Evaluating Sediment Transport and Morphological Evolution of a Cross-shore Swash Zone Placement

Description

Crescent Beach, Indiana is regularly nourished from an upland source. The nourishment sediment is transported west by the longshore current towards Burn Harbor and Burns Small Boat Harbor navigation channels. At Burns Small Boat Harbor, the USACE plans to use an innovative dredged sediment placement technique to bring sediment dredged from the harbor to a “cross-shore swash zone” (CSSZ) placement at Portage Park. This provides a unique opportunity to investigate the feasibility of using unconfined swash zone placement into a shore perpendicular spit as a cost-effective method to bring sediment from navigation dredging to the subaerial beach. Allowing the pipe from the dredge to discharge sediment directly into the swash zone and readjusting the pipe position as the shoreline progrades has the potential to build out a shore-perpendicular spit with substantially less equipment requirements on the beach. Natural processes are expected to rework the placed material over a larger stretch of shoreline. Demonstrated success in this project has the potential to make similar strategies more accessible in other settings where it is likely to be successful. Detailed monitoring data that describes hydrodynamic conditions, sediment characteristics, and morphological change after sediment placement is a critical part of this.The goals for this project are to operationally learn about an innovative construction technique, study the morphological evolution of the nourishment, amass a complete data set for future model validation, and estimate future dredging requirements. To achieve these goals, the work addressing this funding opportunity must:· Provide topographic survey data from five to six backpack mounted LiDAR surveys (or similar), covering the subaerial beach in the vicinity of the placement area prior to construction, reasonably promptly after construction, 1 month after construction, in the winter of 2024 preferably following the first storm event to exceed 1 m offshore wave heights for 4 hours, and in the spring of 2025.· Provide data from five to six bathymetric surveys, with comparable coverage to 25 single beam transects encompassing the placement area and surrounding area at similar times to topographic surveys.· Provide continuous wave and current measurements in 5 to 10 m water depths for up to 10 months.· Provide the sediment gradation at 15 to 20 locations along a cross-shore transect from the dune toe to approximately 10 m water depth before the beach nourishment, promptly after construction, and in the spring 2025. The sediment sampling should occur concurrently with bathymetric surveys.· Provide boat support over one to two days for EcoMapper turbidity data collection to be conducted during construction by USACE researchers.· Provide minor cleaning and visual inspections of turbidity sensors to be deployed by the USACE when collecting other data detailed above.· Provide topographic and bathymetric survey data from two surveys of Crescent Beach, Indiana to infer sediment transport updrift of Burns Harbor and Burns Small Boat Harbor for future dredged volume estimation. The topographic survey data shall be collected using a backpack mounted LiDAR system (or similar) and the bathymetric survey data shall consist of 31 cross-shore single beam transects measured at a similar time as the topographic surveys. The two surveys shall be temporally spaced approximately one month apart following a beach nourishment.Quality control, analyze, and document collected field data in a technical report or peer reviewed journal manuscript.

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