoreline change. Federal responsibility for erosion downdrift of the Mattituck Inlet navigation project is determined by two approaches. The first approach evaluates the response of the adjacent shorelines to the project and is termed “explicit” because it gives a direct measure of shoreline recession and advance, hence, eroded and accreted volume, respectively, under standard assumptions. The evaluation includes measured shoreline change and the volume of material impounded updrift of the inlet. The second approach considers responses of the downdrift shoreline evaluated through a sediment budget and is termed “implicit” because it is based on transport rates alongshore and across shore that cannot be directly measured. Removal of material by maintenance dredging, as well as sand and gravel mining under both Federal and local permits, are addressed within the implicit approach. Three alternatives are evaluated for mitigating shore erosion downdrift of Mattituck Inlet. The first alternative continues the present practice of beneficial placement of dredged material on downdrift beaches. This alternative effectively mitigates shore erosion only in the primary erosion area. The second alternative involves annual bypassing of material impounded updrift of the west jetty to downdrift beaches. This activity would increase bypassing rates to an estimated 75 percent of the average annual longshore transport rate. Benefits of this alternative include stabilization of the primary and secondary erosion areas, increased storm protection through wider beaches, and elimination of potential spit breaching adjacent to the inlet. This alternative improves on existing practice and does not mitigate past damage to the downdrift shorelines. The third alternative provides for advanced bypassing of material accumulated in the impoundment fillet, in addition to removal of portions of the flood shoal. An estimated volume of 125,000 cu yd of material is available from these borrow areas for placement on downdrift beaches. The primary benefit of this alternative is increased storm protection along downdrift beaches, eliminating additional land losses and rebuilding costs associated with the Federal navigation project. Additional benefits include reduction of shoaling rates in the navigation channel, improvement of the channel condition, and enhanced circulation in Mattituck Creek.
Description: Technical Report
Gov't Doc #: ERDC/CHL TR-06-1
Rights: Approved for public release; distribution is unlimited
Appears in Collections:Technical Report
Technical Report

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