Spectral signatures of tidal forcing: Spatiotemporal patterns of groundwater–surface water exchange in a tidal creek system

Abstract

Surface water–groundwater (SW–GW) exchange in tidal creeks is governed by a complex interplay of marine, terrestrial, and anthropogenic forcings. Despite this, the spectral signature of tidal controls on SW–GW fluxes and flow directions remains poorly understood, largely due to the lack of methods that resolve both infiltration and exfiltration on tidal timescales over extended periods. In this study we apply a novel physics‐informed neural network (PINN) to invert depth‐resolved sediment temperature time series into continuous, high‐resolution Darcy fluxes along a tidal creek on is island of Texel, the Netherlands. Eight sondes were deployed along the creek for 51 d. Flux inversion showed that a dike–flood gate system separates the creek into two hydrologically distinct compartments: A tidally influenced, net‐infiltrating seaward zone (average daily exchange +0.22 to +0.46 m d ⁻¹ ) and a meteorologically and terrestrially modulated landward zone with persistent net groundwater discharge (−0.07 to −0.06 m d ⁻¹ ). Spectral and wavelet analyses show that the SW–GW exchange spectrum is dominated by the diurnal K1 constituent (15.6–43.0% of total spectral power), with semidiurnal (tidal) M2 cycles appearing only intermittently. The spring–neap cycle imposes a fortnightly modulation on flux amplitudes (spring‐to‐neap ratio = 1.11–1.26), demonstrating a secondary but systematic control beyond the dominant diurnal and semidiurnal constituents. Overall, we show that combining temperature measurements with inversion modeling can resolve highly transient SW–GW exchange in tidal creeks over extended periods and link it to external forcings such as tidal signals and position within the coastal landscape.