Innovative Tools for Inlet Geomorphic Mapping: Testing Emerging Methods at New Pass Inlet, Florida and Merrimack River Inlet, Massachusetts, USA

Coastal inlets serve important navigation and environmental functions for coastal regions. Managing inlets is a complex task that requires a thorough understanding of several key factors, including sediment transport, areas of erosion and deposition, and feature migration within the inlet system. This knowledge can enhance the maintenance of navigational channels, identify sediment borrow areas for coastal engineering projects, and optimize hydrodynamic and sediment transport models. To improve coastal inlet management in the U.S., the U.S. Army Corps of Engineers (USACE) Coastal Inlets Research Program develops tools to reduce Operations and Maintenance (O&M) costs at federally maintained inlets. One such tool is the U.S. Coastal Inlets Atlas, an online database of information for U.S. inlets (Beck & Arnold, 2019). 
This research highlights emerging tools and methodologies to be included in the next generation of the U.S. Tidal Inlet Atlas for inlet geomorphic mapping and analysis that will provide USACE District engineers, scientists, and managers, as well as other public partners, with tools and data to rapidly evaluate O&M alternatives. These tools include workflows to map inlet geomorphic features more accurately and to better track and predict morphologic changes. Emerging methods that were tested in this study include relative relief mapping (Wernette et al., 2016), Geomorphon classification (Jasiewicz & Stepinski, 2013), and chronostratigraphic and conformal mapping analyses (Pearson et al., 2022). These methods make use of publicly available repeat bathymetric data including USACE National Coastal Mapping Program topobathymetric lidar and USACE hydrographic surveys. Workflows to pre-process bathymetry data and conduct the new analyses as well as results from tests cases at New Pass and Merrimack Inlets in the U.S. are presented here. Highlights of the tool and workflow development and testing include: (1) the importance of considering scale when implementing relative relief mapping and geomorphon methods; (2) the importance of choosing the inlet polar grid origin and transect locations for conformal mapping and chronostratigraphic analysis methods. Results of the test study site analyses highlight geomorphic features such as shoals, reveal sediment transport pathways, and provide estimates of shoal and ETD sediment volumes and ages of deposition. The study provides valuable data products and workflows to engineers and scientists interested in applying these approaches to additional inlets. Fully developed workflows and datasets will be included in future iterations of the U.S. Tidal Inlet Atlas for all federal inlets.

Beck, T. M., & Arnold, D. (2019). U.S. Tidal Inlets Atlas: An Update to the CIRP Inlets Database (Coastal and Hydraulics Engineering Technical Note (CHETN) IV–118). USACE, Engineer Research and Development Center.

Jasiewicz, J., & Stepinski, T. F. (2013). Geomorphons—A pattern recognition approach to classification and mapping of landforms. Geomorphology, 182, 147–156. 

Pearson, S. G., Elias, E. P. L., Van Prooijen, B. C., Van Der Vegt, H., Van Der Spek, A. J. F., & Wang, Z. B. (2022). A novel approach to mapping ebb-tidal delta morphodynamics and stratigraphy. Geomorphology, 405, 108185. 

Wernette, P. A., Houser, C., & Bishop, M. (2016). An automated approach for extracting barrier island morphology from digital elevation models. Geomorphology, 262.