Short communication: High-frequency bed elevation measurements using ultrasonic distance sensors

Ultrasonic distance sensors can be used to measure changes in bed elevation at high-resolution and frequency. These non-contact sensors have a conservative resolution of ∼0.1 mm and are sufficiently ruggedized to be placed within the saltation layer, without affecting the flow or causing scour. A cross-shore transect of ultrasonic distance sensors was deployed across the backshore and seaward face of a recovering blowout and foredune at Padre Island National Seashore, Texas to demonstrate the ability of these sensors to measure bed elevation change in aeolian environments. Measuring bed elevation at 1 min intervals over 500 h reveals episodic and dramatic changes in bed elevation in response to both onshore and offshore winds. Consistent with pre- and post-surveys, the change in bed elevation ranged from a couple of centimeters at the majority of station to over 26 cm near the foredune crest. Bed elevation change exhibited a weak covariance along the instrumented transect and wavelet analysis reveals a transition from high-frequency changes (every 12–40 h) in the backshore to low-frequency changes (every 120 h) along the seaward face of the foredune. The ability to measure bed elevation at high-frequency and resolution provides an opportunity to improve sediment transport estimates and ultimately relate erosion and deposition to specific transport events.