Note on a Surface-Film Delineated Lateral Front at the Head of a Shallow Tidal Creek

• Published in: Estuaries and coasts Vol. 46; no. 3; pp. 878 - 890
• Main Author: Uncles, Reginald J.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-05-2023; Springer Nature B.V
• Subjects: Coastal inlets; Coastal Sciences; Creeks; Earth and Environmental Science; Ecology; Environment; Environmental Management; Freshwater; Freshwater & Marine Ecology; Fronts; Froude number; Inflow; Inland water environment; Mud flats; Peak floods; Runoff; Salinity; Salinity effects; Shallow water; Short Communication; Spring tides; Stratification; Surface films; Tidal currents; Vertical profiling; Water and Health; Water bodies; Water inflow; Tamar Estuary, UK; Salinity stratification; Tidal currents; Estuarine circulation; Tamerton Creek, UK; Ernesettle Creek, UK; Tidal intrusion front; Tamerton Lake, UK
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-022-01153-y

Lateral surface frontal systems have been observed in the upper reaches of a small, low freshwater runoff, strongly tidal creek. They are a very striking visual feature of this water body when delineated by large quantities of surface film material. The fronts are mostly associated with a creek cross-section of somewhat reduced width and mudflat depth (the ‘Ridge’) compared with adjacent sections. Images are presented that show the tidal intrusion nature of the front and its subsequent development and final down-creek movement as a buoyant plume. Longitudinal and vertical surveys of salinity during a mean-range tide demonstrate the strong stratification that exists in this shallow water body, which, at high water (HW), is typically 1–2 m deep in the narrow main channel. Velocity measurements indicate that a critical inflow Froude number is associated with the initial formation stage of the front. Subsequent frontal locations and behaviour qualitatively correspond to the relative balance between tidal current and surface-layer buoyancy current speeds. Vertical profiling data and bed-mounted salinity sensors during a strong spring tide with low freshwater runoff demonstrate only minor surface stratification and layering on the flood. Nevertheless, the inflow Froude number exceeds unity at the Ridge at peak flood, which is indicative of up-creek frontal formation, and a strongly stratified plume propagates through the Ridge section on the ebb.