Sand Bypassing Cost and Performance Database

Abstract

The Coastal Engineering Technical Note (CETN) herein describes a database of cost and performance data from sand bypassing projects created as the initial step of developing an overall methodology for evaluating fixed sand bypass plant potential at coastal inlets. BACKGROUND: Discontinuities in the shoreline, i.e., natural inlets, stabilized inlets and harbors, all interrupt the longshore transport of littoral sediments. At inlets and harbors used for navigation, most of which are stabilized with jetties, trapping of littoral sediments in jetty fillets, flood and ebb tidal shoals and the navigation channel cause two main problems. One problem is erosion of downdrift beaches. When sand is trapped in the navigation channel, the second problem is reduced navigation capabilities. Artificial sand bypassing, hereinafter referred to as sand bypassing or simply as bypassing, is the man-induced transfer of sand from the jetty fillets, shoals, or navigation channel to the downdrift beaches to mitigate the problems associated with the inlet or harbor. The majority of sand bypassing is done in association with navigation dredging where sand removed from the navigation channel is placed directly on downdrift beaches or in the nearshore zone. Among U.S Army Corps of Engineers (Corps) coastal navigation projects, sand bypassing using fixed plants is relatively rare. This is also true from a worldwide perspective. Fixed-plant sand bypassing might be applied to more sites. However, the effort required to estimate costs and performance is significantly greater with fixed plants than simply modifying a navigation dredging contract for downdrift beach placement. The goal of the "Sand Bypassing Costs and Performance" Work Unit in the Corps Coastal Navigation and Storm Damage Reduction Research Program is to develop a standard methodology for calculating costs of fixed sand bypass systems using standard Corps cost-estimating techniques. Methods to predict performance of the fixed plant bypass systems (volume bypassed and bypassing rate), will also be provided. The costs and benefits of a fixed plant can then be directly compared to sand bypassing using conventional dredged and beach placement allowing Districts to relatively easily and at a modest cost to compare fixed plants with conventional dredging for maintenance of coastal inlets and downdrift beaches. In theory, this will facilitate selecting the optimum method for inlet maintenance, lowering costs and increasing benefits.

Morphodynamics of barrier-inlet systems in the context of regional sediment management, with case studies from West-Central Florida, USA

“…Direct channel dredging removes problematic shoals in the areas of transit, while so-called "advance dredging" typically expands the volume removed in the vertical and sometimes through increased channel width to accommodate potential future sedimentation, thereby increasing the time interval between dredging. In addition to dredging, navigability at tidal inlets can also be managed through diversion and/ or trapping of sediment transport, and has been implemented through weir structures, jetties, designed sedimentation basins, fixed sediment bypassing plants, and other alternative sediment management techniques (CEM, 2002;Clausner, 1999).…”

A Cost–Benefit Approach to Assess the Physical and Economic Feasibility of Sand Bypassing Systems

“…Loza [9] states that these systems can be classified based on one or a combination of several parameters, including purpose, mobility/flexibility, operation mode, operation schedules and capacity. The most common solution for sand bypassing is a mobile system that utilizes dredgers to recover the sand combined with boats and/or submerged temporary pipelines and booster pumps to transport the sediments and deposit them on downdrift beaches or in the nearshore zone [6,10]. These systems can be relocated to reach various areas of the bypassing site.…”

“…These systems can be relocated to reach various areas of the bypassing site. Another method to perform the sand bypassing involves implementing a bypassing plant in a set location [3,6,10]. The fixed systems are typically composed of a jetty supporting sand recovery equipment and permanent pipelines with intermediate booster pumps [6,9].…”

“…A key parameter for a successful sand bypassing design for a specific site is the sediment transport volume capacity, but the project should also include other aspects, such as coastal processes characterization, waves and currents, bathymetry and topography, river and stream outflows, evolution of the coastal systems, storm impacts, social factors and environmental constraints [7,9]. While it is not within the scope of this work, it is important to acknowledge that sand bypassing systems have associated environmental impacts that demand management and monitoring during both the construction and operational phases of the system [11,12].…”

“…Estimating costs for a fixed system must include the construction of the bypass system, operational expenses (such as electricity, salaries and wages), repair and maintenance costs and the dismantling costs of the system at the end of the lifecycle [3,8]. Clausner [10] suggests that the costs and performance of a fixed system should be estimated to allow for a comparison of costs and benefits with the traditional method of sand bypassing (dredging and deposition). This facilitates the identification of the optimal method for inlet maintenance.…”