A Framework to Simplify Astro‐Meteorological Water Level and Wind Inputs for Modeling Coastal Marsh Ecomorphodynamics

Abstract

AbstractModeling long‐term marsh ecomorphodynamics often requires simplifying hydrodynamic inputs. This is usually achieved by selecting the mean or spring astronomic tidal range. Here, we suggest a new framework to simplify inputs for modeling marsh ecomorphodynamics. First, tidal characteristics that influence plant growth are separated from those responsible for hydrodynamics and sediment transport. The upper range for vegetation growth is set equal to the Median Monthly Maximum High Water plus a positive offset attributed to precipitation. Second, to characterize the hydrodynamics, the measured water levels are partitioned into two components: a high‐frequency signal (<72 hr), which affects both water depths and currents (transport tides), and a low‐frequency signal (>72 hr), which drives sea level anomalies. Transport tides are mainly due to diurnal and semidiurnal astronomic forcing; sea level anomalies are due to both meteorological tides and long‐period astronomic components (weekly to annual). A water level time series can thus be simplified into a time series of tidal cycles, each characterized by a range, period, and sea level anomaly. Given the need to simulate both water depths and currents, a single equivalent tide cannot be identified, that is, a temporal modulation of the tidal cycles (transport tide range and sea level anomaly) must be retained. To reduce input complexity while keeping the modulation, we propose to only simulate the mean, 10th percentile, and 90th percentile of both transport tide range and sea level anomaly. A constant “morphologically equivalent” wind speed reproduces marsh morphology and elevation similar to those obtained with the full wind modulation.