Two-Dimensional Simulations of Long-Term Morphological Evolution Around Tidal Inlets

Abstract

Tidal inlets connect bays or lagoons to the ocean and undergo continuous morphological changes under the action of tides and waves. Numerical simulations of long-term morphological evolution near tidal inlets are computationally expensive because small time steps are needed for numerical stability and accuracy. To speed up the simulations, the morphological acceleration factor (MF) has been introduced to multiply bed changes at each time step. However, there is no practical guidance for determining the maximum allowable MF values. In the present study, systematic sensitivity analysis and model testing have been conducted to assess the allowable MF limits for the Coastal Modeling System (CMS) applied in the simulations of morphology evolution near tidal inlets from 1 year to 100 years under tides only and combined tides and waves. Simulations with MF = 1 are used as the benchmark. The allowable MF limits increase with a decreasing time step, increasing sediment adaptation length, and decreasing nearshore bed slope. For idealized inlets, the upper MF limit is about 80–100 and 35–40 for nearshore slopes of 0.002 and 0.01, respectively, in the 10- to 100-year simulations under tides only and combined tides and waves. In the application at Shark River Inlet, the calculated overall deposition and erosion volumes remain within about 4.56% of the MF = 1 results across all MF values up to 12 and 120 used in the 1- and 10-year simulations, respectively, but the MF limit is up to 6 in the 1-year simulations and up to 40 in the 10-year simulations for bed level changes over transects near jetties. Though the obtained MF limits are specific to the CMS implicit model and may vary in different cases, these findings provide practical guidance for selecting appropriate MF values in the CMS and similar models to balance computational efficiency and accuracy in long-term modeling of coastal inlet morphology evolution.