21 Mar 2024

Pilot Project Using Tickler Chains in Lieu of Deflectors at Fire Island Inlet to Moriches Inlet, New York, Borrow Sites

Abstract: Risk for incidental take of sea turtles and sturgeon exists during hopper dredging operations throughout turtle and sturgeon habitats. Since 1992, draghead deflectors have been the main engineering tool used to minimize incidental hopper dredging takes of sea turtles and are also thought to reduce the chance of sturgeon impingement entrainment. Although reduced, turtle takes still happen annually, and the draghead deflectors reduce dredging productivity, increase fuel usage, and increase costs of operations. As such, there remains a need to research alternative turtle avoidance measures. The non-US dredging industry has used various versions of an engineering control called tickler chains (TC) in lieu of deflectors. If effective, TC could lower dredging costs and increase production in comparison to deflectors. This technical report describes a pilot study where TC were used in lieu of deflectors at Fire Island Inlet, New Y0rk. To the authors’ knowledge, this is the first time since the early 1990s that hopper-dredging has occurred without draghead deflectors along the east coast. No takes were recorded during the pilot study; however, no research was done to determine if sea turtles or sturgeon interacted with the TC. Recommendations for future TC research is provided in this technical report.

27 Sep 2021

Atlantic Sturgeon Movements in Relation to a Cutterhead Dredge in the James River, Virginia

Purpose: This technical note describes a field study investigating the movements of federally endangered Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (ATS), during the summer and fall of 2017 near a cutterhead dredge working in the James River, Virginia, to provide data addressing the concern about the potential impacts of dredging activities (for example, excavation, transit, disposal, sounds, reduced water quality) on the ATS.

20 Aug 2020

PUBLICATION NOTICE: Sediment Sorting by Hopper Dredging and Pump-Out Operations: Sampling Methods and Analysis

Abstract: Hopper dredging operations for beach and nearshore placement typically include periods of overflow, which produces some degree of separation between the size fractions of the dredged sediment. The degree of separation and the controlling factors are presently poorly known. This report focuses on laboratory experiments aimed at determining (1) suitable sampling methods on a dredge, (2) composite sampling techniques to reduce analysis cost, (3) associated sampling intervals to achieve suitable sediment representation of a hopper load, and (4) a hydraulic means of sample splitting. Results showed that no statistical difference exists among the three methods used to sample the hopper weir overflow. The method used to sample deposited hopper sediment identified a bias in the percent fines that resulted from flow sheltering. Further, it was found that composited samples were able to quantify the concentration and percent fines accurately, although an analytical data experiment showed that the accuracy of a composited sample is dependent on the sampling intervals. The accuracy of the fines and concentration from a hydraulic sample splitter was found to be dependent on median grain size, with fine sediment being evenly distributed and coarser sediment increasing the error in concentration and grain size distribution.

25 Jun 2020

PUBLICATION NOTICE: Quantification of the Flow Field around a Draghead Using a Physical Model

Abstract: This study quantifies the hydraulic flow field around a draghead using a 1:7 scaled California and general type draghead. The flow field velocity measurements were taken with each draghead stationary and moving with a prototype speed of 2 knots. The measured velocities increased proportionally with the pumping flow rate. Measured velocities were found to be inversely proportional to the distance from the draghead. As a result, the greatest entrainment velocities for the California draghead were measured between the two visors and below the visors. The entrainment velocities laterally of the dragheads were found to increase by a factor of 2 with the addition of either a concrete or sand bed below the draghead. The measured velocities changed dramatically when the draghead was moving with a prototype speed of 2 knots. The measurement locations to the side of the dragheads did not show the presence of fluid entrainment; instead, the velocities were dominated by the forward motion and subsequent generation of a shear layer around the draghead. The velocities behind the draghead indicated the presence of a wake behind the draghead, with the fluid moving forward at velocity equivalent to or greater than the forward translation speed.

17 Jun 2020

PUBLICATION NOTICE: Sediment Sorting by Hopper Dredging and Pump-Out Operations: Conceptual Model and Literature Review

Abstract: Dredged sediment placed on beaches or nearshore environments is customarily evaluated for compatibility with the native beach sediment to avoid unintended impacts to economic, environmental, or recreational resources. Consequently, some state regulatory authorities establish limits upon the fine-grained content for sediment designated for placement on certain beaches and nearshore environments. Hopper dredging operations for beach and nearshore placement typically include periods of overflow, which is recognized to produce some degree of separation between the size fractions of the dredged sediment. The degree of separation and the controlling factors of separation are presently poorly known and are the subject of this research. This report provides a conceptual model of the hopper dredging and placement processes, including the relevant processes associated with hopper dredge-associated sediment dynamics, generation and transport of the overflow sediment plume, and sediment winnowing at the beach outflow. Prior research is described, and knowledge gaps are identified. Finally, a research plan to validate prior research and to address knowledge gaps is presented. An annotated bibliography of relevant literature is given in an appendix. Documentation of the planned research presented herein will appear in future publications associated with this study.