Bed‐level tools for monitoring erosion and accretion patterns: Flume validation and field testing

Abstract

Monitoring short‐term changes in surface sediment elevation is fundamental to understanding erosion, transport, and deposition dynamics in shallow coastal environments. However, commonly used field approaches, such as horizontal markers, sediment erosion tables, subsurface sediment plates, or erosion pins, are not always cross‐validated under both controlled and field conditions, limiting confidence in their comparative performance. This study experimentally evaluates the performance and potential biases of two widely used and cost‐effective bed‐level monitoring tools: (1) subsurface sedimentation plates (without string, with string, and with string and buoy) and (2) sedimentation bars. Methods were evaluated under controlled conditions in a hydraulic flume using non‐cohesive sandy sediment. Plates and bars were subjected to unidirectional and oscillatory flow regimes at two velocity levels (11 and 23 cm s ⁻¹ ) to compare their erosion responses and assess the hydrodynamic interference generated by their structural components, quantified through Reynolds numbers. A complementary field deployment was conducted over 1 year in a Zostera marina meadow in the Bay of Santander estuary (Spain). Across flume flow regimes and field habitats, bed‐level change estimates were comparable among methods, with no detectable differences within the resolution of the experimental design (minimum detectable difference ≈ 1.9 mm for current‐driven and 2.5 mm for wave‐driven conditions). Although the buoy produced localized turbulence, the resulting shear stress was likely below critical erosion thresholds. Together, the results support the use of sedimentation plates (with or without string or buoy) and bars as practical cost‐effective tools for monitoring short‐term bed‐level change in shallow, non‐cohesive sandy and vegetated environments.