Modeling the effects of aerial temperature and exposure period on intertidal mudflat profiles

Abstract

This research demonstrates how the effect of exposure to air on intertidal flat profile development in cohesive coastal environments can be incorporated into applied numerical modelling. Semi-empirical relationships were used to include the sediment stabilizing effects of exposure on changes to the erosion threshold (Ƭcr; N m−2) and erosion rate (ER; g m−2s−1) during low tide, which also consider the effect of air temperature, T (°C) and exposure duration, D (h). The relationships were based on fundamental forms of the theoretical relationship between water content and evaporation rate, and were fitted to empirical data. Changes were incorporated into the Delft3D model, and scenarios monitored bed level profile development over an annual time scale with different T, sediment stabilizing biofilm biomass (using Chl-a content as a proxy), initial bed composition (mud/sand percentage), and spring and neap tides (regulating current velocity and exposure duration). Model results indicated that the stabilizing effect of exposure will lead to a more flat-topped shape of intertidal mudflats, implying that bed level changes caused by exposure occur lower on intertidal flats compared to runs with no exposure. Higher air temperatures had a greater effect on bed level change, with the maximum accretion of up to 0.039 m (290% higher) occurring in the case of 40 °C compared with the case of no exposure effect with 0.01 m of accretion. Research findings can contribute to understanding of how intertidal flats evolve and is critical to predicting the resilience of these habitats to sea-level rise and warming temperatures.