Inclinometer-Based Reconstruction of Near-Bed Logarithmic Velocity Profiles in Shallow Coastal Waters: Field Evaluation Against an Acoustic Doppler Velocimeter

Abstract

Near-bed mean-flow structure is important to bottom-boundary-layer exchange and sediment-related processes in shallow coastal waters, but vertically resolved observations often require costly acoustic instrumentation. This proof-of-concept study evaluates a scalable framework using one or two tilt current meters (TCMs) for near-bed logarithmic-profile reconstruction. A short (L1) and long (L2) inclinometer were evaluated individually, and their simultaneous measurements at different effective heights were combined into a two-height reconstruction (L3). Reference profiles were obtained from eight sequential Nortek Vector acoustic Doppler velocimeter (ADV) profiles in Bahia de La Paz, Mexico. Reconstructions used a baseline hydraulic roughness length z0 = 0.015 m, with sensitivity over 0.001–0.015 m. L1 and L2 showed median absolute point-wise velocity errors of 0.0281 and 0.0290 m s−1, while L3 reduced this metric to 0.0213 m s−1. Friction–velocity ratios relative to the ADV were 1.13, 0.91, and 0.99 for L1, L2, and L3, respectively, indicating that relative performance depended on the metric considered. An individual TCM represented approximately 9–10% of the quoted ADV instrument price. The framework supports tiered, spatially replicated monitoring when logarithmic-profile assumptions are appropriate.

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